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prof. Ing. Stanislav Zvánovec, Ph.D.

Garant programu Elektronika a komunikace - bakalářský
Garant a tutor programu Elektronika a komunikace - magisterský

Všechny publikace

Connecting Hollow-Core and Standard Single-Mode Fibers With Perfect Mode-Field Size Adaptation

  • DOI: 10.1109/JLT.2023.3329738
  • Odkaz: https://doi.org/10.1109/JLT.2023.3329738
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We propose an approach to interconnect a hollow-core fiber (HCF) of arbitrary core size with standard single-mode fiber with perfect mode-field size adaptation and experimentally achieve for the first time insertion loss agreeing with that predicted by simulations. We demonstrate this using three low-loss HCFs, including 1st window nested antiresonant nodeless fiber (NANF), 2nd window NANF and the state-of-the-art double NANF (DNANF). The connection with a minimum achieved insertion loss of 0.079 dB was permanently secured via gluing and did not degrade during 4 weeks of continuous measurement. To the best of our knowledge, this is the lowest reported value and is comparable to or lower than the connection between dissimilar single-mode fibers (e.g., standard single-mode fiber and dispersion-compensating fiber). We also show that such connection leads to excellent suppression of higher-order modes coupling, of importance to all applications sensitive to multi-path interference. Importantly, obtaining agreement between simulations and experiments validates for the first time the accuracy of the simulations and opens the door to further optimization via simulations with the ability to subsequently achieve the same result experimentally.

End-Capping Hollow-Core Fibers With Suppressed Coupling Into Higher-Order Modes

  • DOI: 10.1109/JSTQE.2024.3381797
  • Odkaz: https://doi.org/10.1109/JSTQE.2024.3381797
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We propose a hollow-core fiber (HCF) end-cap that incorporates a short segment of a single-mode fiber (SMF) that serves as a modal filter. To adapt the end-cap input and output beam to the desired size, the SMF was fusion spliced with short segments of mode-field adapting graded index (GRIN) fibers on both sides. The end-cap is anti-reflective coated to minimize insertion loss and parasitic reflections. The presented proof-of-concept experiments show its ability to suppress coupling into HCFs' higher-order modes. For example, without any end-cap, the extinction ratio between the LP 11 and the fundamental mode was found to be as low as 9 dB when coupling light from a free-space beam that was misaligned by as little as 1.1 ∘ . This was improved to 23 dB when inserting the developed end-cap. Such small angle misalignment often exists when aligning the input beam with 3-axis (x,y,z) stages only (rather than 5-axis that also include pitch and yaw). Finally, we glued the end-cap with the HCF, providing hermetic sealing to the HCF input/output. This is of interest for stable operation in applications that use free-space light launch or require HCF output into free space.

Inkjet-printed high-performance and mechanically flexible organic photodiodes for optical wireless communication

  • Autoři: Ruiz‐Preciado, L.A., Pešek, P., Guerra Yanez, C., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Hernandez‑Sosa, G.
  • Publikace: Scientific Reports. 2024, 14 ISSN 2045-2322.
  • Rok: 2024
  • DOI: 10.1038/s41598-024-53796-5
  • Odkaz: https://doi.org/10.1038/s41598-024-53796-5
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Emerging areas such as the Internet of Things (IoT), wearable and wireless sensor networks require the implementation of optoelectronic devices that are cost-efficient, high-performing and capable of conforming to different surfaces. Organic semiconductors and their deposition via digital printing techniques have opened up new possibilities for optical devices that are particularly suitable for these innovative fields of application. In this work, we present the fabrication and characterization of high-performance organic photodiodes (OPDs) and their use as an optical receiver in an indoor visible light communication (VLC) system. We investigate and compare different device architectures including spin-coated, partially-printed, and fully-printed OPDs. The presented devices exhibited state-of-the-art performance and reached faster detection speeds than any other OPD previously reported as organic receivers in VLC systems. Finally, our results demonstrate that the high-performance of the fabricated OPDs can be maintained in the VLC system even after the fabrication method is transferred to a fully-inkjet-printed process deposited on a mechanically flexible substrate. A comparison between rigid and flexible samples shows absolute differences of only 0.2 b s−1 Hz−1 and 2.9 Mb s−1 for the spectral efficiency and the data rate, respectively.

A Full-Digital M-CAP Receiver With Synchronisation and Adaptive Blind Equalisation for Visible Light Communications

  • Autoři: Li, X., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Alves, L.N., Figueiredo, M., Zhang, M., Mana, S.M., Jungnickel, V., Chvojka, P.
  • Publikace: IEEE/OSA Journal of Lightwave Technology. 2022, 40(8), 2409-2426. ISSN 0733-8724.
  • Rok: 2022
  • DOI: 10.1109/JLT.2021.3135468
  • Odkaz: https://doi.org/10.1109/JLT.2021.3135468
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    With an emphasis on the real-time implementation of a practical carrier-less amplitude and phase (CAP) receiver for visible light communication (VLC), this paper proposes a full-digital architecture for the M -CAP receiver with synchronisation and adaptive blind equalisation. The architecture is mainly based on the observation that a CAP signal can be demodulated using a quadrature and amplitude (QAM) receiver with an added counterclockwise rotation operation. The proposed CAP receiver employs two digital phase-locked loops (DPLL) to realise the symbol timing and carrier synchronisation, which are the most critical issues in practical systems. With the constant-modulus algorithm (CMA) offering the benefit of decoupling carrier and symbol timing synchronisation, the receiver can blindly equalise the distorted signal at the output of symbol timing synchronisation. Finally, the performance of 4/16/64-CAP receivers, which are designed using this architecture and operates at 80/160/240 Mbit/s through a low-pass light-emitting diode (LED) with a 3-dB bandwidth of 7 MHz cascaded with three measured optical wireless channels, is evaluated by Monte Carlo simulations. Results show that the receiver architecture can successfully solve the symbol timing and carrier synchronisation problems and mitigate inter-symbol interference caused by LED and/or wireless channels. The design framework for a full-digital CAP receiver has been laid out in this paper.

A SIMO Hybrid Visible-Light Communication System for Optical IoT

  • DOI: 10.1109/JIOT.2021.3098181
  • Odkaz: https://doi.org/10.1109/JIOT.2021.3098181
  • Pracoviště: Katedra elektromagnetického pole, Katedra radioelektroniky
  • Anotace:
    Visible-light communication (VLC) is an emerging technology utilizing light-emitting diodes and photodetectors (PDs) and cameras [i.e., image sensors (ISs)] as the transmitter and receivers (Rx), respectively, for simultaneous data communications, illumination, localization, and sensing in the indoor optical Internet of Things. We propose a single-input–multiple-output (SIMO) hybrid VLC system using PD-based and IS-based Rxs for simultaneous high-speed and low-speed (i.e., Rb−High and Rb−Low ) data transmission. In addition, we propose amplitude overlapping AOL in the modulation format to increase Rb and reduce the attenuation due to the high-pass filter effect of the bias-T. We experimentally evaluate the performance of the proposed scheme considering the interlink impacts. Results show that at AOL of 0–0.2: 1) the measured bit error rate for the PD-based VLC is below the forward error correction limit of 3.8×10−3 for Rb−Low of 2.5 and 5 kb/s at Rb−High of 35 and 60 Mb/s, respectively, and 2) for the IS-based VLC link with the camera gain of 4 dB and Rb−High of up to 70 Mb/s, the reception success rates are >96 and 90% at Rb−Low of 2.5 and 5 kb/s, respectively.

Advances in Hollow-core to Standard Fiber Interconnection Technology

  • DOI: 10.1117/12.2624102
  • Odkaz: https://doi.org/10.1117/12.2624102
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The attenuation of hollow-core fibers (HCFs) is predicted to surpass the minimum intrinsic attenuation of standard single-mode fibers (SMFs) in the near future. Recent advances in HCF performance and drawing technology have motivated their application not only in telecommunications but also in sensing and high-power delivery. Among HCFs, nested antiresonant nodeless fibers (NANFs) have shown the lowest attenuation values with 0.28 dB/km at 1550 nm and 0.22 dB/km at 1625 nm. Furthermore, the latest generation of NANFs effectively mitigates higher-order modes, which in some applications introduces a significantly limiting factor. As HCFs are becoming more available, their incorporation into standard SMF-based systems needs to be efficiently addressed. Various solutions to the HCF-SMF interconnection have already been proposed, such as the commonly employed fusion splicing with bridge fibers, using tapers to match the mode-fields, employing micro-optics, or using the fiber-array approach. Based on the fiber-array approach we have recently demonstrated losses of only 0.16 dB per interconnection and back reflection below -60 dB. But what if the interconnection itself can provide some additional functionality beyond low loss and low back reflection? Such an approach was already proposed in the micro-optics interconnection providing a function as an optical isolator or a wavelength-division multiplexer. Still, the relatively high complexity of such a device might limit its wider application. In this talk, I will overview current trends in HCF-SMF interconnection techniques which are enabling their incorporation into current SMF-based fiber-optic systems. I will present a future outlook of providing additional functionality to the HCF-SMF interconnection. I will focus on an interconnection technique we developed, based on the fiber-array approach. I will show how components such as an optical filter, a gas cell, or a Fabry-Perot cavity can be easily formed by simple tailoring of the HCF-SMF interconnection.

An Experimental Testbed for Implementation and Validation of Software defined FSO under Atmospheric Conditions using USRPs

  • Autoři: Htay, Z., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Abadi, M.M., Burton, A.
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 59-64. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9908057
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9908057
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose a proof of concept for the software defined-based free space optical communication (FSO) using GNU radio eco-system. We present a highly reconfigurable real-time FSO system to emulate the atmospheric conditions for the medium-to-long transmission range. Using an experimental testbed, we validate the proposed concept utilizing universal software radio peripherals. We show that the software defined FSO system offers greater flexibility, less complexity, and provides real-time signal processing results without the need to change the architecture of the hardware and the physical link space. The system performance is evaluated in terms of the estimated bit error rate under fog and turbulence conditions for 200 m link span.

Analysis and simulation of a hybrid visible-light/infrared optical wireless network for IoT applications

  • Autoři: Kamalakis, T., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Alves, L.N.
  • Publikace: Journal of Optical Communications and Networking. 2022, 14(3), 69-78. ISSN 1943-0620.
  • Rok: 2022
  • DOI: 10.1364/JOCN.442787
  • Odkaz: https://doi.org/10.1364/JOCN.442787
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We analyze the performance of a hybrid visible-light/infrared optical wireless communications network for indoor Internet-of-Things applications. This approach can be used to connect multiple battery-powered sensor nodes using low-cost infrared light emitting diodes to transmit data to a master node located on the ceiling of a room. The master node uses visible light communications to send back an acknowledgment and coordinate the transmission. We present a detailed model for simulating the communications layer and energy usage, which is implemented in Python and is available under an open-source license. The results indicate the suitability of this approach for sporadically transmitting low data rate signals containing sensor readings in line with the massive machine-type communication fifth generation applications.

Demonstration of an Adaptive Fractionally-Spaced Pre-Equaliser to Increase VLC System Data Rates

  • Autoři: Li, X., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Le-Minh, H., Binns, R., Eromosele, A., Archenhold, G.
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9907976
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907976
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper demonstrates a VLC system using an adaptive fractionally-spaced pre-equaliser to extend the modulation bandwidth of the light-emitting diodes (LEDs). The proposed system has the flexibility of compensating for different LEDs by reloading the digital adaptive equaliser’s coefficients without introducing any modification to the hardware. The key enabling power to obtain the optimal equaliser coefficients is from the well-known least mean square (LMS) algorithm. As a by-product, the proposed method offers a novel angle and a method to determine the pre-equaliser coefficients for those systems which do not have the updating algorithm implemented in a real-time manner but have to rely on a stored pre-set coefficient list. Finally, the experimental validation clearly shows the effectiveness of the proposed scheme by means of the improvement in the received eye diagrams.

Demonstration of An Optical Wireless Communication System using a Software-Defined Ecosystem

  • Autoři: Htay, Z., Karanam, B.R., Guerra Yanez, C., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Khalighi, M.A., Abadi, M.M.
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 836-840. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9907956
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907956
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we experimentally demonstrate the implementation of an optical wireless communication system in a software-defined radio platform using GNU radio ecosystem and verify the link performance in terms of bandwidth jitter by changing the interpolation parameters in the software domain. We show that the software-defined optical system provides high reconfigurability and can be easily implemented without the need to change the hardware architecture, thus providing a real-time software-based system that is highly desirable.

Detection of Non-Line-of-Sight Contributions for Visible Light Positioning by Polarization

  • Autoři: De Bruyckner, J., Raes, W., prof. Ing. Stanislav Zvánovec, Ph.D., Stevens, N.
  • Publikace: Proceedings of the IEEE Photonics Conference. Vancouver: IEEE, 2022. ISBN 978-1-6654-3487-4.
  • Rok: 2022
  • DOI: 10.1109/IPC53466.2022.9975725
  • Odkaz: https://doi.org/10.1109/IPC53466.2022.9975725
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible Light Positioning (VLP) provides highly accurate and precise indoor positioning. However, near reflective surfaces, Non-Line-of-Sight (NLOS) contributions compromise the accuracy of VLP. This work demonstrates that the presence of these contributions is detectable based on the polarization state by employing a linear polarizer.

Effect of erbium-doped fiber amplifier loss compensation on 5G new radio millimeter-wave seamless transmission over analog fiber and free space optical fronthaul at 60 GHz

  • DOI: 10.1117/1.OE.61.6.066104
  • Odkaz: https://doi.org/10.1117/1.OE.61.6.066104
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We demonstrate a fifth generation (5G) new radio (NR) signal transmitted by an analog optical and seamless antenna wireless connection at the frequency band of 60 GHz to exploit a high-frequency unlicensed frequency range. An optical frequency doubling technique, using two Mach–Zehnder modulators operating in a carrier suppressed and linear regime, respectively, was adopted to obtain the desired millimeter wave frequency at the photodetector’s output. The proposed system was tested with the 5G NR signals with a maximum bandwidth of 200 MHz and 64 quadrature amplitude modulation format. It was shown that the signal transmitted through the optical fiber and free space optical link with 1 m long seamless antenna transmission at 62 GHz was capable of meeting the signal quality requirements in terms of error vector magnitude. Moreover, the system phase noise performance showed an almost negligible difference between the various system configurations.

Experimental Evaluation of a Hierarchical QAM VLC System

  • Autoři: Guerra Yanez, C., Mederos-Barrera, A., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 545-549. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9907925
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907925
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Hierarchical modulations have been used for the transmission of digital video broadcasting streams. The main objective is to mitigate the effects of noise on the perceived video quality. It is predicted that by the end of2022 video streams will constitute 82% of the total Internet traffic. Therefore, the need for new wireless technology of visible light communication (VLC) to support the Internet of things (IoT) as part of the fifth generation (5G) mobile networks, particularly in radio frequency restricted environments. In a VLC system, hierarchical modulations can enhance the perceived quality of video streaming. In this work, for the first time, a hierarchical quadrature amplitude modulation (HQAM) is proposed and experimentally investigated for transmission of an image at the data rate of S Mbps. The results show the potential of VLC as an enabling technology for video streaming applications in IoT and 5G networks.

Experimental real-time GbE MIMO FSO under fog conditions with software defined GNU Radio platform-based adaptive switching

  • Autoři: Htay, Z., Guerra Yanez, C., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Abadi, M.M., Burton, A.
  • Publikace: Journal of Optical Communications and Networking. 2022, 14(8), 629-639. ISSN 1943-0620.
  • Rok: 2022
  • DOI: 10.1364/JOCN.458562
  • Odkaz: https://doi.org/10.1364/JOCN.458562
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we demonstrate the first, to our knowledge, experimental implementation of a gigabit Ethernet multiple input single output free space optical (FSO) communications link using adaptive switching implemented in the software defined open-source software, GNU Radio, and analyze its performance. A fully functional FSO link with a feedback path is implemented using cost effective off-the-shelf components, i.e., media converters and small form-factor pluggable modules. We propose a switching mechanism at the transmitter to improve the link performance under different fog conditions and provide results for the proposed FSO system compared with a single FSO link. The real-time channel estimation is demonstrated and, based on the channel state information, adaptive switching is carried out in GNU Radio. We show that the proposed system under the heavy fog condition offers almost the same packet error rate under the clear channel but with a reduced data rate by about 100 Mbps (i.e., 600 Mbps).

Fabry-Perot Cavity based on Large-Core Graded-Index Multimode Fibers

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We demonstrate design of fiber F abry-Perot c avities b ased o n large-core graded-index multimode fibers. Smallest full width at half maximum along with maximum transmission is reached for core diameters over 200mm core and reflectivity above 99%.

Fractal Modulation Scheme for Optical Camera Communication

  • Autoři: Mederos-Barrera, A., Guerra Yanez, C., Jurado-Verdu, C., Guerra, V., Rabadan, J., Perez-Jimenez, R., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 140-144. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9908052
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9908052
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    his paper proposes a novel spatial modulation scheme for optical camera communication based on the use of a fractal structure on the transmission. This system is able to send different amounts of data depending on the distance between the transmitter (Tx) and the receiver (Rx). Two simulation experiments were carried out to validate the proposed system. In the first experiment, the number of received bits was obtained as a function of the distance between the Tx and the Rx and compared to a theoretical expression that defines a lower bound. In the second experiment, the communication channel was tested by analyzing the behaviour of the bit error rate against the quantity of noise in the image using the peak signal-to-noise-ratio. It was found that for a PSNR value of 40 dB or more, the system is able to achieve a bit error rate below the forward error correction limit of 3.8⋅10−3. This architecture has potential applications in: hierarchization of data in vehicle-to-vehicle communications, distance multiplexing of data streams in cultural spaces, and security applications.

Full-duplex transmission of multi-Gb/s subcarrier multiplexing and 5G NR signals in 39 GHz band over fiber and space

  • DOI: 10.1364/AO.447529
  • Odkaz: https://doi.org/10.1364/AO.447529
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We propose a stable full-duplex transmission of millimeter-wave signals over a hybrid single-mode fiber (SMF) and free-space optics (FSO) link for the fifth-generation (5G) radio access networks to accelerate the Industry 4.0 transformation. For the downlink (DL), we transmit 39 GHz subcarrier multiplexing (SCM) signals using variable quadrature amplitude modulation (QAM) allocations for multi-user services. As a proof of operation, we experimentally demonstrate the transmission of 3 Gb/s SCM signals (1 Gb/s per user) over a hybrid system consisting of a 10 km SMF and 1.2 m FSO link. For the uplink (UL), satisfactory performance for the transmission of 2.4 Gb/s 5G new radio (NR) signal at 37 GHz over the hybrid system is experimentally confirmed for the first time, to the best of our knowledge. The measured error vector magnitudes for both DL and UL signals using 4/16/64-QAM formats are well below the third generation partnership project (3GPP) requirements. We also further evaluate by simulation the full-duplex transmission over the system in terms of received optical and RF powers and bit error rate performance. A wireless radio distance of approximately 200 m, which is sufficient for 5G small-cell networks, is estimated for both DL and UL direction under the heavy rain condition, based on the available data from Spain. Furthermore, simulation for the DL direction is conducted to verify the superior performance of the system using variable QAM allocation over uniform QAM allocation. Using a variable modulation allocation, up to five users (2 Gb/s per user) can be transmitted over a hybrid 10 km SMF and 150 m FSO link.

General framework for calculating irradiance distributions of symmetric surface sources

  • Autoři: Guerra Yanez, C., Guerra, V., Jurado-Verdú, C., Rabadán, J., Pérez-Jiménez, R., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Optics Express. 2022, 30(24), 43910-43924. ISSN 1094-4087.
  • Rok: 2022
  • DOI: 10.1364/OE.473168
  • Odkaz: https://doi.org/10.1364/OE.473168
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Symmetries in system modeling can be exploited to obtain analytical results on the system behavior and to speed up computations using the symmetric model. This work explores the use of symmetries in radiant surfaces for calculating the induced irradiance distributions by developing a general mathematical expression. The obtained model is applied to flat, cylindrical, and spherical sources to obtain explicit expressions. An experimental evaluation of the flat source is carried out and compared with a traditional point source, and the obtained procedure for the flat scenario is compared with the direct integration approach, which shows an improvement in the computation time of at least two orders of magnitude with a relative root mean square error of less than 10%. The results show that the proposed approach enhances short-range predictions for extended sources. To demonstrate the impact of this in optical wireless communications we have outlined a few applications.

Heterogeneous RoF, RoFSO and RF bidirectional links in n79 5G band

  • Autoři: Vallejo, L., Ing. Jan Bohata, Ph.D., Nguyen, D.N., Ortega, B., Mora, J., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 16-20. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9908007
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9908007
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we demonstrate the experimental transmission of radio signal in the n79 new radio (NR) 5G frequency band over a fronthaul optical infrastructure consisting of a 10 km standard single-mode fiber, 100 m long free-space optics channel and a seamless 2 m long radio frequency link for downlink and uplink characterization. The predefined signal using 64-quadrature amplitude modulation and 20 MHz bandwidth has been used for testing while the error vector magnitude (EVM) parameter was measured. The results are also presented in terms of received optical and electrical power as well as the signal-to-noise ratio. The successful transmission over the whole proposed network with the EVM below the required limit of 9% is demonstrated for the received optical power of 0 dBm and 2.3 dBm for the downlink and uplink, respectively.

Hollow-core to Standard Fiber Interconnection with Customized Air-gap Distance

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    By modifying the design of the interconnection between standard and hollowcore fibers, we achieved low insertion loss while creating a gap in between. This will allow for insertion of thin optical elements such as filters.

Impact of Transmitter Topologies on the Performance of Indoor Visible Light Positioning Systems

  • Autoři: Caudhary, N., Younus, O.I., Alves, L.N., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 43-48. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9908042
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9908042
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The accuracy of received signal strength (RSS)-based visible light-based positioning system in the indoor environment is constrained by the multipath nature of the channel. In this paper, the impact of transmitter (Tx) topology and Tx tilting angle on the accuracy of RSS-based VLP are investigated by considering the multipath environment. Two estimation algorithms are used, linear least square and nonlinear least square, and we show that (i) the Txs topology may have a significant impact on the positioning accuracy, in which the L-shape structure achieves the highest accuracy without considering any Tx tilting angles compared with triangular and diagonal shape structures; and (ii) the use of a triangular shape structure with Tx tilting angles offer the minimum positioning error compared with other structures.

Improved bandwidth performance of hybrid optical wireless communication for an indoor IoT environment

  • DOI: 10.1109/CSNDSP54353.2022.9907901
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907901
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose the hybrid optical wireless communication system using a single light-emitting diode (LED) as a transmitter (Tx) as well as a photodiode and image sensor-based receivers (Rxs) for an indoor IoT environment. The proposed system utilizing a single LED offers simultaneously high- and low-speed transmission capabilities using visible light communication (VLC) and optical camera communication (OCC) links, respectively. The proposed scheme is intended to provide a versatile IoT environment by giving users the choice to switch between links based on device availability. By means of experimental implementation, we show that using a chip LED modulated with bipolar on-off keying modulation format and biased voltage levels improves signal transmission on both VLC and OCC links and thus the throughput of the system. Furthermore, we propose amplitude overlap AOL in the modulation format to improve the data throughput of VLC link. The results depict that error-free transmission is achieved for the VLC link at a data rate of up to 100 Mb/s which is double the 3-dB bandwidth of LED at AOL values of 0.3 and 0.5, and for the OCC link at a data rate of up to 2 kb/s at AOL values of 0 and 0.3.

Low loss and broadband low back-reflection interconnection between a hollow-core and standard single-mode fiber

  • DOI: 10.1364/OE.460635
  • Odkaz: https://doi.org/10.1364/OE.460635
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We report simultaneous low coupling loss (below 0.2 dB at 1550 nm) and low back-reflection (below −60 dB in the 1200-1600 nm range) between a hollow core fiber and standard single mode optical fiber obtained through the combination of an angled interface and an anti-reflective coating. We perform experimental optimization of the interface angle to achieve the best combination of performance in terms of the coupling loss and back-reflection suppression. Furthermore, we examine parasitic cross-coupling to the higher-order modes and show that it does not degrade compared to the case of a flat interface, keeping it below −30 dB and below −20 dB for LP11 and LP02 modes, respectively.

Near-Infrared based Optical Camera Communications

  • DOI: 10.1109/CSNDSP54353.2022.9907899
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907899
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We report, for the first time in the literature, an optical camera communications (OCC) link leveraging a near-infrared band at a wavelength of 850 nm that is visible to a standard camera and undetectable by the human eye. An experimental test-bed is developed and evaluated for the proposed system. The quality of the proposed communication link is measured in terms of the eye diagram and the bit error rate (BER) for different signal bandwidths. We demonstrated that, an acceptable BER (below the forward error correction limit) can be achieved with a data rate of ~2 kbps using a single near-infrared light-emitting diode, a commercially available camera with a 30-frame rate. This work paves the way to enable the use of the OCC links to many internet of things applications with low cost and no additional complexity.

On-demand training of deep learning equalizers for rolling shutter optical camera communications

  • Autoři: Jurado-Verdu, C., Guerra, V., Guerra Yanez, C., Rabadan, J., prof. Ing. Stanislav Zvánovec, Ph.D., Perez-Jimenez, R.
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 145-149. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9907920
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907920
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The camera’s exposure time restricts the reception bandwidth in rolling shutter-based optical camera communication links. Short exposures are preferable for communications, but under these conditions, the camera produces dark images with impracticable light conditions for human or machinesupervised applications. Alternatively, deep learning equalization stages can mitigate the effects of increasing the exposure time. These equalizers are trained using synthetic images based on the camera’s exposure time and row sampling frequency. If these parameters are unknown in advance, another artificial network is used to estimate them directly for the captured images, the estimator. This estimator is trained offline using a vast number (thousands) of representative cases. This work proposes to transfer the attained knowledge from the offline pretrained estimator to the equalizer by using transfer learning techniques. In this way, the equalizers’ training time is significantly reduced (435 times compared to full training). Consequently, transfer learning enables equalizers’ online and on-demand training at reception without interfering with the communications. Results reveal that the complete training requires using exclusively 250 synthetic images to guarantee a communication performance with a bit error rate below 10 -4 after the equalization.

Optical CS-DSB Schemes for 5G mmW Fronthaul Seamless Transmission

  • DOI: 10.1109/JPHOT.2022.3161087
  • Odkaz: https://doi.org/10.1109/JPHOT.2022.3161087
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper describes the experimental demonstration of the hybrid optical/millimeter wave signal generation and transmission over combined optical fiber and free space optics fronthaul network with a seamless antenna link. An electrical bandpass filter is used to filter out the spectrum after photodetection in order to realize the seamless antenna transmission. The successful transmission of 64/256-quadrature amplitude modulation (QAM) 5G signal with up to 200 MHz bandwidth is presented by using two different setups: one is based on two Mach-Zehnder modulators (MZM) and the other employs a directly modulated laser (DML) to provide more cost efficient fronthaul solution. The DML based approach reveals mildly better performance in comparison to the MZMs in terms of higher achieved signal-to-noise ratio and lower error vector magnitude (EVM). More specifically, the best signal-to-noise ratio and EVM achieved with the DML based setup has been 31.5 dB and 3. 3%, respectively, compared to 30.3 dB and 3.8% with the MZMs based setup while transmitting 256-QAM signal with 100 MHz bandwidth. However, both setups kept the EVM well below the given 9% and 4.5% limit for 64- and 256-QAM, respectively.

Optical time domain backscattering of antiresonant hollow core fibers

  • DOI: 10.1364/OE.461873
  • Odkaz: https://doi.org/10.1364/OE.461873
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Today’s lowest-loss hollow core fibers are based on antiresonance guidance. They have been shown both theoretically and experimentally to have very low levels of backscattering arising from the fiber structure – 45 dB below that of traditional optical fibers with a solid silica glass core. This makes their longitudinal characterization using conventional reflectometric techniques very challenging. However, it was recently estimated that when filled with air, their backscattering coefficient increases to about 30 dB below that of standard solid core fibers. This level should be measurable with commercially available high performance optical time domain reflectometers (OTDR). Here we demonstrate – for the first time to the best of our knowledge – the measurement of backscattering from the air inside a hollow core fiber. We show that the characterization of multi-km long hollow core fibers with 15 m spatial resolution is possible using a commercial OTDR instrument. To benefit from its full dynamic range, we strongly suppress the 4% back-reflections that ordinarily occur at the OTDR’s standard fiber output when directly-connected to a hollow core fiber. Furthermore, low coupling loss into the hollow core fiber (0.3 dB in our experiment) also helps to maximize the achievable OTDR signal-to-noise ratio. This approach enables distributed characterization and fault-finding in low-loss hollow core fibers, a topic of increasing importance as these fibers are now starting to be installed in commercial optical communication networks.

Optical Wireless Hybrid VLC/OCC System Based on a Single Centralized LED

  • DOI: 10.1109/CSNDSP54353.2022.9908020
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9908020
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we present the experimental demonstration of a hybrid visible light communications (VLC) and optical camera communications (OCC) system based on a single centralized light emitting diode (LED) coupled with a plastic optical fiber (POF). Two data streams of SS Mb/s and 4 kb/s are point-to-point transmitted simultaneously and passively distributed over a 20 m POF and 3 m free space optics links (FSO), where high- and low-speed signals detection is provided by a photodiode (PD) and an optical camera-based receivers, respectively. The system aims to provide different services and/or applications to the end-user regardless of the employed devices with the lack of intermediate electro-optic conversions, network simplicity and low cost, as major advantages.

Optická vlákna s dutým jádrem pro sítě 5G+

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    With the onset of 5G networks and growing demands on data capacity, fiber-optics and fiber-optic systems are drawing more attention. Their fundamental element being the optical fiber. The conventional optical fiber is a result from decades of technological evolution. Up to now, optical fibers have been used not only in telcom but also for sensing, fiber lasers and high-power delivery. Still conventional optical fibers are made of glass, mostly silica, which limits their performance, e.g. in achieving zero attenuation. Using hollow-core optical fibers brings many advantages as light propagates in air. Currently we are on the verge of commercial application of hollow-core optical fibers which will have significant impact on telecommunications but also on sensory networks, interferometry and lasers from visible to mid-infrared regions.

Optimization and design of a diffuse optical wireless sensor network

  • Autoři: Kamalakis, T., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Nero Alves, L., Khalighi, M.
  • Publikace: Applied Optics. 2022, 61(22), 6599-6608. ISSN 1559-128X.
  • Rok: 2022
  • DOI: 10.1364/AO.463330
  • Odkaz: https://doi.org/10.1364/AO.463330
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Wireless sensor networks (WSNs) are currently being deployed in everyday objects to collect and transmit information related to humidity, temperature, heartbeat, motion, etc. Such networks are part of the massive machine-type communication (mMTC) scenario within the fifth/sixth generation of wireless networks. In this paper, we consider the optimization and design of an optical WSN composed of multiple battery-powered sensor nodes based on light-emitting diode transmitters. Extending our previous work, we take into account both line-of-sight and diffuse-light propagation, and show that in indoor scenarios, diffuse radiation can improve link availability under shadowing/blocking and extend battery life. In order to optimize the optical wireless link parameters, we use a machine-learning approach based on a genetic algorithm to ascertain the performance limits of the system. The presented results indicate that the proposed system is a viable wireless option for WSNs within the context of mMTC.

Performance Analysis of Multiple Access m-CAP for Optical-Based Intra-WBAN Links

  • Autoři: Haddad, O., Khalighi, M.A., Ghassemlooy, Z., Dowhuszko, A.A., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 595-600. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9907910
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907910
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical-based wireless body area networks (WBANs) are a promising solution for remote monitoring of vital signs in radio-frequency sensitive environments such as healthcare facilities. When dealing with a large number of sensors coexisting within the same vicinity, multiple access (MA) solutions are necessary to manage the simultaneous access to the medium. In this paper, we investigate the use of MA multi-band carrierless amplitude and phase (m-CAP) for intra-WBAN links. Using the outage probability criterion, we evaluate the performance of such a solution while accounting for realistic statistical channel models. Furthermore, we study the impact of system parameters such as bandwidth, number of sub-bands, and roll-off factor on the link performance.

Performance analysis of optical extra-WBAN links based on realistic user mobility modeling

  • DOI: 10.1117/1.OE.61.2.026113
  • Odkaz: https://doi.org/10.1117/1.OE.61.2.026113
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We address the features channel characterization and performance evaluation for wireless body-area networks (WBANs) in medical applications during a walk scenario using optical wireless transmission. More specifically, we focus on optical extra-WBAN uplink communication between a central coordinator node (CN) placed on the patient’s body and an access point (AP) in a typical hospital room. To characterize the optical wireless channel, we use a Monte Carlo ray tracing-based method and take into account the effects of body shadowing and mobility based on realistic models, in contrast to the previous simplistic models considered in the literature. Using this approach, we derive the dynamic behavior of the channel DC gain for different configurations of the CNs and APs. Furthermore, based on the obtained results, we develop a statistical channel model based on kernel density estimation, which we use to investigate the impact of CN and AP placement on the communication link parameters. Also, based on the outage probability criterion, we discuss the link performance and further analyze the improvement in performance achieved through spatial diversity, i.e., by using multiple APs in the room, for different photodetector types, under different background noise conditions. The presented results show that CN placement and user’s local and global mobility significantly impact the performance of extra-WBAN links, which can nevertheless be reduced using spatial diversity. Finally, the presented performance analysis shows that a single AP equipped with an avalanche photodiode photodetector allows an acceptable link performance for low-to-moderate background noise conditions, whereas multiple APs equipped with PIN photodetectors should be used in the case of moderate-to-strong background noise.

Performance Evaluation of Seamless 5G Outdoor RoFSO Transmission at 39 GHz

  • DOI: 10.1109/LPT.2021.3134559
  • Odkaz: https://doi.org/10.1109/LPT.2021.3134559
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This letter presents results of an experimental measurement campaign involving the deployment of combined radio over the fiber and radio over free space optics (FSO) technology in the cloud-based fifth generation (5G) fronthaul network operating in the millimeter wave (mmW) area. For this purpose, we have used 10 km of optical fiber, 50 m long outdoor FSO link and 1 m long antenna seamless radio frequency transmission at 39 GHz. The results show excellent performance in terms of the phase noise and the signal-to-noise (SNR) ratio. The error vector magnitude performance depends on the modulation format and are below the standard limits for the 5G new radio signals, with 400 MHz QPSK and 64-QAM showing almost identical results for SNR of up to ~19 dB whereas 256-QAM signal offering the best spectral efficiency. Moreover, we investigate the received mmW signal deterioration due to the atmospheric conditions in the FSO channel.

Quantum Key Distribution for Visible Light Communications: A Review

  • Autoři: Zia-Ul-Mustafa, R., Boroujeni, S.S., Guerra Yanez, C., Ghassemlooy, Z., Le Minh, H., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 13th International Symposium on Communication Systems, Networks and Digital Signal Processing. Piscataway: IEEE, 2022. p. 589-594. ISBN 978-1-6654-1044-1.
  • Rok: 2022
  • DOI: 10.1109/CSNDSP54353.2022.9907896
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907896
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communication (VLC) is a promising technology to improve the capacity of the existing indoor wireless communication systems. However, VLC also comes with security concerns in line with other wireless and wired transmission systems. In this regard, quantum key distribution (QKD) has been proposed as an optimal solution to enhance the security of VLC networks at the physical layer. This paper serves as a review study of the QKD and highlights its state-of-the-art, applications and challenges in the prospect of securing the VLC systems.

Spectrally and power efficient non-DC MIMO super-Nyquist m-CAP with linear pre- and DFE post-equalizer

  • DOI: 10.1016/j.dsp.2022.103744
  • Odkaz: https://doi.org/10.1016/j.dsp.2022.103744
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper investigates a multiple-input multiple-output (MIMO) super-Nyquist multi-band carrier-less amplitude and phase (Sm-CAP) visible light communication system to improve spectral efficiency (SE). In Sm-CAP, SE is improved by violating the frequency-domain orthogonality between sub-bands (SBs) at the cost of introducing a pre-determined inter-band interference. Pre- and post-equalizers are also utilized to ameliorate the inter-symbol, inter-band, and inter-channel interference exhibited by the limited modulation bandwidth of light emitting diodes (LEDs), overlapping SBs, and MIMO channel, respectively. Here, we transmit positive and absolute values of negative data over independent LEDs with no DC-biasing to improve the power efficiency. Results show that, by adopting bit-loading in conjunction with the pre- and post-equalizers, a maximum SE of 10.1 b/s/Hz (or equivalently, a bit rate of ∼151 Mb/s) can be achieved for a bandwidth compression level and a roll-off factor of 10% and 0.1, respectively, at the target forward error correction bit error rate limit of 7%.

The BER performance of a FSO system with polar codes under weak turbulence

  • Autoři: Mohan, N., Ghassemlooy, Z., Li, E., Abadi, M.M., prof. Ing. Stanislav Zvánovec, Ph.D., Hudson, R., Htay, Z.
  • Publikace: IET Optoelectronics. 2022, 16 72-80. ISSN 1751-8768.
  • Rok: 2022
  • DOI: 10.1049/ote2.12058
  • Odkaz: https://doi.org/10.1049/ote2.12058
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The key challenge in free space optical (FSO) communications is combating turbulenceinduced fading. As the channel fading in FSO is quasi‐static, the transmission parameters such as the code rates, transmit power and modulation schemes can be modified with respect to the channel state information transmitted via the feedback path. As a result, adaptive channel coding is considered as one of the practical approaches to improve the FSO link performance. In this study, the FSO system with polar codes is investigated and its performance is analysed by determining the optimum code‐rate required to achieve a bit error rate of 10−9 under weak turbulence. It is shown that, using Monte‐Carlo simulations for the scintillation indices of 0.12 and 0.2, the successive cancelation list (SCL) decoder offers coding gains of 2.5 and 0.3 dB, respectively, as compared with SC decoder, and for the scintillation index of 0.31, the SC decoder offers a coding gain of 2.5 dB compared to that of the SCL decoder for the code rate.

The effect of exposure time on the performance of an underwater optical camera communication system

  • Autoři: Hamidnejad, E., Gholami, A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Montazerolghaem, R., Mannani, M.M.
  • Publikace: Proceedings of the 4th West Asian Symposium on Optical and Millimeter-wave Wireless Communication. Piscataway, NJ: IEEE, 2022. ISBN 978-1-6654-0913-1.
  • Rok: 2022
  • DOI: 10.1109/WASOWC54657.2022.9797914
  • Odkaz: https://doi.org/10.1109/WASOWC54657.2022.9797914
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The camera exposure time could highly affect the performance of an optical camera communication systems. In commercial cameras, the exposure time is calculated as a function of the background light. In this paper, the effect of exposure time on the performance of an underwater optical camera communication (UWOCC) system is investigated various seawaters conditions. Furthermore, the effect of the link depth of UWOCC on the exposure time of a commercial camera is investigated. Monte Carlo is used to model the UWOCC system considering the channel absorption and scattering. Results show that, the exposure time highly affects the bit error rate performance, with the sun light having no significant effect on the exposure time for the clear, coastal and harbor seawaters for the link depth greater than 10, 4, and 0.9 m, respectively.

The Usage of ANN for Regression Analysis in Visible Light Positioning Systems

  • DOI: 10.3390/s22082879
  • Odkaz: https://doi.org/10.3390/s22082879
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we study the design aspects of an indoor visible light positioning (VLP) system that uses an artificial neural network (ANN) for positioning estimation by considering a multipath channel. Previous results usually rely on the simplistic line of sight model with limited validity. The study considers the influence of noise as a performance indicator for the comparison between different design approaches. Three different ANN algorithms are considered, including Levenberg–Marquardt, Bayesian regularization, and scaled conjugate gradient algorithms, to minimize the positioning error (εp) in the VLP system. The ANN design is optimized based on the number of neurons in the hidden layers, the number of training epochs, and the size of the training set. It is shown that, the ANN with Bayesian regularization outperforms the traditional received signal strength (RSS) technique using the non-linear least square estimation for all values of signal to noise ratio (SNR). Furthermore, in the inner region, which includes the area of the receiving plane within the transmitters, the positioning accuracy is improved by 43, 55, and 50% for the SNR of 10, 20, and 30 dB, respectively. In the outer region, which is the remaining area within the room, the positioning accuracy is improved by 57, 32, and 6% for the SNR of 10, 20, and 30 dB, respectively. Moreover, we also analyze the impact of different training dataset sizes in ANN, and we show that it is possible to achieve a minimum εp of 2 cm for 30 dB of SNR using a random selection scheme. Finally, it is observed that εp is low even for lower values of SNR, i.e., εp values are 2, 11, and 44 cm for the SNR of 30, 20, and 10 dB, respectively.

Towards Compact Hollow-Core Fiber Gas Cells

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We demonstrate a 3-way interconnection device (hollow-core fiber, standard single-mode fiber and gas inlet) that is compact, low-loss, and easy-to-use.We demonstrate its performance on fibre purging, observing water vapor via infrared spectroscopy

Towards Illuminating Optical Fiber based Visible Light Communication Uplink

  • DOI: 10.1109/CSNDSP54353.2022.9907971
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907971
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present a novel concept of visible light communication (VLC) uplink by introducing a distributed receiver (Rx) formed by an illuminating optical fiber (IOF) connected to the photodetector. The major functionality of IOF-distributed Rx is to sense/detect the light signal along the fiber span at a range of modulation frequencies coming from an on-off keying modulated light-emitting diode (LED) transmitter. We show that our proposed proof-of-concept of distributed Rx performs below the forward error correction limit of 3.8⋅10−3 at frequencies up to 400kHz. We unveil the signal-to-noise ratio (SNR) limit of 19dB must be maintained for successful data reception. Higher data rates are predicted once the concept is optimized, especially in terms of SNR. The proposed IOF-based scheme can be considered as a solution to the current challenges of VLC uplink.

Towards Optical Camera Communications Using a Shape-tailored Illuminating Optical Fiber

  • DOI: 10.1109/CSNDSP54353.2022.9907989
  • Odkaz: https://doi.org/10.1109/CSNDSP54353.2022.9907989
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We have recently presented a novel concept of optical camera communications (OCC) based on illuminating optical fibers (IOF) as transmitter (Tx). In this paper, we further investigate this concept of IOF-based OCC system by replacing a straight IOF by an L-shaped IOF as the transmitter. An intensity modulated light from a white light emitting diode in the on-off keying format at frequencies of 1800 and 2400Hz is launched into the IOF. We experimentally investigate the impact of IOF bending as well as horizontal and vertical orientations of camera-based receiver on the performance of the IOF-based OCC system. The results depict 100% success of reception is achieved over a transmission distance of 50cm for the IOF bending angle in the range of 0 to 90°, and horizontal and vertical orientations of the camera.

Visible light communication with OLEDs for D2D communications considering user movement and receiver orientations

  • DOI: 10.1364/AO.446927
  • Odkaz: https://doi.org/10.1364/AO.446927
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    With the increasing use of organic light emitting diodes in lights, smart phones, wearable smartwatches, and computers, visible light-based device-to-device (D2D) communications has become more and more relevant. We propose D2D communications using smart phones’ display pixels and their built-in cameras. We investigate the impact of receiver orientation and user mobility on the link performance. We derive a Gaussian model for the probability density function of the delay spread and optical path loss (OPL), and show that the channel delay spread decreases for a typical furnished room compared with an empty room, whereas the former has an increased OPL. In addition, we show that for the case of a furnished room and considering user mobility, the peak OPL values are about 64 and 62 dB, with and without considering the receiver’s random orientation, respectively.

A 40 Mb/s VLC System Reusing an Existing Large LED Panel in an Indoor Office Environment

  • DOI: 10.3390/s21051697
  • Odkaz: https://doi.org/10.3390/s21051697
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    With advances in solid-state lighting, visible light communication (VLC) has emerged as a promising technology to enhance existing light-emitting diode (LED)-based lighting infrastructure by adding data communication capabilities to the illumination functionality. The last decade has witnessed the evolution of the VLC concept through global standardisation and product launches. Deploying VLC systems typically requires replacing existing light sources with new luminaires that are equipped with data communication functionality. To save the investment, it is clearly desirable to make the most of the existing illumination systems. This paper investigates the feasibility of adding data communication functionality to the existing lighting infrastructure. We do this by designing an experimental system in an indoor environment based on an off-the-shelf LED panel typically used in office environments, with the dimensions of 60 × 60 cm2. With minor modifications, the VLC function is implemented, and all of the modules of the LED panel are fully reused. A data rate of 40 Mb/s is supported at a distance of up to 2 m while using the multi-band carrierless amplitude and phase (CAP) modulation. Two main limiting factors for achieving higher data rates are observed. The first factor is the limited bandwidth of the LED string inside the panel. The second is the flicker due to the residual ripple of the bias current that is generated by the panel’s driver. Flicker is introduced by the low-cost driver, which provides bias currents that fluctuate in the low frequency range (less than several kilohertz). This significantly reduces the transmitter’s modulation depth. Concurrently, the driver can also introduce an effect that is similar to baseline wander at the receiver if the flicker is not completely filtered out. We also proposed a solution based on digital signal processing (DSP) to mitigate the flicker issue at the receiver side and its effectiveness has been confirmed.

A Visible Light Positioning System based on Support Vector Machines

  • Autoři: Chaudhary, N., Younus, I., Nazarichaleshtori, Z., Alves, L.N., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 32nd Annual International Symposium on Personal, Indoor and Mobile Radio Communications. Oulu: University of Oulu, 2021. ISSN 1558-2612. ISBN 978-1-7281-7586-7.
  • Rok: 2021
  • DOI: 10.1109/PIMRC50174.2021.9569249
  • Odkaz: https://doi.org/10.1109/PIMRC50174.2021.9569249
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this work, a new indoor visible light positioning algorithm is proposed based on support vector machines (SVM) and polynomial regression. Two different multipath environments of an empty room and a furnished room are considered. The algorithm starts by addressing the received power distance relation, considering polynomial regression models fitted to the specific areas of the room. In the second stage, an SVM is used to classify the best-fitted polynomial, which is used with nonlinear least squares to estimate the position of the receiver. The results show that, in an empty room, the positioning accuracy improvement for the positioning error, ε p of 2.5 cm are 36.1, 58.3, and 72.2 % for three different scenarios according to the regions’ distribution in the room. For the furnished room, a positioning relative accuracy improvement of 214, 170, and 100 % is observed for ε p of 0.1, 0.2, and 0.3 m, respectively.

An Equivalent Circuit Model of a Commercial LED With an ESD Protection Component for VLC

  • DOI: 10.1109/LPT.2021.3095557
  • Odkaz: https://doi.org/10.1109/LPT.2021.3095557
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    An equivalent circuit model for a typical commercial light-emitting diode (LED) used in visible light communication (VLC) applications is proposed. The parameters of the elements in the model are extracted from the measured impedance using a vector network analyser. The model shows high accuracy in fitting the measured results and shows the effect of bonding/packaging parasitics and the electrostatic discharge (ESD) component on the LED’s impedance and bandwidth. This study aims to raise the designer’s awareness when designing and fabricating high-speed LED/ μ LED devices to achieve the optimal modulation bandwidth in the emerging VLC applications.

An Indoor Visible Light Positioning System Using Tilted LEDs with High Accuracy

  • Autoři: Chaudhary, N., Younus, O.I., Alves, L.N., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Le-Minh, H.
  • Publikace: Sensors. 2021, 21(3), 1-16. ISSN 1424-8220.
  • Rok: 2021
  • DOI: 10.3390/s21030920
  • Odkaz: https://doi.org/10.3390/s21030920
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The accuracy of the received signal strength-based visible light positioning (VLP) system in indoor applications is constrained by the tilt angles of transmitters (Txs) and receivers as well as multipath reflections. In this paper, for the first time, we show that tilting the Tx can be beneficial in VLP systems considering both line of sight (LoS) and non-line of sight transmission paths. With the Txs oriented towards the center of the receiving plane (i.e., the pointing center F), the received power level is maximized due to the LoS components on F. We also show that the proposed scheme offers a significant accuracy improvement of up to ~66% compared with a typical non-tilted Tx VLP at a dedicated location within a room using a low complex linear least square algorithm with polynomial regression. The effect of tilting the Tx on the lighting uniformity is also investigated and results proved that the uniformity achieved complies with the European Standard EN 12464-1. Furthermore, we show that the accuracy of VLP can be further enhanced with a minimum positioning error of 8 mm by changing the height of F.

Angled Interconnection Between Standard Single-mode Fiber and Nested Modeless Antiresonant Fibers

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present angled interconnection between standard single-mode fiber and nested nodeless antiresonant fibers achieving an insertion loss of 0.45 dB and return loss below -60 dB over a wide (1450-1650 nm) spectral range.

Design and Implementation of an Optical Camera Communication System for Wireless Sensor Networking in Farming Fields

  • Autoři: Matus, V., Guerra, V., Jurado-Verdu, C., prof. Ing. Stanislav Zvánovec, Ph.D., Rabadan, J., Perez-Jimenez, R.
  • Publikace: Proceedings of the 32nd Annual International Symposium on Personal, Indoor and Mobile Radio Communications. Oulu: University of Oulu, 2021. ISSN 1558-2612. ISBN 978-1-7281-7586-7.
  • Rok: 2021
  • DOI: 10.1109/PIMRC50174.2021.9569653
  • Odkaz: https://doi.org/10.1109/PIMRC50174.2021.9569653
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical camera communication (OCC) is an innovative set of optical wireless communication that exploits the ever-increasing availability of cameras and solid-state lighting equipment to establish low data rate optical links. This paper evaluates the feasibility of implementing OCC links between sensor nodes in a field outdoors and a camera connected to the cloud in an emulated farming environment. The power efficiency and low maintenance constraints of wireless sensor networks (WSN) are considered in the hardware design of the nodes, which include an energy harvesting system. The system is capable of transmitting 7.5 bps per node at distances of about 100 m. The proposed system is considered a cost-effective and scalable solution for WSN in precision farming.

Distributed Multiuser MIMO for LiFi: Experiments in an Operating Room

  • Autoři: Mana, S.M., Jungnickel, V., Bober, L.K., Hellwig, P., Hilt, J., Schulz, D., Paraskevopoulos, A., Freund, R., Hirmanova, K., Ing. Radek Janča, Ph.D., Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: IEEE/OSA Journal of Lightwave Technology. 2021, 39(18), 5730-5743. ISSN 0733-8724.
  • Rok: 2021
  • DOI: 10.1109/JLT.2021.3091385
  • Odkaz: https://doi.org/10.1109/JLT.2021.3091385
  • Pracoviště: Katedra elektromagnetického pole, Katedra teorie obvodů
  • Anotace:
    Networked optical wireless communication, also denoted as LiFi, is expected to play an important role in so-called smart hospitals. In this paper, we present the first experimental study of LiFi in an operating room at Motol University Hospital in Prague, Czech Republic. First, we perform one-to-one measurements using an optical transmitter (Tx) and receiver (Rx) and observe that channels with a free LOS provide sufficient signal strength for mobile communication inside the operating room. Then we combine the individual LOS links into a multiple-input multiple-output (MIMO) link using four distributed transmitters representing a wireless infrastructure, and six distributed receivers representing medical devices. In this configuration, at least two strong singular values of the MIMO channel matrix are observed which allow spatial multiplexing. By appropriately clustering the transmitters and selecting the users, mobile devices can be served in parallel. For data transmission, several multiplexing schemes such as time-division multiple access (TDMA) with one and two best links, TDMA with spatial reuse, space-division multiple access (SDMA) with two best links with and without zero forcing (ZF) are considered. Results show that SDMA with ZF increases the data rate by 2.7 times compared to baseline TDMA, resulting in a total data rate of 600 Mbit/s. CCBY

Experimental Characterization of Fiber Optic Lighting - Optical Camera Communications

  • DOI: 10.1109/PIMRC50174.2021.9569280
  • Odkaz: https://doi.org/10.1109/PIMRC50174.2021.9569280
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we study the novel idea of fiber optic lighting - optical camera communications. We carry out analyses of the proposed scheme employing a light emitting diode (LED) illuminated plastic optical fiber (POF) and a rolling-shutter-based camera as the transmitter and the receiver (Rx), respectively in an indoor static environment. We also provide optical and electrical characterization of the LED and LED coupled POF illumination sources. The experiment results demonstrate that, despite the small diameter of the illuminating POF, flicker-free wireless communications at modulation frequencies of 300 and 600 Hz over the transmission distances of 50 and 75 cm can be achieved. Consequently, we show that a 100 % reception success rate is achieved for the camera-based optical Rx with the exposure time and the gain of 400 µs and 25 dB, respectively.

Experimental comparison of DSB and CS-DSB mmW formats over a hybrid fiber and FSO fronthaul network for 5G

  • DOI: 10.1364/OE.434334
  • Odkaz: https://doi.org/10.1364/OE.434334
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The telecommunication world is experiencing the 5th generation (5G) networks deployment including the use of millimeter wave (mmW) frequency bands to satisfy capacity demands. This leads to the extensive use of optical communications, especially the optical fiber connectivity at the last mile access and the edge networks. In this paper we outline fiber and free space optics (FSO) technologies for use as part of the 5G optical fronthaul network. We investigate two different mmW transmission schemes based on (i) the conventional analog radio over fiber transmission using one Mach-Zehnder modulator (MZM) with double sideband (DSB) optical modulation, and (ii) an optical-based frequency doubling with one MZM biased at the null point to introduce carrier suppression DSB (CS DSB) transmission and second MZM used for data modulation. Both systems are assessed in terms of the error vector magnitude, signal-to-noise ratio, dynamic range and phase noise. We consider a configuration for the fronthaul network in the frequency range 2 (FR2) at 27 and 39 GHz with the scale of bandwidth up to 400 MHz with M-quadrature amplitude modulation and quadrature phase shift keying. Results are also shown for FR1 at 3.5 GHz. Moreover, we investigate for the first time the 5G new radio signal transmission under strong turbulence conditions and show the turbulence-induced FSO link impairment. We finally demonstrate the CS DSB scheme performs well under chromatic dispersion-induced fading for the frequency up to 40 GHz and single mode fiber length of 30 km, whereas the DSB format seems more appropriate for an antenna seamless transmission.

Experimental demonstration of a microwave photonic link using an optically phased antenna array for a millimeter wave band

  • DOI: 10.1364/AO.414069
  • Odkaz: https://doi.org/10.1364/AO.414069
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present a hybrid radiofrequency and microwave photonic link at 25 GHz using the chromatic dispersion of an optical fiber to steer the beam of a three-element planar dipole-based phased antenna array (PAA). Our team has designed and developed an in-house built PAA, experimentally verified its parameters, and successfully demonstrated optically controlled beam steering as measured in an anechoic chamber.Moreover, a detailed analysis of the optically based beam steering in the proposed microwave photonics system has been carried out, with data transmission achieving an error vector magnitude as low as 5.6% for the frequency of 25 GHz and 20 MHz bandwidth.

Experimental Evaluation of a Hermite Function-Based Multicarrier Scheme for VLC

  • Autoři: Guerra Yanez, C., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: Proceedings of the 17th International Symposium on Wireless Communication Systems. Berlin: IEEE, 2021. ISSN 2154-0217. ISBN 978-1-7281-7432-7.
  • Rok: 2021
  • DOI: 10.1109/ISWCS49558.2021.9562218
  • Odkaz: https://doi.org/10.1109/ISWCS49558.2021.9562218
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The use of a wide variety of modulation schemes for visible light communications (VLC) systems has been proposed since the birth of this field, and each of these modulations address some specifications that must be met by the system. Modified Hermite pulses define a family of functions with desirable characteristics regarding their orthogonality and time-frequency behaviour that has been used previously in radio-frequency and ultra wideband communications, ranging and VLC applications. In this work, the first experimental evaluation, to the best of authors' knowledge, of an Hermite function-based multicarrier scheme for VLC is presented and compared with simulations carried out under similar conditions. The results show that, for low modulation orders, the system is able to detect signals even below the noise floor.

Flexible Multiband Signal Transmission using a Directly Modulated Laser over Photonically Generated 40 GHz

  • Autoři: Vallejo, L., Nguyen Dong, N., Ortega, B., Ing. Jan Bohata, Ph.D., Almenar, V., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 2021 Joint European Conference on Networks and Communications & 6G Summit. Porto: IEEE, 2021. p. 160-164. ISSN 2475-6490. ISBN 978-1-6654-1526-2.
  • Rok: 2021
  • DOI: 10.1109/EuCNC/6GSummit51104.2021.9482455
  • Odkaz: https://doi.org/10.1109/EuCNC/6GSummit51104.2021.9482455
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Flexible multiband signal transmission is proposed and demonstrated over photonically generated millimeter wave signal at 40 GHz. The proposed scheme is based on a low cost directly modulated laser (DML) for data transmission and Mach-Zehnder modulator (MZM) for carrier suppressed double sideband modulation as the optical frequency multiplication scheme employed for millimeter wave signal generation. Multiple bands transmission with 50 MHz 16-quadrature amplitude modulation (QAM) have been experimentally demonstrated along 10 km standard single mode fiber (SSMF) link with a total bitrate of 1.2 Gb/s under a minimum RoP of -1.1 dBm. Further experiments with each band employing different modulation formats and bandwidths show successful performance up to 200 Mb/s using quadrature phase shift keying (QPSK), 16-QAM, 64-QAM bands, as a proof of concept towards flexible deployment of future networks, i.e. employing centralized radio access network (C-RAN) architecture.

Fundamental Analysis of Vehicular Light Communications and the Mitigation of Sunlight Noise

  • Autoři: Eso, E., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Sathian, J., Gholami, A.
  • Publikace: IEEE Transactions on Vehicular Technology. 2021, 70(6), 5932-5943. ISSN 0018-9545.
  • Rok: 2021
  • DOI: 10.1109/TVT.2021.3078576
  • Odkaz: https://doi.org/10.1109/TVT.2021.3078576
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Intelligent transport systems (ITS) rely upon the connectivity, cooperation and automation of vehicles aimed at the improvement of safety and efficiency of the transport system. Connectivity, which is a key component for the practical implementation of vehicular light communications (VeLC) systems in ITS, must be carefully studied prior to design and implementation. In this paper, we carry out a performance evaluation study on the use of different vehicle taillights (TLs) as the transmitters in a VeLC system. We show that, the transmission coverage field of view and the link span depend on TLs illumination patterns and the transmit power levels, respectively, which fail to meet the typical communication distances in vehicular environments. This paper proposes an infrared-based VeLC system to meet the transmission range in daytimes under Sunlight noise. We show that, at the forward error correction bit error rate limit of 3.8 × 10 −3 , the communication distances of the proposed link are 63, 72, and > 89 m compared with 4.5, 5.4 and 6.3 m for BMW's vehicle TL at data rates of 10, 6, and 2 Mbps, respectively.

Impact of Receiver Orientation on OLED-based Visible-Light D2D Communications

  • Autoři: Nazarichaleshtori, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Haddad, O., Khalighi, M.-A.
  • Publikace: Proceedings of the 17th International Symposium on Wireless Communication Systems. Berlin: IEEE, 2021. ISSN 2154-0217. ISBN 978-1-7281-7432-7.
  • Rok: 2021
  • DOI: 10.1109/ISWCS49558.2021.9562253
  • Odkaz: https://doi.org/10.1109/ISWCS49558.2021.9562253
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The use of organic light emitting diodes (OLEDs) is being growing in public places, mobile phones, and wearable smartwatches and computers, which facilitate simultaneous illumination, display, and data communications. Therefore, there is a high demand to model the OLED-based visible light communications (VLC) channel in device-to-device (D2D) communications. This paper proposes D2D communications where the information data is transmitted via the smartphone's display pixels and received using the built-in cameras of another smartphone. The impact of the receiver orientation on the channel characteristics is investigated, where two static users face each other and the receiver is intentionally oriented towards the transmitter. It is shown that, in an empty room, the range of delay spreads are around 6 to 7.5 ns and 6 to 10 ns when the distances of the transmitter from the wall are 1.5 and 7.5 m, respectively. Furthermore, in a furnished room, there is a drop in the delay spread at the cost of increased optical path loss compared to the empty room.

Interconnecting Hollow-core Fibers

  • DOI: 10.1109/SUM48717.2021.9505978
  • Odkaz: https://doi.org/10.1109/SUM48717.2021.9505978
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Low-loss hollow-core fiber interconnection to standard optical fibers paves the way for high-finesse resonators, low-noise sensors, high-power delivery and next-generation fiber-optic communications. We will present main interconnection principles, discuss how back-reflection and higher-order mode excitation can be mitigated, and provide application perspectives.

Long-term stability of hollow core to standard optical fiber interconnection

  • DOI: 10.1117/12.2592377
  • Odkaz: https://doi.org/10.1117/12.2592377
  • Pracoviště: Katedra elektrotechnologie, Katedra elektromagnetického pole
  • Anotace:
    In this paper, we present results of long-term stability tests of a low-loss (<0.55 dB) hollow core fiber (HCF) to standard optical fiber interconnection prepared by modified gluing-based fiber-array technology. We measured insertion loss of three interconnected HCF samples over a period of 100 days at room temperature, observing a variation in insertion loss of less than 0.02 dB. Subsequently, we placed the HCF samples in a climatic chamber and heated to +85°C in four cycles. Maximum insertion loss variation of 0.10 dB was observed for HCF samples with angled 8° interconnections and only 0.02 dB for a HCF sample with a flat interconnection.

Low loss and high performance interconnection between standard single‑mode fiber and antiresonant hollow‑core fiber

  • DOI: 10.1038/s41598-021-88065-2
  • Odkaz: https://doi.org/10.1038/s41598-021-88065-2
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We demonstrate halving the record-low loss of interconnection between a nested antiresonant nodeless type hollow-core fiber (NANF) and standard single-mode fiber (SMF). The achieved interconnection loss of 0.15 dB is only 0.07 dB above the theoretically-expected minimum loss. We also optimized the interconnection in terms of unwanted cross-coupling into the higher-order modes of the NANF. We achieved cross-coupling as low as −35 dB into the LP11 mode (the lowest-loss higher-order mode and thus the most important to eliminate). With the help of simulations, we show that the measured LP11 mode coupling is most likely limited by the slightly imperfect symmetry of the manufactured NANF. The coupling cross-talk into the highly-lossy LP02 mode (>2000 dB/km in our fiber) was measured to be below −22 dB. Furthermore, we show experimentally that the anti-reflective coating applied to the interconnect interface reduces the insertion loss by 0.15 dB while simultaneously reducing the back-reflection below −40 dB over a 60 nm bandwidth. Finally, we also demonstrated an alternative mode-field adapter to adapt the mode-field size between SMF and NANF, based on thermally-expanded core fibers. This approach enabled us to achieve an interconnection loss of 0.21 dB and cross-coupling of −35 dB into the LP11 mode.

Multiband IFoF signal transmission based on DML with local photonic 40 GHz up conversion

  • DOI: 10.1109/ISWCS49558.2021.9562239
  • Odkaz: https://doi.org/10.1109/ISWCS49558.2021.9562239
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Multiband data signal transmission using intermediate frequency over fiber (IFoF) is proposed and demonstrated with local photonic millimetre wave (mmW) generation. The proposed scheme is based on a low cost directly-modulated laser (DML) and Mach-Zehnder modulator (MZM) biased at a null point for optical carrier suppression to realize optical frequency multiplication (OFM). Transmission of 4- and 64-quadrature amplitude modulation (QAM) signals providing data rates of 3 and 1.5 Gbps, respectively, over 25 km standard single mode fiber (SSMF) are demonstrated and signals are delivered at 40 GHz to be radiated by the remote radio heads (RRHs). As a proof of concept, also multiband signal of various modulation formats and bandwidths have been transmitted successfully along 25 km fiber link and delivered in the mm W band. Quality signal assessment by error vector magnitude (EVM) measurement at mmW bands is demonstrated and an estimation of the optical sensitivity of the system is provided.

On the 40 GHz Remote Versus Local Photonic Generation for DML-Based C-RAN Optical Fronthaul

  • DOI: 10.1109/JLT.2021.3102818
  • Odkaz: https://doi.org/10.1109/JLT.2021.3102818
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Local and remote photonic millimeter wave (mmW) signal generation schemes are theoretically and experimentally evaluated in order to compare both approaches for practical deployment in a cloud radio access network (C-RAN) fronthaul network. The paper presents a full comprehensive formulation of the frequency response of a system based on a directly modulated laser transmitting data over 40 GHz signal which is generated by external carrier suppressed modulation and optical frequency multiplication. Theoretical and experimental characterization of the system response at baseband and mmW band for local and remote generation setups show very good agreement. The remote configuration leads to a higher electrical output power (i.e., 15 dB higher in 25 km fiber links) than the local generation setup in the mmW band due to the combined effect of chirp and fiber dispersion, although intermodulation distortion is higher in the former case. Transmission experiments using quadrature phase-shift keying (QPSK) signals with 250 MHz bandwidth centered at 0.5 GHz over 10 and 25 km fiber links also confirm the superior performance of the remote setup, whereas the local setup leads to similar results to optical back-to-back (OB2B) measurements, which is also validated with data signals centered at different frequencies within the laser bandwidth frequency range. Finally, experimental results show the quality of the recovered signals in terms of error vector magnitude (EVM) as a function of the received electrical power and demonstrate that no further penalties are introduced by photonic mmW signal generation with respect to electrical back-to-back (EB2B) levels.

Optical camera communications link using an LED-coupled illuminating optical fiber

  • DOI: 10.1364/OL.428077
  • Odkaz: https://doi.org/10.1364/OL.428077
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this Letter, we propose and demonstrate a novel wireless communications link using an illuminating optical fiber as a transmitter (Tx) in optical camera communications. We demonstrate an indoor proof-of-concept system using an illuminating plastic optical fiber coupled with a light-emitting diode and a commercial camera as the Tx and the receiver, respectively. For the first time, to the best of our knowledge, we experimentally demonstrate flicker-free wireless transmission within the off-axis camera rotation angle range of 0–45° and the modulation frequencies of 300 and 500 Hz. We also show that a reception success rate of 100% is achieved for the camera exposure and gain of 200 µs and 25 dB, respectively.

Optical Fiber Delay Lines in Microwave Photonics: Sensitivity to Temperature and Means to Reduce it

  • DOI: 10.1109/JLT.2021.3052609
  • Odkaz: https://doi.org/10.1109/JLT.2021.3052609
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    One of the key functionalities in microwave photonics is to be able to define controllable time delays during the signal processing. Optical fibers are often used to achieve this functionality, especially when a long delay or a widely-tunable delay is needed. However, the stability of this delay in the presence of environmental changes (e.g., temperature) has not, to the best of our knowledge, been reviewed yet. Here, we firstly discuss the impact of temperature-induced variations on the signal propagation time in optical fibers and its implications in microwave photonics. We compare the impact of the thermal sensitivity of various delay lines for applications in which the signal is transported from point A to point B, as well as for applications in which the propagation time through a fiber or the fiber dispersion is used to create a fixed or tunable delay. In the second part of the article we show the impact of fiber thermal sensitivity on a narrow-band microwave photonics filter made of standard single mode fiber (SSMF) and a hollow core fiber (HCF), which has significantly lower thermal sensitivity of propagation time to temperature. The central frequency of the band-pass filter changes almost 16 times more in the filter made of SSMF as compared to that of HCF, dictating very tight (0.05 °C) temperature stabilization for SSMF-based filters. On the basis of our thermal sensitivity analysis we conclude that HCFs are very promising for environmentally stable microwave photonics applications.

Optical Filter-Less WDM for Visible Light Communications Using Defocused MIMO

  • DOI: 10.3390/electronics10091065
  • Odkaz: https://doi.org/10.3390/electronics10091065
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper experimentally investigates, for the first time, a new wavelength-division multiplexing-based visible light communications link based on a defocused non-imaging multiple-input multiple-output (MIMO), which removes the need for tuned optical bandpass filters paired with each receiver. The proposed system is based on using the natural diversity of the individual light emitting diodes (LEDs) within a single light source to generate an H-matrix, which is independent of spatial diversity. We show that, by transmitting K-independent sets of non-return to zero on-and-off keying signals on separate wavelengths, the received superposed symbols can be demultiplexed. The non-imaging MIMO diversity is achieved by considering the power-current characteristics of the light emitting diode, the responsivity of the photodetector array, and the defocused beam spot. The system is empirically verified for K = 3 using red, green, and blue LEDs with Q-factors of 7.66, 7.69, and 4.75 dB, respectively.

Performance Analysis and Software-Defined Implementation of Real-Time MIMO FSO With Adaptive Switching in GNU Radio Platform

  • DOI: 10.1109/ACCESS.2021.3092968
  • Odkaz: https://doi.org/10.1109/ACCESS.2021.3092968
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we provide the first software-based implementation of multiple-input multiple-output (MIMO) free space optical (FSO) link with the adaptive switching based on the software defined radio developed by GNU Radio software system, which emulates the real-time capability of the proposed scheme. We propose a switching mechanism to independently configure each transmitter and receiver, based on the channel state information provided at the transmitter via a feedback link and evaluate the link performance under atmospheric conditions such as fog and turbulence. We also validate the advantages of mitigating both the turbulence and fog in the proposed multiple input multiple output FSO system by means of numerical simulations and the developed GNU Radio software platform. We demonstrate that the proposed system can effectively operate in heavy fog with bit error rates (BER) within the range of 10 −8 to ∼10−7 over link spans of 100, 200 and 300 m. Additionally the system has been shown to mitigate moderate turbulence over a 100 m link span with BER of ∼10−7 .

Performance Analysis of Indoor Vehicular VLC Links for Autonomous Driving

  • Autoři: Eso, E., Jarchlo, E.A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Dressler, F., Sathian, J.
  • Publikace: Proceedings of the 32nd Annual International Symposium on Personal, Indoor and Mobile Radio Communications. Oulu: University of Oulu, 2021. ISSN 1558-2612. ISBN 978-1-7281-7586-7.
  • Rok: 2021
  • DOI: 10.1109/PIMRC50174.2021.9569513
  • Odkaz: https://doi.org/10.1109/PIMRC50174.2021.9569513
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    One of the major challenges in indoor vehicular visible light communications (VVLC) links is associated with the mobility leading to frequent handovers, consequently resulting in increased latency and processing time. Therefore, to address this challenge, an acceptable light coverage within the indoor channel, i.e., cell planning, is of paramount importance. In this paper we investigate the performance of a VLC link for an autonomous indoor vehicle and provide insights on the impact of the distance between light access points, and the light client’s (LC’s) angular field of view (AFOV) employing an imaging optical concentrator with a photodiode. We derive a mathematical expression to determine the optimum AFOV of the LC as a function of other system parameters such as the vertical link distance and incidence angles. Results show step responses in the bit-error-rate (BER) performance as the incidence angle increases outside the AFOV of the LC with the BER degrading sharply from 3.8 × 10 −3 to 4.4 × 10 −1 with a small increment in the incidence angle over 7.35 °.

Performance of Vehicular Visible Light Communications under the Effects of Atmospheric Turbulence with Aperture Averaging

  • DOI: 10.3390/s21082751
  • Odkaz: https://doi.org/10.3390/s21082751
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    n this paper, we investigate the performance of a vehicular visible light communications (VVLC) link with a non-collimated and incoherent light source (a light-emitting diode) as the transmitter (Tx), and two different optical receiver (Rx) types (a camera and photodiode (PD)) under atmospheric turbulence (AT) conditions with aperture averaging (AA). First, we present simulation results indicating performance improvements in the signal-to-noise ratio (SNR) under AT with AA with increasing size of the optical concentrator. Experimental investigations demonstrate the potency of AA in mitigating the induced signal fading due to the weak to moderate AT regimes in a VVLC system. The experimental results obtained with AA show that the link’s performance was stable in terms of the average SNR and the peak SNR for the PD and camera-based Rx links, respectively with <1 dB SNR penalty for both Rxs, as the strength of AT increases compared with the link with no AT.

Polarization Stable Hollow Core Fiber Interferometer With Faraday Rotator Mirrors

  • DOI: 10.1109/LPT.2021.3129591
  • Odkaz: https://doi.org/10.1109/LPT.2021.3129591
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We report the fabrication of a hollow core fiber (HCF) coupled Faraday rotator mirror component with a total insertion loss below 1.1 dB and demonstrate its use in a polarization-stable all-fiber Michelson interferometer. The signal split into the two interferometer arms is performed using a standard 2×2 fused fiber coupler. One of the coupler output ports is permanently and directly connected to the HCF with a low return loss (below −40 dB) and negligible signal coupling into higher-order modes. The demonstrated polarization-insensitive interferometer shows residual peak-to-peak polarization-induced power variations as low as 0.04 dB. The device will be of interest in interferometric applications requiring low thermal sensitivity as the phase drift of light propagating through an HCF is over an order of magnitude less sensitive to temperature than in standard fiber. Moreover, the fiber nonlinearity is almost three orders of magnitude lower in HCFs as compared to standard solid optical fibers.

Sandstorm effect on experimental optical camera communication

  • DOI: 10.1364/AO.405952
  • Odkaz: https://doi.org/10.1364/AO.405952
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Sandstorms can severely affect the reliability of outdoor optical wireless communications (OWC) by diminishing large regions’ visibility. In this work, the effect of a real sandstorm on optical camera communications (OCC) links is experimentally evaluated. Two link ranges are essayed using a cost-efficient telescope-based camera setup with commercial LEDs. Using on–off keying modulation, a data rate of 1035 and 630 bps with error probabilities of 9.14⋅10−5 and 4.1⋅10−3 for 100 m and 200 m, respectively, can be achieved. The signal-to-noise ratio of the links was optimized by tuning the analog amplifier’s gain of the camera, increasing it by up to 9 dB. It is shown that scattering due to the sandstorm can even be beneficial for increasing the data rate in OCC (contrary to classical photodetector-based OWC links), thanks to an increment of 33% on the region of interest dimensions compared to the expected clear air link.

Statistical channel modelling of dynamic vehicular visible light communication system

  • Autoři: Alsalami, F.M., Ahmad, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Haigh, P.A., Haas, O.C.L., Rajbhandari, S.
  • Publikace: Vehicular Communications. 2021, 29 ISSN 2214-2096.
  • Rok: 2021
  • DOI: 10.1016/j.vehcom.2021.100339
  • Odkaz: https://doi.org/10.1016/j.vehcom.2021.100339
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper studies a statistical channel model for dynamic vehicular visible light communication systems. The proposed model considers the effect of variation in inter-vehicular spacing and the geometrical changes on path loss of the channel. The study also considers different weather conditions and vehicle mobility based on a realistic traffic flow model that considers traffic density during different times of the day. Monte Carlo simulation is used to examine the obtained statistical model for different transmission scenarios. In addition, the Kolmogorov-Smirnov test for the statistical model and Monte Carlo simulation has been performed to verify that they represent the same distribution. The results show that the channel statistical distribution varies with the traffic flow and inter-vehicular spacing, which changes at different times of the day. The results also show that the path loss values of the non-line-of-sight component are significantly larger than the path loss values of the line-of-sight component of the channel when a single reflector is considered. However, at rush hours, when inter-vehicle spacing becomes shorter, the path loss value of multiple reflections decreases significantly.

The Evaluation of an RoF System Using FSO and a Seamless Antenna Link for the 5G RAN

  • DOI: 10.1109/ISWCS49558.2021.9562212
  • Odkaz: https://doi.org/10.1109/ISWCS49558.2021.9562212
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The fifth generation of mobile network (5G) places increased demands on the communication infrastructure, which should be formed in particular by optical networks. Moreover, the use of millimeter-wave (mmW) frequency bands contributes to higher degree of the radio frequency and optical systems convergence. Therefore, we show in this paper the comparison between two wireless seamless connections as part of the radio over fiber (RoF) system, namely free space optical link and mmW wireless link operating at the 5G mmW frequency bands of 27 and 39 GHz. We also demonstrate the impact of including a 10 km of optical fiber to a RoF system with a seamless antenna connection at 27 GHz.

The Impact of Blocking and Shadowing on the Indoor Visible Light Positioning System

  • Autoři: Younus, O.I., Chaudhary, N., Nazarichaleshtori, Z., Ghassemlooy, Z., Alves, L.N., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 32nd Annual International Symposium on Personal, Indoor and Mobile Radio Communications. Oulu: University of Oulu, 2021. ISSN 1558-2612. ISBN 978-1-7281-7586-7.
  • Rok: 2021
  • DOI: 10.1109/PIMRC50174.2021.9569377
  • Odkaz: https://doi.org/10.1109/PIMRC50174.2021.9569377
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper addresses the effects of blocking and shadowing due to peoples’ movement on the performance of visible light positioning system based on received signal strength. We consider both line-of-sight and non-line-of-sight paths and using a non-sequential ray-tracing model, the channel is characterised with and without blocking and shadowing. A linear least square with a polynomial regression model is proposed for the position estimation. We show that, the VLP accuracy degrade by ~90 and ~67% due to blocking and shadowing, respectively. Besides, at a confidence interval of 90%, the positioning error ε p of 1.47 m is recorded with human blockage as compared with 0.15 m for the non-blocking cases while shadowing introduces ε p of 0.82 m compared with 0.27 m for the non-blocking case.

The Utilization of Artificial Neural Network Equalizer in Optical Camera Communications

  • DOI: 10.3390/s21082826
  • Odkaz: https://doi.org/10.3390/s21082826
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose and validate an artificial neural network-based equalizer for the constant power 4-level pulse amplitude modulation in an optical camera communications system. We introduce new terminology to measure the quality of the communications link in terms of the number of row pixels per symbol Npps, which allows a fair comparison considering the progress made in the development of the current image sensors in terms of the frame rates and the resolutions of each frame. Using the proposed equalizer, we experimentally demonstrate a non-flickering system using a single light-emitting diode (LED) with Npps of 20 and 30 pixels/symbol for the unequalized and equalized systems, respectively. Potential transmission rates of up to 18.6 and 24.4 kbps are achieved with and without the equalization, respectively. The quality of the received signal is assessed using the eye-diagram opening and its linearity and the bit error rate performance. An acceptable bit error rate (below the forward error correction limit) and an improvement of ~66% in the eye linearity are achieved using a single LED and a typical commercial camera with equalization.

Vehicle-to-Vehicle Relay-Assisted VLC With Misalignment Induced Azimuth or Elevation Offset Angles

  • Autoři: Eso, E., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Pešek, P., Sathian, J.
  • Publikace: IEEE Photonics Technology Letters. 2021, 33(16), 908-911. ISSN 1041-1135.
  • Rok: 2021
  • DOI: 10.1109/LPT.2021.3086836
  • Odkaz: https://doi.org/10.1109/LPT.2021.3086836
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This letter investigates a vehicle-to-vehicle relay-assisted visible light communications link with amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes and analyze the effect of the relay vehicle’s orientation with respect to the source vehicle. Results show up to 150 % increase in the link span under emulated sunlight for the DF relay link compared with AF at the end of the second hop using the same system parameters at the forward error correction bit error rate limit of 3.8×10−3 . A method to mitigate the effect of system performance degradation due to misalignment between communicating vehicles is also proposed.

Vehicular VLC: A Ray Tracing Study Based on Measured Radiation Patterns of Commercial Taillights

  • Autoři: Eldeeb, H.B., Eso, E., Jarchlo, E.A., prof. Ing. Stanislav Zvánovec, Ph.D., Uysal, M., Ghassemlooy, Z., Sathian, J.
  • Publikace: IEEE Photonics Technology Letters. 2021, 33(16), 904-907. ISSN 1041-1135.
  • Rok: 2021
  • DOI: 10.1109/LPT.2021.3065233
  • Odkaz: https://doi.org/10.1109/LPT.2021.3065233
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this letter, we investigate the performance of vehicular visible light communications based on the radiation patterns of different commercial taillights (TLs) using non-sequential ray tracing simulations. Our simulation results indicate a significant variation in the path loss compared with Lambertian model. Based on the ray tracing results, we propose a new path loss model as a function of the propagation distance considering the asymmetrical radiation pattern of TLs. We use this model to derive the attainable transmission distance. We further present the delay spread for various vehicular communication scenarios to demonstrate the effect of neighboring vehicles.

Visible Light Communications for 6G Wireless Networks

  • Autoři: Niarchou, A., Boucouvalas, A.C., Ghassemlooy, Z., Alves, L.N., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the Third South American Colloquium on Visible Light Communications. Rio de Janeiro: IEEE Institute of Electrical and Electronics Engineers Inc., 2021. p. 31-36. ISBN 978-1-6654-4225-1.
  • Rok: 2021
  • DOI: 10.1109/SACVLC53127.2021.9652231
  • Odkaz: https://doi.org/10.1109/SACVLC53127.2021.9652231
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper outlines the potential use of visible light communications (VLC) in sixth generation (6G) wireless networks. In the first section of the paper, the technical aspects are identified as well as the research challenges which have raised the need to evolve from 5 to 6G. In the second section of the paper, we present a vision of 6G technology, focusing on its proposed requirements of future communication applications and scenarios, the possible network architecture, and its key performance indicators. The third section describes VLC technology, features that support its use in 6G networks, service applications and the research challenges that may contribute to the innovation and development of VLC. Finally, the conclusion is presented in the final section.

Wireless Sensor Networks Using Sub-Pixel Optical Camera Communications: Advances in Experimental Channel Evaluation

  • DOI: 10.3390/s21082739
  • Odkaz: https://doi.org/10.3390/s21082739
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical wireless communications in outdoor scenarios are challenged by uncontrollable atmospheric conditions that impair the channel quality. In this paper, different optical camera communications (OCC) equipment are experimentally studied in the laboratory and the field, and a sub-pixel architecture is raised as a potential solution for outdoor wireless sensor networks (WSN) applications, considering its achievable data throughput, the spatial division of sources, and the ability of cameras to overcome the attenuation caused by different atmospheric conditions such as rain, turbulence and the presence of aerosols. Sub-pixel OCC shows particularly adequate capabilities for some of the WSN applications presented, also in terms of cost-effectiveness and scalability. The novel topology of sub-pixel projection of multiple transmitters over the receiver using small optical devices is presented as a solution using OCC that re-uses camera equipment for communication purposes on top of video-monitoring.

400 m rolling-shutter-based optical camera communications link

  • DOI: 10.1364/OL.385423
  • Odkaz: https://doi.org/10.1364/OL.385423
  • Pracoviště: Katedra elektromagnetického pole, Katedra radioelektroniky
  • Anotace:
    In this Letter, we develop a novel technique, to the best of our knowledge, to increase the link span (𝐿𝑠) of a rolling shutter (RS)-based optical camera communications (OCC) system by reducing the spatial bandwidth of the camera in the out-of-focus regions. We demonstrate a 400 m line-of-sight RS-based OCC link, which is to date the longest 𝐿𝑠 reported in these systems, and develop a detection method to extract the information out of the video frames, successfully. The proposed system relaxes the condition of a large surface area for the transmitter light source. Consequently, we show that at 400 m 𝐿𝑠 and exposure times of 100–80 µs, a data rate of 450 bps is achieved successfully.

64-QAM LTE signal transmission at 25 GHz over hybrid SSMF and non-uniform turbulent FSO channel

  • DOI: 10.1109/WASOWC49739.2020.9409970
  • Odkaz: https://doi.org/10.1109/WASOWC49739.2020.9409970
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This contribution describes the impact of non uniform thermal-induced turbulence on 64-QAM LTE signal transmission at 25 GHz millimeter wave (mmW) signal along hybrid RoF/RoFSO links. Microwave photonic signal generation has been employed by using the optical frequency doubling with intensity modulator biased at the minimum transmission point. The optical and electrical power budgets of different scenarios have been defined and error vector magnitude (EVM) performance has been measured. It is shown that the uniform scenario with high turbulence in the middle of the link is the one with greater impact on the quality of the received data.

A Flexible OLED VLC System for an Office Environment

  • Autoři: Nazarichaleshtori, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Eldeeb, H.B., Uysal, M.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249613
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249613
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The potential use of flexible substrate-based organic light emitting diodes (OLEDs) as curved or rolled lighting sources offers news opportunities for the implementation of visible light communications (VLC) in indoor environments. This paper outlines the use of such a system in a furnished office and investigates the impact of the beam pattern of OLED, which is symmetrical and wider than Lambertian, on the VLC system. We present new results of the VLC system performance in terms of the root-mean-square delay spread and the bit error rate (BER) for the link using both flat and half-circular OLEDs. We demonstrate a data rate of 4 Mb/s using both the curved and flat OLEDs for the transmitter’s half-angle within the range of ±90° and ±53°, respectively with a BER below the forward error correction BER limit.

A Full-Duplex Optical Millimeter Waves (60-100 GHz) Radio-over-Fiber System

  • Autoři: Bahrami, A., Ghassemlooy, Z., Mansour Abadi, M., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249545
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249545
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose and simulate the most compact full-duplex optical millimeter wave radio-over-fiber (mmW-RoF) system employing binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) with error-free transmission over 10, 25 and 50 km of single mode fibers (SMF) in up-link (UL) and down-link (DL). We evaluate the EVM values for DL and UL are < 24% for BPSK and QPSK over the 10, 25 and 50 km of SMF.

A Head/Taillight Featuring Hybrid Planar Visible Light Communications/Millimetre Wave Antenna for Vehicular Communications

  • DOI: 10.1109/ACCESS.2020.3006992
  • Odkaz: https://doi.org/10.1109/ACCESS.2020.3006992
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    With the emergence of the fifth generation and beyond mobile networks, both visible light communications (VLC) and radio frequency (RF) or millimetre wave (mmW) systems are expected to maintain the connectivity in various environments. In outdoor environments the link (VLC or RF) availability is paramount, which is affected by channel conditions. In particular, in vehicular communications other vehicles, harsh environment, and road geometry and structure will have the impact on the link connectivity and availability. In such cases, a front-end antenna solution, which benefits both optical and RF communication links, can be seen as an attractive option that can be fitted in future vehicles. In this paper, we present the design and practical implementation of a planar hybrid VLC/mmW antenna operating at 20.8 GHz and show measured results for characterization of RF and VLC links as well as communications performance. We have used the widely adopted on-off keying and quadrature amplitude modulation schemes with different orders todemonstrate data rates of 5 Mb/s and up to 100 Mb/s for the VLC and mmW links, respectively. By measuringthe bit error rate and the error vector magnitude for VLC and RF links, respectively for each modulation we have shown that the proposed hybrid planar antenna is suitable for example in a typical vehicle-to-ehicle communications.

A Multi-Hop Relay Based Routing Algorithm for Vehicular Visible Light Communication Networks

  • Autoři: Yin, R., Ghassemlooy, Z., Zhao, N., Yuan, H., Raza, M., Eso, E., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249630
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249630
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The use of visible light communications (VLC) in intelligent transportation systems is becoming highly popular. In this paper, we present a predictionbased channel gain model and propose a multi-hop relaybased routing algorithm for vehicular VLC communication networks. Using the surrogate modeling lab platform SUMO and Matlab we show that, a stationary velocity of vehicles is better suited to form a good prediction, while the proposed routing algorithm offers improved signal-to-noise ratio.

A Real-time Vehicular Visible Light Communications for Smart Transportation

  • Autoři: Lega, K., Sammeta, S.N.H., Bollepally, D., Mallavarapu, G.K., Eso, E., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249443
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249443
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we demonstrate a real time vehicular visible light communications prototype using Raspberry Pi’s for switching of light emitting diodes, signal processing and detection at the receiver side. The low cost system is attractive offering a communication link span of up to 12 m with error free transmission at a data rate of 9.6 kbps, as it shows good performance in the communication distance achieved.

A Relay-Assisted Vehicular Visible Light Communications Network

  • Autoři: Eso, E., Pešek, P., Chvojka, P., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Sathian, J.
  • Publikace: IEEE Photonics Conference - Proceeding. Vancouver: IEEE, 2020. ISSN 2374-0140. ISBN 978-1-7281-5891-4.
  • Rok: 2020
  • DOI: 10.1109/IPC47351.2020.9252388
  • Odkaz: https://doi.org/10.1109/IPC47351.2020.9252388
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we experimentally demonstrate a relay-assisted vehicular visible light communications (VLC) link using a vehicle taillight. The results show that, the decode-and-forward relay scheme is a suitable candidate for vehicular VLC connectivity as part of the intelligent transport systems.

An Artificial Neural Network Equalizer for Constant Power 4-PAM in Optical Camera Communications

  • Autoři: Younus, O.I., Hassan, N.B., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Nero Alves, L., Haigh, P.A., Le Minh, H.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249579
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249579
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, for the first time, we propose and validate a nonlinear artificial neural network (ANN) equalizer for constant power pulse amplitude modulation (CP 4-PAM) in an optical camera communication (OCC) system. Using the proposed equalizer, we demonstrate experimental-based non-flickering transmission at a data rate of up to 7 kbps using a single light-emitting diode and an image sensor with 30 frames per second rate. The quality of the received signal is introduced based on the eye-diagram opening where we have proved an ability to transmit data with up to 232 bits per frame after the equalizer deployment.

Antenna Phased Array Beamforming at 26 GHz Using Optical True Time-Delay

  • DOI: 10.1109/CSNDSP49049.2020.9249587
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249587
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Multi-element antenna beam steering in freelicence higher frequency bands is one of the crucial features of 5G networks enabling better tracking of the users. In this paper, we present an experimental microwave photonics transmission system operating at 26 GHz where beamforming is fully realized in the optical domain. The system is designed to be deployed as a part of the mobile fronthaul network with an optical fiber span of 15 km. As a proof of concept, a planar 3-element antenna array has been developed and radiation patterns were measured in an anechoic chamber with high agreement between experimental and simulation results.

Bandwidth Dependency of (O)LEDs On Bias Current

  • Autoři: Burton, A., Haigh, P.A., Chvojka, P., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 3rd West Asian Symposium on Optical and Millimeter-wave Wireless Communications - Proceeding. Piscataway: IEEE, 2020. p. 1-6. ISBN 978-1-7281-3767-4.
  • Rok: 2020
  • DOI: 10.1109/WASOWC49739.2020.9410027
  • Odkaz: https://doi.org/10.1109/WASOWC49739.2020.9410027
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This work investigates the modulation bandwidth (Bmod) dependency of organic and non-organic light emitting diodes (OLED\LED) on the applied bias current (IB). The equivalent lumped element transient circuit models are shown with the critical components empirically extracted for both types of device. Four OLEDs of varying sizes are tested in addition to four high power LEDs (white phosphor, red, green and blue). Through analysis of the current-voltage characteristics, the device and dynamic diode resistances are determined as well as the ideality factors. We show that OLEDs have higher ideality factors to the traditional LEDs (almost double) hence the increased turn-on voltage, however have similar AC drive voltage characteristics across the emitting portion of the device between 8-12%. Furthermore, both devices exhibit an increase in Bmod with an increase in IB. It is shown that the OLEDs Bmod increases linearly in relation to IB, reaching ≥80% of the maximal Bmod at ≥60% of their maximum IB rating. Conversely, the LEDs display an exponential rise in Bmod in relation to IB, with ≥80% of the maximal Bmod at ≥35% of their maximum IB rating, with the red LED showing the greatest results at just 17%.

Channel Characterization and Modeling for Optical Wireless Body-Area Networks

  • Autoři: Haddad, O., Khalighi, M.-A., prof. Ing. Stanislav Zvánovec, Ph.D., Adel, M.
  • Publikace: IEEE Open Journal of the Communications Society. 2020, 1 761-776. ISSN 2644-125X.
  • Rok: 2020
  • DOI: 10.1109/OJCOMS.2020.2999104
  • Odkaz: https://doi.org/10.1109/OJCOMS.2020.2999104
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We address channel characterization and modeling for medical wireless body-area networks (WBANs) based on the optical wireless technology. We focus on the intra-WBAN communication links, i.e., between a set of medical sensors and a coordination node, placed on the patient’s body. We consider a realistic mobility model, e.g., inside a hospital room, which takes into account the effect of shadowing due to body parts movements and the variations of the underlying channels. To take into account the global and local user mobility, we consider a dynamic model based on a three-dimensional animation of a walk cycle, as well as walk trajectories based on an improved random way-point mobility model. Then, Monte Carlo ray-tracing simulations are performed to obtain the channel impulse responses for different link configurations at different instants of the walk scenarios. We then derive first-and second-order statistics of the channel parameters such as the channel DC gain, delay spread, and coherence time, and furthermore, propose best fit statistical models to describe the distribution of these parameters for a general scenario.

Channel Characterization for Optical Extra-WBAN Links Considering Local and Global User Mobility,

  • Autoři: Haddad, O., Khalighi, M.-A., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of SPIE Photonics West, OPTO, 2020. Washington: SPIE, 2020. ISSN 0277-786X. ISBN 978-1-5106-3378-0.
  • Rok: 2020
  • DOI: 10.1117/12.2544901
  • Odkaz: https://doi.org/10.1117/12.2544901
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We investigate channel characterization for wireless body-area networks (WBANs) in medical applications using optical signal transmission. More specically, we focus on uplink communication from a central coordinator node (CN), placed on the patient's body, to an access point (AP) in a typical hospital room, which is usually referred to as extra-WBAN link. Using a ray-tracing based approach, we quantify the main characteristics of the optical channel while considering the effects of body shadowing and mobility (accounting for body movements and user global mobility inside the room). Based on the presented results, we discuss the impact of the positions of the CN and the AP on the link parameters. We also evaluate the link performance based on the outage probability criterion, and further quantify the performance improvement achieved by using multiple APs in the room.

Comparison of carrier suppressed and quadrature bias point external modulation for 40 GHz millimeter-wave photonic generation using a 16-QAM signal with directly modulated laser

  • DOI: 10.1109/CSNDSP49049.2020.9249619
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249619
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A directly modulated laser usage is proposed for 16-QAM signal transmission over hybrid optical links using two optical frequency multiplication schemes based on external modulation for 40 GHz millimeter-wave (mmW) signal generation. We provide an experimental comparison of two possible approaches: quadrature bias point external modulation system using additional optical filter and null transmission point with suppressed carrier. The systems are discussed in terms of cost and complexity of mmW photonic transmission. High error vector magnitude performance of mmW transmission over fiber and free space optics links is demonstrated and an estimation of the sensitivity of the systems is provided.

Comprehensive optical and electrical characterization and evaluation of organic light-emitting diodes for visible light communication

  • DOI: 10.1117/1.OE.59.4.046106
  • Odkaz: https://doi.org/10.1117/1.OE.59.4.046106
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In recent years, we have seen an increased use of organic light-emitting diodes (OLEDs) for illumination in indoor environments due to their softer light compared with the conventional inorganic LEDs. In addition, OLEDs have been reported in visible light communication (VLC) systems, specifically for applications with lower data rates, such as information boards, camera communications, and positioning. However, OLEDs need extensive electrical and optical characterization if they are going to be fully exploited in VLC. We investigated characteristics of a range of flexible and rigid OLEDs and compared them with inorganic LEDs. We show that OLEDs have highly linear power–current characteristics, and compared with rigid OLEDs with beam patterns closely matching the Lambertian profile, the flexible OLED’s radiation pattern is wider. Based on the measured experimental data, a new expression for the OLED’s beam pattern, which follows the three-term Gaussian profile, is proposed. Moreover, we show that using larger size OLEDs in VLC links offers improved bit error rate performance over a wide tilting angle of up to 80 deg and a transmission path length of up to 60 cm.

Coverage of a shopping mall with flexible OLED-based visible light communications

  • Autoři: Nazarichaleshtori, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Eldeeb, H.B., Uysal, M.
  • Publikace: Optics Express. 2020, 28(7), 10015-10026. ISSN 1094-4087.
  • Rok: 2020
  • DOI: 10.1364/OE.389814
  • Odkaz: https://doi.org/10.1364/OE.389814
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communications (VLC) can utilize light-emitting diodes (LEDs) to provide illumination and a safe and low-cost broadcasting network simultaneously. In the past decade, there has been a growing interest in using organic LEDs (OLEDs) for soft lighting and display applications in public places. Organic electronics can be mechanically flexible, thus the potential of curved OLED panels/displays devices. This paper provides unique characteristics of a flexible OLED-based VLC link in a shopping mall. We show that, for curved OLED the radiation pattern displays a symmetry, which is wider than Lambertian. A number of scenarios of VLC system with flexible OLED are analyzed. Numerical models for the delay spread and optical path loss are derived, which followed a 2-term power series model for both empty and furnished rooms. We show that using a full-circular OLED for both empty and furnished rooms offers a uniform distribution of emitted power for the same transmission link spans. The link performance using full and half-circular OLED in an empty room shows that the average optical path losses are lower by 5 and 4 dB, compared with the furnished room.

Data Rate Enhancement in Optical Camera Communications Using an Artificial Neural Network Equaliser

  • Autoři: Younus, O.I., Hassan, N.B., Ghassemlooy, Z., Haigh, P.A., prof. Ing. Stanislav Zvánovec, Ph.D., Alves, L.N., Minh, H.L.
  • Publikace: IEEE Access. 2020, 8 42656-42665. ISSN 2169-3536.
  • Rok: 2020
  • DOI: 10.1109/ACCESS.2020.2976537
  • Odkaz: https://doi.org/10.1109/ACCESS.2020.2976537
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In optical camera communication (OCC) systems leverage on the use of commercial off-the-shelf image sensors to perceive the spatial and temporal variation of light intensity to enable data transmission. However, the transmission data rate is mainly limited by the exposure time and the frame rate of the camera. In addition, the camera’s sampling will introduce intersymbol interference (ISI), which will degrade the system performance. In this paper, an artificial neural network (ANN)-based equaliser with the adaptive algorithm is employed for the first time in the field of OCC to mitigate ISI and therefore increase the data rate. Unlike other communication systems, training of the ANN network in OCC is done only once in a lifetime for a range of different exposure time and the network can be stored with a look-up table. The proposed system is theoretically investigated and experimentally evaluated. The results record the highest bit rate for OCC using a single LED source and the Manchester line code (MLC) non-return to zero (NRZ) encoded signal. It also demonstrates 2 to 9 times improved bandwidth depending on the exposure times where the system’s bit error rate is below the forward error correction limit.

Evaluation of Fog Effects on Optical Camera Communications Link

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The applications of Optical Camera Communications (OCC) have been tested for vehicular communications, Internet-of-things (IoT), and other outdoor scenarios due to the vast availability of standard camera equipment. The outdoor channel is, however, affected by atmospheric conditions, ranging from the presence of particles or water drops in the air to thermally induced fluctuations of the refractive index (turbulence). In this work, we experimentally investigate the influence of fog on an OCC link exploiting rolling shutter cameras and using redgreen- blue (RGB) channels inside a laboratory chamber featuring a fog machine. The analysis is performed using the Pearson’s correlation coefficient between test and reference signals as a measure of similarity or decay of the signal attenuation of fog associated with atmospheric visibility.

Exact modeling of photonic crystal fibers for determination of fundamental properties

  • DOI: 10.1016/j.yofte.2020.102177
  • Odkaz: https://doi.org/10.1016/j.yofte.2020.102177
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present a simple but highly accurate modeling technique for real photonic crystal fibers (PCFs) characterization. We determine the influence caused by idealized model parameters. Our technique can be applied to arbitrary PCF air-hole structures, as it takes into account all structural distortions. It requires only an image of the PCF cross-section to create an accurate PCF model. Model outputs are presented in comparison with the measurement of chromatic dispersion curve and the effective mode area. We provide a study on the impact of imprecise determination of glass refractive index on the PCF model accuracy. We demonstrate how the simplification of the air-hole deformations can influence the chromatic dispersion curve. Finally, we show the effect of precise PCF modeling on example of supercontinuum generation.

Expanded Multiband Super-Nyquist CAP Modulation for Highly Bandlimited Organic Visible Light Communications

  • Autoři: Chvojka, P., Haigh, P.A., Minotto, A., Burton, A., Murto, P., Genene, Z., Mammo, W., Andersson, M.R., Wang, E., Ghassemlooy, Z., Cacialli, F., Darwazeh, I., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: IEEE Systems Journal. 2020, 14(2), 2544-2550. ISSN 1932-8184.
  • Rok: 2020
  • DOI: 10.1109/JSYST.2019.2939026
  • Odkaz: https://doi.org/10.1109/JSYST.2019.2939026
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this article, we experimentally demonstrate a novel expanded nonorthogonal multiband super-Nyquist carrier-less amplitude and phase ( m -ESCAP) modulation for bandlimited organic visible light communication (VLC) systems. The proposed scheme has the same bandwidth requirement as the conventional m -CAP while breaking the orthogonality between subcarriers by purposely overlapping them. We compare m -ESCAP with the conventional m -CAP and a compressed nonorthogonal version of m -CAP ( m -SCAP) in terms of measured bit error rate (BER) performance, bit rates, and spectral efficiencies. We show that the m -ESCAP system offers improvement in the bit rate of ∼ 10% and 20% compared to the m -CAP and m -SCAP, respectively, and in the spectral efficiency of ∼ 20% compared to m -CAP. These gains are achieved at the cost of increased BER, which, however, remains below the 7% forward error correction limit.

Experimental and Analytical Investigations of an Optically Pre-Amplified FSO-MIMO System With Repetition Coding Over Non-Identically Distributed Correlated Channels

  • DOI: 10.1109/ACCESS.2020.2964149
  • Odkaz: https://doi.org/10.1109/ACCESS.2020.2964149
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents theoretical and experimental bit error rate (BER) results for a free-space optical (FSO) multiple-input-multiple-output system over an arbitrarily correlated turbulence channel. We employ an erbium-doped fiber amplifier at the receiver (Rx), which results in an improved Rx’s sensitivity at the cost of an additional non-Gaussian amplified spontaneous emission noise. Repetition coding is used to combat turbulence and to improve the BER performance of the FSO links. A mathematical framework is provided for the considered FSO system over a correlated non-identically distributed Gamma-Gamma channel; and analytical BER results are derived with and without the pre-amplifier for a comparative study. Moreover, novel closed-form expressions for the asymptotic BER are derived; a comprehensive discussion about the diversity order and coding gain is presented by performing asymptotic analysis at high signal-to-noise ratio (SNR). To verify the analytical results, an experimental set-up of a 2×1 FSO-multiple-input-single-output (MISO) system with pre-amplifier at the Rx is developed. It is shown analytically that, both correlation and pre-amplification do not affect the diversity order of the system, however, both factors have contrasting behaviour with respect to coding gain. Further, to achieve the target forward error correction BER limit of 3.8×10−3 , a 2×1 FSO-MISO system with a pre-amplifier requires 6.5 dB lower SNR compared with the system with no pre-amplifier. Moreover, an SNR penalty of 2.5 dB is incurred at a higher correlation level for the developed 2×1 experimental FSO set-up, which is in agreement with the analytical findings.

Experimental Demonstration of a 40 Mb/s VLC System Using a Large Off-the-Shelf LED Panel

  • Autoři: Li, X., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Haigh, P.A.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249608
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249608
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper experimentally demonstrates a VLC sys-tem using a large off-the-shelf LED panel with dimensions of 60 × 60 cm 2 and achieves a data rate of 40 Mb/s based on multi-band carrier-less amplitude and phase (CAP) modulation. The proposed system demonstrates the potential of utilising the existing LED-based lighting infrastructure for simultaneous indoor illumination and data communication.

Experimental Evaluation of an Analog Gain Optimization Algorithm in Optical Camera Communications

  • DOI: 10.1109/CSNDSP49049.2020.9249441
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249441
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The operation of Optical Camera Communication systems in outdoor conditions is challenged by interfering sources of light and optical attenuation induced by the atmosphere. The low signal power at the receiver is prone to be affected by the quantization noise at the analog-to-digital converter. In this paper, an algorithm for optimizing the camera’s analog gain has been experimentally evaluated under laboratory conditions. The image quality improvement is estimated by Pearson’s correlation coefficient to a template signal, and it is shown to improve the signal-to-noise ratio up to 27.8 dB.

Experimental multi-user VLC system using non-orthogonal multi-band CAP modulation

  • Autoři: Pešek, P., Haigh, P.A., Younus, O.I., Chvojka, P., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Optics Express. 2020, 28(12), 18241-18250. ISSN 1094-4087.
  • Rok: 2020
  • DOI: 10.1364/OE.393813
  • Odkaz: https://doi.org/10.1364/OE.393813
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper provides experimental results for a multi-user visible light communications system using multi-band carrier-less amplitude and phase (m-CAP) modulation scheme. We optimize the system performance by adapting pulse shaping filter parameters, subcarrier spacing and allocating different baud rates to individual sub-bands called allocated m-CAP (Am-CAP). We show that a maximal system data rate of ∼468 Mb/s for four users can be supported while gaining higher flexibility for optimization and the same or lower computational complexity compared with the conventional m-CAP scheme.

Experimental validation of a 64-QAM LTE radio-over-fiber and free-space optics link at the 2000 nm band

  • DOI: 10.1109/CSNDSP49049.2020.9249581
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249581
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Radio over fiber (RoF) transmission systems have been developing rapidly, especially for applications in 5G networks. In scenarios unsuitable for fiber-optics, radio over free-space optics (RoFSO) presents a suitable solution. Nevertheless, free-space optics (FSO) suffers from atmospheric conditions. The use of the 2000 nm band offers several advantages over the commonly used 1550 nm region. We focus on proof-of-concept evaluation of such a 2000 nm RoFSO transmission system. Measured characteristics are compared with a similar 1550 nm RoFSO system. We demonstrate both systems for QPSK and 64-QAM LTE formats, at 5 GHz and 10 GHz with a 20 MHz bandwidth.

Experimentally Derived Feasibility of Optical Camera Communications under Turbulence and Fog Conditions

  • DOI: 10.3390/s20030757
  • Odkaz: https://doi.org/10.3390/s20030757
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical camera communications (OCC) research field has grown recently, aided by ubiquitous digital cameras; however, atmospheric conditions can restrict their feasibility in outdoor scenarios. In this work, we studied an experimental OCC system under environmental phenomena emulated in a laboratory chamber. We found that the heat-induced turbulence does not affect our system significantly, while the attenuation caused by fog does decrease the signal quality. For this reason, a novel strategy is proposed, using the camera’s built-in amplifier to overcome the optical power loss and to decrease the quantization noise induced by the analog-digital converter of the camera. The signal quality has been evaluated using the Pearson’s correlation coefficient with respect to a reference template signal, along with the signal-to-noise ratio that has been empirically evaluated. The amplification mechanism introduced allows our system to receive the OCC signal under heavy fog by gradually increasing the camera gain up to 16 dB, for meteorological visibility values down to 10 m, with a correlation coefficient of 0.9 with respect to clear conditions.

Fiber-optic Fabry-Perot Interferometry for High-resolution Motion Detection

Flicker-free Multi-channel Transmitter Orientation in Camera based Optical Wireless Communications

  • DOI: 10.1364/CLEOPR.2020.C6F_5
  • Odkaz: https://doi.org/10.1364/CLEOPR.2020.C6F_5
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We demonstrate the camera based optical wireless communications using flicker-free multi-channel transmitter orientation that provide 100 % success of reception over orientation angle of up to 30° at 200 and 400μs camera shutter speed.

Hollow-Core Optical Fibers

  • DOI: 10.13164/re.2020.0417
  • Odkaz: https://doi.org/10.13164/re.2020.0417
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Today hollow-core optical fibers (HCF) are on the verge of surpassing the attenuation benchmark of silica single-mode optical fibers used in optical communication. Compared to solid-core optical fibers, HCFs exhibit ultra-low nonlinearity, high damage threshold, low latency and temperature insensitivity, making them ideal candidates for high-speed data communication, high-resolution sensing, high-power delivery and precise interferometry. The main challenges of low insertion loss, suppressed back-reflections and fundamental mode coupling must be addressed to incorporate HCFs into existing fiber-optic systems to fully exploit their potential. This paper provides an overview of the HCF history, from early papers in the 1980s, over the invention of photonic-bandgap HCFs, to the recent achievements with antiresonant HCFs. Then light guiding mechanisms are presented and key HCF properties are discussed. Interconnection techniques to standard optical fibers are compared with respect to possible HCF applications. Fusion splicing results are presented with an~alternative interconnection solution based on a modified fiber-array technique newly developed by our team. Finally, cutting-edge HCF applications that take advantage of our HCF interconnection, are discussed.

Impact of Channel Correlation on Different Performance Metrics of OSSK-Based FSO Systems

  • DOI: 10.1109/TWC.2019.2955449
  • Odkaz: https://doi.org/10.1109/TWC.2019.2955449
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we study the impact of correlation on the bit error rate (BER) and the channel capacity of a free-space optical (FSO) multiple-input-multiple-output (MIMO) system employing optical space shift keying (OSSK) over a fading channel. In order to study a practical correlated channel, we consider the effect of channel correlation due to both small-and large-scale eddies and show that the use of OSSK over correlated FSO channel can lead to an improved system performance with increasing correlation level of upto 0.9. In this work, we first develop an analytical framework for different performance metrics of the OSSK multiple-input single-output system with correlation and then extend our investigation by proposing an asymptotically accurate mathematical framework for MIMO. We also validate all the analytical results using MATLAB simulations. Finally, we develop an experimental setup of FSO with two correlated links to study the throughput and latency of the links at different turbulence levels.

Impact of Thermal-Induced Turbulent Distribution Along FSO Link on Transmission of Photonically Generated mmW Signals in the Frequency Range 26–40 GHz

  • DOI: 10.1109/JPHOT.2019.2959227
  • Odkaz: https://doi.org/10.1109/JPHOT.2019.2959227
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Microwave photonics is a promising solution to transmit millimeter wave (mmW) signals for the 5th generation (5G) mobile communications as part of a centralized radio access network (C-RAN). In this paper, we experimentally evaluate the impact of turbulent free space optics links on photonically generated mmW signals in the frequency range of 26−40 GHz . We analyze the remote generation of mmW signals over hybrid links based on free-space optics (FSO) and standard single mode optical fiber (SSMF) with −39.97dBm received electrical power and phase noise level at 100kHz as low as −95.92dBcHz at 26GHz . Different thermal distributions along the FSO link have been implemented and Gamma-Gamma model has been employed to estimate the thermally induced turbulence. The results show high electrical power decrease and fluctuation of the generated mmW signal according to the particular level of the turbulence in terms of refractive index structure parameter and thermal distribution along the FSO link. 8Gb/s 16-quadrature amplitude modulation (QAM) data transmission at 42GHz has been demonstrated over the hybrid link with minimal error vector magnitude (EVM) value of 5% whereas turbulent FSO link introduced up to 5dB power penalty.

Implementation and Evaluation of a 10 Gbps Real-time FSO Link

  • Autoři: Htay, Z., Mohan, N., Abadi, M.M., Ghassemlooy, Z., Burton, A., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 3rd West Asian Symposium on Optical and Millimeter-wave Wireless Communications - Proceeding. Piscataway: IEEE, 2020. p. 1-7. ISBN 978-1-7281-3767-4.
  • Rok: 2020
  • DOI: 10.1109/WASOWC49739.2020.9410045
  • Odkaz: https://doi.org/10.1109/WASOWC49739.2020.9410045
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we present and experimentally evaluate a real-time 10 Gbps free-space optical (FSO) link under varying atmospheric conditions. In bandwidth-craving wireless technologies due to the ubiquitous consumption by internet of things devices and requiring high data rate online services, unlicensed FSO systems can be a promising candidate to satisfy the network capacity of the existing data communications technologies. In this work, we verify the experiment using small form-factor pluggable transceivers mounted FPGA as a FSO transmitter and receiver. Here, a high-speed single FSO link is proposed and its performance under turbulence and fog conditions using the dedicated indoor atmospheric chamber is evaluated. We show that, the proposed system under the turbulence condition with a scintillation index of 0.35 offers the same data rate as the link under a clear channel, while the bit error rate increases from 10 -12 to 5 × 10 -4.

Influence of Receiver Orientation on Differential Polarization-based VLC

  • Autoři: De Bruycker, J., Raes, W., prof. Ing. Stanislav Zvánovec, Ph.D., Stevens, N.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249486
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249486
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible Light Communication (VLC) has received substantial research attention in the last decade. The vast majority of VLC focuses on the modulation of the transmitted light intensity. In this work, however, the intensity is kept constant while the polarization direction is deployed as a carrier of information. Data is demodulated using a differential receiver equipped with orthogonal polarizers. An analytical expression to evaluate the Signal-to-Noise Ratio (SNR) as a function of the rotation angle of the receiver is derived and validated in an experimental setup. This work demonstrates the potential of polarization based modulation in the field of VLC.

Investigation of a WDM M-QAM RoF-RoFSO System

  • Autoři: Hamidnejad, E., Gholami, A., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: 3rd West Asian Symposium on Optical and Millimeter-wave Wireless Communications - Proceeding. Piscataway: IEEE, 2020. p. 1-5. ISBN 978-1-7281-3767-4.
  • Rok: 2020
  • DOI: 10.1109/WASOWC49739.2020.9409998
  • Odkaz: https://doi.org/10.1109/WASOWC49739.2020.9409998
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The radio over fiber (RoF) technology combines the advantages of radio frequency (RF) and optical communication systems. Hybrid RoF and radio over free space optics (RoFSO) is a solution for the last mile access networks in urban areas and in areas where installation of RoF links is impractical and costly. In this work we introduce a 4-, 16- and 64- quadrature amplitude modulation (QAM) hybrid RoF-RoFSO communication system and investigated the inter-channel interference and the effects of atmospheric turbulence on the FSO section of the link.

LiFi Experiments in a Hospital

  • Autoři: Mana, S.M., Hellwig, P., Hilt, J., Bober, K.L., Jungnickel, V., Hirmanova, K., Chvojka, P., Ing. Radek Janča, Ph.D., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceeding of the Optical Fiber Communications Conference and Exhibition. Piscataway (New Jersey): IEEE, 2020. ISBN 978-1-7281-6762-6.
  • Rok: 2020
  • Pracoviště: Katedra elektromagnetického pole, Katedra teorie obvodů
  • Anotace:
    We present LiFi channel measurements in a neurosurgery room of Motol University Hospital in Prague. Individual channels are combined into a virtual multiuser MIMO link. We report achievable data rates for different LiFi transmission schemes.

Long-Length and Thermally Stable High-Finesse Fabry-Perot Interferometers Made of Hollow Core Optical Fiber

  • DOI: 10.1109/JLT.2020.2973576
  • Odkaz: https://doi.org/10.1109/JLT.2020.2973576
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We made and characterized two Fabry-Perot interferometer samples made of the latest-generation hollow core fiber with sub-1-dB/km loss. Thanks to this low transmission loss, we achieved a finesse of over 140 and 120, for interferometer lengths of 5 and 23 m, respectively. This resulted in transmission peaks as narrow as 47 kHz. Our all-fiber Fabry-Perot interferometers have standard single-mode fiber pigtails (for easy integration in conventional fiber optic systems) and employ fiber mode field adapters to enable low-loss coupling between the pigtails and the low-loss hollow core fiber. The high-reflectivity mirrors (>98%) were deposited directly on the fiber mode field adapters, which were glued to the hollow core fiber, resulting in permanently-aligned Fabry-Perot interferometers. We also measured how the position of the transmission peaks change with temperature (an important performance metrics for most applications, e.g., when used as a narrow-band band-pass filter) and found that it changed 14.5 times less in our Fabry-Perot interferometer relative to a similar device made of standard single mode fiber.

M-QAM signal transmission at the photonically generated K-band over thermal-induced turbulent FSO links with different turbulence distributions

  • DOI: 10.1364/AO.390103
  • Odkaz: https://doi.org/10.1364/AO.390103
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present a theoretical and experimental study on the impact of different thermal-induced free-space turbulence distributions on the M–quadrature amplitude modulation (M-QAM) signal transmission in radio frequency K-band over hybrid optical links of standard single mode fiber (SSMF) and free-space optics (FSO). Frequency multiplication using an external intensity modulator biased at the null transmission point has been employed to photonically generate radio signals at a frequency of 25 GHz , included for the frequency bands for fifth-generation (5G) mobile networks. Moreover, extensive simulations have been performed for 10Gb/s with 4-, 16-, and 64-QAM over 5 km of SSMF and 500 m long FSO channels under scenarios with different turbulence levels and distributions. Proof-of-concept experiments have been conducted for 20 MHz with 4- and 64-QAM over 5 km of SSMF and 2 m long FSO channels under turbulence conditions. Both theoretical and experimental systems have been analyzed in terms of error vector magnitude (EVM) performance showing feasible transmission over the hybrid links in the received optical power range. Non-uniform turbulence distributions are shown to have a different impact on M-QAM modulation formats, i.e., turbulence distributions with higher strength in the middle of the FSO link reveal a 1.9 dB penalty when using 64-QAM signals compared to a 1.3 dB penalty using 4-QAM signals, whereas higher penalties have been measured when 4-QAM format is transmitted over turbulence distributions with larger magnitude in the second half of the FSO link. The results have been validated by theoretical predictions and lead to practical consequences on future networks’ deployment.

On N-PAM and M-QAM Implementation within the Hybrid RoF-FSO-PON

  • Autoři: Nguyen Dong, N., Ing. Jan Bohata, Ph.D., Vallejo, L., prof. Ing. Stanislav Zvánovec, Ph.D., Ortega, B., Ghassemlooy, Z.
  • Publikace: 3rd West Asian Symposium on Optical and Millimeter-wave Wireless Communications - Proceeding. Piscataway: IEEE, 2020. p. 1-5. ISBN 978-1-7281-3767-4.
  • Rok: 2020
  • DOI: 10.1109/WASOWC49739.2020.9410197
  • Odkaz: https://doi.org/10.1109/WASOWC49739.2020.9410197
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper investigates an optical transmission architecture of a passive optical network (PON), which is compatible with the millimeter-wave radio-over-fiber and free-space optics systems (RoF-FSO) under weak-to-strong atmospheric turbulence (AT) regimes to enable seamless connectivity as part of next-generation broadband wireless access networks. We first analyze and evaluate in simulation the transmission performance of the integrated system at 40 GHz for 10 Gb/s N-pulse amplitude modulation (N-PAM) with N = 2, 4. Link performance shows that, 4-PAM outperforms 2-PAM in terms of tolerance to the combined impairment of fiber chromatic dispersion and AT. We then experimentally demonstrate the proof-of-concept integrated RoF-FSO-PON at 25 GHz using 20 MHz M-quadrature amplitude modulation (M-QAM) signals with M = 4, 16, 64. We show that, for QAM with a higher-order M, the link performance is being more affected by the combined impairments.

Optical Camera Communications for IoT–Rolling-Shutter Based MIMO Scheme with Grouped LED Array Transmitter

  • DOI: 10.3390/s20123361
  • Odkaz: https://doi.org/10.3390/s20123361
  • Pracoviště: Katedra elektromagnetického pole, Katedra radioelektroniky
  • Anotace:
    In optical camera communications (OCC), the provision of both flicker-free illumination and high data rates are challenging issues, which can be addressed by utilizing the rolling-shutter (RS) property of the image sensors as the receiver (Rx). In this paper, we propose an RS-based multiple-input multiple-output OCC scheme for the Internet of things (IoT) application. A simplified design of multi-channel transmitter (Tx) using a 7.2 × 7.2 cm2 small 8 × 8 distributed light emitting diode (LED) array, based on grouping of LEDs, is proposed for flicker-free transmission. We carry out an experimental investigation of the indoor OCC system by employing a Raspberry Pi camera as the Rx, with RS capturing mode. Despite the small area of the display, flicker-free communication links within the range of 20–100 cm are established with data throughput of 960 to 120 bps sufficient for IoT. A method to extend link spans up to 1.8 m and the data throughput to 13.44 kbps using different configurations of multi-channel Tx is provided. The peak signal-to-noise ratio of ~14 and 16 dB and the rate of successfully received bits of 99.4 and 81% are measured for the shutter speeds of 200 and 800 µs for a link span of 1 m, respectively.

Performance Analysis of Optical Intra-WBAN Links

  • Autoři: Haddad, O., Khalighi, M.A., prof. Ing. Stanislav Zvánovec, Ph.D., Adel, M.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249523
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249523
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We evaluate the performance of wireless body area networks (WBANs) in medical applications based on optical wireless transmission. We focus on the intra-WBAN links, where a set of medical sensors transmit the measured data to a coordinator node, placed on the patient’s body. Based on a Monte Carlo ray-tracing approach and considering the effects of body shadowing and mobility, we propose statistical models for the channel DC gain based on kernel density estimation. Then, we investigate the outage probability performance of the different intra-WBAN links and discuss the impact of user mobility and node placement on the patient’s body.

Performance Investigation of OCC-Based Vehicle to Vehicle Communications

  • Autoři: Masjedi Esfahani, N., Gholami, A., Shirvani Kordavani, N., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: 3rd West Asian Symposium on Optical and Millimeter-wave Wireless Communications - Proceeding. Piscataway: IEEE, 2020. p. 1-5. ISBN 978-1-7281-3767-4.
  • Rok: 2020
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents a model for a camera-based vehicle-to-vehicle visible light communications system for investigating the impact of different parameters on the link performance. The model includes a number of key system parameters including light source radiation pattern, camera noise sources, exposure time and atmospheric attenuation. The effect of the camera’s exposure time, the link length, the data rate, different weather conditions and the transmitted power on the system signal to noise ratio are represented. Results show that, at the communications distance of 100 m, with a signal to noise ratio of 20 dB, a data rate can be increased up to 200 kbps.

Performance of an Indoor Flexible OLED-based VLC Link

  • Autoři: Nazarichaleshtori, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: 27th International Conference on Telecommunications - Proceeding. Piscataway, NJ: IEEE, 2020. ISBN 978-1-7281-6587-5.
  • Rok: 2020
  • DOI: 10.1109/ICT49546.2020.09239455
  • Odkaz: https://doi.org/10.1109/ICT49546.2020.09239455
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communications (VLC) is one of the upcoming technology, which utilizes light emitting diodes (LEDs) or organic LEDs (OLEDs) to provide a combination of illumination and data communications. OLEDs have been gaining attention within the VLC research community due to their inherent advantages such as low-cost manufacturing and flexible substrates, which allows having a curved, rolled or folded lighting. This paper presents the impact of a symmetry beam pattern of OLED, which is wider than Lambertian, on the VLC system by considering wavelength-dependent surface materials reflections. A VLC system using flat and half-circular flexible OLEDs for use in an office environment for a number of scenarios is simulated. We obtain channel impulse responses and present the channel DC gain and optical path loss. The system performance is investigated in terms of the bit error rate and the channel capacity.

Performances of Optical Camera-based Vehicular Communications under Turbulence Conditions

  • Autoři: Eso, E., Younus, O.I., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Mansour Abadi, M.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249598
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249598
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we investigate the performance of a vehicular visible light communications (VVLC) link, which uses an incoherent light source as the transmitter (Tx) and an optical camera as receiver, under a turbulent condition. The result shows that in comparison to photodiode based optical wireless communications links using coherent light sources as Txs, the effect of the amplitude fluctuations introduced by turbulence (i.e., up to the refractive index structure parameter of 1.1 × 10^(-10) m^(-2/3)) on the VVLC link is minimal. Consequently, under turbulence the VVLC link performance when using incoherent light sources is not considerably degraded.

Photonic multiple millimeter wave signal generation and distribution over reconfigurable hybrid SSMF/FSO links

  • DOI: 10.1016/j.yofte.2019.102085
  • Odkaz: https://doi.org/10.1016/j.yofte.2019.102085
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Microwave photonics provides attractive solutions for millimeter wave (mmW) signal generation. In this paper, we demonstrate photonically generated multiple mmW signals transmission over a wavelength division multiplexed (WDM) hybrid optical network based on optical fiber and free-space optics (FSO) links. The experimental results demonstrate the generation and reconfigurable signal distribution from a central office to base stations in the frequency range 14 40 GHz with phase noise levels below -87 dBc/Hz. Moreover, 10 Gb/s data transmission has been demonstrated over photonically generated 40 GHz mmW signal. We show that FSO technology provides a possible solution for mmW fronthaul in 5th generation networks to extend the optical access network providing increased wireless accessibility and maintaining transmission capacity.

Polarization Differential Visible Light Communication: Theory and Experimental Evaluation

  • DOI: 10.3390/s20195661
  • Odkaz: https://doi.org/10.3390/s20195661
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible Light Communication (VLC) has received substantial research attention in the last decade. The vast majority of VLC focuses on the modulation of the transmitted light intensity. In this work, however, the intensity is kept constant while the polarization direction is deployed as a carrier of information. Demodulation is realized by using a differential receiver pair equipped with mutually orthogonal polarizers. An analytical expression to evaluate the Signal-to-Noise Ratio (SNR) as a function of the rotation angle of the receiver is derived. It is demonstrated that the signal quality can deteriorate heavily with receiver orientation when using a single differential receiver pair. A way to overcome this drawback using two receiver pairs is described. The analytical expression is experimentally verified through measurements with two different receiver setups. This work demonstrates the potential of polarization-based modulation in the field of VLC, where receiver rotation robustness has been achieved by means of a dedicated quadrant photodiode receiver.

Polarization Division Multiplexing-Based Hybrid Microwave Photonic Links for Simultaneous mmW and Sub-6 GHz Wireless Transmissions

  • DOI: 10.1109/JPHOT.2020.3036440
  • Odkaz: https://doi.org/10.1109/JPHOT.2020.3036440
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A new hybrid microwave photonic link based on a polarization division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed. The link enables co-transmission of millimeter-wave (mmW) and sub-6 GHz wireless signals over a seamless single-mode fiber (SMF) and free-space optics (FSO) channels. Optimization of the chromatic dispersion (CD)-induced power fading regardless of the power fading due to the non-deterministic atmospheric turbulence (AT) is simultaneously demonstrated. Extensive simulation analysis is first presented to examine (i) the impact of CD on mmW (25 GHz) and sub-6 GHz (2.6 GHz) signals, envisioned for the 5th generation networks, and (ii) optimization of CD-induced power fading by changing the phase relations between the optical carrier and optical sidebands in each polarization channel using single tunable polarization controller. A proof-of-concept experiment is finally performed to simultaneously deliver 25 GHz and 2.6 GHz signals with 4/16/64-quadrature amplitude modulation over (i) 20 km SMF and 2 m radio wireless link and (ii) 20 km SMF, 4.2 m FSO (with AT) and 2 m radio wireless links. The optimization of the CD-induced power fading is experimentally verified and link performance shows high tolerance to CD with no power penalties and the measured error vector magnitudes well below the required limits. The predicted bit error rates are also below the forward error correction threshold of 2×10−4

Relayed FSO Links for Ground-to-Train Communications

  • Autoři: Mohan, N., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Mansour Abadi, M., Hudson, R., Bhatnagar, M.R.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249640
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249640
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Relay assisted FSO, which is primarily used as a fading mitigation technique, can be employed to reduce the impact of network layer handover in the context of HST communications. In this paper, we propose a relay-based FSO system to provide ground to train communications and relays the information to the next base stations. Two schemes are analyzed via numerical simulations namely (i) all optical amplify and forward (AOAF); and (ii) AOAF with optical and optical-electronical-optical regeneration schemes in terms of the bit error rate performance and transmission range attained.

Sectorised base stations for FSO ground-to-train communications

  • Autoři: Mohan, N., Abadi, M.M., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Hudson, R., Bhatnagar, M.R.
  • Publikace: IET Optoelectronics. 2020, 14(5), 312-318. ISSN 1751-8768.
  • Rok: 2020
  • DOI: 10.1049/iet-opt.2019.0155
  • Odkaz: https://doi.org/10.1049/iet-opt.2019.0155
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Evolution and accessibility of smart-phones have led to a huge demand in network bandwidth. The ubiquitous use of smart-phones in high-speed trains poses a unique challenge in delivering high-speed internet service on board. This challenge can be overcome by employing free-space optics, an alternative to radio-frequency technology. Previous coverage models for ground–train communications employed single laser systems with a larger divergence angle to cover a larger distance. Larger divergence angles lead to larger geometric losses, which may result in a non-reliable communication link. This study proposes a sectorised multi-beam coverage model with a smaller divergence angle to reduce the impact of geometric losses in the system. This study also proposes two receiver (Rx) architectures for Rxs deployed on the train. Along with geometric losses, the atmospheric attenuation is taken into consideration for the FSO link. The performance of the ground–train communications system in terms of bit-error-rate is evaluated under weak turbulence conditions via numerical simulation.

Should Analogue Pre-Equalisers be Avoided in VLC Systems?

  • DOI: 10.1109/JPHOT.2020.2966875
  • Odkaz: https://doi.org/10.1109/JPHOT.2020.2966875
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communication (VLC) systems are highly constrained by the limited 3-dB bandwidth of light-emitting diodes (LEDs). Analogue pre-equalisers have been proposed to extend the LED's bandwidth at the cost of reduced signal-to-noise ratio (SNR). Compared with the pre-equaliser, the multi-carrier modulation with bit-loading can efficiently use the spectrum beyond the LED's raw 3-dB bandwidth without incuring SNR penalties by employing multiple narrow quasi-flat sub-bands to eliminate the need for equalisation. In this work we show by means of theoretical and experimental investigation that VLC with multi-band carrierless amplitude and phase modulation with bit-loading can outperform VLC with analogue pre-equalisers.

SOA-aided Photonic Signal Generation for Hybrid Fibre and FSO 5G Transmission Links

  • DOI: 10.1117/12.2552726
  • Odkaz: https://doi.org/10.1117/12.2552726
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A 5 Gb/s 32-QAM data transmission over a hybrid standard single-mode fibre (SSMF) and free-space optics (FSO) link has been experimentally demonstrated in the 42 − 90 GHz range for 5G networks deployment. Four-wave mixing (FWM) nonlinear effect in a semiconductor optical amplifier (SOA) experienced by a carrier suppressed double sideband modulated signal has been employed to photonically generate millimetre wave (mmW) signals with reduced electronics bandwidth. Both simulation and experimental results have been shown to describe the error vector magnitude (EVM) performance of the system. Large operation bandwidth is shown in our experimental setup, where measured penalties for 42 and 66 GHz are below 1 dB whereas 90 GHz leads to 3 dB penalty at 12 % EVM threshold. Sensitivity has also been estimated for optical back-to-back (OB2B), after SSMF and hybrid link transmissions for different mmW frequencies.

Spatial frequency-based angular behavior of a short-range flicker-free MIMO–OCC link

  • DOI: 10.1364/AO.404378
  • Odkaz: https://doi.org/10.1364/AO.404378
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we provide a solution based on spatial frequency 𝑓sf to study the angular behavior of a flicker-free, short-range indoor multiple–input multiple–output (MIMO) optical camera communications (OCC) link. We focus on the experimental investigation of OCC’s performance for the transmitters (Txs) [i.e., light-emitting diode (LED) based arrays] located at the same and different distances from the receiver (Rx) with the off-axis rotation angle 𝜃. We have used two 8×8 distributed LED arrays and a commercial low-cost complementary metal-oxide-semiconductor (CMOS) Raspberry Pi camera with the rolling-shutter capturing mode as the Tx and Rx, respectively. The image and the respective communications link quality metrics are measured in terms of the peak signal-to-noise ratio (PSNR) and the rate of successfully received bits with respect to 𝑓sf for different camera shutter speeds (SS). A CMOS image sensor noise characterization is carried in terms of the signal-to-noise ratio (SNR) and PSNR. The proposed study provides a 100% success rate in data reception at the optimum 𝜃 of 50° at lower captured values of 𝑓sf, which is projected onto the image sensor in the form of pixels. Moreover, the effect of channel saturation over 𝑓sf is studied with respect to 𝜃 and SS and we show that, for 𝜃 exceeding the optimum value along transmission range, the 𝑓sf area of the Txs reduces to less than ∼50% of the captured Tx units at 𝜃 of 0°, where no data can be fully recovered.

The First Study of MIMO Scheme Within Rolling-shutter Based Optical Camera Communications

  • DOI: 10.1109/CSNDSP49049.2020.9249566
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249566
  • Pracoviště: Katedra elektromagnetického pole, Katedra radioelektroniky
  • Anotace:
    In this paper, we propose the first study of MIMO (multiple-input multiple-output) scheme using a simplified design of MIMO transmitter (Tx) based on grouping of light-emitting diodes (LED) within an array for flicker-free transmission in optical camera based communications (OCC) link. We carried out an initial experimental investigation of indoor static downlink OCC using a Raspberry Pi camera as the receiver with rolling-shutter capturing mode and a 7.2 cm × 7.2 cm small 64-neopixel LED array as the Tx. The initial study suggests that, despite the small area of the display, communication links from 20 up to 60 cm can be established.

The Impact of Camera Parameters on the Performance of V2V Optical Camera Communications

  • Autoři: Masjedi Esfahani, N., Gholami, A., Shirvani Kordavani, N., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249553
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249553
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper investigates the impact of camera parameters on the performance of camera-based vehicle-to-vehicle optical communications system. Here, we consider the light source radiation pattern, atmospheric attenuation and camera noise sources and investigate the impact of the camera’s exposure time, lens f-number, image sensor size and its resolution on the signal to noise ratio of the system. Results show that, for communications on shorter distances (less than 200 m), lower image sensor resolution exhibits improved performance.

Transmission of 2 bits/symbol over RoF and RoFSO links with different architectures for ubiquitous coverage

  • Autoři: Nguyen Dong, N., Vallejo, L., Ing. Jan Bohata, Ph.D., prof. Ing. Stanislav Zvánovec, Ph.D., Ortega, B., Ghassemlooy, Z.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249594
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249594
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper investigates integrated radio-over-fiber and radio-over-free-space optic links in a passive optical network architecture for ubiquitous wireless coverage. Two optical millimeter-wave generation techniques, namely optical heterodyning and optical modulator-based up-conversion are used. In the first configuration, simulation results are achieved for transmission of 20-40 Gb/s 4-PAM over the 60 GHz heterodyned hybrid link. In the second configuration, the transmission of 20 MHz 4-QAM over the up-converted 25 GHz hybrid system is examined. System performance evaluation and practical feasibility are carried out in terms of the received optical powers, bit error rates, eye diagrams, error vector magnitude and constellation diagrams.

Transmitters for Combined Radio Over a Fiber and Outdoor Millimeter-Wave System at 25 GHz

  • DOI: 10.1109/JPHOT.2020.2997976
  • Odkaz: https://doi.org/10.1109/JPHOT.2020.2997976
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In the modern wireless networks, millimeter-wave radio-frequency (RF) bands are becoming more attractive as they provide larger bandwidth and higher data rates than the today-used systems operating at frequencies below 6 GHz. In addition, according to the fact that coaxial cables exhibit extremely high attenuation for millimeter-wave RF signals, analog radio over fiber techniques (RoF) form a promising technology for delivering unaltered radio waveform to a remote antenna. This paper experimentally analyzes three types of RoF modulations, namely a directly modulated laser, an electro-absorption modulator, and a Mach-Zehnder Modulator. The primary focus is on the implementation of each RoF transmitter in an RoF system, such as those in 5G networks. The experimental study includes a detailed characterization of an RoF system with a 50-m long outdoor free-space RF channel operating in the frequency band of 25 GHz. Frequency response (S-parameters) and third-order nonlinear distortion are investigated in detail. Tests of EVM performance were conducted using an orthogonal frequency division multiplexing signal modulated with 16-quadrature amplitude modulation (16-QAM) with a long-term evolution signal. It is demonstrated that the transmitters studied can operate under a 13.5% EVM limit given for 16-QAM. Apart from the detailed system performance, the considerable power fluctuations in the 25 GHz free-space RF outdoor channel are reported.

Turbulence mitigation in a 28 GHz radio-over-free-space optics link using an integrated Mach-Zehnder interferometer and a diversity combining receiver

  • DOI: 10.1049/iet-com.2019.1166
  • Odkaz: https://doi.org/10.1049/iet-com.2019.1166
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The authors propose an integrated Mach–Zehnder interferometer and diversity combining receiver to mitigate the atmospheric turbulence-induced fading in a millimetre-wave (mmW) radio-over-free-space optics (RoFSO) link. They use a carrier frequency of 28 GHz as recommended for the fifth-generation wireless access networks and consider two optical mmW signal generation schemes, namely double-sideband (DSB) and single-sideband (SSB). In direct detection (DD)-based RoFSO, the link performance is limited by atmospheric turbulence. They show that the proposed Rx can overcome this detrimental effect, which is verified by investigation of a 10 Gb/s 16-quadrature amplitude modulation orthogonal frequency-division-multiplexing signal at 28 GHz over a 1 km free-space optics link under weak and strong turbulence regimes. For the DSB scenario, the proposed Rx offers improved error vector magnitudes of about 0.8 and 5.7%, and modulation error ratios of 1.3 and 4.9 dB under weak and strong turbulence regimes, respectively, compared with the DD receiver (DD Rx). For the SSB scenario under weak turbulence, the proposed Rx achieves a 4 dB improvement in the receiver sensitivity and four orders of magnitude enhancement in the bit error rate over the DD Rx. The proposed Rx can be integrated on a single chip for further cost reduction.

Ultra-wideband mid-infrared supercontinuum generation in liquid-filled circular photonic crystal fiber

  • DOI: 10.1117/1.JNP.14.026016
  • Odkaz: https://doi.org/10.1117/1.JNP.14.026016
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We numerically demonstrate ultra-wideband mid-infrared supercontinuum (SC) generation in a liquid-filled arsenic–selenide circular photonic crystal fiber (C-PCF). The inner ring air-holes are filled with two different nonlinear liquids: chloroform (CHCl3) and carbon disulfide (CS2). Based on simulation results, we show that ultra-wideband SC spectra spanning from 1 to 20  μm can be achieved using only 5-mm long CHCl3 liquid filling with a pump optical pulse of 10-kW peak power at the wavelength of 2.55  μm. In addition, using 5-kW peak power, SC spectrum spanning up to 12  μm is obtained in the case of the CS2 liquid-filled C-PCF.

Unipolar-pulse amplitude modulation frequency division multiplexing for visible light communication systems

  • DOI: 10.1117/1.OE.59.9.096108
  • Odkaz: https://doi.org/10.1117/1.OE.59.9.096108
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) has been proposed in visible light communication (VLC) systems to overcome the dc-biased optical OFDM power consumption issue at the cost of the available electrical spectral efficiency. Due to the implementation of inverse fast Fourier transform, all the optical OFDM schemes including ACO-OFDM suffer from large peak-to-average power ratio (PAPR), which degrades the performance in VLC systems as the light-emitting diodes used as the transmitter have a limited optical power-current linear range. To address the PAPR issue in ACO-OFDM, we introduce a unipolar-pulse amplitude modulation frequency division multiplexing by adopting the single carrier frequency division multiple access (SC-FDMA). This is achieved by considering a PAM as an SC-FDMA data symbol and inserting a conjugate copy of the middle and first SC-FDMA FFT output subcarriers after the middle and last subcarriers, respectively. Simulation results show that, for the proposed scheme, the PAPR is 3.6 dB lower compared with ACO-OFDM. The PAPR improvement is further analyzed with the simulation results demonstrating that the proposed scheme offers 2.5 dB more average transmitted power compared to ACO-OFDM.

Usability of a 5G Fronthaul Based on a DML and External Modulation for M-QAM Transmission Over Photonically Generated 40 GHz

  • DOI: 10.1109/ACCESS.2020.3042756
  • Odkaz: https://doi.org/10.1109/ACCESS.2020.3042756
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we numerically and experimentally present the bandwidth constraints of a cost-effective 5G mobile fronthaul based on a directly-modulated laser for data modulation and a Mach-Zehnder modulator-based optical double sideband with carrier suppression scheme for optical millimeter wave (mmW) signal generation. The effect of chirp, fiber dispersion and a combination of both on different bandwidth M-Quadrature Amplitude Modulation (M-QAM) signals, i.e. M = 4, 16 and 64, at 40 GHz has also been investigated. Simulation results are first carried out to evaluate the impact of higher chirp of the directly-modulated laser on the link performance as a function of modulation format and signal bandwidth. We then experimentally demonstrate the same scheme transmitting M-QAM signals with bandwidths ranging from 50 to 1000 MHz over a 10 km long single mode fiber. Both experimental and simulation results show that larger signal bandwidths lead to higher optical power penalties due to the combined effect with the error vector magnitudes (EVMs), however still satisfying the required limits of 3GPP standard for all QAM signals. Experimental measurements also show the feasibility of including free space optics links in the optical distribution network with no further significant penalties. Finally, a multiband signal (three-band) transmission is demonstrated leading to an increase of the total bitrate with the measured EVMs are well below the EVM requirement.

Utilization of an OLED-Based VLC System in Office, Corridor, and Semi-Open Corridor Environments

  • DOI: 10.3390/s20236869
  • Odkaz: https://doi.org/10.3390/s20236869
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Organic light emitting diodes (OLEDs) have recently received growing interest for their merits as soft light and large panels at a low cost for the use in public places such as airports, shopping centers, offices, and train or bus stations. Moreover, the flexible substrate-based OLEDs provide an attractive feature of having curved or rolled lighting sources for the use in wearable devices and display panels. This technology can be implemented in visible light communications (VLC) for several applications such as visual display, data communications, and indoor localization. This article aims to investigate the use of flexible OLED-based VLC in indoor environments (i.e., office, corridor and semi-open corridor in shopping malls). We derive a two-term power series model to be match with the root-mean-square delay spread and optical path loss (OPL). We show that, for OLED positioned on outer-wall of shops, the channel gain is enhanced in contrast to them being positioned on the inner-wall. Moreover, the channel gain in empty environments is higher compare with the furnished rooms. We show that, the OPL for a 10 m link span are lower by 4.4 and 6.1 dB for the empty and semi-open corridors compared with the furnished rooms, when OLED is positioned on outer-wall of shops. Moreover, the channel gain in the corridor is higher compared with the semi-open corridor. We also show that, in furnished and semi-open corridors the OPL values are 55.6 and 57.2 dB at the center of corridor increasing to 87.6 and 90.7 dB at 20 m, respectively, when OLED is positioned on outer-wall of shops.

Vehicular Visible Light Communications: The Impact of Taillight Radiation Pattern

  • Autoři: Eldeeb, H.B., Eso, E., Uysal, M., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Sathian, J.
  • Publikace: IEEE Photonics Conference - Proceeding. Vancouver: IEEE, 2020. ISSN 2374-0140. ISBN 978-1-7281-5891-4.
  • Rok: 2020
  • DOI: 10.1109/IPC47351.2020.9252554
  • Odkaz: https://doi.org/10.1109/IPC47351.2020.9252554
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We investigate the path-loss of vehicular visible light communications based on the radiation pattern of a commercial car taillight. The measured pattern is incorporated into a ray-tracing model and simulation results indicate up to 4.2 dB variation in the path-loss compared with the Lambertian model.

Visible Light Communications: Filter-less Wavelength Division Multiplexing

  • Autoři: Haigh, P.A., Burton, A., Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Darwazeh, I.
  • Publikace: International Symposium on Communication Systems, Networks and Digital Signal Processing, CNSDSP 2020. Porto: IEEE, 2020. ISBN 978-1-7281-6743-5.
  • Rok: 2020
  • DOI: 10.1109/CSNDSP49049.2020.9249495
  • Odkaz: https://doi.org/10.1109/CSNDSP49049.2020.9249495
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose a new receiver and demodulation method for use in wavelength division multiplexed visible light communications systems, utilising the natural diversity offered by photodiodes. This is based on the wavelength dependent photodiode responsivities, which lead to different signal-to-noise ratios at the receiver. Using this method, it is possible to transmit independent information using on different wavelengths but where signals occupy the same electrical frequency range and where they would, otherwise, interfere. We illustrate and experimentally demonstrate that through simple subtractions the signals can be extracted with the constellations showing Q-factors corresponding to sufficiently low bit error rates.

Visible light communications: increasing data rates with polarization division multiplexing

  • Autoři: Chvojka, P., Burton, A., Pešek, P., Li, X., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Haigh, P.A.
  • Publikace: Optics Letters. 2020, 45(11), 2977-2980. ISSN 0146-9592.
  • Rok: 2020
  • DOI: 10.1364/OL.392167
  • Odkaz: https://doi.org/10.1364/OL.392167
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this Letter, we propose a new configuration for visible light communication systems, which results in doubling of the data rate due to the use of polarization division multiplexing. As light-emitting diodes are unpolarized incoherent light sources, we isolate both the perpendicular 𝑠 and parallel 𝑝 modes for independent modulation. For the first time, to the best of our knowledge, we show that it is possible to transmit and successfully recover two separate orthogonal frequency division multiplexing (OFDM) signals on each polarization (pol-OFDM). Furthermore, we compare the performance of the pol-OFDM system with the transmission of a single conventional OFDM signal without a polarizer over the same physical link. We show that similar bit error rates can be achieved while obtaining ∼45% improvement in both the data rate and spectral efficiency due to polarization multiplexing.

Wideband QAM-over-SMF/turbulent FSO downlinks in a PON architecture for ubiquitous connectivity

  • DOI: 10.1016/j.optcom.2020.126281
  • Odkaz: https://doi.org/10.1016/j.optcom.2020.126281
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We propose and investigate for the first time a seamless millimeter-wave (mmW) radio-over-fiber (RoF) and radio-over-free-space optics (FSO)-based downlink for use in a passive optical network architecture using 4-, 16- and 64-quadrature amplitude modulation (QAM) for broadband wireless access (BWA) networks. The proposed system is implemented in both experiment and simulation to realize continuous and ubiquitous coverage in urban and rural areas. We outline, a proof-of-concept demonstration of 4-, 16- and 64-QAMs at data rates of 34, 67 and 100 Mb/s, respectively transmitted over a 15 km standard single-mode fiber (SMF), which is then optically up-converted to 25 GHz for transmission over a 10 km of SMF and a 2 m of FSO channel under a non-uniform turbulent condition. We show the measured error vector magnitude (EVM) values of 13, 9.2 and 7.3% for 4-, 16- and 64-QAM, respectively, which are below the corresponding standard EVM requirements and therefore confirm the practicality of the proposed hybrid system. Depending on the data rates, each modulation can be adaptively configured. We report a simulation of a 10 Gb/s 4- and 64-QAM hybrid RoF-FSO downlink under an extended non-uniform turbulence regime to verify the feasibility of the proposed scheme for use in practical applications. By implementing the decision-directed carrier phase recovery and linear electrical equalization, EVMs can be efficiently reduced below the required limits. We further evaluate the proposed system performance in terms of the bit error rates, constellation diagrams, received optical and mmW powers. Using state-of-the-art K-band power amplifiers and conical horn antennas, the maximum wireless transmission distance is estimated to be about 135 m for use in the last-mile BWA networks.

A Flexible OLED based VLC Link with m-CAP Modulation

  • Autoři: Nazarichaleshtori, Z., Burton, A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the International Conference on Telecommunications 2019. Dubrovnik: IEEE Croatia Section, 2019. p. 1-6. ISBN 978-1-7281-2092-8.
  • Rok: 2019
  • DOI: 10.1109/ConTEL.2019.8848543
  • Odkaz: https://doi.org/10.1109/ConTEL.2019.8848543
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In recent years there has been a growing interest in using organic light emitting diodes (OLEDs) for illumination in indoor environments. They offer attractive features such as flexibility and large active areas at a low cost; they are energy efficient and have higher illumination levels compared to silicone based LEDs. In addition, the utilization of OLEDs have increased in devices such as smart mobile phones and TVs because of their low thickness. This paper investigates the performance of an OLED based visible light communications (OVLC) system, using a curved and flat OLED with multiband carrierless amplitude and phase (m-CAP) modulation for m = 2 at different angles of incidence on the optical receiver. It is shown that the BER performance is improved (i.e., below the forward error correction (FEC) limit of 3.8×10-3) with the curved OLED when the optical receiver moving along a circular path for the viewing angles greater 40o compared to the flat OLED, which is advantageous in device to device communications.

A Simplified Model for the Rolling Shutter Based Camera in Optical Camera Communications

  • Autoři: Li, X., Hassan, H.N., Burton, A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Perez-Jimenez, R.
  • Publikace: Proceedings of the International Conference on Telecommunications 2019. Dubrovnik: IEEE Croatia Section, 2019. p. 1-5. ISBN 978-1-7281-2092-8.
  • Rok: 2019
  • DOI: 10.1109/ConTEL.2019.8848504
  • Odkaz: https://doi.org/10.1109/ConTEL.2019.8848504
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A simplified model of the camera for optical camera communications (OCC) based on the rolling shutter effect is proposed and experimentally verified. In OCC, the key parameters are the exposure time, which is proportional to the DC gain and inversely proportional to the bandwidth, and the rolling shutter delay or the sampling period. We demonstrate a good agreement between experimental and numerically simulated results for the proposed receiver model.

All-optical relay-assisted FSO systems

  • DOI: 10.1049/PBTE078E_ch8
  • Odkaz: https://doi.org/10.1049/PBTE078E_ch8
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this chapter, an all-optical FSO relay-assisted system is proposed to mitigate the destructive effects of the distance-dependent AT-induced fading. Relays are inserted directly in the link in order to reduce the AT-induced link loss, thus extending the link span and ensuring higher link availability as well as improving the overall system performance. Two all-optical relaying schemes are proposed and investigated, namely all-optical amplify-and-forward (AOAF) and all-optical regenerate-and-forward (AORF) FSO relay-assisted approaches. For the AOAF approach, the performance analysis of triple-hop AOAF FSO communications is done under the impact of nonhomogeneous atmospheric turbulence. The AORF relaying approach is then proposed to overcome the limitation imposed by AOAF system, where the signal and noise are accumulated at each relay, thus limiting the number of relay nodes that can be used.

Demonstration of a Hybrid FSO/VLC Link for the Last Mile and Last Meter Networks

  • DOI: 10.1109/JPHOT.2018.2886645
  • Odkaz: https://doi.org/10.1109/JPHOT.2018.2886645
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, a hybrid free-space optical and visible light communication (FSO/VLC) system was experimentally demonstrated as a solution to overcome the last mile and last meter access networks bandwidth bottleneck. We evaluate the system performance of a multiband carrier-less amplitude and phase ( m -CAP) modulation scheme for a range of FSO/VLC link lengths and m -CAP parameters (i.e., the roll-off factor of the filters and a number of subcarriers) in terms of the data rate Rb (i.e., spectral efficiency). We show that for the configuration with a 1-m VLC link the 10-CAP offers more than a 40% improvement in the measured Rb compared to 2-CAP for the same bit error rate target. The Rb penalty due to the extension of a VLC-link span from 1 to 3 m reaches to 12.6 Mb/s for the 10-CAP scheme (i.e., ∼ 39% degradation in Rb ). To fully cover all aspects of the hybrid FSO/VLC system, we also investigate the atmospheric turbulence effect on the 500-m FSO link where Rb is decreased by 30% for the refractive index structure parameter C2n of 2.4 ×10−15 m −2/3 compared to a clear channel condition.

Duobinary Modulation for Visible Light Communications

  • Autoři: Chvojka, P., Haigh, P.A., Darwazeh, I., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Duobinary Modulation for Visible Light Communications. Piscataway: Institute of Electrical and Electronic Engineers, 2019. p. 52-56. ISSN 2575-4912. ISBN 978-1-7281-0546-8.
  • Rok: 2019
  • DOI: 10.1109/EuCNC.2019.8801992
  • Odkaz: https://doi.org/10.1109/EuCNC.2019.8801992
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The paper proposes and experimentally investigates the performance of the duobinary transmission technique for a highly bandlimited VLC system. By adding a controlled amount of inter-symbol interference (ISI) into the transmitted signals through the use of pulse shaping filters, data rate can be doubled within the same signal bandwidth. To gain full insight into duobinary signalling, the so-called modified binary scheme is also tested. Bit error rate (BER) performance of both systems is measured for a range of data rates and compared to BERs for ideal binary and traditional on-off keying non-return to zero (OOK-NRZ) formats, across the same physical link. We show the duobinary system can support higher bit rates and lower BER than OOK-NRZ while requiring half the bandwidth of the binary scheme.

Efficient Exploitation of Radio Frequency and Visible Light Communication Bands for D2D in Mobile Networks

  • DOI: 10.1109/ACCESS.2019.2954049
  • Odkaz: https://doi.org/10.1109/ACCESS.2019.2954049
  • Pracoviště: Katedra elektromagnetického pole, Katedra telekomunikační techniky
  • Anotace:
    The concept of device-to-device (D2D) communication, combining common radio frequency (RF) and visible light communication (VLC), is seen as a feasible way how to cope with spectrum crunch in the RF domain and how to maximize spectral efficiency in general. In this paper, our objective is to decide when RF should be utilized or if VLC proves to be the more profitable option. The selection between RF and VLC is defined as a multi-objective optimization problem targeting primarily to minimize the outage ratio while the secondary objective is to maximize the sum capacity of D2D pairs, composed by D2D transmitters and D2D receivers. To solve this problem, we design a centralized low-complexity heuristic algorithm selecting either RF or VLC band for each D2D pair relying on the mutual interference among the pairs. For interpretation of the mutual interference among the D2D pairs, we exploit directed weighted graphs adopted from the graph theory. The simulation results show that the proposed algorithm outperforms state-of-the-art algorithms in terms of the outage ratio, sum capacity and average energy efficiency. What is more, despite a very low complexity, the proposed algorithm reaches a close-to-optimum performance provided by the exhaustive search algorithm.

Enabling VLC and WiFi Network Technologies and Architectures Toward 5G

  • Autoři: Alimi, I.A., Abdalla, M.A., Rodriguez, J., Monteiro, P.P., Teixeira, A.L., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: Optical and Wireless Convergence for 5G Networks. New York: IEEE Press, 2019. p. 101-122. ISBN 978-1-119-49158-3.
  • Rok: 2019
  • DOI: 10.1002/9781119491590.ch5
  • Odkaz: https://doi.org/10.1002/9781119491590.ch5
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In the past few years we have seen a multitude of wireless machine-to-machine (M2M) and Internet of things (IoT) communications applications being deployed. M2M, by nature, needs more analysis before we can understand the basic human need it serves. For small deployment of M2M devices at very low data rates WLAN or ZigBee could be used, whereas for large deployment of M2M cellular networks should be used for connectivity. With M2M and IoT connecting new devices in multitude of environments and application - such as manufacturing floors, energy grids, warehouses, healthcare, transportations, computers, smartphones, traffic lights, and almost anything with a sensor - to the Internet, more data will be generated, thus adding to the problem of transmission channel availability. The existing RF wireless spectrum is outstripping the supply, thus leading to the spectrum congestion. Therefore, spectrum congestion in high density areas scenarios may lead to the limited access to the network. Regardless of the technology (3G, 4G, 5G or Wi-Fi) being adopted, there are only three approaches to increase the capacity of wireless radio systems: (i) release new spectrum and therefore more bandwidth, (ii) more nodes and (iii) improve the spectral efficiency. However, there is one possible alternative complementary technology that can address and overcome the problems which is known as the optical wireless communications (OWC) that includes infrared, visible and ultraviolet sub-bands. Compared to the RF, OWCs offer superior features such as ultra-high bandwidth (THz), free from electromagnetic interference, a high degree of spatial confinement bringing virtually unlimited frequency reuse, cost effective with no licensing fee, and inherent physical security.

Equivalent Circuit Model of High Power LEDs for VLC Systems

  • Autoři: Li, X., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Zhang, M., Burton, A.
  • Publikace: Proceedings of the 2nd West Asian Colloquium on Optical Wireless Communications 2019. Piscataway, NJ: IEEE, 2019. p. 90-95. ISBN 978-1-7281-3767-4.
  • Rok: 2019
  • DOI: 10.1109/WACOWC.2019.8770209
  • Odkaz: https://doi.org/10.1109/WACOWC.2019.8770209
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The equivalent circuit model for two commercial high power LEDs for illuminance is proposed and extensive measurements have been carried out to verify the accuracy of the model. In addition, the frequency response of two LEDs in the optical domain can be estimated using the transfer function of electrical equivalent circuit. It is shown that, the electrical parasitics in the chip and packaging introduce significant attenuation beyond a resonance frequcency. Care should be taken when designing high-speed driver and/or equalization circuits for VLC systems.

Experimental all-optical relay-assisted FSO link with regeneration and forward scheme for ultra-short pulse transmission

  • DOI: 10.1364/OE.27.022127
  • Odkaz: https://doi.org/10.1364/OE.27.022127
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents experimental results for an all-optical free-space optical (FSO) relay-assisted system by employing an all-optical regenerate and forward (AORF) scheme in order to increase the transmission link span. The ultra-short pulse (i.e., 2 ps) regeneration technique based on Mamyshev method is adopted. We have developed a dedicated experimental test-bed composed of optical fiber components and FSO links to demonstrate the proposed scheme and evaluate its performance in terms of the Q-factor and bit error rate (BER) under turbulence regimes for both single and dual-hop network architectures. We show that, using the AORF a hundred times improvement in the BER performance is achieved compared to the amplify-and-forward scheme for a fixed signal-to-noise ratio under turbulence conditions.

Experimental analysis of a triple-hop relay-assisted FSO system with turbulence

  • DOI: 10.1016/j.osn.2017.11.002
  • Odkaz: https://doi.org/10.1016/j.osn.2017.11.002
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper outlines experimental investigation of the performance of the wireless optical network based on an all-optical triple-hop free space optical (FSO) communications employing amplify-and-forward relaying under the influence of atmospheric turbulence. We present new results for the bit error rate (BER) performance for seven possible turbulence network scenarios for relay-assisted FSO link and validate them with numerical simulations based on Gamma-Gamma turbulence model showing a good agreement between them. We also show results, which elucidate the impact of non-homogeneous turbulence along the entire transmission link span for the multiple-hop relay-assisted FSO system. More specifically we show that the BER performance considerably deteriorates for the case where turbulence is near to the receiver end. We outline that for a target BER of 10−4 the signal-to-noise ratio penalty can be as high as 9 dB compared to the case with no turbulence.

Experimental Demonstration of Vehicle to Road Side Infrastructure Visible Light Communications

  • Autoři: Eso, E., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Gholami, A., Burton, A., Hassan, N.B., Younus, I.
  • Publikace: Proceedings of the 2nd West Asian Colloquium on Optical Wireless Communications 2019. Piscataway, NJ: IEEE, 2019. p. 85-89. ISBN 978-1-7281-3767-4.
  • Rok: 2019
  • DOI: 10.1109/WACOWC.2019.8770186
  • Odkaz: https://doi.org/10.1109/WACOWC.2019.8770186
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The increasing use of light emitting diodes in traffic lights offer excellent opportunities for implementation of visible light communications (VLC) based wireless technology as part of intelligent transport systems in smart environments. In this paper, we experimentally demonstrate vehicle to infrastructure (V2I) communications based on the VLC technology using a real traffic light and a camera over a link span of up to 80 m. We show a reduction in the modulation depth of the signal from 100% to 50% in order to track the light source when sending ‘0’ symbols. Also presented is the effect of operating the camera in the focused and defocused modes. The results show transmission success rates of 100% and 90% over link spans of 70 m and 80 m, respectively under specific test conditions.

Experimental Investigation of Neuron Based Motion Detection in Internet of Things using Optical Camera Communications

  • DOI: 10.1109/ICT.2019.8798857
  • Odkaz: https://doi.org/10.1109/ICT.2019.8798857
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper experimentally investigates the performance of visible light based optical camera communications (OCC) link with motion detection (MD) for the optical Internet of things applications. This efficient MD can be considered another functionality of OCC in addition to traditional features of vision, illumination data communications and sensing. The experiments were conducted in an indoor static downlink OCC system employing a mobile phone front camera is employed as the receiver and an 8 × 8 red, green, and blue (RGB) light-emitting diode array as the transmitter. The motion is detected by observing the user’s finger movement in the form of centroid through the OCC link via a camera. The experiment results demonstrate that, the proposed scheme can detect all considered motions accurately with acceptable bit error rate (BER) performances at a transmission distance of up to 80 cm. We show a BER of 1.7 × 10-3 below the forward error correction limit of 3.8 × 10-3 over a transmission distance of up to 1 m. The proposed neuron based MD combined together with OCC can be considered an efficient system, which provides illumination, communications, and motion detection in a convenient smart home environment.

Experimental Investigation of the Effects of Fog on Optical Camera-based VLC for a Vehicular Environment

  • Autoři: Eso, E., Burton, A., Hassan, N.B., Abadi, M.M., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the International Conference on Telecommunications 2019. Dubrovnik: IEEE Croatia Section, 2019. p. 1-5. ISBN 978-1-7281-2092-8.
  • Rok: 2019
  • DOI: 10.1109/ConTEL.2019.8848552
  • Odkaz: https://doi.org/10.1109/ConTEL.2019.8848552
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The widespread increase in the use of light emitting diodes in vehicle's head and taillights and also the use of dashboard cameras provides great prospects for the optical camera based visible light communications (VLC) technology in intelligent transport systems. In this paper, we experimentally investigate the impact of fog on the optical camera based VLC technology for vehicle-to-vehicle (V2V) communications. A range of meteorological visibilities between 5-120 m is considered based on realistic inter-vehicle distances in practical vehicular environments and using a real car taillight as the transmitter. We show a reduction in the index of modulation of the signals from 1 to 0.75 and 0.5 to allow for tracking purposes of the light source when sending `0' symbols. The results show that, the link is error-free up to 20 m meteorological visibility for the three modulation index scenarios and degrades considerably below 10 m meteorological visibility.

Experimental photonic 40 - 90 GHz millimetre-wave signal generation and 10 Gb/s 32-QAM signal transmission over hybrid fiber/FSO 5G networks

  • DOI: 10.1109/ICTON.2019.8840435
  • Odkaz: https://doi.org/10.1109/ICTON.2019.8840435
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We experimentally demonstrate photonic millimetre wave signal generation and distribution over hybrid networks based on wired and wireless links. Optical frequency multiplication based on carrier-suppressed modulation has been employed for generating millimetre wave signals in the 40 - 90 GHz frequency range and 10 Gb/s 32-QAM signals have been successfully transmitted over fiber/FSO networks showing the potentiality of such architectures for future 5G networks deployment in terms of flexibility and coverage.

Experimental validation of indoor relay-assisted visible light communications for a last-meter access network

  • Autoři: Pešek, P., prof. Ing. Stanislav Zvánovec, Ph.D., Chvojka, P., Ghassemlooy, Z., Nor, N.A.M., Tabeshmehr, P.
  • Publikace: Optics Communications. 2019, 451 319-322. ISSN 0030-4018.
  • Rok: 2019
  • DOI: 10.1016/j.optcom.2019.06.071
  • Odkaz: https://doi.org/10.1016/j.optcom.2019.06.071
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper provides experimental results for a relay-assisted visible light communications (VLC) link usinga white light-emitting diode (LED) for a last-meter access network. We demonstrate that a relay-based VLCscheme improves the system performance, especially for link spans longer than 5 meters, in the presence ofblocking and shadowing by redirecting the transmitted signal. We also demonstrate a multiband carrier-lessamplitude and phase modulation (m-CAP) VLC link where the decode-and-forward (DF) relay scheme offersimprovement in the data rate by 25% and 60% when compared to the amplify-and-forward (AF) relay-basedlink and single VLC link over a 7 m transmission distance respectively.

Filter-less WDM for visible light communications using colored pulse amplitude modulation

  • DOI: 10.1364/OL.44.004849
  • Odkaz: https://doi.org/10.1364/OL.44.004849
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper demonstrates, for the first time, a new wavelength-division multiplexing (WDM) scheme for visible light communications using multi-level coloured pulse amplitude modulation (M-CPAM). Unlike traditional WDM, no optical bandpass filters are required and only a single optical detector is used. We show that, by transmitting n independent sets of weighted on-off keying non-return-to-zero data on separate wavelengths over a line-of-sight transmission path, the resultant additive symbols can be successfully demodulated. Hence, the data rates can be aggregated for a single user or divided into individual colours for multiple user access schemes. The system is empirically tested for M = 4 and 8 using an off-the-shelf red, green and blue (RGB) chip light emitting diode (LED). We demonstrate that for M = 4, using the R and B chips a bit error rate (BER) of ≤10-6 can be achieved for each wavelength at bit rates up to 10 Mbps, limited by the LEDs under test. For M = 8 using R, G and B a BER of ≤10-6 can be achieved for each wavelength at bit rates up to 5 Mbps.

Highly-efficient and low return-loss coupling of standard and antiresonant hollow-core fibers

  • DOI: 10.1364/FIO.2019.FW5B.2.pdf
  • Odkaz: https://doi.org/10.1364/FIO.2019.FW5B.2.pdf
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We show results on adopting our new technique, developed for connecting solid-core fibers with hollow-core photonic bandgap fibers, to connect solid-core with antiresonant hollow core fibers. We achieved insertion loss below 0.5 dB per connection.

Hybrid Super-Nyquist CAP Modulation based VLC with Low Bandwidth Polymer LEDs

  • Autoři: Haigh, P.A., Chvojka, P., Minotto, A., Burton, A., Murto, P., Wang, E., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Cacialli, F., Darwazeh, I.
  • Publikace: Proceedings of the IEEE International Symposium on Personal, Indoor and Mobile Radio Communications. Piscataway, NJ: IEEE, 2019. p. 1-6. ISSN 1558-2612. ISBN 978-1-5386-8110-7.
  • Rok: 2019
  • DOI: 10.1109/PIMRC.2019.8904212
  • Odkaz: https://doi.org/10.1109/PIMRC.2019.8904212
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communication systems often suffer from high frequency attenuation when transmitting outof- band. This effect has been ameliorated by multi-band modulations such as multi-band carrier-less amplitude and phase (m-CAP), which minimises the effect of decreased high frequency magnitude and maximises signal-to-noise ratio-per-sub-band. On the other hand, in the pass-band region, super-Nyquist CAP (SCAP) can offer throughput improvements with no additional complexity at the receiver, at the cost of bit error rate. We propose, for the first time, a new hybrid SCAP modulation format that takes advantageous of both SCAP (i.e. overlapped sub-bands within the modulation bandwidth) and conventional m-CAP (orthogonally spaced bands outside the modulation bandwidth) while maintaining isolation between noise sources. We show higher baud rates within the passband region whilst supporting out-of-band transmission at lower error vector magnitudes.

Implementation and Evaluation of a Gigabit Ethernet FSO Link for 'The Last Metre and Last Mile Access Network'

  • Autoři: Abadi, M.M., Ghassemlooy, Z., Mohan, N., prof. Ing. Stanislav Zvánovec, Ph.D., Bhatnagar, M.R., Hudson, R.
  • Publikace: Proceedings of the 2019 IEEE International Conference on Communications Workshops. Piscataway: IEEE, 2019. p. 1-6. ISBN 978-1-7281-2373-8.
  • Rok: 2019
  • DOI: 10.1109/ICCW.2019.8757150
  • Odkaz: https://doi.org/10.1109/ICCW.2019.8757150
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose a simple and a low cost 1 Gbps Ethernet free-space optical (FSO) communications link, which can be used both for the last meter and last mile access networks. In the emerging fifth generation wireless systems, which require at least an order of magnitude increase in the peak data rates and three orders of magnitude increase in network capacity with reduced latency, deploying multiple technologies will play a crucial role to meet these requirements. One possible complementary wireless technology to the radio frequency is the unlicensed FSO, which can bridge the gap between the existing RF wireless and optical fibre communication networks by providing high data rates, low installation costs and high energy efficiency. In this work, we propose a high-speed FSO system, which can be readily implemented using off the shelf components, and assess its performance experimentally under turbulence and fog conditions using the dedicated indoor atmospheric chamber. We show that, the proposed system under the turbulence condition with a scintillation index of 𝟎. 𝟒𝟑 offers almost the same data rate (i.e., ~99%) as the link under a clear channel, while the packeterror- rate reduces from 𝟏𝟎−𝟑 to 𝟐 × 𝟏𝟎−𝟐.

Indoor Intruder Tracking Using Visible Light Communications

  • DOI: 10.3390/s19204578
  • Odkaz: https://doi.org/10.3390/s19204578
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper proposes a comprehensive study of indoor intruder tracking using visible light communication (VLC). A realistic indoor VLC channel was developed, taking into consideration reflections, shadowing, and ambient noise. The intruder was considered smart and aiming to escape tracking. This was modelled by adding noise and disturbance to the intruder’s trajectory. We propose to extend the application of minimax filtering from state estimation in the radio frequency (RF) domain to intruder tracking using VLC. The performance of the proposed method was examined and compared with Kalman filter for both VLC and RF. The simulation results showed that the minimax filter provided marginally better tracking and was more robust to the adversary behavior of the intruder than Kalman filter, with less than 0.5 cm estimation error. In addition, minimax was significantly better than Kalman filter for RF tracking applications.

Interference cancellation in MIMO NLOS optical-camera-communication-based intelligent transport systems

  • Autoři: Hassan, N.B., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Biagi, M., Vegni, A.M., Zhang, M., Huang, Y.
  • Publikace: Applied Optics. 2019, 58(34), 9384-9391. ISSN 1559-128X.
  • Rok: 2019
  • DOI: 10.1364/AO.58.009384
  • Odkaz: https://doi.org/10.1364/AO.58.009384
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The ever-increasing number of vehicles on a global level signifies the need for communications between vehicles and the surrounding environment. Visible light communications (VLC) is a viable complementary technology to congested radio-frequency-based wireless systems. In order to increase the reliability of the VLC link, two novel algorithms based on (i) channel inversion (CI) and (ii) frame subtraction and CI (FSCI) schemes are proposed to successfully extract the data in a non-line-of-sight multiple-input–multiple-output spatial-division multiplexing optical camera communications system. We have adopted differential modulation and frame subtraction schemes and proposed a unique packet structure to mark the packet and the position of the footprint of transmitters (Txs) in the image frame. We show that the FSCI scheme with much simpler receiver structures can offer almost the same bit error rate performance compared with the hybrid selection/equal gain combining (HS/EGC) technique at lower transmit power (illumination) levels of <13dBm for a single Tx and improved performance at higher illumination levels of >20dBm for multiple Txs. Compared with HS/EGC, CI schemes have a higher tolerance to the spacing between Txs, where the payload threshold level can be set to a fixed value of 0.5.

Investigation into Using Compensation for the Nonlinear Effects of the Output of LEDs in Visible Light Communication Systems

  • Autoři: Burton, A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Haigh, P.A., Minh, H.L., Li, X.
  • Publikace: Proceedings of the 2nd West Asian Colloquium on Optical Wireless Communications 2019. Piscataway, NJ: IEEE, 2019. p. 80-84. ISBN 978-1-7281-3767-4.
  • Rok: 2019
  • DOI: 10.1109/WACOWC.2019.8770197
  • Odkaz: https://doi.org/10.1109/WACOWC.2019.8770197
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper investigate the effects of the nonlinear output power to the input current transfer function of a light emitting diode (LED) used as the transmitter in visible light communication systems, and proposes a compensation technique to mitigate the non-linearity. Using an off the shelf red, amber, blue, green (RAGB) LED the nonlinear transfer function is measured and then compensated for. The results show that, for the green LED, which has the highest degree of nonlinearity, an improvement in the received error vector magnitude (EVM)of almost 7 dB can be achieved. We also show that, the improvement in EVM over the uncompensated scheme decreases with increased LED linearity.

Low-Loss and Low-Back-Reflection Hollow-Core to Standard Fiber Interconnection

  • DOI: 10.1109/LPT.2019.2902635
  • Odkaz: https://doi.org/10.1109/LPT.2019.2902635
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present a new approach to permanently inter-connect hollow-core fiber (HCF) to solid-core fiber, which does not involve fusion splicing. Our approach is based on a modification of the glue-based fiber-array technology routinely used for fiber pigtailing of planar lightwave circuits. The resulting interconnection provides for a low insertion loss due to the fact that the HCF microstructure is not deformed during the gluing (low temperature) process that is almost impossible to achieve with the standard (high temperature) fusion splicing method. Furthermore, this low-temperature technique enables the deposition and preservation of thin films deposited at the solid-to-hollow core fiber interface, allowing for additional functionality without the introduction of extra losses or any increase in complexity. To demonstrate this, we have applied an anti-reflection (AR) coating. A further feature of our approach is the ability to control very precisely the length of the graded-index (GRIN) fiber mode field (MF) adapter inserted in between the standard single-mode fiber (SMF-28) and the HCF. We show experimentally how the length of the GRIN fiber MF adapter influences the coupling between the SMF-28 and the fundamental as well as the higher-order modes of the HCF. We coupled between SMF-28 [10μm mode field diameter (MFD)] and the fundamental mode of a 19-cell hollow-core photonic bandgap fiber (HC-PBGF, 21.1μm MFD) with the lowest-ever reported insertion loss of 0.30dB per interface.

M-QAM transmission over hybrid microwave photonic links at the K-band

  • DOI: 10.1364/OE.27.033745
  • Odkaz: https://doi.org/10.1364/OE.27.033745
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Two experimental configurations of a hybrid K-band (25 GHz) microwave photonic link (MPL) are investigated for seamless broadband wireless access networks. Experimental configurations consist of optical fiber, free-space optics (FSO) and radio frequency (RF) wireless channels. We analyze in detail the effects of channel impairments, namely fiber chromatic dispersion, atmospheric turbulence and multipath-induced fading on the transmission performance. In the first configuration, transmission of the 64-quadrature amplitude modulation (QAM) signal with 5, 20 and 50 MHz bandwidths over 5 km standard single-mode fiber (SSMF), 2 m turbulent FSO and 3 m RF wireless channels is investigated. We show that, for QAM with a high bandwidth, the link performance is being affected more by atmospheric turbulence. In the second configuration, the 20 MHz 4/16/64-QAM signals over a 50 km SSMF and 40 m FSO/RF wireless links are successfully transmitted with the measured error vector magnitude (EVM) values of 12, 9 and 7.9%, respectively. It is shown that, for all transmitted microwave vector signals, the bit error rate is lower than the hard-decision forward-error-correction limit of 3.8×10−3. Moreover, an extended FSO link span of 500 m for 25 GHz hybrid MPL with 16-QAM at 10 Gb/s under the weak and strong turbulence regimes is evaluated via simulation analysis to mimic a practical outdoor system.

Mitigation of dispersion and turbulence in a hybrid optical fibre and free-space optics link using electronic equalisation

  • Autoři: Nguyen Dong, N., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: Optik : International Journal for Light and Electron Optics. 2019, 196 ISSN 0030-4026.
  • Rok: 2019
  • DOI: 10.1016/j.ijleo.2019.163154
  • Odkaz: https://doi.org/10.1016/j.ijleo.2019.163154
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Transmission of a 25 Gbps non-return to zero signal over a hybrid link of 20 km standard single-mode fibre and 500 m free-space optics under weak-to-moderate turbulence regimes is demonstrated via simulation to provide a practical solution for the last-mile access networks. Even though there are several complex mitigating methods to reduce the waveform distortions caused by both the fibre chromatic dispersion and atmospheric turbulence, we provide and discuss a simple approach using an electrical equalizer at the receiver. The simulation results demonstrate that, the proposed equalization technique offer about an order of magnitude improvement in the bit error rate at the received optical power of -20 dB m and a receiver sensitivity gain of 1.5 dB at the 7% forward error correction limit.

Non-Line-of-Sight MIMO Space-Time Division Multiplexing Visible Light Optical Camera Communications

  • Autoři: Hassan, N.B., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Biagi, M., Vegni, A.M., Zhang, M., Luo, P.
  • Publikace: IEEE/OSA Journal of Lightwave Technology. 2019, 37(10), 2409-2417. ISSN 0733-8724.
  • Rok: 2019
  • DOI: 10.1109/JLT.2019.2906097
  • Odkaz: https://doi.org/10.1109/JLT.2019.2906097
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, a non-line-of-sight multiple-input multiple-output space and time division multiple access optical camera communications system is proposed for an indoor environment. Mask matching and equal-gain combining (EGC) schemes as well as differential modulation and frame subtraction are used. We propose a unique packet structure to label the transmitters and a new detection method for data extraction from the captured video streams. We outline a comprehensive theoretical model and have developed an experimental testbed to evaluate the performance of the proposed system. The results highlight that zooming and defocusing of the camera does not have a significant impact on the system performance, therefore the aperture can be set to its maximum value. The system performs well over a link span of 10 m with a low transmit power of 12 mW and in the presence of ambient light due to the non-linear conversion of RAW to JPEG. Using mask matching and EGC improves the tolerance of the system to the noise.

Non-Orthogonal Variable Multi-Band Carrier-Less Amplitude and Phase Modulation with Reduced Subcarriers

  • Autoři: Tabeshmehr, P., Olfat, A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 2nd West Asian Colloquium on Optical Wireless Communications 2019. Piscataway, NJ: IEEE, 2019. p. 16-20. ISBN 978-1-7281-3767-4.
  • Rok: 2019
  • DOI: 10.1109/WACOWC.2019.8770194
  • Odkaz: https://doi.org/10.1109/WACOWC.2019.8770194
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we theoretically investigate the impact of power allocation for subcarriers on the bit error rate (BER) performance of a non-orthogonal variable multi-band carrierless amplitude and phase modulation (m-CAP) scheme within the contest of visible light communications. We consider subcarriers with different bandwidth as well as sub-carrier with overlapping in order to efficiently utilize the passband region of the system frequency response for data transmission. We show that, for the proposed scheme the average BER performance is improved by up to 20% compared to the conventional m-CAP system.

On Optically Pre-amplified FSO-MISO Non-identical Links with Correlation: Experiment and Analysis

  • Autoři: Priyadarshani, R., Bhatnagar, M., Ing. Jan Bohata, Ph.D., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: 2019 IEEE Global Communications Conference (GLOBECOM) - Proceedings. San Francisco: American Institute of Physics and Magnetic Society of the IEEE, 2019. p. 1-6. ISSN 2576-6813. ISBN 978-1-7281-0962-6.
  • Rok: 2019
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, various link characteristics and bit error rate (BER) performance of a free-space optical (FSO) multiple-input-single-output (MISO) system with repetition cod- ing (RC) is investigated both experimentally and theoretically. The study is performed in the presence of atmospheric turbulence (AT) over a correlated channel with an erbium-doped fiber am- plifier employed at the receiver (Rx). It is shown experimentally that the measured AT levels of two parallel links are different and the links experience non-identical fading influence. The analytical BER expression for an optically pre-amplified correlated FSO- MISO system with non-identical AT channel is derived. The BER results of the considered system with pre-amplifier is compared with the BER results of an FSO system without pre-amplifier, and it is shown analytically that a 2×1 FSO system with pre-amplifier offers better BER performance in terms of coding gain of 6 dB over the system without pre-amplifier. Moreover, it is also shown that the FSO system with RC gives better performance with identical links as compared to non-identical links. Further, it is also revealed that the diversity order of the considered system is independent of correlation and use of pre-amplifier. All the analytical results are validated by comparing them with Matlab simulations.

Optical camera communication system for Internet of Things based on organic light emitting diodes

  • DOI: 10.1049/el.2018.8037
  • Odkaz: https://doi.org/10.1049/el.2018.8037
  • Pracoviště: Katedra elektromagnetického pole, Katedra radioelektroniky
  • Anotace:
    The inclusion of organic light emitting diodes (OLEDs) in high-end devices, such as TVs and smart-phones, along with the insertion of cameras embedded in daily use devices, provides the opportunity to establish optical camera communication (OCC) systems based on OLED emitters for Internet of Things (IoT). This Letter presents an experimental demonstration of this OLED-based OCC system for IoT. The results suggest that despite the low emitted power of OLED devices, long range links can be established based on OCC. One outdoor and two indoor scenarios are tested, validating BER below 10−6 for short range and give just 3.56×10−3 for long range links.

Optical Hybrid Fiber/Free-Space and 25 GHz Wireless Transmission using LTE M-QAM Signals

  • DOI: 10.1109/WPMC48795.2019.9096169
  • Odkaz: https://doi.org/10.1109/WPMC48795.2019.9096169
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We experimentally demonstrate a seamless hybrid transmission of radio-over-fiber (RoF), radio-over-free-space optics (RoFSO) and millimeter wave wireless link using long-term evolution (LTE) 4/16/64-QAM signals for broadband wireless access applications. The signals are transmitted and evaluated over the hybrid channel consisting of 5 km of standard single-mode fiber (SMF), 2 m FSO under the turbulence level up to 3.2×10-11 m-2/3 and 3.3 m 25 GHz wireless channel. The performance shows that, the error vector magnitudes (EVM) are below the 3GPP standard for 4/16/64-QAM signals. We show that, the bit error rate (BER) for all signals is below the forward error correction limit of 10-3. We also perform simulation analysis at higher bit rates of 10 and 15 Gb/s for the hybrid link of SMF (5 km) and FSO (extended up to 500) m under the turbulence level of 1.3×10-15 m-2/3 for the practical outdoor scenario. We achieved acceptable performance for 4- and 16-QAM at 10 and 15 Gb/s.

Performance evaluation of neural network assisted motion detection schemes implemented within indoor optical camera based communications

  • DOI: 10.1364/OE.27.024083
  • Odkaz: https://doi.org/10.1364/OE.27.024083
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper investigates the performance of the neural network (NN) assisted motion detection (MD) over an indoor optical camera communication (OCC) link. The proposed study is based on the performance evaluation of various NN training algorithms, which provide efficient and reliable MD functionality along with vision, illumination, data communications and sensing in indoor OCC. To evaluate the proposed scheme, we have carried out an experimental investigation of a static indoor downlink OCC link employing a mobile phone front camera as the receiver and an 8 × 8 red, green and blue light-emitting diodes array as the transmitter. In addition to data transmission, MD is achieved using a camera to observe user’s finger movement in the form of centroids via the OCC link. The captured motion is applied to the NN and is evaluated for a number of MD schemes. The results show that, resilient backpropagation based NN offers the fastest convergence with a minimum error of 10−5 within the processing time window of 0.67 s and a success probability of 100 % for MD compared to other algorithms. We demonstrate that, the proposed system with motion offers a bit error rate which is below the forward error correction limit of 3.8 × 10−3, over a transmission distance of 1.17 m.

Performance Evaluation of Various Training Algorithms for ANN Equalization in Visible Light Communications with an Organic LED

  • Autoři: Nazarichaleshtori, Z., Haigh, P.A., Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: Proceedings of the 2nd West Asian Colloquium on Optical Wireless Communications 2019. Piscataway, NJ: IEEE, 2019. p. 11-15. ISBN 978-1-7281-3767-4.
  • Rok: 2019
  • DOI: 10.1109/WACOWC.2019.8770203
  • Odkaz: https://doi.org/10.1109/WACOWC.2019.8770203
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper evaluates the effect of training algorithms in an artificial neural network (ANN) equalizer for a feedforward multi-layer perceptron configuration in visible light communication systems using a low bandwidth organic light source. We test the scaled conjugate-gradient, conjugate-gradient backpropagation and Levenberg-Marquardt back propagation (LM) algorithms with 5, 10, 20, 30, and 40 neurons. We show that, LM offers superior bit error rate performance in comparison to other training algorithms based on the mean square error. The training methods can be selected based on the trade-off between complexity and performance.

Precise Measuring Test Bed for Characterization of Mode Field Distribution in Different types of Multimode Fibers

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper we present experimental results from precise measurements of mode field distribution in various commercial multimode (MM) fiber types. We characterize the mode field distribution by the encircled flux (EF) parameter. EF determines optimal launch conditions in the core of the MM fiber, which is crucial especially for accurate characterizing of insertion losses at fiber connections, e.g. in data centers. For the purpose of EF measurement, a universal testbed enabling mode field characterization, integral optical power estimation or fiber connector cleanness evaluation has been proposed and experimentally verified. The uniqueness of the proposed testbed lies in backlighting of the tested MM fiber. This backlighting enables accurate positioning of the MM fiber end-face with the collimating lens to measure in the near-field area. The testbed allows the deployment of variable MM fibers and is also wavelength independent. Therefore it has the high potential within growing usage of plastic or large core fibers for short-range communications, e.g. in automotive or avionics. The obtained results are discussed within a selected real application. Moreover, since the mode field distribution is evaluated even for fibers, which do not have available any standards for EF characterization, we present new recommendations for optimal launch conditions in such fibers.

Radio over 50 km Fiber and Joint 80 m FSO/Wireless Links Using Photonic Frequency Doubling for 5G

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present the experimental demonstration of photonic doubling to achieve 25 GHz millimeter wave signal generation, following the 5th generation network frequency band recommendations. A hybrid optical network combining up to 50 km long radio over fiber and 40 m long radio over free space optics systems plus 40 m long radio frequency (RF) 25 GHz wireless channel is demonstrated. The proposed system employs double sideband suppressed carrier modulation with 27 dB optical carrier suppression ratio and RF carrier phase noise below - 107 dBc/Hz with 10 kHz offset. Furthermore, the proposed system is optimized in terms of RF input power and the system quality is tested in terms of error vector magnitude for different modulation formats and variable fiber section lengths.

Seamless 25 GHz Transmission of LTE 4/16/64-QAM Signals Over Hybrid SMF/FSO and Wireless Link

  • DOI: 10.1109/JLT.2019.2945588
  • Odkaz: https://doi.org/10.1109/JLT.2019.2945588
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We propose and experimentally demonstrate a photonics-assisted converged radio-over-fiber (RoF), radio-over-free-space optics (RoFSO) and millimeter-wave (MMW) wireless transmission system for use in broadband wireless access (BWA) networks. The focus is at the emerging frequency band of 25 GHz, as recommended for fifth-generation networks. As a proof-of-concept demonstration, all-optical up-converted long-term evolution test models with 4-, 16- and 64-quadrature amplitude modulation (QAM) are transmitted and evaluated over the proposed hybrid link under weak-to-strong atmospheric turbulence regimes. Link performance shows that, the error vector magnitudes are below the 3GPP standard for 4-, 16- and 64-QAM. We also show that, for all QAM signals under turbulence conditions, the bit error rate performance is below the forward error correction limit of ${10^{ - 3}}$ . Simulation analysis is also performed for the 10 Gb/s hybrid systems under turbulence for an extended FSO link up to 500 m to emulate a practical outdoor environment. Furthermore, we analytically estimate the attainable MMW wireless range for different rain rates in Prague, Czech Republic. The obtained experimental and simulation results confirm the feasibility and potential of the proposed hybrid system for next-generation last mile BWA networks.

Strategies for Organic VLC: Effects of Clipping on the Performance of Multi-Band CAP Modulation with Polymer-based Light-Emitting Diodes

  • Autoři: Haigh, P.A., Chvojka, P., Minotto, A., Burton, A., Murto, P., Wang, E., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Cacialli, F., Darwazeh, I.
  • Publikace: Strategies for organic VLC: effects of clipping on the performance of multi-band CAP modulation with polymer-based light-emitting diodes. Stevenage, Herts: The Institution of Engineering and Technology (IET), 2019. p. 1-3. vol. 2019. ISBN 978-1-83953-185-9.
  • Rok: 2019
  • DOI: 10.1049/cp.2019.1035
  • Odkaz: https://doi.org/10.1049/cp.2019.1035
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We investigate for the first time, the effect of signal clipping on multi-band carrier-less amplitude and phase (m-CAP) modulation in visible light communications. We experimentally demonstrate that an improvement in Q-factor by up to ~2.25 dB can be achieved with a clipping level of 50%.

Structurally-modified tapered optical fiber sensors for long-term detection of liquids

  • DOI: 10.1016/j.yofte.2018.11.010
  • Odkaz: https://doi.org/10.1016/j.yofte.2018.11.010
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present an improvement of tapered optical fiber (TOF) sensor’s response for the detection of liquids, which is achieved by TOF surface structural modification. Our TOF sensors utilize the refractometric principle with enhanced evanescent-wave overlap due to the wavelength of 1550 nm and TOF waist diameters of 4–6 μm. The structural modification is achieved by long-term TOF exposition to hygroscopic liquid analytes and ambient atmosphere. To analyze the structural modification process, long-term as well as proof-of-principle tests have been carried out to evaluate TOF sensors stability in terms of sensitivity and resolution. Maximum sensitivity of over 2100 dB/RIU has been reached when TOF is used to detect a liquid analyte with refractive index of 1.415. Increase of more than 1400 dB/RIU is attributed to the enhanced sensitivity. Sample TOF sensors were then linearly calibrated and have been tested in more than one year-long continuous measurement campaign. Resolution better than 7x10^-4 for a refractive index range of from 1.405 to 1.425 with working point drift below 2x10^-4 over 12 months period has been achieved. Our results and observations are suitable for reliable, low-cost and application-tailored TOF sensor development.

The first tests of smartphone camera exposure effect on optical camera communication links

  • DOI: 10.1109/ConTEL.2019.8848559
  • Odkaz: https://doi.org/10.1109/ConTEL.2019.8848559
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we study the effect of smartphone camera exposure on the performance of optical camera communications (OCC) link. The exposure parameters of image sensor sensitivity (ISO), aperture and shutter speed are included. A static OCC link with a 8×8 red, green and blue (RGB) LED array employed as the transmitter and a smartphone camera as the receiver is demonstrated to verify the study. Signal-to-noise ratio (SNR) analysis at different ISO values, the effect of aperture and shutter speed on communication link quality is performed. While SNRs of 20.6 dB and 16.9 dB are measured at 1 m and 2 m transmission distance, respectively for a ISO value of 100, they are decreased to 17.4 dB and 13.32 dB for a ISO of 800. The bit error rate (BER) of a 1 m long OCC link with a camera’s shutter speed of 1/6000 s is 1.3×10 −3 (i.e., below the forward error correction BER limit of 3.8×10 −3 ) and is dropped to 0.0125 at a shutter speed of 1/20 s. This study provides insight of the basic smartphone settings and the exposure adjustment for further complex OCC links.

Visible light communications: multi-band super-Nyquist CAP modulation

  • DOI: 10.1364/OE.27.008912
  • Odkaz: https://doi.org/10.1364/OE.27.008912
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we experimentally demonstrate the performance of a non-orthogonal multi-band super-Nyquist carrier-less amplitude and phase (m-SCAP) modulation for visible light communications (VLC). We break the orthogonality between sub-bands in the frequency domain by compressing the spectrum, purposely overlapping them, and introducing inter-band interference (IBI). We demonstrate that our proposed system can tolerate IBI, and hence spectral efficiency can be increased without introducing additional complexity to the receiver. We show that m-SCAP can tolerate up to 30% and 20% compression for 4- and 16-level quadrature amplitude modulation, respectively, thus leading to an improvement in spectral efficiencies up to 40% and 25%, respectively, at the cost of bit error rate performance, which however remains below the 7% forward error correction limit. Moreover, the experimental results are supported by numerical simulations.

24-26 GHz radio-over-fiber and free-space optics for fifth-generation systems

  • DOI: 10.1364/OL.43.001035
  • Odkaz: https://doi.org/10.1364/OL.43.001035
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This Letter outlines radio-over-fiber combined with radio-over-free-space optics (RoFSO) and radio frequency free-space transmission, which is of particular relevance for fifth-generation networks. Here, the frequency band of 24–26 GHz is adopted to demonstrate a low-cost, compact, and high-energy-efficient solution based on the direct intensity modulation and direct detection scheme. For our proof-of-concept demonstration, we use 64 quadrature amplitude modulation with a 100 MHz bandwidth. We assess the link performance by exposing the RoFSO section to atmospheric turbulence conditions. Further, we show that the measured minimum error vector magnitude (EVM) is 4.7% and also verify that the proposed system with the free-space-optics link span of 100 m under strong turbulence can deliver an acceptable EVM of <9% with signal to noise ratio levels of 22 dB and 10 dB with and without turbulence, respectively.

A Survey on Recent Advances in Organic Visible Light Communications

  • Autoři: Nazarichaleshtori, Z., Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Haigh, P.A.
  • Publikace: Proceedings of the 11th International Symposium on Communication Systems, Networks & Digital Signal Processing. Piscataway: IEEE, 2018. p. 1-6. ISBN 978-1-5386-1335-1.
  • Rok: 2018
  • DOI: 10.1109/CSNDSP.2018.8471788
  • Odkaz: https://doi.org/10.1109/CSNDSP.2018.8471788
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communication (VLC) employs light emitting diodes (LEDs) to provide illumination and data communications simultaneously. Organic LEDs (OLEDs) employing small molecules and long-chain polymers PLEDs, have been gaining attention within the VLC research community due to their inherent advantages such as flexible substrates and low-cost manufacturing. However, the carrier mobility of organic semiconductors is much slower than the devices composed of metal alloys, such as gallium nitride, thus leading to a restriction in the OLED modulation bandwidth. The manufacturing processes, materials and the photoactive size of the devices can affect the raw bandwidth of OLEDs. To increase the transmission speeds, novel approaches have been proposed including equalization techniques, signalling schemes and the optimum driver circuits. The paper provides a survey on the evolution of OLED-based VLC systems, and the respective challenges and recent progresses.

Analysis of Nyquist Pulse Shapes for Carrierless Amplitude and Phase Modulation in Visible Light Communications

  • Autoři: Haigh, P.A., Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Darwazeh, I.
  • Publikace: IEEE/OSA Journal of Lightwave Technology. 2018, 36(20), 5023-5029. ISSN 0733-8724.
  • Rok: 2018
  • DOI: 10.1109/JLT.2018.2869022
  • Odkaz: https://doi.org/10.1109/JLT.2018.2869022
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper proposes and experimentally demonstrates, for the first time, two new candidate pulse shapes for carrierless amplitude and phase modulation in the context of visible light communications. It is commonly accepted that the pulse shape at the heart of the Hilbert pair used to generate the required orthogonal signal spaces should be the square-root raised cosine. In this paper, we introduce two additional candidate pulse shapes, namely the first csv pulse and the so-called better-than-Nyquist pulse. We demonstrate experimentally that the better-than-Nyquist pulse offers superior bit-error rate performance compared to the square-root raised cosine and Xia pulses under additive white Gaussian noise channel conditions, while offering lower computational complexity.

Application of Conventional G.652 Optical Fibers with Increased Evanescent-wave Overlap for Detection of Liquids

  • DOI: 10.1109/CSNDSP.2018.8471779
  • Odkaz: https://doi.org/10.1109/CSNDSP.2018.8471779
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The paper discusses conventional telecommunication silica single-mode optical fiber tapers acting as sensors of liquids based on the refractometric principle. Wavelength of 1550 nm is exploited not only due to the facile system integration but especially for the increased evanescent-wave overlap. Based on the simulation results, numerous sensor samples with waist diameters ranging from 4 to 6 um were prepared in precisely controlled conditions. Proof-of-principle tests were carried out to prove sensitivity enhancement of more than 1400 dB/RIU. Sensitivity enhancement was achieved by a structural modification of the tapered fiber surface. A maximum sensitivity of over 2000 dB/RIU was reached. Our results are essential for reliable, low-cost application of developed sensors, in particular, those used for monitoring of gasoline quality. Furthermore the observed long-term attenuation increase can also be critical for many telecommunication components, especially for those exposed to varying ambient atmosphere.

Differential Signalling in Free-Space Optical Communication Systems

  • Autoři: Abadi, M.M., Ghassemlooy, Z., Bhatnagar, M.R., prof. Ing. Stanislav Zvánovec, Ph.D., Khalighi, M.-A., Lavery, M.P.J.
  • Publikace: Applied Sciences. 2018, 8(6), ISSN 2076-3417.
  • Rok: 2018
  • DOI: 10.3390/app8060872
  • Odkaz: https://doi.org/10.3390/app8060872
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we review the differential signalling techniques and investigate its implementation of in free-space optical (FSO) communication systems. The paper is an extended version of our previous works, where the effects of background noise, weak turbulence and pointing errors (PE) were investigated separately. Here, for the first time, we present a thorough description of the differential signalling scheme including for combined effects. At first, we present an extension of the analysis of differential signalling to the case of moderate to strong atmospheric turbulence. Next, we investigate a more general case where both channel turbulence and PE are taken into consideration. We provide closed-form expressions for the optimal detection threshold and the average bit-error-rate, and present a set of numerical results to illustrate the performance improvement offered by the proposed differential signalling under various turbulence and PE conditions.

Experimental Demonstration of High-Speed 4 × 4 Imaging Multi-CAP MIMO Visible Light Communications

  • Autoři: Werfli, K., Chvojka, P., Ghassemlooy, Z., Hassan, N.B., prof. Ing. Stanislav Zvánovec, Ph.D., Burton, A., Haigh, P.A., Bhatnagar, M.R.
  • Publikace: IEEE/OSA Journal of Lightwave Technology. 2018, 36(10), 1944-1951. ISSN 0733-8724.
  • Rok: 2018
  • DOI: 10.1109/JLT.2018.2796503
  • Odkaz: https://doi.org/10.1109/JLT.2018.2796503
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In general, visible light communication (VLC) systems, which utilise white light-emitting diodes (LEDs), only offer a bandwidth limited to the lower MHz region. Therefore, providing VLC-based high data rate communications systems using VLC becomes a challenging task. To address this challenge, we propose a solution based on multiplexing in both the frequency and space domains. We experimentally demonstrate a 4 × 4 imaging multiple-input multiple-output (MIMO) VLC system (i.e., space multiplexing) utilising multiband carrierless amplitude and phase (m-CAP)modulation (i.e., frequency multiplexing). Independently, both MIMO and m-CAP have separately shown the remarkable ability to improve the transmission speeds in VLC systems, and hence, here we combine them to further improve the net data rate. We investigate the link performance by varying the number of subcarriers m, link distance L, and signal bandwidth Bsig. From all the values tested, we show that a data rate of ∼249 Mb/s can be maximally achieved for m= 20,Bsig = 20 MHz, and L = 1m, at a bit error rate of 3.2 × 10−3 using LEDswith∼4MHz bandwidth.

Experimental Investigation of the Effective Spectrum Bandwidth of the FSO Link with Scintillation

  • Autoři: Nazarichaleshtori, Z., Gholami, A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the First West Asian Colloquium on Optical Wireless Communications - WACOWS 2018. Isfahan: Isfahan University of Technology, 2018. p. 1-5. ISBN 9789717121208.
  • Rok: 2018
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In free space optical (FSO) communications, the link performance is highly dependent on the atmospheric conditions including turbulence, which causes fluctuations in both the intensity and the phase of the received optical wavefront. In this paper, we experimentally investigate the FSO link considering the ambient temperature and the sun irradiation angle parameters. Furthermore, we investigate the scintillation effect on the FSO link in the frequency domain and present temporal spectra of the irradiance fluctuations. It is worth since it can be helpful to compensate the scintillation effect in a FSO link using adaptive optical alignment system. In addition, we show the measured effective spectrum bandwidth of fluctuations in moderate turbulence is less than 250 Hz for a 220 m link length, and evaluate the environmental effects on it under different turbulence conditions.

Experimentally and analytically derived generalized model for the detection of liquids with suspended-core optical fibers

  • DOI: 10.1016/j.yofte.2018.08.005
  • Odkaz: https://doi.org/10.1016/j.yofte.2018.08.005
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A generalized model for the detection of liquids within suspended-core microstructured optical fibers has been experimentally and theoretically derived. The sensor detection is based on the refractometric principle of transmission losses due to the overlap of the evanescent field with the liquid analyte. A number of parameters, including fiber core diameter and filling length, have been included in the general model. Specially tailored suspended-core fibers were manufactured with the core diameters within the range of 2.4 um to 4.0 um. Five selected liquid analytes were used to cover the refractive index range of 1.35 to 1.42. Based on experiments, the characteristics of the parameters of the semi-empirical model have been determined by a genetic algorithm using 283 measurement data sets. The model can be used to design sensors for the detection of liquid analytes as it provides a set of parameters allowing to optimize the sensor’s sensitivity for a wide scale of applications. Finally, numerical simulations of the system were carried out by an eigenmode routine to support the results of the generalized model.

High-efficiency coupling to small-core microstructured fibers for broadband dispersion characterization

  • DOI: 10.1117/12.2289783
  • Odkaz: https://doi.org/10.1117/12.2289783
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    n this paper we investigate several silica-based suspended core microstructured fibers optical (SC-MOFs) in regards to providing the high efficiency coupling for broadband dispersion measurement. We present free-space optic and butt coupling setup capable of coupling signal from standard single mode fibers (SMF) into SC-MOF with core diameter of less than 4 μm and coupling efficiency over 50%. We then investigate SC-MOF’s effective mode area, nonlinearity coefficient and chromatic dispersion curve, using both modeling of the fibers and measurements. Lastly, we have investigated the effects of the aspheric lens on broadband coupling for the chromatic dispersion measurement.

Hybrid RoF-RoFSO System Using Directly Modulated Laser for 24 – 26 GHz 5G Networks

  • DOI: 10.1109/CSNDSP.2018.8471867
  • Odkaz: https://doi.org/10.1109/CSNDSP.2018.8471867
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present an experimental hybrid radio over fiber (RoF) and radio over free space optics (RoFSO) system employing a directly modulated laser (DML) for a radio frequency band of 24 – 26 GHz. Moreover, a 3.6 m long radio free space link is combined with a pair of wideband antennas. We outline the specific settings of the proposed high-frequency system for deployment in the centralized fronthaul networks as part of the 5th generation wireless technologies. We show a potential extension in terms of the added optical loss when using a 100 MHz signal bandwidth. In order to determine the optimum system performance, the setting of directly-modulated laser bias current is investigated. Measured results illustrate that the performance of the proposed system is less susceptible for up to medium turbulence conditions by maintaining an error vector magnitude (EVM) value below the limit of 9 %, given for 64- quadrature amplitude modulation (64-QAM). The lowest recorded EVM of the whole system for 64-QAM and a 100 MHz bandwidth at a frequency 24 GHz is 4.1 % while using a band pass filter to reduce amplified spontaneous emission noise in the system.

Impact of Camera Lens Aperture and the Light Source Size on Optical Camera Communications

  • Autoři: Hassan, N.B., Huang, Y., Shou, Z., Ghassemlooy, Z., Sturniolo, A., prof. Ing. Stanislav Zvánovec, Ph.D., Luo, P., Le-Minh, H.
  • Publikace: Proceedings of the 11th International Symposium on Communication Systems, Networks & Digital Signal Processing. Piscataway: IEEE, 2018. p. 1-5. ISBN 978-1-5386-1335-1.
  • Rok: 2018
  • DOI: 10.1109/CSNDSP.2018.8471766
  • Odkaz: https://doi.org/10.1109/CSNDSP.2018.8471766
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we investigate the defocused image in optical camera communications and the use three parameters including half power full width, maximum intensity, and slopes of the hazy area to characterize the blurred image. The paper outlines theoretical analysis for the blurry image using the captured image of the light source and the circle of confusion. An experimental test bed is developed to investigate the effect of width, height and slopes of the image of defocusing of the camera. Results show that for a larger aperture, which results in higher received power, the interference level between two light sources is increased due to defocusing of the camera.

Impact of Defocusing of the Camera Lens on the Image in Optical Camera Communications

  • Autoři: Hassan, N.B., Huang, Y., Shou, Z., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Zhang, M., Tang, X.
  • Publikace: Proceedings of the First West Asian Colloquium on Optical Wireless Communications - WACOWS 2018. Isfahan: Isfahan University of Technology, 2018. p. 1-5. ISBN 9789717121208.
  • Rok: 2018
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose a theoretical model for the intensity of a blurred image of a light source (LS) due to defocusing in optical camera communications. The blurred image is characterized with four parameters of half power full width, maximum intensity, left and right slope of hazy area and we relate them to the LS, channel, and camera settings. We experimentally investigate the impact of these parameters on characterization of the blurred image and compare it with the predicted data. The results show that if the size of the LS compared to its distance from the camera is less than a certain value set by the camera settings, the interference level between two close LSs increases, i.e. by increasing the link span, the size of the image increases.

Impact of PMD Changes to Optical Link Performance in a Harsh Environment

  • DOI: 10.1364/LAOP.2018.Tu4A.30
  • Odkaz: https://doi.org/10.1364/LAOP.2018.Tu4A.30
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical networks are commonly deployed in harsh environmenst. Based on measurement we provide new statistics of optical link performance in high-variant temperature environment with the impact of polarization mode dispersion to the system reliability.

Impact of Precise Measurements of Multi-Mode fiber components for Data Centers

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Multi-mode fiber (MMF) networks are under higher pressure with the wide deployment of high data-rate transmission systems. Reachable distance and system reliability in particular is essential for MM fiber usage in strategic areas like avionics or big data centers. Therefore, knowledge of the mode-field distribution within MMFs is crucial for proper design and optimization of such MMF systems. An optimally excited mode-field in MMFs leads to lower insertion losses (IL) at MMF connections and also contributes to achieving a higher effective modal bandwidth (EMB). To properly measure IL in a MM network and characterize the network for high data rates, the encircled flux (EF) parameter determines an ideal mode distribution in a MMF. This paper studies all above-mentioned aspects, to fully describe mode behavior in MM fiber connections. Moreover, potential accidents in terms of MM fiber offset in adaptors are tested and completed with simulations. Behavior of different optical sources on EF is presented.

Investigation of WDM VLC Using Standard 5 mm RGB LEDs

  • Autoři: Burton, A., Ghassemlooy, Z., Darwazeh, I., prof. Ing. Stanislav Zvánovec, Ph.D., Haigh, P.A., Le Minh, H.
  • Publikace: Proceedings of the 11th International Symposium on Communication Systems, Networks & Digital Signal Processing. Piscataway: IEEE, 2018. p. 1-6. ISBN 978-1-5386-1335-1.
  • Rok: 2018
  • DOI: 10.1109/CSNDSP.2018.8471898
  • Odkaz: https://doi.org/10.1109/CSNDSP.2018.8471898
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper investigates wavelength division multiplexing (WDM) uisng standard off-the shelf commercial 5 mm red, green, blue chip light-emitting diodes for visible light communications (VLC). From the initial observations of the illuminance footprint, it is found that the illumination overlap from each of the three colours is difficult to achieve a white light due to the physical layout of the emitting elements. We experimentally demonstrate that WDM is only achievable with a horizontal misalignment of +/- 0.5 cm or +/- 2 cm of the origin at a transmission span of 10 and 40 cm. Furthermore, with respect to the angular misalignment, WDM is achievable within a cone area of +5o of the origin at 10 cm distance and only along the origin at a distance of 40 cm.

Mobile User Connectivity in Relay-Assisted Visible Light Communications

  • DOI: 10.3390/s18041125
  • Odkaz: https://doi.org/10.3390/s18041125
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we investigate relay-assisted visible light communications (VLC) where a mobile user acts as a relay and forwards data from a transmitter to the end mobile user. We analyse the utilization of the amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes. The focus of the paper is on analysis of the behavior of the mobile user acting as a relay while considering a realistic locations of the receivers and transmitters on a standard mobile phone, more specifically with two photodetectors on both sides of a mobile phone and a transmitting LED array located upright. We also investigate dependency of the bit error rate (BER) performance on the azimuth and elevation angles of the mobile relay device within a typical office environment. We provide a new analytical description of BER for AF and DF-based relays in VLC. In addition we compare AF and DF-based systems and show that DF offers a marginal improvement in the coverage area with a BER < 10(-3) and a data rate of 100 Mb/s. Numerical results also illustrate that relay-based systems offer a significant improvement in terms of the coverage compared to direct non-line of sight VLC links.

Modified Octagonal Photonic Crystal Fiber for Residual Dispersion Compensation over Telecommunication Bands

  • DOI: 10.13164/re.2018.0010
  • Odkaz: https://doi.org/10.13164/re.2018.0010
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A modified octagonal photonic crystal fiber (MO-PCF) is proposed and numerically investigated for the purpose of residual dispersion compensation in the optical transmission link. The results show that the proposed fiber with optimized parameters exhibits ultraflattened negative dispersion over the 300 nm band (1380 nm to 1680 nm) with an average dispersion of –506 ps/(nm·km) and an absolute dispersion variation of 11.3 ps/(nm·km). In addition to large negative dispersion, the proposed MO-PCF also exhibits high birefringence in the order of 0.0207 at the 1550 nm wavelength. The proposed MO-PCF can be advantageously used especially for residual chromatic dispersion compensation in the wavelength-division-multiplexing optical fiber transmission system. The proposed fiber design is easy to draw and is tolerant to manufacturing imperfections.

Non-line-of-sight 2 × N indoor optical camera communications

  • DOI: 10.1364/AO.57.00B144
  • Odkaz: https://doi.org/10.1364/AO.57.00B144
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We propose, for the first time to the best of our knowledge, a novel non-line-of-sight 2 × N indoor optical camera communication system, where N is the number of pixels in the camera with a unique packet structure and a detection methodology for extracting the data from the recorded video streams. A comprehensive theoretical model for the proposed system is presented. The proposed system is experimentally investigated, and the measured results show that higher International Standards Organization (ISO) levels and exposure times lead to a reduced transmit power level by 3 dB for every doubling of the exposure time and ISO at a bit error rate of 10−3. It is also shown that when the overlapping area of two interfering transmitters is larger than approximately 30% of the footprints, the data cannot be recovered.

Non-Orthogonal Multi-band CAP for Highly Spectrally Efficient VLC Systems

  • Autoři: Haigh, P.A., Chvojka, P., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Darwazeh, I.
  • Publikace: Proceedings of the 11th International Symposium on Communication Systems, Networks & Digital Signal Processing. Piscataway: IEEE, 2018. p. 1-6. ISBN 978-1-5386-1335-1.
  • Rok: 2018
  • DOI: 10.1109/CSNDSP.2018.8471870
  • Odkaz: https://doi.org/10.1109/CSNDSP.2018.8471870
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this work we propose and experimentally demonstrate a novel non-orthogonal multi-band carrier-less amplitude and phase (NM-CAP) scheme for bandlimited visible light communication systems in order to increase the spectral efficiency. We show that a bandwidth saving up to 30% can be achieved thus resulting in 44% improvement in the measured spectral efficiency with no further bit error rate performance degradation compared to the traditional m-CAP scheme. We also show that higher order systems can provide higher bandwidth compression than low order systems. Furthermore, with no additional functional blocks at the transmitter or the receiver the proposed scheme introduces no extra computational complexity.

Optical Internet of Things within 5G: Applications and Challenges

  • DOI: 10.1109/IOTAIS.2018.8600894
  • Odkaz: https://doi.org/10.1109/IOTAIS.2018.8600894
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The fifth generation (5G) telecommunications standards are being developed to meet the growing demands for high-speed wireless networks (i.e., few tens of Gigabits per second). The 5G standard stems largely from an increasing number of users and plethora of different devices, collectively referred to as smart devices, connecting to a network as part of Internet-of-Things (IoT). A few potential technologies have emerged for 5G such as millimeter waves, massive multiple-input multiple-output, and small cell communications. Although these technologies would satisfy the requirements of 5G, there is a complementary alternative wireless technology of optical wireless communications (OWC), which is being considered. As part of OWC, visible light communications (VLC) and optical camera communications (OCC) are the most attractive options for 5G networks and beyond. VLC with huge frequency spectrum integrated with IoT can open up a wide range of indoor and outdoor applications as part of future smart environments. This paper provides an overview of the all-optical IoT (OIoT) focusing on VLC and OCC based potential applications and challenges as part of 5G standards.

Outage Analysis of a SIMO FSO System Over an Arbitrarily Correlated M -Distributed Channel

  • Autoři: Priyadarshani, R., Bhatnagar, M.R., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: IEEE Photonics Technology Letters. 2018, 30(2), 141-144. ISSN 1041-1135.
  • Rok: 2018
  • DOI: 10.1109/LPT.2017.2776963
  • Odkaz: https://doi.org/10.1109/LPT.2017.2776963
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this letter, we present the outage performance analysis of a single-input multiple-output free-space optical system with selection combining over an arbitrarily correlated Málaga (M) -distributed channel. A novel and generalized analytical expression for the joint probability density function of the received signal-to-noise ratio, using Green’s matrix approximation, is derived in the form of power series. The proposed expression is valid for an arbitrary correlation model and can be mapped to most of the other existing distributions characterizing different atmospheric turbulence conditions. Moreover, mapping of correlated M -distribution to correlated Gamma–Gamma and K distributions is illustrated with the help of derived analytical results; correctness of the mapped distributions is verified by simulation.

Performance of Space Shift Keying over a Correlated Gamma-Gamma FSO-MISO Channel

  • Autoři: Priydarshani, R., Jaiswal, A., Bhatnagar, M.R., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 11th International Symposium on Communication Systems, Networks & Digital Signal Processing. Piscataway: IEEE, 2018. p. 1-6. ISBN 978-1-5386-1335-1.
  • Rok: 2018
  • DOI: 10.1109/CSNDSP.2018.8471780
  • Odkaz: https://doi.org/10.1109/CSNDSP.2018.8471780
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we present bit error rate (BER) analysis of space shift keying (SSK) for a free space optical multiple-input-single-output system over an arbitrarily correlated Gamma-Gamma channel for different correlation models under moderate and strong turbulence. We first derive the probability density function (pdf) of difference of two arbitrarily correlated random variables, and then derive a novel analyt- ical expression for the average BER of the SSK scheme using the derived pdf. It is observed that the BER performance of the SSK scheme for considered system remains unaltered irrespective of the correlation model/level for rho< 0.795 and for rho > 0.795, the BER performance improves.

Polarization-maintaining Fiber-optic Gyroscope Using a Closed-loop with Kalman Filtering

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents results from the development of a fiber-optic gyroscope based exclusively on polarization-maintaining (PM) components. The main element represents the gyroscope coil, which consists of a 400m-long depressed-cladding PM fiber. To reduce temperature and stress effects, the gyroscope coil is wound in a quadrupolar fashion, which significantly reduces the inhomogeneous distribution of temperature and mechanical stress over the entire fiber coil. This results in mitigation of the so-called Shupe effect. We have employed a super-fluorescent fiber source to overcome the limiting effect of nonlinearities in order to improve the gyroscope performance. We compared the performance of a commercial super-luminescent LED and two types of in-house built super-fluorescent fiber sources realized by PM Erbium-doped fibers. We studied the effect of fiber doping, pumping powers and fiber length on the performance of the fiber-optic gyroscope. Using a digital feedback loop a gyroscope’s dynamic range can be dramatically increased and precision improved as well. In addition, Kalman filtering is proposed to further reduce parasitic drift effects. Conventional tools such as Allan variance are presented, depicting our long-term fiber-optic gyroscope development.

Undersampled Pulse Width Modulation for Optical Camera Communications

  • Autoři: Luo, P., Jiang, T., Haigh, P.A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceeding of the 2018 IEEE International Conference on Communications Workshops. Piscataway, NJ: IEEE, 2018. p. 1-6. ISSN 2474-9133. ISBN 978-1-5386-4328-0.
  • Rok: 2018
  • DOI: 10.1109/ICCW.2018.8403732
  • Odkaz: https://doi.org/10.1109/ICCW.2018.8403732
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    An undersampled pulse width modulation (UPWM) scheme is proposed to enable users to establish a non-flickering optical camera communications (OCC) link. With UPWM, only a digital light emitting diode (LED) driver is needed to send signals using a higher order modulation. Similar to other undersample-based modulation schemes for OCC, a dedicated preamble is required to assist the receiver to indicate the phase error introduced during the undersampling process, and to compensate for nonlinear distortion caused by the in-built gamma correction function of the camera. To test the performance of the UPWM-based OCC system, an experimental test-bed is developed. The experimental results show that the proposed system is able to achieve a data rate of 150 bps (spectrum efficiency of 5 bits/symbol) at a bit error rate of 6.76×10-4, which is well below the forward error correction limit of 3.8×10−3, over a link span of 1 m using a Huawei Nexus 6P smartphone with a frame rate of 30 fps.

Undersampled-based Modulation Schemes for Optical Camera Communications

  • Autoři: Luo, P., Zhang, M., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Feng, S., Zhang, P.
  • Publikace: IEEE Communications Magazine. 2018, 56(2), 204-212. ISSN 0163-6804.
  • Rok: 2018
  • DOI: 10.1109/MCOM.2018.1601017
  • Odkaz: https://doi.org/10.1109/MCOM.2018.1601017
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Widespread use of white light-emitting diodes and ubiquitous smart devices offer the opportunity to establish visible light communications (VLC) which has become a hot research topic based on the growing number of publications over the last decade. Camera-based VLC, namely optical camera communications (OCC), provide many unique features when compared with a single photodiode-based system, such as the ability to separate incident light in spatial and color domains. OCC technology represents a promising approach to utilize the benefits of VLC in beyond-5G scenarios and is one of the key technologies of the Internet of Things. Establishing a long communication channel in OCC, as well as non-flickering illumination in using low-frame-rate camera detectors, requires special modulation schemes. This article provides an overview of the principles of three categories of modulation schemes for OCC systems using a low-frame-rate camera detector. In addition, a series of undersampled modulation schemes are proposed and discussed to achieve flicker-free OCC with higher spectral efficiency. In addition, framing structures are designed to solve problems occurring in OCC systems using particular modulation schemes. To evaluate the performance of these modulation schemes, measured bit error rate values are shown. Finally, challenges in the implementation of OCC systems are also outlined.

UPWM-based Pulse Position Modulation for Optical Camera Communications

  • Autoři: Luo, P., Jiang, T., Haigh, P.A., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 11th International Symposium on Communication Systems, Networks & Digital Signal Processing. Piscataway: IEEE, 2018. p. 1-6. ISBN 978-1-5386-1335-1.
  • Rok: 2018
  • DOI: 10.1109/CSNDSP.2018.8471874
  • Odkaz: https://doi.org/10.1109/CSNDSP.2018.8471874
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    An undersampled pulse width modulation (UPWM)-based pulse position modulation (UPPM) scheme with the ability to support backward compatibility of UPWM is proposed for the rolling shutter-based optical camera communication systems. An adaptive-modulation scheme and a dedicated segment waveform are also proposed to increase the throughput and to solve several potential problems. Experimental tests are performed to proof the feasibility of the proposed UPPM scheme.

Adaptation of Mode Filtering Technique in 4G-LTE Hybrid RoMMF-FSO for Last-mile Access Network

  • DOI: 10.1109/JLT.2017.2708324
  • Odkaz: https://doi.org/10.1109/JLT.2017.2708324
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper demonstrates a hybrid radio over multi-mode fibre and free space optics (RoMMF-FSO) system that can be used to extend the transmission range of the 4th generation long-term evolution (4G-LTE) signal in access networks. A single mode filtering technique (SMFT) is used to enhance 4G-LTE performance. The proposed scheme is evaluated in terms of the system transfer function, laser beam profile, and error vector magnitude (EVM). We show that using SMFT increases the RoMMF-FSO system bandwidth by 2 GHz and improves the received optical power by 13.6 dB. Moreover, the proposed system enhances the EVM by 4%. The measured results show that using a 1 km MMF instead of a 1 km SMF will marginally increase the measured EVM from ~6.6% to ~7% with a 0.2 dB power penalty with respect to the LTE EVM limit of 12.5% as is specified for 16-quadrature amplitude modulation. The proposed system is validated practically under atmospheric turbulence conditions to mimic the outdoor environment. Measured EVM results are verified theoretically through transmitting LTE signals with turbulent using log-normal model. We also show that for a FSO link span of 500 m to meet the EVM target of 12.5% the SNR power penalties are ~2 dB and ~11 dB for Rytov variance of 1.2×10sup>-4 and 0.1, respectively compared with no turbulence.

Adaptation of transmitting signals over joint aged optical fiber and free space optical network under harsh environments

  • DOI: 10.1016/j.ijleo.2017.08.004
  • Odkaz: https://doi.org/10.1016/j.ijleo.2017.08.004
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Over the last two decades, a large amount of optical fiber (OF) cables has been deployed as part of the global communication networks. Both the aging of OFs as well as the need to increase transmission data rates, particularly in the backbone, have become hot topics. We present the study of the aged OF deployment in various optical networks including free space optics (FSO) link as a part of modern optical communication networks. Here, we show extended results obtained using a dedicated OF testbed focusing on the long-term monitoring of polarization mode dispersion (PMD) because of its time-varying nature. The adaptation of polarization multiplexed radio over fiber (RoF) and radio over FSO (RoFSO) systems as well as 10 Gbps on-off-keying (OOK) non-return-to-zero (NRZ) intensity modulation with the direct detection system, which is common cost-effective transmission system in passive networks, are demonstrated. Moreover, simulation of 100 and 200 Gbps return-to-zero (RZ) differential quadrature phase shift keying (DQPSK) with direct detection is outlined to verify the impact of aged OF network connected with FSO under turbulence conditions. Results reveal more than 6 dB of power penalty with the aged OF route for 100 Gbps systems. In addition, there is a 0.8 dB power penalty due to the strong seasonal induced PMD fluctuations. The influence of scintillations in terms of Rytov variance for the FSO link is also investigated for weak to moderate turbulence. Finally, we derive an expression for the long-term mean PMD value determined over one-month measured frequency response.

Analysis of nonline-of-sight visible light communications

  • DOI: 10.1117/1.OE.56.11.116116
  • Odkaz: https://doi.org/10.1117/1.OE.56.11.116116
  • Pracoviště: Katedra elektromagnetického pole, Katedra radioelektroniky
  • Anotace:
    We analyze the channel properties of a nonline-of-sight (NLOS) ceiling-to-device and device-to device visible light communication systems by considering various receivers' orientation and variable fields of view (FOVs). Analyses based on the recursive indoor channel model show that for a particular transmitter configuration, the pure NLOS path can offer higher 3-dB channel bandwidth (up to 14 MHz) compared with the link with LOS and NLOS components. We also show how the receiver rotation (orientation) influences the probability of receiving signals via the NLOS path compared with the LOS and NLOS paths. Moreover, based on the experimental campaign, we demonstrate that shadowing observed at the receiver due to people’s movement results in decreased received power level (up to 1.8 dB), thus resulting in reshaping of the probability density function of received power.

Combination of Visible Light and Radio Frequency Bands for Device-to-Device Communication

  • Pracoviště: Katedra elektromagnetického pole, Katedra telekomunikační techniky
  • Anotace:
    Future mobile networks are supposed to serve high data rates to users. To accommodate the high data rates, a direct communication between nearby mobile terminals (MTs) can be exploited. This type of communication in mobile networks is known as Device-to-device (D2D). Furthermore, a communication in high frequency bands, such as, visible light communication (VLC), is also foreseen as an enabler for the high data rates. In a conventional D2D communication, pairs of the communicating MTs should reuse the same frequencies to maximize spectral efficiency of the system. However, this implies either interference among the D2D pairs or a need for complex resource allocation algorithms. In this paper, we introduce a new concept for D2D communication combining VLC and RF technologies in order to maximize capacity of the system. The objective of this paper is to analyze operational limits of the proposed concept and to assess potential capacity gains to give motivation for future research in this area. Thus, we also discuss several practical issues related to the proposed RF--VLC D2D concept and outline major research challenges. The performance analysis carried out in this paper shows that the RF--VLC D2D is able to improve the capacity in an indoor scenario by a factor of 4.1 and 1.5 when compared to standalone RF D2D and VLC D2D, respectively.

Combined Effect of Turbulence and Aerosol on Free Space Optical Links

  • Autoři: Libich, J., Perez, J., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Nebuloni, R., Capsoni, C.
  • Publikace: Applied Optics. 2017, 56(2), 336-341. ISSN 1559-128X.
  • Rok: 2017
  • DOI: 10.1364/AO.56.000336
  • Odkaz: https://doi.org/10.1364/AO.56.000336
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Despite the benefits of free-space optical (FSO) communications, their full utilization is limited by the influence of atmosphere weather conditions. Such as fog, turbulence, smoke, snow and others. In urban environments, additional environmental factor such as smog and dust particles due to air pollution caused by the industry and motor vehicles may affect the FSO link performance, which has not been investigated in detail yet. Both smog and dust particles cause absorption and scattering of the propagating optical signal, thus resulting in high attenuation. This work investigates the joint impact of the atmospheric turbulence and dust particle imposed scattering on the FSO link performance as part of the last mile access network in urban areas. Propagation of an optical wave is at first analyzed based on the micro-physic approach and the extinction caused by small particles is determined. An experimental measurement campaign using a dedicated test chamber is carried out to assess the FSO link performance operating wavelengths of 650 and 830 nm and under the dust and turbulent conditions. The measured attenuation and the Q-factor in terms of the velocity of particle flow and the turbulence strength are analyzed. We show that for an air flow of 2 m/s the Q-factor is almost 3.5 higher at the wavelength of 830 nm than at 670 nm. However, for wavelength of 670 nm the FSO link is less affected by the increase in airflow compared to 830 nm. The Q-factor reduces with turbulence. Under similar turbulence conditions, for the ash particles the Q-factor is higher than that of sand particles.

Detailed Analysis of Multi-Mode Optical Components for Utilization in Data Centers

  • DOI: 10.1109/GIIS.2017.8169800
  • Odkaz: https://doi.org/10.1109/GIIS.2017.8169800
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Due to the high demands for the reliability of data centers, the determination of properly excited optical field inside the multimode (MM) fiber core belongs to the key parameters while designing such a MM optical system architecture for data centers. Appropriately excited mode field of the MM fiber provides optimal power budget in connections, leads to the decrease of insertion losses (IL) and achieves effective modal bandwidth (EMB), which is essential for high data rates. Crucial is especially the encircled flux (EF) parameter, which should be properly defined for combinations of variable optical sources and MM fiber infrastructure to provide proper mode-field distribution. In this paper, we present detailed investigation and measurements of the mode field distribution for short MM optical data center links with the emphasis on their reliability. Such characterization is essential for the design of large MM networks. Various scenarios were tested in terms of IL and mode-field distribution to reveal potential problematic scenarios. Furthermore, we focused via simulations and experiments on the estimation of particular defects and errors, which can realistically occur like eccentricity or connector misalignment. Their dependence on EF statistics and functionality of data center infrastructure was evaluated. Finally, we provide recommendations for data center systems and networks, using OM3 MM fiber connections

Development and Characterization of Highly Nonlinear Multicomponent Glass Photonic Crystal Fibers for Mid-infrared Applications

  • Autoři: Němeček, T., doc. Ing. Matěj Komanec, Ph.D., Suslov, D., Peterka, Pavel, Pysz, D., Buczynski, R., Nelsen, B., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proc. SPIE 10232, Micro-structured and Specialty Optical Fibres V. Bellingham (stát Washington): SPIE, 2017. Proceeding of SPIE. vol. 10232. ISSN 1996-756X. ISBN 978-1-5106-0966-2.
  • Rok: 2017
  • DOI: 10.1117/12.2265722
  • Odkaz: https://doi.org/10.1117/12.2265722
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present a detailed chromatic dispersion characterization of heavy-metal oxide (HMO) glass photonic crystal fibers (PCFs) suitable for mid-infrared applications. Based on previous work with hexagonal and suspended-core fibers the focus was placed on determination of the chromatic dispersion curve to reach precise correlation between simulation model and real fiber based on both a post-draw model correction and broadband chromatic dispersion measurement. The paper covers the fiber design, discusses fiber manufacturing, presents measurements of fiber chromatic dispersion, provides the simulation model correction and finally proposes further applications. Selected fiber designs from simulation model were fabricated by the stack-and-draw technique. The dispersion measurement setup was based on an unbalanced Mach-Zehnder interferometer. The influence of optical elements on the measurement results and broadband coupling is discussed. We have proved that the critical factor represents the accuracy of the refractive index equation of the HMO glass and real fiber structure. By improved technique we reached the zero-dispersion wavelength with a reasonable precision of less than 30 nm.

Effect of Correlation on BER Performance of the FSO-MISO System With Repetition Coding Over Gamma–Gamma Turbulence

  • DOI: 10.1109/JPHOT.2017.2738098
  • Odkaz: https://doi.org/10.1109/JPHOT.2017.2738098
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In free space optical (FSO) communication systems, atmospheric turbulence is the major cause of bit error rate (BER) performance degradation. The error performance of the system can be significantly improved with the help of spatial diversity by employing multiple transmit or receive apertures. However, correlation of channels under turbulence in the case of small separation between transmit apertures can substantially reduce the benefits of spatial diversity. Still, a thorough analysis of the system performance in terms of diversity order and coding gain for the FSO multiple-input single-output (MISO) system under turbulence influenced correlated channels has not been studied when the repetition coding is used to achieve improved BER performance. In this paper, we provide unique results of the BER performance analysis of the considered correlated FSO-MISO system over Gamma–Gamma distributed turbulence channel. Using the joint moment generating function of received signal-to-noise ratio (SNR), a novel generalized approximate BER expression is derived, followed by convergence test of the power series based BER expression using the Cauchy’s ratio test. Then, an asymptotic analysis at high SNR is performed to obtain a novel closed-form expression for BER of FSO-MISO system. We also derive expressions for coding gain, diversity gain, and coding gain loss due to correlation in channels. Although the effect of correlation in channels on the BER performance of the system is analyzed under different scenarios, while it is observed that it does not affect the diversity order; it significantly degrades the coding gain of the considered system.

Experimental Demonstration of Undersampled Color-Shift Keying Optical Camera Communications

  • Autoři: Luo, P., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Feng, S., Zhang, M.
  • Publikace: IEEE/CIC International Conference on Communications in China - Proceedings. Piscataway, NJ: IEEE, 2017. ISBN 978-1-5386-4502-4.
  • Rok: 2017
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    An undersampled color shift keying (UCSK) scheme is proposed to support non-flickering red, green, and blue based optical camera communications (OCC). A dedicated framing structure is proposed to allow the receiver to obtain the camera´s gamma curve and specify the phase error. A proof-of-concept experimental test-bed is developer to evaluate the bit error rate (BER) and error vector magnitude performance of the proposed OCC systém. The experimental results show that the proposed systém is able to achieve a data rate of 150 bps with a BER of 1.7x10-3 over a link span of up to 30 m, which is more than adequate for vehicle-to-vehicle communications.

Experimental Investigation of All-Optical Relay-Assisted 10 Gbps FSO Link over the Atmospheric Turbulence Channel

  • DOI: 10.1109/JLT.2016.2629081
  • Odkaz: https://doi.org/10.1109/JLT.2016.2629081
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents novel experimental results for a 10 Gbps triple-hop relay-based all-optical free space optical (FSO) system by employing the amplify-and-forward (AF) relaying scheme. We provide a mathematical framework for the end-end signal-to-noise ratio (SNR) and the bit-error rate (BER) performance and confirm that the derived analytical results reasonably match experimental results especially at relatively high SNR. The evaluated BER performances under different atmospheric turbulence regimes (modeled by the Gamma-Gamma distribution) show that the considered relay-assisted FSO system offers a significant performance improvement for weak to strong turbulence regimes, even without knowledge of the channel state information. More precisely, at a target BER of 10-5 the proposed scheme offers ~ 5 dB and ~4 dB of SNR gain compared to the direct transmission for turbulence strengths C_n^2 of 3.8×10^(-10) m-2/3 and 5.4 ×10^(-12) m-2/3, respectively.

Hard switching in hybrid FSO/RF link: Investigating data rate and link availability

  • Autoři: Abadi, M.M., GHASSEMLOOY, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Bhatnagar, M.R., Wu, Y.
  • Publikace: 2017 IEEE International Conference on Communications Workshops (ICC Workshops) - Proceedings. IEEE, 2017. p. 463-468. ISBN 978-1-5090-1525-2.
  • Rok: 2017
  • DOI: 10.1109/ICCW.2017.7962701
  • Odkaz: https://doi.org/10.1109/ICCW.2017.7962701
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper investigates the performance dependence of a hybrid free space optical (FSO)/radio frequency (RF) communication system on the data rate, link distance and link availability. In existing hybrid FSO/RF systems with hard switching, an algorithm is used to switch between FSO and RF and vice versa based on the feedback of the channel state information. In particular, two methods based on time hysteresis (TH) and power hysteresis (PH) are widely used in hard switching protocols. Although switching parameters including the time and power thresholds have been studied, the effect of link parameters has not been investigated in the literature. In this paper, we analyse the performance of a hybrid FSO/RF system under realistic channel conditions for both TH and PH switching schemes. By means of analysis and simulation, we show that increasing the data rate of individual FSO or RF link does not necessarily result in higher data rate and improved link availability in a hybrid FSO/RF system.

Impact of Link Parameters and Channel Correlation on the Performance of FSO Systems with Differential Signalling Technique

  • Autoři: Abadi, M.M., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Bhatnagar, M.R., Khalighi, M.-A., Wu, Y.
  • Publikace: Journal of Optical Communications and Networking. 2017, 9(2), 138-148. ISSN 1943-0620.
  • Rok: 2017
  • DOI: 10.1364/JOCN.9.000138
  • Odkaz: https://doi.org/10.1364/JOCN.9.000138
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We investigate the effects of link parameters and the channel correlation coefficient (CC) on the detection threshold, Q-factor, and bit-error-rate (BER) of a free space optical system employing the differential signalling (DS) scheme. In systems employing DS scheme, the mean value of the signal is used as the detection threshold level, provided that differential links are identical or highly correlated. However, in reality the underlying links are not essentially identical and have a low level of correlation. To show the significance of the link parameters as well as CC, we derive analytical relations describing the effect of weak turbulence and we determine the improvement of Q-factor with the channel correlation. Further, for the same signal-to-noise ratio, we demonstrate that a link with a higher extinction ratio offers an improved performance. We also propose a closed-form expression of the system BER. We present experimental results showing improved Q-factor for the correlated channel case, compared to the uncorrelated channel.

Indoor Positioning Using a Single Transmitter for Visible Light Communication Systems

  • Autoři: Al-Nassrawi, M., Le-Minh, H., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., The Son, T., Zhang, M.
  • Publikace: First South American Colloquium on Visible Light Communications 2017 - Proceedings. Santiago: Universidad de Santiago de Chile, 2017. ISBN 978-1-5386-1781-6.
  • Rok: 2017
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The paper introduces a concept for the visible light communications (VLC) based positioning systém, which uses minimum number of transmitters. The method is based on the estimation of the user´s velocity between the previous and current user positions. On the move, the user´s position is estimated based on the velocity of the user when it is moving, the received signal strength indicator from a single active transmitter and the initial user position obtained once at the beginning. In practice, the general indoor illumination utilises multiple LED arrays, which is suitable for the proposed systém as it forms a multiple input and multiple outputs (MIMO) VLC systém offering the capability for determining the initial position. In addition, the proposed MIMO VLC offers the self-correction scheme to complete the channel state information matrix with missing elements during the pilot signal period. Simulation results show that the method is effective in obtaining the position of the user on the move.

Influence of camera setting on vehicle-to-vehicle VLC employing undersampled phase shift on-off keying

  • DOI: 10.13164/re.2017.0946
  • Odkaz: https://doi.org/10.13164/re.2017.0946
  • Pracoviště: Katedra elektromagnetického pole, Katedra radioelektroniky
  • Anotace:
    This paper focuses on the performance analysis of a camerabased vehicle-to-vehicle visible light communication system employing undersampled phase shift on-off keying modulation under interference scenario. Two Nissan Qashqai front lights with daylight running light emitting diodes based lamps are used for communications. The bit error rate (BER) performance of the proposed system is experimentally measured for a transmission span up to 24mfocusing mostly on the side interference due to reflections. Based on experimental data we demonstrate reduction of the system performance due to the side reflection and illumination of the detector by other light sources which have to be taken into account during further data processing. We provide with further statistics for particular shutter speed and transmitter power setting and discuss BER improvement especially to meet FEC via the method of the adaptive region of interest.

Long-term Polarization Mode Dispersion Evolution and Accelerated Aging in Old Optical Cables

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Today's optical networks are composed of thousands of kilometers of aging optical cables. Many of these cables are located in harsh environments which contribute to induced birefringence of the fibers and a corresponding increase of polarization mode dispersion (PMD). This paper introduces derived statistics from the longest-known running evaluation of a PMD measuring campaign and an investigation into how higher optical power affects these aging systems. Results indicate strong seasonal dependence of PMD on temperature for an optical cable testbed exposed to atmospheric changes, leading to a 16 % increase of mean PMD value in summer. This fluctuation causes bit error rate (BER) limits to be exceeded for 10 Gbps and 40 Gbps non-return-to-zero (NRZ) signals which is a critical issue for applications where high reliability is required. Moreover, due to the high optical power load within old optical infrastructures, a more than 0.15 dB increase of relative loss per year in tested routes, compared to reference routes, has been observed.

Multi-band Carrier-less Amplitude and Phase Modulation for VLC: An Overview

  • Autoři: Chvojka, P., Werfli, K., Haigh, P.A., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Bhatnagar, M.R.
  • Publikace: First South American Colloquium on Visible Light Communications 2017 - Proceedings. Santiago: Universidad de Santiago de Chile, 2017. ISBN 978-1-5386-1781-6.
  • Rok: 2017
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The rapid development of solid-state lighting technologies has been the stimulus for visible light communications (VLC) to be the focus of enormous interest over the last decade. The key feature of simultaneous data transmission and illumination using white light-emitting diodes (LEDs) makes VLC a potential candidate for future power efficient communication networks that aim to meet the ever-increasing demands for high-speed internet services. Researchers, motivated by the success of VLC technology, have developer a number of techniques and methods to support communication systems with both high transmission speeds and spectral efficincy. Here, we povide an overview of the multi-band carrier-less amplitude and phase (m-CAP) modulation technique enabling highly spectrally efficient VLC links in bandlimited environments.

On the dispersion and mode-field characterization of photonic crystal fibers for nonlinear application

  • DOI: 10.1109/ICACOMIT.2017.8253404
  • Odkaz: https://doi.org/10.1109/ICACOMIT.2017.8253404
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present a detailed procedure of precise chromatic dispersion and mode field characterization of unknown photonics crystal fibers for their further utilization in nonlinear applications. To verify our methods an Endlessly single-mode photonic crystal fiber (ESM-PCF) was used. A finite-element method simulation software was utilized for mode field distribution and chromatic dispersion simulation based on the particular fiber structure. Subsequently, a measurement setup for dispersion characterization was proposed, based on the Mach-Zehnder interferometer. Experiment results include as well the influence of various optical elements in the configuration on the measured fiber parameters. Second experimental setup was realized with the possibility of parallel mode-field diameter measurement and visualization of the fiber core structure. Effective area and dispersion measurements results were compared to the simulation outputs. We achieved up to 5 nm accuracy of zero-dispersion wavelength for a 28 cm long ESM-PCF and maximum mismatch of 2 μm2 with effective mode-field area determination. Our procedures and characterization outputs could be applied to specialty optical fiber design and characterization mainly for nonlinear applications such as supercontinuum generation.

On the m-CAP Performance with Different Pulse Shaping Filters Parameters for Visible Light Communications

  • Autoři: Chvojka, P., Werfli, K., prof. Ing. Stanislav Zvánovec, Ph.D., Haigh, P.A., Hubata-Vacek, V., Dvořák, P., Pešek, P., Ghassemlooy, Z.
  • Publikace: IEEE PHOTONICS JOURNAL. 2017, 9(5), ISSN 1943-0655.
  • Rok: 2017
  • DOI: 10.1109/JPHOT.2017.2749203
  • Odkaz: https://doi.org/10.1109/JPHOT.2017.2749203
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In pulse shaping filters, parameters such as the roll-off factor and the symbol span, which determine the overall performance, are of great importance when implementing a real-time system due to limited hardware resources. In this paper, we experimentally investigate a multiband carrier-less amplitude and phase (m-CAP) VLC system employing such filters and assess the link performance for a range of filter lengths and show the relationship between the system data rate (or spectral efficiency) and computational complexity. We show that lower order m-CAP can offer the same system performance as higher order systems while offering much lower computational complexity. By optimizing the filter parameters and the order m of an m-CAP VLC link, we achieve the largest improvement in the data rate and bandwidth efficiency of 9.69% and 40.43%, respectively when compared with 2- and 8-CAP. We also show that the m-CAP VLC link with m≥6 can be designed with the same filter parameters to demonstrate a link with both the highest data rate and spectral efficiency simultaneously in contrast to lower order systems.

Refractometric Detection of Liquids Using Tapered Optical Fiber and Suspended Core Microstructured Fiber: A Comparison of Methods

  • DOI: 10.1364/AO.56.002388
  • Odkaz: https://doi.org/10.1364/AO.56.002388
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Detecting explosive, flammable or toxic industrial liquids reliably and accurately is a matter of civic responsibility which cannot be treated lightly. Tapered optical fibers (TOFs) and suspended core microstructured optical fibers (SC MOFs) were separately used as sensors of liquids without being compared to each other. We present a highly-sensitive time-stable TOF sensor incorporated in the pipeline system for in-line regime of measurement. The paper is furthermore focused on the comparison of this TOF and SC MOF of similar parameters for detection of selected liquids. A validated method that incorporates TOF and SC MOF of small core (waist) diameter for refractometric detection is presented. The principle of detection is based on the overlap of an enhanced evanescent wave with a liquid analyte which either fills the cladding holes of the SC MOF, or surrounds the waist area of the TOF. Optical power within the evanescent wave for both sensing structures and selected liquid analytes is analyzed. Measurement results concerning TOF and SC MOF are compared. Calculations to ascertain the limit of detection (LOD) for each sensor and the sensitivity (S) to refractive indices of liquid analytes in the range of 1.4269 to 1.4361 were performed at a wavelength of 1550 nm with the lowest refractive index step of 0.0007. Results affirming that S = 600.96 dB/RIU and LOD = 0.0733 RIU for the SC MOF and S = 1143.2 dB/RIU and LOD of 0.0026 RIU for the TOF sensor were achieved, clearly illustrating that TOF based sensors can reach close to two times greater sensitivity and 30-times higher limit of detection. The paper extends the comparison of the fiber sensors by discussing the potential applications.

Thulium pulsed laser for nonlinear applications in specialty optical fibers: Design and experimental verification

  • Autoři: doc. Ing. Matěj Komanec, Ph.D., Chvojka, P., Němeček, T., Suslov, D., prof. Ing. Stanislav Zvánovec, Ph.D., Redwan, A.
  • Publikace: 2nd International Conference on Automation, Cognitive Science, Optics, Micro Electro-­Mechanical System, and Information Technology (ICACOMIT). San Francisco: American Institute of Physics and Magnetic Society of the IEEE, 2017. p. 142-146. ISBN 978-1-5386-0510-3.
  • Rok: 2017
  • DOI: 10.1109/ICACOMIT.2017.8253403
  • Odkaz: https://doi.org/10.1109/ICACOMIT.2017.8253403
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present results from the development of an pulsed thulium laser for near-infrared and mid-infrared nonlinear applications utilizing specialty optical fibers. The laser is based on a gain-switched seed-laser and three amplification stages, where output pulse peak powers in order of kilowatts maximum are expected. The laser is at first analyzed in a simulation software. Pre-amplification stage is discussed, with focus on low-noise signal amplification. Following the pre-amplification stage setting the second gain stage is evaluated incorporating a thulium-fiber of 3m length with increased rare-earth dopant ratio. Finally, a power-booster stage is analyzed in simulation environment to reach peak power of kilowatts. Based on the developed thulium pulsed laser, results from nonlinear phenomena modelling and experiments in the vicinity of 2000 nm are presented. Specialty optical fibers based on fluoride and chalcogenide glass are evaluated.

Time transfer over 1900 km of DWDM network

  • Autoři: Škoda, P., Radil, J., Vojtěch, J., Smotlacha, V., Munster, P., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 40th International Conference on Telecommunications and Signal Processing - Proceedings. Piscataway (New Jersey): IEEE, 2017. p. 698-701. ISBN 978-1-5090-3982-1.
  • Rok: 2017
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Since a dedicated optical infrastructure for atomic clock comparison is extremely expensive, we present our tests allowing sharing optical DWDM network. We expanded optical reach of our atomic clock comparison systém and demonstrated the transfer on time information over 1900 km of DWDM systém with other 8 neighbouring optical channels. NRENs have good potential to host time comparison applications for the academic community over long distances.

Variable m-CAP for Bandlimited Visible Light Communications

  • Autoři: Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Werfli, P., Haigh, P.A., Ghassemlooy, Z.
  • Publikace: 2017 IEEE International Conference on Communications Workshops (ICC Workshops) - Proceedings. IEEE, 2017. p. 1-5. ISBN 978-1-5090-1525-2.
  • Rok: 2017
  • DOI: 10.1109/ICCW.2017.7962624
  • Odkaz: https://doi.org/10.1109/ICCW.2017.7962624
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The multi-band carrier-less amplitude and phase (m-CAP) modulation technique has been demonstrated as a significant candidate for use in visible light communication (VLC) systems, as spectral efficiency becomes ever more important. When employing m-CAP modulation, the signal bandwidth is typically split into m equally distributed subcarriers regardless of the −3 dB bandwidth. Thus, in this paper we investigate the impact of splitting the signal bandwidth into unequally spaced subcarriers on the m-CAP VLC system performance. We demonstrate that by allocating different bandwidths for individual subcarriers, we can achieve up to 36% improvement in data rate for 6-CAP (i.e. 6 subcarriers). We show that the higher the order of the variable m-CAP, the more significant improvement in data rate becomes even for a highly bandlimited VLC system when compared to the conventional m-CAP scheme.

Visible Light Communications – A Review

  • Autoři: GHASSEMLOOY, Z., Popoola, W.O., Tang, X., prof. Ing. Stanislav Zvánovec, Ph.D., Rajbhandari, S.
  • Publikace: IEEE COMSOC MMTC Communications – Frontiers. 2017, 12(3), 6-13.
  • Rok: 2017
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    As part of the possible future heterogeneous networks, the emerging visible light communications (VLC) could be a significant game changer in indoor environments as a complementary technology to radio frequency (RF) based wireless technologies. This paper provides an overview of VLC technology.

Visible Light Communications Based on Street Lighting

  • Odkaz: https://doi.org/10.1201/9781315367330
  • Pracoviště: Katedra elektroenergetiky, Katedra elektromagnetického pole
  • Anotace:
    Modern street lighting represents the pervasive utilization of light-emitting diode (LED) lamps to illuminate urban and rural areas. In addition, LEDbased lighting sources can also be utilized for outdoor data communications and localization. The replacement of traditional street incandescent and fluorescent-based lights by highly efficient LED lights is taking place on a global level. This chapter highlights the main features of LED public lighting systems that could be used for visible light communications (VLC). First, a description of state-of-the-art street lighting, including its main functions, control systems, and typical parameters, is provided. Then the main aspects associated with lighting performance and aging are outlined. The remainder of the chapter is devoted to recent studies on public lighting for VLC purposes, focusing on ray tracing simulations, noise parameters, and delay profiles among other topics.

Visible Light Communications with Hybrid OFDM-PTM

  • Autoři: Ghassemlooy, Z, Ebrahimi, F., Rajbhandari, S., Olyaee, S., Tang, X., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 13th IEEE International Wireless Communications and Mobile Computing Conference - Proceedings. Piscataway, NJ: IEEE, 2017. p. 894-898. ISBN 978-1-50904-372-9.
  • Rok: 2017
  • DOI: 10.1109/IWCMC.2017.7986404
  • Odkaz: https://doi.org/10.1109/IWCMC.2017.7986404
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In visible light communications (VLC) system, the linearity of the light emitting diode is an issue when being intensity modulated with an analogue signal. In optical orthogonal frequency division multiplexing (O-OFDM) based VLC systems, the source nonlinearity imposes a tight restriction on the achievable peak-to-average-power-ratio. To address this issue, we propose a hybrid OFDM-PTM (pulse time modulation) scheme, where a bipolar O-OFDM signal is converted into digital PTM formats for switching 'on' and 'off' the light source. The simulation results demonstrate that the proposed scheme offers an improved bit error rate performance compared to the traditional asymmetrically clipped O-OFDM (ACO-OFDM)

VLC with Organic Photonic Components

  • DOI: 10.1201/9781315367330
  • Odkaz: https://doi.org/10.1201/9781315367330
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In recent years, organic small molecule and polymer light-emitting diodes (LEDs) and photodetectors (PDs) have been used as optoelectronic components in visible light communications (VLC). The first study appeared in [1] which demonstrated data transmission rates in the hundreds of kb/s region is possible. This was further improved by using advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) [2]. Ethernet transmission speeds were reported for the first time in [3] and was achieved using the multilayer perceptron artificial neural network equalization technique. The current state-of-the-art transmission speeds available in organic VLC (OVLC) transmission is 55 Mb/s using aggregated wavelength multiplexed data streams [4]. This chapter gives an overview of organic based VLC focusing on the LED technology trends, organic LED (OLED) based devices, the organic semiconductors, and visible light photodetectors. To enhance the OLED-based VLC links blue filtering and a number of equalization schemes including artificial neural network equalizer, decision feedback equalizer, and linear equalizer are discussed and their performance are compared and contrasted. Finally an experimental allorganic VLC system employing both OLED and organic photodetectors employing artificial neural network base equalizer is introduced and its performance is evaluated. The chapter is completed with concluding remarks.

Wavelength Conversion of the 100 kHz, 100 W Picosecond Thin-disk Laser from Deep-UV to Mid-IR

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The 100-kHz picosecond 100-W thin-disk laser has been developed. The application potential of the laser is extended by wavelength conversion which spans from deep-ultraviolet into mid-infrared. The fundamental wavelength of 1030 nm was converted into second (515 nm), third (343 nm), fourth (257.5 nm), and fifth (206) harmonics by cascaded second harmonic and sum frequency generation. Generation of longer wavelengths by optical parametric generation and amplification covers the region from 1.8 μm to 2.4 μm.

A New Concept of Multi-Band Carrier-less Amplitude and Phase Modulation for Bandlimited Visible Light Communications

  • Autoři: Werfli, K., Haigh, P., Ghassemlooy, Z., Hassan, N.B., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 10th International Symposium on Communication Systems, Networks and Digital Signal Processing - Proceeding. Piscataway: IEEE, 2016. p. 1-5. ISBN 978-1-5090-2526-8.
  • Rok: 2016
  • DOI: 10.1109/CSNDSP.2016.7573916
  • Odkaz: https://doi.org/10.1109/CSNDSP.2016.7573916
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose a novel method of multiband carrier-less amplitude and phase (m-CAP) modulation for optical wireless communication (OWC) systems. In conventional m-CAP systems, the total signal bandwidth is divided into m equally distributed subcarriers. In this work, for the first time, we set the subcarrier bandwidths such that the first subcarrier is the same as the LED bandwidth, and subsequently distribute the remaining bandwidth equally between m− 1 subcarriers. We show that using m = 4, 6, 8 and 10 subcarriers and 16- QAM, the first subcarrier is able to achieve a bit error rate (BER) target of 10 −4 (i.e., which is below the 7% forward error correction (FEC) BER limits of 3.8 × 10 −3) at Eb/N0 = 15.5 dB. This is a power penalty of ∼1.5 dB to achieve the same average performance as the first five, four and three subcarriers of the conventional 10, 8 and 6-CAP and a power penalty of ∼1 dB for new 4-CAP to achieve the average performance of the first two subcarriers of the conventional 4-CAP. Consequently, using the proposed m-CAP concept we show a reduction in the complexity by reducing the number of finite impulse response (FIR) filters by 80%, 75%, ∼67% and 50% in contrast to the conventional 10, 8, 6, and 4-CAP, respectively.

An Overview of Optical Wireless Communications

  • Autoři: Ghassemlooy, Z., Uysal, M., Khalighi, M.A., Ribeiro, V., Moll, F., prof. Ing. Stanislav Zvánovec, Ph.D., Belmonte, A.
  • Publikace: Optical Wireless Communications An Emerging Technology. Basel: Springer, 2016. p. 1-23. ISSN 1860-4862. ISBN 978-3-319-30200-3.
  • Rok: 2016
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We are continuously witnessing the emergence of new data services and applications in wireless transmission systems, in particular mobile broadband services, which require enhancing user’s experience. The existing radio frequency based wireless communications are facing challenges in so far as being able to cope with these varied, sophisticated and bandwidth hungry services and applications. The ever evolving optical wireless communications (OWC) technology with its unique features such as a license-free frequency spectrum, an inherent security, and significantly higher transmission rates is seen as a potential alternative and complementary to the radio frequency based wireless communications, which can address some of these challenges. This technology can be used for short to long distance applications as in indoor visible light communications, ultra-violet, and free space optics. The chapter gives an overview of the OWC system focusing on the historical development and current status, as well as existing and envisioned applications areas.

Analyses of Dual Polarization WDM and SCM Radio over Fiber and Radio over FSO for C-RAN Architecture

  • DOI: 10.1109/WOCC.2016.7506564
  • Odkaz: https://doi.org/10.1109/WOCC.2016.7506564
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, the transmission schemes for Centralized Radio Access Network Architecture (C-RAN) based on combination of two technologies - Radio over Fiber (RoF) and Radio over FSO (RoFSO) are simulated and experimentally verified. The proposed setups are optimized for Long Term Evolution (LTE) with 20 MHz bandwidth using 64 Quadrature amplitude modulation in terms of Error Vector Magnitude (EVM). At the first, the measurements of Polarization Division Multiplexing using combination of RoF a RoFSO (PDM-RoF/FSO) is compared with simulation models. This is further extended by combination of PDM-Wavelength Division Multiplexing (WDM)-RoF/FSO and PDM-Subcarrier Multiplexing (SCM)-RoF/FSO, respectively. Results indicate better performance of PDM-SCM-RoF/FSO than WDM RoF/RoFSO in terms of launch power to reach EVM limit.

Characterization of Dual-Polarization Analogue Radio over Fiber Fronthaul for LTE C-RAN Architecture

  • DOI: 10.1109/CSNDSP.2016.7573934
  • Odkaz: https://doi.org/10.1109/CSNDSP.2016.7573934
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper the results from extended measurement of dual-polarization (DP) analogue radio over fiber (RoF) in a long term evolution (LTE) cloud radio access network (C-RAN) architecture are presented. This technique is proposed for fiber connections between central offices and remote base stations. Investigation of various optical fiber length is carried out to determine the best system performance in terms of error vector magnitude (EVM) and bit error rate. Maximal achieved distance for the case of LTE bandwidth of 20 MHz is 50 km displaying permissible EVM value of 8.5 % at the radio frequency of 2.6 GHz when using 64 QAM modulation scheme.

Characterization of the organic LED based visible light communications

  • Autoři: Chvojka, P., Dvořák, P., Pešek, P., prof. Ing. Stanislav Zvánovec, Ph.D., Haigh, P.A., Ghassemlooy, Z.
  • Publikace: 10th International Symposium on Communication Systems, Networks and Digital Signal Processing - Proceeding. Piscataway: IEEE, 2016. ISBN 978-1-5090-2526-8.
  • Rok: 2016
  • DOI: 10.1109/CSNDSP.2016.7573912
  • Odkaz: https://doi.org/10.1109/CSNDSP.2016.7573912
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents experimental results on a visible light communications system utilizing organic light-emitting diodes (OLEDs) and 16-quadrature amplitude modulation. The modulation bandwidth of the OLED device is limited to 310 kHz and the signal is generated on carrier frequencies f(c) = {100, 200, 300} kHz for use across different regions of the OLED frequency response. We demonstrate how setting a specific carrier frequency can affect the system performance. The supported bit rates are 220, 640 and 260 kb/s for f(c) = 100, 200 and 300 kHz, respectively. The angular dependence of the system performance is also analysed.

Circular Lattice Photonic Crystal Fiber for Mid-IR Supercontinuum Generation

  • DOI: 10.1109/LPT.2016.2615657
  • Odkaz: https://doi.org/10.1109/LPT.2016.2615657
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This letter introduces specific design features of a proposed chalcogenide photonic crystal fiber for ultra-wideband supercontinuum generation in the mid-infrared region. The fiber is optimized to include a circular photonic crystal lattice having tremendous potential in the fields of spectroscopy, food quality control, pulse compression, gas sensing and various nonlinear applications. By tailoring the zero-dispersion wavelength up to 2.0 μm and 2.5 μm, we have reached supercontinuum generation in the anomalous dispersion regime with the entire design hinging upon fibers based on two types of chalcogenide glass - arsenic-selenide and arsenic-sulfide, where supercontinuum broadening from 1.2 μm to 9.3 μm is made possible.

Comparison of Optical and Electrical based Amplifyand-and-Forward Relay-Assisted FSO Links over Gamma-Gamma Channels

  • Autoři: Nor, N.A.M., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Ali Khalighi, M., Bhatnagar, M.R.
  • Publikace: 10th International Symposium on Communication Systems, Networks and Digital Signal Processing - Proceeding. Piscataway: IEEE, 2016. p. 1-5. ISBN 978-1-5090-2526-8.
  • Rok: 2016
  • DOI: 10.1109/CSNDSP.2016.7574020
  • Odkaz: https://doi.org/10.1109/CSNDSP.2016.7574020
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Relay-assisted or multi-hop free space optical communications is an efficient solution that offers diversity, which can significantly improve the link availability. Albeit this potential, the turbulence-induced fading can still impact the system performance. This paper investigates through numerical simulations the effect of turbulence by comparing the bit error rate (BER) performance for all-optical and conventional amplifyand- forward dual-hop relaying systems. For the latter case, two options of the erbium-doped fiber amplifier (EDFA) and the semiconductor optical amplifier (SOA) are studied, showing that the advantages of the EDFA solution where EDFA outperforms SOA by ~3 dB in term of signal to noise ratio (SNR) for Rytov variance 􀣌􀡾 􀫛 = 􀫚. 􀫟 at a target BER of 10-5. Under the same turbulence regime, we further investigate the effect of aperture averaging in relay-assisted links and show that a significant BER improvement can be achieved. The results show that SNR gain of ~5.5 dB is achieved when the receiver aperture size increases from 100 mm to 300 mm at a target BER of 10-5.

Detection of liquids in the near and mid-infrared based on lead-silicate suspended-core microstructured fibers

  • DOI: 10.1117/12.2237887
  • Odkaz: https://doi.org/10.1117/12.2237887
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper reports on our recent progress with lead-silicate suspended-core microstructured optical fibers (SC- MOFs) for the detection of liquids. Simulations for SC-MOFs with one micrometer core diameter and of two different glass compositions with refractive indices of 1.67 and 1.89 at 1550 nm are discussed. Mode-field area study is performed for liquid analytes within refractive index range of 1.65-1.75. Experimental results of evanescent-wave refractometry are presented, with an impact study of uneven analyte-filling impact on the sensor performance. Studied SC-MOFs can find their application as monitoring sensors of various liquid quality especially when spectroscopic approach is pursued.

Diversity for Mitigating Channel Effects

  • Autoři: Ghassemlooy, Z., Popoola, W., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Optical Wireless Communications An Emerging Technology. Basel: Springer, 2016. p. 431-450. ISSN 1860-4862. ISBN 978-3-319-30200-3.
  • Rok: 2016
  • DOI: 10.1007/978-3-319-30201-0
  • Odkaz: https://doi.org/10.1007/978-3-319-30201-0
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    There is a need to compensate for the power fluctuations in free space optical (FSO) communication links due to the turbulence and other atmospheric phenomena. In order to overcome atmospheric turbulence induced fades, several techniques have been proposed. These include: spatial transmitter/receiver diversity, adaptive beam forming based on the wave front phase error measurement and the setting of the opposite phase aberration on the beam by a deformable mirror, wavelength diversity, multiple-beam communication and novel modulation techniques. In this chapter, the performance of FSO systems with spatial and time diversities is presented. To illustrate the diversity techniques, only the subcarrier intensity modulation scheme will be considered. The diversity techniques outlined can however, be extended to other modulation schemes without any loss of generality. The spatial diversity analysis is based on the linear combining techniques: equal gain combining, maximum ratio combining and selection combining. Inter-symbol interference is not being considered since terrestrial FSO links are basically a line-of-sight technology with the negligible delay spread. The chapter also outlines experimental results for verification of the diversity schemes for FSO links. To ensure link availability at all weather conditions the chapter also presents measurement campaign for an outdoor FSO/radio frequency link.

Dual Purpose Antenna for Hybrid Free Space Optics/RF Communication Systems

  • Autoři: Abadi, M. M., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Smith, D., Bhatnagar, M. R., Wu, Y.
  • Publikace: IEEE/OSA Journal of Lightwave Technology. 2016, 34(14), 3432-3439. ISSN 0733-8724.
  • Rok: 2016
  • DOI: 10.1109/JLT.2016.2571846
  • Odkaz: https://doi.org/10.1109/JLT.2016.2571846
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The concept of hybrid free space optical/radio frequency (FSO/RF) communications has been considered for the last mile access network applications. The existing schemes mostly use two separate transceiver antennas for outdoor terrestrial links of few kilometres long. In this article, we propose and investigate a single hybrid FSO/RF antenna that could be used in high-speed access networks. We outline the design procedures based on the concept of Cassegrain antenna and shows how the FSO transceiver is incorporated into the original design. The proposed antenna is fabricated and extensive measurements are carried out for the radiation pattern, return loss, RF signal-to-noise ratio and the FSO received power. By performing link budget analysis and the results obtained from experiments, we demonstrate the operation of proposed hybrid antenna with 1×3 single-input multiple-output configuration and an equal gain combining at the receiver under moderate regime turbulence regime.

Effect of Optimal Lambertian Order for Cellular Indoor Optical Wireless Communication and Positioning Systems

  • Autoři: Wu, D., Ghassemlooy, Z., Zhong, W., Khalighi, M. A., Minh, H. L., Chen, C., prof. Ing. Stanislav Zvánovec, Ph.D., Boucouvalas, A. C.
  • Publikace: Optical Engineering. 2016, 55(6), 066114-1-066114-8. ISSN 0091-3286.
  • Rok: 2016
  • DOI: 10.1117/1.OE.55.6.066114
  • Odkaz: https://doi.org/10.1117/1.OE.55.6.066114
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We propose and analyze an optimized Lambertian order (OLO) of light-emitting diode for both indoor cellular optical wireless communication (OWC) and positioning systems. We carry out analysis for the system consisting of a Lambertian source and a tilted optical receiver, and develop an expression for OLO for 4-, 6- and 9-cell configurations. We investigate the channel characteristics including the optical path loss, impulse response, transmission bandwidth and positioning accuracy for the proposed systems with and without OLO, showing that there is a significant improvement in the transmission bandwidth as well as the positioning accuracy when employing OLO. For example for a 4-cell configuration with the optimum Lambertian order, 99% of cumulative distribution function of the estimation errors is within the Cramer-Rao bound (CRB) accuracy of 6.7 - 26.7 cm, compare to the CRB accuracy of 12.8 - 29.7 cm for the Lambertian order of m = 1.

Evaluation of Multi-band Carrier-less Amplitude and Phase Modulation Performance for VLC under Various Pulse Shaping Filter Parameters

  • Autoři: Chvojka, P., Haigh, P.A., prof. Ing. Stanislav Zvánovec, Ph.D., Pešek, P., Ghassemlooy, Z.
  • Publikace: Proceedings of the 13th International Joint Conference on e-Business and Telecommunications. Porto: SciTePress - Science and Technology Publications, 2016. p. 25-31. ISBN 978-989-758-196-0.
  • Rok: 2016
  • DOI: 10.5220/0005956900250031
  • Odkaz: https://doi.org/10.5220/0005956900250031
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In multi-band carrier-less amplitude and phase modulation (m-CAP), the transmitter and receiver pulse shaping filters have a significant impact on the signal performance. Since m-CAP is an emerging and promising modulation format for visible light communications (VLC), it is necessary to balance the system performance and the filter length, due to limited integration density in FPGAs. In this paper we investigate the m-CAP VLC system performance for different number of sub-bands m = {2, 5, 10} under varying finite impulse response (FIR) filter parameters, such as the filter length Lf and the roll off factor β. We show that increasing both β and Lf improves the bit error rate (BER) performance of the system substantially. We demonstrate that a BER target of 10-4 is achieved using Lf ≤ 12 for m = 5 and 10 for low order subcarriers. Moreover, the BER limit is attained for β = 0.2 by all subcarriers, except the last two for m = 5 and 10, which is a significant improvement, even considering the slightly increased excess bandwidth in comparison to the literature.

Experimental optimization of the hybrid RoMMF-FSO system using mode filtering techniques

  • Autoři: Al-Musawi, H. K., Cseh, T., Ing. Jan Bohata, Ph.D., Pešek, P., Ng, W. P., Ghassemlooy, Z., Udvary, E., Berceli, T., Fellow, L., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: IEEE International Conference on Communications - Proceeding. Piscataway, NJ: IEEE, 2016. pp. 405-410. ISBN 978-1-5090-0448-5.
  • Rok: 2016
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper proposes an optimum hybrid radio over multi-mode fiber and free space optics (RoMMF–FSO) system to enhance the last mile bottleneck issues of wireless communication systems. Single mode fiber (SMF) and gradient index (GRIN) lenses are used as mode filtering techniques to optimize the system performance by mitigating the modal effects produced by multimode optical fiber networks. We characterize the system based on the beam profile, transfer function, and error vector magnitude (EVM) measurements. The results reveal that both techniques can improve the EVM performance significantly by ~19% and ~30% using a SMF filter and SMF-GRIN lenses, respectively. Furthermore, the analysis of the obtained measurements show the SMF-GRIN lenses is more effective than SMF only with lower EVM values and negligible difference in the optical launch power.

Experimental verification of long-term evolution radio transmissions over dual-polarization combined fiber and free-space optics optical infrastructures

  • DOI: 10.1364/AO.55.002109
  • Odkaz: https://doi.org/10.1364/AO.55.002109
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper describes the experimental verification of the utilization of long-term evolution (LTE) radio over fibre (RoF) and radio over free space optics (RoFSO) systems using dual-polarization signals for cloud radio access network (C-RAN) applications determining the specific utilization limits. A number of FSO configurations is proposed and investigated under different atmospheric turbulence regimes in order to recommend the best setup configuration. We show that the performance of the proposed link based on the combination of RoF and RoFSO for 64-QAM at 2.6 GHz is more affected by the turbulence based on the measured difference error vector magnitude value of 5.5 %. It is further demonstrated the proposed systems can offer higher noise immunity under particular scenarios with the signal-to-noise ratio reliability limit of 5 dB in the radio frequency domain for RoF and 19.3 dB in the optical domain for combination of RoF and RoFSO links.

Extended Measurement Tests of Dual Polarization Radio over Fiber and Radio over FSO Fronthaul in LTE C-RAN architecture

  • Autoři: Ing. Jan Bohata, Ph.D., Pešek, P., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z.
  • Publikace: "2016 IEEE 12th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob)". Piscataway, NJ: IEEE, 2016. p. 476-481. ISBN 978-1-5090-0723-3.
  • Rok: 2016
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper we present experimental results from extended measurement campaign for an analog dual polarization (DP) radio over fiber and radio over free space optics (FSO) link as part of the cloud mobile network architecture. System utilization with long-term evolution (LTE) test models is described and different link types are evaluated in terms of the error vector magnitude (EVM). Results imply that combined radio over fiber and radio over FSO schemes in combination with Erbium-doped fiber amplifier (EDFA) can provide almost the same performance for a fiber subpart length of between 10 km to 50 km. Moreover, both sub-systems can operate with a high dynamic range and meet the required EVM limit of 9% for 64- quadrature amplitude modulation (QAM) with the minimum optical signal to noise ratio (OSNR) of 24 dB for a 50 km fiber link and a LTE bandwidth 20 MHz. In addition, the combination of 10 km fiber and FSO link is tested under turbulence FSO channel condition showing EVM values below the threshold of 9 % even under a strong turbulence regime.

Fiber Optic Refractometric Sensors Using a Semi-ellipsoidal Sensing Element

  • DOI: 10.1364/AO.55.002574
  • Odkaz: https://doi.org/10.1364/AO.55.002574
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We present theoretical and experimental results for the fiber optic refractometric sensor employing a semiellipsoidal sensing element made of polymethyl methacrylate. The double internal reflection of light inside the element provides sensitivity to the refractive index of the external analyte. We demonstrate that the developed sensor, operating at a wavelength of 632 nm, is capable of measurement within a wide range of refractive indices from n=1.00 to n=1.47 with sensitivity over 500 dB/RIU. A comparison of the developed sensor with two more complex refractometric sensors, one based on tapered optical fiber and the other based on suspended-core microstructure optical fiber, is presented.

FSO Detection Using Differential Signaling in Outdoor Correlated-Channels Condition

  • Autoři: Abadi, M. M., Ghassemlooy, Z., Khalighi, M., prof. Ing. Stanislav Zvánovec, Ph.D., Bhatnagar, M. R.
  • Publikace: IEEE Photonics Technology Letters. 2016, 28(1), 55-58. ISSN 1041-1135.
  • Rok: 2016
  • DOI: 10.1109/LPT.2015.2480011
  • Odkaz: https://doi.org/10.1109/LPT.2015.2480011
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this letter, we introduce a detection technique based on differential signaling scheme for outdoor free space optical communications. This method requires no channel state information (CSI) and does not suffer from the computational load compared with the conventional receivers, where adjusting dynamically the detection threshold level (either based on CSI knowledge, or by using pilots) leads to increased computational time and reduced link throughput. This letter shows that the performance of the proposed technique only depends on the correlation of propagating optical beams. Especially under highly correlated-channels condition the fluctuation of the detection threshold level in the receiver is significantly small. We also show experimentally that under weak turbulence regime the variance of detection threshold level reduces for the correlated channel.

Fundamental investigation of extending 4G-LTE signal over MMF/SMF-FSO under controlled turbulence conditions

  • Autoři: Al-Musawi, H.K., Cseh, T., Ing. Jan Bohata, Ph.D., Pešek, P., Ng, W.P., Ghassemlooy, Z., Udvary, E., prof. Ing. Stanislav Zvánovec, Ph.D., Ijaz, M.
  • Publikace: 10th International Symposium on Communication Systems, Networks and Digital Signal Processing - Proceeding. Piscataway: IEEE, 2016. pp. 1-6. ISBN 978-1-5090-2526-8.
  • Rok: 2016
  • DOI: 10.1109/CSNDSP.2016.7574035
  • Odkaz: https://doi.org/10.1109/CSNDSP.2016.7574035
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we propose a hybrid radio over multi-mode/single-mode fibre and free space optics (RoMMF/SMF-FSO) system to enhance the 4th generation-long term evolution (4G-LTE) signal performance when used in local area access networks. A single mode fibre pigtailed gradient index lens is used to minimise the modal effect of the optical link at different turbulence strengths. The proposed system is characterised in terms of the system transfer function, error vector magnitude (EVM), and optical launch power (OLP). Results demonstrate the robustness of the proposed scheme in terms of increased available passband bandwidth by 2 GHz and improving the transmission shape by reducing the system transfer function ripple by more than 5 dB. Successful transmission of the 4G-LTE signal is achieved over a MMF/SMFFSO channel with a 1.5 dB power penalty under the higher turbulence level (i.e., Rytov variance of 0.1).

Optical Camera Communications

  • Autoři: Ghassemlooy, Z., Luo, P., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Optical Wireless Communications An Emerging Technology. Basel: Springer, 2016. p. 447-568. ISSN 1860-4862. ISBN 978-3-319-30200-3.
  • Rok: 2016
  • DOI: 10.1007/978-3-319-30201-0
  • Odkaz: https://doi.org/10.1007/978-3-319-30201-0
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communications (VLC) has been evolving at a much faster rate because of the development of high energy efficient white light emitting diodes (LED). For the first time, we see a unique device which offers triple functionalities of illumination, data communications and indoor localization, thus opening up the opportunities for applications at homes, offices, planes, trains, etc. In modern vehicles with LED-based head and tail lights, VLC can be used for car-to-car communications to convey regular traffic information to other vehicles as well as the road side infrastructure. Cameras are also being widely used in vehicles for monitoring speed, collision detection avoidance, traffic sign and object recognition. The VLC technology employing the camera as a receiver opens up new possibilities offering multiple functionalities including data communications. This chapter gives an overview of the optical camera communications and outlines the technological concept behind it.

Preparation and Testing of Fiber Tapers for Repeatable Detection of Selected Hydrocarbons

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Tapered optical fibers were prepared by heating of a section of the single-mode optical fiber using the tapering apparatus equipped by hydrogen-oxygen flame. Prepared samples of taper waist diameter of 6.1 μm and 3.4 μm were characterized and used as sensors working on refractometric principle of detection at a wavelength of 1550 nm. The repeatability of sensitivity measurement for selected liquids (hydrocarbons) was successfully tested with maximum of deviation of 0.1 dB from the mean value. The samples returned to baseline after purifying very well. Maximum of deviation of 0.05 dB from the mean value was calculated from measured data. OCIS codes: 280.0280

Quantized Feedback-Based Differential Signaling for Free-Space Optical Communication System

  • Autoři: Bhatnagar, M.R., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Khalighi, M.-A., Abadi, M.M.
  • Publikace: IEEE Transactions on Communications. 2016, 64(12), 5176-5188. ISSN 0090-6778.
  • Rok: 2016
  • DOI: 10.1109/TCOMM.2016.2614817
  • Odkaz: https://doi.org/10.1109/TCOMM.2016.2614817
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We propose a quantized feedback based differential signaling scheme for 2 × 1 free space optical (FSO) multiple-input single-output communication systems. The analytical bit error rate (BER) for the proposed differential signaling schemes is derived and compared to existing differential signaling schemes for FSO systems. The asymptotic BER of the proposed scheme is also determined and it is shown by using the asymptotic BER expression that the proposed scheme achieves full spatial diversity of two. Moreover, the effect of the feedback error on the performance of the proposed scheme is studied and it is demonstrated by simulation-based and analytical results that the proposed scheme significantly outperforms a previously-proposed differential signaling scheme in terms of turbulence fades reduction for tolerable feedback errors.

Suspended-core silica and lead-silicate fibers for nonlinear application and sensing purposes

  • DOI: 10.1117/12.2227105
  • Odkaz: https://doi.org/10.1117/12.2227105
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    We report development of suspended-core silica and lead-silicate microstructured optical fibers for detection of liquids and supercontinuum generation. Theoretical analysis of effective mode area, dispersion curve, nonlinear coefficient and mode-field overlap is presented. For a specific lead-silicate fiber we determinated the zero dispersion wavelength at 1113 nm with a nonlinear coefficient of 1321 W-1km-1. For detection of liquids both silica and lead-silicate fibers are found to be suitable in different refractive index ranges 1.38-1.44 and 1.68-1.74 respectively. Coupling efficiency into all studied fibers over 40%; fiber attenuation was measured by the cut-back technique and is approximately 2 dB/m for silica glass fibers and over 3 dB/m for lead-silicate fibers.

Using differential signalling to mitigate pointing errors effect in FSO communication link

  • Autoři: Abadi, M. M., Ghassemlooy, Z., Bhatnagar, M. R., prof. Ing. Stanislav Zvánovec, Ph.D., Khalighi, M. A., Maheri, A. R.
  • Publikace: IEEE International Conference on Communications - Proceeding. Piscataway, NJ: IEEE, 2016. p. 145-150. ISBN 978-1-5090-0448-5.
  • Rok: 2016
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we investigate a differential signalling (DS) scheme to mitigate pointing errors effect in intensity-modulation/direct-detection (IM/DD) free space optical (FSO) communication systems with the non-return-to-zero on-off keying (NRZ-OOK) modulation format. The most common approach to detect a digital signal is based on comparing the received signal with an optimal threshold level. Normally, this optimal threshold level is set at the mean value of the signal in a clear channel. However, this detection threshold method is inefficient in a channel with fading effects. DS has been reported to mitigate the fluctuation of optimal detection threshold in NRZ-OOK IM/DD FSO communication systems only to combat atmospheric fading effects (e.g., fog and turbulence) and to reduce the background noise of the received signal. In this paper, we adopt the DS scheme to mitigate the optimal detection threshold level fluctuations induced by pointing errors. We also discuss the conditions in which DS cancels out the fluctuation of threshold level. The proposed technique is supported by carrying out experimental investigation of the FSO link with pointing errors. Measured results confirm that the effect of PE on the received signal was highly correlated (i.e., 𝝆=𝟎.𝟗𝟐, where 𝝆 is the correlation coefficient between channels) thus resulting in reduced variance value of the combined signal threshold level. We also derive an expression for bit-error-rate for the system which is supported by simulation.

10 Gbps All-Optical Relay-Assisted FSO System Over a Turbulence Channel

  • DOI: 10.1109/IWOW.2015.7342268
  • Odkaz: https://doi.org/10.1109/IWOW.2015.7342268
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Relay-assisted free space optics (FSO) communications becomes one of the promising solutions to improve the FSO link capabilities by implicitly reducing the transmission distance and exploiting distance-dependent fading variance of turbulence. Highly motivated by the capabilities of the system, this paper presents bit error rate (BER) performance of an all-optical 10-Gbps FSO relay based system using amplify-andforward signaling is investigated through numerical simulations and experimental implementation. Results show that BER improves up to several orders of magnitudes when using relay based links over the same turbulent distance.

A Multi-CAP Visible Light Communications System with 4.85 b/s/Hz Spectral Efficiency

  • Autoři: Haigh, P., Burton, A., Werfli, K., Minh, H. L., Bentley, E., Chvojka, P., Popoola, W. O., Papakonstantinou, I., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: IEEE Journal on Selected Areas in Communications. 2015, 33(9), 1771-1779. ISSN 0733-8716.
  • Rok: 2015
  • DOI: 10.1109/JSAC.2015.2433053
  • Odkaz: https://doi.org/10.1109/JSAC.2015.2433053
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper we experimentally demonstrate a multiband carrier-less amplitude and phase modulation format for the first time in VLC. We split a conventional carrier-less amplitude and phase modulated signal into m subcarriers in order to protect from the attenuation experienced at high frequencies in low-pass VLC systems. We investigate the relationship between throughput/spectral efficiency and m, where m = {10, 8, 6, 4, 2, 1} subcarriers over a fixed total signal bandwidth of 6.5 MHz. We show that transmission speeds (spectral efficiencies) of 31.53 (4.85), 30.88 (4.75), 25.40 (3.90), 23.65 (3.60), 15.78 (2.40), 9.04 (1.40) Mb/s (b/s/Hz) can be achieved for the listed values of m, respectively.

An European View on the Next Generation Optical Wireless Communication Standard

  • Autoři: Jungnickel, V., Uysal, M., Serafimovski, N., Baykas, T., O’Brien, D., Ciaramella, E., Ghassemlooy, Z., Green, R., Haas, H., Haigh, P.A., Gil Jimenez, V.P., Miramirkhani, F., Wolf, M., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of IEEE Wireless Communications and Networking Conference VCNC. Piscataway: IEEE, 2015. p. 106-111. ISBN 978-1-4799-8928-7.
  • Rok: 2015
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical wireless technology uses light for mobile communications. The idea is to simultaneously combine the illumination provided by modern high-power light-emitting diodes (LEDs) with high-speed wireless communications. There have been numerous practical demonstrations of this concept, and the technology is now well matured to be deployed in practice. Independent market analysts forecast a high-volume market for mobile communication devices connected to the ubiquitous lighting infrastructure. This paper aims to make optical and wireless industries aware of the requirement for standardization in this area. The authors present the view of the European COST 1101 research network OPTICWISE towards a next-generation optical wireless standard aiming at data rates from 1 Mbit/s to 10 Gbit/s. Besides key technical insights, relevant use cases and main features are described that were recently adopted by the IEEE 802.15.7r1 working group. Moreover, a channel model is introduced to enable assessment of technical proposals.

Channel Characteristics of Visible Light Communications Within Dynamic Indoor Environment

  • Autoři: Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Haigh, P. A., Ghassemlooy, Z.
  • Publikace: IEEE/OSA Journal of Lightwave Technology. 2015, 33(9), 1719-1725. ISSN 0733-8724.
  • Rok: 2015
  • DOI: 10.1109/JLT.2015.2398894
  • Odkaz: https://doi.org/10.1109/JLT.2015.2398894
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communications (VLC) is a new emerging technology, which provides both data transmission and illumination by utilizing the visible range (370–780 nm) of the electromagnetic spectrum. In order to maximize the available data rate and enhance the users mobility within an indoor environment, it is essential to characterize the communication channel. In this paper, we present both analytical and experimental results for a VLC system affected by movement of people for different indoor conditions (i.e., furnished office room, empty hall, and corridor). VLC systems utilize multiple light-emitting diodes mounted in the ceiling and the configuration is based on the nondirected line of sight. We consider random movement of people within the room, focusing on the impacts of shadowing and blocking on mobility and link system performance by investigating changes in the channel characteristics using the cumulative distribution function of the received power distribution and the delay profile. We demonstrate the behaviour of communication channels for different scenarios from corridor, the most robust against people movement induced fading, to the office rooms and halls, the most vulnerable to the received power fluctuation.

Channel Characterization of a Last-mile Access Radio Over Combined Fibre and Free-Space Optics System

  • Autoři: Ing. Jan Bohata, Ph.D., prof. Ing. Stanislav Zvánovec, Ph.D., Abadi, M.M., Ghassemlooy, Z.
  • Publikace: Proceedings of The International Conference on Automation Cognitive Science Optics Micro Electro-Mechanical System, and Information Technology. Piscataway: IEEE, 2015. pp. 180-184. ISBN 978-1-4673-7407-1.
  • Rok: 2015
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper we characterize a radio over fiber and radio over free space optic system for the last mile access network in urban areas and as a solution to the cellular backhaul networks. Special focus is put on the performance of such systems under the atmospheric turbulence. We show that the proposed system performance is almost the same for the entire frequency range of 0.4 - 4 GHz under the weak or no turbulence regimes. Finally we show that for proposed system with BPSK and QPSK at different RF carrier frequencies the turbulence effect has marginal impact.

Characterization of Dual-Polarization LTE Radio over a Free-Space Optical Turbulence Channel

  • DOI: 10.1364/AO.54.007082
  • Odkaz: https://doi.org/10.1364/AO.54.007082
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A dual polarization (DP) radio over a free-space optical (FSO) communication link using a long-term evolution (LTE) radio signal is proposed and analyzed under different turbulence channel conditions. Radio signal transmission over the DP FSO channel is experimentally verified via error vector magnitude statistics. Based on the results we show that transmitting of the LTE signal over the FSO channel is a potential solution for the last-mile access or backbone networks, when using multiple-input multiple-output based DP signals.

Experimental verification of an all-optical dual-hop 10 Gbit/s free-space optics link under turbulence regimes

  • DOI: 10.1364/OL.40.000391
  • Odkaz: https://doi.org/10.1364/OL.40.000391
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This Letter presents original measurement results from an all-optical 10 Gbit/s free-space optics (FSO) relay link involving two FSO links and an all-optical switch. Considering the fact that reported analyses of relay links are dominated by analytical findings, the experimental results represent a vital resource for evaluating the performance of relay FSO links in the presence of atmospheric turbulence. Bit-error-rate (BER) performance of the relay system is tested for single and dual-hop links under several turbulence regimes. Furthermore, results from this measurement are used to ascertain real parameters of the outdoor links and to improve the accuracy of simulation results. Results show that using a dual-hop FSO link against a single FSO link could result in up to four orders of magnitude improvement in BER in the presence of atmospheric turbulence.

Experimental Verification of Visible Light Communications based on Multi-Band CAP Modulation

  • Autoři: Haigh, P., Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Le, S. T., Kanesan, T., Doran, N.J., Papakonstantinou, I., Darwazeh, I., Giacounidis, E.
  • Publikace: Proceedings of Optical Fiber Communication Conference. Washington: OSA, 2015. ISBN 978-1-55752-937-4.
  • Rok: 2015
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A multi-band CAP system is experimentally demonstrated for the first time in VLC. We show that with an 8-CAP testbed spectral efficiencies (~4.75 b/s/Hz) at a realistic distance of 1 m can be reached

Fire Emissivity Detection by a Microwave Radiometer

  • DOI: 10.1109/LGRS.2015.2474121
  • Odkaz: https://doi.org/10.1109/LGRS.2015.2474121
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this letter detectability of a fire by a microwave radiometer is investigated. In order to understand the fire from radiometric point of view, parameters of the fire emissivity had to be determined. Therefore representative fire types were analyzed and fire spot emissivity values have been derived from measured data. Four typical burning fuels were tested – gasoline, wood, flood-trash and straw. Also parameters of a scenario in which the fire temperature was changed was set and analyzed in order to investigate detectable radiometric contrasts. As a result specific values of a fire spot emissivity are presented. Obtained results can provide indispensable inputs for designers of microwave fire detection instruments.

Improvements in Combined Radio over Multimode Fibre and Radio over FSO Systems by Applying Mode Filtering

  • Autoři: Cseh, T., Al-Musawi, H.K., Abadi, M.M., Ghassemlooy, Z., Ng, W.P., Udvary, E., Berceli, T., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 17th International Conference on Transparent Optical Networks. Piscataway: IEEE, 2015. ICTON. ISSN 2162-7339. ISBN 978-1-4673-7880-2.
  • Rok: 2015
  • DOI: 10.1109/ICTON.2015.7193688
  • Odkaz: https://doi.org/10.1109/ICTON.2015.7193688
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, the combination of radio over multimode fibre and radio over free space optical systems are experimentally investigated. A mode filtering technique is adopted in order to deal with the modal effects in such hybrid systems. Considering mode filtering effect, we have determined transfer function and performed link budget analysis. Measurement of the error vector magnitude (EVM) was accomplished to verify the efficiency of the proposed systems in dealing with the modal effect. The obtained results are below the 8% 3GPP-LTE EVM requirement for different free space optical channel conditions including fog and turbulence.

Investigation LTE Radio over a Free-Space Optical link in turbulence regime

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A dual polarization (DP) radio over a free-space optical (FSO) communication link using a long-term evolution (LTE) radio signal is proposed and analyzed under different turbulence channel conditions. Radio signal transmission over the DP FSO channel is experimentally verified by means of error vector magnitude (EVM) statistics. Based on the results we show that transmitting the LTE signal over the FSO channel is a potential solution for the last-mile access or backbone networks, when using multiple-input multiple-output based DP signals.

Liquid Analytes Filling Process in Suspended-core Silica Fibers

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Liquid filling into silica suspended-core microstructured optical fiber capillaries is studied for the application as a liquid sensor. Liquid analytes with various refractive index are theoretically and experimentally compared with respect to their density, viscosity and repeatable measurement. Maximum filling lengths are derived and their dependence on filling time is analyzed. Degradation effects on suspended-core microstructured optical fiber are observed for particular liquid analytes.

Multi-band Carrier-less amplitude and Phase Modulation for Bandlimited Visible Light Communications Systems

  • Autoři: Haigh, P. A., Le, S. T., prof. Ing. Stanislav Zvánovec, Ph.D., Ghassemlooy, Z., Luo, P., Xu, T., Chvojka, P., Kanesan, T., Giacoumidis, E., Canyelles-Pericas, P., Minh, H. L., Popoola, W., Rajbhandari, S., Papakonstantinou, I., Darwazeh, I.
  • Publikace: IEEE WIRELESS COMMUNICATIONS. 2015, 22(2), 46-53. ISSN 1536-1284.
  • Rok: 2015
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Visible light communications is a technology with enormous potential for a wide range of applications within next generation transmission and broadcasting technologies. VLC offers simultaneous illumination and data communications by intensity modulating the optical power emitted by LEDs operating in the visible range of the electromagnetic spectrum (~370–780 nm). The major challenge in VLC systems to date has been in improving transmission speeds, considering the low bandwidths available with commercial LED devices. Thus, to improve the spectral usage, the research community has increasingly turned to advanced modulation formats such as orthogonal frequency-division multiplexing. In this article we introduce a new modulation scheme into the VLC domain; multiband carrier-less amplitude and phase modulation (m-CAP) and describe in detail its performance within the context of bandlimited systems.

Multi-band Carrier-less Amplitude and Phase Modulation for Highly Bandlimited Visible Light Communications - Invited paper

  • Autoři: Haigh, P.A., Aguado, A., Ghassemlooy, Z., Chvojka, P., Werfli, K., prof. Ing. Stanislav Zvánovec, Ph.D., Ertunc, E., Kanesan, T.
  • Publikace: Proceedings of The International Conference on Wireless Communications and Signal Processing. Piscataway: IEEE, 2015. p. 1-5. ISBN 978-1-4673-7687-7.
  • Rok: 2015
  • DOI: 10.1109/WCSP.2015.7341338
  • Odkaz: https://doi.org/10.1109/WCSP.2015.7341338
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper we present new numerical results for the signal-to-noise ratio and bit error rate (BER) performances of multi-band carrier-less amplitude and phase (m-CAP) modulation in the context of a highly bandlimited visible light communications (VLC) link. Light-emitting diodes are used as the transmitter and are modelled in this work as an ideal first order analogue low-pass filter. The link bandwidth is given as unity, while the filter cut-off frequency is set to 0.1. The number of bands, or subcarriers, is selected as m = 1, 2, 5 and 10. Here, we show that under such a high bandwidth constraint, using m = 10 subcarriers can result in 40% and 17% improvement in bit rate compared to m = 1 and 2, and m = 5 subcarriers, respectively for the same BER target.

Multi-band Carrier-less Amplitude and Phase Modulation with Decision Feedback Equalization for Bandlimited VLC Systems

  • Autoři: Werfli, K., Haigh, P.A., Ghassemlooy, Z., Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Rajbhandan, S., Iong, S.
  • Publikace: Proceedings of 4th International Workshop on Optical Wireless Communications. Istambul: IEEE, 2015. p. 6-10. ISBN 978-1-4673-7726-3.
  • Rok: 2015
  • DOI: 10.1109/IWOW.2015.7342255
  • Odkaz: https://doi.org/10.1109/IWOW.2015.7342255
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents simulation results that show the principle of implementing multi-band carrierless amplitude and phase (m-CAP) modulation enhanced by the decision feedback equalizer (DFE) for a bandlimited visible light communications (VLC) system. When deploying different number of sub-carriers m = {1, 2, 5, 10}, we show the bit error rate (BER) performance of m-CAP over a fixed system bandwidth of 1 Hz with and without a DFE. We show that we can achieve a BER of 10-4 for the m-CAP system for m = {1, 2}, which is well below the 7% and 20% forward error correction (FEC) BER limits of 3.8×10-3 and 2×10-2, respectively.

Multimode fiber tapers for reproducible refractometric liquid detection

  • DOI: 10.1117/1.OE.54.4.047102
  • Odkaz: https://doi.org/10.1117/1.OE.54.4.047102
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper describes the refractometric detection of liquids based on silica multimode optical fibers which were tapered to increase the evanescent-wave overlap for higher sensor sensitivity. By precisely monitoring the production process, consistent sample parameters were achieved. More than 200 tapers with a taper waist diameter range from 6.0 to 76.3 μm were prepared from polymer-clad silica and gradient-index multimode fibers. U-shaped fiber taper sensitivities were analytically compared with straight tapers with resulting intensity sensitivities of over 200%/RIU. Crucial parameters for real sensor applications, such as measurement repeatability, reproducibility, and long-term stability, were further studied for polymer-clad silica straight tapers. Longterm stability was monitored showing stable measurement results over a 6 months long interval. Measurement repeatability and reproducibility with standard deviations of 0.55%/RIU and 2.26%/RIU, respectively, were achieved.

Performance Analysis of All-Optical Amplify-and-forward FSO relaying over atmospheric turbulence

  • Autoři: Nor, N. A.M., Ghassemlooy, Z., prof. Ing. Stanislav Zvánovec, Ph.D., Khalighi(, M. A.
  • Publikace: Proceedings of 2015 IEEE Student Conference on Research and Development. San Francisco: American Institute of Physics and Magnetic Society of the IEEE, 2015. p. 289-293. ISBN 978-1-4673-9572-4.
  • Rok: 2015
  • DOI: 10.1109/SCORED.2015.7449342
  • Odkaz: https://doi.org/10.1109/SCORED.2015.7449342
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we present the Bit Error Rate (BER) analysis of a 10 Gbps triple-hop relay-assisted Free Space Optics (FSO) system using amplify-and-forward scheme over atmospheric turbulence. We investigate the performances of onoff keying non-return-to-zero (NRZ) and return-to-zero (RZ) modulation schemes through numerical simulations and by considering the average bit-error rate and the Q-factor, and show the advantage of using RZ pulse shaping. Furthermore, we present some experimental results that show how the eye diagram improves by increasing the number of hops.

Soft-glass Fiber Modules for NIR/MIR High-power Lasers, Supercontinuum Sources and Sensing Applications

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents results from the development of soft-glass fiber modules for near- and mid-infrared applications. They can be utilized especially in applications such as high-power lasers, supercontinuum generation and spectroscopy. The technology of fiber processing, preparation and connectorization has been mastered in cooperation with SQS Fiber optics in the frame of joint cooperation in several co-running projects; the high-power lasers and supercontinuum generation is prepared with the IPE Academy of Sciences of the Czech Republic. We have studied soft-glass fibers including chalcogenide arsenic-selenide, lead-silicate and zirconium-fluoride glass materials. Crucial optical signal factors for specific purposes such as operational wavelength, insertion-loss on the soft-glass-silica-glass boundaries, back-reflected optical power reduction to prevent lasing, power-induced heat generation issues and mode-field mismatch must be taken into account. Technological aspects then include bending radii, glass fragilities and glass toxicities. Results from laboratory measurements will be shown to verify the theoretical dispersion calculation. Results from technological tests of chalcogenide arsenic-selenide fiber module, lead-silicate microstructured fiber free-space optic coupling and zirconium-flouride glass processing challenges will be as well presented more in detail.

Suspended-core microstructured fiber for 2 refractometric detection of liquids

  • DOI: 10.1364/AO.54.008899
  • Odkaz: https://doi.org/10.1364/AO.54.008899
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A silica suspended-core microstructured optical fiber sensor for detection of liquids, operating at 1550 nm, is analyzed. The sensing principle is based on the evanescent wave overlap into a tested analyte, which is filled via capillary forces into the cladding holes. Validations for analytes in the refractive index range of 1.35–1.43 are carried out with liquid-analyte-filling-length limits being studied both theoretically and experimentally. We prove, for the first time to our knowledge, that an extreme sensitivity of 342.86 dB/RIU and resolution of 4.4 × 10−5 can be achieved. This sensor represents a high-quality alternative for applications requiring a facile, low-cost solution.

Visible Light Communications towards 5G

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of co-operating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks.

Artificial Neural Network Utilization for FSO Link Performance Estimation

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper describes FSO link performance prediction based on available meteorological data using different Artificial Neural Network (ANN) approaches. Several types of ANNs were compared and their performance were evaluated. The paper introduces an ANN application utilizing real delayed data. This approach has been validated to be more precise than common feed-forward neural networks.

Comparison of Different Combining Methods for Space-Diversity FSO Systems

  • Autoři: Abadi, M.M., Ghassemlooy, Z., Smith, D., Ng, W.P., Khalighi, M.A., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 2014 9th International Symposium on Communication Systems, Networks & Digital Signal Processing. Piscataway: IEEE, 2014. p. 1023-1028. ISBN 978-1-4799-2581-0.
  • Rok: 2014
  • DOI: 10.1109/CSNDSP.2014.6923979
  • Odkaz: https://doi.org/10.1109/CSNDSP.2014.6923979
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper gives an overview of different signal combining schemes for free space optical (FSO) communication systems employing spatial diversity (SD) for the case of lognormal weak turbulence atmospheric channels. The receiver configurations are explained and categorized into two domains, namely optical and electrical. Moreover, a new combining scheme in the electrical domain, called “logical” domain combining, is introduced. We present closed-form expressions of bit-error-rate for the combining schemes, considering the typical case of a single-input multiple-output (SIMO) system. Through some numerical analyses, we show that depending on the number of receivers and the turbulence strength, the proposed logical combining method outperforms the other ones.

Experimental characterization and mitigation of turbulence induced signal fades within an ad hoc FSO network

  • DOI: 10.1364/OE.22.003208
  • Odkaz: https://doi.org/10.1364/OE.22.003208
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical beams propagating through the turbulent atmospheric channel suffer from both the attenuation and phase distortion. Since future wireless networks are envisaged to be deployed in the ad hoc mesh topology, this paper presents the experimental laboratory characterization of mitigation of turbulence induced signal fades for two ad hoc scenarios. Results from measurements of the thermal structure constant along the propagation channels, changes of the coherence lengths for different turbulence regimes and the eye diagrams for partially correlated turbulences in free space optical channels are discussed. Based on these results future deployment of optical ad hoc networks can be more straightforwardly planned.

Fused fiber components for "eye-safe" spectral region around 2 um

  • Autoři: Písařík, M., Peterka, P., prof. Ing. Stanislav Zvánovec, Ph.D., Baravets, Y., Todorov, F., Kašík, I., Honzátko, P.
  • Publikace: Optical and Quantum Electronics. 2014, 46(4), 603-611. ISSN 0306-8919.
  • Rok: 2014
  • DOI: 10.1007/s11082-013-9801-2
  • Odkaz: https://doi.org/10.1007/s11082-013-9801-2
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Thulium-doped fiber lasers operating at wavelengths around 2 μ m are rapidly developing a new class of coherent light sources with a high slope efficiency reaching 70 %. The 2- μ m radiation sources have many advantages over the 1- μ m sources, e.g., better eye-safety, relaxed non-linear limits and often more efficient material processing. Particularly important application of 2- μ m fiber lasers is in a highly-efficient generation of wideband mid-infrared radiation through third order nonlinear effects in soft-glass fibers. In this paper we report on the development of passive components intended for fiber laser operation around 2 μ m, namely fiber couplers and wavelength division multiplexers for combination of 1.6- and 2- μ m radiation. Three commercially available fibers were used for the preparation of these components. The measured characteristics of the components are compared and the limitations are discussed, particularly the two-mode operation and high bend loss. Specific fiber designs are proposed in order to optimize the performance of the wavelength division multiplexer.

Outdoor Atmospheric Influence on Polarization Mode Dispersion in Optical Cables

  • DOI: 10.1109/URSIGASS.2014.6929421
  • Odkaz: https://doi.org/10.1109/URSIGASS.2014.6929421
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Oscillation of phenomena birefringence under atmospheric conditions is reported. Paper contains measured values of polarization mode dispersion from long term monitoring scenario and gives illustration about measuring of long time installed cables. Several commonly utilizing measuring techniques were used to determine birefringent properties of the fibers. Results are correlated with temperature changes during different terms to achieve proper comprehensive conception of progress.

Polymer-Clad Silica Tapers for Liquid Sensing: Long-term Measurement Repeatability and Production Imperfections

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Polymer-clad silica fiber tapers for refractometric detection of liquids are presented. Experimental study of sensor stability and measurement reproducibility is carried out, providing stable sensitivities with respect to production imperfections.

Practical Implementation and Performance Study of a Hard-Switched Hybrid FSO/RF Link under Controlled Fog Environment

  • Autoři: Lee, I.E., Ghassemlooy, Z., Ng, W.P., Gourdel, V., Khalighi, M.A., prof. Ing. Stanislav Zvánovec, Ph.D., Uysal, M.
  • Publikace: 2014 9th International Symposium on Communication Systems, Networks & Digital Signal Processing. Piscataway: IEEE, 2014. p. 368-373. ISBN 978-1-4799-2581-0.
  • Rok: 2014
  • DOI: 10.1109/CSNDSP.2014.6923856
  • Odkaz: https://doi.org/10.1109/CSNDSP.2014.6923856
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The availability and performance of terrestrial free-space optical (FSO) communication systems are heavily deterred by the fluctuating conditions of the atmospheric channel, particularly in the presence of visibility-limiting fog effects. In this paper, we examine the viability of deploying hybrid FSO and radio frequency (RF) links through an experimental study, which takes advantage of a dedicated laboratory atmospheric chamber to emulate the fog scenarios encountered on outdoor environment. In particular, a root mean square power detector is developed and introduced in the system under study to monitor the signal quality of the primary FSO link. The quasi-linear output voltage characteristics of the power detector device is utilized as a useful decision metric to implement hard switching in a hybrid FSO/RF link based upon the changes in the visibility. Our measurement results reveal that the selection of a desirable threshold voltage is dependent upon the intended data rate and minimum achievable bit error rate, in order to enable effective switching between the FSO and RF links.

Relative Intensity Noise of Vertical-Cavity Surface-Emitting Lasers Subject to Variable Polarization-Optical Feedback

  • Autoři: Ahmed, S.N., Ghassemlooy, Z., Busawon, K., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of 3rd International Workshop on Optical Wireless Communications 2014. Piscataway: IEEE, 2014. p. 21-24. ISBN 978-1-4799-6676-9.
  • Rok: 2014
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, the influence of variable polarization angle of the optical feedback on the relative intensity noise (RIN) of a vertical-cavity surface-emitting laser (VCSEL) is experimentally investigated. VCSEL lases in two orthogonally polarized (XP and YP) modes. For the dominant polarization mode (i.e. XP) the RIN is minimum at a polarization angle of 0o, while it is a minimum at 90o for the suppressed polarization mode (YP) it is minimum at a polarization angle of 90o. Furthermore, for a high optical feedback level the RIN of the XP mode increases rapidly with the polarization angle, whereas for the YP mode the RIN is low for angles > 45°. In addition, result shows that the relaxation oscillations are damped due to the optical feedback. We also show that as the polarization angle of the optical feedback increases a number of spectral lines appear in VCSEL spectrum, thus representing the complex dynamics behavior induced by the feedback.

Reliability of aircraft multimode optical networks

  • DOI: 10.1117/1.OE.53.9.096102
  • Odkaz: https://doi.org/10.1117/1.OE.53.9.096102
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Results from tests and analyses of multimode optical fibers for an avionic optical network under a variety of stress conditions are presented. Experiments revealed vibrational and temperature changes of distinct multimode fibers. Results lead to the discussion of influenced insertion losses and especially reduced bandwidth corresponding to modal distribution changes. It was determined that these crucial parameters could affect system reliability when an airplane network intersects thermal and vibrational variable environments.

Verification of VIS and NIR Light Propagation Parameters in Higher Skin Layers by Monte Carlo Simulation

  • Autoři: Němeček, T., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of 26th Conference and Exhibition on Optical Communications 2014. Praha: Agentura Action M, 2014. pp. 16-19. ISBN 9788086742397.
  • Rok: 2014
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Monte Carlo method was utilized to analyze light propagation in a homogeneous material of human tissue. Tests analyzed and determined photons’ trajectories based on material parameters. These results were verified by measurement. Optical fiber was used as an injector to precisely set all input parameters. Field surface distribution was afterwards captured by camera and in the next step processed and compares to an analytical approach.

Analyses of Optical Packet Switch Based on Enhanced Nonlinearity Fibers

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents final results from an optical packet switch developed in a joint project of CTU in Prague, SQS Fiber optics, Czech Republic and the Academy of Sciences of the Czech Republic. Conventional highly nonlinear fibers were theoretically and experimentally evaluated and confronted with novel extremely nonlinear soft-glass nonlinear fibers and microstructured fibers developed in the framework of the project. Fiber characterization was carried out with respect to nonlinearity, attenuation and stimulated Brillouin scattering threshold limitations. Nonlinear switching technique based on four-wave mixing was evaluated with respect to switching parameters such as modulation format insensitivity, polarization insensitivity and conversion efficiency. BER tests were performed at 10Gbps, verifying optical packet switch functionality with further simulations for advanced modulation formats.

Comparison of Masking Functions for Elevated Wireless RF and Optical Links

  • Autoři: Vojtěch, J., Fukal, P., Chvojka, P., Libich, J., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of 3rd International Conference on Wireless Communications and Mobile Computing. Valencia: University of Valencia, 2013. pp. 43-46. ISSN 2227-331X.
  • Rok: 2013
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Wireless optical links can due to the wide bandwidths available considerably improve so far reached bit rates over atmosphere medium. Nevertheless several propagation phenomena like fog scattering, thermal turbulences restrict their widespread use. The paper is focused on comparison of elevated link performance and coverage RF links and optical links for the case when users are within street canyons. Results from the measurement of fog attenuation were implemented in a simulation tool from millimeter wave bands, in order to characterize a masking function generally used to find nonblocked connections from users within street canyons from/to the satellites

Experimental Validation of Fog Models for FSO under Laboratory Controlled Conditions

  • Autoři: Ijaz, M., Ghassemlooy, Z., Ke-minh, H., prof. Ing. Stanislav Zvánovec, Ph.D., Perez, J., Pešek, J., Fišer, O.
  • Publikace: Proceedings of the 24th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC). Piscataway: IEEE, 2013. p. 19-23. ISBN 978-1-4577-1348-4.
  • Rok: 2013
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we present the experimental results forfree space optics (FSO) communication systems operating at visible and near infrared wavelengths (from 0.6 μm to 1.6 μm) under fog conditions. Different empirical fog models are typically used to characterize the fog attenuation of optical beam in FSO systems. A number of empirical fog models are evaluated in order to verify them experimentally and to fill several unmeasured gaps within the entire spectrum from the visible – near infrared (NIR) range for light to dense fog conditions. The experimental results in the controlled laboratory fog environment are compared with the selected empirical fog models in order to practically validate their performance over wide range of wavelengths. The results indicate wavelength dependency of the fog attenuation for visibilities higher than 15 m, whereas the cases with shorter visibilities contradict the Kim model.

Laboratory and Outdoor Availability and Spatial Coherence Tests of Wireless Optical Links

  • DOI: 10.1109/IWOW.2013.6777788
  • Odkaz: https://doi.org/10.1109/IWOW.2013.6777788
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Wireless optical links can bring new added technologic approach atop of today’s wireless networks forming their backbones and subparts. However several measurements have to be performed in order to get close insight on their availability within infrastructures. The paper reports recent tests at the Czech Technical University in Prague in cooperation with Northumbria University. New testbeds have been developed for outdoor and indoor measurements. Together with reports from packet and BER measurements, paper introduces complementary results on spatial coherence measurements for single link influenced by turbulence.

Laboratory Measurement of Turbulence Influence on Optical Pulses

  • Autoři: Libich, J., Chvojka, P., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 24th Conference and Exhibition on Optical Communications 2013 Proceedings. Praha: Zeithamlová Milena Ing. - Agentura Action M, 2013. p. 51-53. ISBN 978-80-86742-37-3.
  • Rok: 2013

On the Sensitivity of Fire Detection by a Microwave Radiometer

  • Autoři: Dvořák, P., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the International Geoscience and Remote Sensing Symposium (IGARSS 2013). Sydney: IEEE, 2013. pp. 402-405. ISBN 978-1-4799-1114-1.
  • Rok: 2013
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In the paper the detectability of a fire by a microwave radiometer is investigated. Simulations of several scenarios and together with outdoor measurement were performed in order to confirm detectability of the fire of specific temperature distributions and dimensions. Various scenarios for fire sensing were numerically modeled and simulated. Real parameters of antenna radiation pattern and radiometer sensitivity were taken into account. The concept of fire detectability verification was tested on real measurement data and then applied in a large scale on analyses of scaled airborne sensing of an environment. The results clearly indicate the possibilities and limits of detection with currently available radiometers.

Route diversity analyses for free-space optical wireless links within turbulent scenarios

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Free-Space Optical (FSO) communications link performance is highly affected when propagating through the time-spatially variable turbulent environment. In order to improve signal reception, several mitigation techniques have been proposed and analytically investigated. This paper presents experimental results for the route diversity technique evaluations for a specific case when several diversity links intersects a common turbulent area and concurrently each passing regions with different turbulence flows.

Tapered Optical Fibers for Reproducible Detection of Liquids

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Fiber taper refractometric sensors for detection of liquids are presented. Almost one hundred tapers of a wide waist diameter range were reproducibly prepared from multimode and polymer-clad silica fibers. Sensitivity above 400%/RIU was achieved.

Testing of Optical Fiber Components for Harsh Environmets

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical fibers provide many benefits to the telecommunication systems and their usage has more and more current even in the avionics industry [1]. It offers an attractive solution for airplanes, such a replacing copper conductors to reduce weight of the plane, electro-magnetic interference, bring high-speed communications connection, implementation of optical sensors, etc. Nevertheless for extremely high requirements on safety it is also necessary to precede all inflight influences. For summary of potential threats see e.g. [2]. One can easily found a several conditions of a harsh environment or an unfriendly fiber surrounding which could have a fatal impact to the transmission characteristic as attenuation statistics leading to link drops, time jitters or pulse degradations in time domain. There are different temperature gradients on the deck through which the infrastructure can pass while experiencing differentiated degradation and thus changed conditions within a physical layer. This paper is focused on an analysis of temperature-depended influences on insertion losses and other parameters of optical connectors, combining two types of multimode fibers, purposed for installation within an aircraft optical network.

Analyses of Optical Packet Switching Techniques Based on Nonlinear Materials with Respect to Various Label Formats

  • DOI: 10.1117/12.907767
  • Odkaz: https://doi.org/10.1117/12.907767
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    All-optical networks introduce the indisputable solution for future networking especially due to discarding slow and power-demanding electronic processing. Ultrafast data communications ultimately head towards all-optical packet data transfer and optical IP routing. In this paper, nonlinear switching techniques are evaluated with respects to particular types of nonlinear fibers with regards to their specific parameters. Optical packet labeling is discussed, considering label allocation between ITU-grid defined data wavelengths. Possible aspects of a highly-nonlinear fiber, untapered and tapered chalcogenide fibers integration into the optical switch were investigated both theoretically and experimentally.

Atmosphere Analysis and Measurements via Free-Space Optical Network

  • DOI: 10.1109/CONIELECOMP.2012.6189914
  • Odkaz: https://doi.org/10.1109/CONIELECOMP.2012.6189914
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Free-space optical link is an alternative instrument to transmission of information in data rates up to tenths of gigabits per second. Although evolution of this technology has been proceeded for several years, many factors affecting propagation of optical beam still have not been suitable minimized. Therefore several mitigation techniques are tested nowadays. In this paper, influences of atmosphere and rain are discussed with respect to particular diversity techniques. First results from a measurement campaign are introduced.

Combined Measured Characteristics of Microwave Radiometer and Free-Space Optical Link

  • Autoři: Dvořák, P., Libich, J., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 2012 IEEE Antennas and Propagation Society International Symposium. Piscataway: IEEE, 2012. pp. IF56.10. ISSN 1522-3965. ISBN 978-1-4673-0462-7.
  • Rok: 2012
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The paper introduces a utilization of a radiowave radiometer based subsystem for on-line monitoring and prediction of actual atmospheric influences for adjacent free space optical link. A measurement campaign has been accomplished with focus on atmospheric effects relating with reliability of free-space optical links. Together with the optical link, the microwave radiometer and meteorological stations were accommodated to the campaign in order to observe noise temperature changes joined by time variant fluctuations of temperature, humidity, pressure and refractivity. Combined characteristics of atmospheric parameters were evaluated and the metric based on noise temperature was proposed for the precipitation detection preceding optical link fades.

Correction of Thermal Deviations in Fabry-Perot Resonator Based Measurements of Specific Gases in MillimeterWave Bands

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Due to the thermal expansivity of the material used in the Fabry-Perot resonator mirrors, the resonator cavity length can change and this might therefore have an impact on the resonant frequency during high-resolution spectroscopy measurements. Based on measurements and simulations, this paper discusses the influences of temperature on the precise determination of gas attenuation measured in a Fabry-Perot resonator. Several measures to mitigate such influence and to correct the measured results were tested. A correction method for the measured data was proposed.

Development of Model for Mesh Wireless Optical Networks

  • Autoři: Libich, J., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 24th Conference and Exhibition on Optical Communications 2012 Proceedings. Praha: Agentura Action M, 2012. pp. 47-49. ISBN 978-80-86742-36-6.
  • Rok: 2012
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Wireless communication becomes more and more important technology for backbone segments. Demand on data quantity grows up with improved quality multimedia and increasing number of various online services enabling sharing information, pictures, movies and other data. Wide bandwidth may be reached by using of optical wireless technology, which offers advantages of secure transfer, no need of licensing or absence of interference. On the orther band, propagation through atmosphere is confined by fading and fluctuation of the received optical power which lead to decreased availability. This paper deals with suppression of these undesirable effects in mesh free-space optical networks utilizing the route diversity due to rerouting of the dataflow. Based on the measurement data and simulation analysis availability of multiple diversity links in mesh networks are discussed.

Emission spectroscopic measurement in Fabry-Perot resonator: Different methods of spectra evaluation

First Results of Rain Spatial Parameters Analyses for Optical Links

  • DOI: 10.1109/EuCAP.2012.6206163
  • Odkaz: https://doi.org/10.1109/EuCAP.2012.6206163
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Even though rain does not introduce the main negative influence affecting optical systems, it can cause high link outages. This paper represents an extension of a previous work related to rain spatial classification. It was found that the rain spatial parameter concept can also be extremely effectively applied to terrestrial and HAP systems, although specific adjustments have had to be made to the method. The method describing the spatial influence of rainfall on terrestrial radio microwave systems is now being tested with respect to optical links. The differences between both microwave and optical systems are discussed with regard to the new derived dependences.

Long-term Measurements of Refractive Index Structure Constant in Atmospheric Boundary Layer

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Results of long-term measurements of the refractive index structure constant in the boundary layer are introduced. The measurements were made on a 150-meter-high lattice mast equipped by nineteen meteorological sensors and one pressure sensor at the bottom of the mast. The Kolmogorov statistical theory of turbulence was used to calculate the refractive index structure constant C2n , allowing us to present annual cumulative distribution functions (CDFs) and seasonal quantiles. The quantiles of measured height dependence of the refractive index structure constant are also shown and compared with existing models (Hufnagel/Andrews/Phillips, SLC Day and Gurvich). Parameters of a linear model were calculated to fit the measured median height profile of the refractive index structure constant with the uncertainty of measurements also being addressed.

Measurement Statistics of Three Joint Wireless Optical Links

  • Autoři: Libich, J., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 2012 International Workshop on Optical Wireless Communications. Piscataway: IEEE, 2012. pp. 1-3. ISBN 978-1-4673-2734-3.
  • Rok: 2012
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Optical beams are highly affected by an atmosphere.Time and spatially variable distribution of the refractive index as well as different weather conditions result in fluctuation and attenuation of the optical beam. In order to improve signla reception, several mitigation techniques were developed for instance spatial diversity, auto-tracking, adaptive optics etc. This paper discusses utilization of route diversity in FSO networks primarily to increase the availability of the link based on three links diversity measurements.

Mitigation of Time-spatial Influence in Free-space Optical Networks Utilizing Route Diversity

  • DOI: 10.1117/12.907928
  • Odkaz: https://doi.org/10.1117/12.907928
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    New communication systems are emerging with growing demand on the data traffic. Fiber optics allow us to transfer data of rates higher than hundreds gigabits per second. These systems are usually used for backbone networks, although using of these systems is appearing in last mile connections. Wireless communication systems are still more and more popular owing to fast and cheaper deployment contrary to wire or fiber communication systems. On the other hand, wireless communication systems including free-space optics (FSO) are affected by weather conditions. In order to mitigate these effects, several mitigation techniques were investigated. For instance spatial diversity using more than one transmitter or receiver, auto-tracking of an optical beam, wavelength diversity utilizing radio band links as a backup etc. FSO links may be used in FSO networks to connect several building of a corporation, hospital or university campus. In case of proper network topology, route diversity can contribute to availability enhancement. In this paper, mitigation technique based on the route diversity is presented. Results are compared with hybrid FSO link.

Optical Packet Switch Development and Switching Technique Analysis

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Future of data networks indisputably stands in all-optical processing, components and communication. Ultrafast data transfers of enormous capacity head towards IP-routed optical packet networks. This paper focuses on the routing process and the switching matrix with respect to novel modulation formats appearing in optical data communication. Four-wave mixing switching technique is evaluated to achieve packet switching insensitive to data speed, modulation format and state of polarization. Best up to date peak-to-peak ratio for the routed signal in respect to the original was achieved exploiting the four-wave mixing effect in a highly-nonlinear fiber, with 12dB peak-to-peak ratio, whereas obtaining flat conversion profile from 1535 to 1565nm. Application of chalcogenide fibers promises even better results according to simulation models and achieved chalcogenide taper parameters. Frequency plan is presented proposing two variants with more possible outputs in a high-cost model and vice-versa.

Performance Analysis of Hybrid FSO/RF Link

  • DOI: 10.1109/EuCAP.2012.6206446
  • Odkaz: https://doi.org/10.1109/EuCAP.2012.6206446
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Free-space optical (FSO) links are perspective wireless optical communication systems utilizing modulated laser radiation to transmission of information. Because of propagation of the light through an atmosphere in case of a terrestrial link, strong dependence on weather conditions is observed. Several mitigation techniques were investigated, for an instance beam tracking, spatial diversity in multiple-input multiple-output systems and a wavelength diversity technique. In this paper, performance of FSO and radio-frequency (RF) hybrid link working at the wavelength of 850 nm and 5 GHz, respectively, is analyzed in specific urban area.

Short-term Prediction and Detection of Dynamic Atmospheric Phenomena by Microwave Radiometer

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Specific utilization of a microwave radiometer for online monitoring, detection and, especially, prediction of particular dynamic atmospheric phenomena such as precipitation and cloudiness is proposed in the paper. The ground-based microwave radiometer and meteorological stations were incorporated into the measurement campaign in order to observe and analyze actual brightness temperature changes. The characteristics of atmospheric parameters recorded over a period of 14 months were evaluated and new applications for rain forecasting and cloud detection, using specific features of signal variance, were proposed and validated.

Adaptive Techniques in Free-Space Optical Networks

  • Autoři: Libich, J., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 23rd Conference and Exhibition on Optical Communications 2011 - Scientific Section Proceedings. Praha: Agentura Action M, 2011. pp. 52-54. ISBN 978-80-86742-32-8.
  • Rok: 2011
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Free-space optical link is an alternative instrument to transmission of information in data rates up to tens gigabits per second. Although evolution of this technology proceeds several years, many factors still affect propagation of optical beam. Therefore several mitigation techniques are used or in a state of research. Between the most significant appertain beam tracking, adaptive optics, diversity techniques or new modulation schemes. In this paper, diversity techniques are discussed. First result from a measurement campaign are introduced.

Analysis of Rain Influence on Joint Millimeter and Optical Elevated Links

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D., Libich, J.
  • Publikace: Proceedings of the 5th European Conference on Antennas and Propagation (EuCAP). Piscataway: IEEE, 2011. pp. 182-185. ISBN 978-88-8202-074-3.
  • Rok: 2011
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Free Space Optical communications can be used for elevated links, even though many factors can affect an optical beam causing an extinction or fluctuation of the received optical signal. This paper brings an analysis of rain influence on elevated links for cases of alone links or diversity configurations of either two millimeter or two free-space optical links. Simulation results of diversity gain statistics of a joint millimeter and optical link are discussed as well.

Development of an optical packet switch based on a chalcogenide fiber taper

  • DOI: 10.5716/2251-2233_NTC12
  • Odkaz: https://doi.org/10.5716/2251-2233_NTC12
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Development of a novel optical packet switch for future all-optical packet switching, IP routing and highly-sophisticated label formats is presented. Chalcogenide-based nonlinear fabrics were analyzed for utilization in the proposed switching configuration. Particular results from simulations and measurements during research of the optical packet switch will be introduced. The future essential research challenges of such a system development are discussed as well.

Diversity Statistics of Free Space Optical Links Affected by Rain

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: PIERS 2011 Suzhou Proceedings. Cambridge, MA: The Electromagnetics Academy, 2011. p. 395-398. ISSN 1559-9450. ISBN 978-1-934142-18-9.
  • Rok: 2011
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Free Space Optical systems introduce prospective technology for fast data trans- missions; nevertheless atmosphere radically in°uences availability of these systems. Between one of the highest affections belongs rain attenuation. The paper discuses several aspects dealing with route diversity utilization in Free Space Optical network. Based on simulations particular link deployment cases were analyzed.

Elliptic and Hyperbolic Dielectric Lens Antennas in mm-Waves

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Dielectric lenses can substantially improve antenna parameters, especially the planarity of radiated waves and the antenna gain. The paper deals with their application in millimeter-wave band. The main goal concerns the introduction of characteristics and differences between the most commonly used types of dielectric lens antennas, i.e. elliptic and hyperbolic. Their particular features as well as behavior of radiating systems incorporating the lenses are investigated. Specific features of these lenses are discussed for both, near-field and farfield based on simulation and measurement results.

FSO Link Performance Modelling Using Artificial Intelligence

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper introduces an artificial neural network model created for weather influence evaluation of FSO link. Basic neural cluster analysis is performed and neural network model creation is discussed.

Future All-Optical Packet Switched Networks Based on Highly Nonlinear Components

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Novel optical packet switch for future all-optical packet switched networks and IP routing is presented. Chalcogenide-based nonlinear glass fabrics are evaluated for the proposed switching configuration. Particular research results of the optical packet switch development will be introduced. Future major research challenges are discussed as well, focusing on sophisticated labeling techniques.

Improved axial feeding of Fabry-Perot resonator for high-resolution spectroscopy applications

  • DOI: 10.1002/mop.26344
  • Odkaz: https://doi.org/10.1002/mop.26344
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This article presents the methods of broadband axial feeding of a Fabry-Perot resonator. The resonator was originally designed with the radial excitation for the absorption measurement in the frequency band ranging from 18 to 80 GHz. If the frequency stays below ~26.4 GHz, the excitation of resonator is less satisfactory, since at the frequency in question, the value of Fresnel number of resonator drops to one. For the broadband measurement of gaseous samples' emission spectra, the excitations for frequencies lower than 26.4 GHz were analyzed using the capacitive coupling and two newly proposed couplings.

Influences of Turbulences in Near Vicinity of Buildings on Free-space Optical Links

  • DOI: 10.1049/iet-map.2010.0630
  • Odkaz: https://doi.org/10.1049/iet-map.2010.0630
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Free-space optical systems offer many advantages for modern wireless communication compared to classical radioband systems. Nevertheless, unlike fibre optics, their availability is highly affected by atmospheric disturbances. This study discusses the influences of temperature gradients around buildings that cause turbulent areas within the atmosphere, leading to the spatial change of the refractive index and consequently resulting in the bending or widening of transmitted optical beams. The influences of a nearby building on free-space optical links are discussed on the basis of measured data.

Investigation of Pulse Regimes of a Fiber Ring Laser

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The exploitation of particular nonlinear effects in optical materials often requires higher light densities. One of attractive solutions stands in concentrating light into ultra-short pulses by utilizing fiber lasers either with active or passive mode-locking. A fiber laser was developed for the wavelengths close to the upper edge of the telecommunication C-band (around 1565 nm). The pulse regime of the fiber laser in the scale of picoseconds was achieved by the nonlinear polarization rotation effect. The proper polarization states in the ring cavity were adjusted by polarization controllers. Various laser regimes were investigated.

Parametric and Raman Amplification in Optical Highly Nonlinear Fibers

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Broadband amplification has recently drawn attention, as higher data bit rates are to be propagated and the C-band capacity is limited. Therefore a simulation program for hybrid amplifier combining parametric and Raman effects was developed. Femtosecond passively mode locked laser was created to provide signal source for experimental part. Various delay-lines were studied to provide single-shot measurement techniques.

Sensitivity of Fabry-Perot Resonator Based Measurements of Gas Absorptions

  • Autoři: Piksa, P., prof. Ing. Stanislav Zvánovec, Ph.D., Černý, P.
  • Publikace: PIERS 2011 Suzhou Proceedings. Cambridge, MA: The Electromagnetics Academy, 2011. pp. 497-501. ISSN 1559-9450. ISBN 978-1-934142-18-9.
  • Rok: 2011
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In order to reach maximum sensitivity of gas attenuation measurements and to propose optimal parameters of the new developed spectrometer, the coupling characteristics of several resonator based measurement approaches were analyzed. Three types of resonator feed were investigated the rst based on a radial feeding of a resonator cavity, second one using axially alignment feeding with two ports (transmission measurement) and the last having one axial port feeding (reflection measurement method). Based on both analytically derived relations and results form simulations, the optimal setting of coupling is proposed in the paper. Analytical results covering a wide range of couplings were validated by spectroscopic measurements of particular gases attenuations.

Utilization of Route Diversity in Free-Space Optical Networks

  • Autoři: Libich, J., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of Avionics, Fiber-Optics and Photonics Technology Conference 2011. Piscataway: IEEE Photonics Society, 2011. pp. 65-66. ISBN 978-1-4244-7344-1.
  • Rok: 2011

Validation of Rain Spatial Classification for High Altitude Platform Systems

  • DOI: 10.1109/TAP.2011.2152325
  • Odkaz: https://doi.org/10.1109/TAP.2011.2152325
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Previous work on rain spatial classification for terrestrial PMP radio systems has been extended in this communication to stratospheric systems-high altitude platform systems. It was found that the rain spatial parameter concept can also be effectively applied to HAP systems, although specific adjustments have had to be made to the method. The differences between terrestrial and stratospheric systems are discussed with regard to the new derived dependences.

An Evaluation of Approaches for Modeling of Terrestrial, HAP and Satellite Systems Performance during Rain Events

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents the results from site-specific simulations of route diversity performance in case of High Altitude Platform system, terrestrial system and satellite system during specific rain events. Based on the radar rainfall database, route diversity dependences on altitude of transmitter were studied using the simulation tool. The main goal of the paper is to adopt concept for HAP systems from investigations of both terrestrial point-to-multipoint systems and satellite systems operating in millimeter frequency bands.

Analysis of Fiber Pulse Replicators for Single-Shot All-Optical Measurements

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Several approaches of ultra-short optical pulse replication in a fiber are analyzed in the paper. Aspects of one pulse replication as well as a pulse-pair replication are discussed more in detail. Based on measurement and simulation results the specifics for replicator utilization in the regenerative resonator configuration are proposed.

Broadband Axial Excitation of Fabry-Perot Resonator

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The paper presents the broadband axial excitation of the Fabry-Perot resonator as well as its comparison with the standard radial excitation (via a dielectric foil) and two types of axial excitations (electric and inductive coupling) are discussed. The resonator was designed for the frequency range from 18 to at least 80 GHz. For the broadband measurement of the emission spectra, the excitation for the frequency range 18 - 26.5 GHz was proposed. Moreover, the excitations performance was measured and evaluated for the frequencies up to 40 GHz.

Gas Absorption Measurement of Selected Stratospheric Substances by Fabry-Perot Resonator

  • Autoři: Piksa, P., prof. Ing. Stanislav Zvánovec, Ph.D., Černý, P., Libich, J., Varga, J., Koubek, J.
  • Publikace: Proceedings of PIERS 2010 in Cambridge. Cambridge, MA: The Electromagnetics Academy, 2010. pp. 1081-1083. ISSN 1559-9450. ISBN 978-1-934142-14-1.
  • Rok: 2010
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A simple Fabry-Perot resonator based measurement system was utilized for measurements of attenuation characteristics of stratospheric gases. Representative of very-short lived gases - dibromomethane - as well as Carbonyl sulfide were measured in selected microwave bands occupied by Satellite to ground or High Altitude Platform Systems.

Heterodyne Detector for Absorption Microwave Spectroscopy

  • DOI: 10.1109/COMITE.2010.5481853
  • Odkaz: https://doi.org/10.1109/COMITE.2010.5481853
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The paper describes the heterodyne detector suitable for the microwave spectroscopy. At the lower frequencies (from the spectroscopic point of view), the measured gas is commonly saturated and the absorption measurement is impossible. The discussed heterodyne detector can measure with high dynamic range exceeding 90 dB. In addition, it enables to measure the weak signals or even very low changes in strong signals.

New Approach to Modeling of Diffuse Reflection and Scattering for Millimeter-wave Systems in Indoor Scenarios

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A new approach to modeling diffuse reflection and scattering for millimeter-wave band based on a fast and simple semi-deterministic principle is presented. The model is based on the combination of pre-computed radiation patterns and a fast semi-deterministic algorithm. The principle and function of this model are explained as well as tested in a common indoor are compared with results received from a classical ray-based model and significant differences are discussed in detail.

Optical Approximations for Simulations of Submillimeter Systems

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D., Šubrt, L.
  • Publikace: Proceedings of the 4th European Conference on Antennas and Propagation. Piscataway: IEEE, 2010. pp. 1-3. ISBN 978-84-7653-472-4.
  • Rok: 2010
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Propagation aspects of systems working in millimeter and submillimeter bands can be solved by quasioptical approaches including Gaussian beams. Reflections from rough surfaces nevertheless introduces complex problem. It can be very well solved by an approximation using methods from free space optics with incorporation of particular corrections of the pure optical approaches. The paper discusses the advantages and drawback of these simulation approaches, based on measurement and analyses of electromagnetic wave propagation.

Simplified Fourier Transform Microwave Spectrometer

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The Fourier Transform Microwave Spectrometer (FTMW) is subject to simplification by means of the spectral analyser, instead of the super-heterodyne receiver. The paper is focused on the FTMW arrangement, the procedures of the resonator tuning and optimization of the excitation impulse length. In the paper, the virtues of the FTMW technique are demonstrated on the comparison of the emission and the absorption spectra.

Single-shot All-optical Sampling Oscilloscope using a Polarization-maintaining Resonator for Pulse Replication

  • DOI: 10.1002/mop.25509
  • Odkaz: https://doi.org/10.1002/mop.25509
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    An all-optical single-shot sampling oscilloscope with a picosecond resolution is developed. An innovative approach for data pulse replication using a polarization-maintaining resonator is employed. Pulses are sampled in a highly nonlinear fiber. Acquired data are used for pulse shape reconstruction. Proposed setup eliminates the need of a delay line.

Specific Millimeter-Wave Features of Fabry-Perot Resonator for Spectroscopic Measurements

  • Autoři: Piksa, P., prof. Ing. Stanislav Zvánovec, Ph.D., Černý, P.
  • Publikace: Microwave and Millimeter Wave Technologies from Photonic Bandgap Devices to Antenna and Applications. Vukovar: In-Teh, 2010. p. 451-468. ISBN 978-953-7619-66-4.
  • Rok: 2010
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The chapter book is focused on research of specific features of Fabry-Perot resonator for spectroscopic measurements. The Fabry-Perot resonator provides an interesting tool enabling an enhancement of the sensitivity of the gas absorption as well as emission measurement in microwave and millimetre-wave spectroscopy. The theoretical background together with results of numerical simulation and measurement results are presented.

Specific Usage of a Wire-Grid Polarizer For Millimeter Waves

  • Autoři: Piksa, P., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 4th European Conference on Antennas and Propagation. Piscataway: IEEE, 2010. pp. 1-3. ISBN 978-84-7653-472-4.
  • Rok: 2010
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A polarization grid is a part of the microwave spectroscopy measurement system and therefore its properties have influence on the measurement sensitivity. The properties of grids were determined for both polarizations from measurement and simulations of the developed samples. The improvement of sensitivity of the spectroscopic measurement inheres in use of polarizer within the vertical polarization.

Thermal Influences of Buildings on Availability of Free Space Optical Links

  • Autoři: Libich, J., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of Mosharaka International Conference on Communications Networking & Information Technology. Amman: Jordan University of Science and Technology Faculty of Engineering, 2010. pp. 1-4. ISBN 978-9957-486-09-9.
  • Rok: 2010
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Free space optical systems bring many advantages to modern wireless communication compared to classical radio-band systems. Nevertheless, their availability is contrary to fiber optics highly affected by atmosphere. The paper discusses influences of temperature gradients around buildings causing turbulent areas within atmosphere that lead to the spatial change of refraction index and consequently result in bending or widening of transmitted optical beams. Based on measured data, the influences of a nearby building on the free space optical link are discussed.

Beam Propagation Simulations of Quasioptical Systems

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A quasioptical approach using Gaussian beams can be applied to enumerate propagation aspects at millimetre and submillimetre wave bands. The paper introduces results obtained by a measurement campaign focused on Gaussian beam aspects. Based on measured statistics, simulations by using a quasioptical approach were introduced. Results from simulatin of system within indoor environment were compared to those obtained by classical ray-tracing method and specific features of both approaches were revealed.

Quasioptical Beam Propagation for Remote Sensing

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A development of millimeter waveband indoor sensors has brought new research challenges especially with respect to the sensing within complex environments. To investigate the propagation aspects for these systems the quasioptical approaches including Gaussian beams of basic and higher orders can be utilized. Difference between conventional and Gaussian beam based models can be significant especially for remote sensing systems being deployed within indoor scenarios. The paper discusses the advantages and drawback of these simulation approaches, based on measurement and analyses of electromagnetic wave propagation.

Route Diversity Simulations in Multi-HAP Networks during Heavy Rainstorms

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Route diversity is one of the available techniques to improve system availability of High Altitude Platform (HAP) networks during rainstorms. Route diversity was simulated in both time and space using radar rainfall data. The propagation aspects of HAP service as observed at the user ground station were analyzed based on their analogy to terrestrial point-to-multipoint systems.

The use of the Fabry-Perot interferometer for high resolution microwave spectroscopy

  • DOI: 10.1016/j.jms.2009.03.015
  • Odkaz: https://doi.org/10.1016/j.jms.2009.03.015
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A simple Fabry-Perot interferometer was used for measurements of microwave spectra. Both basic experimental arrangements, absorption and emission, were tested on the rotational spectra of acetonitrile. The interferometric results obtained were compared with the spectra measured using a standard high resolution microwave spectrometer.

Time Domain Detection of Interference Signals using Ultra Wideband Techniques

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A specific time domain approach to the detection of services within a particular channel using ultra wideband pulse techniques is introduced. The investigation is based on measurements and simulations of several ultra wideband pulses propagating and reflecting within a particular scenario and received together with an interfered narrowband signal.

UHF RF Identification Distance in Indoor Areas

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    UHF RFID read range tests have been performed with a novel electrically small low-profile TAG antenna equipped with an artificial-like surfaces providing very good immunity against the influence of a near human body. The RFID system equipped with this antenna has been tested for the detection of a person in indoor and outdoor areas within 869 MHz band and reached read range up to 9 m.

UHF RF Identification of People in Indoor and Open Areas

  • DOI: 10.1109/TMTT.2009.2017305
  • Odkaz: https://doi.org/10.1109/TMTT.2009.2017305
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    UHF RFID read range tests have been performed with a novel electrically small low-profile TAG antenna equipped with artificial-like surfaces providing very good immunity against the influence of a near human body. The RFID system equipped with this antenna has been tested for the detection of a person in indoor and outdoor areas within 869 MHz band and reached read range up to 9 and 16 m, respectively.

Validation of Route Diversity Schemes of Two Joint HAP LInks

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    High Altitude Platforms (HAP) can bring a possibility of a very fast additional coverage e.g. in the case of catastrophes, when existing networks collapse, or could be utilised as alternatives to satellite or terrestrial systems. In this paper electromagnetic wave propagation aspects for HAP systems are discussed. In the first part, atmospheric gas attenuation for inter-HAP links is determined. Next part of the paper deals with the influence of rain on millimetre wavelength links between user stations and High Altitude Platform. Typical route diversity scheme given by the recommendation ITU-R P. 618 used for satellite links cannot be accurately applied. Based on simulation results HAPs are analyzed and particular corrections for the Czech Republic are proposed.

A Study of Gas and Rain Propagation Effects at 48GHz for HAP Scenarios

  • DOI: 10.1155/2008/734216
  • Odkaz: https://doi.org/10.1155/2008/734216
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The atmosphere and rainfall significantly limit the performance of millimeter wave links and this has to be taken into account, particularly, during planning of high altitude platform (HAP) networks. This paper presents results from the measurement and simulation of these phenomena. A simulation tool from our previous analyses of terrestrial point-to-multipoint systems has been modified for HAP systems. Based on a rainfall radar database and gas attenuation characteristics as measured by a Fabry-Perot resonator, the performance of a simple link, two-branch diversity links, and more complicated HAP scenarios are discussed.

Dielectric Lens Utilization for Fabry-Perot Resonator Optimal Coupling

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper introduces the Fabry-Perot resonator designed for the frequency band 18-80 GHz. The Fabry-Perot improvement using a hyperbolical lens, which transforms the spherical wave, radiated by the standard horn antennas to the plane wave irradiating the coupling foil of the resonator is discussed. This approach helps to efficiently couple the energy into and out of the resonator. The quality factors (loaded as well as unloaded) were evaluated from the measured frequency responses of the resonances. These quality factors show the effectiveness of used lenses and functionality of the resonator within the frequency band 75-110 GHz, which is higher than the designed band.

Dispersion and Pulse Interferences Investigation for UWB Signal Propagation

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The Ultra WideBand (UWB) technology utilizing nanosecond pulses has been one of the main phenomena in communications and radar applications for several years. This paper discusses the basic measurement techniques of impulse systems, particularly focusing on the dispersion and pulse interferences of the UWB propagation channel. Propagation aspects of two-ray approach are investigated in depth, using both measurements and simulations.

Full-Wave Modeling of Fabry-Perot Resonator in Millimeter Waves

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    One of two numerical principles on dielectric materials in connection with Multi Level Fast Multipole Method (MLFMM) and Uniform Theory of Diffraction (UTD) approximation of Method of Moments (MoM) have to be applied to analyze electrically large structures at higher frequencies. The paper deals with a development and comparison of several models of Fabry-Perot resonator for spectroscopic measurement of both gas attenuation and spontaneous emission. A simplified model capable to solve the resonator performance up to 110 GHz (i.e. the radius of the mirrors corresponding to 55 times wavelength) is introduced.

Higher Modes of Sub-millimetric Fabry-Perot Resonator

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The atmospheric attenuation is very often neglected within propagation of electromagnetic waves at lower frequencies but it has significant effects on millimeter, sub-millimeter and terahertz links. Based on a previous measurement campaign, this paper presents results from simulation of the Fabry-Perot resonator utilized for the gas attenuation measurements. The gas attenuation has proved to be highly influenced by higher modes arising from the resonator cavity. Their dependence on particular measurement deployment is analyzed in the paper.

On the Indoor Propagation of UWB Signals

  • Autoři: Urban, R., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of the 14th Conference on Microwave Techniques COMITE 2008. Praha: Československá sekce IEEE, 2008. pp. 77-80. ISBN 978-1-4244-2137-4.
  • Rok: 2008
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The large bandwidth of Ultra Wideband systems allows an achievement of extremely high data rates, and moreover utilization of high spectral capacity. The paper introduces the specific features of UWB signal propagation. Based on simulations and measurements the differences to classical narrowband systems are analyzed. Analyses are focused mainly on two-path propagation aspects, taking into account overlapping of a direct and a reflected UWB pulse. Based on such approach more complicated models and analyses of UWB system deployment in indoor environment can be accomplished.

PMP System Analyzing Based on Rain Spatial Model

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Signal propagation at frequencies above 10 GHz suffers from significant attenuation due to rain. Given the non-uniform spatial distribution of the rain rate, the route diversity concept can be utilized to plan point-to-multipoint (PMP) systems. Outages within systems were studied using space-time simulations of PMP under specific conditions. PMP system performance was analyzed based on the rain spatial parameter and on a derived system outage improvement probability.

Propagation of Elmg. Waves for Communication Systems from Microwave to Optical Regions

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 18th International Travelling Summer School on Microwave and Lightwaves - Proceedings. Brno: VUT v Brně, FEKT, Ústav radioelektroniky, 2008. pp. 26-42.
  • Rok: 2008
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The paper analyses approaches to the solution of electromagnetic wave propagation within broad spectrum - from GHz up to THz. It describes particular influences on transmitted signal (atmospheric attenuation, rain, scattering, Gaussian beam etc) and the utilization within particular frequency bands is demonstrated based on results from simulations and measurements.

Gas Attenutation Measurement by Utilization of Fabry-Perot Resonator

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The atmosphere significantly limits the performance of millimetre-wave and terahertz systems. The aim of this paper is to introduce a development and an improvement of Fabry-Perot resonator utilized especially for gas attenuation measurements. The measurement setup and results from simulations and laboratory measurements performed via Fabry-Perot resonator are discussed as well.

Influence of Rain Event Area on PMP System Performance

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, the influence of the area size covered by rain on the efficiency of route diversity applied in systems during the rain event is analyzed for specific areas with a range of dimensions, from small areas up to those with diameters of 150 km x 150 km. The derivation of rain spatial parameter statistics and their validity in terms of the size of the investigated area are discussed.

Optimization of Beam Focusing Into the Stark´s Cell for MM-Wave Spectroscopy

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents an analysis of the power distribution behind dielectric lens and optimization of the beam focusing by double sided dielectric lens into the Stark´s cell as a particular part of spectroscopic measuring equipment.

Theory of Characteristic Modes: Getting More Insight into Linear Antenna Behavior

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The Theory of Characteristic Modes is a very useful tool to get physical insight into antenna behavior. It is possible to easily obtain resonant frequencies, modal radiation Q or bandwidth, modal currents and modal radiation patterns. The paper is intended to study well known linear antennas under this new point of view.

Základy šíření vln pro plánování pozemních rádiových spojů

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Kniha je věnována základům problematiky šíření elektromagnetických vln pro pozemní rádiové komunikační systémy. Je zde vysvětlena fyzikální podstata šíření vln v atmosféře, jenž rádiové spoje ovlivňuje zásadním způsobem. Podrobně jsou dále rozebrány i jednotlivé vlivy troposféry a ionosféry. Jsou popsány i techniky používané k modelování šíření vln pro potřeby návrhu jednotlivých rádiových služeb z širokého kmitočtového spektra.

Dependence of Area-Averaged Rain Rate on PMP System Coverage Planning

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, area-averaged rain rate calculation using the ITU-R statistical model is discussed and its accuracy investigated. The influence of its proper determination on the coverage planning of PMP systems is revealed. Moreover, a model modification which better fits the local conditions prevailing in the Czech Republic is provided.

Measurement of Shielding Effectiveness of Small Enclosures

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The evaluation of the Shielding Effectiveness (SE) brings great challenges from the EMC measurement point of view. Particularly in the case of measurement of small enclosures, many different approaches can be used. Therefore, based on an extensive measurement campaign, various aspects of measurement of the shielding effectiveness of small metallic enclosures were investigated. Significant results of this campaign are discussed in this paper.

Modeling in Education of Antennas

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The paper is focused on the key role of modeling in education process in the field of antennas. Attention is turned not only to the modeling, but to the whole structure of education. Depending on the level of study, the balanced structure of the education is based on the appropriate amount of the theory followed by the computer simulations, the theoretical and engineering design and development, the measurement and final evaluation, which acts as the feedback between the initial goals and the final results.

On the Proper Utilization of Site Diversity Mechanism in Millimeter-Wave Band PMP Systems

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper the analytical study of a Point-to-Multipoint (PMP) system behavior during rainstorms is discussed. The proper utilization of the site diversity mechanism for two diversity links as well as in the complex point-to-multipoint system scenario is investigated. The yield of the site diversity utilization in terms of link lengths, angular separation and rain parameters is presented.

Rain Spatial Classification for Availability Studies of Point-to-Multipoint Systems

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A new approach to rain spatial classification according to its impact on system performance is proposed in the paper, using a single rainfall spatial parameter. The work is based on extensive simulation of point-to-multipoint systems using rainfall radar data.

Wave Propagation Simulations at 48 GHz for HAPs Using Rainfall Radar Data

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper presents the concept of site-specific simulations of multiple High Altitude Platform (HAP) system performance during specific rain events. The concept has been adopted from investigations of terrestrial point-to-multipoint systems operating in millimetre frequency bands. A simulation tool has been developed. Based on the radar rainfall database, various aspects of system performance such as site diversity can be studied using the simulation tool.

3D Prediction of Electromagnetic Wave Propagation ofr Wideband Systems Working in MM Band

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Proceedings of Workshop 2005 - Part A,B. Praha: České vysoké učení technické v Praze, 2005. pp. 364-365. ISBN 80-01-03201-9.
  • Rok: 2005
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The employment of frequencies above about 42 GHz (e.g. for Local Multipoint Distributions Systems -LMDS) has great challenges from electromagnetic wave propagation point of view. Propagation are for example attenuated due to rain or affected by diffraction. Tool for 3D prediction of electromagnetic wave propagation of systems working in millimeter band has been designed. The diffraction on dielectric wedgein millimeter frequency band has been investigated both theoretically and experimentally to provide knowledge support for ray tracing/launching calculations.

Effects of Rain Rate Spatial Distribution on Pont-to-Multipoint Systems

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this article the analysis of the statistical variations in spatial organization of precipitation and its influence on point-to-multipoint systems is presented.

Investigation of Significant Uncertainties in EMC Measurement

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This paper describes some aspects of determination of uncertainty in EMC measurements. Basic outline of the resulting measurement uncertainty range is presented. The main aim is to investigate the most significant components of the total uncertainty - imperfections due to the antenna factor of a receiving antenna and site imperfection of a measurement place.

Millimeter-wave Systems Outage Improvements During Rain Events

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The motivation of this work is to offer a simple way to evaluate possibilities of the site diversity employment for specific scenarios in millimeter-wave band. Outage improvement has been studied using space-time simulations of a point-to-multipoint system in a specific area under a specific rain conditions. System outage improvement probability was derived as a function of the rain fade margin, angle separation and distances hubs. Some of the simulation results at 42 GHz are presented as well.

Normalized Site Attenuation (NSA) Measurement

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Normalized site attenuation testing (NSA) is the process to evaluate the quality of test site for EMC testing. The standard EMC measurement uses the NSA in the frequency range 30 MHz - 1 GHz. It is supposed the use of higher frequencies for EMC measurement in a near future, where the measurement of wall reflections is usually recommended for site testing. Experiences based on the measurement of NSA, the antennas and its calibration (antenna factor), polarization and geometry of measurement and parasitic influence of floor reflections are mentioned in the paper. Problems of EMC test sites are also discussed with pedagogical aspects from point of view Electromagnetic Field Theory and its simulation tools.

Normalized Site Attenuation Measurement Above 1 GHz

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The article describes an application and the results of new site-qualificatioin technique suitable for frequencies above 1 GHz.

Rain Dependant Site Diversity Outage Improvements Statistics for Systems Working in Millimeter-Wave Band

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The signal propagation at the frequencies above 10 GHz suffers from significant attenuation due to rain, which in case of point-to-multipoint systems is unlikely to be compensated for by available fade margin alone. For this reason and especially thanks to the non-uniform spatial distribution of the rain rate, it is suitable to utilize site diversity concept during planning of point-to-multipoint wireless systems. A database of radar data for numerous types of rain events has been established to enable system testing under different conditions. Outage improvement was studied using space-time simulations of point-to-multipoint systems in a specific area under a specific rain conditions. System outage improvement probability was derived as a straightforward function of the rain fade margin, angle separation and distances of main and diversity hubs. Some of the simulation results at 42 GHz and corresponding outage improvement probability using the site diversity are presented as well.

Shielding Effectiveness Measurement Issues for Small Enclosures

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Shielding Effectiveness (SE) is one of the major aspects of any EMC design process. In this paper, a detailed analysis of measurement issues of a shielding effectiveness of relatively small metallic enclosures is presented. An extensive measurement campaign has been done to investigate various aspects of measurement of the small enclosures shielding effectiveness.

Simulace multimediálních bezdrátových systémů pracujících v milimetrových pásmech

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Seminář o řešení projektu GA ČR 102/03/H109 v roce 2005. Brno: VUT v Brně, Fakulta elektrotechniky a komunikačních technologií, 2005. pp. 18-19. ISBN 80-214-3013-3.
  • Rok: 2005
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    V tomto článku jsou prezentovány analýzy a metodiky pro výpočet časoprostorových statistik point-to-multipoint systémů pro specifické oblasti a za daných srážkových událostí. Hlavním cilem je vývoj a využití specifického simulačního programu při zkoumání účinků srážkových událostí na chování systémů využívajících prostorové diverzity.

Simulations of Site Diversity Based Outage Improvements for Point-to-Multipoint Systems in Millimeter-Wave Band

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Outage improvement was studied using space-time simulations of a PMP system in millimeter-wave bands in a specific area under a specific rain conditions. System outage improvement probability was derived as a straightforward function of the rain fade margin, angle separation and distances of main and diversity hubs. Some of the simulation results at 42 GHz and corresponding outage improvement probability using the site diversity are presented as well.

Utilization of Rainfall Data

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: 9th International Student Conference on Electrical Engineering. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2005. pp. C16.
  • Rok: 2005
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The non-uniform spatial distribution of the rain rate allows to utilize several propagation impairment mitigation techniques during planning of point-tomultipoint wireless systems. In this paper, the approaches to the rainfall data preprocessing for space-time simulations of milimeter point-to-multipoint radio systems are presented. A database of radar data for numerous types of rain events has been established to enable system testing under different conditions. Various aspects of the system performance like site diversity can be evaluated by the simulation tool.

Vliv rozložení deště na PMP systémy

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Odborné semináře - Sborník za rok 2004/2005. Praha: Československá sekce IEEE, 2005. pp. 55-58. ISBN 80-86582-17-5.
  • Rok: 2005
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Šíření signálu na kmitočtech vyšších než 10 GHz je specifické zejména tím, že je silně ovlivňováno deštěm. Tento článek se zabývá analýzou zlepšení výpadků systémů typu point-to-multipoint pracujících v milimetrových pásmech pro specifické oblasti a za daných dešťových podmínek. Byla nalezena závislost pravděpodobnosti zlepšení výpadků systému na zvolených rezervách na únik vlivem deště, na úhlové separaci, na vzdálenostech k hlavní a diverzitní základnové stanici a na prostorovém rozložení deště.

Časoprostorové modelování MWS systémů pracujících v milimetrových pásmech

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Odborné semináře - Sborník za rok 2003/2004. Praha: Československá sekce IEEE, 2004. pp. 61-64. ISBN 80-86582-14-0.
  • Rok: 2004
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Plánování rozmístnění nových komunikačních systémů pracujících v milimetrových pásmech představuje velmi zajímavou výzvou pro systémové inženýry a to zejména z hlediska šíření elektromagnetických vln. Tento článek se zabývá dominantními vlivy ovlivňujícími šíření signálu LMDS systémů (pro frekvence vyšší než 30 GHz). Je představen nový simulační software pro LMDS a výsledky prvních simulací.

Educational Support of The Course "Propagation of Electromagnetic Waves and Frequency Planning"

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This project is focused on preparation and accomplishing of practical and experimental exercises for new course "Propagation of Electromagnetic Waves and Frequency planning". Students will be able to verify their theoretical knowledge by practical measurements of coverage signal level and other parameters of wireless local networks (WLAN) in the frequency band 2,4 GHz. These exercises will demonstrate current possibilities of computer connection to networks by this modern technology as well.

Měření a simulace pokrytí 802.11b WLAN sítí

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Seminář o řešení projektu GA ČR 102/03/H109. Brno: VUT v Brně, FEI, Ústav radioelektroniky, 2004. p. 9. ISBN 80-214-2559-8.
  • Rok: 2004

Shielding Efficiency Waveguide Measurements at 400 MHz

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Knowledge of shielding efficiency of plane materials like shielding panels, special paints, windows foils etc. is demanded for construction of shielded boxes, enclosures and for other applications. Waveguide measurement unit was specially designed and manufactured to measure the high level of shielding efficiency of thin conductive materials in the frequency band of 40 MHz. Dynamic range of measurement up to 100 dB was reached. Shielding efficiency of various materials was measured and compared to measurements in free space. The waveguide unit development brought several advantages which had to be addressed. The main problems were caused by reflections of the inserted material under the test with high attenuation of the relatively short waveguide. Waveguide, broadband transitions design, attenuators arrangements and the material under test attachment were designed using both the simulations and experiments.

Shielding Materials Waveguide Measurement about 400 MHz

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Knowledge of shielding materials attenuation is highly demanded for construction of shielded boxes or spaces and for other applications. In the paper the measurement of shielding materials attenuation up to 100 dB is presented. The main focus is given to a design of measurement unit and demonstration of measured data.

Signal Propagation Simulation Tool for LMDS

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The deployment of newly emerging communication systems working in the millimeter-waves frequency bands are a challenge for designers also from electromagnetic waves propagation point of view. This article deals with main phenomena that affect signal propagation for Local Multipoint Distribution Systems (LMDS) at frequencies above 30 GHz. A new propagation simulation tool for LMDS is presented. Some of the simulation results are depicted as well.

Simulace multimediálních bezdrátových systémů

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Seminář o řešení projektu GA ČR 102/03/H109. Brno: VUT v Brně, FEI, Ústav radioelektroniky, 2004. pp. 18-19. ISBN 80-214-2730-2.
  • Rok: 2004

Šíření elektromagnetických vln

Site Diversity Time-Space Simulations for LMDS

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    For point to multi-point systems working in millimeter frequency bands high reliability of the links is required. The attenuation due to rain is the main limiting factor. Site diversity can be used as one of the propagation impairment mitigation techniques. A propagation simulation tool to study a performance of Local Multipoint Distribution Systems (LMDS) has been developed to enable site-specific time-space simulations. Actual rainfall radar data were utilized as input. Simulations for various site diversity employments, network configurations, hub and terminal station locations, and under different propagation conditions (rain events) were accomplished. The results can be used for planning and optimization of specific point-to-multipoint network.

Site-Specific Space-Time Simulations of LMDS Performance Using Radar Rainfall Data

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper a concept of site-specific space-time simulations rain events are presented based on actual radar data. A database of radar data for numerous types of rain events has been established to enable system testing under different conditions. Various aspects of the system performance like site diversity can be evaluated by the simulation tool.

Space-Time Simulations of Point-to-multipoint Radio Systems Performance During Rain Events Using Radar Data

Time-space modeling of MWS systems working in millimeter wavebands

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The deployment of newly emerging communication systems working in the millimeter-waves frequency bands are a challenge for designers also from electromagnetic waves propagation point of view. This paper deals with main phenomena that affect signal propagation for Multimedia Wireless Systems (MWS) at frequencies above 30 GHz. A new propagation simulation tool for MWS is presented. Some of the simulation results are depicted as well.

Development of Synchronization System for Measurement of Electromagnetic Radiation

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The development of synchronization systém for measurement of electromag. radiation is described in this article. Measurement systém consists of transmitter and receiver, both are controlled by two laptops through standard seriál bus RS232. Laptops are connected through two Sony Ericsson PC cards GC75, which use circuit-switched data (CSD) or general packed radio services (GPRS) for communication.

Measurement and Prediction of Signal Propagation for WLAN Systems

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This article is focused on measurement and prediction of signal propagation for WLAN (Wireless Local Area Network) systems in frequency bands 2.4 GHz and 5.2 GHz. At first WLAN standards are summarized and then two empirical models are described. Results of narrowband and wideband measurement campaign and estimated empirical parameters for coverage models are finally discussed.

Measurement of Signal Coverage in 1.9 and 2.45 GHz Frequency Bands

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: Odborné semináře - Sborník za rok 2002/2003. Praha: ČVUT FEL, Katedra elektromagnetického pole, 2003. pp. 23-27. ISBN 80-86582-12-4.
  • Rok: 2003
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    This article is focused on measurement and prediction of signal propagationfor mobile and WLAN (Wireless Local Area Network) systems in frequency bands 1.9 GHz and 2.4 GHz. At first, two empirical models and measurement of signal coverage are descrived. Results of narrowband measurement compaign and estimated empirical parameters for coverage models are finally discussed.

Podpora výuky předmětu šíření vln a kmitočtové plánování

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Cílem projektu je příprava praktických a experimentálních úloh nově připravovaného předmětu magisterského strukturovaného studia Šíření vln a kmitočtové plánování. Studenti si při měření rozložení výkonové úrovně a dalších parametrů bezdrátové sítě W-LAN (na frekvenci 2,4 GHz) a současné teoretické predikci těchto hodnot budou moci sami ověřit chování elektromagnetických vln uvnitř budov. Jednotlivé úlohy budou rovněž demonstrovat součastné možnosti propojování počítačů do sítí pomocí této moderní technologie.

Results of Indoor Propagation Measurement Campaign for WLAN Systems Operating in 2.4 GHz ISM Band

Results of Indoor Propagation Meausurement Campaign for WLAN Systems Working at 2.45 GHz

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D., Válek, M.
  • Publikace: Poster 2003. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2003. p. C36. ISSN 0277-786X. ISBN 0-8194-5368-4.
  • Rok: 2003
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this article the indoor measurement campaign in 2.45 ISM frequency band is described. Two types of measurements and data processing - narrowband and wideband - are presented. The empirical parameters for standard indoor propagation models have been derived. Time variations of WLAN signal were investigated considering both the position and the azimuthal orientation of the commercial PCMCIA WLAN card. The results enable planning of indoor WLAN network - both the coverage and QoS - for conventional usage of WLAN services (WLAN card in a notebook).

Šíření elektromagnetických vln

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Seznámení s odbornými tématy, kterým se v současné době věnuji na katedře. Obsahuje modelování šíření elmg. vln v mobilních komunikacích pro systémy s prostorovou diverzitou, pro systémy procující v milimetrových pásmech a vývoj efektivních modelů šíření signálu a speciálního softwaru k dané problematice. Kromě softwarového modelování rovněž zkoumám i parametry a principy šíření signálu v reálném prostředí. Za tímto účelem provádíme mobilní měření v pásmech 900, 1900 MHz, měření rozložení výkonové úrovně a dalších parametrů bezdrátových sítí W-LAN (2,45 GHz) a systémů pracujících v milimetrových pásmech.

Šíření elektromagnetických vln

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    Příspěvek pojednává o metodách výuky šíření elektromagnetických vln na katedře elektromagnetického pole ČVUT v Praze.

Wideband Measurement of Insertion Loss of Shielding Materials

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    The aim of this paper is description of development of unique workplace capable of wideband measurement of insertion loss of shielding materials from frequencies about tens of MHz. Special attention is dedicated to construction of ferrite absorber wall and to chosen method of measurement of material insertion loss. Some of results of measurements are presented and discussed as well.

Wireless LAN Networks Design: Site Survey or Propagation Modeling?

  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    There are two basic ways to deploy wireless LAN access points in an indoor scenario: manual deployment using a site survey based on empirical measurements or planning using a software tool with built-in signal propagation models. In this paper advantages and disadvantages of both ways are discussed. The planning based on propagation modeling is recognized as a highly preferable approach for design of large WLANs. Experimental data in this papaer were processed in MATLAB.

Coverage of Picovells by GSM Signal

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: WORKSHOP - Vzdělávací fórum - nabídka aktivit. Praha: ČVUT FEL, Katedra elektromagnetického pole, 2002. p. 20. ISBN 80-86582-07-8.
  • Rok: 2002

Coverage Prediction for GSM Picocells

  • Autoři: prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: POSTER 2002 - Book of Extended Abstracts. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2002. pp. C30.
  • Rok: 2002

Indoor Propagation Measurement for Wireless Systems Operating in 2.45 GHz ISM Band

Šíření elektromagnetických vln

Vývoj synchronizačního zařízení pro zónové měření v procesu měření ELEKTROMAGNETICKÉHO VYZAŘOVÁNÍ

  • Autoři: Bártík, H., prof. Ing. Stanislav Zvánovec, Ph.D.,
  • Publikace: WORKSHOP - Grantové fórum. Praha: ČVUT FEL, Katedra elektromagnetického pole, 2002. pp. 72-73. ISBN 80-86582-06-X.
  • Rok: 2002

Za stránku zodpovídá: Ing. Mgr. Radovan Suk