Lidé

Ing. Jan Spáčil

Všechny publikace

Demonstration of M-QAM OFDM bidirectional 60/25 GHz transmission over 10 km Fiber, 100 m FSO and 2 m radio seamless heterogeneous fronthaul link

  • DOI: 10.1016/j.yofte.2022.103161
  • Odkaz: https://doi.org/10.1016/j.yofte.2022.103161
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    In this paper, we demonstrate the experimental transmission of 16- and 64- quadrature amplitude modulation (QAM) Long Term Evolution - Orthogonal Frequency Division Multiplexing (LTE-OFDM) signals by using millimetre wave frequencies at 60 GHz and 25 GHz for downlink and uplink, respectively, over a heterogeneous optical fronthaul infrastructure. A directly modulated laser was employed for both links, which enables the cost-effective full-duplex system proposal. The bidirectional link consists of a 10 km of single mode fiber, a 100 m long free space optics channel and 2 m long wireless radio link, which brings flexibility for future wireless networks. The error vector magnitude (EVM) parameter is measured for a range of the received optical and electrical power as well as the signal-to-noise ratio. A comprehensive estimation of penalty factors in the different network segments is presented. The successful transmission over the whole proposed network with the EVM below the required limit of 9 % for 64-QAM with 20 MHz bandwidth is experimentally demonstrated for the received optical power of −2.7 dBm and −1 dBm for the downlink and uplink, respectively.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

Pre-Assessment of Radiated Fields from Small Electronic Submodules

  • DOI: 10.13164/re.2018.0640
  • Odkaz: https://doi.org/10.13164/re.2018.0640
  • Pracoviště: Katedra elektromagnetického pole
  • Anotace:
    A novel approach to the evaluation of electromagnetic field radiated from devices by using a small shielded enclosure in presented. Several EMC problems can be identified by employing the computations of a Radiated Model device, such as the model the Submodule-on-Motherboard structure described here. The combination of a numerical approach, through a validation model and measurements, must be done during the design phase in multiple iterative loops to minimize the risk of non-compliance of the final qualification proces. Ths novel combined approach requires little investment and is highly efficient for industrial applications.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk