Ing. Carlos Guerra Yánez

This work explores the requirements on the minimum horizontal and vertical size in therms of pixels for the transmitters on the registered image frame, analysing the communication performance in therms of bandwidth, SNR and synchronisation; applying signal and image processing methods to decode the information signals from multiple sources, analysing different cases to take advance of the spacial diversity that the image sensor provides, comparing the processing time require to perform the proposed algorithms, seeking for an approximation to the real time processing of the image frames.

Polarization-sensitive receivers for single photons are of crucial importance in various applications within the fields of quantum communication and quantum sensing, and are more commonly implemented in free-space optics rather than in optical fibers. This is primarily due to the unpredictable and varying birefringence in single-mode optical fibers. We present a method for birefringence compensation in an all-fiber detection setup that relies solely on coincidence measurements of a polarization-entangled state, or known correlations in a prepare-andmeasure scenario. We define coincidence entropies as functions of the measured coincidence counts. These quantify the randomness of measurement outcomes, remain independent of the transmitted Bell state, and serve as indicators of the degree of entanglement. By leveraging coincidence entropy as a cost function in a gradient descent algorithm, we are able to align the polarization bases between two distinct polarization-sensitive receivers. Additionally, coincidence entropies can be employed to monitor the quality of entanglement transmission, thereby enhancing the system’s ability to detect potential eavesdropping attempts, such as intercept-resend quantum attacks.

This letter proposes a novel dual-layer security framework for visible light communication (VLC) by integrating the BB84 quantum key distribution (QKD) protocol with beam directivity-based physical layer security (PLS). This combined approach enhances resilience against eavesdropping threats, offering stronger security compared to individual techniques, particularly in highly secure environments. The analysis indicates that in the first layer, simulated in MATLAB® , the QKD system with multiphoton source benefits from an increased average number of photons, improving the secret key fraction and enhancing resistance to quantum channel attenuation. However, this advantage comes at the expense of heightened vulnerability to photon number splitting (PNS) attacks. To mitigate this, the second layer, location-based PLS, which is implemented on an experimental testbed, restricts Eve’s access to the VLC data channel by leveraging beam directivity. Within the limitations defined by the controlled indoor setup, the obtained results demonstrate that even under a strong PNS attack, Eve’s best bit error rate (BER) remains higher at 2.4×10−2 compared to Bob’s worst BER at 3.7×10−3 , ensuring secure communication.

Maintaining reliable performance of optical camera communication (OCC) in low visibility scenarios, such as dense fog, is challenging due to light scattering and attenuation. Here, we present a side-emitting fiber-based OCC system that performs below the forward error correction (FEC) limit in visibilities close to five meters, corresponding to a propagation loss of almost 4 dB/m. We use an RGB laser source instead of a conventional LED source, resulting in a significantly brighter image on the camera and enabling three-channel wavelength-division multiplexing. We prove the robustness of the proposed OCC system with measured bit error rate (BER) of 1.8 × 10−4 to 1.6 × 10−3 for visibilities of 20.8 down to 4.5 m, respectively, all BER values below the FEC limit. Our results show application potential in areas with low visibility where reliable OCC can ensure human safety.

Semantic communication subverts classical communication techniques by changing the focus on the preservation of meaning rather than on correctly transmitting logical bits. This is achieved by implementing a semantic encoder/decoder pair that operates at a higher level of abstraction and takes into account the nature of the source and destination, as well as their shared knowledge. One approach for the implementation of semantic encoder/decoder pairs is the use of artificial neural networks, and in particular, variational autoencoders. In this work, we propose the use of hierarchical quadrature amplitude modulation to improve the perceived quality of data in a semantic communication link using a variational autoencoder. We show that the use of the hierarchical modulation consistently improves the performance of the semantic communication link in terms of the SSIM under noisy channel scenarios, even achieving the overcoming of noise for signal-to-noise ratio values above 10 dB.

In this paper, we experimentally demonstrate and analyze the performance of software-defined radio (SDR)-based hybrid optical wireless communication (OWC) links for indoor Internet-of-Things (IoT) networks. We propose all-optical hybrid visible light communication (VLC) and optical camera communication (OCC) using a single light emitting diode (LED) as a transmitter and photodiode (PD) and image sensor (IS) based receivers for simultaneous high-and low-speed data transmission. We present a testbed using an SDR platform, i.e., the ADALM-PLUTO, to transmit and receive high-and low-speed signals in the very-high frequency band and a media converter as part of an OWC link. We evaluate the performance of the proposed hybrid system employing a chip LED modulated with quadrature phase shift keying signal in terms of the bit error rate and the reception success rate Rrs. We show that the proposed scheme can provide an independent link performance, irrespective of the significant differences between the operating data rates of VLC and OCC links. The results show that for a link span of 1 m, we achieve (i) error-free detection for high-speed PD-based VLC; and (ii) 100 % Rrs at varying modulation frequencies for low-speed IS-based OCC.

In this paper, we experimentally demonstrate and analyze the performance of a software-defined radio (SDR)-based all-optical multiple-input multiple-output (MIMO) wireless hybrid communication link for indoor Internet of Things (IoT) sensor networks. We propose an all-optical hybrid scheme using two light-emitting diodes (LEDs) as transmitters (Tx) and photodiode (PD)- and image sensor (IS)-based receivers for simultaneous high- and low-speed data transmission capabilities using visible light communication (VLC) and optical camera communication (OCC) links, respectively. We present a testbed using an SDR platform to transmit and receive high- and low-speed signals and a media converter to introduce them into an optical link. We evaluate the performance of the proposed SDR-based all-optical MIMO wireless hybrid scheme: 1) a single-input multiple-output (SIMO) link employing a single-chip LED for reference, and 2) a MIMO link employing two-chip LEDs modulated with a quadrature phase shift keying signal, in terms of the bit error rate and reception success rate of high-speed VLC and low-speed OCC links, respectively. We show that the proposed scheme can provide independent link performance, irrespective of the significant differences between the operating Rb of VLC and OCC. By means of the proposed testbed and measurements, we provide a versatile solution to implement all-optical hybrid links for low-rate IoT environments.

We demonstrate the resilience of a side-emitting fiber-based optical camera communication (OCC) channel under severe fog conditions. For visibility of only 6.2 m, the link provides reliable communication vital for outdoor emergency services.

Digital Twin (DT) technology is often used to replicate physical systems in the digital domain and gain access to monitoring, managing, automating, and predicting the system's behavior and state. The modeling of the physical magnitudes becomes important when performing any possible operations on the obtained data sets. This article discusses the modeling and procedures used for the development of a base for DT systems with optical wireless communications (OWC). OWC is adversely affected by wireless channel impairments that must be addressed for reliable communications. The impact of atmospheric turbulence affects the free-space optical (FSO) links, which are a branch of optical wireless communication (OWC). This current research provides insight into a machine learning-based prediction model for predicting the scintillation index of an FSO link using a turbulence emulator chamber. The paper also discusses the fundamental concepts of DT development from the point of view of real-time data flow, implemented through an OWC link, highlighting connection interfaces and automatic control. In the context of DTs, modeling approaches and integration of intelligent systems play a crucial role. This article combines these two areas to provide some initial observations of the research activities carried out towards the development of a proof-ofconcept base for DT employing OWC as part of its target system and as the data interface.

Wearable communication is one of the key drivers in the Internet of Things (IoT) and body area networks for transmitting vital sensory data. Wearable devices must be lightweight, flexible, and have low energy consumption. In this context, optical wireless communication offers several significant advantages, such as immunity to the radio frequency-induced electromagnetic interference, broad unlicensed spectrum, and enhanced physical layer security. Wearable devices employing light-emitting diodes coupled to side-emitting optical fibers form energy-efficient, lightweight, flexible, and omnidirectional distributed optical transmitters, which are ideal for IoT applications. In this paper, we propose an optical camera communication (OCC)–based wearable system with a unique image processing algorithm capable of detecting and recovering data from distributed transmitters of arbitrary shapes. Experimental results demonstrate the feasibility of the proposed system, where for distances up to 4 m, the bit error rate (BER) performance is well below the forward error correction BER limit with values as low as 5.5×10−5. The presented results demonstrate the potential of OCC-based systems using side-emitting fibers for IoT applications.

In this work, we present the first steps towards the use of visible light communications (VLC) as an extension of the physical layer of low-rate wireless personal area network architectures for indoor links. We present a testbed using a software-defined radio (SDR) platform, i.e., the ADALMPLUTO active learning module, to transmit and receive low-rate signals in the VHF band and a media converter to introduce them in a VLC link. We report error-free detection up to 1 m using a lens in the transmitter to reduce the beam width to 5 degrees.

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.

Optical camera communication (OCC) using side-emitting fibers offers new transmission possibilities, as side-emitting fibers gradually emit light along the fiber length, thus acting as a distributed light source. In this paper, we explore side-emitting fiber-based OCC architecture, focusing on the integration of wavelength division multiplexing (WDM). WDM enabled us to achieve simultaneous transmission of two data streams over a single 1-m long side-emitting fiber, effectively doubling data throughput. Results indicate successful data transmission with minimal bit error rates (BER) under the forward error correction (FEC) limit of 3.8. 10 -3 , demonstrating the potential of side-emitting fibers and WDM in enhancing OCC systems by adding additional transmission channels.

This research conducts a performance analysis on a real-time experimental multi-quadrature amplitude modulation (M-QAM) free-space optical (FSO) system under different fog conditions. The study focuses on experimental investigations to assess the system's tolerance and performance. Experimental results will contribute to a comprehensive understanding of the reliability aspects of the M-QAM FSO system, offering practical insights that are vital for real-world applications in challenging atmospheric conditions

The use of quantum key distribution (QKD) to improve security may impact the quality of service (Qos) of high rate classical data links. The key generation process with an empty buffer can be modeled as a queuing system, and data throughput limits can be determined using queueing theory to assess the impact on the QoS. The proposed key generation model is based on an on-demand paradigm. Based on the results of this study, a discrete variable (DV)-QKD-secured link could be designed using the data rate bounds to guarantee a given QoS. Furthermore, we validate the derived bounds by comparing the theoretical derivations with simulations. We show that in a one-time-pad system, the achievable throughput approaches 0.59 times the secret key rate as the key length increases. In the case of a key scheme with key reuse, the throughput is asymptotically linear with the number of key reuses, and the slope of the curve corresponds to the secret key rate multiplied by a function of the protocol and channel characteristics. The analysis is carried out on optical fiber and free-space links.

Long-distance time and frequency transfer methods in optical fiber links have matured in recent years, including into this parallel operation with data. On other hand quantum entanglement transfer over shared fiber are really rare. This paper presents the initial steps of verifying the potential for sharing classical data transfer with the transfer of entangled states on the same fiber.

Long-distance time and frequency transfer methods in optical fiber links have matured in recent years, including into this parallel operation with data. On other hand quantum entanglement transfer over shared fiber are really rare. This paper presents the initial steps of verifying the potential for sharing classical data transfer with the transfer of entangled states on the same fiber.

This paper presents an asymmetric full-duplex solution based on visible light communications (VLC) for indoor wired and wireless hybrid signal transmission. The signal is distributed by a polymer optical fiber (POF) link and passively radiated. The proposed system includes two VLC links: a low-speed downlink and a high-speed uplink using an image sensor (IS) and photodiode detection (PD) based receivers. PD-based system communication performance is evaluated by means of error vector magnitude (EVM) for different modulation orders quadrature phase shift keying (QPSK), 16- and 64-quadrature amplitude modulation (QAM), while the IS-based system is characterized in terms of the success of reception (SoR). High-speed data transmission up to 160 Mbps with a 16-QAM modulation scheme and low-speed data transmission up to 500 bps with 98.6% of SoR using a non-return zero on–off keying (NRZ-OOK) scheme over a 1.5 m optical wireless link are demonstrated. Finally, simulations of the wireless channel are performed to evaluate the misalignment tolerance of the system; and, to estimate the uplink performance at longer distances.

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.

This paper outlines the concept of a multilevel bipolar on-off keying hybrid optical wireless communication (OWC) system using a single light-emitting diode (LED) as a transmitter as well as photodiode and camera-based receivers for versatile indoor Internet of Things applications. The proposed system offers simultaneous high- and low-speed transmission capabilities using visible light communication (VLC) and optical camera communication (OCC) links, respectively. By means of experimental implementation, we show that the hybrid OWC system employing a chip LED modulated with a multilevel signal improves the data rate Rb as well as the bit error rate and reception success rate of VLC and OCC links, respectively, by doubling the bandwidth. We show that the proposed scheme can provide an independent link performance, irrespective of significant differences between the operating Rb of VLC and OCC over a range of transmission spans L . We demonstrate that the throughput of the VLC link is improved by up to ∼ 100 Mb/s, which corresponds to twice the LED bandwidth, using direct modulation, different amplitude levels, and optimizing the received optical power of the hybrid OWC link. Error-free data transmission for the OCC link is achieved for all values of Rb , amplitude overlap of 0 and 0.3, and a range of L .

Quantum Key Distribution (QKD) is a promising tool for secure communication in the near future. In combination with one-time-pad technique, it provides an unconditionally secure communication channel (meaning that it is secure against an adversary, even with unlimited computational power), at least in principle. However, a major implementation challenge for some schemes is the reliable creation, transportation, and measurement of entangled photon pairs over long-distance fiber networks. Our project aims to explore the possibilities for distributing quantum information on an existing network infrastructure while measuring the effects of real-world conditions. We characterized a commercial source of entangled photons. We measured its spectrum, brightness (1.6 +/- 0.3) x10(4) pairs/s/mu W, and performed quantum state tomography (QST) to reconstruct the density matrix of the quantum state. Our implementation focuses on an all-fiber solution, which would enable a simplified QKD implementation. In laboratory conditions, we achieved the visibility equal to (0.957 +/- 0.004) as a mean in both bases with a coincidence rate of (275 +/- 4) counts/s and successfully ran QKD protocol with secret key rate of (86 +/- 1) bits/s and average quantum bit error rate (QBER) of (4.8 +/- 0.7) %.

We present a distributed receiver for visible light communication based on a side-emitting optical fiber. We show that 500 kbps data rate can be captured with a bit-error rate below the forward-error correction limit of 3.8·10−3 with a light-emitting diode (LED) transmitter 25 cm away from the fiber, whereas by increasing the photodetector gain and reducing the data rate down to 50 kbps, we improve the LED-fiber distance significantly up to 4 m. Our results lead to a low-cost distributed visible-light receiver with a 360° field of view for indoor low-data rate, Internet of Things, and sensory networks.

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.

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.

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).

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.

The current situation in the world with the COVID-19 pandemic has reinforced a pre-existing trend based on increasing the use of gamification tools in education to motivate students. In this work, a study based on a Markov model is proposed to assess motivation during the training process in higher education. The evolution of Faculty of Business Administration graduates when using a gamified smartphone application (HEgameApp) has been measured. The behavior of graduates is assessed through collaboration in fora created by HegameApp, and the recognition given by their classmates. A utility function is defined to obtain a statistical estimator used in the assignment of motivational states of the study participants. In addition, a decrement function is assigned to the value of the components of the utility function to estimate the time variation of motivation during the process of knowledge assimilation. The proposed solution shows that when graduates are involved in using the app, they significantly increase their academic outcomes and satisfaction while receiving the lectures. In addition, the positive feedback perceived through the application fora has a measurable effect on their motivation.

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.

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.

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.

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.

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.

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.