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Guest Editorial: Selected papers from the 8th Biennial Colloquium & 6th International Workshop on Optical Wireless Communications

2023; Institution of Engineering and Technology; Volume: 17; Issue: 4 Linguagem: Inglês

10.1049/ote2.12103

1751-8776

Mónica Figueiredo, Stanislav Zvánovec, Rafael Pérez‐Jiménez, Luis Filipe Mesquita Nero Moreira Alves,

Optical Wireless Communication Technologies

Since 2011, optical wireless communication (OWC) technologies have gained momentum. OWC has been supported by an active research community, and entrepreneurs who have shown the merits of these technologies by showcasing real-time demonstrators and commercial OWC solutions. These technologies include visible light communications (VLC), underwater VLC, Li-Fi, optical camera communications (OCC), visible light positioning, visible light sensing and free space optics, among others. They have been shown to be an efficient means to satisfy the demanding requirements of backhaul and access network levels, and also to provide a means for accurate indoor positioning and sensing, or enable wireless communication in non-RF friendly environments. As a result, it is envisaged to become an indispensable part of 6G and will complement other communication methods to benefit our daily lives. This Special Issue contains a group of 10 selected papers accepted at the 8th Colloquium & 6th International Workshop on Optical Wireless Communications, co-located with the International Symposium on Communication Systems, Networks & Digital Signal Processing (CSNDSP 2022). This Special Issue has provided the best paper authors' the opportunity to extend their work beyond what was presented at this event, enabling new results and development to further advance the respective fields. Accepted papers can be clustered into three main categories, namely theoretical, applications and performance oriented. The papers lying in the first category exhibit novelties in modelling of optical wireless channel, non-linear effects and synchronisation issues. The papers in this category are of Combeau et al., Vieira et al., and Rodrigues et al. The second category of papers presents different approaches to using OWC concepts in short and medium range applications. These papers are of Younus et al., Rêgo et al., and Uleru et al. The last category proposes new techniques to evaluate performance in systems employing OWC concepts, such as screen to the camera, light-emitting diode (LED) to multispectral camera, LED matrix arrays or reconfigurable intelligent surface (RIS) based OWC. These papers are of Yokar et al., Moreno et al., Mohammadi et al., and Salehiyan et al. A brief presentation of each of the paper in this Special Issue follows. In paper 1, Combeau et al. propose a method for the optical characterisation of materials to enable realistic channel simulation based on Monte-Carlo Ray-Tracing algorithms. They conduct some experimental measurements in environments containing the materials sought and then apply an optimisation algorithm which searches for the parameters of the material reflection models. Therefore minimising the difference between the optical measurement and the simulation. Results show that the proposed method produces a correct estimate of the Bidirectional Reflectance Distribution Function albedos, provided that the models correspond well to the reflection behaviour of the materials, and that the materials have a significant influence on the measured optical power. In Paper 2 Vieira et al. investigate the accuracy of the generalised memory polynomial (GMP) for the non-linear modelling of optical Fast-OFDM links. After model validation using measured data of a 10 km single mode fibre link, the GMP is used for performance investigations of a distortion compensation approach to optical Fast-OFDM, for up to 16PAM modulation formats and different numbers of Fast-OFDM subcarriers. This work also investigates the influence of the zero padding length on the performance of optical Fast-OFDM. The proposed distortion compensation scheme shows significant performance improvements relative to conventional system implementation. In paper 3, Rodrigues et al. address the issue of carrier synchronisation in a multi-user communication system based on a central digital multiband Carrierless Amplitude and Phase optical transmitter, which broadcasts data on multiple channels to a number of low-cost/low-power devices in Internet-of-Things (IoT) scenarios. A simulation model for the traditional Costas Loop applied in this context is presented along with performance results that show the feasibility of this approach and identify possible issues and viable solutions. In paper 4, Younus et al., investigate the use of an indoor visible light system to provide a three dimensional (3D) high-accuracy positioning solution. It leverages the use of a single LED at the transmitter and an image sensor at the receiver (Rx). The proposed system can retrieve the 3D coordinate of the Rx using a combination of the angle of arrival and received signal strength (RSS). To mitigate the error induced by the lens at the Rx, a novel method is proposed and experimentally tested, which outperforms previously reported RSS under all circumstances and is immune to varying exposure times. In Paper 5, Rêgo et al., propose an algorithm for recovering transmitted static identifiers (IDs) in rolling shutter based OCC positioning systems. The goal is to allow the correct decoding when the ID frame is only partially detected in the image. Simulation results show that the maximum distance at which the IDs recovery can be guaranteed is increased by 2.5-fold with the proposed algorithm, for 6-bit, 8-bit and 10-bit code words. An experimental validation algorithm was also proposed, using image processing techniques to extract the bitstream and test the ID recovery process. The proposed algorithm is shown to improve the frame recovery success rate for a given distance, even in the presence of bit errors in the extracted data. In paper 6, Uleru et al. explore the use of VLC to establish a wireless link between neurons in spiking networks. Instead of the traditional wavelength division multiplexing approach in electro-optical spiking neural networks (SNN), this paper explores the use of non-orthogonal multiple access (NOMA) with a pulse amplitude modulation (PAM) scheme. To evaluate NOMA with PAM, they implement an electro-optical SNN that controls the force of two anthropomorphic fingers actuated by the shape memory alloy-based actuators. An optical reference channel is used to dynamically adjust the optical receiver's gain to improve the receiver's decoding performance. Experimental results demonstrate that the electro-optical SNN can maintain control over the fingers and hold an object under varying channel conditions. Hence, the proposed system offers robustness against dynamic optical channels induced by the relative motion of neurons. In paper 7, Yokar et al., experimentally demonstrate that smartphone-to-smartphone based visible light communications (S2SVLC) systems can support high-quality multimedia transmissions. Different performance metrics are used in this analysis, such as the mean square error estimation, peak signal-to-noise (PSNR) degradation, bit error rate (BER) and data rate achieved. The analysis was conducted for different typical practical background illuminations (i.e. normal illumination and dark condition), distances, tilting, and rotation angles. The PSNR and BER are determined for different frame sizes in the S2SVLC system to provide an insight of system performance. Presented results indicate how the data transmission under different conditions impacts the system's performance. In Paper 8, Moreno et al. explore the use of multispectral cameras to take advantage of the LED behaviour and provide new features to OCC links. The idea is to detect differences in LED spectral response curves, when their temperature changes, to obtain more than one communication channel using the same LED device. This new approach also resorts to equalisation techniques in the receiver to improve the extraction of the transmitted signal. For the specific multispectral camera employed in the experiments, up to two distinct channels could be obtained with the same transmitter at different temperatures. However, authors also noticed that obtaining satisfactory results is highly dependent on the variation that temperature causes in the spectral signatures of the LEDs, so further experiments are recommended in future work with different devices. In paper 9, Mohammadi et al. investigate how to minimise the secrecy outage probability (SOP) at the location of the legitimate user (LU) for a multiple-input single-output-VLC scenario. To mitigate the effect of the eavesdropper, they derive the optimal beamforming coefficients which are used at the transmitter LED array with the aim of maximising the signal-to-noise ratio at the LU. Simulation results show that the proposed SOP-based LED arrangement with optimal beamforming offers up to 3 dB gain in transmit power compared to the classical uniform LED arrangement with sub-optimal zero-forcing beamforming. Moreover, they show that by using the proposed method, the SOP is kept below a desired threshold, over a wider area inside the indoor environment compared to classical methods. Finally, in paper 10, Salehiyan et al. explore the use of a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS), in a non-orthogonal multiple-access visible light communication system, to improve the performance. They considered two data recovery schemes, single-user detection (SUD) and successive interference cancellation (SIC), and formulate a sum-rate optimisation problem for two operating modes of STAR-RIS. They have also compared energy-splitting and mode-switching cases and showed that these two modes have the same performance. Finally, numerical results for SUD and SIC schemes and two benchmarking schemes and timesharing and max-min fairness are presented, and spectral- and energy-efficiency, number of STAR-RIS elements, the position of users and access point are discussed. Papers selected for this Special Issue show that fundamental investigation in OWC technologies is a crucial and necessary process to unlock its full potential, address challenges, and ensure its relevance and impact in various applications. The fundamental investigation presented in these papers is expected to help researchers and engineers gain a deep understanding of the underlying principles and mechanisms of a broad range of technologies that use light as the medium for wirelessly transmitting information. These developments have the potential to foster additional innovation, facilitate future problem-solving and optimisation strategies, and ultimately contribute to mature OWC technologies. Data sharing is not applicable to this article as no new data were created or analyzed in this study. Dr. Mónica Jorge Carvalho de Figueiredo is an associate professor at the Polytechnic of Leiria since 2012 and a researcher at Telecommunications Institute. She received a PhD in Electrical Engineering from the University of Aveiro, Portugal in 2012. She has published more than 35 articles in peer reviewed journals and conferences, in the areas of high speed digital electronic systems, reconfigurable systems for telecommunications, edge computing with artificial intelligence and visible light communications. She has served as a reviewer for several international journals. She is also the CEO and co-founder of TWEVO Lda., a startup providing reliable and intelligent solutions for the Industry 4.0. Prof. Stanislav Zvanovec received his MSc and PhD degrees from the Faculty of Electrical Engineering, Czech Technical University (CTU) in Prague, in 2002 and 2006, respectively. He is currently working as a Full Professor, the Deputy Head of the Department of Electromagnetic Field and head of Wireless and Fiber Optics at CTU (optics.elmag.org). His current research interests include free space optical, visible light communications and fibre optical systems, OLED-based technologies and RF over optics. He is the author of two books (and co-author Visible Light Communications: Theory and Applications), several book chapters and more than 300 journal articles and conference papers. More details: zvanovec.elmag.org. Prof. Rafael Pérez-Jiménez, born in Madrid in 1965. BSc & MEng (UPM, 1991), PhD in Engineering (ULPGC, 1991) and in History (ULL, 2020). Full Professor since 2003 at ULPGC. He has directed or participated in 12 transnational research projects, 26 official national projects in competitive calls and more than 30 relevant contracts with companies and administrations. He has authored more than 100 indexed journal papers, and more than 200 communications to international peer-reviewed conferences. His main research area corresponds to the development of optical wireless communication systems, especially for IoT and medium/low speed links, both in the vehicular and domestic environment. Since 2020 is coordinator in the area of Communications Technology of the Spanish Research Agency. Luis Filipe Mesquita Nero Moreira Alves ([email protected]) graduated in 1996 and received his MSc degree in 2000, both in Electronics and Telecommunication Engineering from the University of Aveiro. In 2008, he obtained the PhD degree in Electrical Engineering from the University of Aveiro. His PhD thesis was on high bandwidth gain product amplifiers for optical wireless applications. He is currently with the Department of Electronics Telecommunications and Informatics from the University of Aveiro, where he lectures electronic related subjects to both graduate and undergraduate students. Since 2008, he has been the lead researcher at the Integrated Circuits Group from the Instituto de Telecomunicações – Aveiro. His current research interests are on: (i) design and performance analysis of visible light communications systems; (ii) Visible Light communications systems applied to IoT scenarios; (iii) IoT sensing devices, especially focused on SAW (surface acoustic wave) and memristive devices; (iv) sensing and stimulation devices for implantable medical devices; (v) analogue integrated circuit design for sensing and instrumentation applications. He has served as member of the COST actions IC1401 (MemoCiS), IC1101 (OPTICWISE) and CA19111 (NEWFOCUS). He has participated/leaded several research projects at both national and international levels, such as, NeuralStimSpinal (H2020/FET), VisIoN (H2020/MSCA-ITN), OWIN6G (HORIZON/MSCA-ITN), LITES (EU/CIP-ICT-PSP) SGH (P2020/SI I&DT), RTMGear (FP7/CleanSky), VLCLighting (IT/Internal), amongst others. Luis Nero Alves has participated in the technical programme committee of several international conferences on optical communications. He has served as a reviewer for several international journals (IEEE/PTL, IEEE/JLT, IEEE/TCASI, IEEE/TCASII, IEEE/TCSVT, Elsevier/OC, amongst others). Luis Nero Alves as authored/co-authored several conference and journal papers on the aforementioned topics.