PHY (Session1) – RIS/OWC

Wednesday, 8 June 2022, 10:30-12:00, Room A306

Session Chair: Laurent Ros (GIPSA-lab & INPG & CNRS organisation, FR)

Smart Wireless Environments Enabled by RISs: Deployment Scenarios and Two Key Challenges

George C. Alexandropoulos (University of Athens, Greece); Maurizio Crozzoli (Telecom Italia, Italy); Dinh-Thuy Phan-Huy (Orange, France); Konstantinos D. Katsanos (National and Kapodistrian University of Athens, Greece); Henk Wymeersch (Chalmers University of Technology, Sweden); Petar Popovski (Aalborg University, Denmark); Philippe Ratajczak and Yohann Benedic (Orange Innovation, France); Marie-Helene Hamon (Orange Labs, France); Sebastien Herraiz Gonzalez (Orange Innovation, France); Raffaele D’Errico (CEA, LETI & Université Grenoble-Alpes, France); Emilio Calvanese Strinati (CEA-LETI, France)
Reconfigurable Intelligent Surfaces (RISs) constitute the enabler for programmable propagation of electromagnetic signals, and are lately being considered as a candidate physical-layer technology for the demanding connectivity, reliability, localization, and sustainability requirements of next generation wireless communications networks. In this paper, we present various deployment scenarios for RIS-enabled smart wireless environments that have been recently designed by the ongoing EU H2020 RISE-6G project. The scenarios are taxonomized according to performance objectives, in particular, connectivity and reliability, localization and sensing, as well as sustainability and secrecy. We identify various deployment strategies and sketch the core architectural requirements in terms of RIS control and signaling, depending on the RIS hardware architectures and their respective capabilities. Furthermore, we introduce and discuss, via preliminary simulation results and reflectarray measurements, two key novel challenges with RIS-enabled smart wireless environments, namely, the area of influence and the bandwidth of influence of RISs, which corroborate the need for careful deployment and planning of this new technology.

A Novel RIS-Aided EMF-Aware Beamforming Using Directional Spreading, Truncation and Boosting

Nour Awarkeh (France); Dinh-Thuy Phan-Huy (Orange, France); Raphael Visoz (Orange Labs, France); Marco Di Renzo (CentraleSupelec-University, France)
This paper investigates beamforming in a wireless communication system, with the objective of providing highly spectral efficient radio links without violating the Electromagnetic Field Exposure constraint. We address a drawback of massive multiple-input multiple-output maximum ratio transmission beamforming, which yields the creation of undesired high exposure regions in the vicinity of the antenna. Such regions are concentrated in few directions (around the antenna) corresponding to the best propagation paths between the antenna and the receiver. In this paper, we propose novel electromagnetic field aware beamforming scheme, that (i) spreads the beamforming radiation pattern in the angular domain by adding artificial propagation paths thanks to reconfigurable intelligent surfaces, (ii) truncates the pattern in strong directions (ii) boosts the pattern in weak directions, and compare it to existing solutions. We show that the proposed novel scheme outperforms existing solutions in terms of received power at the target, without violating the exposure constrain.

Closed-Form Approximation of the EE-SE Trade-Off for Multi-Hop MIMO-RIS Communication Systems

Fabien Héliot, Marjan Abbasi Mosleh and Rahim Tafazolli (University of Surrey, United Kingdom (Great Britain))
Energy efficiency (EE) is one of the main design criterion for the current and next generation of communication systems. Whereas, reflective intelligent surface (RIS) is foreseen to be a key enabler of the next generation of communication systems by facilitating the propagation of radio frequency signals, and in turn, possibly improving its spectral efficiency (SE) and/or EE. This paper investigates both the EE and SE of a multi-hop multi-antenna RIS-aided communication system through its fundamental trade-off. To this end, we first provide a generic and accurate closed-form approximation (CFA) of the SE (ergodic capacity) for multi-hop multi-antenna RIS-aided systems and verify its accuracy through simulations for various numbers of antennas/phase shifters and hops. Based on this expression, we then derive a novel and accurate CFA of the fundamental EE-SE trade-off for multi-hop multi-antenna RIS-aided systems. We subsequently use our CFA to analyse the variations of the EE as a function of the number of antennas/phase shifters and hops when considering a realistic power consumption model. It turns out that increasing the number of hops is more energy efficient than increasing the number of antennas/phase shifters and that multi-hop communication with RIS is not necessarily always more energy efficient than classic multi-antenna communication, as it is for instance the case in a simple device-to-device communication scenario.

Vehicular Visible Light Communications Noise Analysis and Autoencoder Based Denoising

Bugra Turan, Emrah Kar and Sinem Coleri (Koc University, Turkey)
Vehicular visible light communications (V-VLC) is a promising intelligent transportation systems (ITS) technology for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications with the utilization of light-emitting diodes (LEDs). The main degrading factor for the performance of V-VLC systems is noise. Unlike traditional radio frequency (RF) based systems, V-VLC systems include many noise sources: solar radiation, background lighting from vehicle, street, parking garage, and tunnel lights. Traditional V-VLC system noise modeling is based on the additive white Gaussian noise assumption in the form of shot and thermal noise. In this paper, to investigate both time-correlated and white noise components of the V-VLC channel, we propose a noise analysis based on Allan variance (AVAR), which provides a time-series analysis method to identify noise from the data. We also propose a generalized Wiener process-based V-VLC channel noise synthesis methodology to generate different noise components. We further propose a convolutional autoencoder (CAE) based denoising scheme to reduce V-VLC signal noise, which achieves reconstruction root mean square error (RMSE) of 0.0442 and 0.0474 for indoor and outdoor channels, respectively.

Turbo-DC-FSK: Joint Turbo Coding and FSK-Based Modulation for Visible Light Communications

Paul Miqueu (University Grenoble Alpes, CNRS, Grenoble INP, GIPSA-Lab, France); Muhammad Jehangir Khan (Université Grenoble Alpes, CNRS, Grenoble INP, GIPSA-Lab, France); Yannis Le Guennec (University Grenoble Alpes, CNRS, Grenoble INP, GIPSA-Lab, France); Laurent Ros (GIPSA-lab & INPG & CNRS organisation, France)
In this article, we propose and analyze a joint Turbo coding and DC-FSK modulation scheme (Turbo-DC-FSK) dedicated to visible light communications (VLC). This method is an adaptation to satisfy the VLC requirements of the Turbo-FSK technique initially developed for the long range low power Radio-Frequency context in CEA-LETI (during PhD of Yoann Roth, in collaboration with Gipsa-lab). It requires a change in the modulation alphabet generation and the addition of a constant component (DC) to the generated waveforms. This scheme involves the FSK-based modulation at the transmitter side, i.e., DC-FSK, and a Turbo-decoder scheme at the receiver side, i.e., BCJR algorithm. Simulation results shall confirm that Turbo-DC-FSK can achieve around 6 dB energy gain over regular VLC state-of-the-art DC-FSK modulation at a BER = 10−4. Using λ parallel branches, a desired balance between energy efficiency and spectral efficiency is achieved.

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