PHY1  – Reconfigurable intelligent surfaces

Wednesday, 7 June 2023, 11:00-12:30, Room G2

Session Chair: Hmaied Shaiek (CNAM, France)

The Extended Vienna System-Level Simulator for Reconfigurable Intelligent Surfaces 
Le Hao (Technische Universität Wien, Austria); Stefan Schwarz and Markus Rupp (TU Wien, Austria)
Reconfigurable intelligent surfaces (RISs) have been considered a promising research direction for the next generation of wireless communications. It is essential to perform extensive simulations in a system-level simulator (SLS) to analyze the system performance of RIS-assisted large-scale wireless networks. This paper introduces the RIS-tailored Vienna SLS that utilizes the MATLAB ray tracer to realize RIS-assisted transmissions. A recently published free space pathloss model for RIS (RISFSPL) has been adopted to be compatible with our SLS. In addition, we modified the ray tracing (RT) model based on the RISFSPL model to obtain a more precise pathloss in a realistic environment. In this way, we realize the advantages of both the RISFSPL and RT models. We verified the system performance through simulations in a single-input single-output (SISO) scenario with random and optimized RIS phase shifts. Furthermore, we analyzed the system performance through simulations in a complex scenario that consists of multiple base stations (BSs), RISs, and users. Keywords—Reconfigurable Intelligent Surface (RIS); Intelligent Reflecting Surface (IRS); System level simulation; 6G

Ergodic Rate Analysis and Optimization of Full-Duplex STAR-RIS Communication Systems 
Justin Jose (Indian Institute of Technology Indore, India); Parvez Shaik (Texas A & M University at QATAR, Qatar & Texas A & M University, Qatar); Shubham Bisen and Vimal Bhatia (Indian Institute of Technology Indore, India)
Recently, the concept of simultaneo usly transmitting and reflecting based reconfigurable intelligent surface (STARRIS) has attracted research interest due to its capability ofserving both half-spaces unlike conventional reflecting-only RIS. In this paper, we perform ergodic rate (ER) analysis for fullduplex based STAR-RIS communication and then maximize the same subject to quality-of-service constraints of the users. We first present closed-form expressions of ER for both uplink and downlink users over generalized Nakagami-m fading channels. Further, to minimize the effects inter-user interference and residual self-interference, particle swarm optimization algorithm is employed in jointly optimizing the transmission amplitude, element partitioning and user transmit powers. Extensive MonteCarlo simulations are carried out over different system parameters to verify accuracy of the results and useful inferences are obtained.

Impact of Multiple RIS on Channel Characteristics: An Experimental Validation in Ka Band
Taghrid Mazloum (CEA- LETI, France); Luca Santamaria (Greenerwave, France); Frederic Munoz (CEA LETI & University of Grenoble-Alpes, France); Antonio Clemente (CEA-Leti, France); Jean-Baptiste Gros, Youssef Nasser, Mikhail Odit and Geoffroy Lerosey (Greenerwave, France); Raffaele D’Errico (CEA, LETI & Université Grenoble-Alpes, France)
In this work, we present the results of an experimental validation of the use of multiple Reconfigurable Intelligent Surfaces (RISs) in indoor scenarios. The setup employs a Transmitting and a Reflecting RIS in the Ka band with more than 400 elements each. Two different 1-bit Unit Cell (UC) based on PIN-diode technologies have been designed to realize the RISs. The Transmitting RIS (T-RIS) is used on the Base Station (BS) side to perform steering towards the User Equipment (UE), or the Reflecting RIS (R-RIS) acting as extender. The channel responses are analysed over a wide band (25-35 GHz) to investigate the impact of the phase distribution over RISs, as well as the antenna employed on the BS or UE side. Finally, the Multi Path Components (MPCs) in different Line of Sight and Obstructed Line of Sight, are estimated by means of space-alternating generalized expectation-maximization (SAGE) wideband algorithm, and analysed to highlight the use of RISs.

Cell-Edge Performance Booster in 6G: Cell-Free Massive MIMO vs. Reconfigurable Intelligent Surface 
Wei Jiang (German Research Center for Artifitial Intelligence (DFKI GmbH), Germany); Hans D. Schotten (University of Kaiserslautern, Germany)
User experience in mobile communications is vulnerable to worse quality at the cell edge, which cannot be compensated by enjoying excellent service at the cell center, according to the principle of risk aversion in behavioral economics. Constrained by weak signal strength and substantial inter-cell interference, the cell edge is always a major bottleneck of any mobile network. Due to their possibility for empowering the next-generation mobile system, reconfigurable intelligent surface (RIS) and cell-free massive MIMO (CFmMIMO) have recently attracted a lot of focus from academia and industry. In addition to a variety of technological advantages, both are highly potential to boost cell-edge performance. To the authors’ best knowledge, a performance comparison of RIS and CFmMIMO, especially on the cell edge, is still missing in the literature. To fill this gap, this paper establishes a fair scenario and demonstrates extensive numerical results to clarify their behaviors at the cell edge.

On Beam Widening for RIS-Assisted Communications Using Genetic Algorithms 
Maarouf Al Hajj (Orange Labs, France); Khaled Tahkoubit (CEA-Leti, France); Hmaied Shaiek (CNAM, France); Valery Guillet (Orange Labs, France); Didier Le Ruyet (CNAM, France)
As future wireless communication systems aim to achieve increased data rates, system capacity, and reduced latency and power consumption, they have shifted towards higher frequency bands such as Millimeter Wave (mmWave) and Terahertz spectrums. However, these spectrums pose challenges in terms of the quality of the communication link, including large path-loss and limited coverage, as well as difficulties in system and antenna design. Reconfigurable Intelligent Surfaces (RISs) have recently been proposed as a promising low-cost and low-power consumption solution to enhance the performance of wireless communication systems. However, beamforming with RISs can be difficult, especially in the presence of beam widening requirements, which aim to produce wide beams for cell or sectorwide broadcasting, among other applications. In this paper, a new approach for beam widening in RIS-assisted communications using genetic algorithms is proposed. The focus is on using phaseonly tapering to achieve wide beams while minimizing sidelobes (SSL) and beam ripple. To address this problem, two cost functions are developed and optimized using genetic algorithms. The optimization results in a codebook of 1-bit phase patterns with varying beamwidths, making it possible to widen the beams without requiring extra controllers or specific element designs. The proposed approach is evaluated through simulation results, which demonstrate its effectiveness in achieving wide beams while maintaining a low level of sidelobes and beam ripple.

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