Reconfigurable Intelligent Surface Aided Multi-User Communications: State-of-the-Art Techniques and Open Issues

Munyaradzi Munochiveyi,Arjun Chakravarthi Pogaku,Miroslav Voznak,Dinh-Thuan Do,Nhan Duc Nguyen,Anh-Tu Le

doi:10.1109/access.2021.3107316

Abstract

Reconfigurable intelligent surface (RIS)-aided communication is considered as an exciting research topic in academic and industrial communities since it provides an emerging affordable solution to achieve high quality and secure next-generation wireless systems. Especially, the deployment of RIS in multi-user wireless networks promises to reduce system hardware costs, signal processing complexity, as well as energy consumption due to small size, lightweight and ability to actively shape the wireless propagation environment. Further, by realizing a cost-effective radio environment, RIS-aided communication can be implemented to be an appealing technology for future integration with other emerging wireless applications and communication systems. Despite the positive appeal, RISs face new challenges that hinder integrating efficiently into wireless networks, such as network secrecy performance and system sum-rates, as well as achieving efficient deployment design in highly dynamic and time-varying wireless environments. To this end, we overview recent state-of-the-art techniques to address the above issues faced in the integration of RISs with various emerging multi-user communication techniques, such as Unmanned Aerial Vehicles (UAVs), Non-Orthogonal Multiple Access (NOMA), Millimeter Wave (mmWave) and Terahertz (THz) communications, Physical Layer Security (PLS), massive antennas, and Simultaneous Wireless Information and Power Transfer (SWIPT). Finally, we highlight promising future research directions of RIS-aided communication in Cell-Free Massive Multiple-Input-Multiple-Output (MIMO) systems, Rate-Splitting Multiple Access (RSMA), Light Fidelity (LiFi), and Cognitive Radio (CR) systems.

Highlights

The authors attempted to solve this intractable problem by using classical combinatorial optimization techniques such as special ordered set of type 1 (SOS1) and the reformulationlinearization (RL) methods to handle the max-min Signal-toInterference-plus-Noise Ratio (SINR) design put in place by the optimization of Intelligent Reflecting Surface (IRS) discrete phase shift variables
This study considers lots of perspectives from physical characterization and channel modeling, to key results reported in recent studies, mainly
Optimization along with solution methods are introduced for RISaided wireless systems

Summary

INTRODUCTION

T HE idea of integrating reconfigurable intelligent surfaces (RISs), known as Intelligent Reflecting Surface (IRS), with various next-generation multi-user technologies is based on the principal idea of migrating beamforming usually executed at the radio front-end of base stations (BS), VOLUME 4, 2016. The authors studied the weighted sum-power optimization problem by jointly designing the transmit TPC matrices and IRS continuous phase shifts subject to individual receiver Quality-of-Service (QoS) constraints. In [28], the authors proved numerically that in RIS-aided cell-free networks, the joint design of the beamforming BS vector and the discrete RIS phase shifts maximizes the weighted sum-rate of users facing transmit power and RIS phase shift constraints. The authors in [46] considered a system model in which the UAV is installed with RIS assisted uplink wireless communication system and investigated the problem of maximizing the secure energy efficiency of RIS. The maximization problem is tackled by jointly optimizing the user association, transmit power, UAV’s trajectory and phase shift in continuous mode at both RIS and UAV. Simulation results showed that the secrecy performance rate was improved using the proposed system and the robustness

RIS-AIDED MMWAVE AND THZ COMMUNICATIONS

RIS-AIDED SWIPT

Findings

CONCLUSION