Reconfigurable Intelligent Surface (RIS) Aided Multi-User Networks: Interplay Between NOMA and RIS

TL;DR

This paper investigates how reconfigurable intelligent surfaces (RIS) can enhance multi-user networks employing NOMA and OMA, analyzing static and dynamic configurations, deployment strategies, and proposing joint beamforming designs for RIS-aided NOMA systems.

Contribution

It characterizes the capacity region of RIS-aided single-antenna NOMA networks, compares static and dynamic RIS configurations, and introduces novel joint beamforming strategies for multi-antenna NOMA with RIS.

Findings

Dynamic RIS configuration is capacity-achieving.

Asymmetric RIS deployment favors NOMA, symmetric favors OMA.

Proposed joint beamforming strategies improve NOMA performance.

Abstract

This article focuses on the exploitation of reconfigurable intelligent surfaces (RISs) in multi-user networks employing orthogonal multiple access (OMA) or non-orthogonal multiple access (NOMA), with an emphasis on investigating the interplay between NOMA and RIS. Depending on whether the RIS reflection coefficients can be adjusted only once or multiple times during one transmission, we distinguish between static and dynamic RIS configurations. In particular, the capacity region of RIS aided single-antenna NOMA networks is characterized and compared with the OMA rate region from an information-theoretic perspective, revealing that the dynamic RIS configuration is capacity-achieving. Then, the impact of the RIS deployment location on the performance of different multiple access schemes is investigated, which reveals that asymmetric and symmetric deployment strategies are preferable for NOMA and OMA, respectively. Furthermore, for RIS aided multiple-antenna NOMA networks, three novel joint active and passive beamformer designs are proposed based on both beamformer based and cluster based strategies. Finally, open research problems for RIS-NOMA networks are highlighted.