Coverage Characterization of STAR-RIS Networks: NOMA and OMA

TL;DR

This paper investigates the coverage capabilities of STAR-RIS aided two-user networks, optimizing resource allocation for NOMA and OMA to significantly extend coverage compared to traditional RISs.

Contribution

It introduces a joint optimization framework for resource allocation and STAR-RIS coefficients for NOMA and OMA, providing optimal solutions and demonstrating coverage improvements.

Findings

STAR-RIS significantly extends coverage compared to conventional RIS.

Optimal resource allocation solutions are derived for both NOMA and OMA.

The proposed methods achieve convex optimization problems with efficient solutions.

Abstract

The novel concept of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) is investigated, where incident signals can be transmitted and reflected to users located at different sides of the surface. In particular, the fundamental coverage range of STAR-RIS aided two-user communication networks is studied. A sum coverage range maximization problem is formulated for both non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA), where the resource allocation at the access point and the transmission and reflection coefficients at the STAR-RIS are jointly optimized to satisfy the communication requirements of users. For NOMA, we transform the non-convex decoding order constraint into a linear constraint and the resulting problem is convex, which can be optimally solved. For OMA, we first show that the optimization problem for given time/frequency resource allocation is convex. Then, we employ the one dimensional search-based algorithm to obtain the optimal solution. Numerical results reveal that the coverage can be significantly extended by the STAR-RIS compared with conventional RISs.