Ergodic Rate Analysis of STAR-RIS Aided NOMA Systems

TL;DR

This paper derives closed-form expressions for ergodic rates in STAR-RIS aided NOMA systems, showing that these systems outperform conventional RIS in terms of rate performance, especially at high SNRs.

Contribution

It provides the first analytical ergodic rate expressions for STAR-RIS aided NOMA systems, highlighting their advantages over conventional RIS systems.

Findings

Ergodic rates increase with the number of STAR-RIS elements.

High SNR slopes are constant for cell-edge users.

STAR-RIS aided NOMA outperforms conventional RIS aided NOMA.

Abstract

This letter analyzes the ergodic rates of a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided non-orthogonal multiple access (NOMA) system, where the direct links from the base station to cell-edge users are non-line-of-sight due to obstacles, and STAR-RIS is used to provide line-of-sight links to these cell-edge users. By fitting the distribution of the composite channel power gain to a gamma distribution, we derive the closed-form expressions of ergodic rates and high signal-to-noise ratio (SNR) slopes for cell-edge users. Numerical results reveal that 1) the ergodic rates increase with the number of STAR-RIS elements, and the high SNR slopes are fixed as constants; 2) STAR-RIS aided NOMA systems achieve higher ergodic rates than conventional RIS aided NOMA systems.