Multi-STAR-RIS-Assisted NOMA Networks: Optimal Design and Performance Analysis

Abstract

This letter presents an optimization-oriented performance analysis of non-orthogonal multiple access (NOMA) networks assisted by multiple simultaneously transmitting and reflecting reconfigurable intelligent surfaces (multi-STAR-RIS). Under imperfect successive interference cancellation (ipSIC), approximate analytical expressions for the outage probability (OP) and ergodic rate are derived. Building upon these results, we reformulate the OP into a convex form, thereby establishing a unified framework for both performance analysis and system optimization. Numerical results demonstrate that multi-STAR-RIS deployment not only compensates for the absence of a direct link but also significantly enhances the outage performance and ergodic rate. Notably, the proposed convex reformulation is validated in two ways: the analytical curves align closely with Monte Carlo simulations, and the convex-optimized solution achieves the global optimum of the reformulated problem.