Joint Optimization of Multi-STAR-RIS aided NOMA Systems

Abstract

The multiple simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) aided non-orthogonal multiple access (NOMA) systems was studied in this paper, where the STAR-RISs employ the energy splitting (ES) protocol. To maximize the sum-rate of users, we formulate the optimization problem, and the beamforming vectors of multi-STAR-RIS and power allocation for each user were jointly optimized. To efficiently solve the problem, the problem was decomposed into two subproblems, and then we alternately solve the two subproblems. Simulation results illustrate that when multiple STAR-RISs are deployed, the sum rate increases with STAR-RIS's number. Moreover, the application of multiple ES STAR-RISs in NOMA can further increase the sum rate compared to the conventional RIS.