On the achievable capacity of RIS-NOMA networks: A perspective on elements number

Abstract

In this paper, a novel reconfigurable intelligent surface (RIS) assisted cooperative network with non-orthogonal multiple access (NOMA) is analyzed, considering the fairness of users. Specifically, the influence of RIS elements number to the system performance is studied, i.e., the power allocation of NOMA and sum-rate. Since the exact closed-form expression of the RIS elements number N is difficult to be obtained, we turn to study the equivalent sum-rates for our proposed two decoding methods at the high signal-to-noise ratio (SNR) region to analyze approximate solution of N, recalled this result as “equivalent point”. The simulation results show that, when N is less than the equivalent point, the sum-rate obtained by the first decoding method is greater. On the contrary, when N is greater than this equivalent point, the sum-rate obtained by the second decoding method is higher.