Performance Analysis of Distributed Reconfigurable Intelligent Surface Aided NOMA Systems

This paper investigates the performance of spatially distributed reconfigurable intelligent surface (RIS)-aided non-orthogonal multiple access (NOMA) systems over Rician fading channels, where the spatial locations of multiple RISs are modeled by invoking the stochastic geometry. Accurate and asymptotic closed-form expressions in terms of the outage probability and ergodic rate are derived based on an optimal selection scheme. Accordingly, diversity orders are obtained to gain more insights on the considered network. It is revealed by simulations that the outage behaviour of distributed RIS-NOMA system outperforms that of RIS-aided orthogonal multiple access (OMA) and conventional multiple relays-aided NOMA counterparts, and the ergodic rate of distributed RIS-NOMA is superior to that of distributed RIS-OMA in the low signal-to-noise ratio region. Additionally, the performance enhancements through more densely deployed of RISs and/or more reflecting elements of RIS as well as the increased Rician factors are corroborated by the simulations.