Multiple reconfigurable intelligent surfaces assisted downlink NOMA system

Paper has considered multiple reconfigurable intelligent surfaces (RISs) assisted downlink non-orthogonal multiple accesses (NOMA) system, referred to as MR-NOMA. Multiple RISs create a line-of-sight (LOS) channel between BS and users to improve network coverage, especially in high frequencies and severe path attenuation scenarios. In MR-NOMA, all RISs are in series and activated simultaneously; therefore, multiplicative beamforming gain from the inter-RIS channels is achieved. Bit error probability (BEP) under the Rician fading channel is derived and compared with simulation results. It is observed that BEP performance depends on the number of passive reflecting elements, Rician factor, and positions of RISs panels in the MR-NOMA.