Performance Analysis of the STAR-RIS-Assisted Downlink NOMA Communication System With MRC

We discuss a simultaneously transmitting and reflecting-reconfigurable intelligent surface (STAR-RIS)-assisted downlink non-orthogonal multiple access (NOMA) communication system. STAR-RIS employs the energy splitting protocol for transmitting and reflecting the incident signals to users located on different sides of the surface. To study the impact of multiple antennas on the system performance, we perform maximum ratio combining (MRC) at NOMA users and beamforming towards STAR-RIS at the base station (BS). We model the distribution of cascaded Rician fading channels for the proposed system. Closed-form expressions of outage probability, asymptotic outage probability, and system throughput are derived. All theoretically derived results are verified via Monte Carlo simulation.