Analytical Characterization of Coverage Regions for STAR-RIS-Aided NOMA/OMA Communication Systems

We provide an analytical characterization of the coverage region of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided two-user downlink communication systems. The cases of orthogonal multiple access (OMA) and non-orthogonal multiple access (NOMA) are considered, under the energy-splitting (ES) protocol. Results confirm that the use of STAR-RISs is beneficial to extend the coverage region, and that the use of NOMA provides a better performance compared to the OMA counterpart. However, the effect of imperfect successive interference cancellation degrades the performance of NOMA and needs to be considered for a realistic analysis.