Ergodic Rate Analysis and Phase Design of STAR-RIS Aided NOMA With Statistical CSI

In this letter, we consider a simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided non-orthogonal multiple access (NOMA) downlink communication system. The base station (BS) is a uniform linear array (ULA) consisting of $M$ -elements. The expressions of the statistic of signal-to-interference-noise ratio (SINR) are derived with the statistical characteristics of the channels and they are maximized to design the phase shift matrices for reflection and transmission. Furthermore, the approximate analytical expressions of the ergodic rate are derived and the asymptotic performance is analyzed. It is found from the approximate analytical expressions that increasing the size of the ULA at BS and the STAR-RIS size can effectively improve the ergodic rate of the system. The simulation results validate the validity of the theoretical analysis and the design of the phase shift matrices.