Robust Beamforming and Rate Optimization for RIS-Aided Symbiotic Radio Systems With RSMA

In this letter, we propose a robust beamforming and rate optimization algorithm to improve spectral efficiency and transmission robustness by applying rate-splitting multiple access (RSMA) in reconfigurable intelligent surface (RIS)-aided symbiotic radio systems. Specifically, RSMA is used to serve all primary receivers on the same spectrum resource. Then, we formulate an optimization problem to minimize the total transmit power via the phase shift matrix of RIS, the beamforming vector of the base station, and the common rate parameter. To deal with this non-convex problem, we present an iteration-based optimization algorithm based on successive convex approximation and the alternating optimization method. Simulation results demonstrate that the proposed algorithm has 17.2% reduction in transmission power and 6.58% increase in the common rate compared to the other algorithms.