Joint Beamforming Optimization for STAR-RIS Aided NOMA ISAC Systems

In this letter, we investigate the simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided non-orthogonal multiple access (NOMA) integrated sensing and communication (ISAC) systems. To suit the desired sensing beampattern, we formulate a matching error minimization problem by jointly optimizing the base station active beamforming, STAR-RIS passive beamforming, power allocation factors and time allocation variables, while meeting the requirement for minimum communication rate. It is non-trivial to solve the formulated optimization problem directly. Accordingly, we develop an alternative optimization algorithm by dividing the original problem into three subproblems, and each subproblem is solved based on the successive convex approximation and semidefinite relaxation techniques. The final solutions are obtained by alternatively optimizing three subproblems until convergence. In the end, simulation results demonstrate the validity of the proposed scheme.