Joint Beamforming and Rate Splitting Design for RIS Assisted RSMA Systems

Rate splitting multiple access (RSMA) is a promising technology for enabling massive connectivity and improving spectral efficiency in future wireless networks. Nevertheless, the randomness of the wireless environment can degrade the performance of the RSMA system. Reconfigurable intelligent surface (RIS) can intelligently regulate the channel to expand the network coverage and enhance the throughput of RSMA system. In this paper, we consider an RIS-aided RSMA communication system, where the users are divided into central users (CUs) and edge users (EUs). CUs and EUs are matched into separate groups to share the specific resource blocks. We aim to maximize the sum rate of EUs by jointly optimizing the active beamforming at the base station (BS), the passive beamforming at the RISs, and the rate splitting factors for each user, subject to the constraints on the users’ minimum rate and the total transmit power. To solve the formulated highly non-convex problem, we decouple the original problem into two subproblems and propose an alternating algorithm. Simulation results show that the proposed scheme can increase the sum rate of EUs by 16%-40% compared to conventional baseline methods.