Selective Multi-User Cooperative Rate Splitting Assisted by Reconfigurable Intelligent Surface

Rate splitting multiple access (RSMA) has emerged as a powerful multiple access technique for wireless communications. In this paper, RSMA is integrated with cooperative relaying and reconfigurable intelligent surfaces (RIS) to enhance the spectral efficiency of multi-user communication. We propose a selective approach that chose some users to decode the common stream using successive interference cancellation (SIC) and treat the private streams as noise. While the other users do not decode the common stream, they treat it as noise. The selection is based on the condition of the users' channel. The user with the worst channel condition is selected to treat the common stream as noise. The performance of the proposed system is measured in terms of Max-Min rate of the users. Alternative optimization (AO) is used to jointly optimize the time slot allocation, precoding matrix, common rate allocation, and phase shifts of RIS in the direct and cooperative phase iteratively. Numerical results show that the proposed selective cooperative rate splitting assisted by RIS (CRS-RIS) improves significantly the Max-Min rate when compared with other existing systems.