Secure Communications Based on RIS in Multi-User RSMA Systems

This paper considers a rate-splitting multiple access (RSMA) system and employs reconfigurable intelligent surfaces (RIS) to enhance the physical layer security. Specifically, a multi-user communication system consists of a multi-antenna base station, multiple legitimate users and an eavesdropper. The worst-case secrecy rate maximization is formulated as a non-convex problem by jointly optimizing the RIS phase shift vector, the beamforming vectors of common stream and private streams. To cope with the non-convex problem, an alternative optimization algorithm including two subproblems is proposed. Besides, several kinds of successive convex approximation methods are used to transform the constraints into a processable form. Finally, the simulation results verify that the proposed RSMA scheme outperforms the state-of-the-art schemes.