Secure Multicast Communications via RIS Against Eavesdropping and Jamming With Imperfect CSI

Eavesdropping and jamming pose great threats to the security of wireless communication. In this paper, a secure multicast communication system of transmitting different messages to a group of users based on reconfigurable intelligent surfaces (RIS) is considered, in the presence of both a jammer and an eavesdropper whose channel state information (CSI) is not perfectly known. Specifically, we aim to maximize secrecy rate of the multicast system by jointly optimizing the beamforming at base station and the phase shift at RIS. To solve the non-convexity optimization problem, we first introduce slack variables to equivalently transform the problem. Then, an alternative algorithm consisting of two subproblems is designed to deal with the joint optimization problem. Besides, general sign-definiteness transformation is tailored to address the CSI uncertainty and successive convex approximation methods are proposed to transform non-convex constraints. Finally, simulation results demonstrate the effectiveness of the proposed scheme compared with existing approaches, and reveal the impact of key parameters on the security performance.