Secure Communication Based on Reconfigurable Intelligent Surface in Satellite Communications with Similar Channels

In this paper, we investigate physical layer security (PLS) for terrestrial RIS-assisted multibeam satellite commu-nications with similar channels. Deploying the reconfigurable intelligent surface (RIS) in each beam, and we use inter-beam in-terference and the channel variability from the RIS to the satellite user and eavesdroppers to enhance satellite security. Specifically, considering the constraints of the secrecy rate, we formulate a problem to minimize the total power by jointly optimizing the satellite beamforming and the RIS beamforming. To solve the problem, the original problem is decoupled into two non-convex optimization sub-problems, i.e., the active and the passive beamforming optimization problem. Then, semidefinite relax-ation (SDR) is used to solve the active beamforming optimization problem. The maximum ratio transmission-based beamforming and SDR are employed separately to solve passive beamforming optimization problem in each beam. The alternating optimization (AO) is utilized to solve the original problem and the convergence is proven. We have carried out simulations to evaluate the effectiveness of our proposed approach, the results show that the proposed algorithms have superior system performance.