Joint Secure Beamforming for RIS-Aided Integrated Multibeam-Satellite Terrestrial Networks

This paper focuses on a reconfigurable intelligent surface (RIS) enabled integrated multibeam-satellite terrestrial network, which consists of a satellite, a base station (BS), an RIS, multiple earth stations (ESs), an eavesdropper (Eve) and a terrestrial user (TU). In such a network, the satellite provides broadband services to multiple ESs, while the BS transmits friendly interference to the Eve for crippling confidential information interception with the help of the RIS. To enhance the security performance, we provide a theoretical modelling secrecy rate (SR) and formulate the SR maximization problem subject to the signal-to-interference-plus-noise ratio (SINR) requirements, the total transmit power limit and the RIS unitmodulus constraints. By combining approaches like alternative optimization (AO), bisection search, semi-definite programming (SDP), eigenvalue decomposition, and Gaussian randomization, we then propose a joint secure beamforming scheme to solve the non-convex optimization problem and thus identify the optimal beamforming designs for the satellite, the BS, and the RIS. Simulation results indicate the effectiveness of security enhancement via the proposed joint secure beamforming scheme.