Secure Satellite Transmission With Active Reconfigurable Intelligent Surface

The long distance characteristic of satellite transmission makes it difficult to achieve secure communication due to the highly correlated channels. This letter investigates secure satellite multicast transmission in the presence of an eavesdropper (Eve), where the direct links from the satellite to its users and Eve are blocked by obstacles, and an active reconfigurable intelligent surface (RIS) is adopted to rebuild the satellite downlinks and eliminate the “double fading” effect. By assuming imperfect wiretap channel state information is available, our objective is to maximize the minimal secrecy energy efficiency while guaranteeing the transmit power budgets at the satellite and RIS. In order to solve the above intractable optimization problem, an alternating optimization scheme is proposed, where the successive convex approximation method and Nemirovski Lemma are utilized to obtain the beamforming weight vectors with a fixed reflective factor while the optimization of the reflective factor is solved using the S-Lemma with fixed beamforming weight vectors, iteratively. Finally, our simulation results demonstrate that the proposed scheme outperforms the existing benchmark schemes.