Robust Secure Beamforming for Multiuser Satellite-Terrestrial Communications via Active RIS

This paper proposes a joint beamforming scheme that leverages the security and robustness of satellite-terrestrial communications, facilitated by an active reconfigurable intelligent surface (RIS). The aim is to improve the communication performance for terrestrial users in the secondary network without compromising the experience of the satellite users. Additionally, the study takes into account the effects of imperfect channel conditions, which is exacerbated by the amplifying capabilities of the active RIS. The primary objective is to minimize the transmission power from the BS, ensuring the secure transmission for the primary users and the communications quality for the cognitive user are both met. To address the non-convex nature of the cooperative beamforming problem, an effective alternating optimization strategy is devised. Ultimately, the simulation results highlight the active RIS’s potential for conserving power in satellite-terrestrial communications.