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.

I. Introduction

Satellite communication are poised to significantly broaden the scope of network connectivity and enhance communication efficiency, thereby occupying a pivotal role in the evolution towards 6G technology[1]. The expansive reach of satellite communication, which transcends geographical constraints, unfortunately, also makes satellite signals more susceptible to interception by unauthorized individuals. Moreover, the shared frequency spectrum between the satellite and terrestrial networks, while beneficial for increasing the system’s spectral efficiency, introduces significant co-frequency interference issues within the satellite-terrestrial communications (STC) [2], [3]. Consequently, the challenge of enhancing the security capabilities of STC presents itself as a critical area for exploration and research.