Joint Optimization for ASTARS aided Satellite Communication Networks

Satellite communication is a crucial component for achieving global communications in sixth generation (6G). Due to the large distance between the satellite and the terrestrial users, the multiplicative fading effects of traditional passive simultaneous transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) are more severe in satellite communication. Motivated by the active simultaneous transmitting and reflecting surfaces (ASTARSs), a novel ASTARS-aided non-orthogonal multiple access (NOMA) satellite communication network is proposed in this paper. We propose a dynamic NOMA pairing strategy that allows the satellite to flexibly select pairing schemes. Then, we formulate an optimization problem to maximize the channel capacity. A two-layer optimization algorithm is proposed, where the outer layer selects the NOMA user pairing schemes, while the inner layer alternately optimizes the NOMA power allocation factors, the satellite precoding matrix and the ASTARS phase shift matrices. To solve the non-convex optimization problem, successive convex approximation and penalty-based method are employed.