Robust Beamforming for Enhancing User Fairness in Multibeam Satellite Systems With NOMA

This paper proposes a downlink transmission scheme exploiting robust beamforming in conjunction with non-orthogonal multiple access for multibeam satellite systems to enhance the spectral efficiency and user fairness. Specifically, by employing the imperfect channel state information and considering the fairness among multiple satellite terminals (STs), we first formulate an optimization problem to maximize the sum $\alpha$-fair utility, while guaranteeing the transmit power budget and quality-of-service requirement of each ST. Since the original problem is nonconvex, we then adopt a discretization method to convert the channel uncertainty into deterministic forms, and propose an iterative penalty function algorithm combined with sequential convex approximation to obtain the optimal solution. Finally, simulation results are given to confirm the effectiveness and superiority of the proposed scheme over some existing works. It is also shown that our scheme can achieve a good balance between the system performance and user fairness.