Joint Phase Shift and Receive Combiner Design for RIS-Based Satellite Communications

Recent studies on a reconfigurable intelligent surface (RIS)-assisted satellite–aerial–terrestrial integrated network have been focused on improving the received signal quality of the terrestrial user (TU) by adjusting the phase of the incident signal at the RIS. The phase adjustment function of the RIS may, on the contrary, amplify the intersatellite interference (ISI) signal to degrade the entire system's performance. Therefore, we jointly investigate an optimal phase control at the RIS and an optimal receive combining at the TU to maximize the TU's received signal-to-interference-plus-noise ratio (SINR). Utilizing the generalized eigenvectors to maximize the SINR, the iterative joint beamforming algorithm (IJBA) is proposed to determine optimal passive beamforming and receive combining vectors. In addition, we have proven that there is always convergence in the IJBA. To reduce the computational complexity caused by the iterative search in the IJBA, the noniterative joint beamforming algorithm is proposed while guaranteeing the performance of the IJBA for a sufficient number of passive reflecting elements. Simulation results demonstrate that the proposed algorithms effectively alleviate the ISI and maximize the TU's received SINR.