Joint Beamforming Design for Reconfigurable Intelligent Surface-Assisted LEO Satellite Constellation Communication

Abstract

Low earth orbit (LEO) satellite constellation, as a typical non-terrestrial network (NTN), can provide ubiquitous connectivity for 6G wireless networks with low transmission delay. However, satellite communications (SATCOM) are still hampered by challenges such as scarcity of spectrum resources and significant path losses. In this paper, reconfigurable intelligent surfaces (RIS) are deployed to enhance the performance of long-distance satellite-terrestrial communication. Further, by exploring inter-satellite links, a joint active beamforming at satellites and passive beamforming at RIS design algorithm is proposed to improve the weighted sum rate (WSR) of satellite-terrestrial communication in the presence of inter-satellite interference due to spectrum sharing. Specifically, we adopt alternating optimization (AO) method to split the original problem into two sub-problems and then solve them step by step. Firstly, given passive beamforming at RIS, we solve the active beamforming design problem with a closed-form solution. Secondly, given the active beamforming, we design passive beamforming for RIS through the alternating direction method of the multipliers. Theoretical analysis and extensive numerical simulations demonstrate the effectiveness of our proposed algorithm in RIS-assisted LEO satellite constellation communications.