RIS-Enhanced LEO Satellite Communication: Joint Passive Beamforming and Orientation Optimization

• Published in: 2022 IEEE Globecom Workshops (GC Wkshps) pp. 874 - 879
• Main Authors: Zheng, Ziyuan, Jing, Wenpeng, Lu, Zhaoming, Wen, Xiangming
• Format: Conference Proceeding
• Language: English
• Published: IEEE 04.12.2022
• Subjects: Array signal processing; Downlink; Low Earth Orbit; Low earth orbit satellites; Performance gain; reconfigurable intelligent surface; RIS-assisted communication; Satellite communication; Satellites; Simulation; Throughput
• DOI: 10.1109/GCWkshps56602.2022.10008708

Low Earth orbit (LEO) satellite communication (SatCom) systems have emerged as a key enabler to provide ubiquitous connectivity in the upcoming generation networks. Yet the conflict between power-limited link budget and long-distance path loss restricts the universal application of LEO SatCom. Fortunately, the reconfigurable intelligent surface (RIS) technique can be an efficient solution to address this issue. In this paper, we incorporate a RIS into the LEO SatCom system to enhance its downlink transmission by introducing a controllable reflection link. A joint RIS passive beamforming and orientation optimization problem is formulated to maximize average throughput at the ground terminal (GT) during the service. The formulated non-convex problem has the unit-modulus constraint on the phase shifters and the piecewise RIS radiation coefficient function related to the predictable satellite trajectory. A two-stage optimization framework is proposed to equivalently solve two sequential subproblems. Specifically, for the passive beamforming subproblem, a closed-form solution is derived at first in compliance with the phase alignment principle. Then, an iterative algorithm is proposed to approximately solve the orientation optimization subproblem. Simulation results show the substantial performance gains on link budget and throughput achieved by the proposed RIS-assisted LEO SatCom scheme.