RIS-Assisted Energy-Efficient LEO Satellite Communications with NOMA

TL;DR

This paper introduces an energy-efficient RIS-assisted NOMA communication framework for LEO satellite networks, optimizing power and beamforming to significantly improve energy efficiency over benchmarks.

Contribution

It presents a novel joint optimization approach for power and passive beamforming in RIS-assisted LEO satellite NOMA systems, addressing non-convex challenges.

Findings

Achieves 21.47% higher energy efficiency than benchmark.

Achieves 54.9% higher energy efficiency than conventional NOMA.

Provides an effective alternating optimization solution for complex joint problems.

Abstract

This paper proposes an energy-efficient RIS-assisted downlink NOMA communication for LEO satellite networks. The proposed framework simultaneously optimizes the transmit power of ground terminals of the LEO satellite and the passive beamforming of RIS while ensuring the quality of services. Due to the nature of the considered system and optimization variables, the energy efficiency maximization problem is non-convex. In practice, obtaining the optimal solution for such problems is very challenging. Therefore, we adopt alternating optimization methods to handle the joint optimization in two steps. In step 1, for any given phase shift vector, we calculate satellite transmit power towards each ground terminal using the Lagrangian dual method. Then, in step 2, given the transmit power, we design passive beamforming for RIS by solving the semi-definite programming. We also compare our solution with a benchmark framework having a fixed phase shift design and a conventional NOMA framework without involving RIS. Numerical results show that the proposed optimization framework achieves 21.47\% and 54.9\% higher energy efficiency compared to the benchmark and conventional frameworks.