Energy Efficient Design for SIM-NOMA-Enabled Satellite Beam-Hopping System

Conventional satellite beam-hopping (BH) systems rely on phased-array antennas for multiple-input multiple-output (MIMO) beamforming, requiring numerous high-power radio frequency (RF) chains that degrade energy efficiency (EE). To address this, this paper employs stacked intelligent metasurfaces (SIM) to enable a non-orthogonal multiple access (NOMA) based low-Earth-orbit (LEO) satellite BH network. SIM can facilitate electromagnetic wave-domain beamforming, eliminating energy-intensive high-resolution digital-to-analog converters-based digital beamforming. We formulate a joint optimization problem to maximize system EE by designing wave-based beamforming at SIM and NOMA user power allocation, subject to transmit power constraints and user quality-of-service (QoS) requirements. The nonlinear variables and fractional formulation induce non-convexity in this problem, and an alternating quadratic transform-central gradient algorithm is proposed as the solution to this challenge. Simulation results demonstrate that: 1) Our proposed algorithm can achieve convergence under various SIM configurations; 2) Compared to conventional MIMO beamforming schemes, the proposed SIM-NOMA scheme achieves higher system EE with the minimum number of antennas. Even when the number of antennas in the MIMO system is increased threefold, SIM-NOMA still maintains a significant performance advantage.