RIS-Aided LEO SatCom with LEO-GEO Inter-System Interference Mitigation: Joint Multi-Satellite Multi-RIS Beamforming

The growing interest in deploying satellite communication (SatCom) systems results in a proliferation of both Geostationary Earth Orbit (GEO) and Low Earth Orbit (LEO) satellites, leading to the risk of inter-system interference between GEO and LEO systems, which can result in degraded communication performance or even complete system failure. Under this context, this paper investigates Reconfigurable Intelligent Surface (RIS)-aided LEO SatCom with LEO-GEO inter-system interference mitigation. Specifically, multiple satellites and multiple RISs are operated in a cooperative manner with properly designed joint beamforming. We formulate a minimum signal-to-interference-plus-noise (SINR) maximization problem exploiting statistical channel state information (CSI), subject to LEO-GEO interference mitigation constraint. We propose an alternating optimization (AO)-based algorithm, combined with quadratic transform and manifold optimization techniques, to design the cooperative multi-satellite multi-RIS beamforming iteratively. Numerical results show that the proposed scheme ensures the mitigation of LEO-GEO interference while effectively improving the performance of LEO SatCom.