Robust Hybrid Beamforming Design for RSMA-assisted Multicast Multi-Beam LEO Systems

Hybrid beamforming (HBF) offers significant advantages for massive multiple-input multiple-output (mMIMO) multi-beam low earth orbit (LEO) satellite systems, due to its ability to reduce hardware complexity and increase spectral efficiency. However, in practical multi-beam LEO systems, angle errors and imperfect channel state information at the transmitter (CSIT) present major challenges for traditional HBF techniques, which assume perfect channel characteristics. To address these challenges, a robust HBF method designed for multi-beam LEO systems is introduced, integrating wide beam (WB)-based analog beamformer with a digital precoder assisted by rate-splitting multiple access (RSMA). Furthermore, to solve the digital precoding problem, we employ a semi-definite programming (SDP) method augmented with penalty functions to transform the original non-convex problem into a convex one and solve it iteratively. Finally, simulation results demonstrate that the proposed HBF method can significantly enhance ergodic sum rate, outperforming traditional HBF methods in terms of rate performance.