Robust Precoding for Massive MIMO Multi-Stream Multi-Satellite Systems

This paper investigates robust downlink precoding design for a massive multiple-input and multiple-output satellite (SAT) communication system. To break through the limitation of single data stream transmission per user terminal (UT) in most recently considered SAT communications, we first show that multi-stream transmission per UT requires SAT cooperation and equipping multiple antennas at the UT. To tackle such a complicated scenario, we employ the minimum mean square error (MSE) metric so that random matrix theory can be used to obtain a statistical MSE matrix for robust precoding design. Leveraging majorization theory, we provide a rigorous theoretical analysis of the optimal structure of the precoding matrix based on statistical MSE matrices. The analysis reveals an optimal precoding structure for a total power constraint case, while also indicating that such an optimal structure is not applicable to a more practical per-antenna constraint case. We then propose a heuristic per-antenna power constraint precoding design. Simulation results corroborate the effectiveness and robustness of the proposed design.