Robust Downlink Transmission for 6G LEO-MIMO Satellite Systems

Abstract

In this paper, we investigate downlink transmission schemes robust to the Doppler frequency offset (DFO) induced by high mobility for low earth orbit multiple-input and multiple-output satellite communication systems. Considering the impact of DFO, we derive the closed-form expressions for the downlink achievable rates with maximum ratio transmission (MRT) and maximum average signal-to-leakage-plus-noise ratio (MASLNR) precoding. Numerical results show that the derived closed-form expressions are accurate and the DFO severely affects system performance. In order to relieve the impact of DFO, we propose an adaptive DFO compensation algorithm based on the precompensation design and beam alignment. Numerical results verify the effectiveness of the proposed DFO compensation algorithm.