Downlink Transmit Design for Massive MIMO LEO Satellite Communications

This paper investigates the downlink (DL) transmit design for massive multiple-input multiple-output (MIMO) low-earth-orbit (LEO) satellite communication systems, where only slow-varying statistical channel state information is exploited at transmitter. The model DL MIMO LEO system established, in which both and user terminals (UTs) are equipped with uniform planar arrays. Observing rank-one property of matrices, we show that single-stream precoding each UT optimal choice maximizes ergodic sum rate. favorable result simplifies complicated covariance matrices into vectors without any loss optimality. Then, an efficient algorithm devised to compute vectors. Furthermore, formulate approximate based on upper bound rate, optimality still holds. We that, this case, can be simplified scalar variables, effective developed. In addition, a low-complexity learning framework proposed optimizing variables. Simulation results demonstrate approaches achieve significant performance gains over existing schemes.