Massive MIMO Downlink Transmission for LEO Satellite Communications

We investigate the downlink (DL) transmit strategy
for massive multiple-input multiple-output (MIMO) low-earthorbit
(LEO) satellite communication (SATCOM) systems, in which
only the slow-varying statistical channel state information is
known at the transmitter side. First, we establish the massive
MIMO LEO satellite channel model, in which the uniform planar
arrays are deployed at both the satellite and user terminals (UTs).
Building on the rank-one property of satellite channel matrices, we
show that transmitting a single data stream to each UT is optimal
for the ergodic sum rate maximization. This result is of great
importance for massive MIMO LEO SATCOM systems, since
the sophisticated design of transmit covariance matrices is turned
into that of precoding vectors, with no loss of optimality at all.
Furthermore, we conceive an algorithm to compute the precoding
vectors. Simulation results show the significant performance gains
of the proposed approaches over the previous schemes.