Capacity Comparison of Beam Coverage Modes in ZF Satellite MIMO Downlink With LOS Channels

This article investigates a multiuser satellite multiple-input–multiple-output (MIMO) downlink comprising a multibeam satellite and multiple terrestrial users. To investigate the impact of beam coverage on system capacity in satellite MIMO systems, two beam coverage modes, overlapping coverage and hexagonal coverage, are considered and their capacity performance is analyzed and compared thoroughly. Given identical coverage area and an equal number of beams, the half-power beamwidth and peak gain for each coverage mode are first derived, and the channel matrices are obtained. On this basis, the capacity performance of two beam coverage modes is analyzed and compared in the single-user scenario, dual-user scenario, and multiuser scenario analytically or numerically. The results indicate that hexagonal coverage generally outperforms overlapping coverage because of its higher beam gain; however, overlapping coverage demonstrates better performance in scenarios with highly concentrated user distributions because its multiple beams are larger and completely coincident, compensating for its smaller beam gain. The conclusions provide a reference for the arrangement of multiple beams in the satellite MIMO systems.