Equalization performance under clock frequency errors among Rx antennas for LEO-MIMO communications

This paper describes multiple-input multiple-output (MIMO) techniques for downlink transmission of low Earth orbit (LEO) satellites equipped with multiple antennas, called LEO-MIMOs, to increase the capacity of LEO satellite systems [1]. The LEO-MIMO communications system performs spatial multiplexing transmissions from LEO satellites with multiple antennas to a base station (BS) connected with multiple remote antennas. In LEO-MIMO communications, the clock supply sources of BS multiple antennas are assumed to be independent due to remote placement. In this case, if there are large amounts of clock frequency errors among remote antennas, MIMO equalization performances are degraded. This paper presents the LEO-MIMO equalization performance using not only zero forcing (ZF) but also the minimum mean square error (MMSE) algorithm while undergoing different channel correlations and independent sampling of frequency errors. Computer simulations revealed that MMSE could better mitigate noise components caused by asynchronous sample timing among multiple receiving antennas.