A Comparison of Precoding Techniques for The Dual Polarised Land Mobile Satellite Channel

The dual polarised MIMO land mobile satellite channel offers spatial multiplexing gain for mobile broadcasting systems. Antenna diversity in satellite systems is difficult to obtain, due to the nature of the satellite channel and the absence of scatterers in the vicinity of the satellite transmitter; therefore dual polarisation offers a potential solution in achieving diversity. Receiver based equalisation has been explored for the LMS channel to date; this paper aims to explore the potential of transmitter based equalisation by investigating existing precoders and their performance in the dual polarised MIMO LMS channel. The case of a single-user is considered in which interference arises from cross-polarisation effects caused by propagation between two orthogonally circularly polarised transmit and receive antennas. To mitigate the effects of interference on the performance of the channel, precoding algorithms are implemented on the data to be transmitted whilst assuming channel state information at the transmitter is available. Linear precoding techniques, i.e. channel inversion, regularised channel inversion, selective channel inversion & correlation rotation, in addition to the nonlinear precoding technique, Tomlinson-Harashima Precoding, are implemented and the error performance is investigated in three user environments; open rural, suburban and urban. The effects of the power loss and the increased dynamic range of the signal associated with each precoder are explored. The precoding analysis has been conducted using channel measurements recently obtained during the MIMOSA campaign conducted by the European Space Agency (ESA).