Performance of an SC-FDE SATCOM System in Block-Time-Invariant Orthogonal MIMO Channels

A multiple-input multiple-output (MIMO) satellite communications system for fixed-satellite services (FSS) is considered. The MIMO Line-of-Sight (LOS) satellite channel is optimized to achieve maximum spectral efficiency. This requires an orthogonal MIMO channel matrix, ending up with large antenna spacing of the ground terminal antennas. As the main drawback, considerable propagation delays between the MIMO paths are observed, and the MIMO signal sub-streams interfere asynchronously in the order of several tens or hundreds of a symbol duration at the receiver. To cope with these delays, we propose a system architecture that uses a sufficiently large guard-interval or cyclic prefix between successive data blocks. The delay equalization at the receiver is then performed by a zero-forcing frequency domain equalizer for single-carrier transmission (SC-FDE). Thanks to the orthogonality of the considered MIMO channel, the SC-FDE architecture achieves even perfect spatial equalization of the multiplexed signal streams at considerably low implementation effort. The capacity reduction caused by the guard-interval is, moreover, mitigated by long data blocks, which can be used because of the long channel coherence times in FSS applications. The system concept reveals superior BER and transinformation performance, which is verified through fair comparison with current single-input single-output (SISO) systems. If the channel orthogonality is violated through narrow antenna spacing, the system performance degrades dramatically.