Impact of receiver structure and timing offset on MIMO spatial multiplexing

Multiple antenna enhancements via symbol timing relative offsets (MAESTRO) was recently introduced as a scheme to improve the performance of a V-BLAST like multi-antenna system by introducing sub-symbol timing offsets between the transmit antennas. In this paper we address the role of receiver structure on performance and investigate the optimal choice of the time offset parameter. A similar timing offset V-BLAST scheme was also introduced by Shao et al., where the authors use a zero-forcing (ZF) receiver and conclude the system outperforms V-BLAST only for small block sizes. We show that the zero-forcing (ZF) receiver suggested by Shao et al. is deficient and is the main reason for some of the drawbacks observed by them. The optimal ZF receiver is derived, and along with the linear MMSE receiver, is shown to exhibit no such weaknesses. The problem of optimal offset is also examined and the optimal offset for a 2 times 2 MIMO system derived.