Tomlinson-Harashima Precoded MIMO in wireless networks: to THP or not to THP?

We investigate a wireless network architecture that utilizes Tomlinson Harashima Precoded Multiple Input Multiple Output (THP MIMO) technique for improved system capacity. We consider THP MIMO in a multi user scenario, together with a proposed smart scheduling technique and we explore the capacity performance through extensive capacity analysis considering varying SNR levels, varying number of users and number of transmit/receive antennas, under fading and shadowing, also considering errors in channel state information (CSI). We also evaluate the complexity of THP MIMO and present a low-complexity scheduling algorithm that employs Gram-Schmidt algorithm for incremental implementation of THP’s QR factorization. In the end, we identify the network and channel conditions under which THP MIMO can be preferred over classical conventional MIMO, and we conclude that for practical transceivers with up to four antennas, THP MIMO can provide significant capacity enhancement over conventional MIMO at lower complexity, performing slightly below the sum rate capacity bound. Another important advantage that is observed in this study is better immunity of THP MIMO to CSI errors, as compared to conventional MIMO.