BD-QRD, block thp and constrained sphere decoding for multi-user MIMO systems

This paper presents a multi-user MIMO transceiver design with a block-based decomposition and precoding scheme. To exploit spatial diversity, we propose to use block-diagonal QR decomposition (BD- QRD) to decompose the channel matrix. To eliminate multiple access interference (MAI), block- Tomlinson-Harashima precoding (B-THP) is further proposed to be combined with BD-QRD so that the equivalent channel matrix after precoding at the transmitter becomes a block diagonal matrix. On the other hand, the block-based sorting is adopted to balance the energy spread among all spatial pipes for BD-QRD and thus the performance can be further enhanced. With these decomposition and precoding techniques at the transmitter, the sphere decoding (SD) techniques can be employed at the receiver with a small revision to constrain the search space. We show that the proposed BD-QRD, B-THP, and constrained SD for multi-user MIMO systems retaining the spatial diversity, outperform the conventional QRD-THP and BD-SVD in the interested SNR region.