Combination of block diagonalization and THP transmit filtering for downlink beamforming in multi-user MIMO systems

In this paper we compare three spatial multiplexing techniques suitable for the use in the multi-user multiple-input multiple-output (MU MIMO) downlink. The first one is a linear method called bloek diagonalization (BD) and is based on the singular value decomposition (SVD). The second one is Tomlinson-Harashima Precoding Transmit Wiener Filtering (THF´ TxWF). The third one is a new technique that combines the advantages of BD and THP transmit filtering. We investigate the influence of different degrees of channel state information at the transmitter on their bit error performance. We show that the combination of THP TxWF for single-antenna nsers and BD for multiple-antenna nsers can improve the overall system performance and has better bit error performance with perfect as well as imperfect channel state information at the transmitter.