Tomlinson-Harashima precoding: a continuous transition from complete to statistical channel knowledge

Tomlinson-Harashima precoding (THP) for a system with multiple transmit antennas and non-cooperative receivers is considered (broadcast channel). Design of THP for this channel is typically based on complete CSI at the transmitter, which is not available in mobile wireless systems. For larger Doppler frequencies it even performs significantly worse than linear precoding or simple beamforming due to its high sensitivity to parameter errors. We apply a novel optimization criterion based on partial CSI to THP. For this robust design it is shown that a continuous transition from complete to statistical CSI is achieved and that THP is now guaranteed to perform always better than or equal to linear precoding