Reduced-complexity linear and nonlinear preceding for frequency-selective MIMO channels

Focusing on systems with simple non-cooperating receivers, we present an approach to reduce the complexity of multi-user preceding schemes for frequency-selective MIMO channels. The transmit Wiener filter (TxWF) and Wiener Tomlinson-Harashima precoding (THP) both provide attractive performance, but the complexity involved in their computation may be prohibitive. We develop the reduced-complexity multi-user multi-stage TxWF (MSTxWF) by applying the multi-stage decomposition known from receive processing to the TxWF. We show that the block-Lanczos algorithm can be used for efficiently computing the reduced rank MSTxWF. Moreover, we extend the MSTxWF approach to Wiener temporal THP, resulting in a reduced-complexity nonlinear precoding scheme. Simulation results demonstrate that both schemes can provide close to optimum performance at significantly reduced complexity.