Low complexity soft-interference cancellation turbo equalization for MIMO systems with multilevel modulations

This paper presents a low complexity soft-interference cancellation equalizer (SICE) for the turbo detection of multiple-input multiple-output (MIMO) systems operating in time dispersive channels. The SICE contains three time-invariant linear filters: a feedforward filter, a causal feedback filter and an anti-causal feedback filter. The feedforward filter is designed to suppress the intersymbol interference (ISI) due to time dispersive channels and the multiplexing interference from multiple transmit antennas. The causal (or anti-causal) feedback filter is developed to remove the residual interference caused by the symbols transmitted before (or after) the symbol under detection. The performance of the proposed SICE is verified through both extrinsic information transfer chart (EXIT) analysis and computer simulations. The analytical and simulation results demonstrated that the inclusion of the anti-causal soft decision during SICE is critical to the system performance. The EXIT chart analysis shows that the SICE performance approaches the ideal matched filter bound as the iteration progresses.