Efficient MIMO DS-UWB Downlink Chip-Level MMSE Equalization Using Subband Adaptive Interference Mitigation Techniques

An adaptive subband chip-level equalizer is investigated for downlink multiple-input-multiple-output (MIMO) direct-sequence (DS) ultrawideband (UWB) systems to cope with intersymbol interference (ISI) and multiple-access interference (MAI) in multipath fading channels. The subband decomposition technique with multiple analysis and synthesis filter banks (FBs) is employed to substantially improve the downlink reception of mobile-terminal (MT) receivers. This chip equalizer utilizes subband adaptive interference suppression techniques based on the minimum mean square error (MMSE) criterion. A reduced-complexity chip-level MMSE equalization scheme is proposed by making full use of the reduced-rank (RR) multistage matrix Wiener filter (MMWF) and the matrix conjugate gradient (MCG) architectures in subbands. Simulations are conducted to provide a comparative evaluation of the proposed subband chip equalizer with other existing full-band and subband chip equalizers.