Limits in FIR subband beamforming for spatially spread near-field speech sources

This paper analyses optimal subband beamforming performance mainly aimed at speech enhancement and acoustic echo suppression for personal communication devices, personal computers and wireless cellular telephones. The focus is on theoretical limits of finite impulse response (FIR) beamformers for spatially spread sources in the array near-field. Performance of the Wiener solution is compared to the direct maximization of the array gain for different lengths of the FIR filters and different source interference spreads. The evaluation is performed individually in sub-bands with constant increasing logarithmic bandwidth. Results show that the difference between the Wiener solution and the direct array gain maximization is less than 2 dB in the measure of Signal-to-Noise plus Interference Ratio (SNIR), for small interference spread. With increasing interference spread the difference in SNIR performance increases, in favor of the array gain maximization.