A frequency-invariant fixed beamformer for speech enhancement

Fixed beamformers maintain response that is independent of the signal and interference statistics. Frequency-invariant fixed beamformers can achieve constant beamwidth across all frequencies which results in lower signal distortion and they have lower computation complexity compared to its adaptive counterpart. However, unlike data-dependent beamformers, their sidelobe attenuation is poor with respect to the direction of the interferences. In this paper we propose a method to improve the sidelobe attenuation while retaining the advantages of lower computational complexity and frequency-invariance. This is achieved by introducing frequency-invariant nulls in the interference directions. We also show how the weights for each null direction can be combined with the fixed beamformer to form the effective weights of the proposed beamformer.