Robust focusing for wideband MVDR beamforming

In this paper, we propose and study two robust methods for coherent focused wideband Minimum Variance Distortionless Response (MVDR) beamforming. The focusing procedure introduces a frequency dependent focusing error which causes performance degradation, especially at high Signal to Noise Ratio (SNR) values. The proposed robust methods aim at reducing the sensitivity of the coherent MVDR to focusing errors. The first method is based on modifying the beamformer optimization problem and generalizing it to bring into account the focusing transformations and the second is based on modifying the focusing scheme itself. A numerical study demonstrates a significant performance improvement of the proposed robust schemes when applied, using the Wavefield Interpolated Narrowband Generated Subspace (WINGS) focusing transformation.