Mitigating Multiple Moving Interferers With the Hybrid Double Zero MVDR Beamformer

Interferers with a high bearing rate challenge the ability of the minimum variance distortionless response (MVDR) beamformer to place accurate notches in the direction of the interferer. Consequently, the MVDR notch location always slightly lags the interferer’s actual location, degrading the MVDR’s ability to suppress moving interferers. Creating a flatter and broader notch is a more effective approach to dealing with the interferer’s motion. This paper proposes a hybrid double zero (HDZ) MVDR beamformer that generalizes the double zero (DZ) MVDR beamformer proposed by Tuladhar and Buck in 2015. The DZ MVDR beamformer constraints the array polynomial to be the square of a lower-order polynomial so that all beampattern notches are second-order roots of the array polynomial. However, constraining every notch to be a second-order notch reduces the degrees of freedom (DoF) available for background white noise attenuation. In contrast to the DZ beamformer, the HDZ beamformer factors the beampattern into adaptive and fixed components. The adaptive component has wide notches to suppress moving interferers, while the fixed component improves the white noise gain (WNG) and ensures the array weight vector length matches the array size. The HDZ beamformer spends fewer DoFs on adaptive nulling than the original DZ beamformer, freeing more DoFs for WNG. Simulations and microphone array experiment results show that the HDZ beamformer outperforms the competing beamformers in terms of array output power and WNG.