A Hybrid Double Zero MVDR Beamformer That is Universal Over the Number of Second Order Notches

In a dynamic environment, close-range and fast-moving interferers transit the resolution cells rapidly, challenging the minimum variance distortionless response (MVDR) beamformer’s ability to place accurate notches in each interferer’s direction. One common approach to overcome this problem is to apply a broader or wider notch at the interferer location. The hybrid double zero (HDZ) MVDR beamformer is a simple and robust method to form a wider notch by implicitly generating second-order notches in the beampattern. The HDZ beampattern is a product of adaptive and fixed factors. The adaptive component has wide second-order 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. However, the challenge for the HDZ beamformer is choosing the ideal number of second-order notches to suppress the moving interferers in a dynamic environment. In practice, the number of moving interferers is unknown and may also change over time. Therefore, an HDZ beamformer with a fixed number of second-order notches may not effectively suppress all the moving interferers if the number of interferers surpasses the number of second-order notches. The need for a time-varying number of second-order notches leads us to design a universal HDZ (UHDZ) beamformer that is universal over this parameter. The UHDZ beamformer rivals the best beamformer in a set of HDZ beamformers with a fixed number of second-order notches without needing prior knowledge of the number of moving interferers or the environment. This paper evaluates the performance of the UHDZ beamformer in simulations and microphone array experiments that include multiple moving interferers.