A double zero MVDR beamformer that is universal over number of second-order notches

Abstract

Adaptive beamformers, like the minimum variance distortionless response (MVDR) beamformer, suffer from interferer direction mismatch due to interferer motion. This mismatch reduces interferer suppression and degrades the beamformer’s performance. Applying a flatter and broader notch near the interferer location effectively suppresses moving interferers. The double zero MVDR (DZ MVDR) adaptive beamformer [Tuladhar & Buck, JASA, 2015] produces second-order notches in the interferer’s directions by squaring the array polynomial of a subarray SMI MVDR beamformer. The performance of the DZ MVDR beamformer depends on the chosen number of second-order notches by applying different subarray aperture sizes. If the number of interferers in a dynamic environment is known, then the ideal number of second-order notches can be implemented. In practice, the number of interferers is an unknown and often time-varying parameter. To address this challenge, we propose a universal DZ (UDZ) MVDR beamformer that is universal over the number of second-order notches. This universal beamformer requires fewer degrees of freedom than competing beamformers to suppress the interferers, thus providing a better white noise gain in the array output. We present simulation results illustrating the benefits of the UDZ MVDR beamformer in the presence of multiple moving interferers. [Work supported by ONR 321US.]