Robust DMR and multi-rate adaptive beamforming

Dominant mode rejection (DMR) is an approach to adaptive beamforming in which only the large eigenvalues of the correlation matrix and their eigenvectors are used. It requires fewer snapshots due to the reduced degrees-of-freedom. Once the partial eigendecomposition has been performed, a variety of opportunities arise to adjust the algorithms on a beam-by-beam basis without significant additional computations. A modification is developed to improve the robustness to signal mismatch. An approach to controlling the quiescent beam pattern that works for ocean acoustic noise is also presented. The standard approaches fail because source array elements are usually spaced closer than one-half wavelength so that the noise is correlated. Finally a two stage adaptive approach is introduced. It involves a slowly adapting algorithm optimized for nearly stationary conditions followed by a thresholded DMR that rapidly adapts to dynamic interference, but only when the interference is strong.