Delay-and-sum beamforming based on the diagonal reducing method

The delay-and-sum beamforming method (DAS) is robust, as a consequence, it is widely used in the underwater array signal processing. However, the array gain of the DAS method is limited, and is restricted to the array aperture. To tackle this problem, we propose a DAS method based on the diagonal reducing method in the data covariance matrix. Firstly, a reducing value is subtracted from the diagonal elements of the covariance matrix, so as to reduce the noise. As a consequence, a new covariance matrix includes less noise component. Then, the DAS method is applied using this new covariance matrix to obtain the beam output, and we can obtain high array gain when compared with the traditional DAS method. The analytic solution and approximate solution of reducing value are obtained under the constraint condition that the output signal-to-noise ratio (SNR) attains its maximum. The simulation and the experimental results show that the diagonal reducing method reduces some ambient noise, the output array gain is increased.