Abstract
The array gain degrades significantly suffering from a decrease of signal spatial coherence caused by imperfectly correlated acoustic channels with spatial and temporal fluctuations. For a long linear array collecting signals in the range-dependent ocean waveguide, the amplitude and phase of the received signals show more viriation over the elements, which causes the signal coherence to attenuate seriously. The gain of traditional beamformers, such as the conventional beamformer (CBF), minimum variance distortionless response beamformer (MVDR-BF), and eigenvalue beamformer (EBF), will deviate from their ideal values. In this paper, a matched-phase weighting beamformer (MPBF) is proposed to obtain high gain in an ocean waveguide. The variational phase of acoustic channel transfer functions over the elements can be compensated for by matched-phase weighting, and then, the acoustic channel spatial coherence can be restored to achieve a high gain. The weighting-matrix of MPBF is obtained by the received signals; hence, environmental parameters or channel transfer functions do not have to be estimated. Simulations and experiments considering a long horizontal uniform linear array (HLA) in the slope region receiving a narrow-band signal from a deep-water source (upslope waveguide) are performed. The results demonstrate that MPBF can achieve a higher gain than CBF, MVDR-BF and EBF in a complex ocean waveguide.
Highlights
A long linear array has a great advantage in detecting weak signals from underwater targets
Comparing the performances of conventional beamformer (CBF), minimum variance distortionless response beamformer (MVDR-BF), eigenvalue beamformer (EBF) and matched-phase weighting beamformer (MPBF), the results demonstrate that MPBF can restore acoustic channel coherence and improve array gain (AG) in the range-dependent ocean waveguide
We propose the matched-phase weighting method, which is valid for compensating the phase variation of the acoustic channel transfer function and enhancing the spatial coherence of acoustic channels to obtain a higher gain in the inhomogeneous ocean waveguide
Summary
A long linear array has a great advantage in detecting weak signals from underwater targets. The subarray division needs to predict the signal coherence length This process attenuates the gain of the whole array, which weakens the advantage of the detection using a long linear array. In the range-dependent ocean waveguide, the received signals have nonuniform amplitude/phase (the phase difference is not constant) over the elements and the signal coherence decreases with element separation In this case, the conventional method is unable to compensate for the phase difference.
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