Abstract
To acquire the enhanced underwater ship-radiated noise signal in the presence of array shape distortion in a passive sonar system, the phase difference of the line-spectrum component in ship-radiated noise is often exploited to estimate the time-delay difference for the beamforming-based signal enhancement. However, the time-delay difference estimation performance drastically degrades with decreases of the signal-to-noise ratio (SNR) of the line-spectrum component. Meanwhile, although the time-delay difference estimation performance of the high-frequency line-spectrum components is generally superior to that of the low-frequency one, the phase difference measurements of the high-frequency line-spectrum component often easily encounter the issue of modulus 2π ambiguity. To address the above issues, a novel time-frequency joint time-delay difference estimation method is proposed in this paper. The proposed method establishes a data-driven hidden Markov model with robustness to phase difference ambiguity by fully exploiting the underlying property of slowly changing the time-delay difference over time. Thus, the phase difference measurements available for time-delay difference estimation are extended from that of low-frequency line-spectrum components in a single frame to that of all detected line-spectrum components in multiple frames. By jointly taking advantage of the phase difference measurements in both time and frequency dimensions, the proposed method can acquire enhanced time-delay difference estimates even in a low SNR case. Both simulation and at-sea experimental results have demonstrated the effectiveness of the proposed method.
Highlights
W represents the weighted least-square (WLS) estimation of time-delay difference at frame t, f, ηwhere ∆τm,t k,t m,k,t, and ∆ φm,k,t denote the estimate of frequency, signal-to-noise ratio (SNR), and phase difference for the kth linespectrum component at frame t, T stands for the number of frames, and K1 is the number of the detected low-frequency line-spectrum components, w is approximately given by respectively
We proposed a time-frequency joint time-delay difference estimation method for signal enhancement in the distorted towed hydrophone array
Since the phase difference measurements in both time and frequency dimensions are exploited jointly, the proposed method has the capability of acquiring enhanced time-delay difference estimates even in the low SNR case
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Time-delay difference estimation exploiting phase difference measurements of line-spectrum components of the underwater ship-radiated noise signal is still an open problem for beamforming-based signal enhancement in the presence of array shape distortion, in the low SNR case. A data-driven HMM with robustness to phase difference ambiguity is established to acquire enhanced time-delay difference estimates by taking advantage of the underlying property of slowly changing time-delay difference over time; The phase difference measurements available for time-delay difference estimation are extended from that of low-frequency line-spectrum components in a single frame to that of all detected line-spectrum components in multiple frames; The signal enhancement performance of the proposed method with a distorted array is close to that of the existing approach with a known array shape, even if the SNR of all the line-spectrum components is as low as 4 dB.
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