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Studies Of Underwater Signal Processing Based On Continuous Wavelet Transform

Posted on:2004-01-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:X LiFull Text:PDF
GTID:1118360122961028Subject:Signal and Information Processing
Abstract/Summary:PDF Full Text Request
During underwater signal processing, parameter estimation and target identification are two kinds of important problems. To precisely estimate the target parameters and identify the right target will guarantee the effective operation of underwater counterwork and anti-counterwork, so as to keep an active position for a country in new situation of ocean strategy. These years wavelet theory has been widely applied in underwater signal processing. Whereas its excellent time-frequency localization, this dissertation takes Continuous Wavelet Transform(CWT) as research tool and devoted to systematic research and deep exploration of two aspects in underwater signal processing field-estimation of parameters and target classification and identification.Firstly the estimation of instantaneous frequency is discussed. The 'Simple' method based on CWT is inducted to underwater signal processing to estimate the instantaneous frequency of echo. In essential, this method is to extract the wavelet ridge from the maximum of continuous wavelet transform, according to the corresponding relationship between wavelet ridge and signal frequency, finally to obtain the estimated instantaneous frequency. Based on the method, this dissertation deals with several kinds of signals including Cosine Wave(CW), Linear Frequency Modulated(LFM) and multi-component signal, Furthermore the systematic comparison of estimation effect among CWT and several other usual methods as well Cramer-Rao Bound(CRB) is given. During the instantaneous frequency estimation of LFM, there exists some error in the edge, so in the dissertation, a fitting method is proposed to modify it. From the computer simulation, the following result is obtained: For CW , the method based on CWT is most effective, and with the SNR rising, the error curve of it is more and more closer to CRB. For LFM, the method based on WVD gives the best result, and the effects of CWT and STFT are similar For multi-component signal, Compared to STFT and WVD, CWT is a better choice.Secondly the estimation of DOA is studied. At first some modification is made in conventional beam forming of frequency domain, namely to estimate DOA by arrays outputs on compensated spacial frequency points of echoes. Then the CWT is utilized to signal processing in space-frequency domain for estimation of DOA, and the corresponding modification is also made. In the dissertation, the computer simulations of DOA estimation for both narrow-band and wide-band echoes are given, so do the necessary comparison among several methods and CRB. From the result weget the following conclusion: For narrow-band signal, the effect of the method based on FFT is best. For wide-band signal, when SNR is up to certain degree(higher than -7dB or so), the curves of square error of modified methods are more obvious and closer to CRB. For an echo composed of more than one frequency or direction, space-frequency distribution could show more direct information of frequency and direction, which is more advantaged to make precise judge and estimation for DOA of echo.Finally the target classification and identification are studied. Aiming at five kinds of targets from Geneva Lake which are rock, sand, pebble, grit and sullage, thefeatures we extracted based on the CWT time-frequency matrix are singular values,some parameters of histogram and invariant moment. From the result we conclude:For these five kinds of targets, the parameters of histogram are more effective than singular values. The identification rate of the former could be above 90% , whereas the later is below 80%. For three kinds of targets involving sand, grit and sullage, the feature of singular values excels that of invariant moment, the identification of the former could be to 92%, whereas the later is 84%. Analyzing the features this dissertation extracts, we can find that the features of rock and sullage are more similar, so do pebble and grit, and the features of sand are obviously distinguished.As to the estimation of instantaneous frequency and DOA, s...
Keywords/Search Tags:Continuous Wavelet Transform, Instantaneous frequency, Time-frequency analysis, Linear fitting, Target model, Estimation of DOA, Beam forming in frequency domain, Short-Time Fourier Transform(STFT), Wigner-Ville Distribution(WVD)
PDF Full Text Request
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