A resampling-based ultra-short baseline underwater acoustic time delay estimation method

Abstract

The application discloses a kind of based on resampling ultra-short baseline underwater acoustic time delay estimation method, it is suitable for obtaining the time delay information of two different position hydrophones in ultra-short baseline positioning system.The underwater acoustic signal captured by the hydrophone is obtained after noise reduction filtering processing, and the carrier signal with single frequency band is obtained, and the single frequency sample is selected by short-time Fourier transform method, and the signal frequency is determined after analyzing multiple sampling points, and resampling is carried out;The signal after resampling is Fourier transformed again, so that the phase of the underwater acoustic signal captured by any hydrophone is obtained, and the phase difference is calculated, that is, the time delay of the signal between two hydrophones.The application has higher time delay estimation accuracy, smaller calculation amount, and can quickly complete the time delay information between the target signals collected by each hydrophone in the ultra-short baseline array, and the method does not need to know the specific waveform of target signal, and can be used for unknown waveform signal detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of phase analysis of hydrophone, in particular to a method for estimating underwater acoustic time delay of super short baseline based on resampling. BACKGROUND

[0002] Due to the complexity of the water environment, the types of carriers available for underwater communication are limited, and currently only acoustic signals are widely used. The super short baseline positioning technology relying on acoustic signals is a technology widely used in underwater environment to obtain the position of the target, which has the characteristics of reliable positioning effect, high precision, small space occupation, etc.

[0003] One of the research focuses of the super short baseline positioning technology is the time delay acquisition of the hydroacoustic signals received by each array element on the hydroacoustic array. Due to the complexity of the underwater environment and the propagation characteristics of acoustic signals in water, accurate acquisition of time delay information has always been a key point and difficulty of the super short baseline positioning technology. At the same time, the accurate acquisition of time delay is also affected by the reception quality of the signal receiving unit to the hydroacoustic signal, the hydroacoustic signal processing algorithm and other aspects. As for the time delay acquisition algorithm, the current mainstream methods include correlation method, signal matching filter method, etc. The former needs to perform correlation operation on all sampling points of the entire signal, and the operation amount is large. The latter needs to know the target signal waveform to perform matching filtering on the target signal.

[0004] Resampling is a common method for sample data processing, mainly divided into upsampling and downsampling. Proper resampling can make the limited data set produce better results. The present application applies interpolation resampling to interpolate and resample the acoustic signal samples according to a certain algorithm, which can make the data samples obtained by limited sampling frequency more accurately positioned to the phase of the acoustic signal. SUMMARY

[0005] In view of the above problems, the present application provides a method for estimating underwater acoustic time delay of super short baseline based on resampling, which is suitable for acquiring time delay signals of two hydrophones at different positions in a super short baseline positioning system. After the hydrophone captures the underwater acoustic signal, a carrier signal with a single frequency band is obtained after noise reduction filtering processing. A single frequency part of the processed carrier signal is selected, a sufficient number of sampling points are analyzed as a whole to determine the frequency and resample, and the resampled signal is subjected to Fourier transform to obtain the phase of the underwater acoustic signal captured by any hydrophone on the hydroacoustic array. Further, the phase difference and time delay of the underwater acoustic signals captured by the two hydrophones are obtained.

[0006] The present application adopts the following technical solutions:

[0007] Step 1: Collecting underwater acoustic signal:

[0008] The underwater acoustic signals are received by an underwater acoustic array, each hydrophone of which is connected to a signal modulation unit, a programmed amplifier and an A / D sampling module, and the obtained sampling data is transmitted to a signal processing unit through a signal transmission unit for signal processing;

[0009] Step 2: Extracting single-frequency samples of the underwater acoustic signals:

[0010] In an ultra-short baseline positioning system, the underwater acoustic signal collection array is provided with a plurality of hydrophones; the sound source signals received by the hydrophones have time delays, and the distance between the hydrophones is less than the wavelength of the target frequency band signals, so that the phase difference corresponding to the time delay is within [-π, π];

[0011] The underwater acoustic signals collected by any two different hydrophones are filtered and subjected to short-time Fourier transform to obtain waveform signals L1 and L2, and then single-frequency portions are extracted therefrom;

[0012] The extracted single-frequency portions in L1 are equally divided into three parts, i.e., a front part, a middle part and a rear part; when the number of periods of each part is the same, the middle part of the single-frequency portion is extracted as a single-frequency sample; if the number of periods is different, other single-frequency portions in the waveform signal L1 are extracted, and the extraction of the single-frequency sample is performed again;

[0013] After the extraction of the single-frequency sample in the waveform signal L1, a portion of L2 in the same time period is extracted as a single-frequency sample of the waveform signal L2. Since the single-frequency sample contains multiple periods, and the time delay between L1 and L2 is within one period, after the time period corresponding to the single-frequency sample of L1 is determined, the portion in the corresponding time period of L2 can certainly be used as a single-frequency sample.

[0014] The accurate signal frequency f in the single-frequency sample is obtained by the following formula:

[0015]

[0016] Wherein N is the number of periods contained in the single-frequency sample signal, t is the time length of the single-frequency sample, n is the number of sampling points contained in the single-frequency sample, and fs is the sampling frequency;

[0017] Thus, the extraction of the single-frequency sample of the underwater acoustic signal captured by the hydrophone is completed;

[0018] The single-frequency samples obtained after the single-frequency extraction of the waveform signals L1 and L2 are Ls1 and Ls2, respectively;

[0019] Step 3: Interpolation resampling and phase acquisition for the extracted single-frequency samples:

[0020] The Ls1 and Ls2 (collectively referred to as Ls) are subjected to interpolation resampling, and the obtained resampling sequence is y(i) for i = 1, and:

[0021] y(1) = Ls(1) (2)

[0022] For any 1 < i < Nw, there is

[0023]

[0024] Where TR is the resampling period, i.e. the time length between two resampling points, TC is the number of periods contained in the resampled sequence, tn is the sampling time corresponding to the i-th resampling point, Nw is the number of resampling points, generally an integer power of 2, so as to perform subsequent Fourier transform, f is the signal frequency, fs is the original sampling frequency, and [] represents rounding down;

[0025] After completing resampling, the fast Fourier transform is performed on the resampled sequence y(i), and the phase calculation is performed on the complex number corresponding to the TC+1-th point of the transform result, so that the phases Φ1 and Φ2 corresponding to the single-frequency samples Ls1 and Ls2 are obtained, and thus the phase difference Φ = Φ1-Φ2 is obtained.

[0026] Step 4: obtaining the time delay of the signals received by the two hydrophones from the phase acquisition result:

[0027] According to the phase difference Φ, the time delay of the signals received by the two hydrophones is obtained according to formula (4):

[0028] Δt = ΦT / (2π) (4)

[0029] The present application has the following beneficial effects:

[0030] The present application has high time delay estimation accuracy, small calculation amount, and can quickly complete the time delay information acquisition of the target signals collected by the hydrophones in the ultra-short baseline array, and the present method does not need to know the specific waveform of the target signal, and can be used for unknown waveform signal detection. BRIEF DESCRIPTION OF DRAWINGS

[0031] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0032] Figure 1 The flow chart of the method of the present application is shown in FIG. 1.

[0033] Figure 2 The schematic diagram of the underwater acoustic signal acquisition unit is shown in FIG. 2.

[0034] Figure 3 The time domain representation of the underwater acoustic signal is shown in FIG. 3.

[0035] Figure 4 The schematic diagram of the signal sampling points before resampling is shown in FIG. 4.

[0036] Figure 5A schematic diagram of the resampled signal sampling points. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail with reference to the accompanying drawings.

[0038] The present application provides a resampling-based ultra-short baseline underwater acoustic time delay estimation method for obtaining the phase difference of any two different position hydrophones in an ultra-short baseline positioning system.

[0039] After the hydrophone captures the underwater acoustic signal, the underwater acoustic signal is subjected to noise reduction filtering processing to obtain a carrier signal with a single frequency band and weak noise. A single frequency part in the processed carrier signal is selected, and after overall analysis of a sufficient number of sampling points, a single frequency sample is obtained, the frequency is determined, and resampling is performed. Fast Fourier transform is performed on the resampled signal to obtain the phase of the underwater acoustic signal captured by any hydrophone on the underwater acoustic array, and then the phase difference and time delay of the underwater acoustic signals captured by two hydrophones are obtained.

[0040] In the ultra-short baseline positioning system, the underwater acoustic signal collection array is composed of multiple hydrophones, all of which are located on the same spatial plane S1. Since the spatial positions of each hydrophone are different, the sound source signal is unique, and therefore the time points at which the sound source signal reaches each hydrophone are generally different, that is, there is a time delay between the sound source signals received by each hydrophone. In the ultra-short baseline positioning system, the distance between each hydrophone is generally less than the wavelength of the target frequency band signal, so the phase difference corresponding to the time delay is between [-π, π], and the time delay value can be obtained through the frequency and the phase difference, that is, the phase difference can be obtained to obtain the time delay.

[0041] As shown in Figure 1 , the specific steps are as follows:

[0042] Step 1: Collecting underwater acoustic signals.

[0043] The underwater acoustic signals are received by the underwater acoustic array. As shown in Figure 2 , each hydrophone in the underwater acoustic array is connected with a signal modulation unit, a program-controlled amplifier and an A / D sampling module, and the obtained sampling data is transmitted to the signal processing unit through the signal transmission unit for signal processing.

[0044] Step 2: Extracting a single frequency part in the underwater acoustic signal.

[0045] After the underwater acoustic signals collected by any two hydrophones are subjected to signal filtering in step 1, the obtained waveform signals are L1 and L2, respectively. By means of a high sampling rate, a certain frequency relatively single segment in the waveform signal is determined by short-time Fourier transform, which is set as a single frequency part.

[0046] The single frequency part extracted in L1 is divided into three parts, front, middle and back. When the number of periods in each part is the same, the middle part of the single frequency part is extracted as the single frequency sample. If the number of periods is different, other single frequency parts in the waveform signal L1 are extracted, and the extraction of the single frequency sample is performed again.

[0047] After the single frequency sample extraction in the waveform signal L1, the part of L2 in the same time period is extracted as the single frequency sample of the waveform signal L2. Since the single frequency sample contains multiple periods, and the time delay between L1 and L2 is within one period, after determining the time period corresponding to the single frequency sample of L1, the part in the corresponding time period of L2 can be determined as the single frequency sample.

[0048] The accurate signal frequency f in the single frequency sample is obtained by the following formula:

[0049]

[0050] Where N is the number of periods contained in the single frequency sample signal, t is the time length of the single frequency sample, n is the number of sampling points contained in the single frequency sample, and fs is the sampling frequency.

[0051] Thus, the single frequency sample extraction of the underwater acoustic signal captured by the hydrophone is completed. After the single frequency sample extraction of L1 and L2 signals, the extracted single frequency samples are Ls1 and Ls2 respectively, and Ls1 and Ls2 have the same and determined phase difference Φ as the original underwater acoustic signal, as shown in Figure 3 .

[0052] Step 3: Resampling and phase acquisition based on single frequency part of underwater acoustic signal

[0053] After obtaining the single frequency samples Ls1 and Ls2 (collectively referred to as Ls) of the underwater acoustic signal, resample them according to the following formula (2). The sampling points before resampling are shown in Figure 4 .

[0054] The resampled sequence obtained after resampling is y(i), and for i = 1, we have:

[0055] y(1) = Ls(1) (2)

[0056] For any i > 1, we have:

[0057]

[0058] Where TR is the resample period, i.e. the time length between two resample points; TC is the number of periods contained in the resampled sequence; tn is the sampling time corresponding to the i-th resample point; Nw is the number of resample points, which is taken as 2 raised to the power of n in order to perform subsequent Fourier transform; f is the signal frequency of the single-frequency sample; fs is the sampling frequency of the AD sampling module; and [] represents rounding down.

[0059] The resampled signal sample point sequence is shown in Fig. 2. Figure 5

[0060] After resampling, the resampled sequence y(i) is subjected to fast Fourier transform. Since the resampled sample points contain TC whole signal periods, the phase of the complex number corresponding to the (TC+1)-th point of the transform result is calculated, i.e. the phases Φ1 and Φ2 corresponding to the single-frequency samples Ls1 and Ls2 are obtained, and thus the phase difference Φ is obtained.

[0061] Step 4: obtaining the time delay of the signals received by the two hydrophones from the phase acquisition result:

[0062] After obtaining the phase difference of the underwater acoustic signals received by the two hydrophones through step 3, it is shown in Fig. 3 that the phase difference of the signals received by the two different points in the transmission process of the single-frequency underwater acoustic signal and the time delay thereof have a strict mathematical relationship. The relationship is specifically expressed as: Figure 3

[0063] Δt = ΦT / (2π) + nT (4)

[0064] Where f is the signal frequency, T is the signal period, and n is a finite integer. However, in the ultra-short baseline positioning system, the distance between any two elements is less than the wavelength c / f, and the time delay Δt is between [-T / 2, T / 2], i.e. n = 0, so:

[0065] Δt = ΦT / (2π) (5)

[0066] Thus, the time delay of the signals received by any two hydrophones at different positions in the ultra-short baseline positioning system can be obtained.​​

Claims

1. A method for estimating the underwater acoustic time delay of an ultra-short baseline based on resampling, characterized in that, It includes the following steps: Step 1: Collect underwater acoustic signals: Receive underwater acoustic signals through an underwater acoustic array. Each hydrophone of the underwater acoustic array is connected to a signal modulation unit, a programmable amplifier, and an A / D sampling module. The obtained sampling data is transmitted to a signal processing unit through a signal transmission unit for signal processing; Step 2: Extract single-frequency samples of underwater acoustic signals: After filtering the underwater acoustic signals collected by two different hydrophones, waveform signals L1 and L2 are obtained respectively; through short-time Fourier transform, the single-frequency parts are extracted from the waveform signals L1 and L2; The single-frequency part extracted from the waveform signal L1 is evenly divided into three parts: front, middle, and rear. When the number of periods in each part is the same, the middle part of the single-frequency part is extracted and used as the single-frequency sample of L1; if the number of periods is different, other single-frequency parts of the waveform signal L1 are extracted, and the extraction of the single-frequency sample is performed again; after successfully extracting the single-frequency sample of the waveform signal L1, the sample extraction for the same time period is performed on the waveform signal L2 as the single-frequency sample of L2; The precise signal frequency f in the single-frequency sample is obtained through the following formula: where N is the number of periods contained in the single-frequency sample signal, t is the duration of the single-frequency sample, n is the number of sampling points contained in the single-frequency sample, and fs is the sampling frequency; Thus, the extraction of the single-frequency samples of the underwater acoustic signals captured by the hydrophones is completed, and they are respectively set as Ls1 and Ls2; Step 3: Perform interpolation resampling and phase acquisition on the extracted single-frequency samples: Perform interpolation resampling on the single-frequency samples. The obtained resampled sequence is y(i). For i = 1, there is: y(1) = Ls(1) For any 1 < i < Nw, there is where TR is the resampling period, that is, the duration between two resampling points; TC is the number of periods contained in the resampled sequence; tn is the sampling moment corresponding to the i-th point obtained by resampling; Nw is the number of resampling points; f is the signal frequency; fs is the original sampling frequency, and the symbol [] represents rounding down; After completing the resampling, perform a fast Fourier transform on the resampled sequence y(i), and calculate the phase of the complex number corresponding to the (TC + 1)-th point of the transformation result, that is, the phases Φ1 and Φ2 corresponding to the single-frequency samples Ls1 and Ls2 are obtained, and thus the phase difference Φ = Φ1 - Φ2 is obtained; Step 4: Obtain the time delay of the signals received indirectly by the two hydrophones from the phase acquisition result: According to the following formula, the time delay of the signals received indirectly by the two hydrophones is obtained through the phase difference Φ: Δt = ΦT / (2π).

2. The method for estimating ultra-short baseline underwater acoustic time delay based on resampling according to claim 1, wherein: In the ultra-short baseline positioning system, an underwater acoustic signal acquisition array is provided with several hydrophones; there is a time delay between the sound source signals received by each hydrophone, and the distance between each hydrophone is less than the wavelength of the target frequency band signal. Therefore, the phase difference corresponding to the time delay is within [-π, π].

3. The method for estimating ultra-short baseline underwater acoustic time delay based on resampling according to claim 1, wherein: The number of resampling points Nw is taken as an integer power of 2.

4. The ultra-short baseline underwater acoustic time delay estimation method based on resampling according to claim 1, characterized in that: The phase difference between the underwater acoustic signals acquired by two different hydrophones is the same as the phase difference between the single-frequency samples Ls1 and Ls2 extracted from their waveforms.

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