Method for improving positioning accuracy of ultra-short baseline system by resisting multi-path time delay estimation

Abstract

The method for improving the positioning precision of an ultra-short baseline system by anti-multipath time delay estimation comprises the following steps: when the ultra-short baseline positioning is performed by using a wideband correlation time delay estimation method, there are multiple correlation peaks in the change curves of R13 (τx) and R24 (τx), respectively; the position of the maximum peak value is found first; then, from the position, the first correlation peak with a peak height of more than 0.707 times of the highest peak and a peak width within a certain range corresponding to the frequency band of the response signal is found; the time delay difference corresponding to the position of the correlation peak is the time delay difference τx or τy of the direct wave; the time delay difference τx or τy is substituted into the formula, respectively, to obtain the accurate positioning of a measured target T in a coordinate system established by an ultra-short baseline array. The method is used for amplitude and width processing on a correlation sequence after interference suppression and correlation filtering of a received signal, the time delay of the direct wave is found, the misjudgment probability is reduced, and the positioning precision of the ultra-short baseline is ensured.

Description

Technical Field

[0001] This invention belongs to the field of underwater target positioning, and in particular relates to a method for improving the positioning accuracy of ultra-short baseline systems by anti-multipath delay estimation. Background Technology

[0002] Ultra-short baseline (USBR) positioning systems are characterized by their small size, ease of installation, and flexible use, thus playing an increasingly important role in the exploration and development of marine resources. USBR arrays are typically rigidly mounted on a boom at the center or side of the support vessel. During operation, they are lowered underwater, and transponders are installed on the underwater target (T). Underwater target positioning and tracking are achieved through the USBR positioning principle. Its working principle diagram is shown below. Figure 1 The ultra-short baseline array uses an orthogonal cross array, with the four receiving elements distributed as follows: Figure 1 As shown, T represents an underwater target equipped with a transponder.

[0003] Traditional ultra-short baseline (USB) positioning often uses CW pulses as the response signal, utilizing the phase difference between array elements for target localization. However, this method is frequently plagued by problems such as phase ambiguity, quadrant distortion, and multipath interference, and its positioning accuracy is also quite limited. In the past two decades, international USB positioning has adopted a broadband spread spectrum response scheme. This scheme can enhance the system's anti-interference capability, improve signal processing gain, and achieve higher positioning accuracy.

[0004] Underwater acoustic channels are time- and space-varying multipath channels. In a multipath channel model, R represents the distance from the sound source to the receiver. At the receiver, the direct signal and each reflected signal superimpose. Generally, the direct wave arrives before the reflected wave. Multipath interference makes it difficult to detect and estimate the parameters of the direct signal (along the direct sound ray R). Conventional time delay estimation uses the method of finding the maximum value of the correlation peak. However, in cases of severe multipath interference, the superimposed correlation peak often exceeds the correlation peak value of the direct wave. If the location of the correlation peak is determined solely by finding the maximum value of the correlation sequence, errors will obviously occur, leading to discrete positioning data that fails to reflect the true situation. Summary of the Invention

[0005] The purpose of this invention is to propose a method for improving the positioning accuracy of ultra-short baseline systems by resisting multipath delay estimation. This method overcomes the jump in delay estimation caused by strong multipath in shallow water, accurately estimates the direct wave delay, eliminates false peaks, reduces the probability of misjudgment, and ensures the positioning accuracy of ultra-short baseline systems.

[0006] To achieve the purpose of this invention, the following technical solution is adopted:

[0007] This invention discloses a method for improving the positioning accuracy of an ultra-short baseline (USBS) system through anti-multipath delay estimation. The USBS system comprises an USBS array, signal processing equipment, a main unit, and an underwater transponder. The USBS array is an orthogonal cross array, comprising a first element, a second element, a third element, a fourth element, and a transmitting transducer. The USBS array is rigidly mounted on a lifting mast at the center or side of the support vessel and is lowered underwater during operation. The underwater transponder is mounted on the underwater target T. A coordinate system is established on the USBS array, with the transmitting transducer as the origin, the first and third elements as the X-axis, and the second and fourth elements as the Y-axis. With the Z-axis perpendicular to the ultra-short baseline array, the array aperture D1 between the first and third array elements and the array aperture D2 between the second and fourth array elements are pre-calibrated, and the sound velocity in the working area is obtained. When the ultra-short baseline positioning system is working, the host controls the transmitting transducer to emit a broadband query sound signal through the signal processing equipment. After underwater acoustic propagation, it is received by the underwater transponder. After confirmation by the underwater transponder, it returns a response signal of a different system than the broadband query sound signal. This response signal is received by the first, second, third, and fourth array elements, respectively. The coordinate position of the target T relative to the ultra-short baseline array is calculated using formulas (1) and (2).

[0008]

[0009]

[0010] Where c is the speed of sound in water;

[0011] D1 is the spacing between the first array element (1) and the third array element (3);

[0012] D2 is the spacing between the second array element (2) and the fourth array element (4);

[0013] R - The distance between the target T and the coordinate circle. t is the time required from when the signal is emitted by the transmitting transducer to when the underwater transponder receives the signal and returns to the transmitting transducer;

[0014] τ x - The time delay difference between the received signals of the first array element (1) and the third array element (3) in the X-axis direction;

[0015] τy - the time delay difference of the received signals of the second array element (2) and the fourth array element (4) in the Y-axis direction.

[0016] Delay difference τ x Equation (3) is the cross-correlation time delay estimation formula, obtained by estimating the time delay of the signals received by the first and third array elements.

[0017] R 13 (τx )=E[x1(t)x3(t)]=IFFT{X1(f)X * Formula (3)

[0018] Among them: X1(f)=FFT[x1(t)],X3(f)=FFT[x3(t)],X * 3(f) is the complex conjugate of X3(f).

[0019] x1(t) and x3(t) are the received signals from the first and third elements of the X-axis of the base array coordinate system, respectively. 13 (τ x The cross-correlation function of the first and third array elements is given by the signal processing device. The received signals from the first and third array elements along the X-axis of the array coordinate system are obtained by performing Fourier transforms on each element and then multiplying their conjugates to obtain the cross-power spectrum. The cross-power spectrum of the first and third array elements is then subjected to an inverse Fourier transform to obtain the correlation function. This correlation function is input into the detection module, where R is displayed. 13 (τ x The curves representing the change of the correlation function are plotted, with the horizontal axis representing time and the vertical axis representing the change of the correlation function. The time delay τ corresponding to the position of the maximum peak in these curves is identified. x ;

[0020] Delay difference τ y The time delay is estimated by the signals received from the second and fourth array elements. Formula (4) is the cross-correlation time delay estimation formula.

[0021] R 24 (τ y )=E[x2(t)x4(t)]=IFFT{X2(f)X * Formula (4)

[0022] Where: X2(f) = FFT[x2(t)], X4(f) = FFT[x4(t)], X * 4(f) is the complex conjugate of X⁴(f).

[0023] x2(t) and x4(t) are the received signals from the second and fourth elements of the Y-axis of the base array coordinate system, respectively. 24 (τ y The cross-correlation function of the second and fourth array elements is given by the signal processing device. The received signals from the second and fourth array elements along the Y-axis of the array coordinate system are obtained by performing Fourier transforms on each element and then multiplying their conjugates to obtain the cross-power spectrum. The cross-power spectrum of the second and fourth array elements is then subjected to an inverse Fourier transform to obtain the correlation function. This correlation function is input into the detection module, where R is displayed. 24 (τ yThe curves representing the change of the correlation function are plotted, with the horizontal axis representing time and the vertical axis representing the change of the correlation function. The time delay τ corresponding to the position of the maximum peak in these curves is identified. y ;

[0024] Where: in R 13 (τ x ) and R 24 (τ x The curve of the change contains multiple related peaks. First, find the position of the maximum peak. Then, from this position, find the first related peak whose height is more than 0.707 times the height of the maximum peak and whose width is within a certain range of the width corresponding to the response signal frequency band. The time delay difference corresponding to the position of this related peak is the time delay difference τ of the direct wave. x or τ y The time delay difference τ x or τ y Substituting into formulas (1) and (2) respectively, we obtain the precise positioning of the target T on the coordinate system established by the ultra-short baseline array.

[0025] The anti-multipath broadband ultra-short baseline positioning delay estimation method of the present invention, wherein: the finally selected correlation peak is the first peak in the variation curve that satisfies the conditions that the peak height is more than 0.707 times the peak height of the highest peak and the peak width is a certain peak width corresponding to the frequency band of the response signal.

[0026] The anti-multipath broadband ultra-short baseline positioning delay estimation method of the present invention includes: the signal processing device (7) performs adaptive line spectrum enhancement processing between performing Fourier transform to obtain cross power spectrum and inverse Fourier transform, which reduces interference and misjudgment probability.

[0027] The multipath-resistant broadband ultra-short baseline positioning delay estimation method of the present invention, wherein: the peak width selection condition is 0.9 to 1.1 times the relevant peak width corresponding to the response signal frequency band.

[0028] The anti-multipath broadband ultra-short baseline positioning delay estimation method of this invention is mainly used in maritime emergency rescue. Due to the complex on-site operating environment and the serious impact of shallow water multipath, the received signal has a long extension, resulting in multiple correlation peaks in the waveform of the calculated correlation sequence. The waveform of the correlation peak is also distorted. In addition, the array opening angle of this device is large, and the correlation peaks superimposed by multipath are often larger than the correlation peak value of the direct wave. If the position of the correlation peak is determined by simply finding the maximum value of the correlation sequence, it will obviously be wrong, resulting in discrete positioning data that cannot reflect the true situation.

[0029] This invention proposes a multipath-resistant broadband ultra-short baseline positioning delay estimation method. After interference suppression, the received signal is correlated by matched filtering (MF). Then, the correlation sequence is processed for amplitude and width discrimination to find the direct wave delay, reduce the probability of misjudgment, and ensure the positioning accuracy of ultra-short baseline. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of an ultra-short baseline system in the anti-multipath broadband ultra-short baseline positioning delay estimation method of the present invention;

[0031] Figure 2 The cross-correlation function R displayed in the detection module 24 (τ y The curve of change;

[0032] Figure 3 After adaptive line spectrum enhancement processing Figure 2 R shown 24 (τ y The curve of change;

[0033] Figure 4 From Figure 3 The final relevant peak was found.

[0034] exist Figure 1 In the diagram, number 1 represents the first array element; number 2 represents the second array element; number 3 represents the third array element; number 4 represents the fourth array element; number 5 represents the transmitting transducer; number 6 represents the ultra-short baseline array; number 7 represents the signal processing equipment; number 8 represents the main unit; and number 9 represents the underwater transponder. Detailed Implementation

[0035] like Figure 1 As shown, the ultra-short baseline system of the present invention comprises an ultra-short baseline array 6, a signal processing device 7, a host 8, and an underwater transponder 9. The ultra-short baseline array 6 adopts an orthogonal cross array, which includes a first array element 1, a second array element 2, a third array element 3, a fourth array element 4, and a transmitting transducer 5. The ultra-short baseline array 6 is rigidly mounted on a lifting mast at the center or side of the working mother ship and is lowered underwater during operation. The underwater transponder 9 is mounted on the underwater target T. An array coordinate system is established on the ultra-short baseline array 6, with the transmitting transducer 5 as the origin of the coordinate system, the first array element 1 and the third array element 3 as the X-axis, the second array element 2 and the fourth array element 4 as the Y-axis, and the perpendicular to the ultra-short baseline array 6 as the Z-axis. The array aperture D1 between the first array element 1 and the third array element 3 and the array aperture D2 between the second array element 2 and the fourth array element 4 are pre-calibrated, and the sound velocity in the working area is obtained.

[0036] When the ultra-short baseline positioning system is working, the host 8 controls the transmitting transducer 5 to emit a broadband query sound signal through the signal processing device 7. After propagation through underwater acoustics, the signal is received by the underwater transponder 9. After confirmation by the underwater transponder 9, a response signal of a different system than the broadband query sound signal is returned. This response signal is received by the first array element 1, the second array element 2, the third array element 3, and the fourth array element 4, respectively. The coordinate position of the target T relative to the ultra-short baseline array 6 is calculated using formulas (1) and (2).

[0037]

[0038]

[0039] Where c is the speed of sound in water;

[0040] D1 is the spacing between the first array element 1 and the third array element 3;

[0041] D2 is the spacing between the second array element 2 and the fourth array element 4;

[0042] R - The distance between the target T and the coordinate circle. t is the time required from when the signal is emitted from the transmitting transducer 5 to when the underwater transponder 9 receives the signal and returns to the transmitting transducer 5;

[0043] τ x - The time delay difference between the received signals of the first array element 1 and the third array element 3 in the X-axis direction;

[0044] τ y -The time delay difference between the received signals of the second array element 2 and the fourth array element 4 in the Y-axis direction.

[0045] Delay difference τ x Equation (3) is the cross-correlation time delay estimation formula obtained by estimating the time delay of the received signals from the first array element 1 and the third array element 3.

[0046] R 13 (τ x )=E[x1(t)x3(t)]=IFFT{X1(f)X * Formula (3)

[0047] Among them: X1(f)=FFT[x1(t)],X3(f)=FFT[x3(t)],X * 3(f) is the complex conjugate of X3(f).

[0048] x1(t) and x3(t) are the received signals from the first element 1 and the third element 3 of the X-axis of the base array coordinate system, respectively. 13 (τ xThe cross-correlation function of the first array element 1 and the third array element 3 is given by the signal processing device 7. The received signals from the first array element 1 and the third array element 3 along the X-axis of the array coordinate system are subjected to Fourier transforms and then multiplied conjugately to obtain the cross-power spectrum. Adaptive line spectrum enhancement processing is then performed. Finally, the cross-power spectrum of the first array element 1 and the third array element 3 is subjected to an inverse Fourier transform to obtain the correlation function. This correlation function is then input into the detection module, where R is displayed. 13 (τ x The curve representing the change of the correlation function is shown on the horizontal axis, where the horizontal axis represents time and the vertical axis represents the change of the correlation function.

[0049] Delay difference τ y The time delay is estimated by the signals received from the second array element 2 and the fourth array element 4. Formula (4) is the cross-correlation time delay estimation formula.

[0050] R 24 (τ y )=E[x2(t)x4(t)]=IFFT{X2(f)X * Formula (4)

[0051] Where: X2(f) = FFT[x2(t)], X4(f) = FFT[x4(t)], X * 4(f) is the complex conjugate of X⁴(f).

[0052] x2(t) and x4(t) are the received signals from the second element 2 and the fourth element 4 of the Y-axis of the base array coordinate system, respectively. 24 (τ x The cross-correlation function of the second array element 2 and the fourth array element 4 is given by the signal processing device 7. The received signals from the second array element 2 and the fourth array element 4 along the Y-axis of the array coordinate system are obtained by performing Fourier transforms and conjugate multiplication to obtain the cross-power spectrum. Adaptive line spectrum enhancement processing is then performed. Finally, the cross-power spectrum of the second array element 2 and the fourth array element 4 is subjected to inverse Fourier transform to obtain the correlation function. This correlation function is then input into the detection module, where R is displayed. 24 (τ y The curves representing the change of the correlation function are plotted, with the horizontal axis representing time and the vertical axis representing the change of the correlation function. The time delay τ corresponding to the position of the maximum peak in these curves is identified. y .

[0053] The invented method for improving the positioning accuracy of ultra-short baseline systems through anti-multipath delay estimation involves identifying multiple correlation peaks in the variation curves of the correlation functions R13(τx) and R24(τy). First, the location of the maximum peak is found, and then, from this location, such as... Figure 3As shown, find the first correlated peak whose peak height is more than 0.707 times that of the highest peak and whose peak width is within the frequency band of the response signal. The time delay difference corresponding to the position of this correlated peak is the time delay difference τ of the direct wave. y The peak width of this peak is 0.9 to 1.1 times the corresponding peak width of the response signal frequency band, which will reduce the time delay difference τ of the direct wave. y Substituting into formula (2), we obtain the precise position of the vertical coordinate of the target T in the matrix coordinate system. Similarly, we obtain the time delay difference τ of the direct wave. x Substituting into formula (1), we can obtain the precise position of the horizontal coordinate of the target T in the matrix coordinate system.

[0054] Figure 3 After adaptive line spectrum enhancement processing Figure 2 R shown 24 (τ y The variation curve of the curve can be suppressed by adaptive line spectrum enhancement processing to suppress weak interference peaks on the variation curve.

[0055] The foregoing description provides an exemplary account of the present invention, but its scope of protection is not limited thereto. Any non-substantial modifications made using the inventive concept and technical solution, or the direct application of the inventive concept and technical solution to other situations without modification, are all within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for improving the positioning accuracy of an ultra-short baseline system by resisting multipath delay estimation, wherein the ultra-short baseline system includes: The system consists of an ultra-short baseline array (6), signal processing equipment (7), a main unit (8), and an underwater transponder (9). The ultra-short baseline array (6) is an orthogonal cross array, which includes: a first array element (1), a second array element (2), a third array element (3), a fourth array element (4), and a transmitting transducer (5). The ultra-short baseline array (6) is rigidly mounted on a lifting mast at the center or side of the working mother ship. When in operation, it is lowered underwater. The underwater transponder (9) is mounted on the underwater target T. An array coordinate system is established on the ultra-short baseline array (6), with the transmitting transducer (5) as the origin of the coordinate system, the first array element (1) and the third array element (3) as the X-axis, the second array element (2) and the fourth array element (4) as the Y-axis, and the axis perpendicular to the ultra-short baseline array (6) as the Z-axis. The array aperture D1 between the first array element (1) and the third array element (3) and the array aperture D2 between the second array element (2) and the fourth array element (4) are pre-calibrated, and the sound velocity in the working area is obtained. When the ultra-short baseline positioning system is working, the host (8) controls the transmitting transducer (5) to emit a broadband query sound signal through the signal processing equipment (7). After underwater acoustic propagation, it is received by the underwater transponder (9). After confirmation by the underwater transponder (9), it returns a response signal of a different system than the broadband query sound signal. The response signal is received by the first array element (1), the second array element (2), the third array element (3) and the fourth array element (4) respectively. The coordinate position of the target T relative to the ultra-short baseline array (6) is calculated using formula (1) and formula (2). Official (1); Official (2); in, C —Speed ​​of sound underwater; D 1 represents the distance between the first array element (1) and the third array element (3); D 2 represents the distance between the second array element (2) and the fourth array element (4); R —The distance between the target T and the origin of the coordinate system. t The time required for a signal to be sent from the transmitting transducer (5) to be received by the underwater transponder (9) and returned to the transmitting transducer (5); —The time delay difference between the received signals of the first array element (1) and the third array element (3) in the X-axis direction; In the Y-axis direction, the time delay difference between the received signals of the second array element (2) and the fourth array element (4) is... The time delay is estimated by the received signals from the first array element (1) and the third array element (3). Formula (3) is the cross-correlation time delay estimation formula. Official (3); in: The conjugate of complex numbers, x 1 (t), x 3 (t) The received signals are from the first element (1) and the third element (3) of the X-axis of the base array coordinate system, respectively. The signal processing device (7) obtains the cross-correlation function of the first array element (1) and the third array element (3) by performing Fourier transforms on the received signals of the first array element (1) and the third array element (3) along the X-axis of the array coordinate system and then multiplying them by their conjugates to obtain the cross-power spectrum. The cross-power spectrum of the first array element (1) and the third array element (3) is then subjected to an inverse Fourier transform to obtain the correlation function. This correlation function is then input into the detection module and displayed in the detection module. The curves representing the change of the correlation function are plotted, with the horizontal axis representing time and the vertical axis representing the change of the correlation function. The time delay corresponding to the location of the maximum peak in these curves is identified. ; Time delay difference The signal delay is estimated by the signals received by the second array element (2) and the fourth array element (4). Formula (4) is the cross-correlation delay estimation formula. Official (4); in: The conjugate of complex numbers, , The received signals are from the second element (2) and the fourth element (4) of the Y-axis of the base array coordinate system, respectively. The signal processing device (7) obtains the cross-correlation function of the second array element (2) and the fourth array element (4) by performing Fourier transforms on the received signals of the second array element (2) and the fourth array element (4) along the Y-axis of the array coordinate system and then multiplying them by their conjugates to obtain the cross-power spectrum. The cross-power spectrum of the second array element (2) and the fourth array element (4) is then subjected to an inverse Fourier transform to obtain the correlation function. This correlation function is then input into the detection module and displayed in the detection module. The curves representing the change of the correlation function are plotted, with the horizontal axis representing time and the vertical axis representing the change of the correlation function. The time delay corresponding to the location of the maximum peak in these curves is identified. ; Its characteristic is that: in the cross-correlation function and The curve shows multiple related peaks. First, locate the position of the maximum peak. Then, starting from this position, find the first related peak whose height is at least 0.707 times the height of the maximum peak and whose width is within a certain range of the response signal's frequency band. The time delay difference corresponding to the position of this related peak is the time delay difference of the direct wave. or The time delay difference or Substituting into formulas (1) and (2) respectively, we obtain the precise positioning of the target T on the coordinate system established by the ultra-short baseline array.

2. The method for improving the positioning accuracy of an ultra-short baseline system by anti-multipath delay estimation as described in claim 1, characterized in that: The final selected correlation peak is the first peak in the variation curve that meets the conditions of having a peak height at least 0.707 times the peak height of the highest peak and a peak width corresponding to a certain peak width of the response signal frequency band.

3. The method for improving the positioning accuracy of an ultra-short baseline system by anti-multipath delay estimation as described in claim 2, characterized in that: The signal processing device (7) performs adaptive line spectrum enhancement processing between Fourier transform to obtain cross power spectrum and inverse Fourier transform. The adaptive line spectrum enhancement processing reduces interference and the probability of misjudgment.

4. The method for improving the positioning accuracy of an ultra-short baseline system by anti-multipath delay estimation as described in claim 3, characterized in that: The peak width selection condition is 0.9 to 1.1 times the relevant peak width corresponding to the response signal frequency band.

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