Method for accurately obtaining time delay of direct wave through frequency domain pulse compression up-sampling

Abstract

The invention provides a method for accurately obtaining time delay of a direct wave through frequency domain pulse compression up-sampling. The method comprises the following steps of: obtaining a transmitted local copy signal and a signal received after being propagated by a certain distance; fourier transform is carried out on the received signal to a frequency domain, and frequency domain conjugate multiplication is carried out on the received signal and a local copy signal; performing high-frequency zero padding on the obtained signal subjected to frequency domain pulse compression to obtain up-sampling frequency domain data subjected to pulse compression; carrying out inverse Fourier transform to obtain a time domain signal after pulse compression up-sampling; performing Hilbert transform to obtain an envelope signal; and setting a threshold coefficient, and searching a first maximum value to obtain an accurate time delay estimation value of the direct wave. According to the method provided by the invention, the time delay of the direct wave can be solved through Hilbert transform, setting a threshold value and searching for the first maximum value, and the problem of false peaks when the direct wave is enhanced due to multipath superposition is solved. In the frequency domain, fast, efficient and accurate time delay estimation can be realized only by performing inverse Fourier transform to the time domain in a zero padding manner.

Description

Technical Field

[0001] The invention relates to the technical field of signal processing, and in particular to a method for accurately obtaining direct wave delay by up-sampling frequency-domain pulse compression. Background Art

[0002] The accuracy of delay estimation is limited by the sampling frequency of the signal. Therefore, the most effective way to improve the accuracy of delay estimation is to increase the sampling rate of the signal or upsample. Currently, most processing methods perform time domain interpolation on the signal and then perform related operations. This requires a lot of calculations and is not suitable for real-time processing systems.

[0003] In the prior art, however, the upsampling multiples through interpolation can only be integers; in a multipath propagation environment, if the reflection surface through which the signal passes has a high reflection coefficient, such as a smooth seabed, sea surface or underwater rock structure, the energy loss of the reflected wave will be less. In this case, although the signal has been reflected multiple times, the intensity of the reflected wave may exceed the direct wave absorbed or attenuated by the water body due to multipath superposition, so the traditional maximum value method may not be the direct wave delay. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for accurately obtaining the direct wave delay by frequency domain pulse compression upsampling, so as to solve the problems raised in the above background technology. The present invention solves the problem of large amount of calculation in the current time domain interpolation and then related delay acquisition. At the same time, the present invention can perform non-integer multiple upsampling, and solves the problem of incorrect delay calculation when the direct wave is not the strongest in a multipath propagation environment.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solution: a method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling, comprising the following steps:

[0006] Step 1: Obtain the transmitted local copy signal and the received signal after propagation over a certain distance;

[0007] Step 2: Convert to frequency domain through Fourier transform and perform frequency domain conjugate multiplication;

[0008] Step 3: Conjugate multiplication in the frequency domain to obtain the signal after pulse compression;

[0009] Step 4: The pulse compressed signal is high-frequency zero-filled and inverse Fourier transformed to obtain a time domain signal;

[0010] Step 5: Perform Hilbert transform to obtain envelope signal;

[0011] Step 6: Set the threshold coefficient and find the first maximum value to obtain the accurate delay estimate of the direct wave.

[0012] Furthermore, a frequency domain pulse compression method is adopted to directly fill high frequency zeros after conjugate multiplication in the frequency domain.

[0013] Furthermore, the Hilbert transform is used to set the threshold and find the first maximum value to obtain the direct wave delay.

[0014] Furthermore, in step 2, pulse compression is matched filtered in the frequency domain and converted to the frequency domain through Fourier transform, and the formula is as follows:

[0015] R(f)=F o{s1(n)}

[0016] Among them, Fo represents Fourier transform, s1(n), (0≤n≤N) represents the signal received after propagating through a certain distance, and s(n) represents the transmitted local copy signal.

[0017] Furthermore, the frequency domain response of the matched filter is multiplied by the conjugate frequency domain representation of the transmitted signal:

[0018] H(f)=F o{s(n)} *

[0019] Furthermore, the signal after pulse compression is:

[0020] Y(f)=R(f)·H(f)

[0021] Furthermore, assuming that upsampling is required by a factor of M / N, the high frequencies of Y(f) are padded with zeros:

[0022]

[0023] The compressed time domain signal is obtained by inverse Fourier transform:

[0024] y(t′)=F -1 {Y′(k)}

[0025] Furthermore, Hilbert transform is performed on y(t′):

[0026]

[0027] Furthermore, take the signal envelope:

[0028]

[0029] Set a threshold coefficient K, and let the maximum value of yy(t′) be a. Then traverse yy(t′) to find the first maximum value greater than K*a. The delay corresponding to the delay is the direct wave delay.

[0030] Beneficial effects of the present invention:

[0031] 1. The frequency domain pulse compression upsampling method accurately obtains the direct wave delay. The direct wave delay can be obtained by Hilbert transforming and then setting the threshold to find the first maximum value. Non-integer multiple upsampling can be performed, and the processing process is more flexible. It solves the problem of incorrect delay calculation when multiple transmitted signals are stronger than the direct wave due to multi-path superposition.

[0032] 2. The frequency domain pulse compression upsampling method accurately obtains the direct wave delay and transfers the signal to the frequency domain for processing. At the same time, it only needs to fill the frequency domain with zeros and then inverse Fourier transform to the time domain to achieve fast, efficient and accurate delay estimation. The frequency domain pulse compression method is used to directly fill the high frequency with zeros after conjugate multiplication in the frequency domain, which solves the problem of large amount of calculation in the current time domain interpolation and then related delay acquisition. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention provides a flow chart of signal processing in a method for accurately obtaining direct wave delay by frequency domain pulse compression up-sampling. DETAILED DESCRIPTION

[0034] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0035] Example 1

[0036] See also Figure 1 The present invention provides the following technical solution: a method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling, characterized in that it includes the following steps:

[0037] Step 1: Obtain the transmitted local copy signal and the received signal after propagation over a certain distance;

[0038] Step 2: Convert to frequency domain through Fourier transform and perform frequency domain conjugate multiplication;

[0039] Step 3: Conjugate multiplication in the frequency domain to obtain the signal after pulse compression;

[0040] Step 4: Perform high frequency zero padding on the pulse compressed signal and then perform inverse Fourier transform to obtain a compressed time domain signal;

[0041] Step 5: Perform Hilbert transform to obtain envelope signal;

[0042] Step 6: Set the threshold coefficient and find the first maximum value to obtain the accurate delay estimate of the direct wave.

[0043] Based on the above method flow, the frequency domain pulse compression upsampling method accurately obtains the direct wave delay. The direct wave delay can be obtained by Hilbert transforming and then setting the threshold to find the first maximum value. Non-integer multiple upsampling can be performed, and the processing process is more flexible. It solves the problem of incorrect delay calculation when multiple transmitted signals are stronger than the direct wave.

[0044] Example 2

[0045] In this embodiment, it is assumed that the transmitted local copy signal is s(n), and the received signal after propagation over a certain distance is s1(n), (0≤n≤N). First, the received echo signal is pulse compressed. The pulse compression of the present invention performs matched filtering in the frequency domain. Through Fourier transform to the frequency domain:

[0046] R(f)=F o{s1(n)}

[0047] Where Fo represents Fourier transform.

[0048] The frequency domain response of the matched filter is multiplied by the conjugate frequency domain representation of the transmitted signal:

[0049] H(f)=F o{s(n)} *

[0050] The signal after pulse compression is:

[0051] Y(f)=R(f)·H(f)

[0052] Assuming that M / N times upsampling is required, Y(f) is padded with zeros at high frequencies:

[0053]

[0054] The compressed time domain signal is obtained by inverse Fourier transform:

[0055] y(t′)=F -1 {Y′(k)}

[0056] Perform Hilbert transform on y(t′):

[0057]

[0058] Get the signal envelope:

[0059]

[0060] Set a threshold coefficient K, and let the maximum value of yy(t′) be a. Then traverse yy(t′) to find the first maximum value greater than K*a. The delay corresponding to the delay is the direct wave delay.

[0061] This method transfers the signal to the frequency domain for processing. At the same time, it only needs to fill the frequency domain with zeros and then inverse Fourier transform to the time domain to achieve fast, efficient and accurate delay estimation. It adopts the frequency domain pulse compression method and directly fills the high frequency with zeros after conjugate multiplication in the frequency domain, which solves the problem of large amount of calculation in the current time domain interpolation and then related delay acquisition.

[0062] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention.

[0063] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling, characterized in that: The following steps are involved: Step 1: Obtain the transmitted local copy signal and the received signal after propagation over a certain distance; Step 2: Convert to frequency domain through Fourier transform and perform frequency domain conjugate multiplication; Step 3: Obtain the pulse compressed signal after frequency domain conjugate multiplication; Step 4: Obtain the time domain signal after compression upsampling by high frequency zero padding and inverse Fourier transform; Step 5: Perform Hilbert transform to obtain envelope signal; Step 6: Set the threshold coefficient and find the first maximum value to obtain the accurate delay estimate of the direct wave.

2. The method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling according to claim 1 is characterized in that: The frequency domain pulse compression method is adopted, and high frequency zero is directly filled after frequency domain conjugate multiplication.

3. The method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling according to claim 1 is characterized in that: The direct wave delay is obtained by Hilbert transform and then setting the threshold to find the first maximum value.

4. The method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling according to claim 1 is characterized in that: In the step 2, pulse compression is matched filtered in the frequency domain and converted to the frequency domain through Fourier transform. The formula is as follows: R(f)=F o{s1(n)} Among them, Fo represents Fourier transform, s1(n), (0≤n≤N) represents the signal received after propagating through a certain distance, and s(n) represents the transmitted local copy signal.

5. The method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling according to claim 4 is characterized in that: The frequency domain response of the matched filter is multiplied by the conjugate frequency domain representation of the transmitted signal: H(f)=F o{s(n)} *。 6. The method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling according to claim 5, characterized in that: The signal after pulse compression is: Y(f)=R(f)·H(f).

7. The method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling according to claim 6, characterized in that: Assuming that M / N times upsampling is required, Y(f) is padded with zeros at high frequencies: The compressed time domain signal is obtained by inverse Fourier transform: y(t′)=F -1 {Y′(k)}。 8. The method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling according to claim 7, characterized in that: Perform Hilbert transform on y(t′):

9. The method for accurately obtaining direct wave delay by frequency domain pulse compression upsampling according to claim 8, characterized in that: Get the signal envelope: Set a threshold coefficient K, and let the maximum value of yy(t′) be a. Then traverse yy(t′) to find the first maximum value greater than K*a. The delay corresponding to the delay is the direct wave delay.

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