Method for resisting complex modulation intermittent sampling and forwarding interference of radar

Abstract

A method for resisting complex modulation intermittent sampling and forwarding interference of a radar comprises the steps that noise reduction processing is conducted on an interfered echo module value based on a wavelet transform method, the maximum value and the minimum value of the echo module value obtained after noise reduction processing are extracted, a threshold value is calculated through weighting, and the interfered time domain position in an echo is obtained through binarization comparison; performing narrow pulse elimination on the interference position to realize interference signal elimination; establishing a sparse recovery regularization model based on the signal frequency domain sparse characteristic after the dechirp processing for the target echo after the narrow pulse elimination, solving the regularization sparse recovery model through a convex optimization method to obtain a target echo frequency spectrum, and obtaining a target time domain echo through inverse Fourier transform and inverse dechirp processing; carrying out matched filtering pulse compression to obtain a radar detection result resisting complex modulation intermittent sampling forwarding interference; according to the method, complex intermittent sampling forwarding interference can be effectively suppressed, target detection is realized, complex modulation parameters of the intermittent sampling forwarding interference do not need to be relied on, and compared with a traditional method, the method has higher universality.

Description

Technical Field

[0001] The invention belongs to the technical field of radar electronic countermeasures, and in particular relates to a radar anti-complex modulation intermittent sampling forwarding interference method. Background Art

[0002] With the rapid development of RF store-and-forward technology, radar jamming has achieved a technological leap from non-coherent to coherent. Intermittent sampling and forwarding jamming solves the problem of jammer transmit-receive isolation through low-rate sampling and forwarding, and can produce dense false target deception jamming effects on radar. In view of the strong regularity of false targets in intermittent sampling and forwarding jamming, complex modulation intermittent sampling and forwarding jamming has become a research hotspot, such as segmented frequency shifting, smart noise composite modulation intermittent sampling and forwarding jamming, etc. Complex modulation intermittent sampling and forwarding jamming can reduce the regularity of jamming targets and produce jamming effects that combine deception and suppression, which is one of the main threats to current radar detection.

[0003] The intermittent sampling forwarding interference suppression method includes receiving end signal processing and transmitting end waveform design. Based on the prior knowledge of the linear frequency modulation waveform transmitted by the radar, the receiving end signal processing is performed through band-stop filtering and time-frequency filtering. The band-stop filtering method designs a band-stop filter in the frequency domain to form a notch at the interference signal spectrum. The time-frequency filtering method first de-skews the signal, and then designs a two-dimensional time-frequency filter according to the energy distribution in the time-frequency domain. Under the prior information of the repetition period and duty cycle of the intermittent sampling forwarding interference, the interference energy and false target gain can be suppressed by designing the waveform and non-matching filter at the transmitting end. However, complex modulation reduces the regularity of the energy of the intermittent sampling forwarding interference in the frequency domain and the time-frequency domain, resulting in a decrease in the performance of the above interference suppression method. In addition, complex modulation makes the extraction of the prior parameters of the intermittent sampling forwarding interference more complicated, which also leads to the deterioration of the performance of the interference suppression method based on waveform design.

[0004] In order to solve the problem of degraded interference suppression performance of intermittent sampling forwarding caused by complex modulation, the present invention proposes a method for resisting complex modulation intermittent sampling forwarding interference. The method obtains the time domain position of the complex modulation intermittent sampling forwarding interference signal by time domain noise reduction of the interfered signal, and then uses a narrow pulse removal method to remove the interfered segment echo, and obtains the complete echo signal through de-skewing and sparse recovery processing, and finally obtains the anti-interference target detection result. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a radar anti-complex modulation intermittent sampling forwarding interference method, which can suppress segmented frequency shift and smart noise composite modulation intermittent sampling forwarding interference, and accurately obtain target detection results without estimating complex modulation parameters. It can also resist slice forwarding and intermittent sampling forwarding interference, has strong universality, and has broad application prospects in the fields of air defense radar, anti-missile radar, guidance radar, airborne fire control radar and inverse synthetic aperture radar.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a radar anti-complex modulation intermittent sampling forwarding interference method, s1. obtain radar orthogonal demodulation echo data, use wavelet transform processing to reduce echo modulus noise, calculate the maximum and minimum values ​​of the echo modulus after noise reduction processing, and calculate the threshold value based on this numerical value weighted, extract the sequence with the threshold value greater than the threshold value as the corresponding time domain position of the intermittent sampling forwarding interference signal; s2. based on the intermittent sampling forwarding interference time domain position time domain narrow pulse removal sequence, and the corresponding position IQ echo narrow pulse Impulse removal processing; s3. Establish a regularized sparse recovery model based on the sparse characteristics of the frequency domain signal; the target signal after de-skew processing is similar to the impulse response in the frequency domain, and it has sparse characteristics in the frequency domain. A sparse recovery model in the frequency domain is established. By solving the regularized sparse recovery model, the complete target echo signal spectrum can be obtained; s4. The target echo signal after de-skew in the time domain is obtained by inverse Fourier transform, and the time domain target echo signal is obtained after inverse de-skew processing; s5. The anti-interference detection result can be obtained by matched filter pulse compression processing.

[0007] Further, the specific steps of s1 are:

[0008] It is known that the discrete sampling target echo is s, and the complex modulated intermittent sampling forwarding interference signal is s j , the noise signal is n, then the interfered radar echo is:

[0009] r=s+s j +n (1)

[0010] For the obtained modulus value of the interfered echo data |r|, the wavelet transform is used to perform noise reduction processing, and the smoothed time domain echo envelope data |r 1 |;

[0011] For the time domain echo envelope data after noise reduction, the maximum and minimum values ​​are calculated as max|r 1 | and min|r 1 |, on this basis, the threshold ξ is calculated as follows:

[0012]

[0013] Wherein, κ is a threshold weighting factor, which needs to make the threshold extract the interfered signal as completely as possible. On this basis, the following steps are performed to obtain the interference time domain position indication vector p:

[0014]

[0015] For the interfered echo data, narrow pulse removal is performed to obtain the echo data after narrow pulse removal. 2 ;

[0016]

[0017] Further, the specific steps of s2 are:

[0018] For the data after narrow pulse processing, de-skewing is performed to obtain the de-skewing signal r 3 Assuming the de-skewed signal is x, the signal after de-skew processing is

[0019] r 3 =r 2 ⊙x (5)

[0020] Where ⊙ is the dot product.

[0021] Further, the specific steps of s3 are:

[0022] A regularized sparse recovery model is established for the frequency domain interference-free data after de-skewing, and the complete interference-free frequency domain signal is obtained by solving the regularized model.

[0023] A diagonal matrix is ​​established based on vector 1-p, and the rows of the matrix with all zeros are removed to obtain the matrix P. Since the undisturbed signal segment is the same before and after the narrow pulse is removed, it can be obtained:

[0024] Pr 3 =Ps 1 (6)

[0025] In the above formula, s 1 =s⊙x represents the de-skewing of the target echo to be recovered. Theoretically, the target signal after de-skewing is an impulse function in the frequency domain, which has the sparse characteristics in the frequency domain. Therefore, its sparse recovery regularization model can be established. Assuming that the reconstructed signal spectrum is S 1 , F represents the discrete Fourier transform matrix, where:

[0026]

[0027] Then formula (6) can be expressed as:

[0028] Pr 3 =PF -1 S1 (8)

[0029] Let y = Pr 3 , which is the target echo compression data after narrow pulse removal and de-skewing, the sparse recovery model can be expressed as:

[0030]

[0031] PF -1 S 1 =y (9)

[0032] Since the objective function and constraints can be converted into real functions of the real and imaginary parts of the variables, and the one-norm is a convex function, and the linear constraints are also convex sets, formula (9) can be directly solved by the convex optimization method, and the target echo spectrum obtained by sparse recovery is:

[0033]

[0034] Further, the specific steps of s4 are:

[0035] Perform inverse Fourier transform processing on the target echo spectrum data obtained by sparse recovery to obtain the target echo data with de-skewing processing;

[0036]

[0037] Further, the specific steps of s5 are:

[0038] For the de-skewing target echo, inverse de-skewing is performed, and matched filter pulse compression is performed to obtain the detection result.

[0039] The beneficial effects of the present invention are as follows: the present invention extracts the time domain position of the interference signal by performing binary comparison on the echo model after noise reduction processing, and uses a narrow pulse elimination method to eliminate the interfered echo fragment, without relying on the complex modulation parameters of the intermittent sampling and forwarding interference signal, and has stronger universality; by de-skewing the echo after interference elimination, and using a sparse recovery method to obtain a complete echo signal, the radar detection signal processing gain loss and excessive false alarm problems caused by narrow pulse elimination are solved; the present invention can suppress the segmented frequency shift and smart noise composite modulation intermittent sampling and forwarding interference, and accurately obtain the target detection result. Since the present invention does not need to estimate complex modulation parameters, the present invention can also resist the interference of slice forwarding and intermittent sampling and forwarding, and has strong universality, and has broad application prospects in the fields of air defense radar, anti-missile radar, guidance radar, airborne fire control radar and inverse synthetic aperture radar; the parts not introduced in detail in the present invention are existing common technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described below in conjunction with the accompanying drawings:

[0041] Figure 1 Flowchart for resisting complex modulation intermittent sampling and forwarding interference;

[0042] Figure 2 It is the echo amplitude interfered by the intermittent sampling forwarding modulated by smart noise;

[0043] Figure 3 It is to use the time domain echo envelope after wavelet transform noise reduction and the narrow pulse removal threshold;

[0044] Figure 4 This is the echo time domain result diagram after narrow pulses are removed;

[0045] Figure 5 Intermittent sampling and forwarding of pulse compression results before and after interference suppression for smart noise modulation;

[0046] Figure 6 The pulse compression results before and after the interference suppression of the intermittent sampling forwarding of the segmented frequency shift modulation;

[0047] Figure 7 Pulse compression results before and after intermittent sampling and forwarding interference suppression. DETAILED DESCRIPTION

[0048] The present invention is further described in detail below in conjunction with embodiments and specific implementation modes:

[0049] Example 1

[0050] In the simulation experiment, the radar transmits a pulse signal with a time width of 32us, a bandwidth of 8MHz, and a pulse repetition period of 1ms. The jammer intermittent sampling period is 8us, the duty cycle is 25%, and the jammer styles are smart noise modulation intermittent sampling forwarding interference, segmented frequency shift intermittent sampling forwarding interference, and intermittent sampling forwarding interference. A target is set in the scene, 1.5km away from the reference position, the signal-to-noise ratio is 10dB, and the interference-to-signal ratio is set to 15dB. The present invention is used to perform interference suppression and target echo recovery under the above parameter settings.

[0051] like Figure 1 As shown in the figure, a radar anti-complex modulation intermittent sampling forwarding interference method is shown in the figure. It is known that the discrete sampling target echo is s and the complex modulation intermittent sampling forwarding interference signal is s. j , the noise signal is n, then the interfered radar echo is:

[0052] r=s+s j +n (1);

[0053] Step 1: For the obtained modulus value of the interfered echo data |r|, use wavelet transform to perform noise reduction and smooth the time domain echo envelope data |r 1 |;

[0054] Step 2: For the time domain echo envelope data after noise reduction, calculate the maximum and minimum values ​​as max|r 1 | and min|r 1 |, on this basis, the threshold ξ is calculated as follows:

[0055]

[0056] Wherein, κ is a threshold weighting factor, which needs to make the threshold extract the interfered signal as completely as possible. On this basis, the following steps are performed to obtain the interference time domain position indication vector p:

[0057]

[0058] For the interfered echo data, narrow pulse removal is performed to obtain the echo data after narrow pulse removal. 2 .

[0059]

[0060] Step 3: De-skewing the data after narrow pulse processing to obtain the de-skewing signal r 3 , assuming the de-skewed signal is x, then the de-skewed signal is

[0061] r 3 =r 2 ⊙x (5)

[0062] Where ⊙ is the dot product.

[0063] Step 4: For the frequency domain interference-free data after de-skewing, a regularized sparse recovery model is established, and the complete interference-free frequency domain signal is obtained by solving the regularized model.

[0064] A diagonal matrix is ​​established based on vector 1-p, and the rows of the matrix with all zeros are removed to obtain the matrix P. Since the undisturbed signal segment is the same before and after the narrow pulse is removed, it can be obtained:

[0065] Pr 3 =Ps 1 (6)

[0066] In the above formula, s 1 =s⊙x represents the de-skewing of the target echo to be recovered. Theoretically, the target signal after de-skewing is an impulse function in the frequency domain, which has the sparse characteristics in the frequency domain. Therefore, its sparse recovery regularization model can be established. Assuming that the reconstructed signal spectrum is S1 , F represents the discrete Fourier transform matrix, where:

[0067]

[0068] Then formula (6) can be expressed as:

[0069] Pr 3 =PF -1 S 1 (8)

[0070] Let y = Pr 3 , which is the target echo compression data after narrow pulse removal and de-skewing, the sparse recovery model can be expressed as:

[0071]

[0072] PF -1 S 1 =y (9)

[0073] Since the objective function and constraints can be converted into real functions of the real and imaginary parts of the variables, and the one-norm is a convex function, and the linear constraints are also convex sets, formula (9) can be directly solved by the convex optimization method, and the target echo spectrum obtained by sparse recovery is:

[0074]

[0075] Step 5: Perform inverse Fourier transform on the target echo spectrum data obtained by sparse recovery to obtain the de-skewed target echo data.

[0076]

[0077] Step 6: For the de-skewing target echo, perform inverse de-skewing processing and execute matched filter pulse compression processing to obtain the detection result.

[0078] Figure 2 It is the echo amplitude affected by the intermittent sampling and forwarding interference modulated by smart noise, where the smart noise time width is 2us, and the noise template is white noise. It can be seen from the figure that the interference signal amplitude is significantly higher than the target echo amplitude, and it is a periodic pulse signal. Affected by the white noise modulation, the single interference slice is widened to 4us, and the amplitude envelope fluctuates greatly.

[0079] Figure 3 It is the time domain echo envelope after wavelet transform denoising and the narrow pulse removal threshold, where the weighting factor is 0.25.

[0080] Figure 4This is the echo time domain result diagram after narrow pulse removal. The smart noise modulated intermittent sampling and forwarding interference signal with an amplitude higher than the threshold in the echo has been removed, and the target echo at the corresponding position has also been removed.

[0081] Figure 5 For smart noise modulation, intermittent sampling is used to forward the pulse compression results before and after interference suppression. Figure 5 (a) is the pulse compression result before interference suppression, which contains dense false targets and the real target is completely suppressed, so the real target signal cannot be obtained. Figure 5 (b) is the pulse compression result after suppressing the smart noise modulation intermittent sampling and forwarding interference by using the present invention, and the target located at a position of 1.5km can be obtained. The results show that the present invention can suppress the smart noise modulation intermittent sampling and forwarding interference and recover the target signal.

[0082] Figure 6 The pulse compression results before and after the intermittent sampling forwarding interference suppression of the segmented frequency shift modulation are shown in Figure 1. The radar signal is divided into four segments, each with a length of 8us, and the frequency shifts of the four segments are 300kHz, 0kHz, -200kHz and 100kHz respectively. Figure 6 (a) is the pulse compression result before interference suppression. The real target is completely suppressed. Figure 6 (b) is the pulse compression result after interference suppression, which can obtain the target located at a position of 1.5 km. The results show that the present invention can suppress the intermittent sampling forwarding interference of segmented frequency shift modulation and recover the target signal.

[0083] Figure 7 For intermittent sampling and forwarding of pulse compression results before and after interference suppression, Figure 7 (a) is the pulse compression result before interference suppression, which contains dense false targets and cannot obtain the real target signal. Figure 7 (b) is the pulse compression result after interference suppression, which can obtain the target located at a position of 1.5 km. The results show that the present invention can suppress intermittent sampling forwarding interference and recover the target signal.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A radar anti-complex modulation intermittent sampling forwarding interference method, characterized in that: s1. Obtain radar orthogonal demodulation echo data, use wavelet transform to reduce echo modulus noise, calculate the maximum and minimum values ​​of the echo modulus after noise reduction, and calculate the threshold based on this value weighted calculation, extract the sequence with a threshold greater than the threshold as the corresponding time domain position of the intermittent sampling interference signal; s2. Based on intermittent sampling, forward the interference time domain position time domain narrow pulse removal sequence, and perform narrow pulse removal processing on the corresponding position IQ echo; s3. A regularized sparse recovery model is established based on the sparse characteristics of the frequency domain signal; the target signal after de-skew processing is similar to an impulse response in the frequency domain, and it has sparse characteristics in the frequency domain. A sparse recovery model in the frequency domain is established, and the complete target echo signal spectrum can be obtained by solving the regularized sparse recovery model; s4. The target echo signal after de-skew in the time domain is obtained by inverse Fourier transform, and the time domain target echo signal is obtained after inverse de-skew processing; s5. The anti-interference detection result can be obtained by matched filter pulse compression processing.

2. The radar anti-complex modulation intermittent sampling forwarding interference method according to claim 1 is characterized in that: The specific steps of s1 are: It is known that the discrete sampling target echo is s, and the complex modulated intermittent sampling forwarding interference signal is s j , the noise signal is n, then the interfered radar echo is: r=s+s j +n (1) For the obtained modulus value |r| of the interfered echo data, the wavelet transform is used to perform noise reduction processing, and the smoothed time domain echo envelope data |r1| is obtained; For the time domain echo envelope data after noise reduction, the maximum and minimum values ​​are calculated as max|r1| and min|r1|, respectively. On this basis, the threshold ξ is calculated as follows: Wherein, κ is a threshold weighting factor, which needs to make the threshold extract the interfered signal as completely as possible. On this basis, the following steps are performed to obtain the interference time domain position indication vector p: For the interfered echo data, narrow pulse elimination processing is performed to obtain the echo data r2 after narrow pulse elimination; 3. The radar anti-complex modulation intermittent sampling forwarding interference method according to claim 1 is characterized in that: The specific steps of s2 are: De-skewing is performed on the data after narrow pulse processing to obtain the de-skewing signal r3. Assuming that the de-skewing signal is x, the de-skewing signal is r3＝r2⊙x (5) Where ⊙ is the dot product.

4. The radar anti-complex modulation intermittent sampling forwarding interference method according to claim 1 is characterized in that: The specific steps of s3 are: A regularized sparse recovery model is established for the frequency domain interference-free data after de-skewing, and the complete interference-free frequency domain signal is obtained by solving the regularized model. A diagonal matrix is ​​established based on vector 1-p, and the rows of the matrix with all zeros are removed to obtain the matrix P. Since the undisturbed signal segment is the same before and after the narrow pulse is removed, it can be obtained: Pr3=Ps1 (6) In the above formula, s1 = s⊙x represents the de-skewing of the target echo to be recovered. Theoretically, the target signal is an impulse function in the frequency domain after de-skewing, which has the sparse characteristics of the frequency domain. Therefore, its sparse recovery regularization model can be established. Assume that the reconstructed signal spectrum is S1, and F represents the discrete Fourier transform matrix, where: Then formula (6) can be expressed as: Pr3=PF -1 S1 (8) Let y = Pr3, which is the target echo compression data after narrow pulse removal and de-skewing, then the sparse recovery model can be expressed as: Since the objective function and constraints can be converted into real functions of the real and imaginary parts of the variables, and the one-norm is a convex function, and the linear constraints are also convex sets, formula (9) can be directly solved by the convex optimization method, and the target echo spectrum obtained by sparse recovery is:

5. The radar anti-complex modulation intermittent sampling forwarding interference method according to claim 1 is characterized in that: The specific steps of s4 are: Perform inverse Fourier transform processing on the target echo spectrum data obtained by sparse recovery to obtain the target echo data with de-skewing processing; 6. The radar anti-complex modulation intermittent sampling forwarding interference method according to claim 1 is characterized in that: The specific steps of s5 are: For the de-skewing target echo, inverse de-skewing is performed, and matched filter pulse compression is performed to obtain the detection result.

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