Time-frequency filtering based integrated detection and interference suppression method for direct wave interference

Abstract

The present invention discloses a method for suppressing direct wave interference in integrated detection and interference based on time-frequency filtering. The method includes: the integrated detection and interference system receives a detection echo containing direct wave interference and samples it to obtain a digital signal; the digital signal of the detection echo is segmented and subjected to windowed short-time Fourier transform to obtain a signal with two-dimensional time-frequency representation; two-dimensional time-frequency analysis is performed on the detection echo to determine the time-frequency filtering threshold, a time-frequency filter is constructed to filter out the direct wave interference in the echo; the inverse short-time Fourier transform is performed on the signal after filtering out the direct wave to obtain the time domain of the integrated system echo after filtering. The present invention can achieve the suppression of direct wave interference of the integrated detection and interference system on the radar, and effectively reduce the influence of the direct wave interference of the opponent's radar transmitted signal on the detection performance of the integrated detection and interference system of our side.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar and electronic countermeasures, and particularly relates to a direct wave interference suppression method for integrated detection and jamming based on time-frequency filtering. Background Art

[0002] With the rapid development of software and hardware technologies, the combat modes of all parties in electronic warfare have gradually evolved from the combination of independent devices to integrated, modular, and integrated electronic warfare systems. When designing an integrated detection and jamming system, in order to jam the opponent's radar, the transmitted signal of the integrated system needs to be in the same frequency band as the opponent's radar signal. Therefore, while interfering with the opponent, the detected echo of our side will also be mixed with the co-frequency transmitted signal of the opponent's radar, thus having a strong direct wave impact on the detection of our side and deteriorating the detection performance of our side. Therefore, it is necessary to suppress the direct wave interference of the opponent's radar to improve the detection performance of our integrated detection and jamming system.

[0003] In the literature Zhang Chaogang. Suppression of Direct Wave and Jamming Signals in External Radiation Source Radar [D]. University of Electronic Science and Technology of China, 2010, it is proposed to use an adaptive filtering algorithm for parameter estimation and then use the ICA algorithm for separating co-frequency interference, and the radar detection performance is improved by 35 dB. However, when the peak discrimination in the time-frequency two-dimensional correlation is not high, the detection performance is not as expected.

[0004] In the literature Zhang Dongpo, Lou Caiyi, Peng Xiaoming, Wang Yulong. Research on Continuous Wave Interference Suppression in Integrated Electronic Warfare Systems [J]. Journal of China Academy of Electronics and Information Technology, 2012, 7(01): 47-51., a jamming suppression method based on the fractional Fourier transform is proposed, which improves the signal-to-interference ratio and signal-to-noise ratio. However, there is still a high energy overlap between the direct wave signal and the echo signal of the integrated system in the fractional Fourier transform domain. While suppressing the direct wave, it will cause a large loss of echo information, resulting in pulse compression mismatch, main lobe and side lobe reduction, and deterioration of the detection result. Summary of the Invention

[0005] The purpose of the present invention is to provide a direct wave interference suppression method for integrated detection and jamming based on time-frequency filtering.

[0006] The technical solution for achieving the purpose of the present invention is: a direct wave interference suppression method for integrated detection and jamming based on time-frequency filtering, including:

[0007] The integrated detection and jamming system receives the detected echo containing direct wave interference and samples it to obtain a digital signal;

[0008] The digital signal of the detected echo is segmented and windowed short-time Fourier transformed to obtain a signal with two-dimensional time-frequency representation;

[0009] Perform two-dimensional time-frequency analysis on the detected echo, determine the time-frequency filtering threshold, construct a time-frequency filter, and filter out the direct wave interference in the echo;

[0010] Perform inverse short-time Fourier transform on the signal with the direct wave filtered out to obtain the time domain of the filtered integrated system echo.

[0011] In a second aspect, the present application also provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the method described in the first aspect above is implemented.

[0012] In a third aspect, the present application also provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, the method described in the first aspect above is implemented.

[0013] In a fourth aspect, the present application also provides a computer program product, including a computer program. When the computer program is executed by a processor, the method described in the first aspect above is implemented.

[0014] Compared with the prior art, the significant advantages of the present invention are as follows: The present invention proposes a method for suppressing direct wave interference based on time-frequency filtering. When the integrated system transmits and the detection and interference sharing integrated waveform of the other party's radar signal are in the same frequency band, for the direct wave signal mixed in the detection echo of the integrated system, according to its two-dimensional aggregation region in time-frequency, the direct wave interference is filtered out, and the detection ability of the integrated system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a process diagram of direct wave interference suppression based on time-frequency filtering.

[0016] Figure 2 is the time domain and frequency domain diagram of the detection echo of the integrated system without interference.

[0017] Figure 3 is the time domain and frequency domain diagram of the detection echo of the integrated system under direct wave interference.

[0018] Figure 4 is the time-frequency diagram of the detection echo of the integrated system under direct wave interference.

[0019] Figure 5 is the time-frequency diagram of the detection echo of the integrated system after direct wave interference suppression.

[0020] Figure 6 is the time domain and frequency domain diagram of the detection echo of the integrated system after direct wave interference suppression.

[0021] Figure 7 is the pulse compression diagram of the detection echo of the integrated system before and after direct wave interference suppression. Detailed implementation mode

[0022] Combined with Figure 1 , a direct wave interference suppression method for integrated detection and interference based on time-frequency filtering mainly includes receiving detection echoes - short-time Fourier transform - time-frequency filtering - inverse short-time Fourier transform. The integrated detection and interference system receives detection echoes containing direct wave interference and samples them to obtain digital signals; divides the digital signals of the detection echoes and performs windowed short-time Fourier transform to obtain signals with two-dimensional time-frequency representation; performs two-dimensional time-frequency analysis on the detection echoes, determines the time-frequency filtering threshold, constructs a time-frequency filter, and filters out the direct wave interference in the echoes; performs inverse short-time Fourier transform on the signals with the direct wave removed to obtain the time domain of the filtered integrated system echoes. It realizes the suppression of radar direct wave interference by the integrated detection and interference system, and achieves the improvement of the detection ability of the integrated detection and interference system. The present invention will be further described in detail below.

[0023] Step 1: The integrated detection and interference system receives detection echoes containing direct wave interference and samples them to obtain digital signals.

[0024] Receive the integrated system detection echo x(t) under direct wave interference, expressed as

[0025] x(t) = s(t) + I(t) + ε(t) (1)

[0026] In the formula, s(t) represents the useful echo signal of the integrated system, I(t) is the interference formed by the direct wave of the other party's radar, and ε(t) is the additive noise.

[0027] Sample the detection echo x(t) affected by the direct wave interference and convert it into a digital signal, expressed as

[0028] x(n) = s(n) + I(n) + ε(n), n = 1, 2, …, N. (2)

[0029] In the formula, s(n) represents the sampled useful echo signal of the integrated system, I(n) is the sampled direct wave interference signal of the other party's radar, and ε(n) is the sampled additive noise signal. Assume that the transmitted signal I(n) of the other party's radar is a linear frequency modulation signal and has the same time width of 10×10 -6 s and the same bandwidth of 40×10 6 Hz. It can be seen that the time domain and frequency domain diagrams of the integrated system detection echo under the condition of no interference are as Figure 2 shown. Assume that the interference-to-signal ratio of the direct wave of the other party's linear frequency modulation radar to the echo of our integrated detection and interference system is 20 dB. It can be seen that the time domain and frequency domain diagrams of the integrated system detection echo under the condition of direct wave interference are as Figure 3 shown.

[0030] Step 2: Segment the digital signal of the detection echo and perform windowed short-time Fourier transform to obtain a signal with a two-dimensional time-frequency representation.

[0031] Select a window function with an appropriate length, equally divide the digital signal into multiple small segments, which can overlap between each other, and then perform windowed Fourier transform on these small segments respectively to obtain the short-time Fourier transform x′(n,k) of the signal x(n), expressed as

[0032]

[0033] In the formula, w(i) is a window function with its origin amplitude normalized, that is, w(0) = 1. STFT[·] is the symbol of short-time Fourier transform. Assuming that the window function length is 45 and the hamming window is selected, it can be seen that the time-frequency diagram of the detection echo of the integrated system under the direct wave interference is as Figure 4 shown.

[0034] Step 3: Perform two-dimensional time-frequency analysis on the detection echo, determine the time-frequency filtering threshold, construct a time-frequency filter, and filter out the direct wave interference in the echo.

[0035] STFT is a linear transformation. Therefore, the result after performing short-time Fourier transform on the signal x(n) can also be expressed as

[0036] x′(n,k) = STFT[s(n) + I(n) + ε(n)]

[0037] = STFT[s(n)] + STFT[I(n)] + STFT[ε(n) (4)

[0038] = s′(n,k) + I′(n,k) + ε′(n,k)

[0039] In the formula, s′(n,k), I′(n,k) and ε′(n,k) are the short-time Fourier transform results of the useful echo sampling signal s(n) of the integrated system, the direct wave interference sampling signal I(n) of the opposing linear frequency modulation radar, and the additive noise sampling signal ε(n) respectively.

[0040] Adopt a method of variance expectation to determine the region where the interference energy is located on the time-frequency diagram and obtain the threshold Thr, expressed as

[0041]

[0042] In the formula, E[·] represents the mathematical expectation symbol, and Var[·] is the variance calculation symbol.

[0043] After determining the threshold, compare the amplitude |x′(n,k)| of the detected echo after short-time Fourier transform with the threshold Thr. If it is greater than the threshold, it is considered a direct wave interference, and thus a time-frequency filter is constructed, expressed as

[0044]

[0045] Use the constructed time-frequency filter to filter the echo after short-time Fourier transform to obtain the time-frequency signal x″(n,k) after removing the direct wave interference, expressed as

[0046] x″(n,k) = x′(n,k)·C(n,k) (7)

[0047] In the confrontation scenario between this integrated detection and jamming system and the other party's linear frequency modulation radar, it is calculated that Thr = 30. It can be seen that the time-frequency diagram of the detected echo of the integrated system after suppressing the direct wave interference is as Figure 5 shown.

[0048] Step 4: Perform inverse short-time Fourier transform on the signal after removing the direct wave to obtain the time domain of the echo of the integrated system after filtering Expressed as

[0049]

[0050] In the confrontation scenario between this integrated detection and jamming system and the other party's linear frequency modulation radar, perform inverse short-time Fourier transform on the signal after time-frequency filtering. It can be seen that the time domain and frequency domain diagrams of the detected echo of the integrated system after suppressing the direct wave interference are as Figure 6 shown. And perform pulse compression processing on the signals before and after interference suppression. It can be seen that the pulse compression diagrams of the detected echo of the integrated system before and after suppressing the direct wave interference are as Figure 7 shown. Before being interfered, the average sidelobe level of the detected echo of the integrated system is -25dB. After being interfered, a suppression interference of -5dB is generated on average, and the detection performance deteriorates to the point where the correct main lobe cannot be obtained. After suppressing the direct wave interference, the average sidelobe level is restored to -20dB, and the correct main lobe can be obtained. After suppressing the direct wave interference, the detection performance of the integrated detection and jamming system is improved.

[0051] The above is only the preferred embodiment of the present invention. It should be noted that for those skilled in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A direct wave interference suppression method for integrated detection and interference based on time-frequency filtering, characterized in that Including: The integrated detection and interference system receives the detection echo containing the direct wave interference and samples it to obtain a digital signal. Specifically: Receiving the detection echo x(t) of the integrated system under the direct wave interference, expressed as x(t) = s(t) + I(t) + ε(t) (1) In the formula, s(t) is the useful echo signal of the integrated system, I(t) is the interference formed by the direct wave of the other party's radar, and ε(t) is the additive noise; Sampling the detection echo x(t) affected by the direct wave interference and converting it into a digital signal, expressed as x(n) = s(n) + I(n) + ε(n), n = 1, 2, …, N (2) In the formula, s(n) is the sampled signal of the useful echo of the integrated system, I(n) is the sampled signal of the direct wave interference of the other party's radar, and ε(n) is the sampled signal of the additive noise; Segmenting the digital signal of the detection echo and performing windowed short-time Fourier transform to obtain a signal with two-dimensional time-frequency representation; Performing two-dimensional time-frequency analysis on the detection echo, determining the time-frequency filtering threshold, constructing a time-frequency filter, and filtering out the direct wave interference in the echo. Specifically: The result after performing short-time Fourier transform on the signal x(n) is expressed as In the formula, STFT is a linear transformation, and s′(n, k), I′(n, k), and ε′(n, k) are the short-time Fourier transform results of the sampled signal s(n) of the useful echo of the integrated system, the sampled signal I(n) of the direct wave interference of the other party's linear frequency modulation radar, and the sampled signal ε(n) of the additive noise, respectively; Using the method of variance expectation to determine the region where the interference energy is located on the two-dimensional time-frequency diagram and obtaining the threshold Thr, expressed as In the formula, E[·] represents the mathematical expectation symbol, and Var[·] is the variance calculation symbol; After determining the threshold, comparing the amplitude |x′(n, k)| of the detection echo after short-time Fourier transform with the threshold Thr. If it is greater than the threshold, it is considered as direct wave interference, and thus a time-frequency filter is constructed, expressed as Using the constructed time-frequency filter to filter the echo after short-time Fourier transform to obtain the time-frequency signal x″(n, k) after removing the direct wave interference, expressed as x″(n, k) = x′(n, k) · C(n, k) (7) Performing inverse short-time Fourier transform on the signal after filtering out the direct wave to obtain the time domain of the echo of the integrated system after filtering.

2. The method for suppressing the direct wave interference of the integrated detection and interference based on time-frequency filtering according to claim 1, wherein Segmenting the digital signal of the detection echo and performing windowed short-time Fourier transform. Specifically: Selecting a window function, equally dividing the digital signal into multiple small segments, and performing windowed Fourier transform on these small segments respectively to obtain the short-time Fourier transform x′(n, k) of the signal x(n), expressed as In the formula, w(i) is the window function with the origin amplitude normalized, that is, w(0) = 1; STFT[·] is the short-time Fourier transform symbol.

3. The method for suppressing direct wave interference in integrated detection and interference based on time-frequency filtering according to claim 1, wherein Perform an inverse short-time Fourier transform on the signal with the direct wave filtered out to obtain the time domain of the integrated system echo after filtering Denoted as 4. A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method described in any one of claims 1 - 3.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that, When this program is executed by the processor, it implements the steps of the method described in any one of claims 1 - 3.

6. A computer program product, comprising a computer program, characterized in that, When this computer program is executed by the processor, it implements the steps of the method described in any one of claims 1 - 3.

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