An intermittent sampling interference suppression method based on non-matching difference feature filtering

Abstract

The application discloses an intermittent sampling interference suppression method based on non-matching difference characteristic filtering, which comprises the following steps: initializing basic parameters of a linear frequency modulation signal and transmitting the linear frequency modulation signal; obtaining an echo signal, performing time-frequency analysis to obtain a two-dimensional time-frequency diagram, performing connected block detection, and estimating key parameters of the intermittent sampling interference; the key parameters comprise a slice width, a slice number and a retransmission number; based on the key parameters, a non-matching filter is constructed; the echo signal is subjected to matching filtering and non-matching filtering, and a filter is defined by using difference characteristics of processing results; the result of the matching filtering is filtered by the filter, and a peak with the largest amplitude is extracted as a detection target. According to the above technical scheme, the filter is designed, the interference suppression effect is good without adjusting the transmission strategy, and the radar anti-intermittent sampling interference capability is enhanced.

Description

Technical Field

[0001] This invention relates to the field of radar anti-jamming technology, and more specifically, to an intermittent sampling interference suppression method based on unmatched difference feature filtering. Background Technology

[0002] Coherent forwarding jamming intercepts the radar transmitted signal, modulates it with a delay, and then forwards a false signal coherent with the radar echo, creating false targets to deceive the radar detection system. Traditional coherent forwarding jamming typically requires receiving the full duration of the radar signal, placing high demands on the jammer's sampling rate and the isolation between the transmitting and receiving antennas. Intermittent sampling jamming, on the other hand, is a novel coherent jamming method based on Digital Radio Frequency Memory (DRFM) technology. Compared to traditional coherent forwarding jamming, it offers advantages such as high efficiency, fast response speed, no need to receive the full duration of the signal, and time-division multiplexing. This technology, through low-rate intermittent sampling and forwarding of the radar signal, can create a series of realistic coherent false targets.

[0003] For signals containing coherent false target groups, identification and analysis are necessary to suppress interference and achieve anti-intermittent sampling interference. Currently, a common anti-intermittent sampling interference technique utilizes time-frequency analysis, targeting the discontinuous characteristics of intermittent sampling interference in the time-frequency domain by removing echo signals from the interference intervals. However, because the continuity of the target echo signal in the frequency domain is disrupted, the target result contains a large number of sidelobes, making this processing method unsatisfactory. Another common approach is to design waveforms based on interference parameter estimation results, ensuring that the sliced ​​signal is orthogonal to other signals to weaken the false targets formed by intermittent sampling interference. However, this method requires real-time generation of the designed waveform based on the parameter estimation results, placing certain demands on the storage and waveform generation capabilities of the implementation hardware. Simultaneously, reconstructing interference slices and constructing unmatched filters through intermittent sampling parameter estimation can weaken interference to some extent, but because the interference signal has a certain degree of coherence with the remaining signal, it cannot completely suppress the interference.

[0004] Therefore, a low-cost, versatile, and less impactful interference suppression method is needed to improve the success rate of combating intermittent sampling interference. Summary of the Invention

[0005] To achieve the above objectives, this application provides an intermittent sampling interference suppression method based on unmatched difference feature filtering, comprising the following steps: Initialize the basic parameters of the linear frequency modulated signal and transmit the linear frequency modulated signal; Echo signals are acquired, and time-frequency analysis is performed to obtain a two-dimensional time-frequency plot. Connected component detection is then performed based on the two-dimensional time-frequency plot to estimate key parameters of intermittent sampling interference. These key parameters include: slice width. Number of slices and number of reposts ; Based on the aforementioned key parameters, an unmatched filter is constructed; Matched and unmatched filtering are performed on the echo signal, and the filter is defined using the difference characteristics; The matched filtering result is filtered by a filter, and the peak with the largest amplitude is extracted as the detection target.

[0006] The basic parameters for initializing a linear frequency modulated signal include: pulse width, frequency repetition, and bandwidth.

[0007] The time-frequency analysis is implemented using the short-time Fourier transform method, including: Use window functions Intercepting the transmitted signal For nearby short-time signals, the Fourier transform of the short-time signal is expressed as: ,in, For the output time-frequency coordinates, For the corresponding timeline, This corresponds to the frequency axis.

[0008] Furthermore, connected component detection includes: Calculate the length of each connected component in the time dimension in a two-dimensional time-frequency graph, and calculate the position and frequency of the top-right pixel of each connected component in the frequency dimension. Remove connected components whose time dimension length exceeds half the pulse width of the transmitted signal; Parameter estimation for intermittent sampling interference.

[0009] The parameter estimation for intermittent sampling interference includes: defining the mean of the remaining connected component in the time dimension as the estimated slice width. Count the frequency axis positions of connected components and the number of times each connected component appears at different frequency axis positions. Define the number of times each connected component appears at different frequency axis positions as the slice count. The maximum number of repetitions at the same frequency axis position is defined as the number of forwardings. .

[0010] Among them, a connected component refers to the signal corresponding to a bright spot or continuous ridge in a two-dimensional time-frequency graph, which is an energy concentration region at a specific time and frequency.

[0011] Furthermore, constructing the unmatched filter includes: The sliced ​​signal is reconstructed using key parameters and transmitted signals, and is represented as follows: ,in, As a discrete-time variable, it represents the instantaneous moment of the signal. This is the slice index within a single period of intermittent sampling interference; Constructing a matched filter, denoted as ; The mismatched filter coefficients are obtained by subtracting the interference slice from the original transmitted signal. , is represented as: - ,in, The original transmitted signal, This is the reconstructed slice signal.

[0012] Furthermore, the filter is defined using the difference features as follows: ,in, This is the pulse compression result obtained from matched filtering. This is the pulse compression result obtained from unmatched filtering. It is the modulo of the difference between the two. Represents the Hilbert transform. This is an adjustable coefficient.

[0013] The result of matched filtering is expressed as follows: .

[0014] The method provided by this invention can design filters based on the understanding of interference parameters, and achieve better suppression effect without adjusting the transmission strategy, thereby enhancing the radar's ability to resist intermittent sampling interference. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the intermittent sampling interference suppression method provided in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the estimation effect of intermittent sampling interference parameters by connected component detection according to an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the results of matched filtering and unmatched filtering of echo signals containing targets and interference, according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the target detection success rate and interference suppression ratio determined by the intermittent sampling interference suppression method provided in the embodiments of the present invention. Detailed Implementation

[0016] The specific implementation of the present invention will now be described in detail with reference to the accompanying drawings.

[0017] The intermittent sampling interference suppression method based on unmatched difference feature filtering provided by this invention is as follows: Figure 1 As shown, it includes the following steps: Step S101: Initialize the basic parameters of the linear frequency modulated signal and transmit the linear frequency modulated signal; In this step, the basic parameters of the linear frequency modulated signal are set according to the detection scenario, including pulse width, repetition rate, bandwidth, etc.; after the basic parameters are initialized, the linear frequency modulated signal is transmitted.

[0018] Step S102: Acquire the echo signal, perform time-frequency analysis on the echo signal, and estimate the key parameters of intermittent sampling interference; First, the original echo signal containing the target and intermittent sampling interference is obtained through time-frequency analysis, resulting in a two-dimensional time-frequency map. The "bright spots" or "continuous ridges" in the two-dimensional time-frequency map correspond to energy concentration regions at specific times and frequencies. These regions are defined as connected components. Connected components can directly reflect the time-frequency variation law of the signal.

[0019] The time-frequency analysis is achieved through the short-time Fourier transform method: first, using a window function... Intercept the transmitted signal For nearby short-time signals, the Fourier transform of the short-time signal is expressed as: ,in, For the output time-frequency coordinates, For the corresponding timeline, This corresponds to the frequency axis.

[0020] Furthermore, based on the 8-neighborhood connectivity rule, connected component detection is performed on the two-dimensional time-frequency graph. Connected components are extracted from the two-dimensional time-frequency graph, and the features of each connected component are statistically analyzed to estimate the key parameters of intermittent sampling interference. Specifically, this includes the following: Calculate the length of each connected component in the time dimension in the time-frequency graph, and calculate the position and frequency of the top right pixel of the connected component in the frequency dimension. Based on the principle of intermittent sampling interference, connected components with a time dimension length exceeding half the pulse width of the transmitted signal are removed; Parameter estimation for intermittent sampling interference includes: estimating the mean of the remaining connected components over the time dimension as the slice width. Count the frequency axis positions of connected components and the number of times each connected component appears at different frequency axis positions. Define the number of times each connected component appears at different frequency axis positions as the slice count. The maximum number of repetitions at the same frequency axis position is defined as the number of forwardings. .

[0021] At this point, the key parameters for estimating intermittent sampling interference include: slice width. Number of slices and number of reposts .

[0022] Step S103: Construct an unmatched filter based on the estimated key parameters of the intermittent sampling interference; At this point, the sliced ​​signal is reconstructed using the estimated key parameters of the intermittent sampling interference and the transmitted signal, as follows: ,in, As a discrete-time variable, it represents the instantaneous moment of the signal. This is the slice index within a single period of intermittent sampling interference.

[0023] Constructing a matched filter, denoted as Since intermittent sampling interference and radar transmitted signals have some coherence, pulse compression processing based on matched filtering can also achieve a certain processing gain and form false targets.

[0024] The unmatched filter is constructed using the reconstructed sliced ​​signal fragments, and the unmatched filter coefficients are obtained by subtracting the interference slices from the original transmitted signal. This can effectively reduce the coherence between interference and the reference signal, as expressed as: - ,in, The original transmitted signal, This is the reconstructed slice signal.

[0025] Step S104: Perform matched filtering and unmatched filtering on the echo signal, define a filter based on the difference between the results of matched filtering and unmatched filtering, and generate pulse compression results. and ; Since the intermittent sampling interference signal segments in the unmatched filter are completely eliminated, the pulse compression result obtained from the unmatched filter... In this process, the false target signal exhibits significant peak shift and peak attenuation compared to the matched filter result, while the target signal only suffers partial energy loss. A filter is constructed using this difference characteristic, expressed as: ,in, This is the pulse compression result obtained from matched filtering. This is the pulse compression result obtained from unmatched filtering. It is the modulo of the difference between the two. Represents the Hilbert transform. This is an adjustable coefficient.

[0026] Step S105: Filter the result of the matched filtering through a filter and extract the peak with the largest amplitude as the detection target; The result of matched filtering is expressed as follows: ; The filter suppresses sampling points with amplitude variations between matched and unmatched filtering. The greater the variation, the more obvious the suppression effect. The peak with the largest amplitude is extracted from the filtered result as the detection target, which can effectively suppress multiple false targets caused by intermittent sampling interference.

[0027] Furthermore, determine whether the detection process has been completed. If not, repeat steps S102-S105 to continue identifying the target.

[0028] To verify the effectiveness of the intermittent sampling interference suppression method provided by this invention, three sets of simulation experiments are provided.

[0029] First, set the basic parameters of the linear frequency modulated signal in the simulation environment, including: radar pulse width of 4µs, multiple cycles of 20µs, bandwidth of 20MHz, and simulation sampling rate of 80MHz.

[0030] Based on the experimental environment, the number of simulated targets was set to 1, the distance to the target was set to 300m, and the parameters for intermittent sampling interference were set, including: slice width of 1µs and number of slices. Nc Number of reposts: 1-2 Qc The signal-to-interference ratio (JSR) is 1-3, and the signal-to-interference ratio (JSR) is 0-30 dB.

[0031] The three sets of simulation experiments aim to verify the accuracy of key parameters of intermittent sampling interference, the effectiveness of the difference feature filter, and the accuracy of target judgment, respectively: Simulation Experiment 1: Four different parameters for intermittent sampling interference were set, and time-frequency analysis was performed on the echo signals generated by different intermittent sampling interferences to obtain time-frequency plots. Connectivity component detection analysis was then performed on the time-frequency plots to estimate the key parameters of the intermittent sampling interference. The results of connectivity component detection on the time-frequency plots under the four different intermittent sampling interference parameters are as follows: Figure 2 As shown, under different intermittent sampling interference parameters, the slice width is estimated by the time dimension length, and the number of slices and forwardings are estimated by the frequency dimension occurrence frequency statistics; the estimated key parameters are consistent with the parameters of the four sets of intermittent sampling interference.

[0032] Simulation Experiment 2: Set a set of parameters for intermittent sampling interference, including: slice width 1µs, slice count 1, forward count 3, and signal-to-interference ratio 20dB. Compare the results of matched filtering and unmatched filtering, design a difference feature filter, and obtain the pulse compression result after filtering.

[0033] like Figure 3 As shown, Figure 3(a) The blue curve represents the pulse compression result obtained after matched filter processing, and the red curve represents the pulse compression result obtained after unmatched filter processing. The target peak is located at cell 159, and the three false target peaks are located at cells 425, 505, and 585. It can be seen that the blue and red curves basically overlap at the target peak position, but there is a significant difference at the false target peak positions. This difference is used to design… Figure 3 The difference feature filter in (b) is used in... Figure 3 (a) Filtering is performed at locations where the red and blue curves differ greatly, in order to filter out false target peaks caused by intermittent sampling interference. Figure 3 (c) shows the pulse pressure results of interference suppression. It can be clearly seen that the target peak becomes the largest peak after interference suppression, which is easy to be detected correctly, and the false target peak formed by interference is suppressed by 15dB.

[0034] Simulation Experiment 3: A set of parameters for intermittent sampling interference was set, including a slice width of 1 μs, 1 slice count, 3 forwarding counts, and an interference-to-signal ratio (SNR) ranging from 0 to 30. The experiment was repeated 1000 times for each SNR, and the average target detection success rate and average interference suppression ratio were calculated after interference suppression at each SNR. The target detection success rate was defined as the proportion of the number of times the extracted maximum peak coordinates matched the true target position after implementing the designed suppression method to the total number of experiments. The interference suppression ratio was defined as the ratio of the magnitude of false targets formed by interference before and after implementing the designed suppression method.

[0035] In this simulation experiment, with an interference-to-signal ratio (SNR) range of 0–30 dB, the target detection success rate and interference suppression ratio of the designed intermittent sampling suppression method are as follows: Figure 4 As shown, when the interference-to-signal ratio (ISR) is 0–4 dB, the time-frequency analysis estimation of interference parameters produces some errors due to the similar strength of the target signal and the interference signal, leading to inaccurate parameter estimation and thus fluctuations in the suppression effect. When the ISR is 5–25 dB, the target detection success rate stabilizes at 100%, and the interference suppression ratio reaches over 15 dB. When the ISR is 26–30 dB, the peak value of the false target formed by the interference, even after suppression, is still higher than the target peak value, making it impossible to detect the target. This experiment verifies the effectiveness and performance boundaries of the proposed method, demonstrating that it can effectively suppress interference and detect targets within the intermittent sampling interference ISR range of 0–25 dB.

[0036] By combining interference cognition and passive filtering, the problem of false targets formed by intermittent sampling interference is solved without adjusting the transmission strategy: an unmatched filter is constructed by reconstructing slices through interference parameter estimation, a filter is constructed by utilizing the difference between the two pulse compression results, and the matched filtering result is filtered to achieve the effect of filtering out false targets formed by intermittent sampling interference and enhance the radar's ability to resist intermittent sampling interference.

[0037] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the present invention is not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for suppressing intermittent sampling interference based on unmatched difference feature filtering, characterized in that, Includes the following steps: Initialize the basic parameters of the linear frequency modulated signal and transmit the linear frequency modulated signal; The echo signal is acquired, and a two-dimensional time-frequency diagram is obtained by performing time-frequency analysis on the echo signal. Based on the two-dimensional time-frequency diagram, connected component detection is performed, and key parameters of intermittent sampling interference are estimated. The key parameters include: slice width. Number of slices and number of reposts ; Based on the aforementioned key parameters, an unmatched filter is constructed; The echo signal is subjected to matched filtering and unmatched filtering, and the filter is defined using the difference characteristics; The matched filtering result is filtered by a filter, and the peak with the largest amplitude is extracted as the detection target.

2. The intermittent sampling interference suppression method based on unmatched difference feature filtering according to claim 1, characterized in that, The basic parameters of the initial linear frequency modulated signal include: pulse width, multiple cycles, and bandwidth.

3. The intermittent sampling interference suppression method based on unmatched difference feature filtering according to claim 1, characterized in that, The time-frequency analysis is achieved through the short-time Fourier transform method, including: Use window functions Intercept the transmitted signal For nearby short-time signals, the Fourier transform of the short-time signal is expressed as: ,in, For the output time-frequency coordinates, For the corresponding timeline, This corresponds to the frequency axis.

4. The intermittent sampling interference suppression method based on unmatched difference feature filtering according to claim 1, characterized in that, The connected component detection includes: The length of each connected component in the time dimension of the two-dimensional time-frequency graph is statistically analyzed, and the position and frequency of the upper right pixel of the connected component in the frequency dimension are statistically analyzed. Remove connected components whose time dimension length exceeds half the pulse width of the transmitted signal; Parameter estimation for intermittent sampling interference.

5. The intermittent sampling interference suppression method based on unmatched difference feature filtering according to claim 4, characterized in that, The parameter estimation for intermittent sampling interference includes: defining the mean of the remaining connected component in the time dimension as the estimated result of the slice width. Count the frequency axis positions of connected components and the number of times each connected component appears at different frequency axis positions. Define the number of times each connected component appears at different frequency axis positions as the slice count. The maximum number of repetitions at the same frequency axis position is defined as the number of forwardings. .

6. The intermittent sampling interference suppression method based on unmatched difference feature filtering according to claim 1, characterized in that, The connected block refers to the signal corresponding to a bright spot or continuous ridge in a two-dimensional time-frequency graph, which is an energy concentration region at a specific time and frequency.

7. The intermittent sampling interference suppression method based on unmatched difference feature filtering according to claim 1, characterized in that, The construction of the unmatched filter includes: The sliced ​​signal is reconstructed using the aforementioned key parameters and the transmitted signal, and is expressed as follows: ,in, As a discrete-time variable, it represents the instantaneous moment of the signal. This is the slice index within a single period of intermittent sampling interference; Constructing a matched filter, denoted as ; The mismatched filter coefficients are obtained by subtracting the interference slice from the original transmitted signal. , represented as: - ,in, The original transmitted signal, This is the reconstructed slice signal.

8. The intermittent sampling interference suppression method based on unmatched difference feature filtering according to claim 7, characterized in that, The filter defined using the difference features is expressed as follows: ,in, This is the pulse compression result obtained from matched filtering. This is the pulse compression result obtained from unmatched filtering. It is the modulo of the difference between the two. Represents the Hilbert transform. This is an adjustable coefficient.

9. The intermittent sampling interference suppression method based on unmatched difference feature filtering according to claim 8, characterized in that, The filtering of the matched filtering result by the filter is expressed as follows: .

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