A DRFM interference suppression method based on post-pulse pressure distribution characteristics

Abstract

The existing time-frequency domain false target jamming suppression method generally requires high jamming parameter estimation accuracy, and the application scene is relatively limited. Therefore, the present application provides a DRFM jamming suppression method based on the spike distribution characteristics after pulse compression. The algorithm does not require prior information of jamming parameters, analyzes and summarizes the spike distribution characteristics after DRFM jamming pulse compression, counts the number of spike intervals according to the spike distribution characteristics, designs a corresponding decision threshold, thereby distinguishes the target and the jamming, and realizes the jamming suppression on this basis. The present application can suppress the false target jamming in a complex electromagnetic environment, and has a low calculation degree, and can improve the anti-jamming capability of the radar.

Description

Technical Field

[0001] This invention belongs to the field of radar countermeasures technology, and specifically relates to a DRFM interference suppression method based on the characteristics of post-pulse compression spike distribution. Background Technology

[0002] With the further development of digital circuits and information processing technology in the field of electronic warfare, Digital Radio Frequency Memory (DRFM) technology has been widely used in jammers. It can sample, delay, and forward radar signals multiple times, utilizing the matched filtering characteristics of pulse compression radar to form coherent interference to mask real targets. Intermittent sampling and forwarding jamming and dense decoy jamming are two typical types of jamming based on DRFM. The difference lies in that the former forwards only a portion of the radar pulse within a single pulse width, while the latter forwards part or even all of the radar pulse within one or more pulse repetition cycles. Linear frequency modulated signals are particularly susceptible to DRFM jamming. To address these two types of jamming, many scholars both domestically and internationally have conducted research on jamming suppression in various processing domains. Spatial domain jamming suppression methods do not distinguish between specific jamming types and have a wide range of applications, but they cannot cope with defensive mainlobe jamming. In the waveform domain, the large computational load, limited applicability, and requirement for accurate estimation of jamming parameters limit the practical application of waveform domain anti-jamming methods. Time-frequency domain jamming suppression methods generally require high accuracy in jamming parameter estimation, limiting their application scenarios. Further research is needed to develop DRFM interference suppression methods with low computational complexity and wide applicability to improve radar anti-jamming capabilities. Summary of the Invention

[0003] To address the above problems, this invention provides a DRFM interference suppression method based on the post-pulse compression spike distribution characteristics, which can suppress DRFM interference in the time domain.

[0004] A DRFM interference suppression method based on the characteristics of post-pulse compression spike distribution includes the following specific steps:

[0005] Step S1: Perform pulse compression processing on the baseband echo of the LFM radar;

[0006] Step S2: The baseband echo after pulse compression is detected using the CA-CFAR algorithm, and the detected peaks and their locations are extracted.

[0007] Step S3 involves performing point clustering processing on the detected peaks, merging information from the same measurement point, reducing the influence of target sidelobes or false target group outer sidelobes, thereby improving the accuracy of the measurement.

[0008] Step S4: After the dots coalesce, the number of peaks and the peak intervals are counted to obtain the number of times each interval occurs.

[0009] Step S5: Compare the number of occurrences of the interval obtained by counting with the interval number threshold α. Among them, the peaks corresponding to the intervals whose occurrence count is not less than the threshold value and the intervals that are integer multiples of the threshold value are judged as interference.

[0010] Step S6: Replace the spikes identified as interference and their vicinity with the receiver noise average power to achieve interference suppression.

[0011] Furthermore, the transmitted signal of the LFM radar is:

[0012]

[0013] Among them, T p Where f is the transmitted signal pulse width, f0 is the carrier frequency, and K is the signal pulse width. r This represents the linear frequency modulation slope.

[0014] Furthermore, the DRFM interference signal is:

[0015]

[0016]

[0017]

[0018]

[0019]

[0020] Among them, S ISDJ For Intermittent Sample-and-Forward Interference (ISDJ), S ISRJ For Intermittent Sample Repeated Forwarding Interference (ISRJ), S ISCJ For intermittent sampling repetitive cyclic interference (ISCJ), S DFTJ For Dense False Target Jailbreak (DFTJ), S MDFTJ For dense false target interference in multi-interference scenarios, rect(t / T) p ) indicates a width of T p A rectangular window J Let N be the jamming amplitude, τ be the number of jamming slices, τ be the delay introduced by the distance between the jammer and the radar, M be the number of times each jamming slice is forwarded, and T be the number of times the jamming slice is forwarded. u = (M+1)T J a = (m(m+1)) / 2 - 1 is the interception delay coefficient for the corresponding slice, b = (n(n+1)) / 2 + n - 1 is the delay coefficient for forwarding each slice, K is the number of false targets, and T I Let K1 and K2 represent the forwarding counts of the two types of dense false target interference, respectively. The two forwarding intervals are as follows: and

[0021] Furthermore, the amplitude expression of the DRFM interference after pulse compression processing is as follows:

[0022]

[0023] |S out | DFTJ =|A J T p sinc(K r T p (t-kT I ))

[0024] Among them, |S out |S represents the amplitude after intermittent sampling and direct forwarding of the interference pulse compression. out | DFTJ The amplitude after pulse compression due to dense false target interference, φ = πK r T u (tT J For intermittent sampling repeated forwarding interference (ISJ), forwarding the sampled signal multiple times is equivalent to shifting the ISDJ pulse compression result multiple times in the distance direction. However, for ISDJ cyclic forwarding interference, only the slice delay of the first forwarding is the same, while the slice delays of subsequent forwardings are different.

[0025] Beneficial effects:

[0026] The most prominent feature and significant beneficial effect of this invention are:

[0027] 1. This invention proposes a DRFM interference suppression method based on the spike distribution characteristics after pulse compression. Addressing the common requirement for high accuracy in interference parameter estimation in time-frequency domain interference suppression methods, this invention eliminates the need for prior information on interference parameters. By analyzing the spike distribution characteristics after DRFM interference pulse compression, it summarizes the patterns of spike intervals, statistically counts the occurrence frequency of spike intervals, and designs corresponding decision thresholds to distinguish between targets and interference. Based on this, interference suppression is achieved. This method achieves high false target rejection and target detection rates while ensuring accurate detection of interference spikes, and also has low computational complexity, effectively improving the radar's anti-interference capability.

[0028] 2. This invention, based on interference suppression in a single interference scenario, performs interference suppression in multiple interference scenarios. It can achieve two different types of false target interference suppression under the condition that the number of occurrences of the interval between false target spikes is not less than an interval threshold, and the number of occurrences of the interval between the target and adjacent false targets is less than an interval threshold. Attached Figure Description

[0029] Figure 1 A schematic diagram illustrating the interference working principle provided by this invention;

[0030] Figure 2 This is a flowchart illustrating the technical solution of the present invention;

[0031] Figure 3 This is a schematic diagram of the DRFM interference pulse compression results provided by the present invention, where a is intermittent sampling direct forwarding interference, b is intermittent sampling repeated forwarding interference, c is intermittent sampling cyclic forwarding interference, d is dense false target interference, and e is dense false target interference with two different false target intervals.

[0032] Figure 4 The diagram shows the statistical results of DRFM interference spike spacing provided by the method of the present invention, where a is intermittent sampling direct forwarding interference, b is intermittent sampling repeated forwarding interference, c is intermittent sampling cyclic forwarding interference, d is dense false target interference, and e is dense false target interference with two different false target intervals.

[0033] Figure 5 This is a schematic diagram of the DRFM interference removal results provided by the present invention, where a is intermittent sampling direct forwarding interference, b is intermittent sampling repeated forwarding interference, c is intermittent sampling cyclic forwarding interference, d is dense false target interference, and e is dense false target interference with two different false target intervals.

[0034] Figure 6 The diagram illustrates the interference suppression performance provided by this invention, where a represents the relationship between the interference-to-signal ratio and the detection rate, b represents the relationship between the interference-to-signal ratio and the rejection rate, c represents the relationship between the slice width and the detection rate, d represents the relationship between the slice width and the rejection rate, e represents the relationship between the number of forwards and the detection rate, f represents the relationship between the number of forwards and the rejection rate, g represents the relationship between the false target interval and the detection rate, and h represents the relationship between the false target interval and the rejection rate. Detailed Implementation

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be clearly and completely described below in conjunction with the embodiments and accompanying drawings of this application.

[0036] Figure 1This is a schematic diagram illustrating the working principle of jamming. Common intermittent sampling and forwarding jamming mainly includes three types: intermittent sampling direct forwarding, repeated forwarding, and cyclic forwarding jamming. Among them, direct forwarding and repeated forwarding jamming both forward the currently intercepted radar signal, the difference being the number of forwardings. Cyclic forwarding jamming, after forwarding the current signal, will also forward all previously intercepted signal segments in reverse order. The interception-forwarding process of intermittent sampling and forwarding jamming will be repeated multiple times until the radar pulse ends. Dense decoy jamming is also a jamming method that uses digital radio frequency memory to intercept, transform, and forward radar transmitted signals. Dense decoy jamming can forward within one or more pulse repetition cycles.

[0037] Figure 2 This is a flowchart illustrating the technical solution of the present invention. Depending on the different implementation stages, the specific steps of this invention include steps S1 to S6:

[0038] Step S1 involves pulse compression processing of the baseband echo from the LFM radar. The data considered is the one-dimensional time-domain baseband echo signal after down-conversion.

[0039] The LFM radar transmits the following signal:

[0040]

[0041] Among them, T p Where f is the transmitted signal pulse width, f0 is the carrier frequency, and K is the signal pulse width. r This represents the linear frequency modulation slope.

[0042] The DRFM interference signal in the baseband echo is:

[0043]

[0044]

[0045]

[0046]

[0047]

[0048] Among them, S ISDJ For intermittent sampling and direct forwarding interference, S ISRJ For intermittent sampling and repeated forwarding interference, S ISCJ For intermittent sampling repetitive cyclic interference, S DFTJ For dense decoy interference, S MDFTJ For dense false target interference in multi-interference scenarios, rect(t / T) p ) indicates a width of T p A rectangular windowJ Let N be the jamming amplitude, τ be the number of jamming slices, τ be the time delay between the jammer and the radar, M be the number of times each jamming slice is forwarded, and T be the number of times the jamming slice is forwarded. u = (M+1)T J a = (m(m+1)) / 2 - 1 is the interception delay coefficient for the corresponding slice, b = (n(n+1)) / 2 + n - 1 is the delay coefficient for forwarding each slice, K is the number of false targets, and T I Let K1 and K2 represent the forwarding counts of the two types of dense false target interference, respectively. The two forwarding intervals are as follows: and

[0049] The amplitude expression of the DRFM interference after pulse compression is as follows:

[0050]

[0051] |S out | DFTJ =|A J T p sinc(K r T p (t-kT I ))|

[0052] Among them, |S out |S represents the amplitude after intermittent sampling and direct forwarding of the interference pulse compression. out | DFTJ The amplitude after pulse compression due to dense false target interference, φ = πK r T u (tT J ),k∈K.

[0053] The ISDJ pulse compression result shows a group of false targets, containing multiple false targets. The false target in the middle is the primary false target, and the rest are secondary false targets. The interval between the primary and secondary false targets is T. J The spacing between false targets within the group depends on sin(Nφ) / sin(φ), and the spacing between each false target is 1 / (K). r T u The magnitude of the false target group also follows sinc(K). r T J (tT J Modulation, its main lobe width is 2 / (K) r T J ).

[0054] For the pulse compression results of ISRJ, it is equivalent to the pulse compression results of ISDJ being shifted multiple times in the range direction. Its pulse compression results appear as multiple groups of false targets, with equal intervals between the target and the main false target, as well as between the main false targets, all of which are T.J .

[0055] For ISCJ, the pulse compression output will have one group of false targets and several independent false targets. The time interval between the independent false targets and the actual targets is (a+b)T. J Therefore, the time interval between independently distributed pseudo-targets is the slice width T. J Integer multiples of.

[0056] For DFTJ, the amplitude of a single dummy target pulse compression follows a sinc function, modulated by the interference amplitude and the signal pulse width. The spacing between each dummy target is equal, and is T. I .

[0057] The simulation scenario assumes the presence of a target and a self-defense mainlobe jammer. This jammer can transmit either intermittent sampling-forward jamming or dense decoy jamming with 1-2 different forwarding intervals at each PRT. Specific parameter settings are shown in Tables 1 and 2.

[0058] Table 1 Radar Parameters

[0059]

[0060] Table 2 Interference Parameters

[0061]

[0062] Based on the parameter settings in Tables 1 and 2, the one-dimensional range image after DRFM interference pulse compression can be obtained as follows: Figure 3 As shown. The simulation results are consistent with the parameter settings.

[0063] Step S2: The baseband echo after pulse compression is detected using the CA-CFAR algorithm, and the detected peaks and their locations are extracted.

[0064] Step S3 involves performing point clustering processing on the detected peaks, merging information from the same measurement point, reducing the influence of target sidelobes or false target group outer sidelobes, thereby improving the accuracy of the measurement.

[0065] Step S4: After the dot pattern coalesces, the number of peaks and the peak intervals are counted to obtain the frequency of all intervals. The peaks are detected by CFAR, and the statistical results of the peak intervals are as follows: Figure 4 As shown. According to the parameter settings in Tables 1 and 2, the statistical peak interval matches the theoretical interval, and according to the sampling unit resolution: ΔR=c / (2f s =3m, the interval error is within the normal range.

[0066] Step S5: Compare the number of occurrences of the interval obtained by statistics with the interval number threshold α. Intervals with an occurrence number not less than the threshold value and spikes corresponding to integer multiples of the interval are judged as interference.

[0067] Step S6: Replace the spikes identified as interference and their vicinity with the receiver's average noise power to achieve interference suppression. Based on the parameter settings in Tables 1 and 2, the interference removal results are as follows: Figure 5 As shown in the simulation results, the present invention can effectively suppress DRFM interference while retaining the target.

[0068] The performance metrics mentioned above are the false target removal rate and the detection rate. The expression for the false target removal rate is: The detection rate P d It is the ratio of the number of times a radar system correctly detects a target, that is, the ratio of the number of times a target is detected to the total number of times a target exists.

[0069] Based on the parameter settings in Tables 1 and 2, Figure 6 The effects of variations in interference-to-signal ratio, slice width, number of forwards, and false target interval on interference detection ratio and interference rejection rate are demonstrated.

[0070] This invention maintains a rejection rate of over 90% for intermittent sampling-forwarding interference under varying interference-to-signal ratios (ISR). When the ISR is greater than 10 dB, the detection rate begins to decline. For dense false target interference, both the rejection and detection rates remain stable above 95%. The reason for this issue in intermittent sampling-forwarding interference suppression is that the detection parameters cannot adaptively adapt to changing interference scenarios. False targets are missed at low ISR, while interference sidelobes mask the target at high ISR.

[0071] When the slice width is large, the present invention can maintain a rejection rate and detection rate of over 90% for intermittent sampling and forwarding interference. However, when the slice width is small, the rejection rate and target detection rate are poor. This is mainly because the detection parameters cannot adaptively adapt to changes in interference parameters. When the slice width is small, false targets are densely distributed and have a certain suppressive effect, thus making it impossible to detect the target.

[0072] This invention maintains a rejection rate and detection rate consistently above 95% regardless of changes in the number of forwards. The number of forwards affects the number of false target groups and the number of false targets within a group, but has almost no impact on the detection of interference spikes.

[0073] This invention maintains a rejection rate consistently above 95% even with varying false target intervals. The detection rate is zero for some false target intervals, but consistently above 95% for the remaining false target intervals. The dip in the detection rate curve is primarily due to: false targets coinciding with the target, or the target being located between two false targets, causing the target to be considered interference and rejected.

[0074] In summary, this invention proposes a DRFM interference suppression method based on the peak distribution characteristics after pulse compression. This invention requires no prior information on interference parameters. By analyzing the peak distribution characteristics after DRFM interference pulse compression, it discovers that the peak intervals follow a certain pattern. Based on this, the frequency of peak interval occurrences is counted, and corresponding decision thresholds are designed to distinguish between targets and interference, thereby achieving interference suppression. Simulation results show that, while ensuring accurate detection of interference peaks, this invention can maintain a false target rejection rate of over 90%.

[0075] The above are merely examples of embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A DRFM interference suppression method based on post-pulse compression peak distribution characteristics, characterized in that, include: Step S1: Perform pulse compression processing on the baseband echo of the LFM radar; Step S2: The baseband echo after pulse compression is detected using the CA-CFAR algorithm, and the detected peaks and their locations are extracted. Step S3 involves performing point clustering processing on the detected peaks, merging information from the same measurement point, reducing the influence of target sidelobes or false target group outer sidelobes, thereby improving the accuracy of the measurement. Step S4: After the dots coalesce, the number of peaks and the peak intervals are counted to obtain the number of times each interval occurs. Step S5: Calculate the number of occurrences of the interval and the interval threshold. The comparison is performed, and the peaks corresponding to intervals that occur at least as many times as the threshold value and integer multiples of that interval are judged as interference; Step S6: Replace the spikes identified as interference and their vicinity with the average noise power of the receiver to achieve interference suppression; Without prior information about interference parameters, by analyzing the peak distribution characteristics after DRFM interference pulse compression, the pattern of its peak interval is summarized. Based on this, the number of times the peak interval occurs is counted and a corresponding decision threshold is designed to distinguish between the target and the interference, and interference suppression is achieved on this basis.

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