Intermittent sampling forwarding interference identification method

Abstract

The invention provides an intermittent sampling forwarding interference identification method. The method comprises the following steps: down-converting a received signal into an intermediate frequency signal; inputting the intermediate frequency signal into a digital channelized receiver for channelized processing to obtain output signals of a plurality of channels; judging whether output signals of a plurality of adjacent channels all exceed a threshold in a time domain; if not, obtaining the instantaneous frequency of the received signal according to the instantaneous frequency of the output signals of the plurality of channels; calculating a difference value between the instantaneous frequency of the received signal and the instantaneous frequency of the radar target signal; judging whether the difference value conforms to the characteristics of intermittent sampling forwarding interference or not; if yes, the received signal is subjected to intermittent sampling forwarding interference, and an interference parameter is obtained according to the difference value; and if not, the received signal is not interfered by intermittent sampling and forwarding. The invention provides an intermittent sampling and forwarding interference identification method, which is used for improving the real-time performance of the intermittent sampling and forwarding interference identification method and the adaptability in different environments.

Description

Technical Field

[0001] The present invention relates to the technical field of radar jamming recognition, and particularly to an intermittent sampling and retransmission jamming recognition method. Background Art

[0002] Intermittent sampling and retransmission jamming belongs to DRFM retransmission jamming. Since its proposal, it has received extensive attention due to its flexible use and high threat level. Because the interference signal has strong coherence with the radar transmitted signal, it can obtain a high coherence gain, which has a great impact on the normal operation of the radar and has become one of the current mainstream jamming methods.

[0003] Currently, the proposed intermittent sampling and retransmission jamming recognition methods can be divided into two categories. One category is to extract high-dimensional feature parameters in different transform domains for comparative analysis, and the other category directly uses intelligent methods such as neural networks to train large models for identifying specific jamming. However, the feature parameter extraction method is greatly affected by radar signal parameters, and the neural network algorithm requires a large amount of computation, making it difficult to meet the real-time requirements of the electronic countermeasure system. Summary of the Invention

[0004] The present invention provides an intermittent sampling and retransmission jamming recognition method to improve the real-time performance and adaptability in different environments of the intermittent sampling and retransmission jamming recognition method.

[0005] The present invention provides an intermittent sampling and retransmission jamming recognition method, including:

[0006] Down-converting the received signal into an intermediate frequency signal, where the received signal includes a radar target signal and an interference signal;

[0007] Inputting the intermediate frequency signal into a digital channelized receiver for channelization processing to obtain output signals of several channels;

[0008] Judging whether there are output signals of multiple adjacent channels exceeding the threshold in the time domain;

[0009] If so, the received signal is under suppression jamming, and the intermittent sampling and retransmission jamming recognition is no longer performed;

[0010] If not, obtaining the instantaneous frequency of the received signal according to the instantaneous frequencies of the output signals of the several channels;

[0011] Calculating the difference between the instantaneous frequency of the received signal and the instantaneous frequency of the radar target signal;

[0012] Judging whether the difference conforms to the characteristics of intermittent sampling and retransmission jamming;

[0013] If so, the received signal is under intermittent sampling and retransmission jamming, and interference parameters are obtained according to the difference;

[0014] If not, the received signal is not affected by intermittent sampling and forwarding interference.

[0015] Optionally, the determination of whether there are output signals of multiple adjacent channels exceeding a threshold in the time domain includes:

[0016] Detecting the amplitude of the output signal of each channel in the time domain;

[0017] Determining whether there are output signals of the multiple adjacent channels whose amplitudes in the time domain exceed the threshold.

[0018] Optionally, the value of the threshold is determined according to the level of the signal-to-noise ratio.

[0019] Optionally, the obtaining of the instantaneous frequency of the received signal based on the instantaneous frequencies of the output signals of the several channels includes:

[0020] Calculating the instantaneous phase of the output signal of each channel based on the CORDIC algorithm;

[0021] Unwrapping the instantaneous phase of the output signal of each channel;

[0022] Based on the unwrapped instantaneous phase of the output signal of each channel, calculating the instantaneous frequency of the output signal of each channel using the phase difference method;

[0023] Performing narrow pulse rejection and split pulse merging within a channel;

[0024] Performing false rejection and cross-channel merging between channels to obtain the instantaneous frequency of the received signal.

[0025] Optionally, the calculating of the instantaneous phase of the output signal of each channel based on the CORDIC algorithm includes:

[0026] Calculating the instantaneous phase of the output signal of each channel using the following formula:

[0027]

[0028] where represents the instantaneous phase of the output signal of the k-th channel, D represents the decimation factor, I k (m) represents the imaginary part of the output signal of the k-th channel, R k (m) represents the real part of the output signal of the k-th channel, and m represents the m-th sampling point.

[0029] Optionally, the calculating of the instantaneous frequency of the output signal of each channel using the phase difference method includes:

[0030] The instantaneous frequency of the output signal of each channel is calculated using the following formula:

[0031]

[0032] where: ω k represents the instantaneous frequency of the output signal of the k-th channel, represents the instantaneous phase of the output signal of the k-th channel after unwrapping.

[0033] Optionally, the instantaneous frequency of the radar target signal includes:

[0034] the pre-stored instantaneous frequency of the radar target signal; or,

[0035] the instantaneous frequency of the radar target signal received in the absence of interference; or,

[0036] the instantaneous frequency of the radar target signal generated using known radar parameters.

[0037] Optionally, the characteristics of the intermittent sampling and forwarding interference include that the time width and time interval of each frequency pulse are approximately equal.

[0038] Optionally, the interference parameters include the interference slice width and the number of interference slices.

[0039] Optionally, obtaining the interference parameters according to the difference includes:

[0040] the time width of the frequency pulse in the difference is the interference slice width;

[0041] the number of frequency pulses in the difference is the number of interference slices.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] Based on the relatively mature digital channelization method in the field of electronic countermeasures, the present invention identifies intermittent sampling and forwarding interference by discriminating the instantaneous frequency characteristics of the signal. Compared with the calculation of single characteristic parameters in the time domain and transform domain used in other identification methods, the instantaneous frequency characteristics adopted by the present invention contain more abundant information, have higher reliability in complex environments, and the characteristic discrimination process only requires simple numerical calculations. Therefore, the present invention has high real-time performance and stability and has broad engineering application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic flowchart of an intermittent sampling and forwarding interference identification method provided by an embodiment of the present invention;

[0045] Figure 2Schematic diagram of the instantaneous frequency of the received signal provided by the embodiment of the present invention;

[0046] Figure 3 Schematic diagram of the instantaneous frequency of the radar target signal provided by the embodiment of the present invention;

[0047] Figure 4 Schematic diagram of the difference between the instantaneous frequency of the received signal and the instantaneous frequency of the radar target signal provided by the embodiment of the present invention. Detailed implementation manners

[0048] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] This embodiment provides an intermittent sampling and forwarding interference recognition method, as Figure 1 shown, including:

[0050] S10: Down-convert the received signal into an intermediate-frequency signal. The received signal includes a radar target signal and an interference signal.

[0051] The interference signal may be broadband suppression interference, narrowband aiming interference, intermittent sampling and forwarding interference, multi-false target interference or range gate pull-off interference, or there may be no interference. This embodiment only considers the case of single interference and does not consider the case of composite interference.

[0052] S11: Input the intermediate-frequency signal into a digital channelized receiver for channelization processing to obtain the output signals of several channels.

[0053] Channelization processing is to divide a broadband signal into multiple channels, mainly including decimation and polyphase filtering. The number of channels is the decimation factor, and the number of channels is determined by the used digital channelized receiver. In this embodiment, the output signals of 64 channels will be obtained after channelization processing.

[0054] S12: Determine whether there are output signals of multiple adjacent channels exceeding the threshold in the time domain.

[0055] Detect the amplitude of the output signal of each channel in the time domain. In this embodiment, the amplitudes of the output signals of 64 channels are detected in the time domain;

[0056] Determine whether the amplitudes of the output signals of multiple adjacent channels in the time domain all exceed the threshold. In this embodiment, the multiple adjacent channels are at least two adjacent channels, and the value of the threshold is determined according to the signal-to-noise ratio. Generally, it can be set as a multiple of the noise floor. The higher the signal-to-noise ratio, the larger the multiple can be set. Among them, the noise floor is the noise power, and the signal-to-noise ratio is the ratio of the signal power to the noise power.

[0057] S13: If so, the received signal is under barrage jamming, and no intermittent sampling and forwarding jamming identification is performed anymore.

[0058] Barrage jamming is an active jamming method that injects jamming signals into the enemy radar to submerge the radar target signal. Intermittent sampling and forwarding jamming belongs to deception jamming and does not belong to barrage jamming. The characteristic of barrage jamming is a relatively wide bandwidth. Assuming the radar bandwidth is 20M, the bandwidth of barrage jamming can generally reach more than 5 times the radar bandwidth. After being under barrage jamming, the frequency information cannot be accurately extracted anymore, so no intermittent sampling and forwarding jamming identification is performed.

[0059] S14: If not, obtain the instantaneous frequency of the received signal based on the instantaneous frequencies of the output signals of several channels.

[0060] Calculate the instantaneous phase of the output signal of each channel based on the CORDIC algorithm. The formula used is as follows:

[0061]

[0062] Among them, represents the instantaneous phase of the output signal of the k-th channel, D represents the decimation factor, I k (m) represents the imaginary part of the output signal of the k-th channel, R k (m) represents the real part of the output signal of the k-th channel, and m represents the m-th sampling point;

[0063] To solve the problem of phase ambiguity, unwrap the instantaneous phase of the output signal of each channel. When the instantaneous phase is greater than π, subtract 2π from the instantaneous phase. When the instantaneous phase is less than -π, add 2π to the instantaneous phase;

[0064] Based on the unwrapped instantaneous phase of the output signal of each channel, calculate the instantaneous frequency of the output signal of each channel using the phase difference method. The formula used is as follows:

[0065]

[0066] Among them: ω k represents the instantaneous frequency of the output signal of the k-th channel, represents the unwrapped instantaneous phase of the output signal of the k-th channel;

[0067] Narrow pulse rejection and split pulse merging are carried out in the channel. After channelization processing, due to the influence of the transient response, rabbit ear effects will occur at the rising and falling edges of the pulse signal. Therefore, it is necessary to reject the generated narrow pulses. At the same time, due to the presence of noise in the actual environment, the points in the pulse that should exceed the threshold do not exceed the threshold, resulting in the pulse being split, and split pulses appear. If split pulses are detected, it is necessary to merge the split pulses to complete the split part in the pulse to improve the detection accuracy. The value of the threshold here is the same as the threshold value in S12;

[0068] False rejection and cross-channel merging are carried out between channels to obtain the instantaneous frequency of the received signal. In order to cover the instantaneous bandwidth, adjacent channels of the channelization filter must overlap, so there will be a phenomenon of single-carrier signal cross-channel output. When a single-carrier signal is output on two channels, the signal on one of the channels is a false output, and it is necessary to reject the false output. Finally, the output signals of all channels are merged to obtain a more accurate instantaneous frequency of the received signal.

[0069] S15: Calculate the difference between the instantaneous frequency of the received signal and the instantaneous frequency of the radar target signal.

[0070] The instantaneous frequency of the radar target signal includes:

[0071] The pre-stored instantaneous frequency of the radar target signal; or,

[0072] The instantaneous frequency of the radar target signal received under interference-free conditions; or,

[0073] The instantaneous frequency of the radar target signal generated using known radar parameters, where the radar parameters include pulse width, bandwidth, carrier frequency, etc.

[0074] S16: Determine whether the difference conforms to the characteristics of intermittent sampling and forwarding interference.

[0075] The characteristics of intermittent sampling and forwarding interference include that the time width and time interval of each frequency pulse are approximately equal.

[0076] S17: If it conforms, the received signal is affected by intermittent sampling and forwarding interference, and interference parameters are obtained based on the difference.

[0077] The interference parameters include interference slice width and the number of interference slices. The interference slice width refers to the duration of each sampling, and the number of interference slices refers to the number of samplings within the repetition period of a pulse. The time width of the frequency pulse in the difference is the interference slice width, and the number of frequency pulses in the difference is the number of interference slices.

[0078] S18: If it does not conform, the received signal is not affected by intermittent sampling and forwarding interference.

[0079] Assume that the bandwidth of the radar target signal is 40 MHz, the pulse width is 20 μs, the pulse repetition period is 100 μs, it is down-converted to an intermediate frequency of 700 MHz, and the signal-to-jamming ratio is 5 dB. Set the sampling period of the intermittent sampling and forwarding interference to 5 μs, and the duration of each sampling is 2.5 μs. Then, four sampling and forwarding operations can be completed within one pulse of the radar target signal. Therefore, four dips will appear on the instantaneous frequency curve of the received signal, as Figure 2 shown. Therefore, the periodic characteristics of the instantaneous frequency can be used to complete the identification of the intermittent sampling and forwarding interference. For the radar target signal, its instantaneous frequency curve is as Figure 3 shown. By subtracting the instantaneous frequency of the radar target signal from the instantaneous frequency of the received signal, the result shown in Figure 4 can be obtained. Figure 4 Four frequency pulses appear in . When the time width and time interval of each frequency pulse are approximately equal, it can be determined that the current radar target signal is affected by the intermittent sampling and forwarding interference.

[0080] To prove the effectiveness of the method in this embodiment, tests are carried out under the condition that the signal-to-jamming ratio is 0 - 10 dB. Different radar parameters and interference parameters are changed during the test, and a total of 100 Monte Carlo simulations are carried out to obtain the recognition correct rate of the intermittent sampling and forwarding interference under different signal-to-jamming ratios, as shown in Table 1. When the signal-to-jamming ratio is greater than 0 dB, the recognition correct rate can reach more than 86%. Thus, the effectiveness of the method in this embodiment can be proved.

[0081] Table 1

[0082]

[0083] Obviously, those skilled in the art can make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalent technologies, this application is also intended to include these changes and modifications.

Claims

1. An intermittent sampling and forwarding interference recognition method, characterized in that Including: Down-converting the received signal to an intermediate-frequency signal, where the received signal includes a radar target signal and an interference signal; Inputting the intermediate-frequency signal into a digital channelized receiver for channelization processing to obtain output signals of a plurality of channels; Judging whether there are output signals of multiple adjacent channels exceeding a threshold in the time domain; If so, the received signal is under suppression interference, and the intermittent sampling and forwarding interference identification is no longer performed; If not, obtaining the instantaneous frequency of the received signal according to the instantaneous frequencies of the output signals of the plurality of channels; Calculating the difference between the instantaneous frequency of the received signal and the instantaneous frequency of the radar target signal; Judging whether the difference conforms to the characteristics of intermittent sampling and forwarding interference; If it conforms, the received signal is under intermittent sampling and forwarding interference, and interference parameters are obtained according to the difference; If it does not conform, the received signal is not under intermittent sampling and forwarding interference.

2. The method according to claim 1, wherein The judging whether there are output signals of multiple adjacent channels exceeding a threshold in the time domain includes: Detecting the amplitude of the output signal of each channel in the time domain; Judging whether there are output signals of the multiple adjacent channels whose amplitudes in the time domain exceed the threshold.

3. The method according to claim 1, wherein The value of the threshold is determined according to the signal-to-noise ratio.

4. The method according to claim 1, wherein The obtaining the instantaneous frequency of the received signal according to the instantaneous frequencies of the output signals of the plurality of channels includes: Calculating the instantaneous phase of the output signal of each channel based on the CORDIC algorithm; Unwrapping the instantaneous phase of the output signal of each channel; Based on the unwrapped instantaneous phase of the output signal of each channel, calculating the instantaneous frequency of the output signal of each channel using the phase difference method; Performing narrow pulse elimination and split pulse merging within the channel; Performing false elimination and cross-channel merging between channels to obtain the instantaneous frequency of the received signal.

5. The method according to claim 4, characterized in that The calculating the instantaneous phase of the output signal of each channel based on the CORDIC algorithm includes: Calculating the instantaneous phase of the output signal of each channel using the following formula: Among them, represents the instantaneous phase of the output signal of the k-th channel, D represents the decimation factor, and I k (m) represents the imaginary part of the output signal of the k-th channel, and R k (m) represents the real part of the output signal of the k-th channel, and m represents the m-th sampling point.

6. According to the method as claimed in claim 5, wherein The calculating the instantaneous frequency of the output signal of each channel using the phase difference method includes: Calculating the instantaneous frequency of the output signal of each channel using the following formula: where: ω k represents the instantaneous frequency of the output signal of the k-th channel, represents the instantaneous phase of the output signal of the k-th channel after unwrapping.

7. The method according to claim 1, wherein The instantaneous frequency of the radar target signal includes: The pre-stored instantaneous frequency of the radar target signal; or, The instantaneous frequency of the radar target signal received under interference-free conditions; or, The instantaneous frequency of the radar target signal generated using known radar parameters.

8. The method according to claim 1, characterized in that The characteristics of the intermittent sampling and forwarding interference include that the time width and time interval of each frequency pulse are approximately equal.

9. The method according to claim 1, wherein The interference parameters include interference slice width and number of interference slices.

10. The method according to claim 9, characterized in that The obtaining the interference parameters according to the difference includes: The time width of the frequency pulse in the difference is the interference slice width; The number of frequency pulses in the difference is the number of interference slices.

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