A method and device for detecting complex radar pulse signals based on matched filtering

Abstract

The present invention relates to a method and apparatus for detecting complex radar pulse signals based on matched filtering. The apparatus includes a specific target matching module and a constant false alarm rate (CFAR) pulse signal detection module electrically connected thereto. In the present invention, the input signal is subjected to matched filtering according to the characteristics of specific target pulse signals in the inventory, and the CFAR pulse signal detection is performed on the signal after matched filtering, and based on this, it is determined whether the input signal contains a target signal. By performing matched filtering on the specific target signal, the output signal has the maximum signal-to-noise ratio. By adopting the matched filtering detection algorithm, the signal detection sensitivity can be greatly improved, and it is ensured that when there is a specific pulse signal in the input, it can be successfully detected. Before performing the specific target matched filtering, channelization processing is performed on the external radar signal, which can greatly reduce the amount of data to be processed, and can also filter out out-of-band noise and improve the signal-to-noise ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of radar pulse signal reconnaissance and interception in electronic reconnaissance, and particularly relates to a method and device for detecting complex radar pulse signals based on matched filtering. Background Art

[0002] In modern electronic reconnaissance, the signal environment is becoming increasingly dense and complex. The proportion of conventional radar systems in the deployed radars is less than 20%, and the vast majority are low probability of intercept (LPI) complex radar systems, and the proportion of LPI complex radar systems is increasing. These LPI radars have more and more functions and uses. A radar may have multiple operating states and multiple systems. At the same time, in order to improve its own performance and anti-jamming capabilities, various complex waveform designs are often adopted. For example, the in-pulse modulation characteristics of radar signals include linear frequency modulation, non-linear frequency modulation, binary coding, quaternary coding, frequency coding, etc. The inter-pulse modulation characteristics include frequency domain modulation and time domain modulation. The frequency domain modulation characteristics include inter-pulse frequency agility, pulse group frequency agility, inter-pulse frequency modulation, simultaneous frequency diversity, and time-sharing frequency diversity, etc. All these pose higher and higher requirements for radar signal detection technology. How to intercept such radar signals, especially the detection of weak signals, has always been a difficult problem in the field of electronic reconnaissance.

[0003] Chinese Patent with the authorization announcement number CN113447893B discloses a method, system and medium for automatically detecting the spectrum of radar pulse signals. It discloses a method for automatically detecting the spectrum of radar pulse signals, which includes: digitally channelizing the intermediate frequency complex signal to obtain the signals of sub-channels; performing adaptive threshold signal detection to obtain the effective signals of sub-channels; respectively performing cross-channel judgment on each pair of adjacent sub-channels to determine the cross-channel situation of adjacent sub-channels; for the sub-channels without cross-channel situation, performing digital channelization and respectively performing adaptive threshold signal detection, and then outputting the effective signals of the next-level sub-channels; for the sub-channels with cross-channel situation, calculating the center frequency and bandwidth of the corresponding cross-channel broadband signal, and configuring the corresponding DDS signal generator and variable bandwidth filter to perform signal matching and detection on the intermediate frequency complex signal. The present invention adopts two-stage channelization detection, realizes automatic update of the noise threshold, and increases the processing of broadband cross-channel signals, so as to detect adaptively according to the bandwidth of broadband radar signals. However, when using the above-mentioned prior art for detection, there is still a deficiency in the low detection rate of weak radar signals emitted by LPI complex radar systems. Summary of the Invention

[0004] The object of the present invention is to provide a method for detecting complex radar pulse signals based on matched filtering to solve the technical problem of low detection rate of weak radar signals emitted by low probability of intercept (LPI) complex radars in the prior art; another object of the present invention is to provide a device for detecting complex radar pulse signals based on matched filtering.

[0005] To achieve the above object, a device for detecting complex radar pulse signals based on matched filtering of the present invention adopts the following technical solutions:

[0006] A device for detecting complex radar pulse signals based on matched filtering, comprising a specific target matched filtering module for performing matched filtering on a signal according to the signal characteristics of a known pulse;

[0007] and a constant false alarm rate (CFAR) pulse signal detection module, electrically connected to the specific target matched filtering module to receive the filtered signal transmitted thereby, for determining a detection threshold and accordingly confirming whether a target signal is contained in the filtered signal.

[0008] Further, it includes a signal acquisition module for acquiring external signals;

[0009] and a digital channelization processing module, electrically connected to the signal acquisition module to receive the signal transmitted thereby, for splitting the original signal into multiple sub-band signals;

[0010] and a low threshold pulse signal detection module, electrically connected to the digital channelization processing module to receive the sub-band signals transmitted thereby, for screening out target points meeting the requirements in the sub-band signals according to set conditions;

[0011] and a digital down-conversion module, electrically connected to the low threshold pulse signal detection module to receive the once-filtered signal transmitted thereby, for converting the once-filtered signal into a baseband signal;

[0012] The specific target matched filtering module is electrically connected to the low threshold pulse signal detection module to receive the baseband signal transmitted thereby.

[0013] Further, the constant false alarm rate pulse signal detection module includes an adaptive threshold detection module.

[0014] A method for detecting complex radar pulse signals based on matched filtering of the present invention adopts the following technical solutions: performing matched filtering on an input signal according to the characteristics of a specific target pulse signal in stock, performing constant false alarm rate pulse signal detection on the signal after matched filtering, and accordingly determining whether a target signal is contained in the input signal.

[0015] Further, the constant false alarm rate pulse signal detection is performed on the signal after matched filtering by using an adaptive threshold detection technique.

[0016] Further, before performing matched filtering, the acquired signal is first subjected to digital channelization processing, then low-threshold pulse signal detection is performed on the signal after digital channelization processing, and then digital down-conversion is performed on the signal detected by the low-threshold pulse signal. The input signal is a baseband signal after digital down-conversion processing.

[0017] Further, when performing digital channelization processing, the input signal is first decimated by a factor of D, then the decimated signal is filtered, and finally D channel sample points are output through an FFT of D points.

[0018] Further, when performing low-threshold pulse signal detection, the calculation formulas for the pulse start and end thresholds are: The calculation formula for the pulse duration threshold is: In the formula represents the signal mean value of n sample points, represents the noise variance of n sample points, and a is a preset constant.

[0019] Further, down-conversion is implemented through a mixer

[0020] Further, when using the adaptive threshold detection technique to perform the constant false alarm rate pulse signal detection, dynamic sample value interception is performed using the sliding windows at the front and rear edges. The sliding windows at the front and rear edges have the same width. Based on the intercepted sample values, a local estimate at the front edge and a local estimate at the rear edge are formed. The larger value of the local estimate at the front edge and the local estimate at the rear edge is taken to determine the background noise and clutter average power estimate of the detection unit, and the threshold is set accordingly.

[0021] The beneficial effects of the present invention are as follows: The specific target matched filtering module performs matched filtering on the specific target signal according to the prediction result, so that the output signal has the maximum signal-to-noise ratio. The constant false alarm rate pulse signal detection module performs constant false alarm rate signal detection on the matched filtering result. By adopting the matched filtering detection algorithm, the signal detection sensitivity can be greatly improved, and it is ensured that when there is a specific pulse signal in the input, it can be successfully detected.

[0022] Further, before performing specific target matched filtering, channelization processing is first performed on the external radar signal, which can filter out out-of-band noise and improve the signal-to-noise ratio of the signal; by performing low-threshold pulse signal detection on the signal after channelization, the detection probability of low signal-to-noise ratio pulse signals is improved, and the signal frequency, signal pulse width, and signal bandwidth are predicted; the digital down-conversion module performs digital down-conversion on the signal to be detected according to the frequency measurement result to become a baseband signal

[0023] Further, when performing channelization processing on the external radar signal, decimation by a factor of D is first performed and then filtering is performed, which can greatly reduce the amount of data to be processed. Description of the Drawings

[0024] Figure 1 It is the structural block diagram of a complex radar pulse signal detection device based on matched filtering of the present invention;

[0025] Figure 2 It is the detection flow chart of a complex radar pulse signal detection method based on matched filtering of the present invention;

[0026] Figure 3 It is the flow chart of the digital channelization processing process;

[0027] Figure 4 It is the result after low threshold pulse signal detection;

[0028] Figure 5 It is the frequency / amplitude representation diagram of the signal after specific target matched filtering for the down-converted signal;

[0029] Figure 6 It is the schematic diagram of constant false alarm rate pulse signal detection. Specific implementation mode

[0030] An embodiment of a complex radar pulse signal detection method based on matched filtering of the present invention:

[0031] The specific process of a complex radar pulse signal detection method based on matched filtering is as Figure 1 shown, including the following steps,

[0032] The first step is to collect radar signals;

[0033] The collected radar signal is a complete original full-band signal, which includes noise signals and may also include radar signals.

[0034] The second step is to perform digital channelization processing on the collected radar signals;

[0035] In this step, a group of band-pass filters with the same performance are used to divide the original full-band signal into multiple sub-band signals. Specifically, the input signal x(n) is a discrete sample set. First, the input signal x(n) is decimated by a factor of D, then the decimated signal is filtered, and finally D sample points of D channels are output after D-point FFT transformation. The processing principle is as Figure 3 shown.

[0036] The third step is to perform low threshold pulse signal detection on the signals after digital channelization processing;

[0037] During the low threshold pulse signal detection process, two thresholds are set to ensure the integrity of pulse detection. Its detection target is to measure the bandwidth, frequency and pulse width of the pulse, and perform screening processing on specific targets according to the signal parameters. Specifically, the set pulse start and end thresholds are Set the pulse duration threshold to where represents the noise mean of n sample points (for the sample points after channelization, sort them according to the amplitude size, and the median value of the sorted channels is the noise in the corresponding channel. Calculate the average value of the noise in all channels to obtain it), represents the noise variance of n sample points, and a is a preset constant (the value of a is generally determined by the false alarm rate, and the default value is set to 4). If the sample points processed in the second step fall between the pulse start and end thresholds and the pulse duration threshold, then screen this target; if the sample points processed in the second step fall outside the pulse start and end thresholds and the pulse duration threshold, then filter out the corresponding target.

[0038] Use the signal processed by low-threshold pulse detection as Figure 4 shown in the figure. Among them, the upper edge line represents the pulse start and end thresholds, the lower edge line represents the pulse duration threshold, and the middle line represents the threshold mean. The signal between the pulse start and end thresholds and the pulse duration threshold (that is, the signal set in the middle) is the signal retained after detection.

[0039] Step 4: Perform digital down-conversion on the signal detected by the low-threshold pulse signal;

[0040] Down-conversion is generally achieved through a mixer, and the mixer realizes frequency band shifting. The mixer is a multiplier. When an ideal mixer multiplies two signals with frequencies f1 and f2, the formula is: cos(f1t)·cos(f2t) = 1 / 2[cos(f1 + f2)t + cos(f1 - f2)t]. The output of the mixer includes sum and difference signals, and the unwanted signals can be filtered out through a filter. According to requirements, the sum frequency signal or the difference frequency signal can be obtained.

[0041] Step 5: Perform specific target matched filtering on the down-converted signal;

[0042] In this step, according to the characteristics of the specific target pulse signal in the inventory, perform matched filtering processing on the baseband signal. The specific process is as follows: Suppose the input signal is s r (t). According to the signal frequency, signal pulse width, and signal bandwidth predicted by the low-threshold detection module, search in the specific pulse signal library and obtain the inventory specific target pulse signal s′ r (t) with the highest similarity. According to the inventory specific target pulse signal, the impulse response function of the matched filter that can match the input signal can be determined as h(t) = s′ * (t0 - t), then the output of the matched filter is The input signal has the maximum signal-to-noise ratio after passing through the matched filter. The frequency domain representation of the matched filter is: y(t) = IFFT(FFT(s r(t)) * FFT(h(t)))。

[0043] Therefore, after a wideband frequency modulation signal undergoes pulse compression processing, the amplitude of the signal that matches the signal recorded in the inventory increases significantly, which is represented as a vertical peak appearing in the frequency - amplitude signal diagram. The result of the signal input in the fourth step after specific target matching filtering is as Figure 5 shown. As can be seen from the figure, between 5x10 4 and 5.5x10 4 there appears a vertical peak with an amplitude exceeding 100.

[0044] Step 6: Perform constant false alarm rate pulse signal detection on the signals retained by specific target matching filtering;

[0045] In this step, an adaptive threshold detection technique is used to detect whether there is a radar signal to be detected in the signals retained in the fifth step. Specifically: there is a sliding window covering several range cells at the front and rear edges of the detection unit. Dynamic reference sampling is carried out using the sliding window. The mean values of the reference sampling form the local estimates at the front and rear edges. The larger value of the front and rear edge samplings is selected to determine the background noise and clutter average power estimates of the detection unit, and the estimated value is multiplied by a multiplier K0 to set the threshold value (the value of K0 is generally determined by the false alarm rate. The lower the false alarm rate, the larger its value. The default value of K0 is set to 5), and then compared with the signal of this detection unit. When the signal of this detection unit is not lower than the set threshold value, it is determined that there is a radar target to be detected; when the signal of this detection unit is lower than the set threshold value, it is determined that there is no radar target to be detected.

[0046] Step 7: Output the detection result.

[0047] In other embodiments, the over - threshold detection technique can also be directly used in Step 6, that is, a fixed threshold is first set. If the signal exceeds the set fixed threshold, it is determined that there is a target, and other signals that do not exceed the threshold are determined to be interference or noise signals. The disadvantage of the over - threshold detection technique is that: however, due to the complex and changeable external environment, the variety of clutter, and the influence of its own internal noise, the false alarm probability will increase sharply, and the detection performance will also decrease sharply.

[0048] An embodiment of a complex radar pulse signal detection device based on matching filtering according to the present invention:

[0049] A complex radar pulse signal detection device based on matching filtering, the structural block diagram of which is as Figure 1As shown, it includes a signal acquisition module, a digital channelization processing module, a low-threshold pulse signal detection module, a digital down-conversion module, a specific target matching filtering module, a constant false alarm rate pulse signal detection module, and an output module. The signal acquisition module is used to acquire external signals. The original signal of the acquired signal is the original full-band signal, including noise signals and possibly radar signals. The signal acquisition module is electrically connected to the digital channelization processing module to send the acquired signal into the digital channelization processing module. The digital channelization processing module divides the original full-band signal into multiple sub-band signals. The digital channelization processing module is electrically connected to the low-threshold pulse signal detection module to send the sub-band signals into the low-threshold pulse signal detection module. The low-threshold pulse signal detection module screens the input sub-band signals to retain the sub-band signals within the threshold range and filter out the sub-band signals beyond the threshold range. The low-threshold pulse signal detection module is electrically connected to the digital down-conversion module to transmit the screened sub-band signals to it. The digital down-conversion module performs down-conversion processing on the sub-band signals to obtain baseband signals. The digital down-conversion module is electrically connected to the specific target matching filtering module to transmit the obtained baseband signals to it. The specific target matching filtering module performs matching filtering processing on the baseband signals according to the signal characteristics of specific target pulses in the inventory, compresses the large time-bandwidth pulse signals into a narrow pulse, thereby improving the system sensitivity. The specific target matching filtering module is electrically connected to the constant false alarm rate pulse signal detection module to transmit the signals after matching filtering to it. The constant false alarm rate pulse signal detection module uses the over-threshold detection method to determine whether there are target signals in the input signals. The constant false alarm rate pulse signal detection module is electrically connected to the output module to transmit the detected target signals to it. The output module is used to output the detected target signals.

[0050] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A complex radar pulse signal detection device based on matched filtering, characterized in that, Including: A signal acquisition module, which is used to acquire external signals; A digital channelization processing module, which is electrically connected to the signal acquisition module to receive the signals transmitted by it, and is used to divide the original signal into multiple sub-band signals; A low-threshold pulse signal detection module, which is electrically connected to the digital channelization processing module to receive the sub-band signals transmitted by it, and is used to screen out the target points that meet the requirements in the sub-band signals according to the set conditions, predict the signal frequency, signal pulse width, and signal bandwidth, and use the signal frequency, signal pulse width, and signal bandwidth as known signal characteristics; A digital down-conversion module, which is electrically connected to the low-threshold pulse signal detection module to receive the once-filtered signal transmitted by it, and is used to convert the once-filtered signal into a baseband signal; A specific target matching filtering module, which is used to perform matching filtering on the signal according to the known signal characteristics, and the specific target matching filtering module is electrically connected to the digital down-conversion module to receive the baseband signal transmitted by it; And A constant false alarm rate pulse signal detection module, which is electrically connected to the specific target matching filtering module to receive the filtered signal transmitted by it, and is used to determine the detection threshold and confirm whether there is a target signal in the filtered signal accordingly.

2. The detection device according to claim 1, characterized in that, The constant false alarm rate pulse signal detection module includes an adaptive threshold detection module.

3. A complex radar pulse signal detection method based on matched filtering, characterized in that, First, perform digital channelization processing on the acquired signal, then perform low-threshold pulse signal detection on the signal after digital channelization processing, predict the signal frequency, signal pulse width, and signal bandwidth, search for specific target pulse signals in a specific pulse signal library according to the predicted signal frequency, signal pulse width, and signal bandwidth, then perform digital down-conversion on the signal detected by the low-threshold pulse signal, perform matching filtering on the input signal according to the specific target pulse signal, the input signal is the baseband signal after digital down-conversion processing, perform constant false alarm rate pulse signal detection on the signal after matching filtering, and judge whether there is a target signal in the input signal accordingly.

4. The detection method according to claim 3, characterized in that, Adopt the adaptive threshold detection technology for the constant false alarm rate pulse signal detection of the signal after matching filtering.

5. The detection method according to claim 3, characterized in that, When performing digital channelization processing, first perform D-fold decimation on the original signal, then filter the decimated signal, and finally output the sample points of D channels through D-point FFT.

6. The detection method according to claim 3, characterized in that, When detecting low-threshold pulse signals, the calculation formulas for the pulse start and end thresholds are as follows: The calculation formula for the pulse duration threshold is: 式中 represents the signal mean of n sample points, represents the noise variance of n sample points, and a is a preset constant.

7. The detection method according to claim 3, characterized in that, The down-conversion is implemented by a mixer.

8. The detection method according to claim 4, characterized in that, When using the adaptive threshold detection technology for the constant false alarm rate pulse signal detection, use the sliding windows at the front and rear edges to perform dynamic sample value interception. The sliding windows at the front and rear edges are of equal width. Form a leading-edge local estimate and a trailing-edge local estimate according to the intercepted sample values, and take the larger value of the leading-edge local estimate and the trailing-edge local estimate to determine the background noise and clutter average power estimate of the detection unit, and set the threshold accordingly.

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