Method and system for suppressing interference for fmcw millimeter wave radar slice reconstruction

Abstract

The application discloses a kind of for FMCW millimeter wave radar slice reconstruction interference suppression method and system, this method is mainly based on short-time Fourier transform and time-frequency domain filter to realize inhibition;After radar transmitter sends radio frequency signal, radio frequency signal is intercepted by jammer, and the signal intercepted by jammer is truncated with equidistant rectangular pulse;Afterwards, the slice generated by truncation is filled according to certain rule to fill the entire time gap, after filling, interference signal is generated, and then the interference signal is transmitted;The interference signal and target echo signal enter radar receiver simultaneously to form retransmission jamming.The short-time Fourier transform is carried out on echo intermediate frequency signal in the application, time-frequency domain is obtained, then binary mask filtering is carried out on time-frequency domain to remove the false target interference, interference suppression can be realized under three C&I interference forms, and in the case of JSR≤40dB, with the advantages of fast response speed, high anti-interference efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the linear frequency modulation system anti-jamming technology, specifically to a kind of for FMCW millimeter wave radar slice reconstruction interference suppression method and system. BACKGROUND

[0002] With the continuous innovation of interference technology and interference equipment, information type interference technology has experienced four stages of development since its appearance, and the interference modes include sweep jamming, aiming and guiding jamming and the most advanced repeater jamming currently used and the like.

[0003] The latest fourth-generation jammer uses DRFM technology in repeater jamming, and the DRFM technology can adapt to complex electromagnetic environment, so that the jamming signal is highly coherent with the transmitted signal, which causes serious interference to radar systems, so the DRFM jamming technology has been paid more and more attention. At present, in the fourth-generation jamming technology, the multi-false-target jamming (spectrum dispersion jamming (SMSP) and slice reconstruction jamming (C&I)) using DRFM technology is the most serious interference to FMCW radar detection system. In 2010, a scholar proposed to use wavelet decomposition technology to extract the phase image coefficient at different decomposition scales as a feature parameter, and then use nearest neighbor classifier, BP neural network and least squares support vector machine to identify the storage repeater jamming; In 2011, a scholar proposed a feature factor detection method based on the fusion of statistical features and intra-pulse fine features, such as maximum variance of segmented autocorrelation, Wigner-Viller distribution amplitude variance and wavelet transform matrix variance, for the detection of range-velocity combined drag jamming by using the feature differences of radar signals in each transform domain; In 2012, a scholar proposed an interference identification method based on the frequency slope characteristics of spectrum dispersion jamming and slice reconstruction jamming, based on instantaneous slope, fractional Fourier transform and matching Fourier transform; In the same year, a scholar proposed an interference detection method based on approximate entropy, which detects the existence of interference by calculating the approximate entropy of time series signal, and the detection effect of deception jamming and noise jamming is significant. However, the above algorithms have the disadvantages of high complexity and slow response speed, and are not applicable to FMCW radar system. SUMMARY

[0004] The present application aims to provide a kind of for FMCW millimeter wave radar slice reconstruction interference suppression method and system, which is mainly based on short-time Fourier transform and time-frequency domain filter to realize suppression, can realize interference suppression under three kinds of slice reconstruction (C&I) interference forms and in the case of JSR≤40dB, and has the advantages of fast response speed, high anti-interference efficiency

[0005] In order to achieve the above object, the present application provides the following technical solutions: in a first aspect, the present application provides a method for suppressing slice reconstruction interference of FMCW millimeter wave radar, comprising:

[0006] The echo radio frequency signal interfered by the slice reconstruction interference is mixed with the transmitted radio frequency signal through the receiver to obtain an intermediate frequency signal;

[0007] A section of the intermediate frequency echo signal is intercepted for time-frequency domain processing to obtain time-frequency domain two-dimensional information;

[0008] After analysis, a real target signal is expressed as a straight line with fixed frequency along the time axis in the time-frequency domain, while the slice reconstruction interference generates a series of false target spectrums at certain intervals in the time-frequency domain, and the spectrum value of the interference signal is within the receiver band of the radar system, thereby forming false target interference; according to this feature, the interference position is found in the time-frequency domain, and a corresponding binary mask image is generated;

[0009] According to the binary mask image, the slice reconstruction interference can be filtered out through a time-frequency domain filter, and the real target signal is extracted from multiple false target interferences.

[0010] In a second aspect, the present application further provides a system for suppressing slice reconstruction interference of FMCW millimeter wave radar, comprising:

[0011] A receiver mixing module mixes the interfered echo signal with the transmitted signal to obtain an intermediate frequency echo signal;

[0012] A short-time Fourier transform module uses short-time Fourier transform to change the intermediate frequency signal from the time domain to the time-frequency domain;

[0013] A binary mask image module finds the interference position in the time-frequency domain, and generates a corresponding binary mask image;

[0014] A filter interference module filters out the interference through the binary mask, averages the weighted time axis after filtering the time-frequency domain graph, and obtains the spectrum result after filtering out the C&I interference.

[0015] In a third aspect, the present application further provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to realize the method of the first aspect.

[0016] In a fourth aspect, the present application further provides a computer readable storage medium, which stores a computer program, and the program is executed by the processor to realize the method of the first aspect.

[0017] In a fifth aspect, the present application also provides a computer program product comprising a computer program which, when executed by a processor, implements the method of the first aspect.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] (1) The implementation is efficient and fast: current suppression algorithms for slice reconstruction interference are complex, and most of the algorithms are not implementable; the real-time performance and algorithm complexity of the algorithms that are implementable cannot be guaranteed in actual engineering implementation, and they cannot be used in millimeter wave radar systems. The algorithm for resisting slice reconstruction interference based on short-time Fourier transform and time-frequency domain filter proposed in the present application can adjust the algorithm complexity and response time according to the actual situation, and the processing flow is efficient, so that the slice reconstruction interference can be suppressed on programmable devices such as FPGAs.

[0020] (2) Strong adaptability to interference: the three forms of slice reconstruction interference have different generation methods, and the algorithm proposed in the present application is effective for all three forms of slice reconstruction interference; and the present application can achieve interference suppression when the jamming-to-signal ratio JSR is less than or equal to 40 dB, and has strong adaptability. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The present application is a flowchart of a method for suppressing C&I interference in a linear frequency modulation continuous wave system.

[0022] Figure 2 The present application is a result graph of an intermittent sampling and repeated forwarding type slice reconstruction interference false target.

[0023] Figure 3 The present application is a time-frequency graph of an intermediate frequency signal affected by slice reconstruction interference.

[0024] Figure 4 The present application is a histogram of time-frequency domain amplitude results.

[0025] Figure 5 The present application is a mask graph against slice reconstruction interference.

[0026] Figure 6 The present application is a comparison graph of the spectrum effect after suppressing interference. DETAILED DESCRIPTION

[0027] As shown in Figure 1 , the present application provides a method for suppressing C&I interference in a linear frequency modulation continuous wave system, comprising:

[0028] Step 1: After the receiver mixes the received signal containing target echoes, spectrum dispersion interference and noise, the signal enters the signal processing module, and the intermediate frequency signal affected by slice reconstruction interference is obtained by sampling through an AD chip.

[0029] Step 2, the sampled intermediate frequency signal enters the short-time Fourier transform, the short-time Fourier transform module includes a data sliding window module, a windowing module and a DFT calculation module. The short-time Fourier transform module performs M-point data sliding window N-point data truncation on the input AD data stream, truncates and adds windowing to reduce the influence of signal sidelobes and spectral leakage, and stores the results of this section in the FIFO after DFT calculation. Time-frequency domain information is obtained after processing a frame of intermediate frequency signal. Parameter N determines the frequency resolution, and parameter M determines the time resolution. When M is reduced, the time resolution is improved, but the calculation amount is also increased, and the required DFT calculation unit in the DFT array also needs to be increased. The time resolution determines the progress of the image mask, and the higher the time resolution, the stronger the recognition and suppression ability of the interference.

[0030] Step 3, the time-frequency domain information enters the binary mask data calculation module, which mainly includes a storage part and a calculation part. The storage part includes a FIFO1 array for buffering time-frequency domain information and a FIFO2 array for storing binary mask images; the calculation part includes a log calculation array, a histogram calculation module and a binary conversion module.

[0031] Step 4, after obtaining the binary mask data, the C&I interference can be filtered out according to the filtering algorithm described above. The mask filtering module includes a signal detection module and a spectrum accumulation module. The signal results calculated by the signal detection module, the binary results output from the FIFO2 and the spectral power spectrum value output the time-frequency domain information after filtering out the interference, and enter the spectrum accumulation module to obtain the accumulated spectrum of the real target.

[0032] Further, after the radar receiver mixes the received signal containing target echo, slice reconstruction interference and noise, the C&I interference produces multiple false targets in the intermediate frequency D band.

[0033] The slice reconstruction interference (C&I) is not implemented by changing the modulation frequency of the intercepted signal, but only by intercepting and copying the intercepted signal. The interference generation process consists of two steps: first, the signal intercepted by the DRFM jammer is truncated with equidistant rectangular pulses, which is the "chopping" step; then the slices generated by the truncation are filled according to a certain rule to fill the entire time gap, and the filled interference signal is generated, which is the "interleaving" step.

[0034] According to the different strategies of intercepting and retransmitting, the slice reconstruction jamming can be divided into interrupted sampling direct jamming (ISDJ), interrupted sampling repeater jamming (ISRJ) and interrupted sampling loop jamming (ISCJ).

[0035] The signal model of various jamming can be expressed as:

[0036] (1) Interrupted sampling direct jamming

[0037]

[0038] wherein, S ISDJ (t) is the signal model of interrupted sampling direct jamming (ISDJ), N is the number of jamming slices, rect function is a rectangular gate function, T J is the jamming slice width, K r is the modulation frequency of the transmitted signal, and τ is the delay of the jammer to the receiver.

[0039] (2) Interrupted sampling repeater jamming

[0040]

[0041] wherein, S ISRJ (t) is the signal mathematical model of interrupted sampling repeater jamming (ISRJ), M is the number of times of retransmission of each jamming slice, T u = (M+1)*T J is the time interval of signal interception by the jammer.

[0042] (3) Interrupted sampling loop jamming

[0043]

[0044] wherein, S ISCJ (t) is the signal mathematical model of interrupted sampling loop jamming (ISCJ), a = (m(m+1)) / 2-1 is the interception delay coefficient of the corresponding slice, and b = (n(n+1)) / 2+n-1 is the delay coefficient of each slice for retransmission.

[0045] The C&I jamming mixes the frequency into the intermediate frequency, and a series of false target peaks are generated at a certain interval in the frequency spectrum, and the false target peaks are similar to the real target peaks, so that the system is difficult to extract the real target parameter information, which is the jamming mechanism of the C&I jamming.

[0046] The short-time Fourier transform is performed on the intermediate frequency signal, so that the signal is transformed from the time domain into the time-frequency domain.

[0047] The present application focuses on analyzing intermittent sampling and repeated forwarding jamming, which generates a series of false target spectra at a certain interval in the time-frequency domain, and the spectrum value of the jamming signal is in the radar system receiver band, thereby forming false target jamming. The false target is difficult to distinguish from the real signal in the frequency spectrum. As known from the above, the greater the number M of interference slice forwarding, the more false targets are generated, and the easier it is to interfere with the radar system.

[0048] After the short-time Fourier transform of the intermediate frequency signal, a two-dimensional time-frequency domain information is obtained, and the normal target signal and other C&I jamming signals are located at different positions in the time-frequency domain. The image mask can be used to distinguish the real signal from the jamming. The image mask is used to shield the image or data to be processed with a certain selected shape, so as to control the processing area of the image or data. The specific image or object used for covering is called a mask or a template. In digital image processing, the mask is a two-dimensional matrix array, and sometimes a multi-value image is used. The image mask is mainly used for: (1) extracting the region of interest (ROI); (2) shielding; (3) making special shape images. A binary image mask is used in the present application.

[0049] The original time-frequency domain matrix is filtered through the binary mask image, the region with the binary mask value of 1 is replaced with the value of the noise region, and the region with the value of 0 is unchanged. The filtered time-frequency domain graph is weighted and averaged along the time axis to obtain the spectrum after filtering out the C&I jamming.

[0050] Based on the same inventive concept, the present application also provides a kind of for linear frequency modulation continuous wave system DRFM jamming suppression system, including:

[0051] The receiver mixing module mixes the echo signal subjected to jamming with the transmitted signal to obtain an intermediate frequency signal;

[0052] The short-time Fourier transform module uses short-time Fourier transform to transform the intermediate frequency signal from time domain signal into time-frequency domain signal;

[0053] The binary mask image module generates a series of false target spectra at a certain interval in the time-frequency domain due to the slice reconstruction jamming, and the spectrum of the jamming signal is in the radar system band. According to this feature, the jamming position is found in the time-frequency domain, and the corresponding binary mask image is generated.

[0054] Because C&I interference and target echo are overlapped in time, frequency, energy and other dimensions, C&I interference produces a series of false targets in the frequency axis at certain intervals, according to this feature, the interference position is found in the time-frequency domain, and a corresponding binary mask image is generated;

[0055] The interference filtering module filters out the interference through the binary mask, and obtains the spectral result after filtering out the interference by weighting and averaging the filtered time-frequency domain graph along the time axis.

[0056] The specific implementation method of each module is the same as the foregoing suppression method, and will not be described here.

[0057] The application will be further described below in combination with the drawings and examples.

[0058] Figure 1 The anti-interference algorithm flow chart of the application is shown: the application proposes a slice reconstruction interference suppression method based on short-time Fourier transform and time-frequency domain filter. The echo signal affected by slice reconstruction interference is mixed with the local oscillator signal, and then the intermediate frequency signal is obtained through the low-pass filter. After sampling, it enters the signal processing module, first performs short-time Fourier transform to obtain the time-frequency spectrum, generates a corresponding binary mask image according to the time-frequency spectrum, and the interference position can be clearly distinguished through the mask image. After filtering, the real target signal value can be obtained.

[0059] Figure 2 The intermittent sampling and repeated forwarding type slice reconstruction interference false target result graph is shown, and it can be clearly seen that the slice reconstruction interference produces multiple in-band false target interferences in the frequency domain. According to the number of times of interference slice forwarding, the number of false target interferences is different. If there is no effective anti-interference measure, the overall radar system working state can be easily affected.

[0060] The application implements the following steps for this interference signal:

[0061] Step one: firstly, the sampled intermediate frequency signal is subjected to STFT transformation, the STFT calculation module comprises a data sliding window module, a windowing module and a DFT calculation module. The STFT calculation module performs M-point data sliding window N-point data truncation on the input AD data stream, then passes through the windowing module to reduce the influence of signal sidelobes and spectrum leakage, increase the frequency measurement dynamic range, then pass through the DFT array to calculate the partial spectrum of each N-point intercepted data, and finally store the spectrum data calculated by the DFT array into the FIFO array. The parameter N determines the frequency resolution, and the parameter M determines the time resolution. When M is reduced, the time resolution is improved, but the calculation amount is also increased, and the required DFT calculation unit in the DFT array also needs to be increased. The STFT calculation framework needs a DFT calculation module that can realize a pipeline working mode and has less resources. The present application uses a partial calculation DFT algorithm to calculate the STFT framework, which reduces the resource usage while meeting the algorithm performance requirements. DFT calculation mainly involves multiplication of intermediate frequency signal value and rotation factor and accumulation operation, so the DFT algorithm of the present application mainly includes three modules, rotation factor reading module, input reading module and DFT PE (processing element) Region. The DFT algorithm is a mature method, and the present application realizes this algorithm on the FPGA platform by using Verilog language.

[0062] Step two: after obtaining the STFT time-frequency domain, the time-frequency domain information enters the binary mask data calculation module, which mainly includes a storage part and a calculation part. The storage part includes a FIFO1 array for buffering time-frequency domain information and a FIFO2 array for storing binary mask image; the calculation part includes a log calculation array, a histogram calculation module and a binary conversion module.

[0063] Step three: after obtaining the binary mask data, the C&I interference can be filtered according to the filtering algorithm in the foregoing text. The mask filtering module includes a signal detection module and a spectrum accumulation module. The signal result calculated by the signal detection module and the binary result output from the FIFO2 are combined to output the time-frequency domain information after filtering out the interference, and then enter the spectrum accumulation module to obtain the spectrum of the real target after filtering out the interference.

[0064] The following simulation is performed using the parameters set in the foregoing text. It is assumed that the slice repetition number M is 5, that is, the number of slice reconstruction interference slices is 5, and the signal-to-interference ratio is equal to 40 dB.

[0065] Figure 3 The slice reconstruction interference intermediate frequency signal time-frequency diagram is shown. The frequency segmentation characteristics of the slice reconstruction interference can be clearly seen. The number of time-frequency diagram segments is equal to the number of slice interference, and there is a slice reconstruction interference signal in all time dimensions.

[0066] Figure 4The time-frequency domain amplitude result histogram is shown, a real target signal is shown as a straight line along the time axis in the time-frequency domain, and the slice reconstruction interference is mixed to obtain an intermediate frequency, and a series of false target spectrums are generated at intervals in the time-frequency domain, so that the false target interference is formed. The real target signal can be obviously distinguished after histogram statistics.

[0067] Figure 5 The anti-slice reconstruction interference mask diagram is shown, the position of the slice reconstruction interference in the time-frequency domain can be found according to the histogram, and a binary mask image is drawn.

[0068] Figure 6 The spectrum effect comparison diagram after the interference is suppressed is shown, and it can be known from the diagram that under the condition that the number of slice interferences M is 5 and the signal-to-interference ratio is equal to 40 dB, multiple false target interferences are generated by the interference signal. The slice reconstruction interference suppression method based on the short-time Fourier transform and the time-frequency domain filter can effectively suppress the false target generated by the slice reconstruction interference, and the real target signal can be identified.

[0069] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the inventive concept, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A method for suppressing reconstruction interference for FMCW millimeter wave radar slices, characterized in that, The echo radio frequency signal interfered by slice reconstruction is received by the receiver and mixed with the transmitting radio frequency signal to obtain an intermediate frequency signal; A section of the intermediate frequency echo signal is intercepted for time-frequency domain processing to obtain two-dimensional time-frequency domain information; The interference position is found in the time-frequency domain to generate a corresponding binary mask image; According to the binary mask image, the slice reconstruction interference is filtered out through a time-frequency domain filter to extract the real target signal from multiple false target interferences. After the radar receiver mixes the received signal containing target echo, slice reconstruction interference and noise, the C&I interference generates multiple false targets in the intermediate frequency D band; the interference generation process includes two steps: first, the signal intercepted by the DRFM jammer is truncated with equidistant rectangular pulses; then the truncated slices are filled according to a certain rule to generate the interference signal; the signal models of various interferences are represented as: (1) intermittent sampling direct retransmission interference (2) intermittent sampling repeated retransmission interference Wherein, S ISDJ (t) is the signal model of direct jamming, N is the number of jamming slices, rect function is the rectangular gate function, T J is the jamming slice width, K r is the modulation frequency of the transmitted signal, and τ is the delay of the jammer to the receiver. (3) intermittent sampling cyclic retransmission interference Wherein, S ISRJ (t) is the signal model of repeated forwarding type interference, M is the number of times of forwarding of each interference slice, T u = (M+1)*T J is the time interval for signal interception by the jammer; The interference position is found in the time-frequency domain based on the following characteristics: a real target signal appears as a straight line with fixed frequency along the time axis in the time-frequency domain, while the slice reconstruction interference generates a series of false target spectrums at certain intervals in the time-frequency domain, and the spectrum values of the interference signal are within the receiver band of the radar system, thereby forming false target interference; where S ISCJ (t) is the signal model of the cyclically repeated jamming, a = (m(m + 1)) / 2 - 1 is the intercept delay coefficient of the corresponding slice, and b = (n(n + 1)) / 2 + n - 1 is the delay coefficient when each slice is repeated. After the intermediate frequency signal is subjected to short-time Fourier transform, a two-dimensional time-frequency domain information is obtained, the normal target signal and other C&I interference signals are located at different positions in the time-frequency domain, and the image mask is used to distinguish the real signal from the interference; the image mask is to shield the image or data to be processed with a selected shape, so as to control the processing area of the image or data. A binary image mask is used.

2. The method of claim 1, wherein, The original time-frequency domain matrix is filtered through the binary mask image, the region with a binary mask value of 1 is replaced with the value of the noise region, and the region with a binary mask value of 0 remains unchanged; the filtered time-frequency domain image is weighted and averaged along the time axis to obtain the spectrum after filtering out the C&I interference.

3. The method of claim 2, wherein, The method of claim 1 is implemented, including:

4. A system for suppression of FMCW millimeter wave radar slice reconstruction interference, comprising: A receiver mixing module mixes the interfered echo signal with the transmitting signal to obtain an intermediate frequency echo signal; A short-time Fourier transform module uses short-time Fourier transform to convert the intermediate frequency signal from time domain to time-frequency domain; A binary mask image module finds the interference position in the time-frequency domain to generate a corresponding binary mask image; A filtering interference module filters out the interference through the binary mask, weights and averages the filtered time-frequency domain image along the time axis to obtain the spectrum after filtering out the C&I interference. The processor executes the program to implement the steps of the method of any one of claims 1-3.

5. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The program is executed by the processor to implement the steps of the method of any one of claims 1-3.

6. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the method of any one of claims 1-3.

7. A computer program product comprising a computer program, characterized in that, ​

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