CN115390019A - Interference suppression method for DRFM interference of linear frequency modulation continuous wave system - Google Patents
Interference suppression method for DRFM interference of linear frequency modulation continuous wave system Download PDFInfo
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Abstract
The invention discloses an interference suppression method for DRFM interference of a linear frequency modulation continuous wave system, which comprises the following steps: after mixing a mixed signal of the target echo signal and the DRFM interference signal with a local oscillator signal, obtaining an interfered intermediate frequency signal through low-pass filtering; and carrying out short-time Fourier transform on the sampled intermediate frequency signal to obtain a time frequency spectrum, finding an interfered position on the time frequency spectrum, generating a corresponding binary mask image, and carrying out interference filtering through a binary mask. The method analyzes the interference form of the frequency spectrum dispersion interference in the intermediate frequency under the linear frequency modulation continuous wave system, further uses short-time Fourier transform to convert the signal from a time domain to a time-frequency domain according to the characteristics of the interference action form, and carries out binary mask filtering on the time-frequency domain to remove the interference; the method can realize interference suppression under the conditions that the number n of the SMSP interference slices is less than or equal to 10 and the interference-to-signal ratio JSR is less than or equal to 40 dB.
Description
Technical Field
The invention relates to an anti-interference technology of a linear frequency modulation system, in particular to an interference suppression method for DRFM interference of a linear frequency modulation continuous wave system.
Background
In recent years, with the rapid development of the field of digital chips represented by FPGAs and DSPs, high-speed and high-precision digital signal processing is easier to realize, and the difficulty in realizing a chirp continuous wave short-range detection system is greatly reduced, so that an interference technology for a chirp continuous wave system is continuously developed. In recent years, electronic countermeasures have been developed rapidly, and various interference means have been developed. Radio proximity detection system interference (referred to as man-made active interference only) can be classified into two categories, energy-type interference and information-type interference, according to the different action routes and interference effects. Information-based interference is the most important and deadly threat to radio proximity detection systems in complex electromagnetic environments in battlefields due to its portability, intelligence and diversity of interference modes.
The current state-of-the-art fourth generation jammers use Digital Radio Frequency Memory (DRFM) technology for forward jamming. The DRFM technology can adapt to a complex and variable electromagnetic environment, so that the interference signal is highly coherent with the transmission signal, and a good interference effect is generated, so that the DRFM technology has been widely applied to a short-range detection countermeasure system, and the DRFM technology is also paid more and more attention in the short-range detection countermeasure system. In the existing radio interference technology, the interference effect of multi-decoy interference (spectrum dispersion interference (SMSP) and slice reconstruction interference (C & I)) in the DRFM technology on a chirp continuous wave short-range detection system is best and the efficiency is best, and for the interference, a large amount of anti-interference research work is done by domestic and foreign scholars. At present, there are two more anti-interference measures studied. The first is to improve the concealment of the detection system, such as the selection of the working frequency, the working frequency of the short-range detection system can be selected to be a frequency band outside the atmospheric transmission window; or a frequency agility or frequency self-adaptive technology is used, and when the interference signal is inconsistent with the working carrier frequency of the detection system, the interference effect is greatly weakened. The scholars propose a dual-channel correlation detection of a variable modulation slope short-range detection system, and the effect of suppressing DRFM interference is provided. The second is an interference suppression method based on signal processing, which is currently the most potential and most studied anti-interference field compared to other anti-interference methods. The countermeasure thought basically adopts 'interference identification-interference elimination', the core of the countermeasure is the interference identification technology, and a characteristic quantity which is stable and has distinctiveness needs to be found. Currently, a commonly used countermeasure method generally improves output SJNR through a filtering and accumulating method, and generally combines with modern signal processing technologies such as time-frequency transform and wavelet transform, and tries to divide interference and signals in a certain dimension, further filter the interference and extract the signals. The scholars provide a cross-correlation detection decision method for resisting intermittent forwarding interference and filtering the interference aiming at a linear frequency modulation system short-range detection system.
Disclosure of Invention
The invention aims to provide an interference suppression method for DRFM interference of a linear frequency modulation continuous wave system.
In order to achieve the purpose, the invention provides the following technical scheme: in a first aspect, the present invention provides an interference suppression method for DRFM interference in chirp-continuous-wave system, including:
the echo signal with interference is subjected to frequency mixing amplification with a transmitting signal through a receiver to obtain an intermediate frequency signal;
changing the intermediate frequency signal from a time domain to a time-frequency domain using a short-time Fourier transform;
SMSP interference generates a plurality of linear frequency modulation interference signals with the same but indefinite slopes on intermediate frequency, and according to the characteristics, an interference position is found on a time-frequency domain, and a corresponding binary mask image is generated by using the interference position;
and carrying out interference filtering through a binary mask, carrying out weighting on the filtered time-frequency domain graph along a time axis, and then averaging to obtain a frequency spectrum result after SMSP interference is filtered.
In a second aspect, the present invention further provides an interference suppression system for DRFM interference of chirp continuous wave system, including:
the receiver frequency mixing module is used for carrying out frequency mixing amplification on the echo signal with the interference and the transmitting signal through a receiver to obtain an intermediate frequency signal;
a short-time Fourier transform module for transforming the intermediate frequency signal from a time domain to a time-frequency domain using a short-time Fourier transform;
the binary mask image module is used for finding an interference position on a time-frequency domain to generate a corresponding binary mask image;
and the interference filtering module is used for filtering interference through a binary mask, and averaging the filtered time-frequency domain graph after weighting along a time axis to obtain a frequency spectrum result after SMSP interference is filtered.
In a third aspect, the present application further provides a computer device, comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the method according to the first aspect when executing the program.
In a fourth aspect, the present application further provides a computer-readable storage medium, on which a computer program is stored, which when executed by a processor, implements the method of the first aspect.
In a fifth aspect, the present application also provides a computer program product comprising a computer program, characterized in that the computer program realizes the method of the first aspect when being executed by a processor.
Compared with the prior art, the invention has the remarkable advantages that:
(1) The anti-interference response speed is fast: the SMSP interference suppression method combining the time-frequency domain transformation and the binary mask time-frequency domain filter can be realized on platforms of programmable devices such as an FPGA (field programmable gate array) and the like, and interference can be rapidly identified and suppressed by means of the platforms.
(2) The anti-interference adaptability is strong: the algorithm provided by the invention not only can identify and suppress the frequency spectrum dispersion interference, but also can identify and suppress the store-and-forward interference of other fourth-generation jammers.
Drawings
Fig. 1 is a flowchart of an interference suppression method for DRFM interference by chirp continuous wave system according to the present invention.
FIG. 2 is a block diagram of a chirped continuous wave proximity detector system.
Fig. 3 is a time-frequency diagram of a spectrally dispersed interference signal.
Fig. 4 is a spectrum of the intermediate frequency disturbed by SMSP.
Fig. 5 is a time-frequency diagram of an intermediate frequency signal interfered by SMSP.
Fig. 6 is a flow chart of SMSP interference suppression based on binary mask time-frequency domain filtering.
Fig. 7 is a graph comparing the spectrum effect after interference suppression.
Detailed Description
As shown in fig. 1, an interference suppression method for DRFM interference of chirp-like continuous wave system includes receiver frequency mixing, short-time fourier transform, binary mask image, and interference filtering, and includes the following specific steps:
And 2, according to the step 1, enabling the sampled digital signals to enter a signal processing module, and carrying out STFT conversion on the sampled intermediate frequency signals, wherein the STFT calculation module comprises a data sliding window module, a windowing module and a DFT calculation module. The STFT calculation module carries out data truncation of N points of a data sliding window of M points on an input AD data stream, then reduces the influence of signal side lobes and frequency spectrum leakage through the windowing module, increases the frequency measurement dynamic range, then calculates partial frequency spectrum of each time of the data truncation of the N points through the DFT array, and finally stores the frequency spectrum data calculated by the DFT array into the FIFO array. The parameter N determines the frequency resolution, the parameter M determines the time resolution, and when M is reduced, the time resolution is improved, but the calculation amount is increased, and the number of DFT calculation units required in the DFT array is increased. The STFT computing framework needs a DFT computing module which can realize a pipeline working mode and has less resource.
And 4, after the binary mask data are obtained according to the step 3, filtering SMSP interference according to a filtering algorithm, wherein the mask filtering module comprises a signal detection module and a frequency spectrum accumulation module, and outputting a frequency spectrum which is finally filtered and interfered according to a signal result calculated by the signal detection module, a binarization result and a frequency spectrum power spectrum value output in the FIFO3.
Further, after the receiver mixes the received signal containing the target echo, the spectrum dispersion interference and the noise, the SMSP interference generates dense false peaks on the intermediate frequency;
setting the complex envelope of the transmitter transmit signal to
In the formula: t is the pulse width; k is the modulation slope;
according to the SMSP interference generation mechanism, the single sub-pulse is
Wherein: a. The J Is the amplitude of the interference; k 'is the frequency modulation slope of the interference, k' = nk, the sub-pulse is copied for n times, and the time domain waveform of the SMSP interference is obtained
The SMSP interference is formed by compressing and copying the transmitting signal of a transmitter and is linear transformation of the transmitting signal; the interference signal has a similar structure with the signal transmitted by the transmitter, and after frequency mixing, a linear frequency modulation signal close to a passband is generated, so that a series of comb-shaped dense false targets are generated on the intermediate frequency of an echo, when the interference power is very high, the SMSP interference not only has a deceptive interference effect, but also has a suppressive interference effect, and the detection tracking performance of a detection system is influenced; because the signal received by the radio frequency front end is small and has high-frequency clutter, an in-band intermediate frequency signal is obtained after amplification and filtering, and then the in-band intermediate frequency signal enters the signal processing module.
Further, a short-time fourier transform is performed on the discrete intermediate frequency signal to transform the signal from a time domain to a time-frequency domain, and the expression:
wherein w (t) is a short time window function having a characteristic of
The target signal in step 2 is represented by a straight line distributed along a time axis and having a single frequency, and a series of comb-shaped dense decoys are represented by a plurality of wideband chirp interferences with a certain slope on the frequency axis in the time-frequency domain, where the slope is determined by the number n of slices of the SMSP interference set by the DRFM interference machine, that is, the number n of interference sub-pulses set in the front, and when n is larger and the interference power is larger, the interference becomes denser.
Furthermore, as the SMSP interference and the target echo are overlapped in multiple dimensions of time, frequency, energy and the like, the SMSP interference generates a plurality of linear frequency modulation interference signals with the same but indefinite slope on the intermediate frequency, and according to the characteristic, the interference position is found on the time-frequency domain, and a corresponding binary mask image is generated by using the interference position;
furthermore, the sampled digital signal enters a signal processing module, and the sampled intermediate frequency signal is subjected to STFT conversion, wherein the STFT calculation module comprises a data sliding window module, a windowing module and a DFT calculation module; the STFT calculation module carries out data truncation of N points of a data sliding window of M points on an input AD data stream, then reduces the influence of signal side lobes and frequency spectrum leakage through the windowing module, increases the frequency measurement dynamic range, then calculates partial frequency spectrum of each time of the data truncation of the N points through the DFT array, and finally stores the frequency spectrum data calculated by the DFT array into the FIFO array.
Further, aiming at the interference mode generated by the SMSP interference at the intermediate frequency, the corresponding binary mask image is generated by using the time-frequency domain data, and a minimum signal-to-noise ratio SNR allowing the detection signal is firstly set on the frequency spectrum req According to SNR req The size divides the time-frequency domain into two parts, one is a noise region, and the other part is a target signal plus interference region, namely a binary mask image is obtained.
Further, filtering the original time-frequency domain matrix through a binary mask image, replacing all regions with binary masks 1 with values of noise regions, and keeping regions with binary masks 0 unchanged, and averaging the filtered time-frequency domain images after weighting along a time axis to obtain a frequency spectrum after filtering the SMSP interference.
The invention also provides an interference suppression system for DRFM interference of a linear frequency modulation continuous wave system, which comprises the following components:
the receiver frequency mixing module is used for carrying out frequency mixing amplification on the echo signal with the interference and the transmitting signal through a receiver to obtain an intermediate frequency signal;
a short-time Fourier transform module, which is a part of the signal processing module, changes the intermediate-frequency signal from a time domain to a time-frequency domain by using short-time Fourier transform;
the method comprises the following steps that a binary mask image module, namely a part of a signal processing module, as SMSP interference and target echo are covered and overlapped in multiple dimensions such as time, frequency, energy and the like, the SMSP interference generates a plurality of same linear frequency modulation interference signals with uncertain slopes on intermediate frequency, according to the characteristic, an interference position is found on a time-frequency domain, and a corresponding binary mask image is generated by using the interference position;
and the interference filtering module, namely a part of the signal processing module, carries out interference filtering through a binary mask, and carries out weighting and averaging on the filtered time-frequency domain graph along a time axis to obtain a frequency spectrum result after SMSP interference is filtered.
The specific implementation method of each module of the system is the same as the interference suppression method, and is not described herein again.
The invention is further illustrated with reference to the following examples.
FIG. 1 shows a block diagram of a chirp physique proximity detection system: the invention mainly researches interference suppression of a linear frequency modulation system in a continuous wave system short-range detection system, and the improved system has the advantages of high distance resolution, no distance blind area, strong interception resistance, simple structure and the like, and is very suitable for short-range detection. The invention provides an SMSP interference suppression method combining time-frequency domain transformation and a binary mask time-frequency domain filter. After mixing a mixed signal of a target echo signal and an SMSP interference signal with a local oscillator signal, obtaining an interfered intermediate frequency signal through low-pass filtering; and carrying out short-time Fourier transform on the sampled intermediate frequency signal to obtain a time frequency spectrum, finding an interfered position on the time frequency spectrum, generating a corresponding binary mask image, and carrying out interference filtering through a binary mask.
Fig. 2 shows a time-frequency diagram of a radio frequency signal of the SMSP interference, and it can be clearly seen that the frequency segmentation characteristic of the SMSP interference is that each segment has the same bandwidth as the transmission signal of the transmitter, but the slope is n times of the transmission signal.
The invention carries out the following steps for such interfering signals:
the method comprises the following steps: firstly, STFT conversion is carried out on sampled intermediate frequency signals, and an STFT calculation module comprises a data sliding window module, a windowing module and a DFT calculation module. The STFT calculation module carries out data truncation of N points of a data sliding window of M points on an input AD data stream, then reduces the influence of signal side lobes and frequency spectrum leakage through the windowing module, increases the frequency measurement dynamic range, then calculates partial frequency spectrum of each time of the data truncation of the N points through the DFT array, and finally stores the frequency 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, and when M is reduced, the time resolution is improved, but the calculation amount is increased, and the number of DFT calculation units required in the DFT array is increased. The STFT computing framework needs a DFT computing module which can realize a pipeline working mode and has less resource. The invention uses partial calculation DFT algorithm to calculate the STFT framework, and reduces the resource usage amount while meeting the algorithm performance requirement. The DFT calculation mainly consists in multiplication and accumulation operation of intermediate frequency signal values and twiddle factors, so the DFT algorithm of the invention is mainly divided into three modules, namely a twiddle factor reading module, an input reading module and a DFT PE (processing element) Region, the DFT algorithm is the existing mature method, and the algorithm is realized on an FPGA platform by using Verilog language.
Step two: after the time-frequency domain after the STFT is obtained, the time-frequency domain enters a mask filtering interference suppression binary mask data calculation module which is mainly divided into a storage part and a calculation part, wherein the storage part comprises an FIFO1 array for caching, an FIFO2 array for storing time-frequency domain data and an FIFO3 array for storing a binary image; the computing part comprises a log computing array, a histogram computing module and a binarization conversion module. The histogram module is composed of a two-dimensional memory matrix, wherein the number of the memory cells represents the number of the spectral power spectrum values counted by the histogram, and the bit width of each memory cell represents the number of each kind. The binarization conversion module uses the threshold value received and calculated before, and binarizes the value output from the FIFO2, splices the originally stored spectrum power value and the binarization result and stores the spliced value into the FIFO3.
Step three: after the binary mask data is obtained, the SMSP interference can be filtered according to the filtering algorithm, the mask filtering module comprises a signal detection module and a frequency spectrum accumulation module, and the frequency spectrum of the interference to be filtered finally is output through the signal result calculated by the signal detection module, the binarization result output in the FIFO3 and the frequency spectrum power spectrum value.
Step four: after the frequency spectrum of the interference is filtered, compared with the frequency spectrum before the interference is filtered, the target signal spectral line is obviously detected. The hardware implementation of the interference suppression algorithm can adapt to interference input under typical parameters through testing, and the interference suppression algorithm has an interference suppression effect.
Assuming that the number n of interfering sub-pulses is 5, i.e. the number of SMSP interfering slices is 5, the interference-to-signal ratio is equal to 35dB.
Fig. 3 shows a time-frequency diagram of the fuse transmission signal and the SMSP interference signal, and the frequency segmentation characteristic of the SMSP interference can be clearly seen, and each segment has the same bandwidth as the fuse transmission signal, but the slope is n times of the transmission signal.
Fig. 4 shows an intermediate frequency spectrum diagram interfered by the SMSP, and an interfered intermediate frequency spectrum is obtained after mixing a received signal containing a target echo, spectrum dispersion interference and noise at a fuse receiving end. As can be seen from the figure, the SMSP interference produces dense ghost peaks at the intermediate frequency, while the real target appears as a single peak in the spectrum. The figure shows the medium frequency spectrum diagrams corresponding to 27dB and 35dB of interference-to-signal ratio respectively, when the interference-to-signal ratio is 35dB, the false peak generated by the SMSP interference will overwhelm the peak of the target signal, and the effect of suppressing interference is formed.
Fig. 5 shows a time-frequency diagram of the if signal interfered by the SMSP, and it can be seen from the time-frequency diagram that the target signal is represented by a straight line with a single frequency distributed along the time axis, and the SMSP interference is a plurality of wideband chirp disturbers with a certain slope generated on the time axis.
Fig. 6 shows a flow chart of SMSP interference suppression based on binary mask time-frequency domain filtering, which can effectively remove the SMSP interference by performing a series of processing on the digital signal after echo intermediate frequency sampling.
Fig. 7 is a graph showing the comparison of the spectrum effect after interference suppression, and it can be seen from the graph that when the number n of interfering sub-pulses is 5, that is, the number of SMSP interference slices is 5, and the interference-to-signal ratio is equal to 35dB, the interference signal completely drowns the target signal. SMSP interference suppression by combining time-frequency domain transformation and a binary mask time-frequency domain filter can effectively suppress SMSP interference and identify a target signal.
Claims (10)
1. An interference suppression method for DRFM interference of a chirp continuous wave system is characterized by comprising the following steps:
the echo signal with interference is subjected to frequency mixing amplification with a transmitting signal through a receiver to obtain an intermediate frequency signal;
changing the intermediate frequency signal from a time domain to a time-frequency domain by using short-time Fourier transform;
SMSP interference generates a plurality of linear frequency modulation interference signals with the same but indefinite slopes on intermediate frequency, and according to the characteristics, an interference position is found on a time-frequency domain, and a corresponding binary mask image is generated by using the interference position;
and carrying out interference filtering through a binary mask, carrying out weighting on the filtered time-frequency domain graph along a time axis, and then averaging to obtain a frequency spectrum result after SMSP interference is filtered.
2. The method of claim 1, wherein the SMSP interference produces ghost peaks at the intermediate frequency after the receiver mixes the received signal containing the target echo, the spectrally dispersive interference, and the noise;
setting the complex envelope of the transmitter transmission signal to
In the formula: t is the pulse width; k is the modulation slope;
according to the SMSP interference generation mechanism, the single sub-pulse is
Wherein A is J Is the amplitude of the interference; k 'is the frequency modulation slope of the interference, k' = nk, the sub-pulse is copied for n times, and the time domain waveform of the SMSP interference is obtained
3. The method of claim 2, wherein the short time fourier transform is performed on the discrete intermediate frequency signal to transform the signal from the time domain to the time-frequency domain, where the expression is:
wherein w (t) is a short time window function having a characteristic of
4. The method of claim 3, wherein the sampled digital signal enters a signal processing module, and the STFT conversion is performed on the sampled intermediate frequency signal, and the STFT calculation module comprises a data sliding window module, a windowing module, and a DFT calculation module; the STFT calculation module carries out data truncation of N points of a data sliding window of M points on an input AD data stream, then increases a frequency measurement dynamic range through a windowing module, then calculates partial frequency spectrum of each time of N point truncation data through a DFT array, and finally stores frequency spectrum data calculated by the DFT array into an FIFO array.
5. The method of claim 4, wherein the time-frequency domain data is used to generate a corresponding binary mask image by first spectrally setting a minimum signal-to-noise ratio (SNR) that allows detection of the signal req According to SNR req The size divides the time-frequency domain into two parts, one is a noise region, and the other part is a target signal plus interference region, namely a binary mask image is obtained.
6. The method of claim 5, wherein the original time-frequency domain matrix is filtered through a binary mask image, all regions with binary mask 1 are replaced by noise region values, and regions with binary mask 0 are unchanged, and the filtered time-frequency domain image is weighted along a time axis and then averaged to obtain the spectrum with SMSP interference removed.
7. An interference suppression system for DRFM interference in chirp spread spectrum systems, comprising:
the receiver frequency mixing module is used for carrying out frequency mixing amplification on the echo signal with the interference and the transmitting signal through a receiver to obtain an intermediate frequency signal;
a short-time Fourier transform module for transforming the intermediate frequency signal from the time domain to the time-frequency domain by using a short-time Fourier transform;
the binary mask image module is used for finding an interference position on a time-frequency domain to generate a corresponding binary mask image;
and the interference filtering module is used for filtering interference through a binary mask, and the filtered time-frequency domain graph is weighted along a time axis and then averaged to obtain a frequency spectrum result after SMSP interference is filtered.
8. 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 steps of the method of any of claims 1-6 are implemented when the program is executed by the processor.
9. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 6.
10. A computer program product comprising a computer program, characterized in that the computer program realizes the steps of the method of any one of claims 1-6 when executed by a processor.
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