Non-cooperative bistatic radar reference signal multipath suppression method and device

Abstract

The present invention provides a non-cooperative bistatic radar reference signal multipath suppression method and device, comprising: obtaining a baseband signal; performing adaptive pulse interception on the baseband signal to obtain a preprocessed signal; obtaining the frequency modulation slope of the preprocessed signal; performing de-skewing demodulation processing on the preprocessed signal to obtain a de-skewing signal; determining the direct wave corresponding frequency component of the single-frequency signal in the de-skewing signal based on the frequency modulation slope; filtering out the multipath corresponding frequency component to obtain a pure direct wave component; and performing frequency modulation slope recovery on the pure direct wave component to obtain a pure direct wave signal. The present invention can effectively remove the multipath signal of the reference channel to obtain a pure direct wave signal, thereby improving the target detection probability of the non-cooperative bistatic radar and effectively suppressing the problems of increased noise power, false targets, and strong and weak target masking effects caused by the multipath of the reference channel.

Description

Technical Field

[0001] The present invention relates to the technical field of radar signal processing, and in particular to a method and device for suppressing multipath of a non-cooperative bistatic radar reference signal. Background Art

[0002] Non-cooperative bistatic radar systems have been a research hotspot in the radar field in recent years. Compared to active radars, non-cooperative bistatic radars have two channels: a surveillance channel and a reference channel. The surveillance channel monitors the target airspace and receives signals transmitted by external emitters that are reflected by the target. The reference channel synchronizes the system by receiving direct-arrival signals from external emitters and acts as a matched filter to correlate the echoes with the surveillance channel. The direct-arrival signals received by the reference channel of an external emitter radar contain noise components, and when there is no line-of-sight between the receiver and the external emitter, multipath interference is also introduced. In this case, the matched filter constructed in the reference channel suffers from a loss in signal-to-noise ratio compared to the ideal filter of an active radar.

[0003] To address the multipath suppression problem in the reference channel, existing channel estimation methods are primarily based on the unique signal structure of signals such as communication broadcasts. For constant modulus continuous wave signals, the constant modulus algorithm is highly effective in multipath suppression. Spatial filtering can also be used to filter out multipath in specific directions. For linear frequency modulation (LFM) signals in pulse regimes, the effectiveness of these methods is significantly reduced, and signal processing currently primarily relies on the time-frequency domain. A typical direct wave purification method involves filtering in the fractional Fourier transform (FFT) domain. Emerging methods further incorporate FM slope estimation to compress the parameter search space. Fractional domain rotation of LFM signals results in a frequency difference between the multipath signal and the direct wave signal that is too small, necessitating the use of higher-order filters to eliminate multipath. Summary of the Invention

[0004] In view of the defects of the prior art, the present invention provides a method and device for multipath suppression of a non-cooperative bistatic radar reference signal.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] In one aspect, the present invention provides a method for multipath suppression of a non-cooperative bistatic radar reference signal, comprising the following steps:

[0007] S1, obtain the radar receiving signal and convert the received signal into a baseband signal;

[0008] S2. Adaptively intercept the baseband signal to obtain a preprocessed signal, where the preprocessed signal consists of a direct wave signal, a multipath signal, and noise;

[0009] S3, obtaining the frequency modulation slope of the preprocessed signal;

[0010] S4, performing a de-skew demodulation process on the pre-processed signal to obtain a de-skew signal, wherein the de-skew signal is composed of single-frequency signals of different frequencies;

[0011] S5. Determine the direct wave corresponding frequency component of the single-frequency signal in the de-ramped signal based on the frequency modulation slope. If the frequency modulation slope is positive, select the signal component with the largest signal frequency as the direct wave corresponding frequency component; if the frequency modulation slope is negative, select the signal component with the smallest signal frequency as the direct wave corresponding frequency component.

[0012] S6. Shift the frequency component corresponding to the direct wave to zero frequency, filter out the frequency component corresponding to the multipath, perform group delay correction on the filtered single-frequency signal, and then shift the frequency to the frequency corresponding to the direct wave to obtain a pure direct wave component.

[0013] S7. Perform frequency modulation slope recovery on the pure direct wave component to obtain a pure direct wave signal.

[0014] Furthermore, the preprocessed signal is obtained according to the following steps:

[0015] S21, performing square-law detection processing on the baseband signal to obtain a signal to be detected;

[0016] S22, initialization flag ;

[0017] S23, Judgment , calculate the left detection threshold of the current signal to be detected, compare the current signal to be detected with the left detection threshold, if the current signal to be detected is greater than the left detection threshold, then set the flag It is determined that this is the rising edge of the pulse, and the process goes to S24; if the current signal to be detected is less than the left detection threshold, the left detection threshold of the next signal to be detected is calculated, and the process goes back to S22;

[0018] S24. Judgment When , calculate the right detection threshold of the current signal to be detected, compare the current signal to be detected with the right detection threshold, if the current signal to be detected is greater than the right detection threshold, then set And determine that this is the pulse falling edge moment, return to S22, and continue to calculate the pulse rising edge moment of the next pulse; if the current signal to be detected is less than the right detection threshold, calculate the right detection threshold of the next signal to be detected, and continue to compare the size of the right detection threshold of the current signal to be detected with that of the next signal to be detected; after calculating all the signals to be detected, go to S25;

[0019] S25. Based on the obtained pulse rising edge time and pulse falling edge time, intercept the baseband signal to obtain a preprocessed signal.

[0020] Furthermore, the left detection threshold is calculated according to the following formula:

[0021] ;

[0022] ;

[0023] ;

[0024] in, is the left detection threshold; is the left threshold factor; is the estimated value of the noise power on the left; is the number of training units on the left; is the false alarm rate on the left side; is the training unit on the left side of the detection unit;

[0025] The right detection threshold is calculated according to the following formula:

[0026] ;

[0027] ;

[0028] ;

[0029] in, is the right detection threshold; is the right threshold factor; is the estimated value of the noise power on the right; is the number of training units on the right; is the false alarm rate on the right side; is the training unit to the right of the detection unit.

[0030] Furthermore, the preprocessed signal is expressed as:

[0031] ;

[0032] in, is the preprocessing signal; transmitting a linear frequency modulation signal to a radiation source; is the propagation loss from the radiation source to the reference channel antenna; N is the number of intercepted points, ; The first k The attenuation coefficient of the multipath; The first k The time delay of each multipath relative to the direct wave; K is the number of multipaths; is the additive white Gaussian noise of the reference channel.

[0033] Furthermore, methods for obtaining the frequency modulation slope of the preprocessed signal include fractional Fourier transform, spectrum zero point time-frequency screening method or adaptive spectrum graph calculation.

[0034] Furthermore, the single-frequency signal is expressed as:

[0035] ;

[0036] in, is the de-skewing signal; is the frequency modulation slope; is the gate function; is the signal carrier frequency; is the initial phase of the signal; is the signal pulse width; For index signals ; Is an imaginary unit.

[0037] Furthermore, when determining the direct wave corresponding frequency component of the single-frequency signal in the de-skewed signal, a low-resolution spectrum estimation method is first used to estimate and find the spectrum peak position, and then a high-resolution method is used to determine the direct wave corresponding frequency component of the single-frequency signal.

[0038] Furthermore, the low-resolution spectrum estimation method includes the Welch method or the correlation function method;

[0039] The high-resolution method includes spectrum refinement method, maximum entropy spectrum method or multiple signal classification method.

[0040] Furthermore, the FM slope of the pure direct wave component is recovered according to the following formula:

[0041] ;

[0042] in, It is a pure direct wave signal; is the pure direct wave component; For index signals ; Is an imaginary unit.

[0043] In another aspect, the present invention provides a non-cooperative bistatic radar reference signal multipath suppression device, comprising:

[0044] The first module is used to obtain the radar receiving signal and convert the received signal into a baseband signal;

[0045] The second module is used to perform adaptive pulse interception on the baseband signal to obtain a preprocessed signal, wherein the preprocessed signal consists of a direct wave signal, a multipath signal and noise;

[0046] The third module is used to obtain the frequency modulation slope of the preprocessed signal;

[0047] A fourth module is configured to perform a de-skew demodulation process on the pre-processed signal to obtain a de-skew signal, wherein the de-skew signal is composed of single-frequency signals of different frequencies;

[0048] The fifth module is used to determine the direct wave corresponding frequency component of the single-frequency signal in the de-skewed signal based on the frequency modulation slope. If the frequency modulation slope is positive, the signal component with the largest signal frequency is selected as the direct wave corresponding frequency component; if the frequency modulation slope is negative, the signal component with the smallest signal frequency is selected as the direct wave corresponding frequency component;

[0049] The sixth module is used to shift the frequency component corresponding to the direct wave to zero frequency, filter out the frequency component corresponding to the multipath, perform group delay correction on the filtered single-frequency signal, and then frequency shift it to the frequency corresponding to the direct wave to obtain a pure direct wave component;

[0050] The seventh module is used to perform frequency modulation slope recovery on the pure direct wave component to obtain a pure direct wave signal.

[0051] Compared with the prior art, the beneficial technical effects of the present invention are:

[0052] The present invention provides a non-cooperative bistatic radar reference signal multipath suppression method and device. The method converts a received signal into a baseband signal and then processes it. The baseband signal is processed using an adaptive pulse interception method, thereby reducing noise energy and multipath signal energy. The method removes the linear modulation of a preprocessed signal through de-skewing demodulation processing, converting the signal into a de-skewing signal composed of single-frequency signals of different frequencies. The frequency component corresponding to the direct wave of the single-frequency signal in the de-skewing signal is then determined through the frequency modulation slope. The frequency component corresponding to the direct wave is then frequency-shifted to zero frequency, and the frequency component corresponding to the multipath is filtered out, thereby obtaining a pure direct wave component. The method also reduces the amount of calculation and resource consumption. Finally, the frequency modulation slope is restored for the pure direct wave component to obtain a pure direct wave signal.

[0053] The present invention can effectively remove the multipath signal of the reference channel, improve the target detection probability of the non-cooperative bistatic radar, and effectively suppress the problems of increased noise power, false targets, and strong and weak target masking effects caused by the multipath of the reference channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0055] Figure 1 A flowchart of a method for multipath suppression of a non-cooperative bistatic radar reference signal provided by an embodiment;

[0056] Figure 2 The simulation provided in one embodiment is affected by multipath interference and noise pollution, wherein: Figure 2 (a) is the time domain waveform of the reference signal subjected to multipath interference and noise pollution; Figure 2 (b) is the time-frequency diagram of the reference signal subjected to multipath interference and noise pollution; Figure 2 (c) The target local result image after cross-correlation between the contaminated reference signal and the echo signal; Figure 2 (d) The target local result image after cross-correlation between the uncontaminated reference signal and the echo signal in the simulation;

[0057] Figure 3 A partial spectrum diagram of a reference signal simulating multipath interference and noise pollution after de-skewing and demodulation is performed, provided in one embodiment;

[0058] Figure 4 A partial diagram of the spectrum of a simulated contaminated reference signal after de-skewing and demodulation and FIR filtering provided by an embodiment;

[0059] Figure 5 A time-frequency diagram of a reference signal recovered by simulation provided by an embodiment;

[0060] Figure 6 A partial diagram of the simulation result of matched filtering using a restored reference signal and an echo signal provided by an embodiment;

[0061] Figure 7 This is a graph of measured radar data provided by an embodiment, wherein: Figure 7 (a) is the time domain waveform of the normalized measured radar reference channel data; Figure 7 (b) is the normalized frequency domain diagram of the measured radar data; Figure 7 (c) is the time-frequency diagram of the measured radar reference channel data;

[0062] Figure 8 A local spectrum diagram of the de-skewed and demodulated measured radar reference channel data provided by an embodiment;

[0063] Figure 9 This is a signal correlation result diagram after processing the measured radar data provided by an embodiment, wherein: Figure 9 (a) is the autocorrelation result diagram of the reference signal before and after the measured radar data is processed; Figure 9 (b) is the cross-correlation result diagram of the reference signal and the echo signal before and after the measured radar data is processed;

[0064] Figure 10 This is a diagram of target detection results before and after processing of multiple pulses of measured radar data provided by an embodiment. DETAILED DESCRIPTION

[0065] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0066] Reference Figure 1 One embodiment provides a method for multipath suppression of a non-cooperative bistatic radar reference signal, comprising the following steps:

[0067] S1, obtain the radar receiving signal and convert the received signal into a baseband signal;

[0068] S2. Adaptively intercept the baseband signal to obtain a preprocessed signal, where the preprocessed signal consists of a direct wave signal, a multipath signal, and noise;

[0069] S3, obtaining the frequency modulation slope of the preprocessed signal;

[0070] S4, performing a de-skew demodulation process on the pre-processed signal to obtain a de-skew signal, wherein the de-skew signal is composed of single-frequency signals of different frequencies;

[0071] S5. Determine the direct wave corresponding frequency component of the single-frequency signal in the de-ramped signal based on the frequency modulation slope. If the frequency modulation slope is positive, select the signal component with the largest signal frequency as the direct wave corresponding frequency component; if the frequency modulation slope is negative, select the signal component with the smallest signal frequency as the direct wave corresponding frequency component.

[0072] S6. Shift the frequency component corresponding to the direct wave to zero frequency, filter out the frequency component corresponding to the multipath, perform group delay correction on the filtered single-frequency signal, and then shift the frequency to the frequency corresponding to the direct wave to obtain a pure direct wave component.

[0073] S7. Perform frequency modulation slope recovery on the pure direct wave component to obtain a pure direct wave signal.

[0074] In a preferred embodiment, the preprocessed signal is obtained according to the following steps:

[0075] S21, performing square-law detection processing on the baseband signal to obtain a signal to be detected;

[0076] S22, initialization flag ;

[0077] S23, Judgment , calculate the left detection threshold of the current signal to be detected, compare the current signal to be detected with the left detection threshold, if the current signal to be detected is greater than the left detection threshold, then set the flag It is determined that this is the rising edge of the pulse, and the process goes to S24; if the current signal to be detected is less than the left detection threshold, the left detection threshold of the next signal to be detected is calculated, and the process goes back to S22;

[0078] S24. Judgment When , calculate the right detection threshold of the current signal to be detected, compare the current signal to be detected with the right detection threshold, if the current signal to be detected is greater than the right detection threshold, then set And determine that this is the pulse falling edge moment, return to S22, and continue to calculate the pulse rising edge moment of the next pulse; if the current signal to be detected is less than the right detection threshold, calculate the right detection threshold of the next signal to be detected, and continue to compare the size of the right detection threshold of the current signal to be detected with that of the next signal to be detected; after calculating all the signals to be detected, go to S25;

[0079] S25. Based on the obtained pulse rising edge and pulse falling edge, intercept the baseband signal to obtain a preprocessed signal.

[0080] The left detection threshold is calculated according to the following formula:

[0081] ;

[0082] ;

[0083] ;

[0084] in, is the left detection threshold; is the left threshold factor; is the estimated value of the noise power on the left; is the number of training units on the left; is the false alarm rate on the left side; is the training unit on the left side of the detection unit; since the signal to be detected has no training unit on the left side during the initial calculation, the signal to be detected is Start testing.

[0085] The right detection threshold is calculated according to the following formula:

[0086] ;

[0087] ;

[0088] ;

[0089] in, is the right detection threshold; is the right threshold factor; is the estimated value of the noise power on the right; is the number of training units on the right; is the false alarm rate on the right side; is the training unit to the right of the detection unit.

[0090] The preprocessed signal is expressed as:

[0091] ;

[0092] in, is the preprocessing signal; transmitting a linear frequency modulation signal to a radiation source; is the propagation loss from the radiation source to the reference channel antenna; N is the number of intercepted points, ; The first k The attenuation coefficient of the multipath; The first k The time delay of each multipath relative to the direct wave; K is the number of multipaths; is the additive white Gaussian noise of the reference channel, with a mean of zero and a variance of .

[0093] The baseband signal is processed by using an adaptive pulse interception method to reduce noise energy and multipath signal energy. When the frequency shift of multipath signals with excessive time delay is greater than half the sampling frequency, aliasing occurs, resulting in confusion in the identification of direct waves after de-skewing and demodulation. Therefore, by reducing the multipath signal energy, the aliasing caused by the frequency shift of multipath signals with excessive time delay is weakened, so that the correct direct wave can be determined after de-skewing and demodulation of the preprocessed signal.

[0094] Methods for obtaining the FM slope of the preprocessed signal include fractional Fourier transform, spectrum zero point time-frequency screening method or adaptive spectrum graph calculation. In this embodiment, fractional Fourier transform is used to obtain the FM slope of the preprocessed signal.

[0095] Performing a de-skew demodulation process on the pre-processed signal to remove the linear modulation of the pre-processed signal to obtain a de-skew signal, wherein the de-skew signal is composed of single frequency signals with different frequencies;

[0096] The de-skewing signal is expressed as:

[0097] ;

[0098] in, is the de-skewing signal; is the frequency modulation slope; is the gate function; is the signal carrier frequency; is the initial phase of the signal; is the signal pulse width; For index signals ; Is an imaginary unit.

[0099] The gate function is defined as:

[0100]

[0101] Based on the FM slope, the direct frequency component of the single-frequency signal is determined. If the FM slope is positive, the signal component with the largest frequency is selected as the direct frequency component; if the FM slope is negative, the signal component with the smallest frequency is selected as the direct frequency component. Specifically, it can be expressed as follows:

[0102] ;

[0103] in, is the function for finding the peak; is the frequency domain of the single-frequency signal; that is, when the frequency modulation slope is positive, the peak signal with the largest signal frequency is selected as the frequency component corresponding to the direct wave; if the frequency modulation slope is negative, the peak signal with the smallest signal frequency is selected as the frequency component corresponding to the direct wave.

[0104] When determining the direct wave corresponding frequency component of the single-frequency signal in the de-skewed signal, a low-resolution spectrum estimation method is first used to estimate and find the spectral peak position. The low-resolution spectrum estimation method is used to make the spectrum smoother, thereby facilitating the search for the peak. The high-resolution method is then used to determine the direct wave corresponding frequency component of the single-frequency signal. The high-resolution method is used to find a more accurate spectral peak near the peak previously found, thereby determining the direct wave corresponding frequency component of the single-frequency signal.

[0105] The low-resolution spectrum estimation method includes the Welch method or the correlation function method;

[0106] The high-resolution method includes spectrum refinement method, maximum entropy spectrum method or multiple signal classification method.

[0107] The FM slope of the pure direct wave component is restored according to the following formula:

[0108] ;

[0109] in, It is a pure direct wave signal; is the pure direct wave component; For index signals ; Is an imaginary unit.

[0110] In one embodiment, a simulation experiment was conducted to verify the effect of the present invention.

[0111] Reference Figure 2 , Figure 2 To simulate the impact of multipath interference and noise pollution, the simulation assumes that there are two targets in the monitoring channel, and the dual-base delays are 40μs and 45μs respectively. Figure 2 As can be seen from (a), the signals are aliased in the time domain and the waveform distortion is very serious; Figure 2 In (b), we can clearly see the direct wave signal with the strongest energy and the multipath signal trailing behind the direct wave. Figure 2 As can be seen in (c), the target at 40μs in the simulation is interfered by the target at 45μs, resulting in many false targets near it and the target cannot be detected. Figure 2 As can be seen in (d), when there is no multipath interference, both targets can be correctly detected.

[0112] Reference Figure 3 , we can see that after de-skewing and demodulation, the multipath signal has a frequency shift relative to the de-skewing result of the direct wave. Therefore, it is necessary to filter out the multipath signal components and retain the direct wave components. The frequency component corresponding to the direct wave is shifted to zero frequency, and the frequency component corresponding to the multipath is filtered out through an FIR low-pass filter. The filtered single-frequency signal is subjected to group delay correction and then frequency-shifted to the frequency corresponding to the direct wave to obtain the pure direct wave component, as shown in Figure 5 As shown. Figure 4 , it can be seen that in the signal spectrum of the filtered single-frequency signal, the frequency components corresponding to the multipath signal have been filtered out. Figure 6 , it can be seen that after filtering out the frequency components corresponding to the multipath Figure 2 The false targets in (c) are eliminated and the targets can be detected correctly.

[0113] Reference Figure 7 , is a measured radar data diagram, showing different results of sampling a pulse signal of the measured signal, and the results are normalized accordingly in different domains. Figure 7 (a) and Figure 7 As can be seen in (b), the signal has been completely distorted in the time domain and frequency domain; Figure 7 (c) The multipath signals behind the direct wave can be seen; that is, the direct waves in different domains are severely interfered by the multipath signals.

[0114] Reference Figure 8, which is the local spectrum diagram after de-skewing and demodulation of the measured radar reference channel data. It can be seen that the direct wave with the highest frequency is smaller than the multipath energy with the smallest delay. Moreover, since this multipath delay is very small, it cannot be observed in the time-frequency diagram. This will generate a false target in front of the target after matched filtering, which will seriously affect the target detection performance.

[0115] The results of the measured radar data signals before and after processing using the method of the present invention are as follows: Figure 9 As shown. Figure 9 From the autocorrelation results of (a), it can be seen that in addition to the main peak, the measured data also has parasitic secondary peaks on both sides of the main peak due to multipath. However, after the processing method of the present invention, the secondary peaks on both sides of the main peak are eliminated, and the direct wave autocorrelation function is restored to a signal with ideal narrowband characteristics. Figure 9 As can be seen in (b), before processing using the method of the present invention, the matching result shows a false target at bistatic range cell 2255, which is located in front of the true target, because the multipath signal strength in the reference channel exceeds the direct wave. This also submerges the true target at bistatic range cell 2262. However, after processing using the method of the present invention, the multipath in the reference channel is filtered out, the false target at bistatic range cell 2255 disappears, and the true target at bistatic range cell 2262 is revealed. This shows that the present invention can effectively remove multipath signals in the reference channel, thereby improving the probability of target detection for non-cooperative bistatic radars.

[0116] The target detection results before and after processing of multiple pulses of measured radar data are as follows: Figure 10 As shown, the CFAR (Constant False Alarm Rate) parameters are the same before and after processing. As can be seen from the figure, when the reference signal is not processed, pulses 3 to 8 do not detect any targets. After processing using the method described in the present invention, previously missed targets can be redetected. Furthermore, due to the presence of multipath signals stronger than the direct wave in the experimental scenario, the directly detected target bistatic distance is smaller than the true distance. As can be seen from the figure, the bistatic distance unit of the same target after processing using the method described in the present invention is larger than before processing. This indicates that strong multipath signals in the reference channel can cause the matched filter target distance to shift, and the method described in the present invention can effectively remove the reference channel multipath signals, improve the detection probability, and suppress false targets caused by the reference channel multipath.

[0117] In one embodiment, a non-cooperative bistatic radar reference signal multipath suppression device is provided, comprising:

[0118] The first module is used to obtain the radar receiving signal and convert the received signal into a baseband signal;

[0119] The second module is used to perform adaptive pulse interception on the baseband signal to obtain a preprocessed signal, wherein the preprocessed signal consists of a direct wave signal, a multipath signal and noise;

[0120] The third module is used to obtain the frequency modulation slope of the preprocessed signal;

[0121] A fourth module is configured to perform a de-skew demodulation process on the pre-processed signal to obtain a de-skew signal, wherein the de-skew signal is composed of single-frequency signals of different frequencies;

[0122] The fifth module is used to determine the direct wave corresponding frequency component of the single-frequency signal in the de-skewed signal based on the frequency modulation slope. If the frequency modulation slope is positive, the signal component with the largest signal frequency is selected as the direct wave corresponding frequency component; if the frequency modulation slope is negative, the signal component with the smallest signal frequency is selected as the direct wave corresponding frequency component;

[0123] The sixth module is used to shift the frequency component corresponding to the direct wave to zero frequency, filter out the frequency component corresponding to the multipath, perform group delay correction on the filtered single-frequency signal, and then frequency shift it to the frequency corresponding to the direct wave to obtain a pure direct wave component;

[0124] The seventh module is used to perform frequency modulation slope recovery on the pure direct wave component to obtain a pure direct wave signal.

[0125] Matters not covered by the present invention are known technologies.

[0126] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0127] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and such modifications and improvements are intended to fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

[0128] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for multipath suppression of reference signals of a non-cooperative bistatic radar, characterized in that: The following steps are involved: S1, obtain the radar receiving signal and convert the received signal into a baseband signal; S2. Adaptively intercept the baseband signal to obtain a preprocessed signal, where the preprocessed signal consists of a direct wave signal, a multipath signal, and noise; S3, obtaining the frequency modulation slope of the preprocessed signal; S4, performing a de-skew demodulation process on the pre-processed signal to obtain a de-skew signal, wherein the de-skew signal is composed of single-frequency signals of different frequencies; S5. Determine the direct wave corresponding frequency component of the single-frequency signal in the de-ramped signal based on the frequency modulation slope. If the frequency modulation slope is positive, select the signal component with the largest signal frequency as the direct wave corresponding frequency component; if the frequency modulation slope is negative, select the signal component with the smallest signal frequency as the direct wave corresponding frequency component. S6. Shift the frequency component corresponding to the direct wave to zero frequency, filter out the frequency component corresponding to the multipath, perform group delay correction on the filtered single-frequency signal, and then shift the frequency to the frequency corresponding to the direct wave to obtain a pure direct wave component. S7. Perform frequency modulation slope recovery on the pure direct wave component to obtain a pure direct wave signal.

2. The non-cooperative bistatic radar reference signal multipath suppression method according to claim 1, wherein: The preprocessed signal is obtained by following the steps below: S21, performing square-law detection processing on the baseband signal to obtain a signal to be detected; S22, initialization flag ; S23, Judgment , calculate the left detection threshold of the current signal to be detected, compare the current signal to be detected with the left detection threshold, if the current signal to be detected is greater than the left detection threshold, then set the flag It is determined that this is the rising edge of the pulse, and the process goes to S24; if the current signal to be detected is less than the left detection threshold, the left detection threshold of the next signal to be detected is calculated, and the process goes back to S22; S24. Judgment When , calculate the right detection threshold of the current signal to be detected, compare the current signal to be detected with the right detection threshold, if the current signal to be detected is greater than the right detection threshold, then set And determine that this is the pulse falling edge moment, return to S22, and continue to calculate the pulse rising edge moment of the next pulse; if the current signal to be detected is less than the right detection threshold, calculate the right detection threshold of the next signal to be detected, and continue to compare the size of the right detection threshold of the current signal to be detected with that of the next signal to be detected; after calculating all the signals to be detected, go to S25; S25. Based on the obtained pulse rising edge time and pulse falling edge time, intercept the baseband signal to obtain a preprocessed signal.

3. The non-cooperative bistatic radar reference signal multipath suppression method according to claim 2, wherein: The left detection threshold is calculated according to the following formula: ； ； ； in, is the left detection threshold; is the left threshold factor; is the estimated value of the noise power on the left; is the number of training units on the left; is the false alarm rate on the left side; is the training unit on the left side of the detection unit; The right detection threshold is calculated according to the following formula: ； ； ； in, is the right detection threshold; is the right threshold factor; is the estimated value of the noise power on the right; is the number of training units on the right; is the false alarm rate on the right side; is the training unit to the right of the detection unit.

4. The non-cooperative bistatic radar reference signal multipath suppression method according to claim 2, wherein: The preprocessed signal is expressed as: ； in, is the preprocessing signal; transmitting a linear frequency modulation signal to a radiation source; is the propagation loss from the radiation source to the reference channel antenna; N is the number of intercepted points, ; The first k The attenuation coefficient of the multipath; The first k The time delay of each multipath relative to the direct wave; is the number of multipaths; is the additive white Gaussian noise of the reference channel.

5. The non-cooperative bistatic radar reference signal multipath suppression method according to claim 1, wherein: Methods for obtaining the frequency modulation slope of the preprocessed signal include fractional Fourier transform, spectrum zero point time-frequency screening method or adaptive spectrum graph calculation.

6. The non-cooperative bistatic radar reference signal multipath suppression method according to claim 1, wherein: The de-skewing signal is expressed as: ； in, is the de-skewing signal; is the frequency modulation slope; is the gate function; is the signal carrier frequency; is the initial phase of the signal; is the signal pulse width; For index signals ; Is an imaginary unit.

7. The non-cooperative bistatic radar reference signal multipath suppression method according to claim 1, wherein: In determining the frequency component corresponding to the direct wave of the single-frequency signal in the de-skewed signal, a low-resolution spectrum estimation method is first used to estimate and find the spectrum peak position, and then a high-resolution method is used to determine the frequency component corresponding to the direct wave of the single-frequency signal.

8. The method for multipath suppression of a non-cooperative bistatic radar reference signal according to claim 7, wherein: The low-resolution spectrum estimation method includes the Welch method or the correlation function method; The high-resolution method includes spectrum refinement method, maximum entropy spectrum method or multiple signal classification method.

9. The non-cooperative bistatic radar reference signal multipath suppression method according to claim 1, wherein: The FM slope of the pure direct wave component is restored according to the following formula: ； in, It is a pure direct wave signal; is the pure direct wave component; For index signals ; Is an imaginary unit.

10. A non-cooperative bistatic radar reference signal multipath suppression device, characterized in that: include: The first module is used to obtain the radar receiving signal and convert the received signal into a baseband signal; The second module is used to perform adaptive pulse interception on the baseband signal to obtain a preprocessed signal, wherein the preprocessed signal consists of a direct wave signal, a multipath signal and noise; The third module is used to obtain the frequency modulation slope of the preprocessed signal; A fourth module is configured to perform a de-skew demodulation process on the pre-processed signal to obtain a de-skew signal, wherein the de-skew signal is composed of single-frequency signals of different frequencies; The fifth module is used to determine the direct wave corresponding frequency component of the single-frequency signal in the de-skewed signal based on the frequency modulation slope. If the frequency modulation slope is positive, the signal component with the largest signal frequency is selected as the direct wave corresponding frequency component; if the frequency modulation slope is negative, the signal component with the smallest signal frequency is selected as the direct wave corresponding frequency component; The sixth module is used to shift the frequency component corresponding to the direct wave to zero frequency, filter out the frequency component corresponding to the multipath, perform group delay correction on the filtered single-frequency signal, and then frequency shift it to the frequency corresponding to the direct wave to obtain a pure direct wave component; The seventh module is used to perform frequency modulation slope recovery on the pure direct wave component to obtain a pure direct wave signal.

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