Time-Frequency Analysis Method of Radar Radiation Source Signal Based on Signal Extraction

Abstract

The present invention discloses a time-frequency analysis method for radar emitter signals based on signal extraction, including: performing spectrum analysis on the radar emitter signals to determine the frequency distribution range of the radar emitter signals; performing digital down-conversion on the radar emitter signals to transform the center frequency of the radar emitter signals to 0; performing low-pass filtering on the radar emitter signals to retain the effective frequency components of the radar emitter signals; based on the radar emitter signals after low-pass filtering, extracting the sampling sequence of the radar emitter signals in a manner of extracting one point at every preset interval number of points; performing time-frequency analysis on the extracted sampling sequence to obtain the time-frequency image of the radar emitter signals. The time-frequency analysis method for radar emitter signals based on signal extraction of the present invention can reduce the signal sampling frequency, improve the frequency resolution, transform the radar emitter signals into high-quality time-frequency diagrams, and can effectively reduce the computational amount of time-frequency analysis.

Description

Technical Field

[0001] The present invention relates to the technical field of signal processing, and particularly relates to a time-frequency analysis method for radar emitter signals based on signal extraction. Background Art

[0002] With the increasingly complex modulation methods of radar signals, traditional signal analysis methods with arrival angle, carrier frequency, arrival time, pulse width, and pulse amplitude as the five characteristic parameters have become difficult to meet the requirements of modern electronic reconnaissance.

[0003] In the analysis of intercepted radar signals, the analysis of internal pulse characteristics (abbreviated as in-pulse analysis) is particularly important. In-pulse analysis mainly identifies the modulation type of radar emitter signals, and then estimates the corresponding parameters or conducts more detailed analysis. Since traditional time-domain or frequency-domain analysis methods are difficult to obtain sufficient information about radar emitter signals, currently common methods are to perform signal analysis in the time-frequency domain, such as time-frequency transformation methods like short-time Fourier transform. However, when directly performing radar emitter signal analysis in the time-frequency domain using traditional time-frequency transformation methods, the finally obtained effective frequency change range is very small, which is not conducive to subsequent signal recognition and other processing.

[0004] With the rise of artificial intelligence algorithms such as deep learning, intelligent recognition of radar emitter signals based on time-frequency transformation images has become a new method for analyzing radar emitter signals currently. However, the time-frequency transformation in existing deep learning intelligent recognition methods is relatively simple, without considering the large differences in pulse width and bandwidth distribution of actual radar emitter signals. Some long pulses may exceed hundreds of thousands of points after sampling, resulting in a large computational amount for time-frequency analysis. And when the time-frequency diagram is too large or the sizes are not uniform, it cannot be input into the deep learning network model. Summary of the Invention

[0005] To solve some or all of the above-mentioned technical problems existing in the prior art, the present invention provides a time-frequency analysis method for radar emitter signals based on signal extraction.

[0006] The technical solution of the present invention is as follows:

[0007] A time-frequency analysis method for radar emitter signals based on signal extraction is provided, and the method includes:

[0008] Perform spectrum analysis on the radar emitter signal to determine the frequency distribution range of the radar emitter signal;

[0009] Perform digital down-conversion on the radar emitter signal to transform the center frequency of the radar emitter signal to 0;

[0010] Perform low-pass filtering on the radar emitter signal to retain the effective frequency components of the radar emitter signal;

[0011] Based on the radar emitter signal after low-pass filtering, decimate the sampling sequence of the radar emitter signal by taking one point every other preset number of interval points;

[0012] Perform time-frequency analysis on the decimated sampling sequence to obtain the time-frequency image of the radar emitter signal.

[0013] In some possible implementation manners, the performing spectrum analysis on the radar emitter signal to determine the frequency distribution range of the radar emitter signal includes:

[0014] Segment the radar emitter signal with a preset length, calculate the power spectrum of each segment of the signal by using fast Fourier transform, add the power spectra of each segment of the signal and calculate the average value to determine the power spectrum corresponding to the radar emitter signal;

[0015] Smooth the power spectrum of the radar emitter signal;

[0016] Calculate the frequency distribution range of the radar emitter signal according to the smoothed power spectrum.

[0017] In some possible implementation manners, use the following formula to calculate and determine the frequency distribution range of the radar emitter signal;

[0018]

[0019]

[0020] Among them, B represents the normalized frequency width of the signal, and represent the normalized cut-off frequencies within the signal bandwidth, represents the normalized frequency center of the signal, P(i) represents the smoothed power spectrum, N f represents the number of points of the fast Fourier transform, i represents an integer from 1 to N in the digital frequency domain f of.

[0021] In some possible implementation manners, multiply the radar emitter signal by to perform digital down-conversion.

[0022] In some possible implementation manners, when performing low-pass filtering on the radar emitter signal, set the cut-off frequency to 0.5B + Δ, where Δ represents the reserved frequency width.

[0023] In some possible implementation manners, the value of the preset number of interval points is below f s / B′, where fs f represents the sampling frequency of the radar radiation source signal, and B′ represents the bandwidth of the radar radiation source signal after low-pass filtering processing.

[0024] In some possible implementation manners, the method further includes:

[0025] When performing decimation on the sampling sequence of the radar radiation source signal, determine the minimum decimation number that does not affect the time-frequency effect, and calculate the corresponding preset interval number according to the minimum decimation number;

[0026] Determine whether the calculated preset interval number does not exceed 1. If so, use the original radiation source signal sampling sequence as the decimated sampling sequence. If not, select an integer between 1 and the calculated preset interval number as the actual preset interval number for decimation.

[0027] In some possible implementation manners, perform time-frequency analysis on the decimated sampling sequence by using short-time Fourier transform.

[0028] In some possible implementation manners, the short-time Fourier transform of the sampling sequence is expressed as:

[0029]

[0030] where STFT x (n,k) represents the short-time Fourier transform of the sampling sequence x(n), w(m) represents the window function, M represents the length of the window, and k represents an integer from 1 to M in the digital frequency domain.

[0031] The main advantages of the technical solution of the present invention are as follows:

[0032] The time-frequency analysis method of the radar radiation source signal based on signal decimation in the present invention can reduce the signal sampling frequency, improve the frequency resolution, transform the radar radiation source signal into a high-quality time-frequency diagram for subsequent signal recognition and other processing by using the signal decimation method, and can effectively reduce the computational complexity of time-frequency analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a flowchart of the time-frequency analysis method of the radar radiation source signal based on signal decimation according to an embodiment of the present invention;

[0035] Figure 2a The time-frequency diagram obtained by performing STFT on an LFM signal according to an embodiment of the present invention;

[0036] Figure 2b is Figure 2a The schematic diagram of the power spectrum of the corresponding LFM signal;

[0037] Figure 2c is Figure 2a The schematic diagram of the smoothed power spectrum of the corresponding LFM signal;

[0038] Figure 2d is Figure 2a The schematic diagram of the power spectrum after down-conversion and low-pass filtering when the corresponding LFM signal is processed using the time-frequency analysis method of radar radiation source signals based on signal extraction;

[0039] Figure 2e is Figure 2a The schematic diagram of the power spectrum after signal extraction when the corresponding LFM signal is processed using the time-frequency analysis method of radar radiation source signals based on signal extraction;

[0040] Figure 2f is Figure 2a The time-frequency diagram obtained after processing the corresponding LFM signal using the time-frequency analysis method of radar radiation source signals based on signal extraction;

[0041] Figure 3 The time-frequency diagram obtained after processing another LFM signal according to an embodiment of the present invention using the time-frequency analysis method of radar radiation source signals based on signal extraction;

[0042] Figure 4 The time-frequency diagram obtained after processing yet another LFM signal according to an embodiment of the present invention using the time-frequency analysis method of radar radiation source signals based on signal extraction;

[0043] Figure 5 The time-frequency diagram obtained after processing an NLFM signal according to an embodiment of the present invention using the time-frequency analysis method of radar radiation source signals based on signal extraction;

[0044] Figure 6 The time-frequency diagram obtained after processing another NLFM signal according to an embodiment of the present invention using the time-frequency analysis method of radar radiation source signals based on signal extraction. Detailed implementation manners

[0045] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and the corresponding drawings. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] The following will detail the technical solutions provided by the embodiments of the present invention in conjunction with the drawings.

[0047] Refer to Figure 1 , an embodiment of the present invention provides a time-frequency analysis method for radar emitter signals based on signal extraction. The method includes the following steps:

[0048] S1. Perform spectrum analysis on the radar emitter signal to determine the frequency distribution range of the radar emitter signal;

[0049] S2. Perform digital down-conversion on the radar emitter signal to transform the center frequency of the radar emitter signal to 0;

[0050] S3. Perform low-pass filtering on the radar emitter signal to retain the effective frequency components of the radar emitter signal;

[0051] S4. Based on the radar emitter signal after low-pass filtering, extract the sampling sequence of the radar emitter signal by extracting one point at every other preset interval number of points;

[0052] S5. Perform time-frequency analysis on the extracted sampling sequence to obtain the time-frequency image of the radar emitter signal.

[0053] The time-frequency analysis method for radar emitter signals based on signal extraction provided by an embodiment of the present invention can reduce the signal sampling frequency, improve the frequency resolution, transform the radar emitter signal into a high-quality time-frequency diagram for subsequent signal recognition and other processing by using the signal extraction method, and can effectively reduce the computational amount of time-frequency analysis, and can perform time-frequency analysis adaptively according to the time width and bandwidth of the signal.

[0054] The following will specifically explain the steps and principles of the time-frequency analysis method for radar emitter signals based on signal extraction provided by an embodiment of the present invention.

[0055] Step S1. Perform spectrum analysis on the radar emitter signal to determine the frequency distribution range of the radar emitter signal.

[0056] To determine the frequency range of a radar emitter signal, it is necessary to first obtain the power spectrum of the signal. In existing radar emitter signal acquisition devices, the signal is generally sampled in two channels (equivalent to twice the sampling frequency) and can be transformed into a digital complex signal for convenient processing.

[0057] Considering that the number of sampling points of the radar emitter signal is usually large, in one embodiment of the present invention, the frequency distribution range of the radar emitter signal is determined by performing spectrum analysis on the radar emitter signal, including the following steps:

[0058] S11, segment the radar emitter signal with a preset length, calculate the power spectrum of each segment of the signal using the fast Fourier transform (FFT), add the power spectra of each segment of the signal and calculate the average value to determine the power spectrum corresponding to the radar emitter signal;

[0059] S12, perform smoothing processing on the power spectrum of the radar emitter signal;

[0060] S13, calculate the frequency distribution range of the radar emitter signal according to the smoothed power spectrum.

[0061] Due to the influence of noise and modulation type, the frequency corresponding to the spectral peak generally does not equal the center frequency. Therefore, after determining the power spectrum corresponding to the radar emitter signal, smoothing processing is performed on the power spectrum.

[0062] Further, set the sampling frequency of the radar emitter signal as f s , set the number of points of the FFT as N f , after smoothing processing, the maximum amplitude of the power spectrum P(i) is P(i0), search for the spectral lines within the 3dB bandwidth, that is, the amplitude of the power spectrum is greater than 0.5P(i0), and calculate the normalized cut-off frequencies within the bandwidth and Then, the frequency distribution range of the radar emitter signal can be calculated and determined using the following formula;

[0063]

[0064]

[0065] where B represents the normalized frequency width of the signal, represents the normalized frequency center of the signal, i represents an integer from 1 to N in the digital frequency domain f of the radar emitter signal, and the frequency distribution range of the radar emitter signal is

[0066] Step S2, perform digital down-conversion on the radar emitter signal to transform the center frequency of the radar emitter signal to 0.

[0067] Specifically, based on the above settings, multiply the radar emitter signal by to perform digital down-conversion so that the normalized value of the center frequency of the signal after down-conversion is 0, thereby adjusting the effective frequency range of the signal to -0.5B to 0.5B.

[0068] Step S3: Perform low-pass filtering on the radar emitter signal to retain the effective frequency components of the radar emitter signal.

[0069] To ensure that no spectral aliasing occurs during signal decimation and to eliminate out-of-band noise, anti-aliasing low-pass filtering needs to be performed on the signal.

[0070] Based on the above settings, the cut-off frequency during low-pass filtering can be set to 0.5B.

[0071] Furthermore, considering the broadening of the spectral lines of radar emitter signals such as non-linear frequency modulation, in order to retain signal energy to a greater extent, a reserved frequency width Δ is set, the cut-off frequency of the low-pass filtering is increased to 0.5B + Δ, and the bandwidth of the complex signal retained is B + 2Δ.

[0072] Step S4: Based on the radar emitter signal after low-pass filtering, decimate the radar emitter signal sampling sequence by extracting one point at every other preset interval number of points.

[0073] Specifically, based on the radar emitter signal after low-pass filtering, decimate the radar emitter signal sampling sequence by extracting one point at every other preset interval number of points D. Among them, the value of the preset interval number of points D is controlled below f s / B′, where f s represents the sampling frequency of the radar emitter signal, B′ represents the bandwidth of the radar emitter signal after low-pass filtering, and based on the above settings, B′ = B + 2Δ.

[0074] After decimation in the above manner, a new sampling sequence is obtained. The sampling frequency of the new sampling sequence is f s / D. When performing the FFT of the same length, the frequency resolution of the new sampling sequence is D times higher than that of the original sampling sequence.

[0075] Furthermore, to prevent the number of points after decimation from being too small and affecting the time-frequency effect during signal decimation, in the time-frequency analysis method provided by an embodiment of the present invention, step S4 may further include:

[0076] When decimating the radar emitter signal sampling sequence, determine the minimum number of decimation points that do not affect the time-frequency effect, and calculate the corresponding preset interval number of points according to the minimum number of decimation points;

[0077] Determine whether the calculated preset number of interval points does not exceed 1. If so, use the original radiation source signal sampling sequence as the sampled sequence obtained by decimation, that is, no decimation is performed. If not, select an integer between 1 and the calculated preset number of interval points as the actual preset number of interval points for decimation.

[0078] Among them, if the calculated preset number of interval points is greater than f s / B′, then select an integer between 1 and f s / B′ as the actual preset number of interval points for decimation.

[0079] Step S5: Perform time-frequency analysis on the sampled sequence obtained by decimation to obtain the time-frequency image of the radar radiation source signal.

[0080] In one embodiment of the present invention, short-time Fourier transform (STFT) is used to perform time-frequency analysis on the sampled sequence obtained by decimation to obtain the time-frequency image of the radar radiation source signal.

[0081] Specifically, the short-time Fourier transform of the sampled sequence is expressed as:

[0082]

[0083] Among them, STFT x (n,k) represents the short-time Fourier transform of the sampled sequence x(n), w(m) represents the window function, M represents the length of the window, and k represents an integer from 1 to M in the digital frequency domain.

[0084] STFT obtains the local frequency information of the signal by adding a sliding window in the time domain. The time resolution and frequency resolution of STFT are affected by the value of M and the window type. Appropriate window functions and window lengths can be set according to actual needs.

[0085] Furthermore, in order to obtain the time resolution corresponding to the frequency resolution, the time resolution unit can be set to 2 to 4 times that of the frequency resolution unit. The longer the decimated data, the larger the sliding step of the FFT is adaptively increased to ensure the correspondence between the time resolution unit and the frequency resolution unit.

[0086] Optionally, in one embodiment of the present invention, linear time-frequency analysis methods such as wavelet transform and time-frequency atoms, or Cohen-class nonlinear time-frequency analysis methods such as Wigner-Ville distribution and Choi-Williams distribution can also be used to perform time-frequency analysis on the sampled sequence obtained by decimation to obtain the time-frequency image of the radar radiation source signal.

[0087] The beneficial effects of the time-frequency analysis method of radar radiation source signals based on signal decimation provided by one embodiment of the present invention are described below with specific examples.

[0088] Taking the experiment with a simulation signal as an example, set the sampling frequency f of the signal s to be 400 MHz, the bandwidth B of the signal to be 5 MHz, the time width T of the signal to be 100 μs, and the number of sampling points N = T / f s to be 40,000 points. If the number of points N for each FFT f is set to 512 points, then the frequency resolution Δf of the signal = f s / N f is only 0.78 MHz, and the number of analysis points ΔN within the entire signal frequency band = N f B / f s is approximately 6 points. At this time, directly calculating the STFT has very low efficiency, and the resulting effective frequency change range is very small. If the number of points N of the FFT is simply increased f to increase the number of analysis points ΔN, it will greatly increase the computational amount and storage space.

[0089] See Figure 2a , Figure 2a which shows the time-frequency diagram obtained after performing STFT on a linear frequency modulation (LFM) signal. Among them, for display purposes, the time-frequency diagram is gray-scaled, and the higher the gray value, the higher the energy. The starting frequency of this LFM signal is 40 MHz, the signal-to-noise ratio (SNR) is 0 dB, and the remaining parameters are the same as the signal parameters set above. Based on the simulation parameters set above, the time-frequency matrix obtained by directly performing STFT on this LFM signal is 512×1600, that is, 1600 times of 512-point FFTs are performed.

[0090] At the same time, based on the simulation parameters set above, use the time-frequency analysis method for radar radiation source signals based on signal extraction provided by an embodiment of the present invention to process this LFM signal, and obtain the power spectrum, smoothed power spectrum, power spectrum after down-conversion and low-pass filtering, power spectrum after extraction, and the final time-frequency diagram of the LFM signal as shown in Figures 2b - 2f . Among them, the final extraction multiple is 38, and the time-frequency matrix is 512×1053.

[0091] By comparing Figure 2a and Figure 2f it can be seen that compared with directly performing STFT on the signal, using the time-frequency analysis method for radar radiation source signals based on signal extraction provided by an embodiment of the present invention to process the signal has greatly improved performance, can clearly reflect the change characteristics of the signal, can significantly improve the frequency resolution of the time-frequency transformation, and reduce the computational amount and storage space.

[0092] Furthermore, in order to verify the effectiveness of the time-frequency analysis method for radar radiation source signals based on signal extraction provided by an embodiment of the present invention, simulation experiments are carried out on signals with different SNRs, different types, and different parameters. SeeFigures 3 - 6 , Figures 3 - 6 respectively show the time-frequency diagrams obtained after processing four different signals using the time-frequency analysis method of radar emitter signals based on signal extraction. Among them, Figure 3 For the corresponding LFM signal, the sampling frequency is 400 MHz, the starting frequency is 40 MHz, the bandwidth is 40 MHz, the pulse width is 10 μs, the SNR is 0 dB, the final extraction multiple is 4, and the time-frequency matrix is 256×1000. Figure 4 For the corresponding LFM signal, the sampling frequency is 400 MHz, the starting frequency is 40 MHz, the bandwidth is 5 MHz, the pulse width is 200 μs, the SNR is -5 dB, the final extraction multiple is 39, and the time-frequency matrix is 512×1026. Figure 5 The corresponding signal is a non-linear frequency modulation (NLFM) signal based on tangent frequency modulation. The SNR of this NLFM signal is 0 dB, the final extraction multiple is 7, the time-frequency matrix is 256×572, and the rest of the parameters are the same as those Figure 3 set for the corresponding LFM signal. Figure 6 The corresponding signal is a non-linear frequency modulation (NLFM) signal based on tangent frequency modulation. The SNR of this NLFM signal is -5 dB, the final extraction multiple is 61, the time-frequency matrix is 512×1312, and the rest of the parameters are the same as those Figure 4 set for the corresponding LFM signal.

[0093] According to Figures 3 - 6 it can be seen that the time-frequency analysis method of radar emitter signals based on signal extraction provided by an embodiment of the present invention has strong adaptability and good estimation performance for different signals under different SNRs.

[0094] Among them, in the above simulation experiment, the time-frequency matrix can be controlled within the range of about 512×1024, and relevant parameters can be flexibly configured according to actual needs to generate time-frequency diagrams of the same size for subsequent processing such as signal recognition.

[0095] It should be noted that in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. In addition, in this article, "front", "rear", "left", "right", "up" and "down" are all referenced based on the placement state shown in the drawings.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A time-frequency analysis method for radar emitter signals based on signal extraction, characterized in that, Including: Performing spectrum analysis on the radar radiation source signal to determine the frequency distribution range of the radar radiation source signal; Performing digital down-conversion on the radar radiation source signal to transform the center frequency of the radar radiation source signal to 0; Performing low-pass filtering on the radar radiation source signal to retain the effective frequency components of the radar radiation source signal; Based on the radar radiation source signal after low-pass filtering, decimating the sampling sequence of the radar radiation source signal by decimating one point every preset decimation interval points; Performing time-frequency analysis on the decimated sampling sequence to obtain the time-frequency image of the radar radiation source signal; The performing spectrum analysis on the radar radiation source signal to determine the frequency distribution range of the radar radiation source signal includes: Segmenting the radar radiation source signal with a preset length, calculating the power spectrum of each segment of the signal using fast Fourier transform, adding the power spectra of each segment of the signal and calculating the average value to determine the power spectrum corresponding to the radar radiation source signal; Smoothing the power spectrum of the radar radiation source signal; Calculating the frequency distribution range of the radar radiation source signal according to the smoothed power spectrum; Calculating and determining the frequency distribution range of the radar radiation source signal using the following formula; ； ； Among them, represents the normalized frequency width of the signal, and represents the normalized cut-off frequency within the signal bandwidth, represents the normalized frequency center of the signal, represents the power spectrum after smoothing, represents the number of points of the fast Fourier transform, represents in the digital frequency domain an integer; The value of the preset number of interval points is within as follows, where represents the radar radiation source signal sampling frequency, represents the bandwidth of the radar radiation source signal after low-pass filtering processing, , represents the reserved frequency width; The method further includes: When decimating the sampling sequence of the radar radiation source signal, determining the minimum decimation points that do not affect the time-frequency effect, and calculating the corresponding preset decimation interval points according to the minimum decimation points; Determining whether the calculated preset decimation interval points do not exceed 1. If so, using the original radiation source signal sampling sequence as the decimated sampling sequence. If not, selecting an integer between 1 and the calculated preset decimation interval points as the actual preset decimation interval points for decimation.

2. The time-frequency analysis method for radar emitter signals based on signal extraction according to claim 1, characterized in that Multiply the radar emitter signal by Perform digital down-conversion.

3. The time-frequency analysis method of radar emitter signals based on signal extraction according to claim 2, characterized in that When performing low-pass filtering on radar emitter signals, set the cut-off frequency to .

4. The time-frequency analysis method of radar emitter signals based on signal extraction according to any one of claims 1-3, characterized in that Performing time-frequency analysis on the decimated sampling sequence using short-time Fourier transform.

5. The time-frequency analysis method for radar emitter signals based on signal extraction according to claim 4, characterized in that The short-time Fourier transform of the sampling sequence is expressed as: ； Among them, represents the short-time Fourier transform of the sampling sequence, represents the window function, represents the length of the window, represents an integer in the digital frequency domain among them.

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