A method and system for identifying in-pulse modulation of radar signals

Abstract

The present invention discloses a method and system for intra-pulse modulation recognition of radar signals, belonging to the technical field of electronic countermeasures, including: obtaining the 3dB bandwidth of the radar signal; in response to detecting that the 3dB bandwidth is greater than a preset bandwidth threshold, inputting the radar signal into a pre-established frequency modulation signal recognition model to output the type of frequency modulation signal, and the type of frequency modulation signal is the recognition result of intra-pulse modulation; in response to detecting that the 3dB bandwidth is not greater than the preset bandwidth threshold, inputting the radar signal into a pre-established phase modulation signal recognition model to output the type of phase modulation signal, and the type of phase modulation signal is the recognition result of intra-pulse modulation; a systematic intra-pulse modulation recognition method is provided for common LPI radar signals, improving the recognition accuracy.

Description

Technical Field

[0001] The present invention relates to a method and system for identifying intra-pulse modulation of radar signals, belonging to the technical field of electronic countermeasures. Background Art

[0002] At present, radars with wide bandwidth and complex waveform systems have been widely used in the military field. The traditional five-parameter identification method based on signal carrier frequency, pulse width, direction of arrival, arrival angle, and signal amplitude has become difficult to effectively identify them. In order to more effectively detect radar signals, identifying the intra-pulse characteristics of radar signals has become an urgent and severe task. The main purpose of intra-pulse characteristic analysis is to realize the automatic distinction and identification of signals with different intra-pulse modulation types, and detect the corresponding intra-pulse modulation parameters (starting frequency, ending frequency, frequency modulation slope, number of code elements, code element width, code element sequence, etc.). Through intra-pulse modulation characteristic analysis, it is not only beneficial to more comprehensively describe radar signals, improve the accuracy of signal sorting and identification, but also can understand the uses and performances of the other party's radars, and can also provide more accurate enemy radar parameters to our jammers, thereby improving the effect of jamming against the enemy. For electronic warfare applications, it has become an inevitable trend to require radar reconnaissance equipment to have real-time intra-pulse analysis capabilities.

[0003] The main signal forms using intra-pulse frequency modulation and phase modulation are pulse compression signals and large time-bandwidth signals. Common LPI radar signals include linear frequency modulation (LFM), non-linear frequency modulation (NLFM), binary phase coding (BPSK), quadrature phase coding (QPSK), frequency coding (FSK), etc. In actual systems, people have studied the intra-pulse modulation characteristics of different radar radiation source signals and proposed various methods for identifying intra-pulse modulation characteristics. However, these methods are only applicable to a few two or three signals and do not fully consider the problems of systematic and real-time identification. How to ensure the real-time performance and the reliability of modulation characteristic identification in complex environments is a very difficult task. Therefore, there is an urgent need for a modulation characteristic identification method with good real-time performance, high reliability, and high systematicness. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for identifying intra-pulse modulation of radar signals, which provides a systematic method for identifying intra-pulse modulation of common LPI radar signals and improves the identification accuracy.

[0005] To achieve the above purpose, the present invention is implemented by adopting the following technical solutions:

[0006] In the first aspect, the present invention provides a method for identifying intra-pulse modulation of radar signals, including:

[0007] Obtaining the 3dB bandwidth of the radar signal;

[0008] In response to detecting that the 3dB bandwidth is greater than a preset bandwidth threshold, input the radar signal into a pre-established frequency modulation signal recognition model to output the type of frequency modulation signal, and the type of frequency modulation signal is the in-pulse modulation recognition result;

[0009] In response to detecting that the 3dB bandwidth is not greater than the preset bandwidth threshold, input the radar signal into a pre-established phase modulation signal recognition model to output the type of phase modulation signal, and the type of phase modulation signal is the in-pulse modulation recognition result.

[0010] Combined with the first aspect, further, the 3dB bandwidth of the radar signal is obtained by the following method:

[0011] The signal bandwidth obtained by subtracting the minimum frequency point from the maximum frequency point exceeding the half-power point is the 3dB bandwidth.

[0012] Combined with the first aspect, further, input the radar signal into a pre-established frequency modulation signal recognition model to output the type of frequency modulation signal:

[0013] Obtain the effective bandwidth of the radar signal, and divide the 3dB bandwidth by the effective bandwidth to obtain the bandwidth ratio;

[0014] In response to detecting that the bandwidth ratio is greater than the preset ratio threshold, output the type of frequency modulation signal as FSK signal;

[0015] In response to detecting that the bandwidth ratio is not greater than the preset ratio threshold, perform short-time Fourier transform on the radar signal, search for the maximum value in the short-time Fourier transform to obtain the time-frequency ridge line, calculate the frequency change rate according to the time-frequency ridge line, if the frequency change rate is less than the preset change rate threshold, output the type of frequency modulation signal as LFM signal, otherwise output the type of frequency modulation signal as NLFM signal.

[0016] Combined with the first aspect, further, the effective bandwidth is the signal bandwidth exceeding the half-power point within one beam of the radar signal.

[0017] Combined with the first aspect, further, the short-time Fourier transform calculation formula is as follows:

[0018]

[0019] where s(τ) is the input radar signal, h * (τ - t) is the conjugate of the analysis window function.

[0020] Combined with the first aspect, further, calculate the frequency change rate according to the time-frequency ridge line:

[0021] Perform a quadratic polynomial curve fitting on the time-frequency ridge line. Use the starting time, middle time, and ending time after linear interpolation of the time-frequency ridge line to divide the entire radar signal into two segments. The segment from the starting time to the middle time is the first segment, and the segment from the middle time to the ending time is the second segment. Calculate the frequency change rates of the first segment and the second segment respectively and take the difference to obtain the final frequency change rate.

[0022] Combined with the first aspect, further, input the radar signal into a pre-established phase modulation signal recognition model and output the phase modulation signal type:

[0023] Obtain the number of spectral peaks after Fourier transform of the radar signal, and perform a discrete Haar wavelet transform on the radar signal to obtain the discrete Haar wavelet transform peak value;

[0024] In response to detecting that the number of spectral peaks is less than or equal to 3 and the discrete Haar wavelet transform peak value is less than a preset peak threshold, output the phase modulation signal type as a single-frequency signal;

[0025] In response to detecting that either the condition that the number of spectral peaks is less than or equal to 3 or the discrete Haar wavelet transform peak value is less than the preset peak threshold is not satisfied, square the radar signal and then perform a Fourier transform to obtain the number of spectral peaks after squaring. If the number of spectral peaks after squaring is less than or equal to 2, output the phase modulation signal type as a BPSK signal. Otherwise, raise the radar signal to the fourth power and then perform a Fourier transform to obtain the number of spectral peaks after the fourth power. If the number of spectral peaks after the fourth power is less than or equal to 2, output the phase modulation signal type as a QPSK signal. Otherwise, output the phase modulation signal type as other signals.

[0026] Combined with the first aspect, further, the calculation formula of the discrete Haar wavelet transform is as follows:

[0027]

[0028] where α is the discrete Haar wavelet transform scale, n is the data length, and s(k) is the original time-domain data.

[0029] Combined with the first aspect, further, the calculation formula of the preset peak threshold is: α is the discrete Haar wavelet transform scale.

[0030] In the second aspect, the present invention also provides a radar signal intra-pulse modulation recognition system, including:

[0031] Bandwidth acquisition module: used to acquire the 3dB bandwidth of the radar signal;

[0032] Frequency modulation signal recognition module: used to, in response to detecting that the 3dB bandwidth is greater than a preset bandwidth threshold, input the radar signal into a pre-established frequency modulation signal recognition model and output the frequency modulation signal type, and the frequency modulation signal type is the intra-pulse modulation recognition result;

[0033] Phase modulation signal recognition module: configured to, in response to detecting that the 3dB bandwidth is not greater than a preset bandwidth threshold, input the radar signal into a pre-established phase modulation signal recognition model, and output the phase modulation signal type, where the phase modulation signal type is the in-pulse modulation recognition result.

[0034] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0035] A method and system for in-pulse modulation recognition of radar signals provided by the present invention, through rough recognition of the 3dB bandwidth of the radar signal, determine whether the radar signal is a frequency modulation signal or a phase modulation signal; if the radar signal is a frequency modulation signal, input the radar signal into a pre-established frequency modulation signal recognition model for further modulation feature recognition to accurately determine which type of frequency modulation signal the radar signal belongs to; if the radar signal is a phase modulation signal, input the radar signal into a pre-established phase modulation signal recognition model for further modulation feature recognition to accurately determine which type of phase modulation signal the radar signal belongs to; in summary, a method and system for in-pulse modulation recognition of radar signals provided by the present invention provide a systematic method for in-pulse modulation recognition of common LPI radar signals, improving the recognition accuracy.

[0036] A method and system for in-pulse modulation recognition of radar signals provided by the present invention, through short-time Fourier transform, search for the maximum value in the short-time Fourier transform to obtain the time-frequency ridge line, calculate the frequency change rate according to the time-frequency ridge line, and distinguish and recognize LFM signals and NLFM signals according to the frequency change rate, improving the recognition accuracy.

[0037] A method and system for in-pulse modulation recognition of radar signals provided by the present invention, according to the number of spectral peaks of the Fourier transform and the discrete Haar wavelet transform, perform reliable recognition on conventional point-frequency signals and other phase modulation signals, improving the recognition accuracy. Description of the Drawings

[0038] Figure 1 is a flowchart of a method for in-pulse modulation recognition of radar signals provided by an embodiment of the present invention. Detailed Embodiments

[0039] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be used to limit the protection scope of the present invention.

[0040] Embodiment 1

[0041] As Figure 1As shown in the figure, an embodiment of the present invention provides a method for identifying in-pulse modulation of radar signals. First, the radar signal is subjected to Fourier transform (FFT) to obtain the 3dB bandwidth of the radar signal. After the radar signal is processed by FFT, the signal spectrum is mainly a single spectral line.

[0042] Perform an N-point Fourier transform X(k) on the input data (radar signal) x(n) of length L, where is the ceiling function.

[0043] Perform M-point data smoothing on the X(k) data, where the number of points for smoothing is 40. Estimate the 3dB bandwidth and the effective bandwidth based on the X(k) data. The 3dB bandwidth is defined as the signal bandwidth obtained by subtracting the minimum frequency point from the maximum frequency point exceeding the half-power point, and the effective bandwidth is defined as the signal bandwidth within a beam of the radar signal that exceeds the half-power point.

[0044] Perform an initial identification (coarse identification) on the radar signal. Compare the 3dB bandwidth with the preset bandwidth threshold T 3dB where T 3dB is 10M. If the 3dB bandwidth is greater than the preset bandwidth threshold, the radar signal is a frequency modulation signal; otherwise, the radar signal is a phase modulation signal.

[0045] If the result of the initial identification of the radar signal is a frequency modulation signal, perform frequency modulation signal identification (fine identification) on the radar signal. That is, in response to detecting that the 3dB bandwidth is greater than the preset bandwidth threshold, input the radar signal into a pre-established frequency modulation signal identification model to output the type of frequency modulation signal, and the type of frequency modulation signal is the result of in-pulse modulation identification.

[0046] Obtain the effective bandwidth of the radar signal, divide the 3dB bandwidth by the effective bandwidth to obtain a bandwidth ratio, and compare the bandwidth ratio with the preset ratio threshold T r where T r is 0.3. If the bandwidth ratio is greater than the preset ratio threshold, output the type of frequency modulation signal of the radar signal as an FSK signal; if the bandwidth ratio is less than or equal to the preset ratio threshold, perform a short-time Fourier transform on the radar signal, search for the maximum value in the short-time Fourier transform to obtain the time-frequency ridge line, perform a fine division of the frequency modulation signal by extracting the characteristics of the time-frequency ridge line, calculate the frequency change rate based on the time-frequency ridge line, and if the frequency change rate is less than the preset change rate threshold T f where T f is 0.15; then the radar signal is an LFM signal, otherwise the radar signal is an NLFM signal.

[0047] The formula for the short-time Fourier transform is as follows:

[0048]

[0049] where s(τ) is the input radar signal, and h * (τ - t) is the conjugate of the analysis window function.

[0050] The calculation method of the frequency change rate is as follows: perform a quadratic polynomial curve fitting on the time-frequency ridge line. Use the three points of the starting moment, the middle moment, and the ending moment after linear interpolation of the time-frequency ridge line to divide the entire radar signal into two segments. The segment from the starting moment to the middle moment is the first segment, and the segment from the middle moment to the ending moment is the second segment. Calculate the frequency change rates of the first segment and the second segment respectively and take the difference to obtain the final frequency change rate.

[0051] If the result of the initial recognition of the radar signal is a phase modulation signal, perform a phase modulation signal recognition (fine recognition) on the radar signal, that is, in response to detecting that the 3dB bandwidth is not greater than the preset bandwidth threshold, input the radar signal into a pre-established phase modulation signal recognition model, and output the phase modulation signal type, where the phase modulation signal type is the in-pulse modulation recognition result.

[0052] Count the number of spectral peaks m of X(k) (i.e., the number of spectral peaks after the Fourier transform of the radar signal), and perform a discrete Haar wavelet transform on the radar signal to obtain the discrete Haar wavelet transform peak value; if the number of spectral peaks is less than or equal to 3 and the discrete Haar wavelet transform peak value is less than the preset peak threshold T h , then output the phase modulation signal type as a single-frequency signal; if either the condition that the number of spectral peaks is less than or equal to 3 or the discrete Haar wavelet transform peak value is less than the preset peak threshold is not satisfied, square the radar signal and then perform a Fourier transform (FFT) to obtain the number of spectral peaks m_psk after squaring. If the number of spectral peaks after squaring is less than or equal to 2, then output the phase modulation signal type as a BPSK signal. If the number of spectral peaks after squaring is greater than 2, raise the radar signal to the fourth power and then perform a Fourier transform to obtain the number of spectral peaks m_psk after the fourth power. If the number of spectral peaks after the fourth power is less than or equal to 2, then output the phase modulation signal type as a QPSK signal, otherwise output the phase modulation signal type as other signals.

[0053] The calculation formula of the discrete Haar wavelet transform is as follows:

[0054]

[0055] where α is the discrete Haar wavelet transform scale, n is the data length, and s(k) is the original time-domain data.

[0056] The calculation method of the Haar wavelet transform scale α is α = f s / B v , f s is the sampling rate, and B v is the effective bandwidth.

[0057] The preset peak threshold T hThe calculation method is as follows

[0058] After the radar signal is squared, there are only 1 to 2 spectral lines at the spectral peak within the 3dB bandwidth, and we determine it as a binary phase-coded signal (BPSK); after the radar signal is processed to the fourth power, there are only 1 to 2 spectral lines at the spectral peak within the 3dB bandwidth, and we determine it as a quaternary phase-coded signal (QPSK).

[0059] A method for identifying the intra-pulse modulation of radar signals provided by an embodiment of the present invention identifies several typical radar radiation source signals: conventional radar signals (CW), linear frequency modulation signals (LFM), non-linear frequency modulation signals (NLFM), binary phase-coded signals (BPSK), quaternary phase-coded signals (QPSK), frequency-coded signals (FSK), where the frequency-coded signal (FSK) supports a maximum of 16 frequency-point FSK signals.

[0060] Embodiment 2

[0061] An embodiment of the present invention provides a system for identifying the intra-pulse modulation of radar signals, including:

[0062] Bandwidth acquisition module: used to acquire the 3dB bandwidth of the radar signal;

[0063] Frequency modulation signal identification module: used to input the radar signal into a pre-established frequency modulation signal identification model in response to detecting that the 3dB bandwidth is greater than a preset bandwidth threshold, and output the type of frequency modulation signal, where the type of frequency modulation signal is the result of intra-pulse modulation identification;

[0064] Phase modulation signal identification module: used to input the radar signal into a pre-established phase modulation signal identification model in response to detecting that the 3dB bandwidth is not greater than a preset bandwidth threshold, and output the type of phase modulation signal, where the type of phase modulation signal is the result of intra-pulse modulation identification.

[0065] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0066] This application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in one or more flows and / or blocks Figure 1 one or more flows and / or blocks Figure 1 or means for implementing the functions specified in one or more blocks

[0067] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in one or more flows and / or blocks Figure 1 one or more flows and / or blocks Figure 1 or means for implementing the functions specified in one or more blocks

[0068] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more flows and / or blocks Figure 1 one or more flows and / or blocks Figure 1 or means for implementing the functions specified in one or more blocks

[0069] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention

Claims

1. A method for identifying in-pulse modulation of radar signals, characterized in that, Including: Obtain the 3dB bandwidth of the radar signal; In response to detecting that the 3dB bandwidth is greater than 10M, input the radar signal into a pre-established frequency modulation signal recognition model, and output the frequency modulation signal type, where the frequency modulation signal type is the in-pulse modulation recognition result; In response to detecting that the 3dB bandwidth is not greater than 10M, input the radar signal into a pre-established phase modulation signal recognition model, and output the phase modulation signal type, where the phase modulation signal type is the in-pulse modulation recognition result; The 3dB bandwidth of the radar signal is obtained by the following method: The signal bandwidth obtained by subtracting the minimum frequency point from the maximum frequency point exceeding the half-power point is the 3dB bandwidth; Input the radar signal into a pre-established frequency modulation signal recognition model and output the frequency modulation signal type: Obtain the effective bandwidth of the radar signal, and divide the 3dB bandwidth by the effective bandwidth to obtain the bandwidth ratio; In response to detecting that the bandwidth ratio is greater than 0.3, output the frequency modulation signal type as FSK signal; In response to detecting that the bandwidth ratio is not greater than 0.3, perform short-time Fourier transform on the radar signal, search for the maximum value in the short-time Fourier transform to obtain the time-frequency ridge line, calculate the frequency change rate according to the time-frequency ridge line. If the frequency change rate is less than 0.15, output the frequency modulation signal type as LFM signal, otherwise output the frequency modulation signal type as NLFM signal; The effective bandwidth is the signal bandwidth of the radar signal within one beam exceeding the half-power point; Calculate the frequency change rate according to the time-frequency ridge line: Perform quadratic polynomial curve fitting on the time-frequency ridge line. Use the starting moment, middle moment, and ending moment after linear interpolation of the time-frequency ridge line to divide the entire radar signal into two segments. The segment from the starting moment to the middle moment is the first segment, and the segment from the middle moment to the ending moment is the second segment. Calculate the frequency change rates of the first segment and the second segment respectively and take the difference to obtain the final frequency change rate; Input the radar signal into a pre-established phase modulation signal recognition model and output the phase modulation signal type: Obtain the number of spectral peaks after Fourier transform of the radar signal, and perform discrete Haar wavelet transform on the radar signal to obtain the discrete Haar wavelet transform peak value; In response to detecting that the number of spectral peaks is less than or equal to 3 and the discrete Haar wavelet transform peak value is less than the preset peak threshold, output the phase modulation signal type as a point frequency signal; In response to detecting that either the condition that the number of spectral peaks is less than or equal to 3 or the discrete Haar wavelet transform peak value is less than the preset peak threshold is not satisfied, square the radar signal and then perform Fourier transform to obtain the number of spectral peaks after squaring. If the number of spectral peaks after squaring is less than or equal to 2, output the phase modulation signal type as BPSK signal. Otherwise, raise the radar signal to the fourth power and then perform Fourier transform to obtain the number of spectral peaks after the fourth power. If the number of spectral peaks after the fourth power is less than or equal to 2, output the phase modulation signal type as QPSK signal, otherwise output the phase modulation signal type as other signals; The calculation formula for the preset peak threshold is as follows: α is the discrete Haar wavelet transform scale.

2. The method for identifying in-pulse modulation of radar signals according to claim 1, wherein The calculation formula of the short-time Fourier transform is as follows: where s(τ) is the input radar signal, and h * (τ - t) is the conjugate of the analysis window function.

3. A method for identifying in-pulse modulation of radar signals according to claim 1, characterized in that The calculation formula of the discrete Haar wavelet transform is as follows: Where α is the discrete Haar wavelet transform scale, n is the data length, and s(k) is the original time-domain data.

4. A radar signal intra-pulse modulation recognition system, characterized in that For implementing the method described in any one of claims 1 to 3, including: Bandwidth acquisition module: used to obtain the 3dB bandwidth of the radar signal; Frequency modulation signal recognition module: It is used to input the radar signal into a pre-established frequency modulation signal recognition model in response to detecting that the 3dB bandwidth is greater than a preset bandwidth threshold, and output the frequency modulation signal type, where the frequency modulation signal type is the in-pulse modulation recognition result; Phase modulation signal recognition module: It is used to input the radar signal into a pre-established phase modulation signal recognition model in response to detecting that the 3dB bandwidth is not greater than a preset bandwidth threshold, and output the phase modulation signal type, where the phase modulation signal type is the in-pulse modulation recognition result.

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