A radar signal modulation type classification method based on pulse compression characteristics

Abstract

The present invention discloses a radar signal modulation type classification method based on pulse compression characteristics, which uses the pulse compression characteristics of radar signals to calculate the main lobe width and pulse width ratio of the signal, the square of the signal, and the fourth power of the signal after pulse compression to identify simple signals, two-phase coded signals, and four-phase coded signals; different delayed autocorrelation coefficients are used to calculate the modulation slope of the remaining classified signals, and linear frequency modulation signals and nonlinear frequency modulation signals are distinguished according to the calculated modulation slope results. The present invention uses the pulse compression characteristics of radar signals, and through convolution operations and other simple operations, it can distinguish simple signals, two-phase coded signals, four-phase coded signals, linear frequency modulation, and nonlinear frequency modulation signals; compared with other algorithms, the amount of calculation is small, and it has the advantages of fast recognition speed, simple process, and low signal-to-noise ratio requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal pulse analysis and recognition, and in particular relates to a radar signal modulation type classification method based on pulse compression characteristics. Background Art

[0002] The pulse modulation characteristics of radar signals are an important part of radar parameters. Common radar pulse modulation forms include simple, two-phase coding, four-phase coding, linear frequency modulation, nonlinear modulation and other modulation forms. Pulse compression technology is the most common signal processing technology for modern radars. It refers to the wide pulses modulated by radar transmission frequency or phase, and the wide pulses are converted into narrow pulse signals by autocorrelation when receiving. Through pulse compression technology, radar can transmit large pulse width signals while obtaining high distance resolution. Simple signals do not use pulse compression technology, so the main lobe width of their signals after autocorrelation is equal to the pulse width of the transmitted signal. The main lobe width of the modulated signal using pulse compression technology after autocorrelation is much smaller than the signal pulse width. Common radar pulse signal classification methods include instantaneous frequency measurement method, time-frequency analysis method, and bandwidth ratio-based method. The instantaneous frequency measurement method uses the instantaneous frequency characteristics of different radar signal pulse modulation characteristics to classify the radar signal pulse modulation characteristics. The instantaneous frequency measurement method is extremely sensitive to noise and is difficult to meet the needs of actual electronic reconnaissance systems. The bandwidth ratio-based method is to calculate the signal and the square of the signal and then calculate the signal bandwidth ratio after fast Fourier transformation to confirm the signal type. In practical applications, radar radiation source signals are subject to noise interference and channel fluctuations during propagation and reception, resulting in large changes in SNR and difficult to accurately measure the spectrum width of the signal. The time-frequency analysis method has a large amount of calculation, many calculation parameters, and poor application effect. Summary of the invention

[0003] The present invention aims to solve the problems raised in the background technology and proposes a radar signal modulation type classification method based on pulse compression characteristics. The method has the advantages of small calculation amount, fast recognition speed, simple process, convenient engineering implementation and low signal-to-noise ratio requirement.

[0004] In order to achieve the purpose of the present invention, the present invention discloses a radar signal modulation type classification method based on pulse compression characteristics, which uses the pulse compression characteristics of the radar signal to calculate the main lobe width and pulse width ratio of the signal, the square of the signal, and the fourth power of the signal after pulse compression to identify the simple signal, the two-phase coded signal and the four-phase coded signal; different delayed autocorrelation coefficients are used to calculate the modulation slope of the remaining signals for classification, and the linear frequency modulation signal and the nonlinear frequency modulation signal are distinguished according to the calculated modulation slope results.

[0005] Furthermore, the method specifically includes the following steps:

[0006] Step 1, perform autocorrelation operation on the radar IQ signal, solve its maximum value, and logarithmically normalize the autocorrelation result according to the maximum value;

[0007] Step 2, detect the 3dB main lobe width of the normalized result, calculate the ratio of the main lobe width to the original signal pulse width, if the ratio is close to 1, determine that the signal is a simple signal, otherwise it is a pulse compression signal;

[0008] Step 3, square the I and Q paths of the IQ signal respectively, repeat steps 1 and 2, and if the ratio is close to 1, it is determined to be a two-phase coded signal;

[0009] Step 4, perform a fourth-power operation on the I and Q paths of the IQ signal respectively, repeat steps 1 and 2, and if the ratio is close to 1, it is determined to be a four-phase coded signal;

[0010] Step 5: Use different delay correlation coefficients to perform delay autocorrelation operations on the remaining unclassified signals, calculate their modulation slopes respectively, and determine whether they are linear frequency modulation signals based on whether the modulation slopes are the same.

[0011] Furthermore, when the ratio of the main lobe width to the original signal pulse width is 1±0.1, the ratio is considered to be close to 1.

[0012] Furthermore, step 1 specifically includes the following steps:

[0013] Perform autocorrelation operation on the signal and normalize the result R according to the following formula: x (t):

[0014]

[0015] Where x(n) is the radar IQ sampling signal and N is the total sampling length.

[0016] Furthermore, in step 2, the normalized result R is calculated x (t) Ratio of 3dB width to original signal pulse width;

[0017] Furthermore, in step 3, when the ratio is close to 1, the signal is a simple signal. For the signal that does not meet the threshold, the real part re and the imaginary part im of x(n) are squared to obtain the y(n) signal according to the following formula:

[0018] y(n).re=(x(n).re) 2

[0019] y(n).im=(x(n).im) 2

[0020] Repeat steps 1 and 2 for y(n) and calculate the normalized result R of y(n) y(t) Ratio of 3dB width to original signal pulse width.

[0021] Furthermore, in step 4, when the ratio is close to 1, the signal is a two-phase coded signal, and the signal that does not meet the threshold is quadratically operated to obtain the z(n) signal:

[0022] z(n).re=(x(n).re) 4

[0023] z(n).im=(x(n).im) 4

[0024] Repeat steps 1 and 2 for z(n) to calculate the normalized result R of z(n) z (t) Ratio of 3dB width to original signal pulse width;

[0025] When the ratio is 1±0.1, the signal is a four-phase coded signal, and the signal that does not meet the threshold is other compressed signals.

[0026] Furthermore, in step 5, different delay coefficients a1 and a2 are selected, where 0.5 < a1 < 1 and 0 < a2 < 0.5, and delay autocorrelation operations are performed to calculate the modulation slopes k1 and k2 respectively;

[0027] When k1=k2, the signal is a linear frequency modulation signal; otherwise, it is a nonlinear frequency modulation signal.

[0028] In order to achieve the purpose of the present invention, the present invention also discloses a radar signal modulation type classification system based on pulse compression characteristics, comprising the following modules:

[0029] The autocorrelation logarithmic normalization module performs autocorrelation operation on the radar IQ signal, solves its maximum value, and logarithmically normalizes the autocorrelation result according to the maximum value;

[0030] The simple signal separation module detects the 3dB main lobe width of the normalized result and calculates the ratio of the main lobe width to the original signal pulse width. If the ratio is close to 1, the signal is determined to be a simple signal, otherwise it is a pulse compression signal.

[0031] The two-phase coded signal separation module performs square operations on the I and Q paths of the IQ signal respectively, repeats the steps adopted by the autocorrelation logarithm normalization module and the simple signal separation module, and if the ratio is close to 1, it is determined to be a two-phase coded signal;

[0032] The four-phase coded signal separation module performs a fourth-power operation on the I and Q paths of the IQ signal, respectively, and the steps adopted by the autocorrelation logarithm normalization module and the simple signal separation module. If the ratio is close to 1, it is determined to be a four-phase coded signal;

[0033] The linear frequency modulation signal and nonlinear frequency modulation signal separation module uses different delay correlation coefficients to perform delay autocorrelation operations on the remaining unclassified signals, calculates their modulation slopes respectively, and determines whether it is a linear frequency modulation signal based on whether the modulation slopes are the same.

[0034] In order to achieve the purpose of the present invention, the present invention also discloses an electronic device, including a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor is used to execute a radar signal modulation type classification method based on pulse compression characteristics.

[0035] Compared with the prior art, the significant progress of the present invention is that: 1) by utilizing the pulse compression characteristics of radar signals, through convolution operations and other simple operations, simple signals, two-phase coded signals, four-phase coded signals, linear frequency modulation and nonlinear frequency modulation signals can be distinguished; 2) compared with other algorithms, the amount of calculation is small, and it has the advantages of fast recognition speed, simple process and low signal-to-noise ratio requirements.

[0036] In order to more clearly illustrate the functional characteristics and structural parameters of the present invention, further description is given below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0038] Figure 1 It is a flow chart of a radar signal modulation type classification method based on pulse compression characteristics;

[0039] Figure 2 This is a schematic diagram for calculating the 3dB main lobe width. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] like Figure 1 , Figure 2As shown, a radar signal modulation type classification method based on pulse compression characteristics is provided. The pulse compression characteristics of the radar signal are used to calculate the main lobe width and pulse width ratio of the signal, the square of the signal, and the fourth power of the signal after pulse compression to identify the simple signal, the two-phase coded signal, and the four-phase coded signal; the modulation slope of the remaining signals is calculated using different delayed autocorrelation coefficients, and the linear frequency modulation signal and the nonlinear frequency modulation signal are distinguished according to the calculated modulation slope results. The specific implementation method includes the following steps:

[0042] Step 1, perform autocorrelation operation on the radar IQ signal, solve its maximum value, and logarithmically normalize the autocorrelation result according to the maximum value;

[0043] Step 2, detect the 3dB main lobe width of the normalized result, calculate the ratio of the main lobe width to the original signal pulse width, if the ratio is close to 1, determine that the signal is a simple signal, otherwise it is a pulse compression signal;

[0044] Step 3, square the I and Q paths of the IQ signal respectively, repeat steps 1 and 2, and if the ratio is close to 1, it is determined to be a two-phase coded signal;

[0045] Step 4, perform a fourth-power operation on the I and Q paths of the IQ signal respectively, repeat steps 1 and 2, and if the ratio is close to 1, it is determined to be a four-phase coded signal;

[0046] Step 5: Use different delay correlation coefficients to perform delay autocorrelation operations on the remaining unclassified signals, calculate their modulation slopes respectively, and determine whether they are linear frequency modulation signals based on whether the modulation slopes are the same.

[0047] Specifically, when the ratio of the main lobe width to the original signal pulse width is 1±0.1, the ratio is considered to be close to 1.

[0048] Specifically, step 1 includes the following steps:

[0049] Perform autocorrelation operation on the signal and normalize the result R according to the following formula: x (t):

[0050]

[0051] Where x(n) is the radar IQ sampling signal and N is the total sampling length.

[0052] Specifically, in step 2, the normalized result R is calculated x (t) Ratio of 3dB width to original signal pulse width;

[0053] Specifically, in step 3, when the ratio is close to 1, the signal is a simple signal. For the signal that does not meet the threshold, the real part re and the imaginary part im of x(n) are squared according to the following formula to obtain the y(n) signal:

[0054] y(n).re=(x(n).re) 2

[0055] y(n).im=(x(n).im) 2

[0056] Repeat steps 1 and 2 for y(n) and calculate the normalized result R of y(n) y (t) Ratio of 3dB width to original signal pulse width.

[0057] Specifically, in step 4, when the ratio is close to 1, the signal is a two-phase coded signal, and the signal that does not meet the threshold is quadratically operated to obtain the z(n) signal:

[0058] z(n).re=(x(n).re) 4

[0059] z(n).im=(x(n).im) 4

[0060] Repeat steps 1 and 2 for z(n) to calculate the normalized result R of z(n) z (t) Ratio of 3dB width to original signal pulse width;

[0061] When the ratio is 1±0.1, the signal is a four-phase coded signal, and the signal that does not meet the threshold is other compressed signals.

[0062] Specifically, in step 5, different delay coefficients a1 and a2 are selected, where 0.5 < a1 < 1, 0 < a2 < 0.5, and a delay autocorrelation operation is performed to calculate the modulation slopes k1 and k2 respectively;

[0063] When k1=k2, the signal is a linear frequency modulation signal; otherwise, it is a nonlinear frequency modulation signal.

[0064] Example

[0065] In one embodiment, the signal form is an IQ complex signal, and the radar signal modulation type classification method based on the pulse compression characteristic is as follows:

[0066] S1. Perform autocorrelation operation on the radar IQ signal, find its maximum value, and logarithmically normalize the autocorrelation result according to the maximum value;

[0067] S2, separate simple signals from signals;

[0068] S3, separating the BPSK signal from the remaining signal;

[0069] S4, separating the QPSK signal from the remaining signal;

[0070] S5. Distinguish between LFM and NLFM signals.

[0071] Specifically, in this embodiment, the specific steps of S2 are:

[0072] S2-1, autocorrelation operation of IQ signal;

[0073] S2-2, calculate the autocorrelation main lobe width;

[0074] S2-3, calculate the main lobe width / pulse width, if it is equal to 1, it is a simple signal, otherwise go to S3.

[0075] Specifically, in this embodiment, the specific steps of S3 are:

[0076] S3-1, IQ signal is I 2 and Q 2 Form a new signal;

[0077] S3-2. Calculation I 2 Q 2 Autocorrelation operation;

[0078] S3-3. Calculation I 2 Q 2 Autocorrelation main lobe width;

[0079] S3-4. Calculation I 2 Main width / pulse width, if equal to 1, it is BPSK signal, otherwise enter S4.

[0080] Specifically, in this embodiment, the specific steps of S4 are:

[0081] S4-1, IQ signal I 4 and Q 4 Form new signals;

[0082] S4-2. Calculation I 2 Q 2 Autocorrelation operation;

[0083] S4-3. Calculation I 2 Q 2 Autocorrelation main lobe width;

[0084] S4-4. Calculation I 2 Main Width / Pulse Width.

[0085] Specifically, in this embodiment, S5 distinguishes between LFM and NLFM, and uses the delay correlation method to calculate the modulation slope of the signal. The specific steps are:

[0086] S5-1, set the delay coefficient to 0.4, and construct signal A1;

[0087] S5-2, take the conjugate of A1 as A1';

[0088] S5-3, multiply A1' and the original signal by point to obtain a new signal B1;

[0089] S5-4, calculate the frequency F1 of B1;

[0090] S5-5, the modulation slope is K1=F1 / 0.4;

[0091] S5-6, set the delay coefficient to 0.6, and construct signal A2;

[0092] S5-7, conjugate A2 to A2';

[0093] S5-8, multiply A2' and the original signal by a dot to obtain a new signal B2;

[0094] S5-9, calculate B2 frequency F2;

[0095] S5-10, modulation slope K2 = F2 / 0.6;

[0096] S5-11, if K1=K2, it is LFM, otherwise it is NLFM.

[0097] Specifically, the related processing methods of different encoding methods are: distinguishing simple signals (NM), two-phase encoders (BPSK), four-phase encoders (QPSK), linear frequency modulation signals (LFM), nonlinear frequency modulation signals (NLFM)

[0098] Original signal bandwidth Pulse compression bandwidth I / Q baseband signal bandwidth <![CDATA[I 4 Q 4 ]]> NM 1 1 1 1 BPSK 1 1 / N 1 1 QPSK 1 1 / N 1 / N 2 LFM 1 1 / M 1 / 2M 1 / 4M NLFM 1 1 / M 1 / 2M 1 / 4M

[0099] Treatment method:

[0100] 1. Pulse compression, i.e. signal autocorrelation, find the 3dB bandwidth;

[0101] 2. IQ data I square Q square, BPSK degenerates into NM signal;

[0102] 3. IQ data I fourth power Q fourth power, QPSK degenerates into mm signal;

[0103] 4. Delay cross-correlation method, calculate the LFM modulation slope. When different delay parameters are selected, the calculation results of LFM are the same, but the calculation results of NLFM are different.

[0104] It should be noted that, in this article, relational terms such as first and second, etc. 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 terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0105] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A radar signal modulation type classification method based on pulse compression characteristics, characterized in that: The pulse compression characteristics of radar signals are used to calculate the ratio of the main lobe width to the pulse width of the signal, the square of the signal, and the fourth power of the signal after pulse compression, and simple signals, two-phase coded signals, and four-phase coded signals are identified; different delayed autocorrelation coefficients are used to calculate the modulation slope of the remaining unclassified signals, and linear frequency modulation signals and nonlinear frequency modulation signals are distinguished according to the calculated modulation slope results; the specific steps include: Step 1, perform autocorrelation operation on the radar IQ signal, solve its maximum value, and logarithmically normalize the autocorrelation result according to the maximum value; Step 2, detect the 3dB main lobe width of the normalized result, calculate the ratio of the main lobe width to the original signal pulse width, if the ratio is 1±0.1, determine that the signal is a simple signal, otherwise it is a pulse compression signal; Step 3, square the I and Q paths of the IQ signal respectively, perform autocorrelation operation on the squared IQ signal, solve its maximum value, and logarithmically normalize the autocorrelation result according to the maximum value, detect the 3dB main lobe width of the normalized result, calculate the ratio of the main lobe width to the original signal pulse width, and if the ratio is 1±0.1, it is determined to be a two-phase coded signal; Step 4, perform a fourth-power operation on the I and Q paths of the IQ signal respectively, perform an autocorrelation operation on the IQ signal after the fourth-power operation, solve its maximum value, and logarithmically normalize the autocorrelation result according to the maximum value. Detect the 3dB main lobe width of the normalized result, calculate the ratio of the main lobe width to the original signal pulse width, and if the ratio is 1±0.1, determine it to be a four-phase coded signal; Step 5: Use different delay correlation coefficients to perform delay autocorrelation operations on the remaining unclassified signals, calculate their modulation slopes respectively, and determine whether they are linear frequency modulation signals based on whether the modulation slopes are the same.

2. The radar signal modulation type classification method based on pulse compression characteristics according to claim 1 is characterized in that: In step 1, the following steps are specifically included: Perform autocorrelation operation on the signal and normalize the result according to the following formula: R x ( n ): ； In the formula, x ( n ) is the radar IQ sampling signal, N is the total sampling length, h is the number of time domain offset points of the autocorrelation function.

3. The radar signal modulation type classification method based on pulse compression characteristics according to claim 2 is characterized in that: In step 2, calculate the normalized result R x ( n )The ratio of 3dB width to the original signal pulse width.

4. The radar signal modulation type classification method based on pulse compression characteristics according to claim 3 is characterized in that: In step 3, the signals that do not meet the simple signal judgment conditions in step 2 are respectively judged by the following formulas: x ( n ) re and the imaginary part im Doing the square operation, we get y ( n )Signal; 。 5. The radar signal modulation type classification method based on pulse compression characteristics according to claim 4 is characterized in that: In step 4, the signal that does not meet the two-phase coding signal judgment condition in step 3 is subjected to a fourth power operation to obtain a z(n) signal; ； When the ratio is 1±0.1, the signal is a four-phase coded signal, and the signal that does not meet the threshold is other compressed signals.

6. The radar signal modulation type classification method based on pulse compression characteristics according to claim 1 is characterized in that: In step 5, select different delay coefficients a 1, a 2, where 0.5< a 1<1,0< a 2<0.5, perform delayed autocorrelation operation and calculate the modulation slope respectively k 1. k 2; when k 1= k 2 The signal is a linear frequency modulation signal; otherwise, it is a nonlinear frequency modulation signal.

7. A radar signal modulation type classification system based on pulse compression characteristics, the system is based on the method according to any one of claims 1 to 6, characterized in that: Includes the following modules: The autocorrelation logarithmic normalization module performs autocorrelation operation on the radar IQ signal, solves its maximum value, and logarithmically normalizes the autocorrelation result according to the maximum value; The simple signal separation module detects the 3dB main lobe width of the normalized result and calculates the ratio of the main lobe width to the original signal pulse width. If the ratio is 1±0.1, the signal is determined to be a simple signal, otherwise it is a pulse compression signal. The two-phase coded signal separation module performs autocorrelation operation on the squared IQ signal to find its maximum value, and logarithmically normalizes the autocorrelation result according to the maximum value, detects the 3dB main lobe width of the normalized result, and calculates the ratio of the main lobe width to the original signal pulse width. If the ratio is 1±0.1, it is determined to be a two-phase coded signal; The four-phase coded signal separation module performs a fourth-power operation on the I and Q paths of the IQ signal, performs an autocorrelation operation on the IQ signal after the fourth-power operation, solves its maximum value, and logarithmically normalizes the autocorrelation result according to the maximum value, detects the 3dB main lobe width of the normalized result, and calculates the ratio of the main lobe width to the original signal pulse width. If the ratio is 1±0.1, it is determined to be a four-phase coded signal; The linear frequency modulation signal and nonlinear frequency modulation signal separation module uses different delay correlation coefficients to perform delay autocorrelation operations on the remaining unclassified signals, calculates their modulation slopes respectively, and determines whether it is a linear frequency modulation signal based on whether the modulation slopes are the same.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the radar signal modulation type classification method based on pulse compression characteristics as described in any one of claims 1 to 6 is implemented.

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