Method for estimating number of intra-pulse code elements of phase-coded radar signal

Abstract

The invention belongs to the technical field of radar signal processing and analysis, and discloses a method for estimating the number of intra-pulse code elements of a phase-coded radar signal, which comprises the following steps of: calculating and processing instantaneous frequency of an input baseband digital signal, and searching the number of code elements corresponding to a peak value of an amplitude correlation value so as to obtain the number of code elements which are optimally matched; the method mainly comprises the following steps: calculating a non-folding phase of an input signal, and filtering by using a differential filter to obtain an instantaneous frequency; and carrying out operations such as average frequency offset, edge, outlier and low value processing, creating corresponding reference data, calculating an amplitude correlation value, and searching the number of code elements corresponding to the maximum correlation value. The method does not limit the type of the phase coding signal and the frequency offset of the pulse, can also adapt to the condition that the pulse edge estimation is inaccurate, uses the differential filter to filter to obtain the instantaneous frequency, can also obtain the instantaneous frequency through the instantaneous phase difference, can still estimate the number of code elements through the same subsequent process, and is high in operation speed and convenient for engineering implementation.

Description

Technical Field

[0001] The present invention relates to the technical field of radar signal processing and analysis, and more specifically to a method for estimating the number of code elements in a pulse of a phase-coded radar signal. Background Art

[0002] Processing and analyzing received radar signals is an important part of electronic reconnaissance. Traditional radar signal processing is based on radar signal pulse descriptors, but with the development of electronic reconnaissance technology, the importance of radar intra-pulse information is increasingly reflected. Phase-coded signals are an important type of radar modulation signals. Common phase-coded signals include two-phase coding, four-phase coding, Frank coding, etc. Radar intra-pulse feature analysis refers to identifying the modulation mode and accurately estimating the modulation parameters. Generally, the first step in the phase-coded signal processing process is to estimate the number of code elements in the pulse, so as to prepare for the subsequent calculation of the code element width, identification of the modulation type, etc. Therefore, the accuracy of the estimation of the number of code elements in the pulse plays an important role in the entire radar intra-pulse analysis process.

[0003] There are various methods for estimating the number of code elements in a pulse of a phase-coded radar signal. Some methods use cyclic spectra, while others extract information and patterns of mutation points within the pulse. The former is computationally complex and requires large amounts of computation, while the latter is computationally simple but its accuracy is greatly affected by the patterns of the code elements.

[0004] Common code element number estimation methods extract information and rules of mutation points in pulses for estimation, which has certain requirements for phase-coded sequences. When there is no code element that is different from the previous and next code elements or the greatest common divisor of the number of consecutive code elements is not 1, this method is difficult to obtain correct results. As the electromagnetic environment becomes increasingly complex, the code rate energy peak obtained by this method is easily affected by noise, resulting in inaccurate estimation. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a method for estimating the number of code elements in a pulse of a phase-coded radar signal, using a differential filter to filter the instantaneous phase to obtain the instantaneous frequency, creating a reference signal to calculate the amplitude-related value, and searching for the peak to obtain the optimal number of code elements. The present invention uses differential filtering to reduce high-frequency components, making the instantaneous frequency smoother, removing the frequency deviation during the processing process, so that the estimation method is not affected by the signal frequency deviation, and does not limit the modulation order of the input signal, and is suitable for two-phase coding, four-phase coding, Frank coding, etc., and has a fast operation speed and is suitable for engineering applications.

[0006] The present invention provides a method for estimating the number of code elements in a pulse of a phase-coded radar signal, which adopts the following technical solution and mainly comprises the following steps: Step 1: Calculate the non-folded phase of the input signal and use a differential filter to filter to obtain the instantaneous frequency; Step 2: intercept the data in the pulse of the instantaneous frequency, remove the frequency deviation, set the data at the edge of the pulse to zero, perform peak clipping on wild values, and set the low value to zero, so as to obtain the instantaneous frequency used to calculate the correlation value; Step 3: traverse different numbers of code elements, create corresponding reference data, calculate the amplitude correlation value, and search for the number of code elements corresponding to the maximum correlation value, which is the estimated value of the number of code elements.

[0007] Furthermore, the method for obtaining the instantaneous frequency in step 1 includes: When the input signal has a frequency deviation, the obtained discontinuous instantaneous phase data is processed into a non-folded phase, and the obtained non-folded instantaneous phase is differentially filtered.

[0008] Furthermore, the method for removing the average frequency deviation in step 2 includes: If the current pulse has frequency deviation, the instantaneous frequency curve calculated in the previous section will have DC bias. To avoid the impact of frequency deviation, the frequency deviation needs to be calculated and removed. The frequency deviation average value is calculated as: in, The instantaneous frequency calculated in the previous section and the pulse data extracted are: is the number of sampling points corresponding to the current pulse width; instantaneous frequency removes frequency deviation: Furthermore, the edge, outlier, and low value processing method in step 2 includes: In order to prevent the edge position data from affecting the correlation value, a small part of the front and back ends of each pulse data point is set to zero; A threshold is set for the instantaneous frequency to perform peak clipping. The calculation formula for the peak clipping threshold is: in, is the sampling rate of the input signal. For the instantaneous frequency obtained, after removing the average frequency deviation, the low-value data within a symbol that is close to 0 is set to zero to reduce the impact of noise.

[0009] Furthermore, the creation of corresponding reference data in step three includes: The reference data is set to 1 at the adjacent code elements of the processed instantaneous frequency low value and the phase transition position of the phase coded signal, and is set to 0 at other positions.

[0010] Furthermore, the step 3 of calculating the amplitude-related value includes: The result of amplitude multiplication and addition within the pulse width range is taken as the amplitude-related value, and the formula is as follows: In summary, the present invention includes at least one of the following beneficial technical effects: The method provided by the present invention estimates the number of code elements in a pulse for a phase-coded radar signal, uses a differential filter to filter, processes the edge / wild value / low value of the instantaneous frequency, creates a reference signal to calculate the amplitude-related value, and searches for the peak value to obtain the optimal code element number estimate. The present invention does not limit the type of phase-coded signal or the frequency deviation of the pulse, and can also adapt to the situation where the pulse edge estimation is inaccurate. In addition, the present invention proposes to use a differential filter to filter to obtain the instantaneous frequency, and can also obtain the instantaneous frequency through the instantaneous phase difference. The subsequent process is the same and the number of code elements can still be estimated. The method has a fast operation speed and is easy to implement in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the process of estimating the number of code elements in a pulse according to the present invention; Figure 2 Flow chart of converting folded phase to unfolded phase; Figure 3 is the characteristic graph of the difference filter; Figure 4 This is a comparison chart of the instantaneous frequency between differential filtering and direct differential; Figure 5 is the instantaneous frequency of each signal and the reference signal diagram; Figure 6 This is a simulation flow chart of estimating the number of code elements in an embodiment of the present application; Figure 7 This is the instantaneous frequency diagram after differential filtering in simulation 1 of the embodiment of the present application; Figure 8 This is the instantaneous frequency diagram after differential filtering in simulation 2 of the embodiment of the present application; Fig. 9 This is a curve diagram of the amplitude correlation value of the Frank36 signal in simulation 2 of the embodiment of the present application. DETAILED DESCRIPTION

[0012] 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; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0013] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0014] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "mounted / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. Example

[0015] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0016] The embodiment of the present invention discloses a method for estimating the number of code elements in a pulse of a phase-coded radar signal. The method estimates the number of code elements in a pulse of a phase-coded radar signal. The method calculates and processes the number of code elements corresponding to the peak value of the instantaneous frequency and the search amplitude correlation value of the input baseband digital signal to obtain the number of code elements with the best match. The specific processing flow of the system is shown in the attached figure. Figure 1 As shown, it mainly includes 3 steps: Step 1: Calculate the non-folded phase of the input signal and use a differential filter to filter to obtain the instantaneous frequency; Step 2: intercept the data in the pulse of the instantaneous frequency, remove the frequency deviation, set the data at the edge of the pulse to zero, perform peak clipping of wild values, set the low value to zero, and other operations to obtain the instantaneous frequency used to calculate the correlation value; Step 3: traverse different numbers of code elements, create corresponding reference data, calculate the amplitude correlation value, and search for the number of code elements corresponding to the maximum correlation value, which is the estimated value of the number of code elements.

[0017] Calculating the instantaneous frequency in step 1 includes: For complex IQ data, the phase value is folded into When the input signal has frequency deviation, the phase changes greatly. At this time, the instantaneous phase data obtained is discontinuous, so it needs to be processed into a non-folded phase.

[0018] The process of converting the folded phase to the unfolded phase is as shown in the attached figure. Figure 2 shown.

[0019] The obtained non-folded instantaneous phase is differentially filtered. The amplitude-frequency response and phase-frequency response of the differential filter are shown in the attached figure. Figure 3 As shown in the figure, the conventional method for calculating the instantaneous frequency is to directly calculate the differential value of the non-folded instantaneous phase. Figure 4 A comparison of the two processing methods is given, and it can be seen that the instantaneous frequency curve obtained by filtering with the differential filter is smoother.

[0020] The processing of instantaneous frequency in step 2 mainly includes: (1) Removing the average frequency deviation If the current pulse has frequency deviation, the instantaneous frequency curve calculated in the previous section will have DC bias. To avoid the impact of frequency deviation, the frequency deviation needs to be calculated and removed. The frequency deviation average value is calculated as: in, The instantaneous frequency calculated in the previous section and the pulse data extracted are: It is the number of sampling points corresponding to the current pulse width.

[0021] Instantaneous frequency to remove frequency deviation:

[0022] (2) Edge, outlier, and low value processing In electronic reconnaissance, the pulse width start and end positions are obtained by pulse detection, and there may be errors that are not the actual edge positions of the pulse. In order to avoid the edge position data affecting the correlation value, A small part at the front and back of each pulse data point is set to zero.

[0023] For the instantaneous frequency obtained, there may be some wild values, and the peak value is extremely large. Here, a threshold is set. in, is the sampling rate of the input signal.

[0024] For the instantaneous frequency obtained, after removing the average frequency deviation, the data in one code element are all close to 0. For these low-value data, they will be affected by noise, and they are set to zero to reduce the influence of noise.

[0025] Calculating the amplitude correlation value and searching for the peak in step 3 mainly includes: The key techniques in this section are creating reference data and calculating amplitude-related values.

[0026] (1) Create reference data As can be seen from the previous section, the low value of the processed instantaneous frequency is 0, while the frequency of the phase-encoded signal at the phase transition position is higher. Based on this feature, a reference signal is created, that is, the reference data is set to 1 at the adjacent code element and the other positions are set to zero. Figure 5It is the reference signal of the instantaneous frequency and the corresponding number of code elements under the example of the four-phase coded signal of Barker code 2, Barker code 7, and 5 code elements.

[0027] (2) Calculate the amplitude-related value The result of amplitude multiplication and addition within the pulse width range is taken as the amplitude-related value, and the formula is as follows: Common phase-coded radar signals Barker Code symbol sequence (1 = +, 0 = -) Barker 2 10 Barker 3 110 Barker 4_1 1101 Barker 4_2 1110 Barker 5 11101 Barker 7 1110010 Barker 11 11100010010 Barker 13 1111100110101 Barker -3 100 Barker -4_1 1011 Barker -4_2 1000 Barker -5 10111 Barker -7 1011000 Barker -11 10110111000 Barker -13 1010110011111 There are 4 phase values ​​for four-phase encoding: The phase value of Frank phase encoding is as follows: Among them, n=0,1,…,N-1, k=0,1,…,N-1, a total of N 2 According to the estimation method proposed by the present invention, two sets of phase coded signals are used to simulate and verify the above estimation method. The simulation process is shown in the attached figure. Figure 6 As shown, the present invention estimates the number of code elements in the pulse of the received pulse signal. In the simulation, a pulse signal with phase coding modulation is first transmitted, and then the receiver collects the signal. Then, pulse search and detection are performed to obtain the number of pulses and the start and end positions of each pulse width. At this time, the data and parameters required by the algorithm of the present invention are available. Finally, the number of code elements in the pulse of each pulse is estimated, and the code element number result is output.

[0028] Simulation 1: Simulation parameters: Sampling rate: 204.8 Msps Number of pulses: 7 Pulse repetition period: 10 us Pulse width: 5 us Frequency deviation of each pulse: [0, 20, 50, -10, -40, -30, 30] MHz Signal type for each pulse: [Barker2, Barker3, Barker-41, Barker5, Barker7,Barker11, Barker13]; Attached Figure 7 This is the instantaneous frequency after differential filtering under the parameter environment of simulation 1. It can be seen that each pulse has a different frequency deviation, and each pulse has a high-frequency component at the position of its symbol phase transition; Input the starting and ending positions of the pulse widths of the above 7 pulses respectively, and estimate the number of code elements of the current pulse; Operation results: [2, 3, 4, 5, 7, 11, 13].

[0029] Simulation 2: Simulation parameters: Sampling rate: 100 Msps Number of pulses: 4 Pulse repetition period: [10, 15, 19, 35] us Pulse width: [4, 5, 15, 20] us Frequency deviation of each pulse: [0, 5, -4, 6] MHz Signal type of each pulse: [5-symbol four-phase encoding, 10-symbol four-phase encoding, Frank16, Frank36]; Attached Figure 8 This is the instantaneous frequency after differential filtering under the parameter environment of simulation 2. It can be seen that each pulse has a different frequency deviation, and each pulse has a high-frequency component at the position where its code element phase changes. Fig. 9 It is the amplitude correlation value when traversing each number of code elements under the Frank36 pulse signal. It can be seen that there is a peak when the number of code elements is 36, and the estimated value of the number of code elements is 36 at this time; Input the starting and ending positions of the pulse widths of the above four pulses respectively, and estimate the number of code elements of the current pulse; Operation results: [5, 10, 16, 36].

[0030] It can be seen from the simulation results that this method can estimate the number of code elements in each pulse.

[0031] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for estimating the number of code elements in a pulse of a phase-coded radar signal, characterized in that: The following steps are involved: Step 1: Calculate the non-folded phase of the input signal and use a differential filter to filter to obtain the instantaneous frequency; Step 2: intercept the data in the pulse of the instantaneous frequency, remove the frequency deviation, set the data at the edge of the pulse to zero, perform peak clipping on wild values, and set the low value to zero, so as to obtain the instantaneous frequency used to calculate the correlation value; Step 3: traverse different numbers of code elements, create corresponding reference data, calculate the amplitude correlation value, and search for the number of code elements corresponding to the maximum correlation value, which is the estimated value of the number of code elements.

2. The method for estimating the number of code elements in a pulse of a phase-coded radar signal according to claim 1, characterized in that: The method for obtaining the instantaneous frequency in step 1 includes: When the input signal has a frequency deviation, the obtained discontinuous instantaneous phase data is processed into a non-folded phase, and the obtained non-folded instantaneous phase is differentially filtered.

3. The method for estimating the number of code elements in a pulse of a phase-coded radar signal according to claim 1, characterized in that: The method for removing the average frequency deviation in step 2 includes: If the current pulse has frequency deviation, the instantaneous frequency curve calculated in the previous section will have DC bias. To avoid the impact of frequency deviation, the frequency deviation needs to be calculated and removed. The frequency deviation average value is calculated as: in, The instantaneous frequency calculated in the previous section and the pulse data extracted are: is the number of sampling points corresponding to the current pulse width; Instantaneous frequency to remove frequency deviation: .

4. The method for estimating the number of code elements in a pulse of a phase-coded radar signal according to claim 1, characterized in that: The edge, outlier, and low value processing method in step 2 includes: In order to prevent the edge position data from affecting the correlation value, a small part of the front and back ends of each pulse data point is set to zero; A threshold is set for the instantaneous frequency to perform peak clipping. The calculation formula for the peak clipping threshold is: in, is the sampling rate of the input signal. For the instantaneous frequency obtained, after removing the average frequency deviation, the low-value data within a symbol that is close to 0 is set to zero to reduce the impact of noise.

5. The method for estimating the number of code elements in a pulse of a phase-coded radar signal according to claim 1, characterized in that: The step 3 of creating corresponding reference data includes: The reference data is set to 1 at the adjacent code elements of the processed instantaneous frequency low value and the phase transition position of the phase coded signal, and is set to 0 at other positions.

6. The method for estimating the number of code elements in a pulse of a phase-coded radar signal according to claim 5, characterized in that: Calculating the amplitude-related value in step 3 includes: The result of amplitude multiplication and addition within the pulse width range is taken as the amplitude-related value, and the formula is as follows: .

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