A method for estimating the number of code elements in a pulse of phase-coded radar signals

Abstract

The present invention belongs to the field of radar signal processing and analysis technology and discloses a method for estimating the number of code elements within a pulse of a phase-coded radar signal. For an input baseband digital signal, the instantaneous frequency is calculated and processed, and the number of code elements corresponding to the peak amplitude correlation value is searched to obtain the optimal number of code elements. The method primarily includes calculating the unfolded phase of the input signal and filtering it using a differential filter to obtain the instantaneous frequency; removing average frequency deviation, edges, outliers, and low-value processing, creating corresponding reference data, calculating amplitude correlation values, and searching for the number of code elements corresponding to the maximum correlation value. This method is not limited to the type of phase-coded signal or the frequency deviation of the pulse and can also adapt to situations where pulse edge estimation is inaccurate. The instantaneous frequency can be obtained by filtering using a differential filter or by instantaneous phase differential. The subsequent process remains the same, and the number of code elements can still be estimated. The calculation speed is fast and engineering implementation is convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of radar signal processing and analysis, and more particularly 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 a crucial aspect of electronic reconnaissance. Traditional radar signal processing relies on radar signal pulse descriptors, but with the advancement of electronic reconnaissance technology, the importance of radar intra-pulse information is becoming increasingly apparent. Phase-coded signals are an important type of radar modulation signal. Common phase-coded signals include binary, four-phase, and Frank coding. Radar intra-pulse feature analysis involves identifying the modulation scheme 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 within the pulse, which facilitates subsequent calculations of code element width and modulation type identification. Therefore, the accuracy of this estimate plays a crucial role in the entire radar intra-pulse analysis process.

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

[0004] Common symbol number estimation methods rely on extracting information about pulse discontinuity points and patterns. This approach places certain demands on the phase-coded sequence. When no symbol differs from the preceding and following symbols, or when the greatest common divisor of the number of consecutive symbols is not 1, these methods struggle to obtain accurate results. Furthermore, as electromagnetic environments become increasingly complex, the resulting symbol rate energy peaks are susceptible to noise, leading to inaccurate estimates. Summary of the Invention

[0005] To address the aforementioned issues, the present invention proposes a method for estimating the number of symbols within a pulse of a phase-coded radar signal. This method uses a differential filter to filter the instantaneous phase to obtain the instantaneous frequency, creates a reference signal to calculate amplitude-related values, and searches for peaks to determine the optimal number of symbols. This method uses differential filtering to reduce high-frequency components, smoothing the instantaneous frequency. Frequency offset is removed during processing, making the estimation method unaffected by signal frequency offset and unrestricted by the modulation order of the input signal. The method is applicable to binary, four-phase, and Frank coding, among others, and boasts high computational speed, making it 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 includes the following steps:

[0007] Step 1: Calculate the unfolded phase of the input signal and filter it using a differential filter to obtain the instantaneous frequency;

[0008] Step 2: intercept the data in the pulse of the instantaneous frequency, remove the frequency deviation, set the data at the pulse edge to zero, perform peak clipping on the outliers, and set the low values ​​to zero, so as to obtain the instantaneous frequency used to calculate the correlation value;

[0009] Step 3: Traverse different numbers of code elements, create corresponding reference data, calculate the amplitude correlation value, and search for the code element number corresponding to the maximum correlation value, which is the estimated value of the code element number.

[0010] Furthermore, the method for obtaining the instantaneous frequency in step 1 includes:

[0011] 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.

[0012] Furthermore, the method for removing the average frequency deviation in step 2 includes:

[0013] If the current pulse has a frequency offset, the instantaneous frequency curve calculated in the previous section will have a DC offset. To avoid the impact of the frequency offset, the frequency offset needs to be calculated and removed. The formula for calculating the average frequency offset is: 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; the instantaneous frequency removes the frequency deviation: Furthermore, the edge, outlier, and low value processing methods in step 2 include:

[0014] 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;

[0015] 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. After removing the average frequency offset from the instantaneous frequency, the low-value data within a symbol close to 0 is set to zero to reduce the impact of noise.

[0016] Furthermore, the creation of corresponding reference data in step 3 includes:

[0017] 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.

[0018] Furthermore, the calculation of the amplitude correlation value in step 3 includes:

[0019] 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:

[0020] The method provided by the present invention estimates the number of code elements within a pulse of a phase-coded radar signal. It uses a differential filter to filter, processes the edges / wild values / low values ​​of the instantaneous frequency, creates a reference signal to calculate amplitude-related values, and searches for peaks to obtain the optimal estimate of the number of code elements. The present invention is not limited to the type of phase-coded signal or the frequency deviation of the pulse, and can also adapt to situations where pulse edge estimates are inaccurate. Furthermore, the present invention proposes using a differential filter to obtain the instantaneous frequency, and can also obtain the instantaneous frequency through instantaneous phase differential. The subsequent process is the same, and the number of code elements can still be estimated. This method has high computational speed and is easy to implement in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the process of estimating the number of code elements in a pulse according to the present invention;

[0022] Figure 2 Flowchart for converting folded phase to unfolded phase;

[0023] Figure 3 is the differential filter characteristic map;

[0024] Figure 4 This is a comparison chart of the instantaneous frequency between differential filtering and direct differential;

[0025] Figure 5 is the instantaneous frequency of each signal and the reference signal diagram;

[0026] Figure 6 This is a simulation flow chart for estimating the number of code elements in an embodiment of the present application;

[0027] Figure 7 This is the instantaneous frequency diagram after differential filtering in simulation 1 of the embodiment of the present application;

[0028] Figure 8 This is the instantaneous frequency diagram after differential filtering in simulation 2 of the embodiment of the present application;

[0029] Figure 9 This is a graph showing the amplitude correlation value of the Frank36 signal in simulation 2 of the embodiment of the present application. DETAILED DESCRIPTION

[0030] 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. 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.

[0031] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "provided with," "mounted / connected," and "connected" should be understood in a broad sense. For example, "connected" can mean 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 an indirect connection through an intermediate medium, and it can be internal communication between two components. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention in specific circumstances. Example

[0033] The present invention will be further described in detail below with reference to the accompanying drawings.

[0034] 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 optimal matching code element number. The specific processing flow of the system is shown in the attached figure. Figure 1 As shown, it mainly includes 3 steps:

[0035] Step 1: Calculate the unfolded phase of the input signal and filter it using a differential filter to obtain the instantaneous frequency;

[0036] Step 2: intercept the data in the pulse of the instantaneous frequency, remove the frequency deviation, set the data at the pulse edge to zero, perform outlier peak clipping, set low value to zero, and other operations to obtain the instantaneous frequency used to calculate the correlation value;

[0037] Step 3: Traverse different numbers of code elements, create corresponding reference data, calculate the amplitude correlation value, and search for the code element number corresponding to the maximum correlation value, which is the estimated value of the code element number.

[0038] Calculating the instantaneous frequency in step 1 includes:

[0039] For complex IQ data, the phase value will be 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.

[0040] The process of converting the folded phase to the unfolded phase is as shown in the attached figure. Figure 2 shown.

[0041] 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 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.

[0042] The processing of instantaneous frequency in step 2 mainly includes:

[0043] (1) Removing the average frequency deviation

[0044] If the current pulse has a frequency offset, the instantaneous frequency curve calculated in the previous section will have a DC offset. To avoid the impact of the frequency offset, the frequency offset needs to be calculated and removed. The formula for calculating the average frequency offset is: in, The instantaneous frequency calculated in the previous section and the pulse data extracted are: The number of sampling points corresponding to the current pulse width.

[0045] Instantaneous frequency deviation removal:

[0046] (2) Edge, outlier, and low value processing

[0047] 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 ends of each pulse data point is set to zero.

[0048] 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.

[0049] For the instantaneous frequency obtained, after removing the average frequency offset, the data within a code element are all close to 0. These low-value data will be affected by noise, and they are set to zero to reduce the influence of noise.

[0050] Calculating the amplitude correlation value and searching for the peak in step 3 mainly includes:

[0051] The key techniques in this section are creating reference data and calculating amplitude-related values.

[0052] (1) Create reference data

[0053] As can be seen from the previous section, the low value of the processed instantaneous frequency is 0, while the frequency of the phase coded 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 5 The instantaneous frequency and the reference signal corresponding to the number of code elements under the four-phase coded signal examples of Barker code 2, Barker code 7, and 5 code elements.

[0054] (2) Calculate the amplitude correlation value

[0055] 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

[0056] Barker Code element 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 four 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 Phase value. 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 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.

[0057] Simulation 1:

[0058] Simulation parameters:

[0059] Sampling rate: 204.8 Msps

[0060] Number of pulses: 7

[0061] Pulse repetition period: 10 us

[0062] Pulse width: 5 us

[0063] Frequency deviation of each pulse: [0, 20, 50, -10, -40, -30, 30] MHz

[0064] Signal type for each pulse: [Barker2, Barker3, Barker-41, Barker5, Barker7,Barker11, Barker13];

[0065] Attachment 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 offset, and each pulse has a high-frequency component at its symbol phase transition position;

[0066] 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;

[0067] Operation results:

[0068] [2, 3, 4, 5, 7, 11, 13].

[0069] Simulation 2:

[0070] Simulation parameters:

[0071] Sampling rate: 100 Msps

[0072] Number of pulses: 4

[0073] Pulse repetition period: [10, 15, 19, 35] us

[0074] Pulse width: [4, 5, 15, 20] us

[0075] Frequency deviation of each pulse: [0, 5, -4, 6] MHz

[0076] Signal type of each pulse: [5-symbol four-phase encoding, 10-symbol four-phase encoding, Frank16, Frank36];

[0077] Attachment 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 of its code element phase transition. Figure 9 is the amplitude correlation value when traversing the 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;

[0078] Input the pulse width starting and ending positions of the above four pulses respectively, and estimate the number of code elements of the current pulse;

[0079] Operation results:

[0080] [5, 10, 16, 36].

[0081] It can be seen from the simulation results that this method can estimate the number of code elements in each pulse.

[0082] The above are all preferred embodiments of the present invention, and are not intended to limit the scope of protection 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 scope of protection 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 unfolded phase of the input signal and filter it using a differential 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 pulse edge to zero, perform peak clipping on the outliers, and set the low values ​​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 code element number corresponding to the maximum correlation value, which is the estimated value of the code element number; The method for removing the average frequency deviation in step 2 includes: If the current pulse has a frequency offset, the instantaneous frequency curve calculated in the previous section will have a DC offset. To avoid the impact of the frequency offset, the frequency offset needs to be calculated and removed. The formula for calculating the average frequency offset is: 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 deviation removal: The edge, outlier, and low value processing methods in step 2 include: 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 offset, the low-value data within a symbol close to 0 are set to zero to reduce the influence of noise; The creation of corresponding reference data in step 3 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 set to 0 at other positions; Calculating the amplitude correlation 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: .

2. The method for estimating the number of code elements in a pulse of a phase-coded radar signal according to claim 1, wherein: 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.

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