Zp89 type frequency shift signal center frequency detection method, device and storage medium
By combining undersampling and energy centroid correction, the accuracy and stability issues of center frequency detection in the ZP89 frequency shift track circuit were resolved, achieving high-precision frequency detection while reducing computational complexity and cost.
Patent Information
- Application Number
- CN202211533828.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-01
- Publication Date
- 2026-02-10
- Estimated Expiration
- 2042-12-01
AI Technical Summary
The center frequency detection accuracy of the ZP89 type frequency shift track circuit is not high. Existing methods suffer from large computational load, low accuracy, and frequency fluctuation problems, making it difficult to meet the requirements of railway standards.
By employing an undersampling method combined with energy centroid correction, and through FFT analysis and spectrum reconstruction, the center frequency is determined using the two-peak and four-peak methods, thereby improving computational accuracy and stability.
The ZP89 frequency shift signal center frequency detection accuracy reached ±0.1Hz, far exceeding the standard requirement of ±1Hz, reducing the computational load and improving product quality and stability.
Smart Images
Figure CN116455714B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the detection of the center frequency of a frequency-shifted signal, specifically to the ZP89 type method, equipment, and storage medium for detecting the center frequency of a frequency-shifted signal. Background Technology
[0002] Frequency-shifting track circuits are an important component of railway signaling equipment, primarily used in track circuits within a section. This signal utilizes the rails as a transmission channel to control the display of passing signals, achieving the purpose of automatically directing train operation. The longer the track circuit section, the higher its impedance, and the greater the influence of its secondary parameters. Low-frequency, low-impedance power supplies are highly susceptible to this interference, exhibiting significant instability. Frequency modulation is employed to shift the low-frequency signal to a higher frequency, thus creating a frequency-modulated signal with a constant amplitude but a frequency that periodically changes with the amplitude of the low-frequency signal.
[0003] In my country's railways, the ZP89 type frequency-shift track circuit uses a phase-continuous frequency-shift keying (FSK) signal, with a waveform as shown in the figure. Figure 2 As shown in the diagram; f1 is the lower sideband, f2 is the upper sideband, and the low frequency is... The center frequency is Frequency-shift signal detection is a method for detecting signals from frequency-shift track circuits, effectively monitoring the signals emitted by these circuits. Currently, there are three main methods for calculating the center frequency of frequency-shift signals: phase estimation, oversampling, and undersampling. Compared to the ZPW2000 frequency-shift track circuit (1700Hz-2600Hz), the ZP89 frequency-shift track circuit operates at a lower frequency (450Hz-850Hz). Therefore, the accuracy of the center frequency obtained using the above three methods is not high. Consequently, the detection accuracy of the center frequency for such low-frequency signals from the ZP89 frequency-shift track circuit needs further improvement. Summary of the Invention
[0004] This invention provides a method, device, and storage medium for detecting the center frequency of ZP89 frequency-shift signals. It solves the problem of occasional large fluctuations in the center frequency in traditional oversampling and undersampling methods. At the same time, it has less computational load and higher calculation accuracy than the phase estimation method. It improves product quality and reduces product cost, thereby improving the overall accuracy of center frequency calculation for ZP89 frequency-shift signals.
[0005] On the one hand, this application provides a method for detecting the center frequency of a ZP89 type frequency-shift signal, which specifically includes the following steps:
[0006] Step 1: Sample the ZP89 frequency shift signal using the undersampling method;
[0007] Step 2: Perform FFT analysis on the sampled data;
[0008] Step 3: Locate the left and right main peaks f1 and f2, and their corresponding left and right secondary peaks f1′1, f1′2, f2′1, and f2′2 on the spectrum obtained in Step 2, for a total of six peaks; Based on the ratio of the amplitudes of the left and right secondary peaks of either the left or right main peak: or The size of the peak value is used to select the two largest peak values (two-peak method) or four largest peak values (four-peak method) to complete the energy centroid correction at point t, and the corrected peak value is obtained.
[0009] Step 4: Calculate the undersampled center frequency f′ based on the corrected peak value obtained in Step 3;
[0010] Step 5: Perform spectrum reconstruction on the calculation results of Step 4 to obtain the center frequency f of the ZP89 type frequency shift signal. b .
[0011] This scheme improves frequency resolution and further enhances calculation accuracy by correcting the energy centroid; the combination of the two-peak and four-peak methods solves the problem of large fluctuations in the center frequency that may occur in frequency domain analysis.
[0012] Based on the above scheme, a further step is to perform FFT analysis on the sampled data after applying a Hanning window in step two.
[0013] Based on the above scheme, the following further steps are taken: In step two, a 1024-point FFT analysis is performed on the sampled data.
[0014] Based on the above scheme, the following further applies: In step two, when the sampled data is less than 1024 points, zeros are padded to the part that is less than 1024 points.
[0015] Based on the above scheme, a further step is: In step three, when the ratio of the amplitudes of the left and right secondary peaks... or When the value is greater than 3 or less than 1 / 3, the two largest peaks on the left and right are selected respectively, for a total of four peaks, to complete the energy centroid correction at point t, thus obtaining the corrected peak value f. maxl1 f maxl2 f maxr1 f maxr2 Otherwise, select the largest peak value from the left and right sides respectively, for a total of two peak values, to complete the energy centroid correction at point t, and obtain the corrected peak value f. maxl f maxr .
[0016] Based on the above scheme, further: In step three, the expression for the energy centroid correction Y at point t is:
[0017]
[0018] Where Y represents the energy centroid correction result, Y n X represents the magnitude of a point in the FFT result. n It represents the frequency of a point in the FFT result.
[0019] Based on the above scheme, a further step is: in step four, the undersampled center frequency f′ b This is the average value of the corrected peak values obtained in step three.
[0020] Based on the above scheme, further steps are taken: In step four, when selecting the four largest peak values in step three for energy centroid correction, the undersampled center frequency f′ is... b The expression is:
[0021]
[0022] When selecting the two largest peak values for energy centroid correction in step three, the undersampled center frequency f′ is... b The expression is:
[0023]
[0024] Secondly, this application also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-described ZP89 type frequency shift signal center frequency detection method.
[0025] Fourthly, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described ZP89 type frequency shift signal center frequency detection method.
[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0027] 1. The technical solution claimed in this invention adopts an undersampling method and improves the calculation accuracy through energy centroid correction. Only 1024 points of FFT calculation are required to make the center frequency accuracy of the ZP89 frequency shift signal reach ±0.1Hz, which far exceeds the ±1Hz requirement of the iron standard.
[0028] 2. The technical solution claimed in this invention solves the problem of large fluctuations in the center frequency that may occur in frequency domain analysis by combining the two-peak method and the four-peak method; it has the technical effects of high calculation accuracy, small calculation amount and high stability of calculation results. Attached Figure Description
[0029] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:
[0030] Figure 1 This is a flowchart of the ZP89 type frequency shift signal center frequency detection method in the embodiment;
[0031] Figure 2 This is a waveform diagram of the ZP89 frequency shift signal in the embodiment;
[0032] Figure 3 This is a schematic diagram of the spectrum of the ZP89 type frequency shift signal in the embodiment;
[0033] Figure 4 This is a spectrum diagram of the ZP89 type frequency shift signal in the embodiment;
[0034] Figure 5 This is another spectrum diagram of the ZP89 type frequency shift signal in the embodiment.
[0035] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. The realization of the object, functional characteristics, and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the accompanying drawings of the embodiments of the present invention will be used in conjunction with the following description. Figures 1 to 5 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0037] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied 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.
[0038] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.
[0039] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.
[0040] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.
[0041] Those skilled in the art will understand that all or part of the steps in the above facts and methods can be implemented by a program instructing related hardware. The program or the program described therein can be stored in a computer-readable storage medium. When the program is executed, it includes the following steps: at this time, the corresponding method steps are introduced. The storage medium can be ROM / RAM, magnetic disk, optical disk, etc.
[0042] Example:
[0043] like Figure 2 As shown in the figure, this embodiment first explains the problems that exist when calculating the center frequency of the ZP89 frequency shift signal using the three methods mentioned in the background technology: phase estimation method, oversampling method, and undersampling method.
[0044] Phase deduction method: Calculate f1 and f2 of the ZP89 frequency shift signal in the time domain, and then based on... Calculate the center frequency. The standard requires the ZP89 frequency shift signal to have a center frequency accuracy of ±1Hz. To achieve this accuracy, the frequency algorithm in the time domain requires a huge amount of computation, placing very high demands on the microcontroller and increasing product costs. For multiple signals, the time-domain frequency algorithm requires a large amount of cached computational data, placing very high demands on the microcontroller's memory capacity.
[0045] Oversampling method: The ZP89 frequency shift signal is sampled using oversampling. After performing FFT on the sampled data, frequency domain analysis is performed to find f1 and f2 in the spectrum, and then based on... Calculate the center frequency. The highest center frequency of the ZP89 frequency-shift signal is 850Hz, with a frequency deviation of 55Hz. According to the sampling theorem, a sampling frequency of at least 1810Hz is required. Furthermore, the standard requires the center frequency accuracy of the ZP89 frequency-shift signal to be ±1Hz. To achieve this accuracy, at least 2048-point FFT is required, which involves a large amount of computation, and the center frequency accuracy is still not high. In addition, the center frequency occasionally fluctuates significantly, with the fluctuation value being approximately half of the low-frequency range.
[0046] Undersampling method: This method samples the ZP89 frequency-shift signal using undersampling, performs FFT on the sampled data, and then performs frequency domain analysis. Undersampling folds the spectrum, so spectrum reconstruction is necessary. f1 and f2 are then found in the reconstructed spectrum, and then... Calculate the center frequency. Undersampling can effectively reduce the amount of computation. A 1024-point FFT can achieve a resolution within 0.5Hz in the frequency domain. However, the calculation accuracy is still poor, occasionally exceeding the accuracy requirement of ±1Hz. Furthermore, the center frequency still has the problem of occasionally fluctuating significantly by half a low-frequency value.
[0047] The ZP89 type frequency shift signal is an oscillating current signal generated by keying a frequency shift oscillator. The expression for the spectrum S(t) of the frequency shift wave after Fourier coefficient expansion after square wave modulation is:
[0048]
[0049] Where A0 is the amplitude of the frequency-shifted signal; f0 is the center frequency of the carrier frequency; f1 is the low-frequency frequency of the signal; and the frequency shift index is... Δf is the signal frequency offset; n = ..., -2, -1, 0, 1, 2, ...
[0050] The spectrum of the ZP89 frequency-shift signal consists of an infinite number of paired sideband components (f0-nf1) and (f0+nf1) around the center frequency f0, with the difference between adjacent frequency components being f1. The ratio of the amplitude of each frequency component to the amplitude A0 of the center frequency is called the relative amplitude.
[0051] The relative amplitude of the center carrier frequency component is:
[0052]
[0053] The relative amplitudes of the odd-order sideband components are:
[0054]
[0055] The relative amplitudes of the even-order sideband components are:
[0056]
[0057] Because the frequency parameters of the ZP89 frequency shift track circuit and the ZPW2000 frequency shift track circuit are configured differently, their frequencies are also different.
[0058] A typical spectrum diagram of the ZP89 frequency shift signal is shown below. Figure 3 As shown, the signal frequency offset Δf = 55Hz, the low-frequency modulation frequency range is 7.0~26.0Hz, m>2, and the spectrum of the ZP89 type frequency shift signal can be determined by calculation using the relative amplitude expression to be a double-peak signal, with the frequencies at the peaks being:
[0059] f 1h =f0-nf1
[0060] f 2h =f0+nf1
[0061] Here, b is an integer near m. It can be seen that the peak of the spectrum of the ZP89 type frequency-shift signal does not correspond to the center frequency of the signal.
[0062] This embodiment provides a method for detecting the center frequency of a ZP89 type frequency-shift signal, which solves the problem of occasional large fluctuations in the center frequency in traditional oversampling and undersampling methods. It also has lower computational complexity and higher accuracy than phase estimation methods, thus improving product quality while reducing product costs. The specific steps include:
[0063] Step 1: Sample the ZP89 frequency shift signal using the undersampling method;
[0064] Step 2: Perform a 1024-point FFT analysis on the sampled data using a Hanning window; if the sampled data is less than 1024 points, pad the less than 1024 points with zeros;
[0065] In spectral analysis following the FFT, theoretically, finding the two largest peaks (left and right) is sufficient to determine the center frequency. However, in practice, however, more issues may arise... Figure 4 or Figure 5 As shown, the location of the main peak cannot be directly determined.
[0066] exist Figure 4In the diagram, peaks 1 and 2 are the two largest peaks on the left and right. However, because their amplitudes are too close to those of the secondary peaks 3 and 4, and considering the errors that occur after FFT, when the main peaks are identified as peaks 1 and 4 or peaks 2 and 3, since they are not paired, the error is half a low-frequency value. In this case, it is necessary to find the four peaks with the largest amplitudes among the six peaks for energy centroid correction. Since these four peaks are necessarily paired, even if the main peaks are incorrectly identified, the error can be offset.
[0067] exist Figure 5 In the middle, the amplitudes of No. 3 and No. 5, and No. 4 and No. 6 are too close. Using the method described above to find the four peaks with the largest amplitudes, there is still a possibility that they are not paired. In this case, it is only necessary to find the two largest peaks on the left and right and perform energy center correction.
[0068] Step 3: Locate the left and right main peaks f1 and f2, and their corresponding left and right secondary peaks f′ on the spectrum obtained in Step 2. 11 f′ 12 f′ 21 f′ 22 There are a total of six peaks; in step three, when the ratio of the amplitudes of the left and right secondary peaks is... or When the value is greater than 3 or less than 1 / 3, the two largest peaks on the left and right are selected respectively, for a total of four peaks, to complete the energy centroid correction at point t. The purpose of energy centroid correction is to further improve frequency resolution and obtain the corrected peak value f. maxl1 f maxl2 f maxr1 f maxr2 Otherwise, select the largest peak value from the left and right sides respectively, for a total of two peak values, to complete the energy centroid correction at point t, and obtain the corrected peak value f. maxl f maxr ;
[0069] In step three, the expression for the energy centroid correction Y at point t is:
[0070]
[0071] Where Y represents the energy centroid correction result, Y n X represents the magnitude of a point in the FFT result. n This represents the frequency of a point in the FFT result;
[0072] Step 4: Calculate the undersampled center frequency f′ based on the corrected peak values obtained in Step 3; when selecting the four largest peak values for energy centroid correction in Step 3, the undersampled center frequency f′ is... b The expression is:
[0073]
[0074] When selecting the two largest peak values for energy centroid correction in step three, the expression for the undersampled center frequency f′ is:
[0075]
[0076] Step 5: Perform spectrum reconstruction on the calculation results of Step 4 to obtain the center frequency f of the ZP89 type frequency shift signal. b .
[0077] This scheme employs an undersampling method and improves computational accuracy through energy centroid correction. Only 1024 points of FFT calculation are required to achieve a center frequency accuracy of ±0.1Hz for the ZP89 frequency-shifting signal, far exceeding the ±1Hz requirement of the standard. The combined use of the two-peak and four-peak methods solves the problem of large fluctuations in center frequency that may occur in frequency domain analysis; it offers the technical advantages of high computational accuracy, low computational load, and high stability of calculation results.
[0078] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.
Claims
1. A method for detecting the center frequency of a ZP89 type frequency-shift signal, characterized in that: Includes the following steps: Step 1: Sample the ZP89 frequency shift signal using the undersampling method; Step 2: Perform FFT analysis on the sampled data; Step 3: Find the left and right main peaks on the spectrum obtained in Step 2. , and its corresponding left and right secondary peaks , , , There are six peaks in total; based on the ratio of the amplitudes of the left and right secondary peaks of either the left or right main peak: or The magnitude of the peak value is used to select the two or four largest peak values to complete the energy centroid correction at point t, resulting in the corrected peak value. This step specifically includes: when the ratio of the amplitudes of the left and right secondary peaks is... or When the value is greater than 3 or less than 1 / 3, the two largest peaks on the left and right are selected respectively, for a total of four peaks, to complete the energy centroid correction at point t, thus obtaining the corrected peak value. Otherwise, select the largest peak value from the left and right sides respectively, for a total of two peak values, to complete the energy centroid correction at point t, thus obtaining the corrected peak value. ; Step 4: Calculate the undersampled center frequency based on the corrected peak value obtained in Step 3. ; Step 5: Perform spectrum reconstruction on the calculation results of Step 4 to obtain the center frequency of the ZP89 frequency shift signal. .
2. The method for detecting the center frequency of a ZP89 type frequency shift signal according to claim 1, characterized in that: In step two, the sampled data is subjected to FFT analysis after being subjected to a Hanning window.
3. The method for detecting the center frequency of a ZP89 type frequency shift signal according to claim 1, characterized in that: In step two, a 1024-point FFT analysis is performed on the sampled data.
4. The method for detecting the center frequency of a ZP89 type frequency shift signal according to claim 3, characterized in that: In step two, when the sampled data is less than 1024 points, zeros are padded to the part that is less than 1024 points.
5. The method for detecting the center frequency of a ZP89 type frequency-shift signal according to claim 1, characterized in that: In step three, the energy centroid correction at point t is performed. The expression is: ； in, This represents the result of energy center of gravity correction. This represents the magnitude of a point in the FFT result. It represents the frequency of a point in the FFT result.
6. The method for detecting the center frequency of a ZP89 type frequency shift signal according to claim 1, characterized in that: In step four, the undersampled center frequency This is the average value of the corrected peak values obtained in step three.
7. The method for detecting the center frequency of a ZP89 type frequency shift signal according to claim 1, characterized in that: In step four, when selecting the four largest peaks in step three for energy centroid correction, the undersampled center frequency... The expression is: ； When selecting the two largest peak values for energy centroid correction in step three, the undersampled center frequency... The expression is: 。 8. A computer device, characterized in that: The method includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements a ZP89 type frequency shift signal center frequency detection method as described in any one of claims 1-7.
9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program that, when executed by a processor, implements a ZP89 type frequency shift signal center frequency detection method as described in any one of claims 1-7.