A method and device for suppressing geomagnetic signal interference based on wavelet transform

Abstract

The application provides a geomagnetic signal interference suppression method and device based on wavelet transform. The method determines whether there is track shunting interference according to signals collected by a geomagnetic sensor. When there is track shunting, the original signals are decomposed in the frequency domain by using an m-level wavelet decomposition method on different resolution levels, and high-frequency components are removed, so that the interference signals are removed. The application uses the characteristic that high-frequency components contain geomagnetic abnormal fields and interference field signals, uses the m-level wavelet decomposition method to remove the interference signals, so that the high-frequency interference signals are suppressed, and the accuracy of positioning by using the geomagnetic signals is ensured.

Description

Technical Field

[0001] This invention belongs to the field of rail transit technology, specifically relating to a method and device for suppressing geomagnetic signal interference based on wavelet transform. Background Technology

[0002] Rail vehicles are essential transportation tools for human travel and freight transport, and providing real-time, reliable positioning information is a crucial measure to ensure their safe operation. Traditional rail vehicles primarily rely on signals or transponders for positioning. The drawback of this method is the need to deploy numerous active and passive devices on the track, resulting in high deployment and maintenance costs. With the successful deployment of the BeiDou-3 network, satellite navigation and positioning systems have begun to be deployed on rail vehicles. However, in tunnel environments, positioning is interrupted due to the inability to receive navigation signals; furthermore, in complex electromagnetic environments, navigation signals themselves are susceptible to interference, making it impossible to provide reliable positioning services for rail vehicles.

[0003] The Earth's magnetic field is an inherent resource, providing humanity with a natural coordinate system. Geomagnetic navigation, which uses real-time geomagnetic data measured by magnetic sensors to match geomagnetic reference maps (calculated by geomagnetic models or obtained through pre-measurement) stored in computers for positioning, has begun to be gradually applied to rail vehicle positioning. However, because rail vehicles often contain a large number of ferromagnetic structures, high-speed vehicles, when encountering oncoming or same-direction passing situations, interact with adjacent vehicles, generating strong induced magnetic field interference. This interference obscures the geomagnetic anomaly field characteristics, ultimately leading to the failure of geomagnetic matching during the interference period. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for suppressing geomagnetic signal interference based on wavelet transform, which can suppress the interference caused by misalignment of trains to geomagnetic signals, thereby ensuring the accuracy of geomagnetic matching positioning of rail vehicles.

[0005] The technical solution for implementing the present invention is as follows:

[0006] On the one hand, the present invention provides a method for suppressing geomagnetic signal interference based on wavelet transform, which specifically includes the following steps:

[0007] The presence of track misalignment interference is determined based on signals collected by the geomagnetic sensor.

[0008] When track misalignment occurs, the m-level wavelet decomposition method is used to perform frequency domain decomposition on the original signal at different resolution levels to remove high-frequency components, thereby eliminating interference signals.

[0009] Furthermore, the geomagnetic sensor described in this invention is a three-axis fluxgate magnetic sensor.

[0010] Furthermore, the present invention describes determining whether track misalignment interference exists based on signals collected by a geomagnetic sensor as follows:

[0011] For the X-axis magnetic field data in the triaxial magnetic field data output by the geomagnetic sensor, the variance C is calculated. k When the C k When the value is greater than μ, it is determined that there is a train misoperation interference;

[0012]

[0013] Where n is the window length for variance calculation, mag i The intensity of the geomagnetic field along the X-axis. denoted as the average magnetic field strength within the window, μ as a pre-set threshold, and k as the time.

[0014] Furthermore, the present invention describes determining whether track misalignment interference exists based on signals collected by a geomagnetic sensor as follows:

[0015] Magnetic sequences are collected at geographically equal intervals, and the similarity r(u,v) between the magnetic sequences of the front and rear of the vehicle is calculated using the following formula. When the similarity r(u,v) is less than a set threshold, it is considered that there is a vehicle misoperation interference.

[0016]

[0017] Where u is the geographically evenly spaced geomagnetic sequence collected by the vehicle's front end, u k-l Let u be the mean of the geomagnetic sequence at the front of the vehicle, and v be the geographically evenly spaced magnetic sequences collected at the rear of the vehicle. k For the k-th geomagnetic data, denoted as the mean of the magnetic sequence at the rear of the vehicle, l is the number of magnetic sequences corresponding to the length of the vehicle body, Nm is the length of the magnetic field sequence window, m represents the starting sequence number of the window, and N represents the ending sequence number of the window.

[0018] Furthermore, the present invention is based on variance C k If the presence of passing interference is determined based on similarity r(u,v), then the final determination is that passing interference exists.

[0019] Furthermore, the threshold μ described in this invention is 2.5 × 10⁻⁶. 7 .

[0020] Furthermore, the wavelet layer number m in this invention is determined by the following formula (2).

[0021] f low *2 m <f s <f low *2 m+1 (3)

[0022] Among them, f low For the magnitude of the low-frequency component, f s This represents the sampling rate of the geomagnetic data.

[0023] Furthermore, the low-frequency component magnitude f of the present invention low The value is 0.16Hz.

[0024] Furthermore, the geomagnetic sensor described in this invention is a triaxial fluxgate magnetometer sensor, and the sampling rate of the sensor is 30Hz.

[0025] On the other hand, the present invention provides a geomagnetic signal interference suppression device based on wavelet transform, which includes a signal processing module. When there is track misalignment interference, the signal processing module uses an m-level wavelet decomposition method to perform frequency domain decomposition on the original signal at different resolution levels, removes high-frequency components, and thus eliminates the interference signal.

[0026] Beneficial effects

[0027] First, this invention utilizes the characteristic that high-frequency components contain geomagnetic anomaly fields and interference field signals, and uses the m-level wavelet decomposition method to remove interference signals, thereby suppressing high-frequency interference signals and ensuring the accuracy of positioning using geomagnetic signals.

[0028] Second, the present invention utilizes the X-axis magnetic field data variance detection method to detect train misoperation interference in the time domain. Since train misoperation has a significant impact on X-axis magnetic field data, this method can accurately detect whether train misoperation interference exists.

[0029] Third, when a train misoperation occurs, due to the randomness of the interference, the similarity of the detection magnetic fields at the front and rear of the train decreases. This invention utilizes this characteristic to calculate the similarity of the magnetic sequences at the front and rear of the train, thereby accurately determining whether a train misoperation occurs.

[0030] Fourth, the present invention uses two detection methods for passing interference to make a joint judgment, which can ensure that the judgment result has higher accuracy.

[0031] Fifth, through experiments, this invention has found that geomagnetic signals that do not contain interference are generally concentrated below 0.16Hz. Therefore, by selecting 0.16Hz as the low-frequency component and removing the high-frequency component, interference signals can be eliminated. Attached Figure Description

[0032] Figure 1 This is a flowchart of a magnetic field interference suppression method based on wavelet transform;

[0033] Figure 2 It is the variance of the geomagnetic intensity along the X-axis of the trajectory vehicle;

[0034] Figure 3 (a) is a schematic diagram showing the similarity of the magnetic field sequences before and after the magnetic interference of the fault-free vehicle. Figure 3 (b) Schematic diagram showing that magnetic interference from misaligned trains occurs, and the magnetic field sequences before and after are no longer similar;

[0035] Figure 4 It is a time-domain and frequency amplitude distribution map of geomagnetic data;

[0036] Figure 5 This is a comparison chart of the original geomagnetic data signal and the low-frequency reconstructed signal. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0038] It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other; and, based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0039] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0040] This application provides a method for suppressing magnetic field interference based on wavelet transform, the specific implementation process of which is as follows:

[0041] First, the geomagnetic sensor collects geomagnetic data in real time; second, time-domain interference detection is performed. If interference is detected, wavelet decomposition is performed on the geomagnetic data to retain the low-frequency components that reflect the overall trend of geomagnetic variation, while removing high-frequency interference components, such as... Figure 1 As shown; the signal is recovered again from the retained frequency components, and the processed geomagnetic data is output; if no interference is detected, the geomagnetic data is output directly. The specific process of each step is explained in detail below:

[0042] I. Geomagnetic Sensor Data Acquisition

[0043] The geomagnetic sensor is physically connected to the data acquisition device. Once the device is powered on, it begins to work, and the high-frequency data collected by the geomagnetic sensor is transmitted at high speed to the data acquisition device.

[0044] In this embodiment, the geomagnetic sensor device adopts a three-axis fluxgate magnetic sensor. Since the train travels at a high speed, the faster the speed and the longer the distance traveled in the same amount of time, in order to maximize the spatial resolution of the geomagnetic data and ensure the geomagnetic matching accuracy, a high sampling rate sensor is required. At the same time, in order to achieve accurate measurement of transient electromagnetic signals and ensure the geomagnetic matching positioning accuracy, the geomagnetic sensor should be a high-speed data processing sensor, and the data transmission system should be a high-speed transmission system.

[0045] II. Interference Detection

[0046] Interference caused by passing trains is mainly affected by the passing of two trains, so the duration of the interference is mainly affected by the length of the train from the interference source.

[0047] The geomagnetic sensor outputs triaxial magnetic field data: lateral (X-axis), forward (Y-axis), and vertical (Z-axis). Since the interference source of passing lanes originates from parallel lanes, it has a particularly significant impact on the lateral magnetic field. Figure 2 As shown, interference detection is achieved by calculating the variance of the X-axis magnetic field. The formula for calculating the magnetic field variance at time k is as follows:

[0048]

[0049] Where n is the window length for variance calculation, and since the interference from the X-axis magnetic field strength is more significant, mag i Let X be the geomagnetic field strength along the X-axis. This represents the average magnetic field strength within the window. Since the variance at the time of interference is significantly higher than at the time of no interference, a suitable threshold μ is set. The threshold setting should be determined by considering the performance of the magnetic sensor and the numerical characteristics of the interference signal. When C... k When the value exceeds the threshold, a signal can be generated indicating that a train misoperation has been detected.

[0050] Furthermore, to accurately detect the presence of interference, this embodiment also designs a dual magnetic interference detection method, such as... Figure 3 As shown, the detection principle is as follows: During vehicle movement, the road magnetic fields detected at the front and rear of the vehicle have similar magnetic field profiles, but also exhibit a time delay. When interference occurs due to passing, the similarity between the detected magnetic fields at the front and rear of the vehicle decreases due to the randomness of the interference. Interference detection can be achieved by calculating the correlation of the magnetic sequences detected at these different positions.

[0051] Magnetic sequences were collected at geographically equal intervals, and the similarity between the magnetic sequences of the front and rear of the vehicle was calculated using the following formula:

[0052]

[0053] Where u is the geographically evenly spaced geomagnetic sequence collected by the vehicle's front end, u k-l Let u be the mean of the geomagnetic sequence at the front of the vehicle, and v be the geographically evenly spaced magnetic sequences collected at the rear of the vehicle. k Let v be the k-th geomagnetic data point, v be the mean of the magnetic sequence at the rear of the vehicle, l be the number of magnetic sequences corresponding to the vehicle length, and Nm be the length of the magnetic field sequence window, where m represents the starting number of the window and N represents the ending number of the window.

[0054] The current and last two sequences are completely identical, with r(u,v) value of 1. Based on experience, the threshold for interference detection is set to 0.9. If r(u,v) < 0.9, it indicates a decrease in magnetic field similarity, and interference has been detected.

[0055] III. Wavelet Decomposition of Geomagnetic Data

[0056] When geomagnetic data contains train mishap interference, the low-frequency components of the geomagnetic signal reflect the overall trend of the signal, while the high-frequency components contain signal details of geomagnetic anomalies and interference fields, such as geomagnetic anomalies caused by regular track laying and magnetic field interference caused by train mishaps. To reduce the impact of magnetic field interference, wavelet decomposition is used to perform frequency domain decomposition on the geomagnetic signal. This preserves the low-frequency components that reflect the overall trend of geomagnetic variation while removing high-frequency interference components, thus suppressing the influence of interference on the geomagnetic signal. The frequency domain decomposition process is as follows: Figure 1 As shown, the signal is decomposed into low-frequency and high-frequency components, which is called the first-level decomposition. Then, the decomposed low-frequency component is further decomposed into low-frequency and high-frequency components, which is called the second-level decomposition, and so on.

[0057] The number of wavelet decomposition layers is affected by the sampling rate of the geomagnetic data and the magnitude of the low-frequency components. The specific formula is as follows:

[0058] f low *2 m <f s <f low *2 m+1 (3)

[0059] Among them, f low For the magnitude of the low-frequency component, f s denoted as the geomagnetic data sampling rate, and m is the wavelet layer number to be determined.

[0060] The “sym8” wavelet fundamental wavelet is used in the embodiments of this application.

[0061] IV. Signal Reconstruction

[0062] Signal reconstruction is the inverse transform of wavelet transform. By reconstructing the low-frequency components, we can obtain the geomagnetic signal after interference suppression, and then use the geomagnetic signal after interference suppression for positioning.

[0063] This invention utilizes the X-axis magnetic field data variance detection method to detect train misoperation interference in the time domain. Upon detection of interference, wavelet decomposition is used to suppress high-frequency interference signals. By limiting the interference suppression process to the time domain interval of the train misoperation interference, only the overall signal variation trend is preserved within the interference interval, effectively suppressing the impact of high-amplitude, high-frequency interference signals on geomagnetic matching positioning. In the non-interference interval, the overall signal variation trend and detailed components are preserved, ensuring no loss of original positioning performance in this interval. Therefore, the interference suppression method effectively reduces the impact of train misoperation interference on the geomagnetic matching positioning of rail vehicles.

[0064] Example:

[0065] In order to preserve the overall trend and detailed components of the signal in the non-interference zone and to ensure that the original positioning performance is not lost in the zone, this application embodiment uses a geomagnetic device mounted on a Harmony locomotive to collect geomagnetic data and verifies the effectiveness of the method of the present invention.

[0066] I. Geomagnetic Sensor Data Acquisition

[0067] A high-precision triaxial fluxgate sensor was used to collect geomagnetic data. The magnetic field resolution was 1 nT and the sampling frequency was 30 Hz. A total of 470 seconds of geomagnetic data was collected, including about 20 seconds of passing interference.

[0068] II. Interference Detection

[0069] Interference detection is achieved by calculating the variance of the X-axis magnetic field, C k The interference threshold is set to 2.5 × 10. 7 This method can successfully detect interference from erroneous vehicles. To further improve the accuracy of interference detection, the similarity r(u,v) between the magnetic sequences of the front and rear of the vehicle is calculated for interference detection.

[0070] III. Wavelet Decomposition of Geomagnetic Data

[0071] The geomagnetic data spectrum was analyzed using short-time Fourier transform. The time-domain and frequency amplitude distributions of the geomagnetic data are as follows: Figure 4 As shown, the low-frequency signal is concentrated in the range of 0 to 0.16 Hz. Given that the sampling rate is 30 Hz, an 8-level wavelet decomposition is used, and the wavelet basis is "sysm8".

[0072] IV. Signal Reconstruction

[0073] After reconstructing the low-frequency components, such as Figure 5 As shown, the low-frequency component can reflect the overall trend of geomagnetic signal changes.

[0074] This application provides a geomagnetic signal interference suppression device based on wavelet transform, including a signal processing module. When track misalignment interference exists, the signal processing module uses an m-level wavelet decomposition method to perform frequency domain decomposition on the original signal at different resolution levels, removing high-frequency components, thereby eliminating the interference signal.

[0075] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for geomagnetic signal interference suppression based on wavelet transform, characterized in that, Specifically, the following steps are included: The presence of track misalignment interference is determined based on signals collected by the geomagnetic sensor. When there is a track misalignment, the m-level wavelet decomposition method is used to decompose the original signal in the frequency domain at different resolution levels to remove high-frequency components, thereby eliminating the interference signal. The determination of whether track misalignment interference exists based on signals collected by the geomagnetic sensor is performed using either method A or method B: Method A: The X-axis magnetic field data in the three-axis magnetic field data output by the geomagnetic sensor is subjected to variance calculation When the , it is determined that there is a wrong vehicle interference; （1） in, The window length for variance calculation. The intensity of the geomagnetic field along the X-axis. This represents the average magnetic field strength within the window. For a pre-set threshold, Indicates time; Method B: Magnetic sequences were collected at geographically equal intervals, and the similarity between the magnetic sequences at the front and rear of the vehicle was calculated using the following formula. When the similarity If the value is less than the set threshold, then a train misoperation is considered to exist. （2） in, Geographically evenly spaced geomagnetic sequences were collected from the front of the vehicle. For the first One geomagnetic data point, This represents the mean of the geomagnetic sequence at the front of the vehicle. Geographically evenly spaced magnetic sequences were collected from the rear of the vehicle. For the first One geomagnetic data point, This represents the mean of the magnetic sequence at the rear of the vehicle. The number of magnetic sequences corresponding to the vehicle body length. The length of the magnetic field sequence window. Indicates the starting number of the window. Indicates the window's termination number.

2. The method for geomagnetic signal interference suppression based on wavelet transform according to claim 1, characterized in that, The geomagnetic sensor is a three-axis fluxgate magnetometer.

3. The method for geomagnetic signal interference suppression based on wavelet transform according to claim 1, characterized in that, When based on variance determining that there is a misregistration disturbance and based on similarity When determining that there is a misregistration disturbance, then a final determination is made that there is a misregistration disturbance.

4. The method for geomagnetic signal interference suppression based on wavelet transform according to claim 1, characterized in that, the threshold value is set to .

5. The method for suppressing geomagnetic signal interference based on wavelet transform according to claim 1, characterized in that, The wavelet layer number m is determined by the following formula (3), （3） wherein, is a low frequency component size, is a geomagnetic data sampling rate.

6. The method for geomagnetic signal interference suppression based on wavelet transform according to claim 5, characterized in that, the low frequency component size is 0.16 Hz.

7. The method for geomagnetic signal interference suppression based on wavelet transform according to claim 1, characterized in that, The geomagnetic sensor is a triaxial fluxgate magnetometer with a sampling rate of 30Hz.

8. A geomagnetic signal interference suppression device based on wavelet transform, employing the interference suppression method of claim 1, characterized in that, The system includes a signal processing module. When track misalignment interference exists, the signal processing module uses an m-level wavelet decomposition method to perform frequency domain decomposition on the original signal at different resolution levels, removing high-frequency components, thereby eliminating the interference signal.

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