Time difference of arrival positioning method based on three-layer ionosphere model and regular station layout

Abstract

The present invention discloses a time difference of arrival positioning method based on a three-layer ionosphere model and regular station layout, which mainly solves the problem of large system error and low positioning accuracy of the existing time difference of arrival positioning method. The steps of the time difference of arrival positioning method are: 1) constructing a Bradley / Dudeney three-layer ionosphere model; 2) regularly arranging the measuring stations; 3) cross-correlation processing the measuring station data; 4) performing time difference positioning on the grid points; 5) using the position coordinates of the selected grid points as the result of the time difference of arrival positioning of the radiation source target to be located. Compared with the existing time difference of arrival positioning method, the present invention has a lower system error and improves the positioning accuracy of the time difference of arrival.

Description

Technical Field

[0001] The present invention belongs to the field of communication technology, and further relates to a time difference of arrival positioning method based on a three-layer ionosphere model and regular station layout in the field of synchronous positioning technology. The present invention can be applied to a shortwave positioning system, using the Bradley / Dudeney ionosphere model to model the shortwave propagation path, regularly arranging the measurement stations, and combining the time difference of arrival positioning technology to achieve the positioning of unknown radiation source targets. Background Art

[0002] The time difference of arrival positioning method of the radiation source target refers to a method of positioning using the time difference. The distance between the radiation source and the monitoring station is determined by measuring the time when the signal arrives at the monitoring station, thereby determining the position of the radiation source. This positioning method is widely used in aviation, navigation, rescue, radio monitoring, electronic countermeasures and other fields. Since the time difference of arrival positioning technology has the characteristics of simple system structure and high positioning accuracy, it has broad application prospects in the field of passive positioning. However, there is currently only a radiation source target arrival time difference positioning method based on a single-layer ionosphere model, which is quite different from the actual ionosphere situation, resulting in the lower limit of the positioning performance being not ideal and a large deviation in positioning accuracy.

[0003] In her paper "Geolocation of unknown emitters using TDOA of pathrays through the ionosphere by multiple coordinated distant receivers" (IEEEICASSP 2018), Wang Ting proposed a method for locating the time difference of arrival of the radiation source target based on a single-layer ionosphere model. The implementation steps of this method are as follows: First, the ray path of the shortwave signal is modeled using a single-layer ionosphere model to obtain the ground distance and group path corresponding to the shortwave propagation path. Then, the shortwave positioning problem is modeled using the time difference of arrival technology, and the positioning problem is described as a nonlinear optimization problem. Finally, the coordinates of the radiation source are solved according to the randomly arranged measurement station positions. Although this method can realize the positioning of the time difference of arrival of the radiation source target, the method still has the disadvantage that the ionosphere model used is a single-layer ionosphere, the ionosphere structure is too simple, and it is quite different from the ionosphere in the real environment, which will produce a large system error, and the measurement stations used are randomly arranged. Different measurement station arrangements will produce different positioning errors. Therefore, the positioning error will change with the change of the distribution of the measurement stations, which will lead to a large system error.

[0004] The China Institute of Radiowave Propagation (the 22nd Institute of China Electronics Technology Group Corporation) proposed a shortwave time difference positioning method based on ionospheric information for vehicle-borne and ship-borne reconnaissance systems in its patent application "A shortwave time difference positioning method based on ionospheric information" (application number: CN 201911069044.9, application publication number: CN 110954865 A). The implementation steps of this method are as follows: First, by randomly arranging in a fan-shaped area, the coordinates of the measurement station are generated to obtain the radio wave environment data. Then, the signal time difference data of the measurement station is extracted, and the ionospheric parameters are inverted and the regional ionosphere is reconstructed. Finally, the arrival time difference positioning is completed. Although this method can achieve shortwave time difference positioning, the method still has some shortcomings. The ionosphere model used is a single-layer ionosphere, the ionosphere structure is too simple, and it is quite different from the ionosphere in the real environment, which will cause large system errors. In addition, the measurement stations used are randomly arranged. Different measurement station arrangements will produce different positioning errors. Therefore, the positioning error will change with the change of the distribution of the measurement stations, which will lead to large system errors. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and to propose an arrival time difference positioning method based on a three-layer ionosphere model and regular station layout, so as to solve the problem of large system errors caused by positioning using a single-layer ionosphere model, and the problem of large positioning errors caused by random layout of measurement stations.

[0006] The specific idea of ​​the present invention to achieve the above-mentioned purpose is that, in the process of locating the time difference of arrival of the radiation source target, the present invention uses the Bradley / Dudeney three-layer ionosphere model to model the shortwave propagation path. Since the Bradley / Dudeney three-layer ionosphere model is divided into the E layer, the linear layer, and the F2 layer from the bottom to the top, it is closer to the actual ionosphere environment than the single-layer ionosphere model. Therefore, by using the Bradley / Dudeney three-layer ionosphere model to model the shortwave propagation path, the problem of large system errors caused by positioning with the single-layer ionosphere model can be solved. In the process of locating the time difference of arrival of the radiation source target, the present invention arranges the measuring stations regularly according to the regular topological structure. Since the positioning error will change with the change of the distribution of the measuring stations, the random arrangement of the stations will cause the positioning result to have a large system error. Therefore, the problem of large positioning errors caused by random arrangement of the measuring stations can be solved by regularly arranging the measuring stations.

[0007] The specific steps for achieving the purpose of the present invention are as follows:

[0008] Step 1: Construct the Bradley / Dudeney three-layer ionosphere model:

[0009] In order of altitude from low to high, the Bradley / Dudeney three-layer ionosphere is divided into the E layer, the linear layer, and the F2 layer from the bottom to the top;

[0010] Step 2: Regularly arrange the measurement stations:

[0011] (2a) selecting a station deployment area based on the radiation source target to be located that has been searched;

[0012] (2b) at least four measuring stations are arranged in a regular topological structure within the station layout area, and each measuring station points in the direction of the radiation source target to be located;

[0013] Step 3: Perform cross-correlation processing on the measurement station data:

[0014] (3a) starting all measurement stations to receive data on the radiation source target to be located;

[0015] (3b) performing cross-correlation processing on the target data of the radiation source to be located received by all measurement stations;

[0016] Step 4: Perform time difference positioning on the grid points:

[0017] (4a) Divide the circular area with a radius of 500 km centered on the radiation source to be located into K grid points with a spacing of 1 km;

[0018] (4b) Calculate the group path from each grid point to the station area;

[0019] (4c) Calculate the time difference between each grid point and the station area;

[0020] (4d) selecting the position coordinates of the grid point corresponding to the minimum value from the absolute value of the time difference between each grid point and the station area and the measured arrival time difference;

[0021] Step 5: Use the position coordinates of the selected grid points as the result of the arrival time difference positioning of the radiation source target to be located.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] First, the present invention applies the Bradley / Dudeney three-layer ionosphere model to the modeling of shortwave propagation paths, and obtains an ionosphere environment closer to the actual situation by dividing the ionosphere into E layer, linear layer, and F2 layer in order from low to high altitudes. This overcomes the defects of the prior art that the ionosphere structure is too simple, the ionosphere is quite different from the actual environment, and a large system error will be generated. This enables the present invention to have a lower system error than the arrival time difference positioning method based on a single-layer ionosphere, and improves the positioning accuracy of the arrival time difference positioning.

[0024] Secondly, the present invention arranges the measuring stations in a regular manner according to a regular topological structure when arranging the measuring stations, thereby overcoming the disadvantage that different arrangement schemes of measuring stations in the prior art will produce different positioning errors due to the random arrangement of the measuring stations, and the positioning error will change with the change of the distribution of the measuring stations, thereby causing a large system error. Therefore, the present invention can have a lower system error than the arrival time difference positioning method with random arrangement of the measuring stations, thereby improving the positioning accuracy of the arrival time difference positioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the present invention;

[0026] Figure 2 A topological diagram formed by four measuring stations of the present invention;

[0027] Figure 3 It is a simulation diagram of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0029] Reference Figure 1 , the specific steps for implementing the present invention are further described.

[0030] Step 1: Construct the Bradley / Dudeney three-layer ionosphere model.

[0031] In order from low to high altitude, the Bradley / Dudeney three-layer ionosphere is divided into the E layer, linear layer, and F2 layer from the bottom to the top.

[0032] The thickness of the E layer, linear layer, and F2 layer are respectively in the range of [30,50], [90,110], and [180,220], and are selected based on the measured data of the international reference ionosphere model, and the unit is km. The electron concentration distribution of the E layer follows the parabolic function form with the opening upward, the electron concentration distribution of the linear layer follows the linear function form, and the electron concentration distribution of the F2 layer follows the parabolic function form with the opening upward; the electron concentration of each layer increases with the increase of altitude.

[0033] Step 2: Arrange the measurement stations regularly.

[0034] The first step is to select the station layout area based on the searched radiation source target to be located.

[0035] In the second step, at least four measuring stations are arranged in the station layout area according to a regular topological structure, and each measuring station points in the direction of the radiation source target to be located.

[0036] The regular topological structure refers to connecting all the measuring stations with line segments, and the pattern formed is any one of a rectangle, a rhombus, a T-shape, a Y-shape, a parallelogram, and a trapezoid. The regular station layout scheme in this experiment is selected as a rectangular station layout. The longitude and latitude of the four measuring stations are [50,50], [50,-50], [-50,50], [-50,-50] (unit: °), and the topological graph formed by the four measuring stations is as follows: Figure 2 shown. Figure 2 The black dots in the figure represent measuring stations, and the dotted lines are the connecting lines between all measuring stations.

[0037] Step 3: Perform cross-correlation processing on the measurement station data.

[0038] The first step is to start all measurement stations to receive data of the radiation source target to be located.

[0039] The second step is to use the formula τ ij =τ i -τ j +n ij , cross-correlation processing is performed on the target data of the radiation source to be located received by all measurement stations. Among them, τ ij represents the arrival time difference measurement value of the data received by the i-th measurement station and the j-th measurement station, τ i represents the received data of the i-th measuring station, τ j represents the received data of the jth measuring station, n ij The noise represents the arrival time difference between the data received at the i-th measuring station and the j-th measuring station, and the noise follows a Gaussian distribution.

[0040] Step 4: Perform time difference positioning on the grid points.

[0041] The first step is to divide the circular area with a radius of 500 km centered on the radiation source target to be located into K grid points with a spacing of 1 km;

[0042] The second step is to calculate the group path from each grid point to the station layout area according to the following formula:

[0043]

[0044] Among them, P krepresents the group path from the kth grid point to the station area, k = 1, 2, 3...K, K represents the total number of grid points, r1 represents the radius from the center of the earth to the bottom of the E layer in the three-layer ionosphere model, r0 represents the radius of the earth, r represents the signal front of the radiation source target to be located, n0 represents the refractive index of the signal propagating in the air, cos represents the cosine operation, β0 represents the angle between the tangent of the signal emitted by the radiation source target to be located and the horizon, r2 represents the radius from the center of the earth to the top of the E layer in the three-layer ionosphere model, n1 represents the refractive index of the signal propagating in the E layer, r3 represents the radius from the center of the earth to the bottom of the F2 layer in the three-layer ionosphere model, n2 represents the refractive index of the signal propagating in the linear layer, r t represents the radius vector of the target signal of the radiation source to be located at the reflection point in the F2 layer, and n3 represents the refractive index of the signal propagating in the F2 layer.

[0045] The third step is to use the formula τ k =P k / c, calculate the time difference from each grid point to the station area, where τ k represents the time difference from the kth grid point to the station layout area, and c represents the speed of light.

[0046] The fourth step is to select the position coordinates of the grid point corresponding to the minimum value from the absolute value of the time difference between each grid point and the station area and the measured arrival time difference.

[0047] Step 5: Use the position coordinates of the selected grid points as the result of the arrival time difference positioning of the radiation source target to be located.

[0048] The effect of the present invention is further described below in conjunction with simulation experiments:

[0049] 1. Simulation experiment conditions:

[0050] The hardware platform of the simulation experiment of the present invention is: the processor is Intel i3-7100 CPU, the main frequency is 3.9GHz, and the memory is 4GB.

[0051] The software platforms for the simulation experiment of the present invention are: Windows 10 operating system and MATLAB R2016a.

[0052] 2. Simulation content and result analysis:

[0053] The simulation experiment of the present invention adopts the present invention and an existing technology (radiation source target arrival time difference positioning method based on single-layer ionosphere model) to respectively perform arrival time difference positioning on the radiation source target with the parameters set in Table 1 below, and obtains the Cramer-Rao lower bound of the positioning result as follows: Figure 3 shown.

[0054] Table 1 Experimental parameter settings list

[0055] Settings Value Total number of measuring stations 4 E layer entrance altitude (km) 6550 E layer half thickness (km) 20 F2 layer entrance height (km) 6690 F2 layer half thickness (km) 100 Height of shortwave signal reflection point (km) 6700 Speed ​​of light (m / s) <![CDATA[3*10 8 ]]> Earth radius (km) 6371 Shortwave signal operating frequency (MHz) 15 Randomly placed station No. 1 latitude and longitude (°) (129.87，39.88) Randomly placed station No. 2 latitude and longitude (°) (130.21，38.55) Randomly placed station 3 latitude and longitude (°) (132.77，33.81) Randomly placed station 4 latitude and longitude (°) (130.45，33.99) Latitude and longitude of station 1 in regular layout (°) (50，50) Latitude and longitude of station 2 with regular station layout (°) (50，-50) Latitude and longitude of station 3 with regular layout (°) (-50，50) Latitude and longitude of station 4 with regular layout (°) (-50，-50)

[0056] The radiation source target arrival time difference positioning method based on the single-layer ionosphere model refers to the radiation source target arrival time difference positioning method proposed by Wang Ting et al. in their paper "Geolocation of unknown emitters using TDOA of path rays through theionosphere by multiple coordinated distant receivers" (IEEE ICASSP 2018).

[0057] Combine the following Figure 3 The simulation diagram of the present invention is further described.

[0058] Figure 3 The method proposed in the present invention is a method for locating the time difference of arrival of a radiation source target based on a single-layer ionosphere model. Under the conditions of time difference of arrival positioning based on an ionosphere model, two different ionosphere models (a three-layer ionosphere model and a single-layer ionosphere model) are used to obtain Cramer-Rao lower bound curves of the time difference of arrival positioning of the two different methods. Figure 3 The horizontal axis in represents the standard deviation of the arrival time difference positioning measurement error, in ns, and the vertical axis represents the Cramer-Rao lower bound of the arrival time difference positioning, in meters. Figure 3 The curve marked with “—○—” in the figure represents the Cramer-Raw lower bound curve of arrival time difference positioning using the method of the present invention using a three-layer ionosphere model and regular station layout. Figure 3 The curve marked with “—□—” in the figure represents the Cramer-Rao lower bound curve of the arrival time difference positioning method of the radiation source target based on the single-layer ionosphere model when using the single-layer ionosphere model and random stations for arrival time difference positioning.

[0059] Depend on Figure 3 It can be seen from the simulation experiment diagram that the present invention has a lower Cramer-Rao lower bound in the range of [0,1000] (unit: ns) of the standard deviation of the arrival time difference measurement error, compared with the radiation source target arrival time difference positioning method based on the single-layer ionosphere model and random stations. This shows that the present invention can effectively improve the positioning accuracy in the arrival time difference positioning of the radiation source target.

[0060] The above simulation experiments show that the method of the present invention can reduce the system error of arrival time difference positioning by applying the Bradley / Dudeney three-layer ionosphere model to the shortwave propagation path modeling and by regularly arranging the measurement stations. It solves the problems in the prior art that the ionosphere structure is too simple, the ionosphere is quite different from the real environment, and random station arrangement will cause large system errors. The method is a practical arrival time difference positioning method.

Claims

1. A time difference of arrival positioning method based on a three-layer ionosphere model and regular station layout, characterized in that: The Bradley / Dudeney three-layer ionosphere model is used to model the shortwave propagation path and the measurement stations are arranged regularly. The steps of the positioning method include the following: Step 1: Construct the Bradley / Dudeney three-layer ionosphere model: In order of altitude from low to high, the Bradley / Dudeney three-layer ionosphere is divided into the E layer, the linear layer, and the F2 layer from the bottom to the top; Step 2: Regularly arrange the measurement stations: (2a) selecting a station deployment area based on the radiation source target to be located that has been searched; (2b) at least four measuring stations are arranged in a regular topological structure within the station layout area, and each measuring station points in the direction of the radiation source target to be located; Step 3: Perform cross-correlation processing on the measurement station data: (3a) starting all measurement stations to receive data on the radiation source target to be located; (3b) According to τ ij =τ i -τ j +n ij Formula, cross-correlation processing is performed on the target data of the radiation source to be located received by all measurement stations, where τ ij represents the arrival time difference measurement value of the data received by the i-th measurement station and the j-th measurement station, τ i represents the received data of the i-th measuring station, τ j represents the received data of the jth measuring station, n ij The noise represents the arrival time difference between the data received at the i-th measuring station and the j-th measuring station, and the noise follows a Gaussian distribution; Step 4: Perform time difference positioning on the grid points: (4a) Divide the circular area with a radius of 500 km centered on the radiation source to be located into K grid points with a spacing of 1 km; (4b) Calculate the group path from each grid point to the station area: Among them, P k represents the group path from the kth grid point to the station area, k = 1, 2, 3...K, K represents the total number of grid points, r1 represents the radius from the center of the earth to the bottom of the E layer in the three-layer ionosphere model, r0 represents the radius of the earth, r represents the signal front of the radiation source target to be located, n0 represents the refractive index of the signal propagating in the air, cos represents the cosine operation, β0 represents the angle between the tangent of the signal emitted by the radiation source target to be located and the horizon, r2 represents the radius from the center of the earth to the top of the E layer in the three-layer ionosphere model, n1 represents the refractive index of the signal propagating in the E layer, r3 represents the radius from the center of the earth to the bottom of the F2 layer in the three-layer ionosphere model, n2 represents the refractive index of the signal propagating in the linear layer, r t represents the radius vector of the target signal of the radiation source to be located at the reflection point in the F2 layer, and n3 represents the refractive index of the signal propagating in the F2 layer; (4c) Calculate the time difference from each grid point to the station area: τ k =P k / c, where τ k represents the time difference from the kth grid point to the station area, and c represents the speed of light; (4d) selecting the position coordinates of the grid point corresponding to the minimum value from the absolute value of the time difference between each grid point and the station area and the measured arrival time difference; Step 5: Use the position coordinates of the selected grid points as the result of the arrival time difference positioning of the radiation source target to be located.

2. The arrival time difference positioning method based on the three-layer ionosphere model and regular station layout according to claim 1 is characterized in that: The thicknesses of the E layer, linear layer, and F2 layer described in step 1 are in the range of [30,50], [90,110], and [180,220], respectively, which are values ​​selected based on the measured data of the international reference ionosphere model, and are in units of km; the electron concentration distribution of the E layer obeys a parabolic function with an opening upward, the electron concentration distribution of the linear layer obeys a linear function, and the electron concentration distribution of the F2 layer obeys a parabolic function with an opening upward; the electron concentration of each layer increases with increasing altitude.

3. The arrival time difference positioning method based on the three-layer ionosphere model and regular station layout according to claim 1 is characterized in that: The regular topological structure in step (2b) means that all measuring stations are connected by line segments, and the pattern formed is any one of a rectangle, a rhombus, a T shape, a Y shape, a parallelogram, and a trapezoid.

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