CN112636893A - Method for improving eLoran system time service precision by using ASF grid and differential station - Google Patents

Method for improving eLoran system time service precision by using ASF grid and differential station Download PDF

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CN112636893A
CN112636893A CN202011365905.0A CN202011365905A CN112636893A CN 112636893 A CN112636893 A CN 112636893A CN 202011365905 A CN202011365905 A CN 202011365905A CN 112636893 A CN112636893 A CN 112636893A
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asf
time
spacial
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eloran
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李云
燕保荣
郭伟
华宇
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National Time Service Center of CAS
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter
    • H04L7/0016—Arrangements for synchronising receiver with transmitter correction of synchronization errors
    • H04L7/002—Arrangements for synchronising receiver with transmitter correction of synchronization errors correction by interpolation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging

Abstract

The invention provides a method for improving the time service precision of an eLoran system by utilizing an ASF grid and a differential station, wherein the differential station carries out real-time difference measurement and calculates a differential correction number model to be transmitted to peripheral users; establishing an ASF grid database by using dynamic measurement data and an inverse bilinear interpolation algorithm; the user calculates the time delay of the user, and calculates the difference correction number according to the difference information to obtain the time component of the ASF; then, searching the located grid, and calculating the space component of the ASF according to the position information and the ASF values of the four vertexes of the grid; and finally, correcting the signal propagation delay by using the time component and the space component together to obtain more accurate signal propagation delay, thereby improving the time service precision of the system.

Description

Method for improving eLoran system time service precision by using ASF grid and differential station
Technical Field
The invention belongs to the technical field of communication, and relates to a time service method.
Background
With the deep and wide application of the GNSS system, the vulnerability of the GNSS system is gradually exposed, and the eLoran system is selected as a backup system of the GNSS system by virtue of the advantages of good signal stability, high reliability, strong anti-interference performance, long propagation distance and the like; however, the eLoran system and the GNSS system have a certain gap in terms of accuracy. Expert scholars in various countries begin to study methods for improving the precision of the eLoran system. The ASF grid improves eLoran precision from spatial dimension, and can realize time service precision superior to 200 ns; the time service precision of the eLoran system is improved by the time dimension of the differential station, and is close to 100 ns. The differential station significantly improves the accuracy of the eLoran system, but has some gap with the GNSS system. How to further improve the precision of the eLoran system and narrow the gap between the precision of the eLoran system and the precision of the GNSS system is an urgent problem to be solved.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method for improving the precision of an eLoran system by comprehensively applying an ASF grid and a differential station.
The technical scheme adopted by the invention for solving the technical problem comprises the following steps:
(1) calculating the large ground wire distance of signal propagation according to the antenna position of the eLoran reference receiver and the transmitting antenna position of the transmitting station, and then calculating the signal propagation one-time delay PF;
(2) measuring and collecting the time difference N between a 1PPS signal output by an eLoran reference receiver and a standard time-frequency signal by using the standard time-frequency signal;
(3) using time difference data N acquired within a set durationiThe PF is deducted to obtain an additional secondary time delay value ASF of the differential station at the ith momentiForecasting the difference correction number model y ═ a in the set time by using least square fitting1t+a0Model coefficient a of1、a0Y represents ASF, t represents time and is sent to the surrounding users;
(4) in an arbitrarily set area, measuring the ASF (acquired Signal propagation time delay) according to an arbitrarily set trackspacial；
(5) If there are k test points in a grid, k spatial components ASF are measuredspacial(ii) a ASF using these k test pointsspacial_jValue back-pushing grid topASF of dotsspacial；
(6) Calculate each vertex ASFspacialAfter the value, according to the format [ Longj,Latij,ASFspacial_j]Stored into ASF grid database, wherein Longj、Latij、ASFspacial_jRespectively representing longitude, latitude and ASF values of the grid vertex;
(7) the user calculates the large ground distance of signal propagation according to the antenna position of eLoran receiver and the transmitting antenna position of the transmitting station, and then calculates the one-time delay PF of signal propagationUser' s；
(8) Calculating ASF time component ASF using difference correction number modeltemperalCorrecting the propagation delay TOA from the time dimension to PFUser' s+ASFtemperal；
(9) Calculating ASF space component by using bilinear interpolation algorithm, and correcting signal propagation delay TOA (time of arrival) ═ PF + ASF from space dimensiontemperal+ASFsapcial。
The step (1) calculates the time delay of signal propagation
Figure RE-GDA0002946319680000021
Wherein n issRepresenting the atmospheric refractive index, C the speed of light, d the distance of the large ground from the launch pad to the test point signal propagation.
The step (4) takes 1PPS output by the GPS receiver or the GNSS receiver or the BD receiver as a reference standard, and compares the reference standard with the time difference M of 1PPS output by the eLoran reference receiver by using a time interval counteriObtaining ASF 'of the test point'i＝MiPF', and then deducting the ASF of the differential station at the same momentiObtaining space component ASF of test point relative to differential stationspacial＝ASF'i-ASFi。
The step (5) establishes a matrix equation according to a bilinear interpolation algorithm, wherein C1, C2, C3 and C4 represent ASF of grid verticesspacial，
Figure RE-GDA0002946319680000022
ASF for obtaining grid vertex by solving matrix equationspacialValues, wherein the coefficient matrix
Figure RE-GDA0002946319680000023
Figure RE-GDA0002946319680000031
Assuming that there are (m-1) × n meshes in one region and there are m × n corresponding mesh vertices, the mesh vertices are arranged to obtain C ═ C [ -n [ -C ] ]1,C2…Cn,Cn+1,Cn+2…C2n,C(m-1)*n+1,C(m-1)*n+2…Cm*n]', equation of the ith test point
(1-αi)·(1-βi)·C2+(1-αi)·βi·C3+αi·(1-βi)·Cn+2+αi·βi·Cn+3＝ASFspacial_iThe matrix equation is A x C ═ ASFspacial_iSolving the matrix equation to obtain C, i.e. ASF of the grid vertexspacialThe value is obtained.
In the step (9), the coordinates of the user are (x, y), and the coordinates of four vertexes of the grid are (x, y) respectively1,y1)、 (x2,y2)、(x3,y3) And (x)4,y4) Four-point ASFspacialASF with values of C1, C2, C3 and C4, respectively, at the point (x, y) to be interpolatedsapcial＝(1-α)[(1-β)*C1+β*C3]+α[[(1-β)*C2+β*C4]]Wherein
Figure RE-GDA0002946319680000032
The invention has the beneficial effects that: the method comprehensively utilizes the advantages of the ASF grid and the differential station technology, corrects the propagation delay of the signal from the space dimension and the time dimension, breaks through the limitation that the grid only corrects the propagation delay from the space dimension, breaks through the limitation that the differential station only corrects the propagation delay from the time dimension, and improves the time service precision of the eLoran system from 100ns to 50ns when only the differential station acts.
Compared with the traditional ASF grid establishing method, the ASF grid establishing method adopts the inverse operation of dynamic testing and bilinear interpolation algorithm and is based on the space component ASF of the test point relative to the differential stationspacialAnd the space component is convenient for a user to correct. Thus, instead of the ASF of the mesh vertices being stored by the mesh database, the ASF of the mesh vertices are stored relative to the spatial components ASF of the differencing stationsspacial。
Drawings
FIG. 1 is a layout of a grid;
FIG. 2 is a schematic diagram of a grid;
FIG. 3 is a flow chart;
FIG. 4 is a dynamic test trace.
Detailed Description
The present invention will be further described with reference to the following drawings and examples, which include, but are not limited to, the following examples.
The invention provides an ASF (enhanced secondary factor) grid of an eLoran (enhanced Long Range navigation) system established by utilizing inverse operation of a bilinear interpolation algorithm, and a user corrects propagation delay of received signals from time and space latitude by utilizing the combined action of the ASF grid and differential information of a differential station, so that the time service precision of the eLoran system is improved.
The idea of the invention is as follows: the differential station must have a standard time-frequency signal, real-time difference measurement is carried out, and a differential correction number model is calculated and transmitted to peripheral users; firstly, an ASF grid database is established by utilizing dynamic measurement data and an inverse bilinear interpolation algorithm. Firstly, a user calculates the time delay of the user, and calculates a difference correction number according to difference information to obtain an ASF time component; then, searching the located grid, and calculating the space component of the ASF according to the position information and the ASF values of four vertexes of the grid; and finally, correcting the signal propagation delay by using the time component and the space component together to obtain more accurate signal propagation delay, thereby improving the time service precision of the system.
The technical scheme of the invention comprises the following steps:
(1) the differential station calculates one-time delay PF according to the position information
And calculating the large ground distance of signal propagation according to the antenna position of the eLoran reference receiver and the transmitting antenna position of the transmitting station, and then calculating the signal propagation one-time delay PF according to a formula (1-1).
Figure RE-GDA0002946319680000041
Wherein n issIndicating the refractive index of the atmosphere, international standard atmospheric regulation ns1.000315, the speed of light C is 0.299792458 km/mus, and d is the distance from the broadcaster to the ground line where the test point signal travels.
(2) Differential station test acquisition data
And measuring and acquiring the time difference N between the 1PPS signal output by the eLoran reference receiver and the standard time-frequency signal by using the standard time-frequency signal, and acquiring one datum every second.
(3) Model for calculating difference correction
PF was subtracted from N using 600 data N collected over 10 minutesiI is more than or equal to 1 and less than or equal to 600, and subtracting PF to obtain ASF value ASF of the differential station at the ith momenti＝NiPF (added secondary delay factor), forecasting a difference correction model within 5 minutes by using least square fitting (modeling the ASF value of the current 10 minutes of the difference station by using least square fitting, and y is a1t+a0Y denotes ASF, t denotes time) y ═ a1t+a0Model coefficient a of1、 a0And sending the data to peripheral users (the distance between the user and the differential station is not more than 55 km).
(4) Testing collected data
In an arbitrarily set area, the propagation delay of the acquired signal is measured according to an arbitrarily set track, and the specific process takes 1PPS output by a GPS receiver (or a GNSS receiver or a BD receiver) as a reference standard, so as to facilitate the acquisition of the signal propagation delayThe time interval counter compares the time difference M of the 1PPS output by the GPS and the 1PPS output by the eLoran reference receiver. MiSubtracting the one-time delay PF ' of the test point to obtain ASF ' of the test point 'i＝MiPF', and then deducting the ASF of the differential station at the same momentiObtaining space component ASF of test point relative to differential stationspacial＝ASF'i-ASFi. The calculation formula of the first time delay PF is shown as 1-1, and ASFspacialThe calculation of (a) is shown in equations 1-2.
ASFspacial＝ASF'i-ASFi (1-2)
(5) ASF value calculation by inverse bilinear interpolation algorithm
If there are k test points in a grid, k spatial components ASF are measuredspacial(ii) a ASF using these k test pointsspacial_jASF of value-backprojection mesh verticesspacial. Firstly, an equation set is established according to a bilinear interpolation algorithm as shown in (1-3), wherein C1, C2, C3 and C4 represent ASF of grid verticesspacial。
Figure RE-GDA0002946319680000051
It is converted into a matrix equation as shown in (1-4) below
Figure RE-GDA0002946319680000052
ASF for obtaining grid vertex by solving matrix equationspacialValues, as shown in 1-5.
Coefficient matrix
Figure RE-GDA0002946319680000053
Figure RE-GDA0002946319680000061
Assuming that there are (m-1) × n meshes in one region and there are m × n corresponding mesh vertices, as shown in fig. 1, the dotted line in the figure is a test trace, and the mesh vertices are first arranged as shown in formulas 1 to 6.
C＝[C1,C2…Cn,Cn+1,Cn+2…C2n,C(m-1)*n+1,C(m-1)*n+2…Cm*n]' (1-6)
The equation of the ith test point is shown in formulas 1-6
(1-αi)·(1-βi)·C2+(1-αi)·βi·C3+αi·(1-βi)·Cn+2+αi·βi·Cn+3＝ASFspacial_i(1-7)
The matrix equation is shown in (1-7)
A*C＝ASFspacial_i (1-8)
Solving the matrix equation to obtain C, i.e. ASF of the mesh vertexspacialThe value is obtained.
(6) Building a grid database
Calculate each vertex ASFspacialAfter the value, according to the format [ Longj,Latij,ASFspacial_j](longitude, latitude and ASF of grid vertex) is stored in ASF grid database, which is convenient for user to query and use.
(7) The user calculates a time delay PF according to the position information
Calculating the large ground wire distance of signal propagation according to the antenna position of eLoran receiver and the transmitting antenna position of transmitting station, and then calculating the one-time signal propagation delay PF according to the formula (1-1)User' s。
(8) Calculating ASF time component ASF using difference correction number modeltemperalCorrecting propagation delay from the time dimension
TOA＝PFUser' s+ASFtemperal (1-9)
(9) Calculating ASF space component by using bilinear interpolation algorithm, and correcting propagation delay from space dimension
According to itselfCoordinates (x, y) and coordinates (x) of four vertices of the located mesh1,y1)、(x2,y2)、(x3,y3) And (x)4,y4) Computing ASF using bilinear interpolation algorithmspacialThe value is obtained. As shown in FIG. 2, assuming A, B, C and D coordinates of four points as shown, the four points ASFspacialASF with values of C1, C2, C3 and C4, respectively, at the point (x, y) to be interpolatedspacialHas a value of
ASFsapcial＝(1-α)[(1-β)*C1+β*C3]+α[[(1-β)*C2+β*C4]]， (1-10)
Wherein
Figure RE-GDA0002946319680000071
Correcting signal propagation delay from spatial dimensions
TOA＝PF+ASFtemperal+ASFsapcial (1-11)
The following examples are given by taking a grid as an example, and experiments were carried out using eLoran broadcasting station (Typha) of national time service center of Chinese academy of sciences, the location of the broadcasting station (109.5431, 34.9486).
The differential station performs the following operations:
(1) calculating a time delay PF from position information
The specific position (106.5, 34.8) of the differential receiver antenna placed by the differential station calculates the geodesic distance 278.6985km of signal propagation according to the antenna position of the eLoran reference receiver and the transmitting antenna position of the broadcasting station, and then calculates the signal propagation time delay PF 92.9310 mus according to the formula (1-1).
(2) Testing collected data
And measuring and acquiring the time difference N between the 1PPS signal output by the eLoran reference receiver and the standard time-frequency signal by using the standard time-frequency signal, and acquiring one datum every second.
(3) Model for calculating difference correction
According to the collected data, the difference correction model in a certain time period is y ═ a1t+a0Wherein t is the data age of the forecasting model, t is more than or equal to 0 and less than or equal to 300s, and the data age is5 minutes, a1＝0.0016,a0＝0.0784。
The establishment of the ASF mesh comprises the following operations:
(1) testing collected data
Data are collected by using a test collection system, and 5 test points are taken from the test track in fig. 4, and are sequentially marked as P1, P2, P3, P4 and P5 from left to right. The secondary delay ASF of the differential station is measured to be 1.4860 mus, the coordinates of the 5 points and the measured ASF and the spatial component relative to the differential station are the ASFsapcialAs shown in the table below.
Table 1 test point location information and ASF spatial components relative to a differential station
Test point Longitude (G) Latitude Distance between two adjacent plates ASF/μs ASFsapcial/μs
P1 106.22 35.24 304.7239 1.5881 0.1021
P2 106.24 35.26 303.1402 1.5819 0.0959
P3 106.26 35.26 301.3090 1.5747 0.0887
P4 106.28 35.26 299.4980 1.5676 0.0816
P5 106.28 35.24 299.2811 1.5668 0.0808
(2) Computing ASF space component value by inverse bilinear interpolation algorithm
The set of equations is set up as follows,
Figure RE-GDA0002946319680000081
let coefficient matrix A
Figure RE-GDA0002946319680000082
A*C＝ASFspacial
Figure RE-GDA0002946319680000083
(3) Building a grid database
TABLE 2 mesh vertex ASF spatial component database
Mesh vertices Longitude (G) Latitude ASFsapcial/μs
C1 106 35 0.1072
C2 106.2 35 0.0722
C3 106 35.2 0.1122
C4 106.2 35.2 0.0759
The user performs the following operations:
(1) calculating a time delay PF from position information
The antenna position (106.1, 35.1) of the user receiver calculates the geodesic distance 314.6520km of signal propagation according to the antenna position of the eLoran receiver and the transmitting antenna position of the transmitting station, and then calculates the time delay PF of signal propagation once according to the formula (1-1)User' s＝1049.8907μs。
(2) Computing ASF time component ASF using difference model and model parameterstemperal0.1256 mus, the propagation delay TOA is corrected from the time dimension by PFUser' s+ASFtemperal＝1050.0163μs
(3) Calculating an ASF space component 0.0919 mu s by using a bilinear interpolation algorithm, and correcting the propagation delay TOA (time of arrival) from the space dimension to be PFUser' s+ASFtemperal+ASFspacial＝1050.1082μs
The measured actual path delay is 1050.1405 mus, the delay corrected by the differencing station and the trellis is 1050.1082 mus, and the difference is 32 ns. Therefore, the time service error of eLoran after comprehensive correction of the differential station and the ASF grid is better than 50 ns.

Claims (5)

1. A method for improving the time service precision of an eLoran system by using an ASF grid and a differential station is characterized by comprising the following steps:
(1) calculating the large ground wire distance of signal propagation according to the antenna position of the eLoran reference receiver and the transmitting antenna position of the transmitting station, and then calculating the signal propagation one-time delay PF;
(2) measuring and collecting the time difference N between a 1PPS signal output by an eLoran reference receiver and a standard time-frequency signal by using the standard time-frequency signal;
(3) using time difference data N acquired within a set durationiThe PF is deducted to obtain an additional secondary time delay value ASF of the differential station at the ith momentiForecasting the difference correction number model y ═ a in the set time by using least square fitting1t+a0Model coefficient a of1、a0Y represents ASF, t represents time and is sent to the surrounding users;
(4) in an arbitrarily set area, measuring the ASF (acquired Signal propagation time delay) according to an arbitrarily set trackspacial；
(5) If there are k test points in a grid, k spatial components ASF are measuredspacial(ii) a ASF using these k test pointsspacial_jASF of value-backprojection mesh verticesspacial；
(6) Calculate each vertex ASFspacialAfter the value, according to the format [ Longj,Latij,ASFspacial_j]Stored into ASF grid database, wherein Longj、Latij、ASFspacial_jRespectively representing longitude, latitude and ASF values of the grid vertex;
(7) the user calculates the large ground distance of signal propagation according to the antenna position of eLoran receiver and the transmitting antenna position of the transmitting station, and then calculates the one-time delay PF of signal propagationUser' s；
(8) Calculating ASF time component ASF using difference correction number modeltemperalCorrecting the propagation delay TOA from the time dimension to PFUser' s+ASFtemperal；
(9) Calculating ASF space component by using bilinear interpolation algorithm, and correcting signal propagation delay TOA (time of arrival) ═ PF + ASF from space dimensiontemperal+ASFsapcial。
2. The method for improving eLoran system time service accuracy using ASF grids and differencing stations as claimed in claim 1, wherein said stepsStep (1) calculating the time delay of signal propagation
Figure FDA0002805421270000011
Wherein n issRepresenting the atmospheric refractive index, C the speed of light, d the distance of the large ground from the launch pad to the test point signal propagation.
3. The method for improving the timing accuracy of eLoran system using ASF grid and difference station as claimed in claim 1, wherein said step (4) is performed by using 1PPS outputted from GPS receiver or GNSS receiver or BD receiver as reference standard, and comparing the time difference M of the reference standard and 1PPS outputted from eLoran reference receiver by using time interval counteriObtaining ASF 'of the test point'i＝MiPF', and then deducting the ASF of the differential station at the same momentiObtaining space component ASF of test point relative to differential stationspacial＝ASF'i-ASFi。
4. The method for improving the timing accuracy of eLoran system using ASF grids and differencing stations as claimed in claim 1, wherein said step (5) establishes matrix equations according to bilinear interpolation algorithm, wherein C1, C2, C3 and C4 represent ASF of grid verticesspacial，
Figure FDA0002805421270000021
ASF for obtaining grid vertex by solving matrix equationspacialValues, wherein the coefficient matrix
Figure FDA0002805421270000022
Figure FDA0002805421270000023
Assuming that there are (m-1) × n meshes in one region and there are m × n corresponding mesh vertices, the mesh vertices are arranged to obtain C ═ C [ -n [ -C ] ]1,C2…Cn,Cn+1,Cn+2…C2n,C(m-1)*n+1,C(m-1)*n+2…Cm*n]', equation of the ith test point
(1-αi)·(1-βi)·C2+(1-αi)·βi·C3+αi·(1-βi)·Cn+2+αi·βi·Cn+3＝ASFspacial_i，
The matrix equation is A C ASFspacial_iSolving the matrix equation to obtain C, i.e. ASF of the grid vertexspacialThe value is obtained.
5. The method for improving eLoran system time service accuracy using ASF mesh and difference station as claimed in claim 1, wherein the user's own coordinates in step (9) are (x, y), and the coordinates of four vertices of the mesh are (x, y) respectively1,y1)、(x2,y2)、(x3,y3) And (x)4,y4) Four-point ASFspacialASF with values of C1, C2, C3 and C4, respectively, at the point (x, y) to be interpolatedsapcial＝(1-α)[(1-β)*C1+β*C3]+α[[(1-β)*C2+β*C4]]Wherein
Figure FDA0002805421270000024
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