CN111766616A - A method for correcting multipath errors at the satellite end of Beidou-2 time transfer satellite - Google Patents

Abstract

The invention provides a method for correcting the multipath error of the Beidou No. 2 time transfer satellite, which is used to solve the problem of the multipath error of the Beidou No. 2 time transfer. The Beidou-2 time transfer satellite-end multipath error correction method selects the MGEX observation station as the data source, and uses the MP sequence to divide the grouped data into segments after grouping, and generates a pseudorange correction information table, so as to be used in the BDS CV and/or Or when BDS PPP time transfer, according to the satellite type, signal frequency point to find the pseudorange correction node information and perform fitting to correct the pseudorange observation value. The invention introduces satellite-end multipath error correction in Beidou time transfer, corrects the pseudorange observation value of Beidou-2 satellite based on the observation data of the global MGEX station, and directly corrects the pseudorange systematically at the user end, which weakens the The influence of satellite-side multipath on time transfer solves the problem of satellite-side multipath error in Beidou-2 time transfer, and improves the accuracy of Beidou-2 time transfer.

Description

A method for correcting multipath errors at the satellite end of Beidou-2 time transfer satellite

technical field

The invention belongs to the field of navigation, and in particular relates to a method for correcting multipath errors at the satellite end of Beidou-2 time transfer satellites.

Background technique

China's BeiDou Navigation Satellite System (BDS) is a global satellite navigation system developed by China. Since December 2012, it has officially provided navigation, positioning and timing services to the Asia-Pacific region. It is one of the four major satellite navigation systems in the world. BDS consists of three parts: space segment, ground segment and user segment. Beidou-2 satellites in orbit include 5 GEO (geostationary earth orbit) satellites (C01-C05), 7 IGSO (inclinedgeosynchronous satellite orbit) (C06-C10) , C13, C16) and 3 MEO (medium earth orbit) satellites (C11, C12, C14), the Beidou-3 system is expected to be completed in June 2020.

The punctuality laboratory participating in the international time comparison mainly conducts remote time comparison through the US Global Positioning System (GPS) and the Russian Global Navigation Satellite System (GLONASS). GPS precision point positioning technology (Precise Point Positioning, PPP) in the distance of hundreds or even thousands of kilometers in the sky frequency stability can reach the order of E-15 ~ E-16, the time transfer method includes GPS common view time transfer (GPS Common-View, GPSCV), GPS all-view time transfer (GPS All-View, GPS AV), GPS carrier phase time transfer (GPS Carrier-Phase, GPS CP). Relying on a single system for time transfer carries significant reliability risks. In the long run, the international time comparison method gradually develops from a single system to a multi-system fusion time comparison direction. In 2015, the CGGTTS V2E co-viewing standard was officially released, and the co-viewing method of GPS, GLONASS, Galileo, BDS and QZSS was clearly defined in the standard. The time transfer based on Beidou co-view in Eurasia has been verified by preliminary experiments. The standard deviation (STD) of BDS CV time comparison is about 2ns to 3ns, and the number of co-view satellites is about 2 to 3. Due to the limited service scope of Beidou-2, the time transfer of BDS PPP is limited to the Asia-Pacific region, and the STD of BDS PPP time comparison is better than 0.5ns.

The Beidou-2 satellite has satellite-side multipath errors, which will produce a systematic error of several decimeters to 1 meter in the pseudorange. The pseudorange deviation of Beidou-2 satellite is closely related to the satellite altitude angle and signal frequency, and the deviation has nothing to do with the receiver antenna type and observation period. Therefore, it is preliminarily concluded that the pseudorange bias originates from Beidou satellite multipath. In the prior art, the research and application of the satellite-side multipath effects of Beidou-2 satellites mainly focus on satellite positioning, and there is a lack of research on the effects of systematic errors on time transfer.

SUMMARY OF THE INVENTION

In order to solve the problem of satellite-side multipath error of Beidou-2 satellite time transfer, the embodiment of the present invention proposes a Beidou-2 time transfer satellite-side multipath error correction method, which uses the data of MGEX observation stations distributed around the world to construct a Beidou-2 pseudo-satellite. The range piecewise linear correction model corrects the pseudorange observations according to the satellite altitude angle, thereby weakening the influence of satellite-side multipath on Beidou time transfer.

In order to achieve the above purpose, the embodiment of the present invention adopts the following technical solutions:

A method for correcting the multipath error of the Beidou-2 time transfer satellite, the method for correcting the multipath error of the Beidou-2 time transfer satellite comprises the following steps:

Step S1, select the MGEX observation station data of the International Global Navigation Satellite Service Organization multi-system observation network as the data source, and group the data source according to the satellite number and signal frequency to obtain grouped data;

Step S2, utilizes the pseudorange multipath combination MP sequence to carry out the segmentation division to each grouping data, constructs the piecewise linear model, and generates the pseudorange correction information table of different types of satellites and different frequency points;

Step S3, when performing time transfer, look up the pseudorange correction node information in the pseudorange correction information table according to the satellite type and the signal frequency point and perform fitting, calculate the pseudorange correction value, and correct the pseudorange observation value. .

In the above scheme, in the step S2, each grouped data is divided into segments, and further segmented according to the change of the altitude angle, and the objective function of the linear model after the segmentation is expressed as:

stf _j (e _j )-f _j+1 (e _j )=0 (1)

In formula (1), j=1,2,...,m-1, m represents the total number of segment nodes; i=1,2...,n represents the MP sequence length of the corresponding segment; f represents the linear correlation with the elevation angle. Piecewise function; MP stands for pseudorange multipath combined observations.

In the above scheme, the MP pseudorange multipath combined observation value is obtained by combining single-frequency pseudorange and dual-frequency carrier phase, and is expressed as:

In formula (2), i and j (i, j=1, 2, 3, i≠j) represent different frequencies; MP represents the combined observation value of pseudorange and multipath; P and L represent the observation value of pseudorange and carrier phase, respectively ; f represents carrier frequency; m represents carrier multipath error; B includes phase ambiguity and hardware delay bias; ε represents observation noise.

In the above scheme, the step S2 specifically includes the following steps:

In step S21, cycle slip detection is performed on the observed value of the carrier phase of each grouped data, and each grouped data is divided into arc segments according to whether cycle slip occurs;

Step S22, calculating the mean value of the MP combined observation value of each arc segment of each grouped data, and subtracting the mean value from all MP observation values;

Step S23, divide the MP combined observation values in the range of 5° to 85° at predetermined intervals, and perform piecewise linear fitting to generate pseudorange correction information tables for different types of satellites and different frequencies.

In the above scheme, in the step S23, the predetermined interval is 5° height angle, and the MP combined observation values in the range of 5° to 85° are divided to obtain a total of 17 parameters to be estimated. For any observation value [e, MP], the observation equation Expressed as:

In formula (3), x represents the value of the parameter MP to be estimated corresponding to the segment node, and j represents the segment corresponding to the height angle e.

In the above solution, the time transfer is the BDS CV of the Beidou satellite and/or the BDS PPP time transfer of the Beidou satellite precise single point positioning.

In the above solution, in the step S3, the pseudorange observation value is corrected during time transfer, which specifically includes the following steps:

In step S31, the Beidou broadcast ephemeris uses frequency B3 as a reference, and corrects the broadcast ephemeris group delay GD:

In formula (4), f ₁ and f ₂ represent the frequency of B1 and B2, respectively, and T _GD1 and T _GD2 represent the group delay of B1 and B2, respectively;

Step S32, the satellite common view equation is expressed as:

表示双频无电离层组合码，

表示卫星坐标，

表示利用双频无电离层组合观测值计算出的天线相位中心坐标；S表示地球自转效应；△t_rel表示相对论效应；△t_trop表示对流层延迟；GD为广播星历群延迟。In formula (5),

represents the dual-frequency ionosphere-free combination code,

represents the satellite coordinates,

Represents the antenna phase center coordinates calculated from the dual-frequency non-ionospheric combined observations; S represents the effect of Earth's rotation; △t _rel represents the relativistic effect; △t _trop represents the tropospheric delay; GD is the broadcast ephemeris group delay.

In the above solution, the correction of the pseudorange observation value is performed directly at the user end.

The present invention has the following beneficial effects:

In the Beidou-2 time transfer satellite-side multipath error correction method according to the embodiment of the present invention, satellite-side multipath error correction is introduced into the Beidou time transfer, and based on the observation data of the global MGEX station, the MP combined observation value and the altitude angle are used to construct a component The segment linear correction model is used to obtain the pseudorange correction information table, and the pseudorange observations of Beidou-2 satellite are corrected. The problem of multipath error at the satellite end of Beidou-2 time transfer has been solved, and the accuracy of Beidou-2 time transfer has been improved.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

FIG. 1 is a schematic flowchart of a method for correcting a satellite-end error of Beidou-2 time transfer according to an embodiment of the present invention.

Detailed ways

The technical problems, technical solutions and advantages of the present invention will be explained in detail below by referring to the exemplary embodiments. The exemplary embodiments described below are only for explaining the present invention, and should not be construed as limiting the present invention. It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art, and not in idealized or overly formal meanings unless defined herein to explain.

The embodiment of the present invention provides a method for correcting the multipath error of the Beidou-2 time transfer satellite. Beidou-2 satellites include 5 GEO (geostationary earth orbit) satellites (C01-C05), 7 IGSO (inclinedgeosynchronous satellite orbit) satellites (C06-C10, C13, C16) and 3 MEO (medium earthorbit) satellites (C11, C12, C14). The Beidou-2 time-transfer satellite-end multipath error correction method is realized by constructing a Beidou-2 time-transfer satellite-end multipath error correction model.

FIG. 1 is a schematic flowchart of the method for correcting the multipath error at the Beidou-2 time transfer satellite. As shown in Fig. 1, the satellite-side multipath error correction method for Beidou-2 time transfer described in this embodiment is described by taking the satellite-side multipath error correction of the IGSO satellite and MEO satellite in Beidou-2 as an example. on other satellites of Beidou-2. The method for correcting multipath errors at the star terminal includes the following steps:

Step S1, select the multi-system observation network (Multi-GNSS experimentcampaign, MEGX) observation station data of the International Global Navigation Satellite System (Global Navigation Satellite System, GNSS) service organization (International GNSS Service, IGS) as the data source, according to the satellite number, signal The frequency points group the data sources to obtain grouped data.

In this embodiment, since the IGSO satellite mainly covers the Asia-Pacific region, and other regions have lower observation angles, the pseudo-range multipath combination (MP) error is relatively large, and it is easy to "contaminate" the overall observation value and reduce the model estimation accuracy. Therefore, when modeling the IGSO pseudorange bias, the observation stations in the Asia-Pacific region should be selected to ensure a complete observation arc. For MEO satellites, monitoring stations distributed over a wide area should be selected as far as possible to ensure that there are sufficient observations in all altitude ranges.

In step S2, each grouped data is divided into segments by using the MP sequence, a segmented linear model is constructed, and pseudorange correction information tables of different types of satellites and different frequency points are generated.

Preferably, in this step, segmentation is performed according to the change of the height angle, and the objective function of the linear model after segmentation is expressed as:

stf _j (e _j )-f _j+1 (e _j )=0 (1)

In formula (1), j=1,2,...,m-1, m represents the total number of segment nodes; i=1,2...,n represents the MP sequence length of the corresponding segment; f represents the linear correlation with the elevation angle. Piecewise function; MP denotes multipath combined observations.

When positioning through the Beidou-2 satellite, the measured distance includes the clock error between the user's receiver and the satellite's atomic clock and the atmospheric refraction delay, rather than the "true distance", which is called pseudorange. In this embodiment, the pseudorange multipath combination (MP) is obtained by combining single-frequency pseudorange and dual-frequency carrier phase, and is expressed as:

In formula (2), i and j (i, j=1, 2, 3, i≠j) represent different frequencies; MP represents the combined observation value of pseudorange and multipath; P and L represent the observation value of pseudorange and carrier phase, respectively ; f represents carrier frequency; m represents carrier multipath error; B includes phase ambiguity and hardware delay bias; ε represents observation noise. The MP combined observations eliminate geometric distance, tropospheric delay, ionospheric delay and clock error, residual carrier phase ambiguity, hardware delay, multipath, and observation noise. Among them, the hardware delay remains unchanged for a short time, and the carrier multipath error is much smaller than the pseudorange multipath error. Therefore, as long as there is no cycle slip in the carrier phase, the MP combination mainly reflects the influence of the pseudorange multipath effect. In actual calculation, firstly, cycle slip detection is performed on the original observation data, then the MP mean value of each complete arc segment is calculated, and finally the MP mean value of the corresponding arc segment is subtracted from all MP values, which is the multipath error.

Further, step S2 specifically includes the following steps:

In step S21, cycle slip detection is performed on the observed value of the carrier phase of each grouped data, and each grouped data is divided into arc segments according to whether cycle slip occurs;

Step S22, calculating the mean value of the MP combined observation value of each arc segment of each grouped data, and subtracting the mean value from all MP observation values;

Step S23, divide the MP combined observation values in the range of 5° to 85° at predetermined intervals, and perform piecewise linear fitting to generate pseudorange correction information tables for different types of satellites and different frequencies.

Since the MP error is relatively large when the elevation angle is low, the model estimation accuracy may be affected. In this embodiment, MP observation values above 5° are selected, preferably at intervals of 5°. In addition, considering that only a few stations have MP observations close to 90°, in order to prevent inaccurate estimation of the linear parameters of this segment due to fewer observations, the elevation angle of the MP sequence is less than 85°. Preferably, the linear fitting adopts the overall least squares method.

In this step, when the altitude angle is at an interval of 5°, there are 17 parameters to be estimated. For any observation value [e, MP], the observation equation is expressed as:

In formula (3), x represents the value of the parameter MP to be estimated corresponding to the segment node, and j represents the segment corresponding to the height angle e.

Due to the large amount of observation data, in order to improve the calculation efficiency, first select a small number of observations to calculate the initial MP node parameters and their covariance matrix; then use the node parameters and covariance matrix as virtual observations to construct a new observation equation; The sequential adjustment method calculates the final MP node parameters in turn.

Table 1 is an example of an IGSO/MEO-based B1I/B2I pseudorange correction information table generated in this embodiment. It should be noted that, in practical application, the node parameters are recalculated according to the historical observation data.

Table 1 B1I/B2I pseudorange correction values of IGSO/MEO

Step S3, when performing BDS CV and/or BDS PPP time transfer, look up pseudorange correction node information in the pseudorange correction information table according to the satellite type and signal frequency point and perform fitting, and perform a fitting on the pseudorange according to the fitting result. Corrected observations.

In this step, taking the BDS CV of Beidou satellites as an example, the multipath error correction at the satellite end is explained. The following calculation process is also applicable to the Beidou precision single-point positioning PPP time transfer, including:

In step S31, the Beidou broadcast ephemeris uses frequency B3 as a reference, and corrects the broadcast ephemeris group delay GD:

In formula (4), f ₁ and f ₂ represent the frequency of B1 and B2, respectively, and T _GD1 and T _GD2 represent the group delay of B1 and B2, respectively;

Step S32, the satellite common view equation is expressed as:

表示双频无电离层组合码，

表示卫星坐标，

表示利用双频无电离层组合观测值计算出的天线相位中心坐标；S表示地球自转效应；△t_rel表示相对论效应；△t_trop表示对流层延迟；GD为广播星历群延迟。In formula (5),

represents the dual-frequency ionosphere-free combination code,

represents the satellite coordinates,

Represents the antenna phase center coordinates calculated from the dual-frequency non-ionospheric combined observations; S represents the effect of Earth's rotation; △t _rel represents the relativistic effect; △t _trop represents the tropospheric delay; GD is the broadcast ephemeris group delay.

和接收机天线相位中心坐标

可计算出每颗卫星的高度角，根据卫星类型、信号频点、高度角对应伪距改正信息表的节点信息进行线性插值，计算出伪距改正值，对伪距观测值进行改正。In this step, the multipath error at the satellite end of Beidou-2 is directly related to the altitude angle.

and receiver antenna phase center coordinates

The altitude angle of each satellite can be calculated. According to the satellite type, signal frequency point, and altitude angle, the node information of the pseudorange correction information table is linearly interpolated, and the pseudorange correction value is calculated, and the pseudorange observation value is corrected.

It can be seen from the above technical solutions that the satellite-side multipath error correction method for Beidou-2 time transfer in this embodiment introduces satellite-side multipath error correction in the Beidou time transfer, based on the observation data of the global MGEX station, using MP combination. Build a piecewise linear correction model based on the observation value and the altitude angle, obtain the pseudorange correction information table, correct the pseudorange observation value of the Beidou-2 satellite, and systematically correct the pseudorange directly on the user side according to the altitude angle, which weakens the many satellites. It solves the problem of multipath error at the satellite end of Beidou-2 time transmission, and improves the accuracy of Beidou-2 time transmission.

The above descriptions are the preferred embodiments of the present invention. It should be noted that the present invention is not limited to the exemplary embodiments disclosed above, and the essence of the description is only to help those skilled in the relevant art to comprehensively understand the specific details of the present invention. For those of ordinary skill in the art, without departing from the principles of the present invention, several improvements and modifications, and easily conceivable changes or substitutions made within the technical scope of the present invention should be covered in the within the protection scope of the present invention.

Claims (8)

1. A Beidou second time transfer satellite-side multipath error correction method is characterized by comprising the following steps:

step S1, selecting data of a multi-system observation network MGEX observation station of the International Global navigation satellite service organization as a data source, and grouping the data source according to a satellite number and a signal frequency point to obtain grouped data;

step S2, segmenting each grouped data by utilizing a pseudo-range multi-path combined MP sequence, constructing a segmented linear model, and generating pseudo-range correction information tables of different types of satellites and different frequency points;

and step S3, searching pseudo-range correction node information in the pseudo-range correction information table according to the satellite type and the signal frequency point during time transmission, fitting, calculating a pseudo-range correction value, and correcting the pseudo-range observation value.

2. The Beidou second time-transfer satellite-side multipath error correction method according to claim 1, wherein in the step S2, each packet data is segmented and further segmented according to altitude angle change, and an objective function of a segmented linear model is represented as:

s.t.f_j(e_j)-f_j+1(e_j)＝0 (1)

in formula (1), j is 1,2, …, m-1, m represents the total number of segmentation nodes; i is 1,2 …, n represents the length of the MP sequence of the corresponding segment; f represents a piecewise function linearly related to the altitude; MP represents pseudorange multipath combination observations.

3. The Beidou second time-transfer satellite-terminal multipath error correction method according to claim 2, characterized in that the MP pseudorange multipath combination observed value is obtained by combining a single frequency pseudorange and a dual frequency carrier phase, and is expressed as:

in formula (2), i and j (i, j ≠ 1,2,3, i ≠ j) represent different frequencies; MP represents pseudo-range multi-path combination observed value; p and L represent pseudorange and carrier phase observations, respectively; f represents a carrier frequency; m represents a carrier multipath error; b comprises phase ambiguity and hardware delay deviation; representing the observed noise.

4. The Beidou second time-transfer satellite-side multipath error correction method according to any one of claims 1 to 3, wherein the step S2 specifically comprises the steps of:

step S21, cycle slip detection is carried out on the carrier phase observed value of each grouped data, and arc segment division is carried out on each grouped data according to whether cycle slip occurs or not;

step S22, calculating the average value of MP combination observation values of each arc segment of each grouped data, and subtracting the average value from all MP observation values;

and step S23, dividing MP combined observed values in the range of 5-85 degrees at preset intervals, and performing piecewise linear fitting to generate pseudo-range correction information tables of different types of satellites and different frequency points.

5. The Beidou second time-transfer satellite-side multipath error correction method according to claim 4, wherein the predetermined interval in the step S23 is a 5 ° elevation angle, 17 parameters to be estimated are obtained by dividing MP combined observation values in a range of 5 ° to 85 °, and for any observation value [ e, MP ], the observation equation is expressed as:

in the formula (3), x represents the value of the parameter MP to be estimated corresponding to the node of the segment, and j represents the segment corresponding to the elevation angle e.

6. The Beidou second time transfer satellite-side multipath error correction method according to claim 5, wherein the time transfer is Beidou satellite common view BDS CV and/or Beidou satellite precise single point positioning BDS PPP time transfer.

7. The method for correcting the multipath error at the Beidou second time-transfer satellite end of claim 5, wherein in the step S3, the pseudo-range observed value is corrected during the time transfer, and the method specifically comprises the following steps:

step S31, the Beidou broadcast ephemeris takes the frequency point B3 as reference, and the broadcast ephemeris group delay GD is corrected:

in the formula (4), f₁And f₂B1 and B2, respectively_GD1And T_GD2Respectively representing the group delay of B1 and B2 frequency points;

at step S32, the satellite co-view equation is expressed as:

in the formula (5), the reaction mixture is,

representing a dual-frequency ionosphere-free combination code,

which represents the coordinates of the satellite or satellites,

representing the antenna phase center coordinate calculated by using the dual-frequency ionosphere-free combined observation value, S representing the earth rotation effect, △ t_relRepresenting relativistic effects △ t_tropRepresenting tropospheric delay; GD is the broadcast ephemeris group delay.

8. The method of claim 7, wherein the correction of the pseudorange observations is performed directly at the user end.

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