Method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system

Abstract

The present invention provides a method for enhancing the availability of an ionospheric grid model in a satellite-based augmentation system, including: dividing four quadrants around a grid point. If the number of piercing points in a certain quadrant is greater than a first threshold, it is an effective quadrant; otherwise, it is an ineffective quadrant. If the number of effective quadrants around the grid point is greater than a second threshold, it is determined that the grid point to be solved is not a grid point at the boundary of the service area; otherwise, it is a grid point at the boundary of the service area. If the grid point to be solved is not a grid point at the boundary of the service area, the piercing points within a first range around the grid point are used to calculate the ionospheric delay of the grid point by using the inverse distance weighted model. And if the grid point to be solved is a grid point at the boundary of the service area, the piercing points within a second range around the grid point are used. If the number of effective quadrants around the grid point is less than the second threshold, the grid point is set as unavailable; otherwise, the ionospheric delay of the grid point is jointly calculated by using the ionospheric delay of the piercing points within the second range and the ionospheric model of the Beidou system.

Description

Technical Field

[0001] The present invention relates to the field of aerospace technology, and particularly to a method for enhancing the availability of an ionospheric grid model of a satellite-based augmentation system. Background Art

[0002] According to the first law of geoscience, that is, geographical attributes have spatial correlation, and nearby things are more similar, the spatial correlation of ionospheric delay correction is relatively strong. Therefore, at present, the BeiDou satellite-based augmentation system uses the ionospheric delays of piercing points within a range of 5°×5° around the grid points, and adopts an inverse distance weighted model to calculate the ionospheric delays of the grid points.

[0003]

[0004] Wherein, is the ionospheric delay value of grid point i, is the ionospheric delay value of piercing point j, and λ ij is the reciprocal of the spherical distance from piercing point j to grid point i.

[0005] Affected by the distribution uniformity and range of monitoring stations, for the ionospheric grid model calculated by this method, in the boundary areas of the service area, due to the lack of piercing points of monitoring stations, the availability of the ionospheric grid model is relatively low, thus affecting the navigation accuracy of the satellite-based augmentation system in the boundary areas. If the search range of piercing points around the grid points is directly expanded and the inverse distance weighted model is still used, due to the increase in the distance between the piercing points and the grid points, the spatial correlation between the ionospheric delays of the piercing points and the grid points will be reduced, thus reducing the calculation accuracy of the ionospheric delays of the grid points. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for enhancing the availability of an ionospheric grid model of a satellite-based augmentation system to solve the problem that the existing ionospheric grid model has relatively low availability in the boundary areas of the service area.

[0007] To solve the above technical problems, the present invention provides a method for enhancing the availability of an ionospheric grid model of a satellite-based augmentation system, including:

[0008] Determine whether the grid point to be solved is a boundary grid point of the service area according to the distribution conditions of piercing points around the grid point;

[0009] If the grid point to be solved is not a boundary grid point of the service area, then use the piercing points within the first range around the grid point and calculate the ionospheric delay of the grid point by using the inverse distance weighted model; and

[0010] If the grid point to be solved is a boundary grid point of the service area, then use the piercing points within the second range around the grid point and re-determine the distribution of piercing points around the grid point.

[0011] Optionally, in the method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system, with the grid point as the center, the area around the grid point is divided into four quadrants. If the number of piercing points in a certain quadrant is greater than the first threshold, it is an effective quadrant; otherwise, it is an ineffective quadrant.

[0012] If the number of effective quadrants containing piercing points is less than the second threshold, the grid point is set to unavailable; otherwise, the ionospheric delay of the grid point is jointly calculated using the ionospheric delays of the piercing points within the second range around the grid point and the Beidou system ionospheric model.

[0013] Optionally, in the method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system, the first range is 5°×5°, the second range is 10°×10°, the number of the first threshold is 3, and the number of the second threshold is 3.

[0014] The Beidou system ionospheric model is the Beidou global ionospheric delay correction model, which includes:

[0015] Nine parameters are used for ionospheric delay correction calculation, and the specific formula is as follows:

[0016]

[0017] In the formula, T ion is the ionospheric delay correction value calculated by the Beidou global ionospheric delay correction model at the epoch, with the unit of meter; M F is the projection function, f is the carrier frequency corresponding to the current signal, with the unit of hertz, a i (i = 1 to 9) are the ionospheric delay correction model parameters, which are broadcast through the satellite's broadcast ephemeris, and A i (i = 0 to 9) are calculated using the non-broadcast parameters in the Beidou space signal interface control file.

[0018] Optionally, in the method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system, it further includes:

[0019] Improve the ionospheric grid model solution method of the satellite-based augmentation system. In areas where the distribution of piercing points is insufficient within the service area of the satellite-based augmentation system, a joint processing algorithm of the measured ionospheric delay of the piercing points and the ionospheric delay calculated by the Beidou global ionospheric delay correction model is adopted, so that the grid points that could not be solved originally become solvable, and the availability of the ionospheric grid model can be improved under the condition of ensuring the ionospheric grid correction accuracy.

[0020] For grid points not in the boundary area of the service area, the inverse distance weighted model is used to solve the ionospheric delay value of the grid points.

[0021] Optionally, in the method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system, it further includes:

[0022] Based on the distribution of piercing points around the grid point, determine whether the grid point to be solved is a grid point in the boundary area of the service area;

[0023] Taking the grid point to be solved as the center, divide a 5°×5° range into four quadrants, and sequentially count the number of piercing points in each quadrant;

[0024] If the number of piercing points in a certain quadrant is greater than 3, then this quadrant is recorded as an effective quadrant;

[0025] If the number of effective quadrants among the four quadrants around the grid point is greater than or equal to three, it indicates that the distribution of piercing points around the grid point to be solved is uniform and has a sufficient number to ensure the solution accuracy of the ionospheric delay of the grid point, and the grid point to be solved is not in the boundary area of the service area; and

[0026] Otherwise, it indicates that the grid point to be solved is in the boundary area of the service area.

[0027] Optionally, in the method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system, calculating the ionospheric delay value of the grid point specifically includes:

[0028] Step 1: Search for all piercing points within a 5°×5° range around the grid point A to be solved;

[0029] Step 2: Using the dual-frequency phase-smoothed pseudorange observations, satellite hardware delays, and receiver inter-frequency biases of the piercing points, calculate the ionospheric delays at each piercing point by using dual-frequency combinations;

[0030] Step 3: Calculate the spherical distance between the piercing point and the grid point;

[0031] Step 4: Using the reciprocal of the spherical distance as the weight, calculate the weighted average of the ionospheric delays of all the searched piercing points around the grid point A as the initial value of the ionospheric delay of the grid point A to be solved;

[0032] Step 5: Using the initial values of the ionospheric delays of the four grid points around the piercing point, interpolate to calculate the estimated value of the ionospheric delay at the piercing point, compare it with the ionospheric delay calculated by the dual-frequency combination of the piercing point, and calculate the grid estimation error of the piercing point;

[0033] Step 6: Statistically calculate the standard mean square error of the grid estimation errors of all the piercing points around the grid point A, and take 3 times the standard mean square error as the error judgment threshold;

[0034] Step 7: Compare the grid estimation errors of all the puncture points around grid point A with three times the standard mean square error one by one. If the grid estimation error is greater than three times the standard mean square error, it is considered that the observation value of this puncture point is abnormal, and a deletion mark is made; and

[0035] Step 8: Use the puncture points after abnormal values are deleted, repeat Steps 1 to 7, and recalculate the ionospheric delay of the grid points to be solved until there are no deleted observation values; obtain the ionospheric delay values of each grid point.

[0036] Optionally, in the method for enhancing the availability of the satellite-based augmentation system ionospheric grid model, it further includes:

[0037] For the grid points in the boundary area of the service area, first judge whether the grid points meet the solution conditions. The grid points that do not meet the solution conditions are directly marked as unavailable; for the grid points that meet the solution conditions, jointly calculate the ionospheric delay of the grid points by using the ionospheric delay of the puncture points within the range of 10°×10° around the grid points and the Beidou global ionospheric delay correction model.

[0038] Optionally, in the method for enhancing the availability of the satellite-based augmentation system ionospheric grid model, it further includes:

[0039] Step 1: Judge whether the grid point B to be solved is solvable; take grid point B as the center, divide the range of 10°×10° around it into four quadrants, and search for all the puncture points within the range of 10°×10° around grid point B; count the number of puncture points in each quadrant. If the number of puncture points in a certain quadrant is greater than 3, mark this quadrant as an effective quadrant; if the number of effective quadrants among the four quadrants around grid point B is greater than or equal to 3, it indicates that the ionospheric delay of grid point B is solvable, otherwise mark grid point B as unavailable;

[0040] Step 2: Use the dual-frequency phase-smoothed pseudorange observation values, satellite hardware delays, and receiver inter-frequency biases of the puncture points, and calculate the ionospheric delay observation values at each puncture point by using dual-frequency combinations;

[0041] Step 3: Use the Beidou global ionospheric delay correction model to solve the estimated value of the ionospheric delay model at the puncture point, and take the difference between the ionospheric delay observation value of the puncture point and the estimated value of the ionospheric delay model as the correction residual of the ionospheric delay model at the puncture point;

[0042] Step 4: Calculate the spherical distance between the puncture point and the grid point, and take the reciprocal of the spherical distance as the weight of the puncture point;

[0043] Step 5: Search for all the puncture points within the range of 10°×10° around grid point B, and calculate the weighted average of the correction residuals of the ionospheric delay model at the puncture points as the correction residual of the ionospheric delay model of the grid point B to be solved;

[0044] Step 6: Calculate the estimated value of the ionospheric delay model for grid point B using the Beidou global ionospheric delay correction model;

[0045] Step 7: Calculate the sum of the ionospheric delay model correction residual and the estimated value of the ionospheric delay model for grid point B as the initial value of the grid ionospheric delay for the to-be-solved grid point B;

[0046] Step 8: Use the initial values of the ionospheric delays of the four grid points around the piercing point to interpolate and calculate the estimated value of the ionospheric delay at the piercing point, compare it with the ionospheric delay calculated by the dual-frequency combination at the piercing point, and calculate the grid estimation error at the piercing point;

[0047] Step 9: Statistically calculate the standard mean square error of the grid estimation errors of all the piercing points around grid point B, and take 3 times the standard mean square error as the error judgment threshold;

[0048] Step 10: Compare one by one the grid estimation errors of all the piercing points around grid point B with 3 times the standard mean square error. If the grid estimation error is greater than 3 times the standard mean square error, it is considered that the observation value of this piercing point is abnormal and a rejection mark is made; and

[0049] Step 11: Use the piercing points after rejecting the abnormal ones, repeat Steps 1 to 10, recalculate the ionospheric delay of the to-be-solved grid point until there are no rejected observations; obtain the ionospheric delay values of each grid point.

[0050] Optionally, in the method for enhancing the availability of the satellite-based augmentation system ionospheric grid model, it further includes:

[0051] For the grid points inside the service area, since there are many piercing points around the grid points and they are relatively evenly distributed, only use the ionospheric delay observation values of the piercing points and adopt the inverse distance weighted model to calculate the ionospheric delay of the grid points.

[0052] Optionally, in the method for enhancing the availability of the satellite-based augmentation system ionospheric grid model, it further includes:

[0053] For the grid points in the boundary area of the service area, the inverse distance weighted model of the piercing points within a range of 5°×5° cannot obtain the accurate ionospheric delay of the grid points. Expand the search range of the piercing points, use the Beidou global ionospheric delay correction model to calculate the ionospheric delay model correction residual of the piercing points, and by fitting the model correction residual with a smaller value, reduce the influence of the ionospheric delay fitting error caused by the increase in distance, and improve the availability of the satellite-based augmentation system grid ionospheric model on the premise of ensuring the accuracy of the grid ionospheric delay solution.

[0054] In the method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system provided by the present invention, by judging whether the grid point to be solved is a grid point at the boundary of the service area according to the distribution conditions of the piercing points around the grid point, if so, the piercing points within the first range around the grid point are used, and the ionospheric delay of the grid point is calculated by using the inverse distance weighted model; if not, the piercing points within the second range around the grid point are used, and the number of piercing points in the four quadrants within the range around the grid point is judged. If the number of valid quadrants is less than the threshold number, the grid point is set as "unavailable"; otherwise, the ionospheric delay of the grid point is jointly calculated by using the ionospheric delay of the piercing points within the second range around the grid point and the Beidou system ionospheric model, thereby improving the availability of the ionospheric grid model of the satellite-based augmentation system on the premise of ensuring the calculation accuracy of the ionospheric delay of the grid point.

[0055] The present invention proposes to use the Beidou global ionospheric delay correction model as the ionospheric background field, calculate the difference between the dual-frequency ionospheric delay observation value of the piercing point and the estimated value of the Beidou global ionospheric delay correction model as the ionospheric model correction residual. In the ionospheric model correction residual, the main spatial correlation of the ionospheric delay is eliminated, and weighted fitting can be carried out within a longer distance range, and the fitting error is less affected by the increase of the distance, so as to obtain a higher-precision ionospheric model correction residual at the grid point, and combine it with the estimated value of the ionospheric model of the grid point calculated by the Beidou global ionospheric delay correction model, and a high-precision ionospheric delay correction of the grid point can be obtained. This method improves the availability of the ionospheric grid model under the condition of ensuring the calculation accuracy of the ionospheric delay of the grid model. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a statistical diagram of the availability of each grid point in the existing grid model calculation method of the satellite-based augmentation system of the Beidou-3 system;

[0057] Figure 2 is a statistical diagram of the availability of ionospheric grid points after adopting the method of the present invention in an embodiment of the present invention;

[0058] Figure 3 is a schematic diagram of the calculation process of the ionospheric delay value of the grid point in an embodiment of the present invention;

[0059] Figure 4 is a schematic diagram of the comparison of the positioning accuracy of the boundary stations in China in a dual-frequency (left), original grid model (middle) and new grid model (right) in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0060] The present invention will be further described below in conjunction with the specific embodiments with reference to the accompanying drawings.

[0061] It should be noted that the components in the accompanying drawings may be exaggerated for illustration purposes and are not necessarily to scale. In the accompanying drawings, the same or functionally identical components are provided with the same reference numerals.

[0062] In the present invention, unless otherwise specified, "disposed on", "disposed above", and "disposed over" do not exclude the presence of intervening elements therebetween. In addition, "disposed on or above" only represents the relative positional relationship between two components, and in certain cases, such as after reversing the product direction, it can also be converted to "disposed under or below", and vice versa.

[0063] In the present invention, the embodiments are only intended to illustrate the solutions of the present invention and should not be construed as restrictive.

[0064] In the present invention, unless otherwise specified, the quantifiers "a" and "one" do not exclude the scenario of multiple elements.

[0065] It should also be noted here that in the embodiments of the present invention, for the sake of clarity and simplicity, only a part of the components or assemblies may be shown. However, those of ordinary skill in the art can understand that, under the teaching of the present invention, the required components or assemblies can be added according to the specific scenario requirements. Additionally, unless otherwise stated, the features in different embodiments of the present invention can be combined with each other. For example, a certain feature in the second embodiment can be used to replace the corresponding or functionally identical or similar feature in the first embodiment, and the resulting embodiment also falls within the scope of the disclosure or the scope of the record of this application.

[0066] It should also be noted here that within the scope of the present invention, the terms "identical", "equal", "equivalent", etc. do not mean that the two values are absolutely equal, but allow for a certain reasonable error. That is to say, the said terms also cover "substantially identical", "substantially equal", "substantially equivalent". By analogy, in the present invention, the directional terms "perpendicular to", "parallel to", etc. also cover the meanings of "substantially perpendicular to" and "substantially parallel to".

[0067] In addition, the numbering of the steps of the methods of the present invention does not limit the execution order of the method steps. Unless otherwise specified, the method steps can be executed in different orders.

[0068] The following further elaborates in detail on the method for enhancing the usability of the ionospheric grid model of the satellite-based augmentation system proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. According to the following description and the claims, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0069] The object of the present invention is to provide a method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system, so as to solve the problem that the existing ionospheric grid model has low availability in the boundary areas of the service area.

[0070] To achieve the above object, the present invention provides a method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system, including: judging whether the grid point to be solved is a grid point at the boundary of the service area according to the distribution conditions of the piercing points around the grid point; if it is not a grid point at the boundary of the service area, using the piercing points within the first range around the grid point, and calculating the ionospheric delay of the grid point by using the inverse distance weighted model; if it is a grid point at the boundary of the service area, judging the number of piercing points within the range around the grid point, and if the number of effective quadrants is less than the threshold number, setting the grid point as "unavailable"; otherwise, jointly calculating the ionospheric delay of the grid point by using the ionospheric delays of the piercing points within the second range around the grid point and the Beidou system ionospheric model.

[0071] The present invention belongs to the technical field of satellite navigation satellite-based augmentation systems, and particularly relates to a calculation method of the ionospheric grid model of the satellite-based augmentation system.

[0072] As Figures 1-2 shown, the technical problem to be solved by the present invention is that when the distribution of monitoring stations is uneven and the number of piercing points is insufficient, the availability of the grid points of the ionospheric grid model of the satellite-based augmentation system in the boundary areas is low, thereby reducing the service accuracy and availability of the satellite-based augmentation system. To solve the above problem, the present invention proposes a calculation method of the ionospheric grid model that integrates the Beidou global ionospheric delay correction model as the background field, improves the availability of the ionospheric grid model in the service boundary areas of the satellite-based augmentation system, and ensures that the correction accuracy of the ionospheric grid model of the satellite-based augmentation system is not reduced. It includes: a distribution area judgment unit for the grid point to be solved, judging whether the grid point is located in the boundary area of the service area according to the distribution of the piercing points around the grid point.

[0073] Taking the grid point to be solved as the center, divide four quadrants within a range of 5°×5°. Calculate the geodetic longitude and latitude coordinates of the ionospheric piercing points of all stations to all satellites, and according to the relationship between the longitude and latitude coordinates of the piercing points and the longitude and latitude coordinates of the grid point, successively count the number of piercing points distributed in each quadrant around the grid point. If the number of piercing points in a certain quadrant is greater than or equal to 3, then this quadrant is marked as an effective quadrant. If the number of effective quadrants among the four quadrants around the grid point is not less than three, this grid point is classified into the central area of the service; if the number of effective quadrants among the four quadrants around the grid point is less than three, this grid point is classified into the boundary area of the service. Successively allocate the distribution areas of all grid points to be solved in the service area.

[0074] An ionospheric delay calculation unit for the grid points in the central area of the service, using the inverse distance weighted model to calculate the ionospheric delay correction at the grid points.

[0075] Search for all piercing points within a 5°×5° range around the grid points to be solved. Using the dual-frequency phase-smoothed pseudorange, satellite hardware delay, and receiver hardware delay of the piercing points, calculate the ionospheric delay observations of each piercing point in sequence.

[0076] T IF =γ[(P 2 -P 1 )-(T GD12 +IFB 12 )]

[0077]

[0078] where T IF is the ionospheric delay of the piercing point calculated using the dual-frequency combination, γ is a coefficient, P i is the phase-smoothed pseudorange, the subscript is the frequency point identifier, T GD12 and IFB 12 are the satellite hardware delay deviation and receiver hardware delay deviation of the two frequencies respectively.

[0079] Calculate the spherical distance between the piercing point and the grid point, and take the reciprocal of the spherical distance as the weight of the piercing point.

[0080] d = r·arccos[cos(B IGP )cos(B ipp )cos(L IGP -L ipp )+sin(B IGP )sin(B ipp )]

[0081]

[0082] In the formula, P is the weight of the piercing point, d is the spherical distance between the piercing point and the grid point, B IGP and B ipp are the latitudes of the grid point and the piercing point respectively, L IGP and L ipp are the longitudes of the grid point and the piercing point respectively, in radians.

[0083] Use the ionospheric delay observations of all piercing points for inverse distance weighted fitting to obtain the initial value of the ionospheric delay correction for the grid points to be solved. Calculate the initial values of the ionospheric delay corrections for all grid points in sequence.

[0084] Reject the gross error of the observed values. For all the above-mentioned piercing points, sequentially search for the positions of the four grid points around each piercing point. Using the initial ionospheric delay values of the grid points around the piercing point, interpolate and calculate the grid estimated value of the ionospheric delay at the piercing point. Subtract the grid estimated value of the ionospheric delay at the piercing point from the observed value of the ionospheric delay at the piercing point calculated using the dual-frequency phase-smoothed pseudorange to obtain the grid estimation error res_i of the piercing point. Calculate the root mean square (rms) of the grid estimation errors of all the piercing points, and take 3 times the rms, i.e., 3rms, as the error judgment threshold T.

[0085] Compare the grid estimation error res_i of each piercing point with the error judgment threshold T one by one. If res_i > T, then consider the observed value of this piercing point as a gross error and mark it as "rejected". These piercing points will no longer participate in the subsequent calculations.

[0086] If there are "rejected" gross error piercing points, recalculate the ionospheric delay of the grid points to be solved according to the above method until there are no "rejected" piercing points. The ionospheric delay values of the grid points in the internal area of the service can be obtained.

[0087] For the ionospheric delay calculation unit of the grid points in the service boundary area, jointly calculate the ionospheric delay of the grid points using the ionospheric delay of the piercing points within the range of 10°×10° around the grid points and the Beidou global ionospheric delay correction model.

[0088] First, determine whether the boundary grid points can be solved after expanding the search range. Taking the grid point as the center, divide the 10°×10° range around it into four quadrants. According to the longitude and latitude coordinates of the monitoring station piercing points and the longitude and latitude coordinates of the grid points, search for all the piercing points within the 10°×10° range around the grid points. Count the number of piercing points in each quadrant. If the number of piercing points in a certain quadrant is greater than 3, then mark this quadrant as a valid quadrant. If the number of valid quadrants among the four quadrants around the grid point is less than three, then mark this grid point as "unusable". If the number of valid quadrants among the four quadrants around the grid point is greater than or equal to three, then the ionospheric delay of this grid point can be solved.

[0089] Using the dual-frequency phase-smoothed pseudorange observed values, satellite hardware delays, and receiver inter-frequency biases of the piercing points, calculate the observed values of the ionospheric delay at each piercing point using dual-frequency combinations.

[0090] Solve the model estimated value of the ionospheric delay at the piercing point using the Beidou global ionospheric delay correction model.

[0091] Calculate the difference between the observed value of the ionospheric delay at the piercing point and the model estimated value of the ionospheric delay, which is denoted as the model correction residual of the ionospheric delay at the piercing point.

[0092] Calculate the spherical distance between the piercing point and the grid point, and take the reciprocal of the spherical distance as the weight of the piercing point.

[0093] Calculate the weighted average of the correction residuals of the ionospheric delay model for all piercing points within a 10°×10° range around the grid point, and use it as the correction residual of the ionospheric delay model for the grid point.

[0094] Use the Beidou global ionospheric delay correction model to calculate the estimated value of the ionospheric delay model for the grid point.

[0095] Calculate the sum of the correction residual of the ionospheric delay model and the estimated value of the ionospheric delay model for the grid point, and use it as the initial value of the grid ionospheric delay for the grid point.

[0096] Reject the gross observation errors. Using the initial values of the ionospheric delays of the four grid points around the piercing point, interpolate and calculate the estimated value of the ionospheric delay at the piercing point, and compare it with the observed value of the ionospheric delay calculated by the dual-frequency combination at the piercing point to calculate the grid estimation error res_i of the piercing point.

[0097] Statistically calculate the root mean square error rms of the grid estimation errors of all piercing points within a 10°×10° range around the grid point, and take 3 times the root mean square error 3rms as the error judgment threshold T.

[0098] Compare one by one the grid estimation error res_i of each piercing point around the grid point with the error judgment threshold T. If res_i is greater than T, it is considered that the observed value of this piercing point is abnormal and a "rejection" mark is made.

[0099] Adopt the piercing points after rejecting the anomalies, repeat the above process, and recalculate the ionospheric delays of each grid point until there are no "rejected" piercing points. Obtain the finally estimated ionospheric delay correction values of each grid point.

[0100] The present invention proposes a method for enhancing the usability of the ionospheric grid model of the satellite-based augmentation system, such as Figure 3 、 4As shown in the figure, this method can effectively improve the availability of the ionospheric grid model of the satellite-based augmentation system. In the central region of the service area, the availability is 100%, and the original ionospheric grid model can be adopted without any impact on users, ensuring the consistency of user service accuracy. In the boundary region of the service area, the availability of the calculation method of the original ionospheric grid model is low. The newly proposed method for enhancing the ionospheric grid model can improve the availability of the ionospheric grid model under the condition of ensuring that the accuracy of the ionospheric grid model does not decrease. Compared with the calculation method of the ionospheric grid model adopted by the Beidou-3 satellite-based augmentation system, the advantages of the present invention are as follows: First, it solves the problem of the small number of piercing points in the boundary region of China and the low availability of the ionospheric grid model. Second, in the central region of the service area, the same calculation method is adopted for the ionospheric grid model, ensuring that there is no impact on the service accuracy of users in the area where the availability is already 100%. Third, it solves the problem that when directly fitting the ionospheric delay of grid points with the ionospheric delay of piercing points in a large range under the condition of expanding the search range of piercing points, the accuracy of the ionospheric delay solution of grid points decreases due to the reduction of spatial correlation. By fitting the correction residuals of the ionospheric delay model of piercing points in a large range, the accuracy of the ionospheric delay solution of grid points is improved.

[0101] Compared with the calculation method of the original ionospheric grid model, the availability of the ionospheric grid points in the boundary region of the service area is significantly improved by the method proposed in the present invention. The PDOP value of users in the boundary region of the service area can be reduced from 2.38 to 2.01, the positioning error can be reduced from 3.25 meters to 2.68 meters, and the service continuity can be increased from 97% to 99%.

[0102] The present invention enhances the availability of the ionospheric grid of the Beidou-3 satellite-based augmentation system. The processing flow is shown in Figure 3 , and the specific implementation method includes:

[0103] Step 1 specifically includes:

[0104] The grid point distribution area judgment unit to be solved judges whether the grid point is located in the boundary region of the service area according to the distribution of piercing points around the grid point.

[0105] Taking the grid point to be solved as the center, the 5°×5° longitude and latitude range around the grid point to be solved is divided into four quadrants, and the distribution numbers of piercing points in the four quadrants around the grid point to be solved are determined.

[0106] Calculate the geodetic longitude and latitude coordinates of the ionospheric piercing points of all stations for all satellites. According to the relationship between the longitude and latitude coordinates of the piercing points and the longitude and latitude coordinates of the grid points, sequentially count the number of piercing points in each quadrant within the 5°×5° longitude and latitude range of the grid points. If the number of piercing points in a certain quadrant is greater than or equal to 3, then this quadrant is marked as a valid quadrant. If the number of valid quadrants among the four quadrants around the grid point is not less than three, this grid point is classified as serving the central region; if the number of valid quadrants among the four quadrants around the grid point is less than three, this grid point is classified as serving the boundary region. Sequentially complete the distribution area judgment of all grid points.

[0107] Step 2 specifically includes:

[0108] The ionospheric delay calculation unit for grid points serving the central region uses the inverse distance weighted model to calculate the ionospheric delay correction at the grid points.

[0109] Search for all piercing points within the 5°×5° range around the grid point to be solved. Using the dual-frequency phase-smoothed pseudorange, satellite hardware delay, and receiver hardware delay of the piercing points, sequentially calculate the ionospheric delay observation values of each piercing point. The calculation formula is

[0110] T IF =γ[(P 2 -P 1 )-(T GD12 +IFB 12 )]

[0111]

[0112] Where T IF is the ionospheric delay of the piercing point calculated using the dual-frequency combination, γ is the coefficient, P i is the phase-smoothed pseudorange, the subscript is the frequency point identifier, T GD12 and IFB 12 are the satellite hardware delay deviation and receiver hardware delay deviation of the two frequencies respectively.

[0113] Calculate the spherical distance between the piercing point and the grid point, and take the reciprocal of the spherical distance as the weight of the piercing point.

[0114] d=r·arccos[cos(B IGP )cos(B ipp )cos(L IGP -L ipp )+sin(B IGP )sin(B ipp )]

[0115]

[0116] Where P is the weight of the piercing point, d is the spherical distance between the piercing point and the grid point, B IGP and B ipp are the latitudes of the grid point and the piercing point respectively, L IGP and L ipp are the longitudes of the grid point and the piercing point respectively, in radians.

[0117] Using the ionospheric delay observations of all piercing points, inverse distance weighted fitting is performed to obtain the initial value of the ionospheric delay correction for the grid points to be solved.

[0118]

[0119] In the formula, T IGP is the ionospheric delay at the grid point, T IF,i is the ionospheric delay observation value of the i-th grid point, and P i is the weight of the i-th grid point.

[0120] Calculate the initial values of the ionospheric delay corrections for all grid points inside the service area in sequence.

[0121] Reject the gross errors in the observations. For all the above-mentioned piercing points, search for the positions of the four grid points around each piercing point in sequence. Using the initial values of the ionospheric delay corrections of the grid points around the piercing point, interpolate to calculate the grid estimated value of the ionospheric delay at the piercing point. Subtract the grid estimated value of the ionospheric delay at the piercing point from the ionospheric delay observation value calculated using the dual-frequency phase-smoothed pseudorange to obtain the grid estimation error res_i of the piercing point. Calculate the root mean square error rms of the grid estimation errors of all piercing points, and take 3 times the standard error 3rms as the error judgment threshold T.

[0122] Compare the grid estimation error res_i of each piercing point with the error judgment threshold T one by one. If res_i > T, it is considered that the observation value of this piercing point is a gross error and make a "rejection" mark. These piercing points will no longer participate in the subsequent calculations.

[0123] If there are piercing points with "rejected" gross errors, recalculate the ionospheric delay of the grid points to be solved according to the above method until there are no "rejected" piercing points. The ionospheric delay value of this grid point can be obtained.

[0124] Repeat step 2 to calculate the ionospheric delay values of all grid points in the internal area of the service in sequence.

[0125] Step 3 specifically includes:

[0126] Judge whether the ionospheric delay of the grid points in the service boundary area is a resolvable unit.

[0127] First, determine whether the number of piercing points within a 10°×10° range at the grid point meets the solution requirements. Taking the grid point as the center, divide the 10°×10° range around it into four quadrants. According to the longitude and latitude coordinates of the piercing points of the monitoring station and the longitude and latitude coordinates of the grid point, search for all piercing points within the 10°×10° range around the grid point. Count the number of piercing points in each quadrant. If the number of piercing points in a certain quadrant is greater than 3, mark that quadrant as a valid quadrant. If the number of valid quadrants among the four quadrants around the grid point is less than three, mark the grid point as "unavailable", then set the ionospheric delay value at this grid point to the default value of 63.875, and repeat step 3 to determine whether the next grid point meets the solution conditions. Otherwise, if the number of valid quadrants among the four quadrants around the grid point is not less than three and meets the solution conditions, proceed to step 4.

[0128] Step 4 specifically includes:

[0129] The ionospheric delay solution unit for grid points in the service boundary area jointly calculates the ionospheric delay of grid points using the ionospheric delay of piercing points within the 10°×10° range around the grid point and the Beidou global ionospheric delay correction model.

[0130] Using the dual-frequency phase-smoothed pseudorange observation values, satellite hardware delays, and receiver inter-frequency biases of the piercing points, calculate the ionospheric delay observation value T at each piercing point through dual-frequency combination IF,i 。

[0131] Use the Beidou global ionospheric delay correction model to solve the ionospheric delay model estimated value T at the piercing point 9ion,i 。

[0132] Calculate the difference between the ionospheric delay observation value and the ionospheric delay model estimated value of the piercing point, denoted as the ionospheric delay model correction residual of the piercing point.

[0133] ΔT i =T IF,i -T 9ion,i

[0134] In the formula, ΔT i is the ionospheric delay model correction residual of the piercing point.

[0135] Calculate the spherical distance between the piercing point and the grid point, and take the reciprocal of the spherical distance as the weight P of the piercing point i 。

[0136]

[0137] In the formula, d i is the spherical distance between the piercing point and the grid point.

[0138] Calculate the weighted average of the ionospheric delay model correction residuals of all piercing points within a 10°×10° range around the grid point, and use it as the ionospheric delay model correction residual of the grid point.

[0139]

[0140] Where ΔT IGP is the ionospheric delay model correction residual of the grid point.

[0141] Use the Beidou global ionospheric delay correction model to calculate the estimated value T of the ionospheric delay model of the grid point 9ion,IGP .

[0142] Calculate the sum of the ionospheric delay model correction residual and the estimated value of the ionospheric delay model of the grid point, and use it as the initial value of the grid ionospheric delay correction of the grid point.

[0143] T IGP = T 9ion,IGP +ΔT IGP

[0144] Where T IGP is the initial value of the grid ionospheric delay correction of the grid point.

[0145] Calculate the initial values of the ionospheric delay corrections of all resolvable grid points in the boundary area of the service area in sequence.

[0146] Reject gross observations. Use the initial values of the ionospheric delays of the four grid points around the piercing point to interpolate and calculate the estimated value of the ionospheric delay of the piercing point, and compare it with the observed value of the ionospheric delay calculated by the dual-frequency combination of the piercing point to calculate the grid estimation error res_i of the piercing point.

[0147] Statistically calculate the root mean square rms of the grid estimation errors of all piercing points within a 10°×10° range around the grid point, and take 3 times the root mean square 3rms as the error judgment threshold T.

[0148] Compare the grid estimation error res_i of each piercing point around the grid point with the error judgment threshold T one by one. If res_i is greater than T, it is considered that the observed value of this piercing point is abnormal and a "rejected" mark is made.

[0149] Adopt the piercing points after rejecting the abnormal ones, repeat the above process, and recalculate the ionospheric delays of each grid point until there are no "rejected" piercing points. Obtain the finally estimated ionospheric delay correction values of each grid point.

[0150] To compare the availability enhancement method of the ionospheric grid model of the satellite-based augmentation system of the present invention with the availability of the ionospheric grid model of the satellite-based augmentation system currently adopted by the Beidou-3 system, Figure 1The availability of the ionospheric grid model of the satellite-based augmentation system currently adopted by the Beidou-3 system is shown in the middle. Figure 2 The availability of the ionospheric grid model of the satellite-based augmentation system of the present invention is shown in the middle. By using the method proposed in the present invention, the availability of grid points in the service boundary area is significantly improved. In addition, six observation stations in the service boundary area are selected for single-frequency single-point positioning calculation. The ionospheric grid model of the satellite-based augmentation system currently adopted by the Beidou-3 system and the ionospheric grid model of the satellite-based augmentation system proposed in the present invention are compared in terms of horizontal positioning error, vertical positioning error, positioning dilution of precision, and positioning continuity. The comparison results are shown in Table 1.

[0151] The results show that the average positioning dilution of precision of the stations in the service boundary area is reduced from 2.38 to 2.01, the average horizontal positioning error is reduced from 1.69 m to 1.37 m, the average vertical positioning error is reduced from 2.78 m to 2.31 m, and the positioning continuity is increased from 97% to 99%.

[0152] Table 1 Comparison of user positioning results in the service boundary area of China before and after adopting the present invention

[0153]

[0154]

[0155] In summary, the above embodiments have described in detail different configurations of the method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system. Of course, the present invention includes but is not limited to the configurations listed in the above embodiments. Any content obtained by transformation based on the configurations provided in the above embodiments belongs to the scope protected by the present invention. Those skilled in the art can draw inferences from one instance to another based on the content of the above embodiments.

[0156] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the system disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method part.

[0157] The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention in any way. Any changes and modifications made by those of ordinary skill in the art of the present invention based on the above disclosure belong to the scope protected by the claims.

Claims

1. A method for enhancing the availability of the ionospheric grid model of a satellite-based augmentation system, characterized in that, it includes: Determine whether the grid point to be solved is a grid point on the boundary of the service area according to the distribution conditions of the piercing points around the grid point; If the grid point to be solved is not a grid point on the boundary of the service area, then use the piercing points within the first range around the grid point, and calculate the ionospheric delay of the grid point using the inverse distance weighted model; and If the grid point to be solved is a grid point on the boundary of the service area, then use the piercing points within the second range around the grid point to re-determine the distribution of the piercing points around the grid point. Taking the grid point as the center, divide the area around the grid point into four quadrants. If the number of piercing points in a certain quadrant is greater than the first threshold, it is an effective quadrant, otherwise it is an invalid quadrant; Among them, if the number of effective quadrants containing piercing points is less than the second threshold, set the grid point as unavailable, otherwise jointly calculate the ionospheric delay of the grid point using the ionospheric delay of the piercing points within the second range around the grid point and the Beidou system ionospheric model, wherein the first range is 5°×5°, the second range is 10°×10°, the number of the first threshold is 3, and the number of the second threshold is 3; The Beidou system ionospheric model is the Beidou global ionospheric delay correction model, which includes: Using 9 parameters for ionospheric delay correction calculation, the specific formula is as follows: Where, T ion is the ionospheric delay correction value calculated by the epoch Beidou global ionospheric delay correction model, with the unit of meter; M F is the projection function, f is the carrier frequency corresponding to the current signal, with the unit of hertz, a i is the ionospheric delay correction model parameter, which is broadcast through the satellite's broadcast ephemeris, where i = 1:9, A i is calculated using the non-broadcast parameters in the Beidou space signal interface control document, where i = 0:

9.

2. The method for enhancing the availability of the ionospheric grid model of a satellite-based augmentation system according to claim 1, characterized in that, it also includes: Improve the solution method of the ionospheric grid model of the satellite-based augmentation system. In areas where the distribution of piercing points in the service area of the satellite-based augmentation system is insufficient, adopt the joint processing algorithm of the measured ionospheric delay of the piercing points and the ionospheric delay calculated by the Beidou global ionospheric delay correction model, so that the grid points that could not be solved originally become solvable, and the availability of the ionospheric grid model can be improved under the condition of ensuring the accuracy of the ionospheric grid correction; For grid points not in the boundary area of the service area, use the inverse distance weighted model to solve the ionospheric delay value of the grid points.

3. The method for enhancing the availability of the ionospheric grid model of a satellite-based augmentation system according to claim 2, characterized in that, it also includes: Judge whether the grid point to be solved is a grid point in the boundary area of the service area according to the distribution of the piercing points around the grid point; Taking the grid point to be solved as the center, divide the area within 5°×5° into four quadrants, and sequentially count the number of piercing points in each quadrant; If the number of piercing points in a certain quadrant is greater than 3, then this quadrant is recorded as an effective quadrant; If the number of effective quadrants among the four quadrants around the grid point is greater than or equal to three, it indicates that the distribution of the piercing points around the grid point to be solved is uniform and has a sufficient number to ensure the solution accuracy of the ionospheric delay of the grid point, and the grid point to be solved is not in the boundary area of the service area; and otherwise, it indicates that the grid point to be solved is in the boundary area of the service area.

4. The method for enhancing the availability of the ionospheric grid model of a satellite-based augmentation system according to claim 3, characterized in that, The specific steps for solving the ionospheric delay value of the grid point include: Step 1: Search for all piercing points within 5°×5° around the grid point A to be solved; Step 2: Using the dual-frequency phase-smoothed pseudorange observations, satellite hardware delays, and receiver inter-frequency biases at the piercing points, calculate the ionospheric delays at each piercing point through dual-frequency combination; Step 3: Calculate the spherical distance between the piercing point and the grid point; Step 4: Using the reciprocal of the spherical distance as the weight, calculate the weighted average of the ionospheric delays of all the piercing points searched around grid point A as the initial value of the ionospheric delay of the grid point A to be solved; Step 5: Using the initial values of the ionospheric delays of the four grid points around the piercing point, interpolate to calculate the estimated value of the ionospheric delay at the piercing point, compare it with the ionospheric delay calculated by the dual-frequency combination at the piercing point, and calculate the grid estimation error of the piercing point; Step 6: Statistically calculate the standard mean square error of the grid estimation errors of all the piercing points around grid point A, and take 3 times the standard mean square error as the error judgment threshold; Step 7: Compare one by one the grid estimation errors of all the piercing points around grid point A with 3 times the standard mean square error. If the grid estimation error is greater than 3 times the standard mean square error, it is considered that the observation value of this piercing point is abnormal and a rejection mark is made; and Step 8: Using the piercing points after rejecting the anomalies, repeat Steps 1 to 7, recalculate the ionospheric delays of the grid points to be solved until there are no rejected observations; obtain the ionospheric delay values of each grid point.

5. The method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system as described in claim 4, characterized in that, it further includes: For the grid points in the boundary area of the service area, first judge whether the grid points meet the solution conditions. The grid points that do not meet the solution conditions are directly marked as unavailable; for the grid points that meet the solution conditions, jointly calculate the ionospheric delays of the grid points using the ionospheric delays of the piercing points within the range of 10°×10° around the grid points and the Beidou global ionospheric delay correction model.

6. The method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system as described in claim 5, characterized in that, it further includes: Step 1: Judge whether the grid point B to be solved is solvable; with grid point B as the center, divide the range of 10°×10° around it into four quadrants, and search for all the piercing points within the range of 10°×10° around grid point B; count the number of piercing points in each quadrant. If the number of piercing points in a certain quadrant is greater than 3, mark this quadrant as an effective quadrant; if the number of effective quadrants among the four quadrants around grid point B is greater than or equal to 3, it indicates that the ionospheric delay of grid point B is solvable, otherwise mark grid point B as unavailable; Step 2: Using the dual-frequency phase-smoothed pseudorange observations, satellite hardware delays, and receiver inter-frequency biases at the piercing points, calculate the ionospheric delay observation values at each piercing point through dual-frequency combination; Step 3: Solve the estimated value of the ionospheric delay model at the piercing point using the Beidou global ionospheric delay correction model, and take the difference between the ionospheric delay observation value at the piercing point and the estimated value of the ionospheric delay model as the ionospheric delay model correction residual at the piercing point; Step 4: Calculate the spherical distance between the piercing point and the grid point, and take the reciprocal of the spherical distance as the weight of the piercing point; Step 5: Search all the puncture points within the range of 10°×10° around the grid point B, calculate the weighted average of the ionospheric delay model correction residuals of the puncture points, and use it as the ionospheric delay model correction residual of the grid point B to be solved; Step 6: Use the Beidou global ionospheric delay correction model to solve the estimated value of the ionospheric delay model of the grid point B; Step 7: Calculate the sum of the ionospheric delay model correction residual and the estimated value of the ionospheric delay model of the grid point B, and use it as the initial value of the grid ionospheric delay of the grid point B to be solved; Step 8: Use the initial values of the ionospheric delays of the four grid points around the puncture point to interpolate and calculate the estimated value of the ionospheric delay of the puncture point, compare it with the ionospheric delay calculated by the dual-frequency combination of the puncture point, and calculate the grid estimation error of the puncture point; Step 9: Statistically calculate the standard mean square error of the grid estimation errors of all the puncture points around the grid point B, and take 3 times the standard mean square error as the error judgment threshold; Step 10: Compare one by one the grid estimation errors of all the puncture points around the grid point B with 3 times the standard mean square error. If the grid estimation error is greater than 3 times the standard mean square error, it is considered that the observed value of this puncture point is abnormal and a rejection mark is made; and Step 11: Use the puncture points after rejecting the abnormal ones, repeat Steps 1 to 10, and recalculate the ionospheric delay of the grid point to be solved until there are no rejected observed values; Obtain the ionospheric delay values of each grid point.

7. The method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system as described in Claim 6, characterized in that, it further includes: For the grid points inside the service area, since there are many puncture points around the grid points and they are relatively evenly distributed, only use the ionospheric delay observed values of the puncture points and adopt the inverse distance weighted model to calculate the ionospheric delay of the grid points.

8. The method for enhancing the availability of the ionospheric grid model of the satellite-based augmentation system as described in Claim 7, characterized in that, it further includes: For the grid points in the boundary area of the service area, when the inverse distance weighted model of the puncture points within the range of 5°×5° cannot obtain the accurate ionospheric delay of the grid points, expand the search range of the puncture points, use the Beidou global ionospheric delay correction model to calculate the ionospheric delay model correction residuals of the puncture points, and reduce the influence of the ionospheric delay fitting error caused by the increased distance by fitting the model correction residuals with smaller values, so as to improve the availability of the ionospheric grid model of the satellite-based augmentation system on the premise of ensuring the solution accuracy of the grid ionospheric delay.

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