An ionospheric delay compensation method for real-time precise point positioning

Abstract

The application discloses an ionosphere time delay compensation method for real-time precise point positioning, and the method comprises the following steps: constructing an ionosphere prediction polynomial fitting model, using STEC historical data of ionosphere products to solve polynomial fitting coefficients in the ionosphere prediction polynomial fitting model, and obtaining a polynomial fitting prediction ionosphere product; using ionosphere product historical data, combining double-frequency phase observation values, constructing ionosphere residual combination observation, calculating ionosphere variation between epoch moments, and generating residual combination observation prediction ionosphere products; and according to satellite states observed by a terminal, automatically selecting the polynomial fitting prediction ionosphere product or the residual combination observation prediction ionosphere product to predict the ionosphere. According to the application, ionosphere product historical information and double-frequency phase observation value information are used to predict the ionosphere slant delay at the current moment, so that the ionosphere product time delay compensation is achieved, the product precision loss is reduced, and the PPP-RTK positioning performance is improved.

Description

Technical Field

[0001] This invention relates to the field of terminal positioning technology, and specifically to an ionospheric delay compensation method for real-time precise single-point positioning. Background Technology

[0002] Satellite-Based Augmentation System (SBAS) uses a network of ground-based reference stations and PPP non-differential positioning technology to estimate state-space representation errors (SSRs), such as precise satellite orbit errors, precise satellite clock errors, fractional phase deviations, and regional atmospheric delay errors. These SSRs are then broadcast to end users via L-band communication satellites or the Internet. End users can then use the SSR products and technologies such as PPP / PPP-AR / PPP-RTK to achieve high-precision positioning.

[0003] For real-time PPP-RTK, end users are required to continuously and in real-time receive SSR data from the server. However, since SSR data is not strictly real-time and involves a certain amount of latency, including network latency, server-side processing latency, communication latency, update frequency, data packet loss, and ionospheric modeling failure, the ionospheric products received by the end user will have a time delay compared to the current epoch, resulting in inaccurate real-time PPP-RTK positioning.

[0004] To address this, Chinese invention patent CN114545458A discloses a high-precision real-time ionospheric modeling method, comprising: Step 1, calculating the ionospheric puncture point location and zenith distance information based on the received real-time precise ephemeris and real-time station coordinates; Step 2, extracting the ionospheric slant delay in real time based on the received real-time precise ephemeris, real-time observation data, and real-time correction data; Step 3, constructing a post-hoc ionospheric TEC model using the non-differenced ambiguity integer solution to obtain hardware delay parameters, and processing the hardware delay parameters in the real-time ionospheric slant delay. Corrections are made; simultaneously, an improved ionospheric projection function is used to convert the ionospheric slant delay into the ionospheric vertical delay; step 4, the ex-post ionospheric total electron content model constructed from multi-source ionospheric data is used as historical data, and a semi-parametric model is used to construct an ionospheric TEC prediction model; step 5, the spherical harmonic function is used to fit the ionospheric vertical delay at each puncture point location to the ionospheric vertical delay provided by the ionospheric TEC prediction model; simultaneously, Kalman filtering is used to estimate the model parameters every 5 minutes, and a real-time global ionospheric grid product is generated. This scheme has the following problems:

[0005] First, the accuracy of this scheme is based on VTEC modeling and forecasting, and its accuracy will be affected by the accuracy of the ionospheric mapping function.

[0006] Second, before performing ionospheric forecasting, this scheme requires converting the ionospheric oblique delay (STEC) to the ionospheric vertical delay (VTEC) using a projection function, fitting the model, and generating a real-time global ionospheric grid model. However, the ionospheric mapping function is an empirical model. Using the ionospheric mapping function to convert STEC to VTEC will introduce errors into the ionospheric sample data, resulting in a loss of accuracy.

[0007] Third, the ionospheric products provided in satellite-based augmentation services are generally STEC modeling products, and the product accuracy must be better than 0.3TEC. This approach is not applicable to satellite-based augmentation services.

[0008] Therefore, it is necessary to improve the existing high-precision real-time ionospheric modeling methods to reduce product accuracy loss and improve PPP-RTK positioning performance. Summary of the Invention

[0009] To address the aforementioned shortcomings, the technical problem to be solved by this invention is to provide an ionospheric delay compensation method for real-time precise single-point positioning, so as to solve the problem that the existing technology introduces errors into the ionospheric sample data, causing accuracy loss, and is not suitable for satellite-based augmentation services.

[0010] Therefore, the present invention provides an ionospheric delay compensation method for real-time precise single-point positioning, comprising the following steps:

[0011] Receive ionospheric products broadcast by satellite-based augmentation services and save them as historical data of ionospheric products;

[0012] A polynomial fitting model for ionospheric forecasting is constructed. The ionospheric slant delay of each grid point of the ionospheric grid is calculated based on historical data of ionospheric products to form STEC historical data. The polynomial coefficients in the polynomial fitting model for ionospheric forecasting are solved by fitting the STEC historical data to obtain polynomial fitting forecast ionospheric products.

[0013] By using historical data of ionospheric products and combining dual-frequency phase observations, an ionospheric residual combination observation is constructed, the ionospheric change between adjacent epochs is calculated, and the ionospheric product is predicted by the residual combination observation.

[0014] Based on the satellite status observed by the terminal, the system automatically selects either a polynomial fitting ionospheric forecast product or a residual combination observation ionospheric forecast product to predict the ionosphere for PPP-RTK positioning. Among these:

[0015] When the satellite observations observed by the terminal are single-frequency observations, the ionosphere is predicted using polynomial fitting of the ionospheric product, and ionospheric parameter constraints are performed.

[0016] When a cycle slip occurs in a satellite observed by the terminal, the ionosphere is predicted using polynomial fitting of the ionospheric product, and ionospheric parameter constraints are performed.

[0017] When the duration of the satellite ionospheric products stored in the terminal is insufficient for fitting, the ionospheric products are predicted using residual combined observations to forecast the ionospheric layer and constrain the ionospheric parameters.

[0018] When the satellite observations obtained by the terminal are dual-frequency observations and no cycle slip occurs, the ionospheric forecast product is predicted using residual combined observations, and ionospheric parameter constraints are performed.

[0019] In the above method, preferably, the ionospheric prediction polynomial fitting model Represented as:

[0020] ;

[0021] in, Is The fitted value of the ionospheric slant delay from time grid point k to satellite s;

[0022] , The starting time of the fitting window, This is the end time of the fitting window;

[0023] These are the polynomial fitting coefficients of the polynomial fitting model for ionospheric prediction, where n represents the fitting order.

[0024] In the above method, preferably, the polynomial fitting coefficients of the ionospheric prediction polynomial fitting model are obtained by using historical STEC data. The fitting residuals of the ionospheric grid were calculated. :

[0025] ;

[0026] in, for Historical STEC data from time grid point k to satellite s. for The fitted value of the ionospheric slant delay from time grid point k to satellite s.

[0027] In the above method, preferably, the following formula is used to calculate and obtain... Ionospheric grid fitting accuracy from time grid point k to satellite s ;

[0028] .

[0029] In the above method, preferably, the fitting coefficients are used. Calculate the current time Ionospheric slant delay forecast from grid point k to satellite s and the accuracy of ionospheric grid forecasts ;

[0030] ;

[0031] ;

[0032] in, For ionospheric product delay, and This is the time delay threshold;

[0033] , The starting time of the fitting window, This represents the end time of the fitting window.

[0034] In the above method, preferably, the current time is calculated using the following formula. Ionospheric grid prediction residuals from grid point k to satellite s ;

[0035]

[0036] in, It is the current moment. The predicted ionospheric slant delay from grid point k to satellite s;

[0037] , , , These are the polynomial coefficients of the ionospheric product;

[0038] These are the coordinates and latitude of terminal r and the latitude of the center of the ionospheric grid;

[0039] These are the coordinates of the terminal r (longitude) and the longitude of the center of the ionospheric grid.

[0040] In the above method, preferably,

[0041] Calculate the current time using the following formula. Terminal ionospheric slant delay forecast from terminal r to satellite s And the accuracy of the terminal ionospheric forecast at the current moment ;

[0042] ,in:

[0043] The predicted ionospheric residuals at four grid points surrounding the terminal r at the current time are obtained through inverse distance interpolation. The formula for inverse distance interpolation is as follows:

[0044] ;

[0045] Let r be the geometric distance from the terminal r to the grid point k.

[0046] = .

[0047] In the above method, preferably,

[0048] An ionospheric residual combined observation model was constructed using dual-frequency observations, and the current forecast time was calculated for satellite s. With time The variation in ionospheric oblique delay between the two, and the combined observation model of ionospheric residuals are as follows:

[0049]

[0050] = ;

[0051] = ;

[0052] in:

[0053] For satellite S, carrier At the present moment With time The integer ambiguity variation between the carrier waves, when the carrier wave... When no cycle slip occurs, =0;

[0054] For satellite s, At the current forecast time With time The integer ambiguity variation between the carrier waves, when the carrier wave... When no cycle slip occurs, =0;

[0055] For satellite s, at the current time With time The ionospheric slack delay variation between;

[0056] To observe noise;

[0057] when Less than the cycle slip test threshold hour, ;

[0058] Current moment With time ionospheric slant delay variation .

[0059] In the above method, preferably, the accuracy of predicting the ionospheric oblique delay change at the current moment is based on the error propagation law and the combined observation model of ionospheric residuals. :

[0060]

[0061] in, For ionospheric product delay, and This is the product latency threshold.

[0062] Accuracy of combined observations of ionospheric residuals ;

[0063] and carrier and Observational measurement accuracy.

[0064] In the above method, preferably, the current time is predicted in the following manner. The predicted ionospheric slant delay from terminal r to satellite s is determined by the following steps:

[0065] calculate Ionospheric slant delay fitting value from time terminal r to satellite s :

[0066] ;

[0067] Calculate the current time Ionospheric slant delay forecast from terminal r to satellite s ;

[0068] ;

[0069] Calculate the current time Accuracy of terminal ionospheric slant delay prediction from terminal r to satellite s;

[0070] ;

[0071] For the ionospheric skew delay accuracy of historical data for ionospheric products;

[0072] These are the polynomial coefficients of the ionospheric product;

[0073] These are the coordinates of the terminal r (longitude) and the longitude of the center of the ionospheric grid.

[0074] For a moment Ionospheric residual from terminal r to satellite s.

[0075] As can be seen from the above technical solution, the ionospheric delay compensation method for real-time precise single-point positioning provided by this invention solves the problem that existing technologies suffer from errors introduced by ionospheric sample data, resulting in accuracy loss, and are not suitable for satellite-based augmentation services. Compared with the prior art, this invention has the following beneficial effects:

[0076] Using historical information from ionospheric products and dual-frequency phase observations, the current ionospheric slant delay is predicted. Based on the satellite status observed by the terminal, the system automatically selects either polynomial fitting to predict ionospheric products or residual combination observations to predict ionospheric products. This process compensates for time delays in ionospheric products, reduces product accuracy loss, and improves PPP-RTK positioning performance. Attached Figure Description

[0077] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments of the present invention or the prior art will be briefly introduced and explained below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0078] Figure 1 The flowchart of an ionospheric delay compensation method for real-time precise single-point positioning provided by the present invention is shown. Detailed Implementation

[0079] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0080] The principle of this invention is as follows:

[0081] Based on historical ionospheric products, the current ionospheric slant delay is predicted, providing accurate ionospheric delay prediction information. When the ionospheric products received by the terminal have a time delay, compensation is made for the accuracy loss caused by this time delay. This avoids the problem of ionospheric parameters not being correctly constrained during PPP-RTK positioning due to decreased or distorted ionospheric product accuracy, which could lead to slow PPP-RTK convergence or even incorrect positioning.

[0082] To provide a clearer explanation and description of the technical solution and implementation of the present invention, several preferred specific embodiments for implementing the technical solution of the present invention are described below.

[0083] It should be noted that the directional terms such as "inner" and "outer", "front" and "back" and "left" and "right" in this article are based on the product's usage status. Obviously, the use of these directional terms does not limit the scope of protection of this solution.

[0084] Please see Figure 1 , Figure 1 The flowchart of an ionospheric delay compensation method for real-time precise single-point positioning provided by the present invention is shown.

[0085] like Figure 1 As shown, the present invention provides a method for real-time precise single-point positioning and ionospheric time delay compensation, comprising the following steps:

[0086] Step 100: The terminal receives the ionospheric products broadcast by the satellite-based augmentation service and saves them as historical data of ionospheric products.

[0087] Step 200: Construct a polynomial fitting model for ionospheric forecasting. Calculate the slant electron content (STEC) of each grid point of the ionospheric grid based on historical ionospheric product data to form historical STEC data. Use the historical STEC data to fit and solve the polynomial fitting coefficients in the polynomial fitting model for ionospheric delay to obtain the polynomial fitting forecast of ionospheric products.

[0088] Step 300: Using historical data of ionospheric products and combining dual-frequency phase observations, construct ionospheric residual combined observations, calculate the ionospheric changes between adjacent epochs, and generate ionospheric products predicted by the residual combined observations.

[0089] Step 400: Based on the satellite status observed by the terminal, automatically select either a polynomial fitting ionospheric prediction product or a residual combination observation ionospheric prediction product to predict the ionosphere for PPP-RTK positioning. Wherein:

[0090] When the satellite observations observed by the terminal are single-frequency observations, the ionosphere is predicted using polynomial fitting of the ionospheric product, and ionospheric parameter constraints are performed.

[0091] When a cycle slip occurs in a satellite observed by the terminal, the ionosphere is predicted using polynomial fitting of the ionospheric product, and ionospheric parameter constraints are performed.

[0092] When the duration of the satellite ionospheric products stored in the terminal is insufficient for fitting, the ionospheric products are predicted using residual combined observations to forecast the ionospheric layer and constrain the ionospheric parameters.

[0093] When the satellite observations obtained by the terminal are dual-frequency observations and no cycle slip occurs, the ionospheric forecast product is predicted using residual combined observations, and ionospheric parameter constraints are performed.

[0094] In the above method, step 200, which obtains the polynomial fitting prediction of the ionosphere, specifically includes the following steps:

[0095] Step 210: Using the ionospheric product model, calculate the slant electron content (STEC) at each grid point in the ionospheric grid to form historical STEC data. .

[0096] The ionospheric product model combines a polynomial model with gridded ionospheric residuals, as shown in the following formula:

[0097] ;

[0098] in:

[0099] It is an epochal moment Historical ionospheric slant delay data from grid point k to satellite s;

[0100] , , , These are the polynomial coefficients of the ionospheric product;

[0101] These are the coordinates and latitude of terminal r and the latitude of the center of the ionospheric grid;

[0102] These are the coordinates of terminal r (longitude) and the longitude of the center of the ionospheric grid.

[0103] It is an epochal moment The grid ionospheric residual from grid point k to satellite s.

[0104] The accuracy of ionospheric skew delay in historical ionospheric product data is .

[0105] Step 220: Construct a polynomial fitting model for ionospheric prediction. .

[0106] ;

[0107] in, It is an epochal moment The ionospheric slant delay fitting value from grid point k to satellite s;

[0108] , The starting time of the fitting window, This is the end time of the fitting window;

[0109] represents the polynomial fitting coefficients of the fitted model, and n represents the fitting order.

[0110] Step 230: Using the sliding window method, in the STEC historical data... Select the STEC historical data from the grid points of the first i epochs and fit the polynomial model. Fitting, solving for the polynomial fitting coefficients ( ).

[0111] Step 240, use the solution to obtain the polynomial fitting coefficients ( The epoch time was calculated using a polynomial fitting model for ionospheric prediction. Ionospheric slant delay fitting value from grid point k to satellite s ionospheric grid fitting residuals Fitting accuracy of ionospheric grid .

[0112] .

[0113] .

[0114] .

[0115] Step 250: Calculate the polynomial fitting coefficients using the methods from step 230. ) and the ionospheric prediction polynomial fitting model to predict the current time Grid point ionospheric slant delay forecast from grid point k to satellite s Current accuracy of ionospheric grid forecast And the ionospheric grid prediction residual at the current moment .

[0116] ;

[0117] ;

[0118] in, For ionospheric product delay, and This is the time delay threshold;

[0119] , The starting time of the fitting window, This represents the end time of the fitting window.

[0120]

[0121] Step 270, using the polynomial coefficients of the ionospheric product , , , And ionospheric products, forecasting the current time Terminal ionospheric slant delay forecast from terminal r to satellite s And the accuracy of the terminal ionospheric forecast at the current moment .

[0122] .

[0123] in:

[0124] The current time is obtained by inverse distance interpolation. Ionospheric residuals at four grid points (k=1, 2, 3, 4) surrounding terminal r .

[0125] The formula for inverse distance interpolation is as follows:

[0126] ;

[0127] This represents the geometric distance from the user's location to grid point k, where k can take values ​​of 1, 2, 3, or 4.

[0128] = .

[0129] In the above method, step 300, generating the residual combined observation forecast ionospheric product, specifically includes the following:

[0130] Step 310, Obtain the epoch time and the current moment The s satellite observation values.

[0131] Step 320: Determine whether the S satellite observation value is a dual-frequency observation value. If not, return to step 310; otherwise, proceed to step 330.

[0132] Step 330: Determine if a cycle slip has occurred. If no cycle slip has occurred, return to step 310; otherwise, proceed to step 340.

[0133] Step 340: Construct the combined observations of ionospheric residuals and calculate the current time. With epochal time Between, the amount of ionospheric change of the S satellite .

[0134] = .

[0135] Specifically:

[0136] = ;

[0137]

[0138] Indicates carrier At the current epoch ionospheric residual combination observations;

[0139] Indicates carrier At the epochal moment ionospheric residual combination observations;

[0140] carrier wavelength, carrier The wavelength; carrier frequency, carrier The frequency;

[0141] For satellite S, carrier At the current epoch Compared to the previous epoch The integer ambiguity variation between the carrier waves, when the carrier wave... When no cycle slip occurs, =0;

[0142] For satellite s, At the current epoch Compared with the previous one The integer ambiguity change between them, when When no cycle slip occurs, =0;

[0143] For satellite s, at the current time Compared to the previous epoch The change in ionospheric slack delay between them Representing an epochal time ionospheric slack delay;

[0144] To observe noise.

[0145] The subscript GF (Geometry-free) represents a geometry-independent combination, also known as an ionospheric residual combination.

[0146] when Less than the cycle slip test threshold At that time, the carrier wave can be considered as and No cycle slips occurred, therefore:

[0147] .

[0148] and The change in ionospheric slack delay between them is:

[0149] .

[0150] According to the law of error propagation, the accuracy of the combined observations of ionospheric residuals is:

[0151] ,in:

[0152] and carrier and Ionospheric observation measurement accuracy;

[0153] The accuracy of the ionospheric slant delay variation is:

[0154] ;

[0155] in, For ionospheric product delay, and This is the product latency threshold.

[0156] Step 350, calculate the current time. At time r, the predicted ionospheric slant delay from terminal r to satellite s and accuracy of ionospheric slant delay forecast .

[0157] .

[0158] .

[0159] = .

[0160] Based on the above description of specific embodiments, the ionospheric delay compensation method for real-time precise single-point positioning provided by the present invention has the following advantages compared with the prior art:

[0161] First, based on historical ionospheric products, a polynomial fitting method is used to predict the ionospheric slant delay at the current epoch. When dual-frequency observations are available, the variation in ionospheric time between epochs can also be calculated using combined ionospheric residual observations to extrapolate the ionospheric slant delay at the current epoch. Simultaneously using both the polynomial fitting method and the combined ionospheric residual observation method to predict the ionospheric slant delay at the current epoch compensates for the accuracy loss in ionospheric products caused by time delays. This effectively compensates for the accuracy loss due to ionospheric product time delays and improves the PPP-RTK positioning performance of the terminal.

[0162] Second, compared to existing ionospheric forecasting methods, this invention uses ionospheric slant-delay STEC for forecasting, avoiding the accuracy loss caused by converting STEC to VTEC for modeling and forecasting. It is more suitable for PPP-RTK positioning, which requires high accuracy in ionospheric product data.

[0163] Third, while proposing the ionospheric prediction method, a method for calculating the accuracy of the ionospheric prediction was also proposed. This accuracy calculation method, when using the polynomial fitting method to predict the ionosphere, calculates the slant delay accuracy of the predicted ionosphere based on the fitting residuals, extrapolation time, and grid interpolation using the error propagation law. When using the ionospheric residual method to predict the ionosphere, it calculates the slant delay accuracy of the predicted ionosphere based on the carrier observation accuracy, the combined accuracy of the ionospheric residual observations, and the extrapolation time using error propagation positioning. The accuracy calculation method is rigorous, and the terminal can use this accuracy information to correctly constrain ionospheric parameters and avoid PPP-RTK positioning errors.

[0164] Fourth, this invention employs both polynomial fitting and ionospheric residual combined observation methods when forecasting the ionosphere, allowing the terminal to choose the appropriate method. The polynomial fitting method relies solely on historical ionospheric products and can be used when satellite cycle slips occur or only single-frequency observations are available. The ionospheric residual combined observation method, however, relies on carrier accuracy for its forecast accuracy, thus offering higher accuracy. In cases with dual-frequency observations and no cycle slips, it can accurately predict the ionospheric slant delay at the current epoch.

[0165] Fifth, the ionospheric prediction accuracy calculation method proposed in this invention is rigorously derived based on the error propagation law. The terminal algorithm can accurately constrain ionospheric parameters based on this accuracy information to achieve accurate PPP-RTK positioning.

[0166] Sixth, in this invention, the terminal can independently choose between two methods for predicting ionospheric slant delay: polynomial fitting and ionospheric residual combined observation, which can compensate for the shortcomings of both methods. Using the polynomial method, ionospheric forecasting can still be performed even when dual-frequency observations are lacking or satellite cycle slips are present; using the ionospheric residual combined observation method, accurate ionospheric forecasting can still be performed even when historical ionospheric product periods are short and cannot be fitted.

[0167] Finally, it should be noted that the terms "comprising," "including," or any other variations thereof as used herein are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising a…" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0168] This invention is not limited to the above-described preferred embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

Claims

1. A method for ionospheric time delay compensation in real-time precise single-point positioning, characterized in that, Includes the following steps: Receive ionospheric products broadcast by satellite-based augmentation services and save them as historical data of ionospheric products; A polynomial fitting model for ionospheric forecasting is constructed. The ionospheric slant delay of each grid point of the ionospheric grid is calculated based on historical data of ionospheric products to form STEC historical data. The polynomial fitting coefficients in the polynomial fitting model for ionospheric forecasting are then solved using the STEC historical data to obtain polynomial fitting forecast ionospheric products. By using historical data of ionospheric products and combining dual-frequency phase observations, an ionospheric residual combination observation is constructed, the ionospheric change between adjacent epochs is calculated, and the ionospheric product is predicted by the residual combination observation. Based on the satellite status observed by the terminal, the system automatically selects either a polynomial-fitted ionospheric forecast product or a residual combination observational ionospheric forecast product to predict the ionosphere for PPP-RTK positioning; where: When the satellite observations observed by the terminal are single-frequency observations, the ionosphere is predicted using polynomial fitting of the ionospheric product, and ionospheric parameter constraints are performed. When a cycle slip occurs in a satellite observed by the terminal, the ionosphere is predicted using polynomial fitting of the ionospheric product, and ionospheric parameter constraints are performed. When the duration of the satellite ionospheric products stored in the terminal is insufficient for fitting, the ionospheric products are predicted using residual combined observations to forecast the ionospheric layer and constrain the ionospheric parameters. When the satellite observations obtained by the terminal are dual-frequency observations and no cycle slip occurs, the ionospheric forecast product is predicted using residual combined observations, and ionospheric parameter constraints are performed.

2. The method according to claim 1, characterized in that, Ionospheric prediction polynomial fitting model Represented as: ； in, Is The fitted value of the ionospheric slant delay from time grid point k to satellite s; , The starting time of the fitting window, This is the end time of the fitting window; These are the polynomial fitting coefficients of the polynomial fitting model for ionospheric prediction, where n represents the fitting order.

3. The method according to claim 2, characterized in that, Using historical STEC data, the polynomial fitting coefficients of the polynomial fitting model for ionospheric prediction were obtained by fitting and solving the model. The fitting residuals of the ionospheric grid were calculated. : ； in, for Historical STEC data from time grid point k to satellite s. for The fitted value of the ionospheric slant delay from time grid point k to satellite s.

4. The method according to claim 3, characterized in that, Calculate using the following formula Ionospheric grid fitting accuracy from time grid point k to satellite s ; 。 5. The method according to claim 1, characterized in that, Using fitting coefficients Calculate the current time Ionospheric slant delay forecast from grid point k to satellite s and the accuracy of ionospheric grid forecasts ; ； ； in, For ionospheric product delay, and For the time delay threshold, for The fitting accuracy of the ionospheric grid from time grid point k to satellite s; , The starting time of the fitting window, This represents the end time of the fitting window.

6. The method according to claim 5, characterized in that, Calculated using the following formula ; in, It is the current moment. Ionospheric slant delay forecast from grid point k to satellite s; , , , These are the polynomial coefficients of the ionospheric product; These are the coordinates and latitude of terminal r and the latitude of the center of the ionospheric grid; These are the coordinates of the terminal r (longitude) and the longitude of the center of the ionospheric grid.

7. The method according to claim 6, characterized in that, Calculate the current time using the following formula. Terminal ionospheric slant delay forecast from terminal r to satellite s And the accuracy of the terminal ionospheric forecast at the current moment ; ,in: The predicted ionospheric residuals at four grid points surrounding the terminal r at the current time are obtained through inverse distance interpolation. The formula for inverse distance interpolation is as follows: ； Let r be the geometric distance from the terminal r to the grid point k. = 。 8. The method according to claim 1, characterized in that, An ionospheric residual combined observation model was constructed using dual-frequency observations, and the current forecast time was calculated for satellite s. With time The variation in ionospheric oblique delay between the two, and the combined observation model of ionospheric residuals are as follows: = ； = ； = ； in: Indicates the current epoch. ionospheric residual combination observations; Representing an epochal time ionospheric residual combination observations; For satellite S, carrier At the present moment With time The integer ambiguity variation between the carrier waves, when the carrier wave... When no cycle slip occurs, =0; For satellite s, At the current forecast time With time The integer ambiguity variation between the carrier waves, when the carrier wave... When no cycle slip occurs, =0; For satellite s, at the current time With time The ionospheric slack delay variation between; To observe noise; when Less than the cycle slip test threshold hour, ; Current moment With time ionospheric slant delay variation .

9. The method according to claim 8, characterized in that, Based on the error propagation law and the combined observation model of ionospheric residuals, the accuracy of predicting the current moment's slant delay change is as follows: : in, For ionospheric product delay, and This is the product latency threshold. Accuracy of combined observations of ionospheric residuals ; and carrier and Observational measurement accuracy.

10. The method according to claim 9, characterized in that, The current time is predicted using the following method. The predicted ionospheric slant delay from terminal r to satellite s is calculated using the following steps: calculate Ionospheric slant delay fitting value from time terminal r to satellite s : Calculate the current time Ionospheric slant delay forecast from terminal r to satellite s ; ； Calculate the current time Accuracy of terminal ionospheric slant delay prediction from terminal r to satellite s; ； For the ionospheric skew delay accuracy of historical data for ionospheric products; , , , These are the polynomial coefficients of the ionospheric product; These are the coordinates of terminal r (longitude) and the longitude of the center of the ionospheric grid. For a moment Ionospheric residual from terminal r to satellite s.

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