Big dipper-based three-frequency double-ionosphere-free combined precision single-point positioning model and method

Abstract

The invention discloses a Beidou satellite-based three-frequency double-ionosphere-free combined precision single-point positioning model and method, and relates to the technical field of satellite positioning. The method comprises the following steps: S1, receiving four Beidou positioning frequency band signals B1I, B3I, B1C and B2a, a PPP-B2b signal and a broadcast ephemeris in real time, and decoding; s2, matching the PPP-B2b signal with a broadcast ephemeris, correcting a calculation result of the broadcast ephemeris by satellite orbit correction information to obtain a real-time satellite orbit coordinate, and correcting a broadcast ephemeris clock error to obtain a real-time accurate clock error; and S3, combining the observation values of three frequencies of BDS-3 in pairs, creating two groups of non-ionosphere observation equations for each satellite, and constructing a three-frequency double-ionosphere combination model. According to the method, the BDS-3 three-frequency observation value is reasonably utilized, the satellite-based PPP positioning performance is improved, and the service range of the PPP is expanded.

Description

Technical Field

[0001] The present invention relates to the field of satellite positioning technology, and in particular to a Beidou satellite-based triple-frequency dual-ionosphere-free combined precise single-point positioning model and method. Background Art

[0002] With the development of BDS-3, the PPP-B2b signals of the three GEO satellites (C59-C61) in the BeiDou-3 nominal space constellation are used as data broadcast channels to provide free real-time PPP (precision point positioning) services for users on the earth's surface and in the near-earth area extending to 1,000 kilometers in the air. Users modify the corresponding broadcast ephemeris into real-time precise ephemeris through the correction parameters such as the precise satellite orbit and clock error of BDS-3 and GPS received, thereby achieving real-time dynamic absolute positioning.

[0003] The integration of multiple frequencies and multiple systems is the development trend of PPP. More satellite signal data will provide more effective redundant information, which can not only improve the efficiency of ambiguity fixation, but also improve the performance of parameter estimation. Most of the current BDS receivers can provide three-frequency or above data, and the current PPP-B2b correction information not only includes the orbit and clock corrections of BDS, but also includes the satellite code deviation corrections of BDS-3 satellites. However, the current three-frequency PPP mostly uses IGS post-precision products, and there is no BDS three-frequency PPP model for PPP-B2b products. The frequency points that different receivers or different project projects need to support will also be different. In terms of the scope of use, traditional PPP positioning relies on the ground network to broadcast precise orbit and clock products. High-precision PPP positioning cannot be achieved in deserts, open seas and other areas. In terms of model solution, the existing PPP-B2b positioning is mostly based on dual-frequency information, and fails to make full use of the three-frequency signals of most equipment.

[0004] To this end, we designed the Beidou satellite-based triple-frequency dual ionospheric-free combined precise point positioning model and method to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the current three-frequency PPP mostly adopts IGS post-precision products, and there is no BDS three-frequency PPP model for PPP-B2b products. The frequency points that different receivers or different project engineering need to support will also be different. The existing PPP-B2b positioning is mostly based on dual-frequency information, and fails to make full use of the three-frequency signals possessed by most equipment. It needs to rely on the ground network to achieve high-precision positioning. The proposed Beidou satellite-based three-frequency dual ionosphere-free combined precise single-point positioning model and method studies and gives a three-frequency PPP model based on PPP-B2b service, reasonably utilizes BDS-3 three-frequency observation values, improves satellite-based PPP positioning performance, and expands the service scope of PPP.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The method for constructing a Beidou satellite-based triple-frequency dual-ionosphere-free combined precise point positioning model includes the following steps:

[0008] Step S1: receiving and decoding the Beidou B1I, B3I, B1C and B2a positioning frequency band signals, PPP-B2b signals and broadcast ephemeris in real time;

[0009] Step S2: The PPP-B2b signal is matched with the broadcast ephemeris, and the satellite orbit correction information is corrected according to the calculation result of the broadcast ephemeris to obtain the real-time satellite orbit coordinates, and the broadcast ephemeris clock error is corrected to obtain the real-time accurate clock error;

[0010] In step S3, the observation values ​​of the three frequencies of BDS-3 are combined in pairs, two sets of ionosphere-free observation equations are created for each satellite, and a three-frequency dual-ionosphere combination model is constructed.

[0011] Preferably, the broadcast ephemeris includes CNAV1 broadcast ephemeris of Beidou satellites or LNAV broadcast ephemeris of GPS satellites.

[0012] Preferably, in step S2, the process of matching the PPP-B2b signal with the broadcast ephemeris is as follows:

[0013] Step S21, information type matching, matching the received type correction information through the state space version number to indicate that all information is generated by the same configuration;

[0014] Step S22, matching the clock correction number with the mask information, matching the clock correction information with the mask information through the satellite mask data version number, determining the satellite pseudo-random noise code corresponding to each satellite correction number, and directly matching the orbit correction number with the mask to determine the satellite number;

[0015] Step S23, matching the clock correction number with the orbit correction number, matching the clock correction number, the orbit correction number and the corresponding satellite pseudo-random noise code through the data correction release number;

[0016] Step S24, the orbit correction number is matched with the broadcast ephemeris, and the matched PPP-B2b correction information is matched with the broadcast ephemeris through the basic navigation message version number and the clock error parameter version number parameter in the broadcast ephemeris.

[0017] Preferably, in step S2, the PPP-B2b satellite orbit correction information is corrected for the calculation result of the broadcast ephemeris to obtain the real-time satellite orbit coordinates, and the calculation formula for the orbit correction is as follows:

[0018] (1);

[0019] (2);

[0020] (3);

[0021] In the formula, is the PPP-Bb orbit correction in the Earth-centered Earth-fixed coordinate system, are the radial, tangential and normal corrections for the PPP-B2b orbit, are radial, tangential and normal direction unit vectors respectively, and are the position and velocity vectors in the Earth-centered Earth-fixed coordinate system, The real-time precise satellite is obtained after performing PPP-B2b orbit correction on the broadcast ephemeris. is the satellite position vector calculated from the broadcast ephemeris.

[0022] Preferably, in step S2, the broadcast ephemeris clock error is corrected to obtain a real-time accurate clock error, and the calculation formula of the clock error correction number is as follows:

[0023] (4);

[0024] In the formula, is the corrected real-time precise clock error, is the broadcast ephemeris satellite clock error, is the PPP-B2b clock correction number, is the speed of light in a vacuum.

[0025] Preferably, in step S3, the observation values ​​of the three frequencies of BDS-3 are combined in pairs, two sets of ionosphere-free observation equations are created for each satellite, and the expression for constructing the three-frequency dual-ionosphere combination model is as follows:

[0026] (5);

[0027] (6);

[0028] In the above formula, the subscript Indicates frequency The ionospheric-free combination of and j, is the user's ionospheric-free pseudorange observation value, is the ionospheric-free carrier observation value, is the geometric distance between the receiver and the satellite, and are the receiver and satellite clock errors, is the speed of light in vacuum, is the tropospheric delay between the satellite and the receiver, Indicates the pseudorange hardware delay at the satellite end. Indicates frequency and j ionosphere-free combination pseudorange hardware delay, is the floating point disambiguation degree, is the ionospheric-free wavelength, and are the observation noise corresponding to the pseudorange and carrier respectively; among them,

[0029] (7);

[0030] In the formula, represents the receiver clock error, represents the pseudorange hardware delay of the ionosphere-free combination at the receiver, represents the ambiguity of the ionospheric-free combination, represents the carrier hardware delay of the ionosphere-free combination at the receiver end, Indicates the carrier hardware delay of the ionosphere-free combination on the satellite side.

[0031] Preferably, after the real-time precise orbit and clock errors calculated by PPP-B2b are corrected as known values, and The receiver clock error is The receiver clock error is unified as a benchmark, and the linearized equation of the ionosphere-free combined pseudorange and carrier observation is obtained as follows:

[0032] (8);

[0033] (9);

[0034] (10);

[0035] In the formula, represents the BDS pseudorange observation value, is the unknown position parameter after linearization The coefficient of and represents the coefficient of the ionospheric combination, , , Indicates frequency The frequency value of Indicates frequency The frequency value of Indicates the satellite frequency The coding difference with the reference frequency B3I, Indicates the receiver frequency and the coding difference of frequency j; represents the difference in hardware delay between two combined observations;

[0036] The expression of the estimated parameters of the single BDS-3 triple-frequency ionosphere-free dual combination of PPP-B2b is:

[0037] (11);

[0038] In the formula, is the unknown position parameter after linearization, and Both represent the ambiguity of the ionospheric-free combination.

[0039] Preferably, the three-frequency dual-ionosphere combination model is compatible with the BDS-3 and GPS dual-system solutions. The BDS-3 dual-ionosphere-free combination is superimposed with the GPS signal L1 band and L2 band ionosphere-free combination. The GPS satellite does not need to correct the differential code deviation. The formula is as follows:

[0040] (12);

[0041] In the formula, is the unknown position parameter after linearization The coefficient of Indicates the clock error at the BDS receiver end, Indicates the clock error at the GPS receiver end, is the tropospheric delay between the satellite and the receiver, represents the BDS pseudorange observation noise, represents the BDS pseudorange observation value after correcting the differential code bias, It represents the GPS pseudorange observation value after correcting the differential code bias. represents the GPS pseudorange observation noise;

[0042] (13);

[0043] In the formula, represents the carrier observation value of the BDS ionosphere-free combination, represents the carrier observation value of GPS ionosphere-free combination, is the ionospheric-free wavelength, is the floating point disambiguation degree, represents the noise of the carrier observations of the BDS ionosphere-free combination, Represents the noise of the carrier observation value of the GPS ionosphere-free combination;

[0044] After BDS-3 corrects the satellite differential code bias, the expression of the estimated parameters of the triple-frequency dual ionosphere combination model is:

[0045] (14);

[0046] In the formula, is the unknown position parameter after linearization, Indicates the BDS ionosphere-free receiver clock error, Indicates the GPS ionospheric-free receiver clock error, Indicates the hardware delay reassembly value, and represents the ionospheric-free combined ambiguity after BDS reorganization, Represents the ionospheric-free combined ambiguity after GPS reorganization.

[0047] A Beidou satellite-based three-frequency dual ionosphere-free combined precise point positioning model, which is a three-frequency dual ionosphere combination model created by using a receiver and a computer server to perform the precise point positioning task of satellite navigation. The formula of the three-frequency dual ionosphere combination model is as follows:

[0048] ;

[0049] ;

[0050] In the above formula, the subscript Indicates frequency The ionospheric-free combination of and j, is the user's ionospheric-free pseudorange observation value, is the ionospheric-free carrier observation value, is the geometric distance between the receiver and the satellite, and are the receiver and satellite clock errors, is the speed of light in vacuum, is the tropospheric delay between the satellite and the receiver, Indicates the pseudorange hardware delay at the satellite end. Indicates frequency and j ionosphere-free combination pseudorange hardware delay, is the floating point disambiguation degree, is the ionospheric-free wavelength, and are the observation noise corresponding to the pseudorange and carrier respectively; among them,

[0051] ;

[0052] In the formula, represents the receiver clock error, represents the pseudorange hardware delay of the ionosphere-free combination at the receiver, represents the ambiguity of the ionospheric-free combination, represents the carrier hardware delay of the ionosphere-free combination at the receiver end, Indicates the carrier hardware delay of the ionosphere-free combination on the satellite side.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention reuses one frequency point and constructs two ionosphere combinations using three frequencies, which effectively shortens the time for PPP convergence. The model is applicable to any three frequency points, and when multi-system solution is adopted, no requirements are made on the combination mode of other systems. It has strong flexibility and good compatibility, effectively solves the technical defects of different receivers or different project engineering needing to support different frequency points, and can achieve high-precision positioning without relying on the ground network. Whether it is static or simulated dynamic positioning, the three-frequency dual ionosphere combination model shows shorter convergence time and higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A flowchart of constructing a triple-frequency dual-ionospheric combination model for Beidou satellite-based triple-frequency dual-ionosphere-free combination precise point positioning in this embodiment;

[0055] Figure 2 Schematic diagram of the number of visible satellites of the base station for Beidou satellite-based triple-frequency dual-ionosphere-free combined precise point positioning in this embodiment;

[0056] Figure 3 Schematic diagram of the base station PDOP value of the Beidou satellite-based triple-frequency dual-ionosphere-free combined precise point positioning in this embodiment;

[0057] Figure 4 Schematic diagram of the three-frequency static positioning result of the Beidou satellite-based three-frequency dual-ionosphere-free combined precise point positioning in this embodiment;

[0058] Figure 5 This is a schematic diagram of the three-frequency simulated dynamic positioning results of the Beidou satellite-based three-frequency dual-ionosphere-free combined precise point positioning in this embodiment. DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0060] The terms and definitions defined in "Beidou Satellite Navigation Terminology" (GB / T 39267-2020) apply to this embodiment.

[0061] Precise Point Positioning (PPP) refers to a method that uses only a single-station GNSS receiver to collect raw observation data, and uses the precise satellite orbits and precise satellite clock errors provided by the International GNSS Services (IGS) or solved by itself to accurately correct or process the errors in the original observation equation to obtain high-precision single-point coordinates at the centimeter to decimeter level. Precise point positioning makes up for the shortcomings of the poor accuracy of standard single-point positioning, and can obtain high-precision positioning results without relying on relative positioning, making it possible to achieve globally unified GNSS high-precision positioning services. PPP has unique application value in the fields of satellite precision orbit determination, earthquake monitoring, crustal movement monitoring, tsunami monitoring, marine development, precision agriculture and autonomous driving.

[0062] The Beidou satellite-based three-frequency dual-ionosphere-free combined precise single-point positioning model construction method proposed in this embodiment is synchronously accompanied by the Beidou satellite-based three-frequency dual-ionosphere-free combined precise single-point positioning method, such as Figure 1 As shown, the specific construction of the triple-frequency dual ionosphere combination model includes the following steps:

[0063] Step S1, data signal reception: real-time reception of Beidou B1I, B3I, B1C and B2a positioning frequency band signals, PPP-B2b signals and broadcast ephemeris, and decoding; receiving signals from any three frequency bands can be used for resolution. Beidou satellites (BDS-3) use CNAV1 broadcast ephemeris, and GPS satellites use LNAV ephemeris.

[0064] Step S2, precise orbit / clock error restoration: First, the PPP-B2b signal is matched with the broadcast ephemeris, and the satellite orbit correction information is corrected according to the calculation result of the broadcast ephemeris to obtain the real-time satellite orbit coordinates, and the broadcast ephemeris clock error is corrected to obtain the real-time precise clock error.

[0065] The PPP-B2b signal is matched with the broadcast ephemeris, including the matching of information type, the matching of clock correction number and mask information, the matching of clock correction number and orbit correction number, and the matching of orbit correction number and broadcast ephemeris. The matching process of PPP-B2b signal and broadcast ephemeris is as follows:

[0066] In step S21, the information type is matched by using the state space version number (Issue of Data, State Space Representation, IOD SSR) to match the four types of correction information received to indicate that all information is generated by the same configuration.

[0067] Step S22, matching the clock correction number with the mask information, through the satellite mask data version number (Issue of Data, PRN mask, IODP), the clock correction information is matched with the mask information, the satellite pseudo-random noise code (PRN number) corresponding to each satellite correction number is determined, and the orbit correction number is directly matched with the mask to determine the satellite number;

[0068] Step S23, matching the clock correction number with the orbit correction number, by matching the clock correction number, the orbit correction number and the corresponding satellite pseudo-random noise code (PRN number) through the data correction release number (Issue of Data, Correction, IOD Corr);

[0069] Step S24, the orbit correction number is matched with the broadcast ephemeris, through the basic navigation message version number (Issue of Data, Navigation, IODN) and the clock error parameter version number (Issue of Data, Clock, IODC) in the broadcast ephemeris, and the matched PPP-B2b correction information is matched with the broadcast ephemeris.

[0070] The PPP-B2b satellite orbit correction information is used to correct the calculation results of the broadcast ephemeris to obtain the real-time satellite orbit coordinates. The calculation formula for the orbit correction is as follows:

[0071] (1);

[0072] (2);

[0073] (3);

[0074] In the formula, is the PPP-Bb orbit correction in the Earth-centered Earth-fixed coordinate system, are the radial, tangential and normal corrections for the PPP-B2b orbit, , For navigation satellites, are radial, tangential and normal direction unit vectors respectively, and are the position and velocity vectors in the Earth-centered Earth-fixed coordinate system, The real-time precise satellite is obtained after performing PPP-B2b orbit correction on the broadcast ephemeris. is the satellite position vector calculated from the broadcast ephemeris.

[0075] PPP-B2b clock correction can directly correct the broadcast ephemeris clock error to obtain real-time accurate clock error. The calculation formula of the clock correction number is as follows:

[0076] (4);

[0077] In the formula, is the corrected real-time precise clock error, is the broadcast ephemeris satellite clock error, is the PPP-B2b clock correction number, is the speed of light in a vacuum.

[0078] In step S3, the observation values ​​of the three frequencies of BDS-3 are combined in pairs, two sets of ionosphere-free observation equations are created for each satellite, and a three-frequency dual-ionosphere combination model is constructed.

[0079] The three-frequency dual-ionosphere combination model uses the observation values ​​of the three frequencies of BDS-3 to combine them in pairs, and creates two sets of ionosphere-free observation equations for each satellite. For example, the first and second frequencies, and the first and third frequencies are combined in an ionosphere-free manner to eliminate the influence of the first-order delay of the ionosphere. The expression for constructing the three-frequency dual-ionosphere combination model in this example is as follows:

[0080] (5);

[0081] (6);

[0082] In the above formula, the superscript s and subscript r represent the GNSS satellite and user receiver respectively, and the subscript Indicates frequency The ionospheric-free combination of and j, is the user's ionospheric-free pseudorange observation value, is the ionospheric-free carrier observation value, is the geometric distance between the receiver and the satellite, and are the receiver and satellite clock errors, is the speed of light in vacuum, is the tropospheric delay between the satellite and the receiver, Indicates the pseudorange hardware delay at the satellite end. Indicates frequency and j ionosphere-free combination pseudorange hardware delay, is the floating point disambiguation degree, is the ionospheric-free wavelength, and are the observation noise corresponding to the pseudorange and carrier respectively; among them,

[0083] (7);

[0084] In the formula, represents the receiver clock error, represents the pseudorange hardware delay of the ionosphere-free combination at the receiver, represents the ambiguity of the ionospheric-free combination, represents the carrier hardware delay of the ionosphere-free combination at the receiver end, Indicates the carrier hardware delay of the ionosphere-free combination on the satellite side.

[0085] After the real-time precise orbit and clock errors calculated by PPP-B2b are corrected as known values, and The receiver clock error is The receiver clock error is unified as a benchmark, and the linearized equation of the ionosphere-free combined pseudorange and carrier observation is obtained as follows:

[0086] (8);

[0087] (9);

[0088] (10);

[0089] In the formula, represents the BDS pseudorange observation value, is the unknown position parameter after linearization The coefficient of and represents the coefficient of the ionospheric combination, , , Indicates frequency The frequency value of Indicates frequency The frequency value of Indicates the satellite frequency The coding difference with the reference frequency B3I, Indicates the receiver frequency and the coding difference of frequency j; represents the difference in hardware delay between two combined observations;

[0090] The expression of the estimated parameters of the single BDS-3 triple-frequency ionosphere-free dual combination of PPP-B2b is:

[0091] (11);

[0092] In the formula, is the unknown position parameter after linearization, and Both represent the ambiguity of the ionospheric-free combination.

[0093] The triple-frequency dual-ionosphere combination model is compatible with the BDS-3 and GPS dual-system solutions. Taking the superposition of the BDS-3 dual-ionosphere-free combination and the GPS signal L1 band and L2 band ionosphere-free combination as an example, the GPS satellite does not need to perform differential code bias (DCB) correction. The formula is as follows:

[0094] (12);

[0095] In the formula, Indicates the clock error at the GPS receiver end, represents the BDS pseudorange observation noise, represents the BDS pseudorange observation value after correcting the differential code bias, It represents the GPS pseudorange observation value after correcting the differential code bias. represents the GPS pseudorange observation noise.

[0096] (13);

[0097] In the formula, represents the carrier observation value of the BDS ionosphere-free combination, represents the carrier observation value of GPS ionosphere-free combination, represents the noise of the carrier observations of the BDS ionosphere-free combination, Represents the noise of the carrier observations of the GPS ionosphere-free combination.

[0098] After BDS-3 corrects the satellite differential code bias, the expression of the estimated parameters of the triple-frequency dual ionosphere combination model is:

[0099] (14);

[0100] In the formula, Indicates the BDS ionosphere-free receiver clock error, Indicates the GPS ionospheric-free receiver clock error, Indicates the hardware delay reassembly value, and represents the ionospheric-free combined ambiguity after BDS reorganization, Represents the ionospheric-free combined ambiguity after GPS reorganization.

[0101] In another application scenario of this embodiment, a three-frequency dual-ionosphere combination model for Beidou satellite-based three-frequency dual-ionosphere-free combination precise point positioning is also proposed. The model is a three-frequency dual-ionosphere combination model created by using a receiver and a computer server to perform the precise point positioning task of satellite navigation. The formula of the three-frequency dual-ionosphere combination model is as follows:

[0102] ;

[0103] ;

[0104] In the above formula, the subscript Indicates frequency The ionospheric-free combination of and j, is the user's ionospheric-free pseudorange observation value, is the ionospheric-free carrier observation value, is the geometric distance between the receiver and the satellite, and are the receiver and satellite clock errors, is the speed of light in vacuum, is the tropospheric delay between the satellite and the receiver, Indicates the pseudorange hardware delay at the satellite end. Indicates frequency and j ionosphere-free combination pseudorange hardware delay, is the floating point disambiguation degree, is the ionospheric-free wavelength, and are the observation noise corresponding to the pseudorange and carrier respectively; among them,

[0105] ;

[0106] In the formula, represents the receiver clock error, represents the pseudorange hardware delay of the ionosphere-free combination at the receiver, represents the ambiguity of the ionospheric-free combination, represents the carrier hardware delay of the ionosphere-free combination at the receiver end, Indicates the carrier hardware delay of the ionosphere-free combination on the satellite side.

[0107] The three-frequency dual-ionosphere combination model of this embodiment collects ZHD0 data of a certain base station to analyze static and dynamic positioning results. Figure 2 is the number of visible satellites of the base station, Figure 3 is the PDOP value of the base station, Figure 4 The three-frequency static positioning results (the left column is the dual ionosphere-free combination, the middle column is the non-difference non-combination, and the right column is the dual system of the three-frequency dual ionosphere combination model of this embodiment), Figure 5 is the result of three-frequency dynamic positioning. Figure 4 and Figure 5IF in the middle represents the dual ionosphere-free combination, UC represents the non-difference non-combination, and E, N, and U represent the dynamic positioning results along the east, north, and vertical directions, respectively. Whether it is static or simulated dynamic positioning, the three-frequency dual ionosphere combination model shows a shorter convergence time and higher accuracy. When simulating dynamic positioning, the non-difference non-combination also has large fluctuations, while the fluctuation amplitude of the dual ionosphere-free combination is significantly smaller.

[0108] pass Figure 2-Figure 5 It can be seen that the positioning accuracy of the model of this embodiment is further improved after using the dual system, which proves that the present invention has good compatibility and makes full use of the information of the two systems. By using the three-frequency signal of the equipment and effectively utilizing the characteristics of the ionosphere, the present invention reuses one frequency point and uses three frequencies to construct two ionosphere combinations, which effectively shortens the PPP convergence time. The model is applicable to any three frequency points, and when using multi-system solution, it does not require the combination of other systems, and has strong flexibility and good compatibility.

[0109] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A Beidou satellite-based triple-frequency dual-ionosphere-free combined precise point positioning model construction method, characterized in that: The following steps are involved: Step S1: receiving and decoding the Beidou B1I, B3I, B1C and B2a positioning frequency band signals, PPP-B2b signals and broadcast ephemeris in real time; Step S2: The PPP-B2b signal is matched with the broadcast ephemeris, and the satellite orbit correction information is corrected according to the calculation result of the broadcast ephemeris to obtain the real-time satellite orbit coordinates, and the broadcast ephemeris clock error is corrected to obtain the real-time accurate clock error; In step S3, the observation values ​​of the three frequencies of BDS-3 are combined in pairs, two sets of ionosphere-free observation equations are created for each satellite, and a three-frequency dual-ionosphere combination model is constructed.

2. The Beidou satellite-based triple-frequency dual-ionospheric-free combined precise point positioning model construction method according to claim 1 is characterized in that: The broadcast ephemeris includes the CNAV1 broadcast ephemeris of the Beidou satellite or the LNAV broadcast ephemeris of the GPS satellite.

3. The Beidou satellite-based triple-frequency dual-ionospheric-free combined precise point positioning model construction method according to claim 1 is characterized in that: In step S2, the process of matching the PPP-B2b signal with the broadcast ephemeris is as follows: Step S21, information type matching, matching the received type correction information through the state space version number to indicate that all information is generated by the same configuration; Step S22, matching the clock correction number with the mask information, matching the clock correction information with the mask information through the satellite mask data version number, determining the satellite pseudo-random noise code corresponding to each satellite correction number, and directly matching the orbit correction number with the mask to determine the satellite number; Step S23, matching the clock correction number with the orbit correction number, matching the clock correction number, the orbit correction number and the corresponding satellite pseudo-random noise code through the data correction release number; Step S24, the orbit correction number is matched with the broadcast ephemeris, and the matched PPP-B2b correction information is matched with the broadcast ephemeris through the basic navigation message version number and the clock error parameter version number parameter in the broadcast ephemeris.

4. The Beidou satellite-based triple-frequency dual-ionospheric-free combined precise point positioning model construction method according to claim 1 is characterized in that: In step S2, the PPP-B2b satellite orbit correction information is corrected for the calculation result of the broadcast ephemeris to obtain the real-time satellite orbit coordinates. The calculation formula for the orbit correction is as follows: （1）； （2）； （3）； In the formula, is the PPP-Bb orbit correction in the Earth-centered Earth-fixed coordinate system, are the radial, tangential and normal corrections for the PPP-B2b orbit, are radial, tangential and normal direction unit vectors respectively, and are the position and velocity vectors in the Earth-centered Earth-fixed coordinate system, The real-time precise satellite is obtained after performing PPP-B2b orbit correction on the broadcast ephemeris. is the satellite position vector calculated from the broadcast ephemeris.

5. The Beidou satellite-based triple-frequency dual-ionospheric-free combined precise point positioning model construction method according to claim 1 is characterized in that: In step S2, the broadcast ephemeris clock error is corrected to obtain the real-time accurate clock error. The calculation formula of the clock error correction number is as follows: （4）； In the formula, is the corrected real-time precise clock error, is the broadcast ephemeris satellite clock error, is the PPP-B2b clock correction number, is the speed of light in a vacuum.

6. The Beidou satellite-based triple-frequency dual-ionospheric-free combined precise point positioning model construction method according to claim 1 is characterized in that: In step S3, the observation values ​​of the three frequencies of BDS-3 are combined in pairs, and two sets of ionosphere-free observation equations are created for each satellite. The expression of the three-frequency dual-ionosphere combination model is as follows: （5）； （6）； In the above formula, the subscript Indicates frequency The ionospheric-free combination of and j, is the user's ionospheric-free pseudorange observation value, is the ionospheric-free carrier observation value, is the geometric distance between the receiver and the satellite, and are the clock errors of the receiver and satellite respectively, is the speed of light in vacuum, is the tropospheric delay between the satellite and the receiver, Indicates the pseudorange hardware delay at the satellite end. Indicates frequency and j ionosphere-free combination pseudorange hardware delay, is the floating point disambiguation degree, is the ionospheric-free wavelength, and are the observation noise corresponding to the pseudorange and carrier respectively; among them, （7）； In the formula, represents the receiver clock error, represents the pseudorange hardware delay of the ionosphere-free combination at the receiver, represents the ambiguity of the ionospheric-free combination, represents the carrier hardware delay of the ionosphere-free combination at the receiver end, Indicates the carrier hardware delay of the ionosphere-free combination on the satellite side.

7. The Beidou satellite-based triple-frequency dual-ionospheric-free combined precise point positioning model construction method according to claim 6 is characterized in that: After the real-time precise orbit and clock errors calculated by PPP-B2b are corrected as known values, and The receiver clock error is The receiver clock error is unified as a benchmark, and the linearized equation of the ionosphere-free combined pseudorange and carrier observation is obtained as follows: （8）； （9）； （10）； In the formula, represents the BDS pseudorange observation value, is the unknown position parameter after linearization The coefficient of and represents the coefficient of the ionospheric combination, , , Indicates frequency The frequency value of Indicates frequency The frequency value of Indicates the satellite frequency The coding difference with the reference frequency B3I, Represents the coding difference between frequency i and frequency j at the receiver; represents the difference in hardware delay between two combined observations; The expression of the estimated parameters of the single BDS-3 triple-frequency ionosphere-free dual combination of PPP-B2b is: （11）； In the formula, is the unknown position parameter after linearization, and Both represent the ambiguity of the ionospheric-free combination.

8. The Beidou satellite-based triple-frequency dual-ionospheric-free combined precise point positioning model construction method according to claim 1 is characterized in that: The triple-frequency dual-ionosphere combination model is compatible with the BDS-3 and GPS dual-system solutions. The BDS-3 dual-ionosphere-free combination is superimposed with the GPS signal L1 band and L2 band ionosphere-free combination. The GPS satellite does not need to correct the differential code deviation. The formula is as follows: （12）； In the formula, is the unknown position parameter after linearization The coefficient of Indicates the clock error at the BDS receiver end, Indicates the clock error at the GPS receiver end, is the tropospheric delay between the satellite and the receiver, represents the BDS pseudorange observation noise, represents the BDS pseudorange observation value after correcting the differential code bias, It represents the GPS pseudorange observation value after correcting the differential code bias. represents the GPS pseudorange observation noise; （13）； In the formula, represents the carrier observation value of the BDS ionosphere-free combination, represents the carrier observation value of GPS ionosphere-free combination, is the ionospheric-free wavelength, is the floating point disambiguation degree, represents the noise of the carrier observations of the BDS ionosphere-free combination, Represents the noise of the carrier observation value of the GPS ionosphere-free combination; After BDS-3 corrects the satellite differential code bias, the expression of the estimated parameters of the triple-frequency dual ionosphere combination model is: （14）； In the formula, is the unknown position parameter after linearization, Indicates the BDS ionosphere-free receiver clock error, Indicates the GPS ionospheric-free receiver clock error, Indicates the hardware delay reassembly value, and represents the ionospheric-free combined ambiguity after BDS reorganization, Represents the ionospheric-free combined ambiguity after GPS reorganization.

9. A Beidou satellite-based triple-frequency dual-ionosphere-free combined precise point positioning model, characterized in that: The model is a three-frequency dual-ionosphere combination model created by using a receiver and a computer server to perform the precise point positioning task of satellite navigation. The formula of the three-frequency dual-ionosphere combination model is as follows: ； ； In the above formula, the subscript Indicates frequency The ionospheric-free combination of and j, is the user's ionospheric-free pseudorange observation value, is the ionospheric-free carrier observation value, is the geometric distance between the receiver and the satellite, and are the clock errors of the receiver and satellite respectively, is the speed of light in vacuum, is the tropospheric delay between the satellite and the receiver, Indicates the pseudorange hardware delay at the satellite end. Indicates frequency and j ionosphere-free combination pseudorange hardware delay, is the floating point disambiguation degree, is the ionospheric-free wavelength, and are the observation noise corresponding to the pseudorange and carrier respectively; among them, ； In the formula, represents the receiver clock error, represents the pseudorange hardware delay of the ionosphere-free combination at the receiver, represents the ambiguity of the ionospheric-free combination, represents the carrier hardware delay of the ionosphere-free combination at the receiver end, Indicates the carrier hardware delay of the ionosphere-free combination on the satellite side.

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