Beidou precise point positioning method based on double-frequency combination

Abstract

The invention relates to the technical field of satellite navigation and positioning, and discloses a Beidou precise point positioning method based on double-frequency combination, which comprises the following steps of: firstly, acquiring an original observation file and various correction files of a double-frequency signal from an IGS official website; a clean observation value is obtained through the steps of data validity checking and data preprocessing; carrying out correction and correction to obtain an error correction value; establishing a Beidou dual-frequency ionospheric elimination combination model, and performing dual-frequency DCB correction on the combination observation value to obtain a corrected dual-frequency combination observation value; constructing a double-frequency ionosphere elimination observation equation, and performing coordinate solution by using Kalman filtering to obtain a positioning result of double-frequency combination; analyzing the positioning result of the double-frequency combination, counting the error value of the positioning result, and evaluating the positioning precision and the convergence time; according to the invention, when DCB correction is considered, a dual-frequency ionosphere-eliminating PPP positioning model is established by using a BDS signal, so that the positioning precision can be remarkably improved, and the convergence time can be shortened.

Description

Technical Field

[0001] The present invention relates to the field of satellite navigation and positioning technology, and in particular to a Beidou precise single-point positioning method based on dual-frequency combination. Background Art

[0002] Precise point positioning (PPP) technology is developed from standard point positioning technology. It only needs to rely on a single GNSS receiver to complete the positioning process. With the help of precise clock and ephemeris products provided by relevant organizations or institutions, each error item is accurately corrected to obtain centimeter-level high-precision positioning results. The whole process does not require the establishment of a base station, the operation is flexible, the distance limit is avoided, and the cost is lower. Therefore, it is widely used in surveying, mapping, remote sensing, geographic information and other fields. The general precise point positioning processing flow includes: data input, data preprocessing, parameter estimation, and result output. Data input is to input existing data files, including observation files and broadcast ephemeris files collected by GNSS receivers, precise orbit and clock corrections, earth rotation parameters, antenna phase corrections, tidal load corrections, and DCB correction files provided by external organizations; data preprocessing is to correct gross errors and detect cycle slips in observation files, and to interpolate the correction files in time and space to obtain initial calculation values; parameter estimation includes forming a dual-frequency ionosphere-free combination or non-difference non-combination function model, a random model and filtering weighted by altitude angle, etc., and finally outputs the station coordinates and covariance matrix, receiver clock error and ambiguity parameters, etc.

[0003] BeiDou Navigation Satellite System (BDS) is a comprehensive navigation and positioning system independently developed by my country. It not only provides basic positioning and navigation services, but also has multiple functions such as time synchronization, inter-satellite augmentation, ground-based augmentation, short message communication and international search and rescue. In July 2020, BeiDou Navigation Satellite System-3 (BDS-3) was officially launched worldwide. Compared with the original BDS-2, BDS-3 has made significant optimizations in the satellite constellation layout. In terms of signal system, BDS-3 has added two new frequencies, B1C and B2a, while retaining the B1I and B3I frequencies of BDS-2. The B2I frequency in BDS-2 has been renamed B2b. Although the frequency has not changed, its modulation method has changed. The addition of new frequency points has further improved the compatibility of the BDS-3 system. Summary of the invention

[0004] The present invention aims to provide a Beidou precise point positioning method based on dual-frequency combination, so as to realize the purpose of establishing a dual-frequency ionospheric elimination PPP positioning model by using BDS signals when considering DCB correction, significantly improving positioning accuracy and shortening convergence time.

[0005] In order to achieve the above object, the present invention provides the following method:

[0006] A Beidou precise point positioning method based on dual-frequency combination provided by the present invention is:

[0007] Step 1: Obtain the original observation files, precise orbits, precise clock errors, and various correction files from the IGS official website;

[0008] Step 2: Obtain clean observation values ​​by performing data validity verification and data preprocessing on the original observation files, precise orbits, precise clock errors, and various correction files;

[0009] Step 3: According to the empirical error processing model, the clean observation value is corrected for satellite clock error, tropospheric error, earth rotation correction and relativistic effect to obtain an error correction value;

[0010] Step 4: Establish the Beidou dual-frequency ionospheric elimination combination model, perform dual-frequency DCB correction on the combined observations, and obtain the corrected dual-frequency combined observations;

[0011] Step 5: construct a dual-frequency ionospheric elimination observation equation using the error correction value and the corrected dual-frequency combination observation value, and use Kalman filtering to solve the coordinates to obtain a dual-frequency combination positioning result;

[0012] Step 6: Analyze the positioning results of the dual-frequency combination, count the error values ​​of the positioning results, and evaluate the positioning accuracy and convergence time.

[0013] Preferably, the dual-frequency signals in step 1 are B1C / B2a, B1C / B2b, B1I / B2a and B1I / B2b.

[0014] Preferably, the step of establishing a Beidou dual-frequency ionospheric elimination combination model in step 4, performing dual-frequency DCB correction on the combined observation value, and obtaining the corrected dual-frequency combined observation value step is achieved by linearizing the dual-frequency observation values ​​of the pseudorange and carrier phase.

[0015] Preferably, the Beidou dual-frequency ionospheric elimination combination model in step 4 is specifically:

[0016]

[0017] in, and They represent the pseudorange observation value and the carrier phase observation value, r and s represent the receiver and the satellite, respectively, and j is used to distinguish the frequency band of the observation value. represents the geometric distance between the satellite and the receiver, and dt s represent the receiver clock error and satellite clock error respectively, is the zenith tropospheric delay, is the corresponding mapping function, and γ j is the ionospheric delay caused by the signal propagation from the satellite to the receiver and its corresponding amplification factor, where γ j =(f1 / f i ) 2 , f represents frequency, b r,j and B r,j are the uncalibrated code delay and uncalibrated phase delay of the receiver, respectively. and Respectively represent the UCD and UPD of the satellite, and The observation noise of the raw pseudorange and carrier phase observations of the satellite and receiver, respectively.

[0018] Preferably, the steps of establishing a Beidou dual-frequency ionospheric elimination combination model, performing dual-frequency DCB correction on the combined observation values, and obtaining the corrected dual-frequency combined observation values ​​include: the DCB is the time delay difference caused by the satellite and the receiver hardware for different frequencies or different ranging codes at the same frequency. If it is the DCB on the receiver side, it needs to be converted into the receiver clock difference for parameter estimation. If it is the DCB on the satellite side, it needs to be corrected.

[0019] Preferably, in step 5, Kalman filter prediction is first performed, that is, in each positioning epoch, the Kalman filter first uses the state equation to predict the current position, speed and receiver clock error of the receiver.

[0020] Preferably, in step 5, a Kalman filter update is performed based on the state prior estimate and the satellite position and velocity provided by the satellite ephemeris to obtain a Kalman filter update result, and a correction amount of the system state estimate and the optimal estimate after correction are obtained through the observed quantity residual.

[0021] Preferably, the observation residual is used to monitor the integrity of the Kalman filter update result of step 5. If the observation residual exceeds the limit, the corresponding satellite observation is eliminated and the Kalman filter is updated again. If the observation residual does not exceed the limit, the corresponding satellite observation is not eliminated and the Kalman filter is not updated again.

[0022] Preferably, the steps of analyzing the positioning results of the dual-frequency combination, counting the error values ​​of the positioning results, and evaluating the positioning accuracy and convergence time include: the evaluation of the positioning accuracy and convergence time specifically refers to analyzing the positioning accuracy and convergence time of the dual-frequency PPP from the three directions of N, E, and U, wherein the positioning accuracy is the average value of the errors in each direction that reaches 0.1m in the three directions and is stable for at least 20 epochs. If it exceeds 0.1m, the accuracy of the last epoch shall prevail. The convergence time refers to the time required for the positioning error to reach within 0.1 meters in the three directions and remain stable for at least 20 epochs.

[0023] The beneficial effects of the present invention are as follows: the present invention linearizes the dual-frequency observation values ​​of pseudorange and carrier phase, uses B1C / B2a, B1C / B2b, B1I / B2a and B1I / B2b dual-frequency signals, constructs a Beidou dual-frequency ionospheric elimination combination model, and uses a state equation to predict the current position, speed and receiver clock error of the receiver. Then, according to the state prior estimation value and the satellite position and speed provided by the satellite ephemeris, a Kalman filter is updated, and a correction amount of the system state estimation value and an optimal estimation value after correction are obtained through the observation quantity residual. Finally, the Kalman filter update result is monitored for integrity using the observation quantity residual. If the observation quantity residual exceeds the limit, the corresponding satellite observation quantity is eliminated and the Kalman filter is updated again. Finally, the positioning result is evaluated, and the influence of DCB on precise single-point positioning is taken into account. The new dual-frequency combination B1C / B2a can effectively improve the positioning accuracy while maintaining a faster positioning convergence speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0025] Figure 1 It is a flow chart of a Beidou precise point positioning method based on dual-frequency combination provided by an embodiment of the present invention.

[0026] Figure 2 It is a schematic diagram of the E-direction error sequence of the positioning result provided by an embodiment of the present invention.

[0027] Figure 3 It is a schematic diagram of an N-directional error sequence of positioning results provided by an embodiment of the present invention.

[0028] Figure 4 It is a schematic diagram of the U direction error sequence of the positioning result provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the technical personnel in the technical field better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in combination with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, device, product or end including a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units inherent to these processes, methods, products or ends.

[0031] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] BeiDou Navigation Satellite System (BDS) is a comprehensive navigation and positioning system independently developed by my country. It not only provides basic positioning and navigation services, but also has multiple functions such as time synchronization, inter-satellite augmentation, ground-based augmentation, short message communication and international search and rescue. In July 2020, BeiDou Navigation Satellite System-3 (BDS-3) was officially launched worldwide. Compared with the original BDS-2, BDS-3 has made significant optimizations in the satellite constellation layout. In terms of signal system, BDS-3 has added two new frequencies, B1C and B2a, while retaining the B1I and B3I frequencies of BDS-2. The B2I frequency in BDS-2 has been renamed B2b. Although the frequency has not changed, its modulation method has changed. The addition of new frequency points has further improved the compatibility of the BDS-3 system.

[0033] The present invention aims to provide a Beidou precise point positioning method based on dual-frequency combination, so as to realize the purpose of establishing a dual-frequency ionospheric elimination PPP positioning model by using BDS signals when considering DCB correction, significantly improving positioning accuracy and shortening convergence time.

[0034] The specific implementation of the present invention provides a Beidou precise point positioning method based on dual-frequency combination, the method is as follows Figure 1 As shown, the following steps are included:

[0035] Step 1: Obtain the original observation files, precise orbits, precise clock errors, and various correction files from the IGS official website.

[0036] In the embodiment of the present invention, the dual-frequency signals in step 1 are B1C / B2a, B1C / B2b, B1I / B2a and B1I / B2b.

[0037] Step 2: Obtain clean observation values ​​by performing data validity checks and data preprocessing on the original observation files, precise orbits, precise clock errors, and various correction files.

[0038] Step 3: Based on the empirical error processing model, the clean observations are corrected for satellite clock error, tropospheric error, earth rotation and relativistic effect to obtain error correction values.

[0039] Step 4: Establish the Beidou dual-frequency ionospheric elimination combination model, perform dual-frequency DCB correction on the combined observations, and obtain the corrected dual-frequency combined observations.

[0040] In the embodiment of the present invention, step 4 is specifically implemented according to the following steps:

[0041] The dual-frequency ionospheric elimination combination model is realized by linearizing the dual-frequency observation values ​​of pseudorange and carrier phase. The dual-frequency combination observation values ​​of pseudorange and carrier phase are as follows:

[0042]

[0043] In formula (1), and They represent the pseudorange observation value and the carrier phase observation value, r and s represent the receiver and the satellite, respectively, and j is used to distinguish the frequency band of the observation value. represents the geometric distance between the satellite and the receiver, and dt s represent the receiver clock error and satellite clock error respectively, is the zenith tropospheric delay, is the corresponding mapping function, and γ jis the ionospheric delay caused by the signal propagation from the satellite to the receiver and its corresponding amplification factor, where γ j =(f1 / f i ) 2 , f represents frequency, b r,j and B r,j They are the uncalibrated code delay (UCD) and uncalibrated phase delay (UPD) of the receiver, and Respectively represent the UCD and UPD of the satellite, and The observation noise of the raw pseudorange and carrier phase observations of the satellite and receiver, respectively.

[0044] The coefficients of the deionospheric combination are defined as:

[0045]

[0046] In formula (2), and is the frequency-dependent amplification factor, f i and f j represents the carrier frequency (i≠j). Generally speaking, the IGS satellite clock product is generated by using the ionospheric combined observations of the first and second frequencies. Therefore, the satellite clock absorbs the ionospheric satellite UCD. The ionospheric single satellite clock error is defined as:

[0047]

[0048] In formula (3), Satellite clock corrections provided for IGS satellite clock products, represents the satellite hardware bias,

[0049] Rewrite equation (3) into dual-frequency form:

[0050]

[0051] The deionized satellite clock is applied to equation (1) together with the DCB correction and linearized:

[0052]

[0053] In formula (6), and They represent the calculated values ​​of the observed values ​​minus the original pseudorange and phase observed values, respectively. is the unit vector from the receiver to the satellite, is a vector of receiver positions relative to an a priori position increment.

[0054] The estimated parameters of the dual-frequency ionospheric PPP model include receiver position, receiver clock error, and tropospheric delay. When all satellites are considered, the single satellite calculation (6) is changed to a matrix form:

[0055]

[0056] in:

[0057]

[0058] In formula (8), the bold symbols correspond to the vectors containing all satellites, and They correspond to the ionospheric pseudorange and phase observation vectors of all satellites, and A is the coordinate vector The design matrix, is an n×m matrix, where n is the number of satellites and m is the number of systems. is an n-dimensional column vector, is the corresponding fuzziness An n×n dimensional matrix, is the ionospheric-free floating point ambiguity, and is the noise corresponding to the observation.

[0059] Step 5: Use the error correction value and the corrected dual-frequency combination observation value to construct the dual-frequency ionospheric observation equation, use Kalman filtering to solve the coordinates, and obtain the positioning result of the dual-frequency combination.

[0060] In an embodiment of the present invention, step 5 is specifically implemented according to the following steps: first, Kalman filter prediction is performed, that is, in each positioning epoch process, the Kalman filter first uses the state equation to predict the current position, velocity and receiver clock error of the receiver, and then, according to the state prior estimate and the satellite position and velocity provided by the satellite ephemeris, the Kalman filter is updated, and the correction amount of the system state estimate and the optimal estimate after correction are obtained through the observation residual. Finally, the Kalman filter update result of step 5 is monitored for integrity using the observation residual. If the observation residual exceeds the limit, the corresponding satellite observation is eliminated and the Kalman filter is updated again.

[0061] Step 6: Analyze the positioning results of the dual-frequency combination, count the error values ​​of the positioning results, and evaluate the positioning accuracy and convergence time.

[0062] In an embodiment of the present invention, step 6 positioning result evaluation specifically refers to analyzing the positioning accuracy and convergence time of the dual-frequency PPP from the three directions of N, E, and U, wherein the positioning accuracy is the average value of the errors in each direction that reaches 0.1m in the three directions and is stable for at least 20 epochs. If it exceeds 0.1m, the accuracy of the last epoch shall prevail. The convergence time refers to the time required for the positioning error to reach within 0.1 meters in the three directions and remain stable for at least 20 epochs.

[0063] In order to verify the positioning accuracy and convergence of the BDS dual-frequency signal B1C / B2a, B1C / B2b, B1I / B2a and B1I / B2b ionospheric elimination combination when considering DCB correction, the experimental positioning results are compared with the real coordinates. The positioning error curves of the dual-frequency ionospheric elimination combination PPP positioning of B1C / B2a, B1C / B2b, B1I / B2a and B1I / B2b in the present invention are shown in the following three directions: Figure 2 , Figure 3 , Figure 4 The positioning RMS value and average convergence time are shown in Table 1. The real coordinates of the test data in the present invention are derived from the station coordinate result file provided by IGS. After inspection, it is found that the new dual-frequency combination B1C / B2a can effectively improve the positioning accuracy while maintaining a faster convergence speed.

[0064] Table 1 RMS value and average convergence time of dual-frequency PPP positioning

[0065]

[0066] The beneficial effects of the present invention are as follows: the present invention linearizes the dual-frequency observation values ​​of pseudorange and carrier phase, uses B1C / B2a, B1C / B2b, B1I / B2a and B1I / B2b dual-frequency signals, constructs a Beidou dual-frequency ionospheric elimination combination model, and uses a state equation to predict the current position, speed and receiver clock error of the receiver. Then, according to the state prior estimation value and the satellite position and speed provided by the satellite ephemeris, a Kalman filter is updated, and a correction amount of the system state estimation value and an optimal estimation value after correction are obtained through the observation quantity residual. Finally, the Kalman filter update result is monitored for integrity using the observation quantity residual. If the observation quantity residual exceeds the limit, the corresponding satellite observation quantity is eliminated and the Kalman filter is updated again. Finally, the positioning result is evaluated, and the influence of DCB on precise single-point positioning is taken into account. The new dual-frequency combination B1C / B2a can effectively improve the positioning accuracy while maintaining a faster positioning convergence speed.

[0067] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical schemes or characteristics in the scheme is not described in detail here; it should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the scheme of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A Beidou precise point positioning method based on dual-frequency combination, characterized in that: The steps of the method include: Step 1: Obtain the original observation files, precise orbits, precise clock errors, and various correction files of the dual-frequency signal from the IGS official website; Step 2: Obtain clean observation values ​​by performing data validity verification and data preprocessing on the original observation files, precise orbits, precise clock errors, and various correction files; Step 3: According to the empirical error processing model, the clean observation value is corrected for satellite clock error, tropospheric error, earth rotation correction and relativistic effect to obtain an error correction value; Step 4: Establish the Beidou dual-frequency ionospheric elimination combination model, perform dual-frequency DCB correction on the combined observations, and obtain the corrected dual-frequency combined observations; Step 5: construct a dual-frequency ionospheric elimination observation equation using the error correction value and the corrected dual-frequency combination observation value, and use Kalman filtering to solve the coordinates to obtain a dual-frequency combination positioning result; Step 6: Analyze the positioning results of the dual-frequency combination, count the error values ​​of the positioning results, and evaluate the positioning accuracy and convergence time.

2. The Beidou precise point positioning method based on dual-frequency combination according to claim 1, characterized in that: The dual-frequency signals in step 1 are B1C / B2a, B1C / B2b, B1I / B2a and B1I / B2b.

3. The Beidou precise point positioning method based on dual-frequency combination according to claim 1, characterized in that: In step 4, the Beidou dual-frequency ionospheric elimination combination model is established, and the dual-frequency DCB correction is performed on the combined observation value to obtain the corrected dual-frequency combined observation value step, which is achieved by linearizing the dual-frequency observation values ​​of the pseudorange and carrier phase.

4. The Beidou precise point positioning method based on dual-frequency combination according to claim 1, characterized in that: The Beidou dual-frequency ionospheric elimination combination model in step 4 is as follows: in, and They represent the pseudorange observation value and the carrier phase observation value, r and s represent the receiver and the satellite, respectively, and j is used to distinguish the frequency band of the observation value. represents the geometric distance between the satellite and the receiver, and dt s represent the receiver clock error and satellite clock error respectively, is the zenith tropospheric delay, is the corresponding mapping function, and γ j is the ionospheric delay caused by the signal propagation from the satellite to the receiver and its corresponding amplification factor, where γ j =(f1 / f i ) 2 , f represents frequency, b r,j and B r,j are the uncalibrated code delay and uncalibrated phase delay of the receiver, respectively. and Respectively represent the UCD and UPD of the satellite, and The observation noise of the raw pseudorange and carrier phase observations of the satellite and receiver, respectively.

5. The Beidou precise point positioning method based on dual-frequency combination according to claim 1, characterized in that: The step of establishing a Beidou dual-frequency ionospheric elimination combination model, performing dual-frequency DCB correction on the combined observation value, and obtaining the corrected dual-frequency combined observation value comprises: The DCB is the delay difference caused by different frequencies or different ranging codes at the same frequency caused by the satellite and the receiver hardware. If it is the DCB on the receiver side, it needs to be converted into the receiver clock difference for parameter estimation. If it is the DCB on the satellite side, it needs to be corrected.

6. The Beidou precise point positioning method based on dual-frequency combination according to claim 1, characterized in that: In step 5, Kalman filter prediction is first performed, that is, in each positioning epoch, the Kalman filter first uses the state equation to predict the current position, speed and receiver clock error of the receiver.

7. The Beidou precise point positioning method based on dual-frequency combination according to claim 6, characterized in that: In step 5, the Kalman filter is updated according to the state prior estimate and the satellite position and velocity provided by the satellite ephemeris to obtain the Kalman filter update result, and the correction amount of the system state estimate and the optimal estimate after correction are obtained through the observation residual.

8. The Beidou precise point positioning method based on dual-frequency combination according to claim 7, characterized in that: Step 5 also includes using the observation residual to monitor the integrity of the Kalman filter update result of step 5. If the observation residual exceeds the limit, the corresponding satellite observation is eliminated and the Kalman filter is updated again. If the observation residual does not exceed the limit, the corresponding satellite observation is not eliminated and the Kalman filter is not updated again.

9. The Beidou precise point positioning method based on dual-frequency combination according to claim 1, characterized in that: The step of analyzing the positioning result of the dual-frequency combination, calculating the error value of the positioning result, and evaluating the positioning accuracy and convergence time includes: The evaluation of positioning accuracy and convergence time specifically refers to analyzing the positioning accuracy and convergence time of dual-frequency PPP from the three directions of N, E, and U, where the positioning accuracy is the average value of the errors in each direction that reaches 0.1m in the three directions and is stable for at least 20 epochs. If it exceeds 0.1m, the accuracy of the last epoch shall prevail. The convergence time refers to the time required for the positioning error to reach within 0.1m in the three directions and remain stable for at least 20 epochs.

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