PPP-B2b correction prediction and update method based on Kalman filter

Abstract

The present invention relates to a Kalman filter-based method for predicting and updating PPP-B2b corrections, comprising the following steps: Step 1: Determining whether the enhanced PPP-B2b signal broadcast by the BeiDou-3 system is interrupted or delayed; and Step 2: Predicting and updating the PPP-B2b corrections based on the determination result of Step 1. This method utilizes the enhanced PPP-B2b signal broadcast by the BeiDou-3 system to ensure the continuity and stability of correction information in user positioning solutions through real-time prediction and updating of PPP-B2b corrections. This method helps alleviate the problems of correction information interruption or delay caused by short-term signal obstruction and message updates.

Description

Technical Field

[0001] The present invention belongs to the field of ship system technology, electronic information system and navigation system technology, and relates to a PPP-B2b correction number prediction and update method, in particular to a PPP-B2b correction number prediction and update method based on Kalman filtering. Background Art

[0002] The PPP-B2b signal is the first high-precision signal released to the public by the BeiDou-3 system. It is broadcast by three geostationary orbit (GEO) satellites to provide users with open and free high-precision services, including orbit and clock correction information.

[0003] In July 2020, the BeiDou-3 system was officially completed and launched. Three of its GEO satellites broadcast PPP-B2b signals over my country and surrounding areas, providing users with real-time orbit, clock, and code bias corrections. By combining broadcast ephemeris with pseudorange and carrier phase observations, users can achieve real-time precise point positioning. During PPP-B2b signal transmission, corrections are broadcast in 63 message types, using multiple fields within the message for inter-message synchronization. Table 1 defines the PPP-B2b message types, of which the first four are most commonly used. The epoch interval for orbit corrections in message type 2 is 48 seconds, and the epoch interval for clock corrections in message type 4 is 6 seconds. To ensure consistency between the information content of different message types and with the broadcast ephemeris, information synchronization is required using identifiers such as IOD SSR, IOD P, IOD N, and IOD Corr. Therefore, there is a problem of early or delayed update of a certain field, which makes the correction number in the positioning solution process unusable, thereby affecting the user's performance of real-time positioning. Based on this, the present invention focuses on the real-time prediction and update method of PPP-B2b correction numbers.

[0004] Table 1 PPP-B2b information type definition

[0005] Information Type Information content 1 Satellite mask 2 Satellite orbit correction number and user ranging accuracy index 3 Inter-code deviation correction 4 Satellite clock correction 5 User ranging accuracy index 6 Clock Correction and Orbit Correction - Combination 1 7 Clock Correction and Orbit Correction - Combination 2 8-62 Reserve 63 Empty information

[0006] After searching, no published patent documents identical or similar to the present invention were found. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the existing technology and propose a PPP-B2b correction number prediction and update method based on Kalman filtering. By utilizing the PPP-B2b enhanced signal broadcast by the BeiDou-3 system, the PPP-B2b correction number can be predicted and updated in real time to ensure the continuity and stability of the correction information in the user positioning solution, and help alleviate the problems of short-term signal obstruction and correction information interruption or delay during message update.

[0008] The present invention solves the practical problem by adopting the following technical solutions:

[0009] A PPP-B2b correction number prediction and update method based on Kalman filtering includes the following steps:

[0010] Step 1: Determine whether the PPP-B2b enhanced signal broadcast by the BeiDou-3 system is interrupted or delayed;

[0011] Step 2: Based on the determination result of step 1, the PPP-B2b correction number is predicted and updated.

[0012] Moreover, the specific steps of step 1 include:

[0013] (1) Capture the PPP-B2b enhanced signal broadcast by the BeiDou-3 system. If the signal cannot be captured, it is determined to be a signal interruption. If the signal is successfully captured, the PPP-B2b message information is parsed.

[0014] (2) If the PPP-B2b message information is successfully parsed and the message synchronization codes are found to be inconsistent among multiple messages, it is determined that the message is being updated. In this case, the signal is also determined to be interrupted or delayed.

[0015] If the PPP-B2b message information is successfully parsed and the message synchronization codes between multiple messages are found to be normal, the message update is determined to be normal and the positioning solution is continued;

[0016] If the PPP-B2b message information fails to be parsed, it is determined to be a signal interruption or delay;

[0017] (3) For signals with normal message updates, the user end uses the Precise Point Positioning (PPP) service solution to determine the user's location. For signals that are judged to be interrupted or delayed, the interruption duration T0 is used to determine whether PPP-B2b correction number information extrapolation is required.

[0018] Moreover, the specific steps of step 2 include:

[0019] (1) When the PPP-B2b signal is interrupted or delayed and the interruption duration is less than the set threshold value T0, the correction information prediction process is entered. The Kalman filter is used to predict and update the satellite orbit correction number, satellite clock correction number and satellite inter-code delay correction number, and it is determined whether the user end uses the precise point positioning (PPP) service solution to determine the user position.

[0020] (2) When the PPP-B2b signal is interrupted or delayed and the delay is greater than the set interruption duration threshold T0, the standard single point positioning (SPP) service solution is used to determine the user location.

[0021] Moreover, the specific steps of predicting and updating the satellite orbit correction number in step 2 (1) include:

[0022] In the PPP-B2b signal, satellite orbit corrections in message type 2 are updated every 48 seconds. The broadcast orbit correction information includes the radial, tangential, and normal components of the orbit correction vector. To meet the user's real-time positioning needs, orbit corrections are updated at every epoch and extrapolated using a Kalman filter, combining the motion trajectory and satellite orbit parameter information provided in the satellite ephemeris.

[0023] ① In the process of constructing the Kalman filter, the estimated parameters are the satellite orbit correction component and its velocity component. The state update equation is constructed with reference to the human satellite orbit theory. The specific formula is as follows:

[0024]

[0025] Where, Corresponding to the orbit correction numbers in radial, tangential and normal directions respectively; Corresponding to the radial, tangential and normal orbit correction velocity components respectively; Δt t,t+1 Represents the time interval from time t to time t+1. In addition, the observation equation is provided with the satellite orbit correction component by the PPP-B2b signal The random model is constructed with reference to the first-order Markov model; the variance value is determined by the satellite user ranging accuracy and ephemeris data in the historical data.

[0026] ② The orbit correction number at each epoch can be obtained by performing state prediction and measurement update through Kalman filtering. In the precise positioning solution, it is necessary to calculate the coordinates of the satellite in the Earth-centered Earth-fixed system, transform the orbit correction number components and calculate the satellite position vector X calculated by the broadcast ephemeris. broadcast Correction can restore the satellite's real-time precise coordinates X orbit , the formula is as follows:

[0027]

[0028]

[0029]

[0030] e along =e radial ×e cross

[0031] In the formula, r, Respectively represent the satellite position and velocity vector in the broadcast ephemeris; e radial 、e along 、ecross correspond to the unit vectors in the radial, tangential and normal directions respectively.

[0032] Furthermore, the specific steps of predicting and updating the satellite clock error correction number in step 2 (1) include:

[0033] In the PPP-B2b signal corrections, the satellite clock corrections in message type 4 are updated every 6 seconds. To meet the user's real-time positioning needs, the satellite clock corrections also need to be estimated at every epoch.

[0034] ① Since most clock corrections are obtained based on fitting of a quadratic polynomial model, in the process of constructing the Kalman filter, its state equation can be constructed with reference to the clock error variation in the satellite ephemeris. Its estimated parameters should also include parameters such as clock error, clock velocity, and clock drift. The specific formula is as follows:

[0035]

[0036] Where C0, C1, and C2 represent the polynomial coefficients of the clock correction number; Represents the clock correction at time t+1. Furthermore, its observation equation is based on the satellite clock correction provided by the PPP-B2b signal. The stochastic model is constructed using a second-order Markov model, and the variance is determined by historical data and ephemeris data.

[0037] ② The clock correction number at each epoch can be obtained by performing state prediction and measurement update through Kalman filtering. The calculated clock correction information is used to correct the broadcast ephemeris satellite clock error t broadcast The precise clock error information t can be obtained satellite , the formula is as follows:

[0038]

[0039] Moreover, the specific method for predicting and updating the satellite inter-code bias correction number in step 2 (1) is:

[0040] When the PPP-B2b signal is briefly interrupted or delayed, the satellite inter-code deviation correction number broadcast at the previous moment can be used for correction. If the correction number information is not updated after the valid data age, the use of PPP-B2b information for high-precision solution can be stopped.

[0041] Advantages and beneficial effects of the present invention:

[0042] The present invention proposes a Kalman filter-based PPP-B2b correction number prediction and update method. By modeling the PPP-B2b correction numbers in the time domain and then using a Kalman filter extrapolation estimation method to compensate for the discontinuity of correction numbers caused by PPP-B2b signal update delays, the method meets the user's real-time PPP positioning needs. When the signal is not delayed, the PPP-B2b satellite correction number information can be used to correct the orbit, clock error, and code deviation, thereby achieving the user's PPP positioning solution. During PPP-B2b signal delays or message updates, the correction number information for the current epoch is unavailable. Using historically stored PPP-B2b correction number information, Kalman filtering can be used to perform extrapolation within a reasonable time, thereby ensuring the continuity of the correction number information and facilitating the availability of PPP solutions on the user side. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flowchart of the PPP-B2b signal interruption determination method of the present invention;

[0044] Figure 2 It is a flow chart of the PPP-B2b correction number prediction and updating method of the present invention. DETAILED DESCRIPTION

[0045] The embodiments of the present invention are further described below in conjunction with the accompanying drawings:

[0046] A PPP-B2b correction number prediction and update method based on Kalman filtering, such as Figure 1 and Figure 2 As shown, the following steps are included:

[0047] Step 1: Determine whether the PPP-B2b enhanced signal broadcast by the BeiDou-3 system is interrupted or delayed;

[0048] like Figure 1 As shown, the specific steps of step 1 include:

[0049] (1) Capture the PPP-B2b enhanced signal broadcast by the BeiDou-3 system. If the signal cannot be captured, it is determined to be a signal interruption. If the signal is successfully captured, the PPP-B2b message information is parsed.

[0050] (2) If the PPP-B2b message information is successfully parsed and the message synchronization codes are found to be inconsistent among multiple messages, it is determined that the message is being updated. In this case, the signal is also determined to be interrupted or delayed.

[0051] If the PPP-B2b message information is successfully parsed and the message synchronization codes between multiple messages are found to be normal, the message update is determined to be normal and the positioning solution is continued;

[0052] If the PPP-B2b message information fails to be parsed, it is determined to be a signal interruption or delay;

[0053] (3) For signals with normal message updates, the user end uses the Precise Point Positioning (PPP) service solution to determine the user's location;

[0054] For signals judged to be interrupted or delayed, the need for PPP-B2b correction information extrapolation is determined based on the interruption duration T0, and then the user end is determined to use the precise point positioning (PPP) service solution or the standard point positioning (SPP) service solution to determine the user's position.

[0055] In this embodiment, the interruption duration threshold T0 is set to 180 seconds.

[0056] The working principle of the method of the present invention for determining whether the PPP-B2b enhanced signal broadcast by the BeiDou-3 system is interrupted is as follows:

[0057] The collected signal first passes through the antenna and RF front-end for signal capture. If the signal cannot be captured, it is determined to be a signal interruption. After the signal is successfully captured, the PPP-B2b message information is parsed. If the message synchronization codes between multiple messages are inconsistent, it is determined that the message is being updated. In this case, the correction number is also considered to be interrupted or delayed. If the message parsing and synchronization code are normal, the positioning solution continues.

[0058] For signals with normal message updates, the user end can use the Precise Point Positioning (PPP) service solution to determine the user's location;

[0059] For epochs judged to be signal interrupted or delayed, the duration of the interruption is used to determine whether PPP-B2b correction information extrapolation is required. This is then used to determine whether the user terminal is using the Precise Point Positioning (PPP) service solution or the Standard Point Positioning (SPP) service solution to determine the user's position. The interruption duration threshold T0 is set based on empirical values ​​and is set to 180 seconds here.

[0060] Step 2: Based on the determination result of step 1, the PPP-B2b correction number is predicted and updated.

[0061] like Figure 2 As shown, the specific steps of step 2 include:

[0062] Moreover, the specific steps of step 2 include:

[0063] (1) When the PPP-B2b signal is interrupted or delayed and the interruption duration is less than the set threshold value T0, the correction information prediction process is entered. The Kalman filter is used to predict and update the satellite orbit correction number, satellite clock correction number and satellite inter-code delay correction number. It is judged that the user end uses the precise point positioning (PPP) service solution to determine the user position.

[0064] (2) When the PPP-B2b signal is interrupted or delayed and the delay is greater than the set interruption duration threshold T0, the standard single point positioning (SPP) service solution is used to determine the user location.

[0065] The specific steps of predicting and updating the satellite orbit correction number in step 2 (1) include:

[0066] In the PPP-B2b signal, satellite orbit corrections in message type 2 are updated every 48 seconds. The broadcast orbit correction information includes the radial, tangential, and normal components of the orbit correction vector. To meet the user's real-time positioning needs, orbit corrections are updated at every epoch and extrapolated using a Kalman filter, combining the motion trajectory and satellite orbit parameter information provided in the satellite ephemeris.

[0067] ① In the process of constructing the Kalman filter, the estimated parameters are the satellite orbit correction component and its velocity component. The state update equation is constructed with reference to the human satellite orbit theory. The specific formula is as follows:

[0068]

[0069] Where, Corresponding to the orbit correction numbers in radial, tangential and normal directions respectively; Corresponding to the radial, tangential and normal orbit correction velocity components respectively; Δt t,t+1 Represents the time interval from time t to time t+1. In addition, the observation equation is provided with the satellite orbit correction component by the PPP-B2b signal The random model is constructed with reference to the first-order Markov model; the variance value is determined by the satellite user ranging accuracy and ephemeris data in the historical data.

[0070] ② The orbit correction number at each epoch can be obtained by performing state prediction and measurement update through Kalman filtering. In the precise positioning solution, it is necessary to calculate the coordinates of the satellite in the Earth-centered Earth-fixed system, transform the orbit correction number components and calculate the satellite position vector X calculated by the broadcast ephemeris. broadcast Correction can restore the satellite's real-time precise coordinates X orbit , the formula is as follows:

[0071]

[0072]

[0073]

[0074] e along =e radial ×e cross

[0075] In the formula, r, Respectively represent the satellite position and velocity vector in the broadcast ephemeris; e radial 、e along 、e cross correspond to the unit vectors in the radial, tangential and normal directions respectively.

[0076] (2) The specific steps of predicting and updating the satellite clock error correction number in step (1) of step 2 include:

[0077] In the PPP-B2b signal corrections, the satellite clock corrections in message type 4 are updated every 6 seconds. To meet the user's real-time positioning needs, the satellite clock corrections also need to be estimated at every epoch.

[0078] ① Since most clock corrections are obtained based on fitting of a quadratic polynomial model, in the process of constructing the Kalman filter, its state equation can be constructed with reference to the clock error variation in the satellite ephemeris. Its estimated parameters should also include parameters such as clock error, clock velocity, and clock drift. The specific formula is as follows:

[0079]

[0080] Where C0, C1, and C2 represent the polynomial coefficients of the clock correction number; Represents the clock correction at time t+1. Furthermore, its observation equation is based on the satellite clock correction provided by the PPP-B2b signal. The stochastic model is constructed using a second-order Markov model, and the variance is determined by historical data and ephemeris data.

[0081] ② The clock correction number at each epoch can be obtained by performing state prediction and measurement update through Kalman filtering. The calculated clock correction information is used to correct the broadcast ephemeris satellite clock error t broadcast The precise clock error information t can be obtained satellite , the formula is as follows:

[0082]

[0083] (3) The specific method for predicting and updating the satellite inter-code bias correction number in step (1) of step 2 is:

[0084] Satellite inter-code bias corrections vary relatively little between epochs, and their valid data age is typically long, allowing correction information to maintain relatively high accuracy within 24 hours. Therefore, there is no need to predict and update inter-code bias corrections at every epoch.

[0085] When the PPP-B2b signal is briefly interrupted or delayed, the satellite inter-code deviation correction number broadcast at the previous moment can be used for correction. If the correction number information is not updated after the valid data age (set as 24 hours in this invention), the use of PPP-B2b information for high-precision solution can be stopped.

[0086] In this embodiment, in order to achieve synchronous processing of various types of signals at various frequencies, it is necessary to first eliminate the influence of inter-symbol deviation. The correction formula is as follows:

[0087]

[0088] Where, is the observed value after signal correction; p sig DCB is the observation value directly captured by the receiver; sig The inter-symbol deviation of the corresponding signal.

[0089] When the PPP-B2b signal is normal, the correction information update process begins, and the Kalman filter performs measurement updates to obtain more accurate parameter estimates for the current epoch.

[0090] The innovation of the present invention is:

[0091] (1) PPP-B2b signal interruption judgment method. By analyzing the message signal, the message interruption, delay and normal signals are rationally classified and identified to determine the selection of the user terminal positioning mode;

[0092] (2) Orbital correction number prediction and update method. Combining the motion trajectory and orbit parameter information provided by the satellite ephemeris, the orbit correction number is rationally extrapolated through the Kalman filter to obtain the orbit correction number information at each epoch;

[0093] (3) Clock correction number prediction and update method. By constructing the Kalman filter equation, the clock error, clock speed and clock drift are set as the parameters to be estimated, and based on the second-order Markov model, a random model is constructed to predict and measure the clock correction number state in real time. The clock correction number of each epoch can be obtained and used to correct the broadcast ephemeris satellite clock error. The precise clock error information can be obtained in real time, thereby meeting the user's demand for real-time clock error during real-time positioning.

[0094] (4) Satellite inter-code bias correction number prediction and update method. Taking full advantage of the relatively small changes in inter-code bias correction numbers between epochs, and using its long data age, the problem of inter-code bias correction number interruption within the valid data age can be avoided, thereby improving the convergence time and accuracy of precise single-point positioning.

[0095] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0096] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0097] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0098] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

Claims

1. A PPP-B2b correction number prediction and update method based on Kalman filtering, characterized by: The following steps are involved: Step 1: Determine whether the PPP-B2b enhanced signal broadcast by the BeiDou-3 system is interrupted or delayed; Step 2: Based on the determination result of step 1, the PPP-B2b correction number is predicted and updated; The specific steps of step 1 include: (1) Capture the PPP-B2b enhanced signal broadcast by the BeiDou-3 system. If the signal cannot be captured, it is determined to be a signal interruption. If the signal is successfully captured, the PPP-B2b message information is parsed. (2) If the PPP-B2b message information is successfully parsed and the message synchronization codes are found to be inconsistent among multiple messages, it is determined that the message is being updated. In this case, the signal is also determined to be interrupted or delayed. If the PPP-B2b message information is successfully parsed and the message synchronization codes between multiple messages are found to be normal, the message update is determined to be normal and the positioning solution is continued; If the PPP-B2b message information fails to be parsed, it is determined to be a signal interruption or delay; (3) For signals with normal message updates, the user terminal uses the precise point positioning (PPP) service solution to determine the user's location. For signals that are judged to be interrupted or delayed, the interruption duration T0 is used to determine whether PPP-B2b correction information extrapolation is required. The specific steps of step 2 include: (1) When the PPP-B2b signal is interrupted or delayed and the interruption duration is less than the set threshold value T0, the correction information prediction process is started. The Kalman filter is used to predict and update the satellite orbit correction number, satellite clock correction number, and satellite inter-symbol delay correction number, and it is determined whether the user end uses the precise single point positioning PPP service solution to determine the user position; (2) When the PPP-B2b signal is interrupted or delayed and the interruption duration is greater than the set threshold T0, the standard single point positioning SPP service solution is used to determine the user's location.

2. The Kalman filter-based PPP-B2b correction number prediction and update method according to claim 1, characterized in that: The specific steps of predicting and updating the satellite orbit correction number in step 2 (1) include: ① In the process of constructing the Kalman filter, the estimated parameters are the satellite orbit correction component and its velocity component. The state update equation is constructed with reference to the human satellite orbit theory. The specific formula is as follows: Where, Corresponding to the orbit correction numbers in radial, tangential and normal directions respectively; Corresponding to the radial, tangential and normal orbit correction velocity components respectively; Δt t,t+1 represents the time interval from time t to time t+1; in addition, the observation equation is provided with the satellite orbit correction component by the PPP-B2b signal The random model is constructed with reference to the first-order Markov model; the variance value is determined by the satellite user ranging accuracy and ephemeris data in the historical data; ② The orbit correction number at each epoch can be obtained by performing state prediction and measurement update through Kalman filtering. In the precise positioning solution, it is necessary to calculate the coordinates of the satellite in the Earth-centered Earth-fixed system, transform the orbit correction number components into coordinates, and calculate the satellite position vector X calculated by the broadcast ephemeris. broadcast Correction can restore the satellite's real-time precise coordinates X orbit , the formula is as follows: And along =and radial ×e cross Where, Respectively represent the satellite position and velocity vector in the broadcast ephemeris; e radial 、e along 、e cross correspond to the unit vectors in the radial, tangential and normal directions respectively.

3. The Kalman filter-based PPP-B2b correction number prediction and update method according to claim 1, characterized in that: The specific steps of predicting and updating the satellite clock error correction number in step 2 (1) include: ① Since most clock corrections are obtained based on fitting of a quadratic polynomial model, in the process of constructing the Kalman filter, its state equation can be constructed with reference to the clock error variation in the satellite ephemeris. Its estimated parameters should also include parameters such as clock error, clock velocity, and clock drift. The specific formula is as follows: Where C0, C1, and C2 represent the polynomial coefficients of the clock correction number; Represents the clock correction information at time t+1; in addition, its observation equation is provided by the satellite clock correction number provided by the PPP-B2b signal; the random model is constructed based on the second-order Markov model; the variance is determined by reference to historical data and ephemeris data; ② The clock correction number at each epoch can be obtained by performing state prediction and measurement update through Kalman filtering. The calculated clock correction information is used to correct the broadcast ephemeris satellite clock error t broadcast The precise clock error information t can be obtained satellite , the formula is as follows:

4. The Kalman filter-based PPP-B2b correction number prediction and update method according to claim 1, characterized in that: The specific method for predicting and updating the satellite inter-code bias correction number in step 2 (1) is: When the PPP-B2b signal is briefly interrupted or delayed, the satellite inter-code deviation correction number broadcast at the previous moment can be used for correction. If the correction number information is not updated after the valid data age, the use of PPP-B2b information for high-precision solution can be stopped.

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