Real-time redundant beidou iii PPP-b2b sub-nanosecond time comparison method

Abstract

The application belongs to the technical field of satellite time comparison. The application provides a real-time redundant Beidou-3 satellite navigation system PPP-B2b sub-nanosecond time comparison method. The method comprises the following steps: acquiring the GEO satellite PPP-B2b information of C59 and C61 in real time, correcting the broadcast ephemeris data broadcast by the Beidou satellite navigation system by using a redundant method, thereby obtaining high-precision satellite orbit broadcast ephemeris and clock difference, combining the pseudo code and carrier phase observation value sent by the Beidou satellite, and using the PPP algorithm to calculate the clock difference of two receivers in real time, and then performing two-site time comparison. The disclosed embodiment can avoid the situation that the PPP cannot be solved due to insufficient availability of the PPP-B2b information in a continuous time period of observation data, so that the solved epoch is more complete.

Description

TECHNICAL FIELD

[0001] The embodiment of the present disclosure relates to the technical field of satellite time comparison, in particular to a real-time redundant Beidou-3 PPP-B2b sub-nanosecond time comparison method. BACKGROUND

[0002] The Beidou-3 satellite navigation system was officially completed in 2020, and its geostationary orbit (GEO) satellite can broadcast PPP-B2b signals in real time. The PPP-B2b signal carries accurate satellite information, and through these information, the satellite orbit and clock error can be corrected, so as to realize more accurate precise point positioning (PPP) and timing. The PPP-B2b technology solves the lag problem of using post-precise ephemeris for precise point positioning in the traditional method, and also overcomes many disadvantages such as network interruption and lack of network facilities when broadcasting satellite correction numbers through the network.

[0003] However, the C59 and C60 satellites of GPS and Beidou-3 broadcast the same PPP-B2b information synchronously, which is unstable and there is a situation of signal loss. SUMMARY

[0004] In order to avoid the shortcomings of the prior art, the present application provides a real-time redundant Beidou-3 PPP-B2b sub-nanosecond time comparison method to solve the problem of unstable synchronization broadcast of the same PPP-B2b information by C59 and C60 satellites in the prior art, and frequent loss of signals.

[0005] According to the embodiment of the present disclosure, a real-time redundant Beidou-3 PPP-B2b sub-nanosecond time comparison method is provided, which comprises:

[0006] Obtaining observation data, satellite ephemeris data and B2b message data of Beidou-3 satellites;

[0007] Calculating the clock error of each satellite at the observation time according to the observation data and the satellite ephemeris data;

[0008] Based on the redundancy method, the clock error is corrected using the B2b message data to obtain a corrected clock error;

[0009] Precise point positioning calculation is performed on the corrected clock error to obtain the target clock error of the two-site receivers, and then two-site time comparison is performed.

[0010] Further, the step of obtaining observation data, satellite ephemeris data and B2b message data comprises:

[0011] acquiring the observation data by using the receiver; wherein the observation data comprises carrier phase and pseudorange and other observation values;

[0012] receiving the satellite ephemeris data by using the receiver; wherein the satellite ephemeris data comprises orbit information and time information of each satellite;

[0013] receiving B2b message data of satellites by using the receiver; wherein the B2b message data comprises satellite orbit correction numbers and clock correction numbers.

[0014] Further, the PPP-B2b message comprises first PPP-B2b message information of C59 satellite and second PPP-B2b message information of C61 satellite.

[0015] Further, in the step of calculating the clock difference of each satellite at the observation time according to the observation data and the satellite ephemeris data, comprising:

[0016] calculating the clock difference of each satellite at the observation time according to the observation data, the orbit parameters, the time information, the earth's gravitational field and the solar radiation pressure.

[0017] Further, in the step of correcting the clock difference by using the B2b message based on the redundancy method to obtain the corrected clock difference, comprising:

[0018] judging whether the signal of the C59 satellite is missing or interfered;

[0019] if the signal of the C59 satellite is complete or not interfered, correcting the clock difference by using the correction numbers in the first PPP-B2b message information of the C59 satellite;

[0020] if the signal of the C59 satellite is missing or interfered, correcting the clock difference by using the correction numbers in the second PPP-B2b message information of the C61 satellite.

[0021] Further, the correction numbers comprise:

[0022] code bias correction numbers, satellite orbit correction numbers and satellite clock correction numbers.

[0023] Further, in the step of performing precise point positioning calculation on the corrected clock difference to obtain the target clock difference of the two receivers, comprising:

[0024] estimating the receiver parameters, troposphere delay, ionosphere delay and multipath effect in the corrected clock difference by using Kalman filter and least square method;

[0025] performing a residual test on a result of the estimation, if a residual is greater than a preset threshold, judging as a gross error, and eliminating the gross error, and re-estimating the receiver parameter, the troposphere delay, the ionosphere delay and the multipath effect; if the residual is less than the threshold, outputting the target clock difference of the receiver.

[0026] The technical scheme provided by the embodiments of the present disclosure can include the following beneficial effects:

[0027] In the embodiments of the present disclosure, by using the real-time redundant Beidou-3 PPP-B2b sub-nanosecond time comparison method, on the one hand, by using the real-time acquired GEO satellite PPP-B2b information of C59 and C61, the broadcast ephemeris data broadcast by GPS and Beidou satellites is corrected by using a redundant method, so as to obtain high-precision satellite orbit broadcast ephemeris and clock difference, and by combining the pseudo-code and carrier phase observation values sent by GPS satellites and Beidou satellites, the clock difference is calculated in real time by using the PPP algorithm, so as to obtain the real-time receiver clock difference result of two places, so as to perform time comparison. On the other hand, it can avoid that the PPP cannot be solved due to insufficient availability of PPP-B2b information in a continuous time period of observation data, so as to make the epoch of the solution more complete. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A step diagram of a real-time redundant Beidou-3 satellite navigation system PPP-B2b time comparison method in an exemplary embodiment of the present disclosure is shown;

[0029] Figure 2 A specific flowchart of a real-time redundant Beidou-3 satellite navigation system PPP-B2b time comparison method in an exemplary embodiment of the present disclosure is shown;

[0030] Figure 3 A PPP-B2b time comparison error curve in a time comparison experiment in an exemplary embodiment of the present disclosure is shown.

[0031] Figure 4 A PPP-B2b time comparison residual curve in a time comparison experiment in an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0032] In the present example embodiment, a real-time redundant Beidou-3 satellite navigation system PPP-B2b sub-nanosecond time comparison method is provided. Referring to FIG. 1, the real-time redundant Beidou-3 satellite navigation system PPP-B2b sub-nanosecond time comparison method can include steps S101-S104. Figure 1

[0033] Step S101: acquiring observation data, satellite ephemeris data and B2b text data; ​

[0034] Step S102: Calculate the clock difference of each satellite at the observation time based on the observation data and the satellite ephemeris data;

[0035] Step S103: Based on the redundancy method, the clock difference is corrected using the B2b message data to obtain the corrected clock difference;

[0036] Step S104: Perform precise single-point positioning calculation on the corrected clock difference to obtain the target clock difference of the receivers in the two locations, and then perform time comparison between the two locations.

[0037] The aforementioned real-time redundant BeiDou-3 PPP-B2b sub-nanosecond time comparison method achieves two main benefits. First, by using real-time acquired PPP-B2b information from C59 and C61 GEO satellites, a redundancy method is employed to correct the broadcast ephemeris data transmitted by the BeiDou Navigation Satellite System, thereby obtaining high-precision satellite orbit broadcast ephemeris and clock bias. Combined with pseudocode and carrier phase observations transmitted by BeiDou satellites, the PPP algorithm is used to calculate the clock bias in real time. Second, this method avoids the inability to calculate PPP due to insufficient availability of PPP-B2b information within continuous time periods of observation data, resulting in a more complete calculated epoch.

[0038] Below, we will refer to Figures 1 to 4 The steps of the above-described real-time redundant BeiDou system PPP-B2b sub-nanosecond time comparison method in this example embodiment will be described in more detail.

[0039] In step S101, as Figure 2 As shown, firstly, the receiver acquires observation data, including carrier phase and pseudorange observations. Simultaneously, the receiver obtains satellite ephemeris data from the navigation satellites, which includes satellite orbit and time information. Furthermore, the receiver also needs to obtain PPP-B2b messages from the C59 and C61 satellites, which contain high-precision parameters for correction.

[0040] Specifically, high-precision GNSS receivers are used to acquire observation data, including carrier phase and pseudorange measurements. This data reflects the distance information between the receiver and each satellite, serving as the basis for subsequent PPP calculations.

[0041] The receiver receives satellite ephemeris data from the BeiDou-3 navigation satellites. The ephemeris data includes orbital and time information for each satellite, accurately describing its spatial position at any given time. The acquired ephemeris data will be used to calculate the satellite's real-time clock difference.

[0042] The receiver receives PPP-B2b messages from both C59 and C61 satellites. The PPP-B2b messages contain high-precision satellite orbit and clock correction numbers, which are obtained by precise measurement and calculation of ground monitoring stations. The contents of the PPP-B2b messages of the C59 and C61 satellites are different, so the receiver can distinguish and process the two messages.

[0043] The observation equation in precise point positioning can be divided into pseudo-range observation equation and carrier phase observation equation, which is represented by formula (1):

[0044]

[0045] Wherein: s represents a satellite; r represents a receiver; i represents a signal frequency; and represent carrier phase and pseudo-range observation values, respectively; is the distance from the satellite to the receiver; dt r is the receiver clock error when the signal arrives at the receiver; dT s is the satellite clock error when the satellite transmits the signal; represents the ionospheric delay caused by the signal frequency, represents the ionospheric delay of the signal with frequency f i in the propagation path; is the projection function of the signal from the satellite to the receiver, represents the zenith troposphere delay of the receiver; λ i represents the wavelength of the carrier phase observation value with frequency f i ; d r,i is the hardware delay of the receiver, is the hardware delay of the satellite, is the ambiguity of the carrier phase, and represent the unaccounted errors of the carrier phase and the pseudo-range, respectively.

[0046] As one of the main error sources in precise point positioning observations, the ionospheric delay can be corrected by the ionosphere-free model when the Beidou satellite navigation system signal passes through the ionosphere. Taking the signals with frequencies f i and f j as examples, the corresponding dual-frequency ionosphere-free model is formula (2):

[0047]

[0048] Substituting formula (1) into formula (2) can obtain formula (3):

[0049]

[0050] The variables in equation (3) can be expressed by equation (4):

[0051]

[0052] In step S102, as shown in the figure, the receiver calculates the coarse clock difference of each satellite at the observation time using the acquired satellite ephemeris data. This calculation needs to take into account the satellite's orbital parameters, time information, and other factors that may affect the satellite's position, such as the Earth's gravitational field and solar radiation pressure, etc. Figure 2

[0053] In step S103, as shown in the figure, the PPP-B2b message is acquired from C59 and C61 satellites, containing satellite orbit correction number Δr i (t) and clock correction number ΔdT i (t). Figure 2 The satellite clock difference dT i (t) is calculated using ephemeris data:

[0054]

[0055]

[0056] Wherein

[0057] and are the initial satellite clock difference provided in the ephemeris data. According to the correction number in the PPP-B2b message, the satellite clock difference is corrected. Taking C59 satellite as the main one, when C59 signal is missing or interfered, switch to use C61 signal:

[0058] r i (t) = r i,C59 (t) if available, else r i,C61 (t)

[0059] dT i (t) = dT i,C59 (t) if available, else dT i,C61 (t)

[0060] Specifically, the correction number in the PPP-B2b message received from C59 and C61 satellites is used to correct the calculated satellite clock difference. Specifically, the receiver first corrects mainly using the PPP-B2b information broadcast by C59 satellite; when C59 signal is missing or interfered, automatically switches to use the PPP-B2b information broadcast by C61 satellite for substitute correction. In this way, the availability and accuracy of the correction number can be guaranteed to the greatest extent.

[0061] ​​

[0062] The calculation methods of the three PPP-B2b correction numbers are as follows:

[0063] (1) Code bias correction number:

[0064] Due to the difference in satellite tracking modes, each observation value contains a bias related to the signal tracking mode. When synchronously processing signals of different frequencies and types, the bias needs to be eliminated first to realize synchronous processing of signals of different types, and the correction algorithm is shown in formula (5):

[0065]

[0066] In the formula: is the observation value of the sig signal after correction; l sig is the observation value directly captured by the sig signal receiver; DCB sig is the code bias of the corresponding signal.

[0067] (2) Satellite orbit correction number:

[0068] The method of orbit correction is to obtain the precise ephemeris recovered from PPP-B2b by using the relatively rough satellite position and velocity calculated from the broadcast ephemeris and the orbit correction parameters broadcast in PPP-B2b.

[0069] The parameters included in the orbit correction information are the components of the orbit correction vector δO in the radial, tangential, and normal directions. The orbit correction value is used to calculate the satellite position correction vector δX, and the satellite position vector X broadcast calculated from the broadcast ephemeris is also used. The correction calculation formula is shown in formula (6):

[0070] X orbit =X broadcast -δX (6)

[0071] In formula (6), X orbit is the more accurate satellite position after correction, X broadcast is the satellite position calculated from the broadcast ephemeris, and δX represents the satellite orbit correction. The correction calculation formula of δX is as follows:

[0072]

[0073]

[0074] e along =e cross ×e radial (9)

[0075] δX=[e radial e along e cross]·δO (10)

[0076] In the above formula: r=X broadcast is the broadcast ephemeris satellite position vector; is the broadcast ephemeris satellite velocity vector; e i is the direction unit vector, i={radial, along, cross} respectively corresponding to the radial, tangential, normal; δO is the orbit correction vector obtained in the PPP information, and the order is the radial, tangential, normal component.

[0077] (3) Satellite clock correction number:

[0078] The parameters included in the clock correction message are the correction parameters relative to the broadcast ephemeris clock. The use method of the correction parameters is shown in formula (11):

[0079]

[0080] In the formula: t broadcast is the satellite clock difference parameter calculated by the broadcast ephemeris; t satellite is the satellite clock difference after the clock correction message correction; c is the speed of light; C0 is the clock correction parameter obtained in the PPP-B2b message.

[0081] In step S104, as shown in Figure 2 , the precise point positioning (PPP) is solved using the corrected satellite clock difference, and the accurate clock difference of the receiver is obtained. Through the above method, not only the time comparison accuracy is improved, but also the reliability and stability of the system in various environments are enhanced.

[0082] Specifically, the receiver parameters, stream layer delay, ionospheric delay and multipath effect in the corrected clock difference are estimated by using Kalman filter and least square method; the estimated results are subjected to residual test, if the residual is greater than the preset threshold, it is judged as gross error, and after eliminating the gross error, the receiver parameters, stream layer delay, ionospheric delay and multipath effect are re-estimated; if the residual is less than the threshold, the target clock difference of the two receivers is output, and then the two-place time comparison is carried out.

[0083] In the whole solving process, using accurate satellite orbit and clock difference data can significantly improve the accuracy of the positioning result. By combining the use of C59 and C61 satellite PPP-B2b signals, not only the time comparison accuracy is improved, but also the stability and reliability of the system in various environments are improved.

[0084] In a specific embodiment, the IGS distribution is used to perform an example experiment on the USUD station and the XIA6 station in a certain country. The station receiver information is shown in Table 1. The date is a certain year, month and day. The experiment uses the BDS-3B1I / B3I ionosphere-free combination and the BDS-3B1I / B3I+GPS L1 / L2 ionosphere-free combination to perform PPP-B2b redundant time comparison of C59 and C61. The GBM post-precise ephemeris solution result is used as a reference to obtain the two-station time comparison error result shown in Figure 3

[0085] Table 1 PPP-B2b time comparison experiment station information

[0086]

[0087] The precise satellite clock error is obtained by the PPP-B2b product correction and the satellite clock error calculated through the navigation message. The ionospheric delay uses the dual-frequency ionosphere-free combination to eliminate the ionospheric influence, and uses the extended Kalman filter to perform parameter estimation. It is a recursive filtering algorithm for estimating system state and updating state and error correction according to measurement data. And use IGS14.atx to eliminate the deviation of phase center and mass center.

[0088] As can be seen from Figure 3 , using the PPP-B2b dual-system dual-frequency ionosphere-free combination and the GBM time comparison of the dual-system ionosphere-free combination has almost no system deviation. The difference between them can more clearly observe the residual error of the PPP-B2b time comparison, Figure 4 is the time difference curve obtained, the time difference fluctuation is kept within 2ns, and the STD of the time comparison and the reference value is 0.544ns.

[0089] Through the above real-time redundant GPS system and Beidou system time comparison method, on the one hand, through the real-time acquisition of C59 and C61 GEO satellite PPP-B2b information, the broadcast ephemeris data of GPS and Beidou satellites is corrected by using the redundant method, so as to obtain high-precision satellite orbit broadcast ephemeris and clock error. Combined with the pseudo code and carrier phase observation value sent by the Beidou satellite, the clock error is calculated in real time by using the PPP algorithm to obtain the time comparison result of two places. On the other hand, it can avoid the situation that the PPP cannot be solved due to the insufficient availability of PPP-B2b information in a continuous period of observation data, so that the epoch of the solution is more complete.

[0090] ​In the description of the disclosure, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the disclosure. In the description of the disclosure, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the specification.

[0091] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the disclosure that follow the general principles thereof and include the known or customary practice of the art in addition to the disclosure. The specification and examples are to be regarded as illustrative only, and the true scope and spirit of the disclosure are indicated by the appended claims.

Claims

1. A real-time redundant BeiDou-3 PPP-B2b sub-nanosecond time comparison method, characterized in that, The method includes: Acquire observation data, satellite ephemeris data, and PPP-B2b message data from BeiDou-3 satellites; wherein the PPP-B2b messages include the first PPP-B2b message information from the C59 satellite and the second PPP-B2b message information from the C61 satellite; The clock difference for each satellite at the observation time is calculated based on the observation data and the satellite ephemeris data; Based on the redundancy method, the clock difference is corrected using the PPP-B2b message data to obtain the corrected clock difference; The corrected clock difference is precisely calculated using single-point positioning to obtain the target clock difference between the receivers in the two locations, and then the time between the two locations is compared. The step of correcting the clock bias using the PPP-B2b message data based on the redundancy method to obtain the corrected clock bias includes: Determine whether the signal of the C59 satellite is missing or interfered with; If the signal of the C59 satellite is intact or there is no interference, the clock error is corrected using the correction array in the first PPP-B2b message information of the C59 satellite; If the signal of the C59 satellite is lost or interfered with, the clock error is corrected using the correction array in the second PPP-B2b message information of the C61 satellite.

2. The real-time redundant BeiDou-3 PPP-B2b sub-nanosecond time comparison method according to claim 1, characterized in that, The steps for obtaining observation data, satellite ephemeris data, and B2b message data from BeiDou-3 satellites include: The observation data is acquired using a receiver; wherein the observation data includes carrier phase and pseudorange observations; The receiver is used to receive the satellite ephemeris data; wherein the satellite ephemeris data includes orbital information and time information for each satellite; The receiver is used to receive PPP-B2b message data from the satellite; wherein the PPP-B2b message data includes satellite orbit corrections and clock corrections.

3. The real-time redundant BeiDou-3 PPP-B2b sub-nanosecond time comparison method according to claim 2, characterized in that, The step of calculating the clock difference of each satellite at the observation time based on the observation data and the satellite ephemeris data includes: Based on the observation data, the orbital information, the time information, the Earth's gravitational field, and the solar radiation pressure, the clock difference for each satellite at the observation time is calculated.

4. The real-time redundant BeiDou-3 PPP-B2b sub-nanosecond time comparison method according to claim 3, characterized in that, The correction array includes: Inter-symbol error correction, satellite orbit correction, and satellite clock error correction.

5. The real-time redundant BeiDou-3 PPP-B2b sub-nanosecond time comparison method according to claim 4, characterized in that, The step of performing precise single-point positioning calculation on the corrected clock bias to obtain the target clock bias of the receivers at two locations includes: The receiver parameters, stromal delay, ionospheric delay, and multipath effect in the corrected clock bias are estimated using a Kalman filter and the least squares method. The estimated results are subjected to residual testing. If the residual is greater than a preset threshold, it is judged as a gross error. After removing the gross error, the receiver parameters, the stromal delay, the ionospheric delay, and the multipath effect are re-estimated. If the residual is less than the threshold, the target clock error of the receiver is output.

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