Beidou wide-area real-time precise time service elasticity maintaining method based on satellite-ground cooperation

Abstract

The invention belongs to the field of satellite navigation high-precision time service, and provides a Beidou wide-area real-time precision time service elasticity maintaining method based on satellite-ground cooperation, and when a ground communication network is normal, Beidou wide-area real-time precision time service is carried out through a normal receiving real-time precision correction product. Outputting a time service result and recording a receiver coordinate and a troposphere delay parameter of the current epoch; when the ground communication network is interrupted, if the broadcast ephemeris is switched, the variance constraint strategy in the parameter estimation is adjusted according to the discontinuity error of the broadcast ephemeris; in parameter estimation, root-mean-square information filtering is carried out based on recorded receiver coordinates and troposphere delay parameters, ambiguity is estimated as time-varying parameters, then clock correction is traced to UTC (k), and then a time service result is obtained and output; when the ground communication network is recovered, whether ambiguity estimation is carried out again or not is judged based on the cycle slip detection result, and then Beidou wide-area real-time precise timing based on the precise correction product continues to be carried out.

Description

Technical Field

[0001] This invention belongs to the field of high-precision timing for satellite navigation, specifically involving a flexible method for maintaining BeiDou wide-area real-time precision timing based on satellite-ground collaboration. Background Technology

[0002] High-precision time and frequency play a crucial role in fields such as communications, power, finance, and defense. Existing wide-area precision time synchronization systems based on the BeiDou Navigation Satellite System, by integrating data from ground-based augmentation networks and onboard atomic clocks, can theoretically achieve sub-nanosecond time transmission and E-14-level frequency stability globally. However, this service relies heavily on a continuous and stable ground communication link to broadcast high-precision spatiotemporal correction information. In practical applications, communication links may be interrupted or unstable due to natural interference, equipment failure, or human factors. This prevents user terminals from obtaining key correction parameters such as precise orbits, clock errors, and atmospheric delays in real time, resulting in severe degradation of time synchronization accuracy and making it difficult to maintain the intended high-performance indicators. This has become a major technical bottleneck restricting its application in high-reliability scenarios. Currently, existing wide-area real-time precision time synchronization methods relying solely on BeiDou broadcast ephemeris data cannot meet the sub-nanosecond performance requirements originally designed for wide-area precision time synchronization systems. Therefore, there is an urgent need for a time synchronization elastic maintenance technology that is designed for network interruption scenarios and does not rely on the continuous broadcast of high-precision correction information. During the interruption of communication links, it is possible to elastically maintain the high-precision time synchronization capability of the original system design specifications. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a flexible maintenance method for BeiDou wide-area real-time precise timing based on satellite-ground coordination, thereby resolving the issues in the prior art. The technical solution adopted by this invention is as follows: A flexible method for maintaining BeiDou wide-area real-time precise timing based on satellite-ground coordination includes: S1, based on the BeiDou wide-area real-time precision time synchronization, if the ground communication network is normal, receives external high-precision satellite orbit clock error correction information through the ground communication network and performs real-time calculation, outputs the time synchronization result and records the receiver coordinates and tropospheric delay parameters of the current epoch. S2, When the ground communication network is interrupted, if the broadcast ephemeris is switched, the variance constraint strategy in the parameter estimation is adjusted according to the discontinuity error of the broadcast ephemeris. S3 uses root mean square information filtering for parameter estimation, estimates the ambiguity as time-varying parameters, then traces the clock difference back to UTC(k) to obtain the time synchronization result and outputs it. S4, when the ground communication network is restored, it is determined whether to re-evaluate the ambiguity based on the cycle slip detection results, and then the BeiDou wide-area real-time precise timing based on the precise correction product continues, and the elasticity maintenance ends.

[0004] Furthermore, when the ground communication network is interrupted, the variance constraint adjustment strategy in parameter estimation includes: determining whether the broadcast ephemeris is switched at this time; if the broadcast ephemeris is switched, calculating the discontinuity error based on the satellite orbit radial component error and clock error, and using the discontinuity error to adjust the variance constraint in parameter estimation based on an empirical threshold.

[0005] Furthermore, S2 includes: S21, when the ground communication network is interrupted and the broadcast ephemeris is switched (if the broadcast ephemeris is not switched, skip S2). S22, Calculate the broadcast ephemeris discontinuity error: (2) in, This indicates an error in the ephemeris discontinuity. and These represent the satellite orbit radial component error and satellite clock error introduced during ephemeris switching, respectively; S23, Variance constraint strategy for parameter estimation based on ephemeris discontinuity error adjustment: (3) in, The variance is calculated based on the initial ambiguity. This indicates that the variance has been reinitialized. This indicates an increase in variance constraints.

[0006] Furthermore, S3 includes: S31, Root Mean Square Information Filtering, uses ambiguity as a time-varying parameter for estimation: Parameters that need to be estimated or adjusted Including time-domain random parameters and time-domain invariant parameters As shown in the following formula: (4) The time-domain random parameters are described by a random noise model of a first-order discrete Gaussian-Markov process, as shown in the following equation: (5) in, For time-domain random parameters, For the relevant time, With zero mean and variance Gaussian white noise; Ambiguity is treated as a time-invariant parameter. The initial value is calculated by subtracting the phase observation from the pseudorange observation. It is used as a constant during filtering estimation and reconverges after cycle slip occurs. The carrier phase ambiguity of each satellite is estimated as a time-domain random parameter, and its process noise is described by a random walk process. An empirical process noise variance is set. as follows: (6) in , Indicates the time interval for solution calculation; S32, trace the receiver clock bias estimation result back to UTC(k): (7) In the formula, Indicates local time. Indicates the time of the BeiDou system. The receiver clock bias obtained through parameter estimation This indicates the receiver hardware time delay. The difference between UTC(k) and the BeiDou system time is shown in equation (8): (8) The time difference between the local time and UTC(k) is obtained as the time synchronization result.

[0007] Furthermore, in S4, when the communication network returns to normal, the method for ending the elasticity maintenance includes: performing cycle slip detection based on the estimated ambiguity parameters; if a cycle slip occurs, re-estimating the ambiguity and resuming the reception of real-time correction products and continuing BeiDou wide-area real-time precise timing; if there is no cycle slip, directly resuming real-time precise timing calculation.

[0008] The present invention has the following beneficial effects: This invention enables the maintenance of sub-nanosecond timing accuracy without relying on external high-precision satellite orbit clock correction products when terrestrial communication networks are interrupted. It achieves this through satellite-ground coordination, parameter estimation algorithms, and reference tracing technology. Specifically, it can achieve a measured timing result with a standard deviation better than 0.25 nanoseconds and a peak-to-peak error of less than 2.2 nanoseconds. This effectively overcomes the bottleneck of traditional methods experiencing a sharp performance drop when links are interrupted, ensuring the high reliability and continuity of BeiDou wide-area real-time precision timing services. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0010] The following will be described in conjunction with embodiments of the present invention. Figure 1The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0011] like Figure 1 This invention proposes a flexible maintenance method for BeiDou wide-area real-time precise timing based on satellite-ground coordination, comprising: S1, BeiDou wide-area real-time precision time synchronization based on terrestrial communication network. If the terrestrial communication network is normal, based on the terrestrial augmentation system, it receives external high-precision satellite orbit clock error correction information through the terrestrial communication network and performs real-time calculation. After tracing the time reference, it outputs the time synchronization result and records the receiver coordinates and tropospheric delay parameters of the current epoch. S2, when the ground communication network is interrupted, if the broadcast ephemeris is switched, the variance constraint strategy in parameter estimation is adjusted according to the discontinuity error of the broadcast ephemeris. The variance constraint adjustment strategy in parameter estimation includes: determining whether the broadcast ephemeris is switched at this time; if the broadcast ephemeris is switched, the discontinuity error is calculated based on the satellite orbit radial component error and clock error, and the variance constraint in parameter estimation is adjusted based on the empirical threshold using the discontinuity error.

[0012] S2 specifically includes: S21, when the ground communication network is interrupted and the broadcast ephemeris is switched (if the broadcast ephemeris is not switched, skip S2).

[0013] S22, Calculate the broadcast ephemeris discontinuity error: (2) in, This indicates an error in the ephemeris discontinuity. and These represent the satellite orbit radial component error and satellite clock error introduced during ephemeris switching, respectively.

[0014] S23, Variance constraint strategy for parameter estimation based on ephemeris discontinuity error adjustment: (3) in, The variance is calculated based on the initial ambiguity. This indicates that the variance has been reinitialized. This indicates an increase in variance constraints.

[0015] S3 uses root mean square information filtering for parameter estimation, estimates the ambiguity as time-varying parameters, then traces the clock difference back to UTC(k) to obtain the time synchronization result and outputs it. S3 specifically includes: S31, Root Mean Square Information Filtering, uses ambiguity as a time-varying parameter for estimation: Parameters that need to be estimated or adjusted Generally includes time-domain random parameters and time-domain invariant parameters As shown in the following formula.

[0016] (4) Zenith tropospheric wet component delay error, receiver clock error, etc. are all time-domain random parameters. Their process noise is usually described by a first-order discrete Gaussian-Markov process random noise model, that is, the transition of each state depends only on the previous state, as shown in the following equation.

[0017] (5) in, For time-domain random parameters, For the relevant time, With zero mean and variance Gaussian white noise. When the correlation time approaches infinity, it can be described by a random walk process; when the correlation time is 0, it can be described by white noise. In practical applications, the zenith tropospheric wet component delay error is more appropriately described by a random walk process, while the receiver clock error is described by a white noise model.

[0018] Theoretically, after a single satellite is acquired and tracked, the integer ambiguity remains unchanged across the continuous visible observation arc, assuming no cycle slips. However, due to uncalibrated phase delays between the receiver and the satellite, it is resolved as a floating-point value rather than an integer. In conventional processing, the ambiguity is treated as a time-invariant parameter. Its initial value is calculated by subtracting the phase observation from the pseudorange observation, and it is treated as a constant during filtering estimation. Reconvergence is performed after a cycle slip occurs.

[0019] When using only broadcast ephemeris, if the ambiguity parameters are treated as time-invariant parameters, the receiver coordinates will remain stable after convergence in a static scene due to the adjustment principles and the different noise variance constraints of each parameter error. The zenith tropospheric delay will also change relatively little over a short period, ultimately leading to a significant portion of the ephemeris error being absorbed by the receiver clock bias, thus greatly affecting timing accuracy. Therefore, this paper considers treating the carrier phase ambiguity of each satellite as a time-domain random parameter for estimation when using only broadcast ephemeris for calculation. A random walk process is used to describe the process noise, and an empirical process noise variance is set here. as follows: (6) in , This indicates the time interval for the calculation.

[0020] S32, trace the receiver clock bias estimation result back to UTC(k): (7) In the formula, Indicates local time. Indicates the time of the BeiDou system. The receiver clock bias obtained through parameter estimation This indicates the receiver hardware time delay. The difference between UTC(k) and the BeiDou system time is shown in equation (8). The time difference between the local time and UTC(k) can be obtained through the above equation, which gives the time synchronization result.

[0021] (8) S4. When the ground communication network is restored, a decision is made based on the cycle slip detection results to determine whether to re-evaluate the ambiguity. Subsequently, BeiDou wide-area real-time precise timing based on the precise correction product continues, and the elastic hold ends. The methods for ending the elastic hold include: performing cycle slip detection based on the estimated ambiguity parameters; if a cycle slip occurs, the ambiguity is re-estimated, the real-time correction product is restored, and BeiDou wide-area real-time precise timing continues; if there is no cycle slip, real-time precise timing calculation is directly resumed.

[0022] S4 specifically includes: S41, cycle slip detection is performed based on the time-varying ambiguity parameters obtained from parameter estimation. If a cycle slip occurs, the ambiguity parameters are re-estimated.

[0023] S42, re-receive external precision orbit clock error correction products, resume step S1, and complete the flexible maintenance of BeiDou wide-area real-time precision timing under this network interruption scenario.

[0024] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, alterations, alterations, or substitutions made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A flexible method for maintaining BeiDou wide-area real-time precise timing based on satellite-ground coordination, characterized in that: include: S1, based on the BeiDou wide-area real-time precision time synchronization, if the ground communication network is normal, receives external high-precision satellite orbit clock error correction information through the ground communication network and performs real-time calculation, outputs the time synchronization result and records the receiver coordinates and tropospheric delay parameters of the current epoch. S2, When the ground communication network is interrupted, if the broadcast ephemeris is switched, the variance constraint strategy in the parameter estimation is adjusted according to the discontinuity error of the broadcast ephemeris. S3 uses root mean square information filtering for parameter estimation, estimates the ambiguity as time-varying parameters, then traces the clock difference back to UTC(k) to obtain the time synchronization result and outputs it. S4, when the ground communication network is restored, it is determined whether to re-evaluate the ambiguity based on the cycle slip detection results, and then the BeiDou wide-area real-time precise timing based on the precise correction product continues, and the elasticity maintenance ends.

2. The flexible maintenance method for BeiDou wide-area real-time precision timing based on satellite-ground coordination according to claim 1, characterized in that, When the terrestrial communication network is interrupted, the variance constraint adjustment strategy in parameter estimation includes: determining whether the broadcast ephemeris is switched at this time; if the broadcast ephemeris is switched, calculating the discontinuity error based on the satellite orbit radial component error and clock error, and using the discontinuity error to adjust the variance constraint in parameter estimation based on an empirical threshold.

3. The flexible maintenance method for BeiDou wide-area real-time precise timing based on satellite-ground coordination according to claim 1, characterized in that, S2 include: S21, when the ground communication network is interrupted and the broadcast ephemeris is switched (if the broadcast ephemeris is not switched, skip S2). S22, Calculate the broadcast ephemeris discontinuity error: (2) in, This indicates an error in the ephemeris discontinuity. and These represent the satellite orbit radial component error and satellite clock error introduced during ephemeris switching, respectively; S23, Variance constraint strategy for parameter estimation based on ephemeris discontinuity error adjustment: (3) in, The variance is calculated based on the initial ambiguity. This indicates that the variance has been reinitialized. This indicates an increase in variance constraints.

4. The flexible maintenance method for BeiDou wide-area real-time precise timing based on satellite-ground coordination according to claim 1, characterized in that, S3 include: S31, Root Mean Square Information Filtering, uses ambiguity as a time-varying parameter for estimation: Parameters that need to be estimated or adjusted Including time-domain random parameters and time-domain invariant parameters As shown in the following formula: (4) The time-domain random parameters are described by a random noise model of a first-order discrete Gaussian-Markov process, as shown in the following equation: (5) in, For time-domain random parameters, For the relevant time, With zero mean and variance Gaussian white noise; Ambiguity is treated as a time-invariant parameter. The initial value is calculated by subtracting the phase observation value from the pseudorange observation value. It is used as a constant during filtering estimation and reconverges after cycle slip occurs. The carrier phase ambiguity of each satellite is estimated as a time-domain random parameter, and its process noise is described by a random walk process. An empirical process noise variance is set. as follows: (6) in , Indicates the time interval for solution calculation; S32, trace the receiver clock bias estimation result back to UTC(k): (7) In the formula, Indicates local time. Indicates the time of the BeiDou system. The receiver clock bias obtained through parameter estimation This indicates the receiver hardware time delay. The difference between UTC(k) and the BeiDou system time is shown in equation (8): (8) The time difference between the local time and UTC(k) is obtained as the time synchronization result.

5. The flexible maintenance method for BeiDou wide-area real-time precision timing based on satellite-ground coordination as described in claim 1, characterized in that, In S4, when the communication network is restored, the method for ending the elasticity maintenance includes: performing cycle slip detection based on the estimated ambiguity parameters; if a cycle slip occurs, re-estimating the ambiguity and resuming the reception of real-time correction products and continuing to perform BeiDou wide-area real-time precise timing; if there is no cycle slip, directly resuming real-time precise timing calculation.

Images