Beidou system clock synchronization method and device

Abstract

The application provides a Beidou system clock synchronization method and device. It relates to the technical field of satellite navigation and time-frequency synchronization, and is invented to solve the problem of serious clock comparison lag and insufficient dynamic error suppression of traditional satellite common view method. The technical method provided by the application comprises: converting the geodetic coordinate system of a ground station into a unified Beidou coordinate system; starting clock synchronization in the Beidou coordinate system, screening common view satellites by comparing the satellite masks of the received signals of the stations, obtaining the measured pseudo distances and measured carriers between the ground stations and the common view satellites within the common view period, dynamically compensating the clock difference by fusing the measured pseudo distances and measured carriers to obtain smooth pseudo distances; calculating the initial clock difference between the ground clock and the satellite clock at each time step according to the smooth pseudo distances, and obtaining the final clock difference of the common view period by using grouped least square fitting, exchanging the final clock difference corresponding to each ground station, and performing clock synchronization according to the final clock difference.

Description

Technical Field

[0001] This invention relates to the field of satellite navigation and time-frequency synchronization technology, to a carrier phase smoothing pseudorange algorithm, and specifically to a common-view clock real-time synchronization method and device based on the BeiDou Navigation Satellite System (BDS). Background Technology

[0002] Clock synchronization technology uses various methods to obtain the time deviation between two or more locations, ultimately calibrating the clock source. The core of various timing devices is the frequency source; counting and reading the signal from the frequency source produces a clock. Therefore, clock synchronization aims to maintain a high degree of consistency in the frequency sources of clocks in different locations. The emergence and development of modern radio technology have allowed for increasingly wider ranges and higher precision in clock synchronization.

[0003] In the current development of the national economy, various clock synchronization technologies provide solid basic support for all sectors. Among the various clock synchronization methods, land-based shortwave and longwave time synchronization technologies have relatively low synchronization accuracy and cannot meet the needs of applications with high accuracy requirements. Although fiber optic time and frequency transmission technology, which is still under research, can achieve picosecond-level accuracy, its equipment is complex and not suitable for large-scale applications.

[0004] Satellite-based clock synchronization technologies can be categorized into one-way time synchronization, common-view clock synchronization, and two-way satellite time-frequency transmission, depending on the comparison process. One-way time synchronization has the lowest cost but low accuracy, and ultimately can only trace back to the system time or Coordinated Universal Time (UTC) of the onboard clock. Two-way satellite time-frequency transmission offers higher accuracy and can synchronize clocks using any clock device as the source, but its hardware is expensive and requires satellite communication resources, resulting in extremely high usage costs. Common-view clock synchronization combines the advantages of both, achieving high accuracy without requiring additional satellite resources, and has a wide range of applications.

[0005] The initial purpose of building the BeiDou system was to break technological monopolies, safeguard national security, and promote socio-economic development. Therefore, this invention aims to conduct research on clock synchronization methods under an inter-satellite common-view approach, based on BeiDou. Constructing an integrated space-ground clock synchronization network and improving my country's terrestrial time and frequency network is of great significance to information technology innovation, socio-economic development, and national defense security. Summary of the Invention

[0006] The technical problem this invention aims to solve is to provide a BeiDou system clock synchronization method that can achieve high-precision real-time synchronization of remote clocks, addressing the severe lag and limited accuracy issues of traditional satellite common-view methods. The purpose of this invention is to address the poor real-time performance and insufficient dynamic error suppression such as multipath effects caused by the fixed 16-minute period in the traditional CGGTTS process. Based on a collaborative architecture of period compression mechanism, satellite mask matching, and dynamic filtering, this invention designs a low-latency, sub-nanosecond-level BeiDou clock real-time synchronization method.

[0007] According to a first aspect of the present invention, a clock synchronization method for the BeiDou system is provided, comprising: Convert the geodetic coordinate system of the ground stations to a unified BeiDou coordinate system; Clock synchronization is enabled in the BeiDou coordinate system. Common-view satellites are selected by comparing the satellite masks of the signals received by the ground station. Within the common-view period, the measured pseudo-range and measured carrier between the ground station and the common-view satellite are obtained. The measured pseudo-range and measured carrier are fused to perform clock error dynamic compensation and obtain smooth pseudo-range. The initial clock difference between the ground clock and the satellite clock at each time step is calculated based on the smoothed pseudo-distance. The final clock difference of the common-view period is obtained by grouped least squares fitting. The final clock differences corresponding to each ground station are exchanged, and clock synchronization is performed based on the final clock difference.

[0008] According to a second aspect of the present invention, a clock synchronization device for the BeiDou system is provided, comprising: The coordinate transformation module is used to convert the geodetic coordinate system of ground stations into a unified BeiDou coordinate system; The dynamic fusion module is used to enable clock synchronization in the BeiDou coordinate system. It filters common-view satellites by comparing the satellite masks of the signals received by the ground station. Within the common-view period, it obtains the measured pseudo-range and measured carrier between the ground station and the common-view satellites. It fuses the measured pseudo-range and measured carrier to perform dynamic clock error compensation and obtain a smooth pseudo-range. The fitting synchronization module is used to calculate the initial clock difference between the ground clock and the satellite clock at each time step based on the smoothed pseudo distance, and to obtain the final clock difference of the common viewing period by grouping least squares fitting. The final clock difference corresponding to each ground station is exchanged, and clock synchronization is performed based on the final clock difference.

[0009] According to a third aspect of the present invention, an electronic device is provided, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when executed by the processor, implements the steps of the BeiDou system clock synchronization method provided in the first aspect of the present disclosure.

[0010] According to a fourth aspect of the present invention, a computer-readable storage medium is provided, on which an information transmission implementation program is stored, which, when executed by a processor, implements the steps of the BeiDou system clock synchronization method provided in the first aspect of the present disclosure.

[0011] The advantages of this invention are that its architecture solves the lag problem through seamless periodic observation, achieves millisecond-level matching of common-view satellites using satellite masks, and, combined with a carrier phase smoothing algorithm, significantly improves synchronization real-time performance and measurement accuracy. This method can be applied to scenarios requiring high-precision clock synchronization, such as power systems and communication base stations. Attached Figure Description

[0012] Figure 1 A flowchart of a clock synchronization method for the BeiDou system; Figure 2 A schematic diagram of a clock synchronization device for the BeiDou system; Figure 3 A schematic diagram of an electronic device. Detailed Implementation

[0013] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0014] Method Implementation Examples According to an embodiment of the present invention, a clock synchronization method for the BeiDou system is provided. Figure 1 The flowchart of the proposed clock synchronization method for the BeiDou system includes: In step S110, the geodetic coordinate system of the ground station is converted into a unified BeiDou coordinate system, specifically including: The BeiDou system uses a custom BeiDou coordinate system (BDCS), which is a coordinate system perpendicular to the Earth's center. It takes the Earth's center of mass as its starting point, the Z-axis as its axis, and is consistent with the Earth's rotation axis. The X-axis is the intersection of the prime meridian plane and the equator, and together with the Z-axis, they form a right coordinate system.

[0015] In this coordinate system, the coordinates of celestial bodies fixed on the Earth's surface do not change with the Earth's rotation, making it suitable for describing the positions of fixed objects such as mountains and buildings on the ground. It's important to note that during satellite co-location, participating stations can determine their positions in advance using precise point positioning. This coordinate system typically uses latitude, longitude, and altitude coordinates, and must first be converted to the ground-based rectangular coordinate system to which BDCS belongs.

[0016] Use Formula 1 to convert the geodetic coordinate system to the BeiDou coordinate system: Formula 1; in,( , , ) represents the coordinates in the BeiDou coordinate system. , , () represents coordinates in the geodetic coordinate system. The radius of curvature of the ellipsoid's malocclusion is given by... This refers to a parameter that describes the degree of flattening of the ellipsoid.

[0017] Formula 3 is used to express the radius of curvature of the ellipsoid's primordial circle: Formula 3; in, This represents the semi-major axis of the ellipsoid, i.e., the equatorial radius.

[0018] In step S120, clock synchronization is initiated in the BeiDou coordinate system. Common-view satellites are selected by comparing the satellite masks of the signals received by the ground station. Within the common-view period, the measured pseudo-range and measured carrier waves between the ground station and the common-view satellites are obtained. The measured pseudo-range and measured carrier waves are fused for dynamic clock bias compensation to obtain a smoothed pseudo-range. Specifically, this includes: A 48-bit binary code is used to represent the satellite mask; Commonly viewed satellites are selected by performing a bitwise AND operation on the satellite masks corresponding to each ground station.

[0019] The traditional processing workflow for global satellite co-view observation data is standardized by the GPS GLONASS Co-view Timing Standard (CGGTTS). The co-view period for each geostationary station is 16 minutes, with the first 2 minutes used for workflow preparation, the middle 13 minutes for tracking satellites and recording observation data, and the last minute for data processing. For example, when the receiver tracks a satellite, it outputs an observation value once per second. In one co-view period, 780 pseudorange values ​​can be obtained for each satellite, and the clock difference between the local clock and the satellite clock can be calculated based on these pseudorange values. The traditional method of exchanging co-view files after the fact typically takes several days or even weeks to complete clock synchronization between stations.

[0020] In this embodiment of the invention, the common-view process and data processing method are improved, achieving seamless and rapid time comparison, which can detect occasional and sudden jumps in the clock source output signal. The common-view period is changed to 100 seconds to enhance the real-time performance of clock synchronization, and the specified time period reserved for process preparation and post-processing data processing is eliminated. After one comparison period ends, the next period begins immediately.

[0021] In each time step of the common-view period, the measured pseudo-range and measured carrier between the ground station and the common-view satellite are acquired. The common-view period is set to 60-100 seconds, the time step interval is set to 1 second, and the receiver outputs the observation value once per second when tracking the satellite.

[0022] In traditional methods, pseudorange observations of navigation signals are susceptible to multipath effects, resulting in low measurement accuracy with errors on the order of meters. However, the carrier frequency is much higher than the pseudorange frequency, and the carrier phase is minimally affected by multipath effects, typically not exceeding 1 / 4. Therefore, millimeter-level carrier phase observation accuracy can be achieved. However, carrier phase measurement faces challenges such as difficulty in calculating integer ambiguity and the inability to accurately determine ambiguity. Therefore, using carrier phase smoothing pseudorange can reduce the random errors of the original pseudorange without introducing fixed ambiguity issues, effectively improving both observation accuracy and computational efficiency.

[0023] Formula 4 is used to describe the observed pseudo-range of the receiver pair and the phase of the carrier: Formula 4; in, Indicates pseudo-distance of the code; This indicates the actual geometric distance between the user's station and the satellite; For satellite clock bias; , To observe random errors; The wavelength of the navigation signal; , These represent the fractional part and integer ambiguity of the carrier phase observation, respectively. Represents the speed of light in a vacuum. Integer ambiguity. Solving for this is very difficult, but its value will not change if the carrier tracking loop does not lose lock. Formula 5 is used to calculate the value for two adjacent observation epochs. The difference between the observed values ​​is calculated, where the subscript represents time. The difference: Formula 5; Formula 5 has eliminated integer ambiguity; ideally, the code pseudorange variation... and carrier phase change The pseudocode should be the same, but in reality, the pseudocode error is different. This is generally a carrier phase error. The accuracy is hundreds of times greater than that of the original value. By combining the two, a pseudorange value with high precision and no integer ambiguity can be obtained. Using Formula 2, the measured pseudorange and the measured carrier wave are fused to obtain the smoothed pseudorange: Formula 2; in, express Smooth pseudo-distance of epochs, This indicates the measured pseudo-distance. Indicates the phase of the measured carrier wave. Indicates the smoothing time constant. This represents the carrier wavelength, typically between 20 and 100 when the receiver outputs an observation value once per second. Indicates the carrier wavelength.

[0024] Dynamic corrections are performed during the raw data stage, thereby obtaining higher precision clock errors directly during the calculation process.

[0025] In step S130, the initial clock difference between the ground clock and the satellite clock at each time step is calculated based on the smoothed pseudo-distance, and the final clock difference for the common-view period is obtained by grouped least squares fitting. The final clock differences corresponding to each ground station are exchanged, and clock synchronization is performed based on the final clock difference. Specifically, this includes: The clock difference is calculated using the existing pseudo-distance solution method; In traditional data processing, the first step is to divide the 780 clock differences into 52 groups of 15 each, perform curve fitting on each group, and select the optimal midpoint. The second step is to perform linear fitting on these 52 midpoints and select the midpoint again. This midpoint is used as the clock difference for the current co-view cycle and saved to the co-view file. Finally, the stations participating in the co-view exchange the co-view file, and the clock differences between the stations are obtained by subtracting the clock differences for the same cycle, thus achieving time transfer.

[0026] In this embodiment of the invention, the following grouping fitting is performed to improve the accuracy of real-time common vision: The initial clock difference calculated at each time step is divided into N groups according to adjacent observation epochs; Within each group, the initial clock difference is fitted using least squares, and the median value is taken as the corresponding fitted clock difference. The N fitted clock differences are then combined and fitted using least squares again, and the median value is taken to obtain the final clock difference for the current common period.

[0027] The data was grouped and least squares fitting was used. The first fitting divided the 100 data points into 10 groups, with each group consisting of 10 adjacent observation epochs. Least squares fitting was performed on each group and the median value was taken. The second fitting was performed on these 10 median values ​​again, and the median value was taken as the final result for this period.

[0028] The final clock difference can be stored in the common-view file for exchange. The difference between the final clock differences of different ground stations and the same common-view satellite can be calculated to obtain the clock synchronization result.

[0029] In this embodiment of the invention, a GPRS network is used for real-time transmission between ground stations, including two stages: satellite mask negotiation to determine common-view satellites and transmission of clock bias results. The GPRS network provides high-speed, continuous wireless data transmission services, enabling real-time transmission of common-view data between multiple stations. Simultaneously, to accelerate data processing efficiency and compensate for the problems caused by eliminating the dedicated data processing time period in the traditional common-view process.

[0030] The GPRS network sends clock difference data and timestamps every 60-100 seconds.

[0031] Device Examples According to an embodiment of the present invention, a clock synchronization device for the BeiDou system is provided. Figure 2 A schematic diagram of a proposed clock synchronization device for the BeiDou system is shown, including: The coordinate transformation module 20 is used to convert the geodetic coordinate system of ground stations into a unified BeiDou coordinate system, specifically for: Use Formula 1 to convert the geodetic coordinate system to the BeiDou coordinate system: Formula 1; in,( , , ) represents the coordinates in the BeiDou coordinate system. , , () represents coordinates in the geodetic coordinate system. The radius of curvature of the ellipsoid's malocclusion is given by... This refers to a parameter that describes the degree of flattening of the ellipsoid.

[0032] Dynamic fusion module 22 is used to enable clock synchronization in the BeiDou coordinate system. It filters common-view satellites by comparing the satellite masks of the signals received by the ground station, obtains the measured pseudo-range and measured carrier waves between the ground station and the common-view satellites within the common-view period, and fuses the measured pseudo-range and measured carrier waves for dynamic clock error compensation to obtain a smoothed pseudo-range. Specifically, it is used for: A 48-bit binary code is used to represent the satellite mask; Commonly viewed satellites are selected by performing a bitwise AND operation on the satellite masks corresponding to each ground station.

[0033] In each time step of the common-view period, the measured pseudo-range and measured carrier between the ground station and the common-view satellite are obtained, where the common-view period is set to 100 seconds; Using Formula 2, the measured pseudorange and the measured carrier wave are fused to obtain the smoothed pseudorange: Formula 2; in, express Smooth pseudo-distance of epochs, This indicates the measured pseudo-distance. Indicates the phase of the measured carrier wave. Indicates the smoothing time constant. Indicates the carrier wavelength.

[0034] The fitting synchronization module 24 is used to calculate the initial clock difference between the ground clock and the satellite clock at each time step based on the smoothed pseudo-distance, and to obtain the final clock difference of the common-view period using grouped least squares fitting. It then exchanges the final clock differences corresponding to each ground station and performs clock synchronization based on the final clock difference. Specifically, it is used for: The initial clock difference calculated at each time step is divided into N groups according to adjacent observation epochs; Within each group, the initial clock difference is fitted using least squares, and the median value is taken as the corresponding fitted clock difference. The N fitted clock differences are then combined and fitted using least squares again, and the median value is taken to obtain the final clock difference for the current common period.

[0035] The clock synchronization result is obtained by subtracting the final clock difference between different ground stations and the same common-view satellite.

[0036] Real-time transmission is achieved between ground stations using a GPRS network.

[0037] Electronic device examples Figure 3 This is a schematic diagram of an electronic device according to an embodiment of the present invention. The electronic device 300 may include at least one processor 310 and a memory 320. The processor 310 can execute instructions stored in the memory 320. The processor 310 is communicatively connected to the memory 320 via a data bus. In addition to the memory 320, the processor 310 can also be communicatively connected to an input device 330, an output device 340, and a communication device 350 via the data bus.

[0038] Processor 310 can be any conventional processor, such as a commercially available CPU. Processors may also include graphics processing units (GPUs), field-programmable gate arrays (FPGAs), systems-on-chips (SoCs), application-specific integrated circuits (ASICs), or combinations thereof.

[0039] The memory 320 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk or optical disk.

[0040] In this embodiment of the present disclosure, the memory 320 stores executable instructions, and the processor 310 can read the executable instructions from the memory 320 and execute the instructions to implement all or part of the steps of the BeiDou system clock synchronization method in any of the above exemplary embodiments.

[0041] Computer-readable storage medium embodiments In addition to the methods and apparatus described above, exemplary embodiments of this disclosure may also be a computer program product or a computer-readable storage medium storing the computer program product, wherein the computer program product includes computer program instructions that can be executed by a processor to implement all or part of the steps described in any of the BeiDou system clock synchronization methods in the exemplary embodiments described above.

[0042] Computer program products can be written in any combination of one or more programming languages ​​to perform the operations of the embodiments of this application. Programming languages ​​include object-oriented programming languages ​​such as Java and C++, as well as conventional procedural programming languages ​​such as C or similar languages, and scripting languages ​​(e.g., Python). The program code can be executed entirely on the user's computing device, partially on the user's device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0043] Computer-readable storage media may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example,, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of readable storage media include: static random access memory (SRAM) having one or more electrically connected wires; electrically erasable programmable read-only memory (EEPROM); erasable programmable read-only memory (EPROM); programmable read-only memory (PROM); read-only memory (ROM); magnetic storage; flash memory; magnetic disk or optical disk; or any suitable combination thereof.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A clock synchronization method for the BeiDou system, characterized in that, Includes the following steps: Convert the geodetic coordinate system of the ground stations to a unified BeiDou coordinate system; Clock synchronization is enabled in the BeiDou coordinate system. Common-view satellites are screened by comparing the satellite mask of the signals received by the station. Within the common-view period, the measured pseudo-range and measured carrier between the ground station and the common-view satellite are obtained. The measured pseudo-range and the measured carrier are fused to perform clock error dynamic compensation to obtain a smooth pseudo-range. The initial clock difference between the ground clock and the satellite clock at each time step is calculated based on the smoothed pseudo-distance, and the final clock difference of the common-view period is obtained by grouped least squares fitting. The final clock differences corresponding to each ground station are exchanged, and clock synchronization is performed based on the final clock difference.

2. The BeiDou system clock synchronization method as described in claim 1, characterized in that, The specific steps of converting the geodetic coordinate system of ground stations into a unified BeiDou coordinate system include: Use Formula 1 to convert the geodetic coordinate system to the BeiDou coordinate system: Official 1; in,( , , ) represents the coordinates in the BeiDou coordinate system. , , () represents coordinates in the geodetic coordinate system. The radius of curvature of the ellipsoid's malocclusion is given by... This refers to a parameter that describes the degree of flattening of the ellipsoid.

3. The BeiDou system clock synchronization method as described in claim 1, characterized in that, The process of filtering common-view satellites by comparing the satellite masks of signals received from the comparison stations specifically includes: The satellite mask is represented by a 48-bit binary code. The common-view satellites are selected by performing a bitwise AND operation on the satellite masks corresponding to each ground station.

4. The BeiDou system clock synchronization method as described in claim 1, characterized in that, The step of acquiring the measured pseudo-range and measured carrier between the ground station and the common-view satellite within the common-view period, and fusing the measured pseudo-range and measured carrier for dynamic clock error compensation to obtain the smooth pseudo-range specifically includes: In each time step of the common-view period, the measured pseudo-range and measured carrier between the ground station and the common-view satellite are obtained, wherein the common-view period is set to 100 seconds; Using Formula 2, the measured pseudo-range and the measured carrier are fused to obtain the smoothed pseudo-range: Official 2; in, express Smooth pseudo-distance of epochs, This indicates the measured pseudo-distance. Indicates the phase of the measured carrier wave. Indicates the smoothing time constant. Indicates the carrier wavelength.

5. A clock synchronization method for the BeiDou system as described in claim 1, characterized in that, The method of obtaining the final clock difference of the common period using grouped least squares fitting specifically includes: The initial clock difference calculated at each time step is divided into N groups according to adjacent observation epochs; Within each group, the initial clock difference is fitted using least squares, and the median value is taken as the corresponding fitted clock difference. The N fitted clock differences are then combined and fitted using least squares again, and the median value is taken to obtain the final clock difference for the current common viewing period.

6. A clock synchronization method for a BeiDou system as described in claim 1, characterized in that, The exchange of the final clock differences corresponding to various ground stations and the clock synchronization based on the final clock differences specifically include: subtracting the final clock differences between different ground stations and the same shared satellite to obtain the clock synchronization result.

7. A clock synchronization method for a BeiDou system as described in claim 1, characterized in that, The method further includes: using a GPRS network for real-time transmission between the ground stations.

8. A clock synchronization device for the BeiDou system, characterized in that, include: The coordinate transformation module is used to convert the geodetic coordinate system of ground stations into a unified BeiDou coordinate system; The dynamic fusion module is used to enable clock synchronization in the BeiDou coordinate system, filter common-view satellites by comparing the satellite mask of the signals received by the station, obtain the measured pseudo-range and measured carrier between the ground station and the common-view satellite within the common-view period, and fuse the measured pseudo-range and the measured carrier to perform dynamic clock error compensation to obtain a smooth pseudo-range. The fitting synchronization module is used to calculate the initial clock difference between the ground clock and the satellite clock at each time step based on the smoothed pseudo distance, and to obtain the final clock difference of the common viewing period by grouping least squares fitting, exchange the final clock differences corresponding to each ground station, and perform clock synchronization based on the final clock difference.

9. An electronic device, characterized in that, include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when executed by the processor, implements the steps of the BeiDou system clock synchronization method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores an implementation program for information transmission, which, when executed by a processor, implements the steps of the BeiDou system clock synchronization method as described in any one of claims 1 to 7.

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