A low earth orbit satellite time synchronization method and system

Abstract

One embodiment of the present application discloses a low-orbit satellite time synchronization method and system, the method comprising: a starboard navigation receiver of a low-orbit satellite receiving and solving signals sent by a Beidou navigation satellite, and outputting starboard observation data to a ground data processing center; the ground data processing center receiving the starboard observation data and IGS data, calculating precise correction data; and performing star-ground time synchronization, inter-satellite time synchronization and ground station time synchronization processing according to the precise correction data sent by the ground data processing center.

Description

Technical Field

[0001] The present invention relates to the field of low-orbit satellites, and more specifically, to a method and system for time synchronization of low-orbit satellites. Background Art

[0002] With the rapid development of low-orbit satellite constellations, navigation augmentation systems based on low-orbit satellites have become a hot topic. By building a low-orbit satellite navigation augmentation system, the high precision, availability, and integrity of the Beidou system are enhanced. LEO satellites are used to directly broadcast navigation augmentation information to users, providing global real-time decimeter-level and post-event centimeter-level high-precision positioning. Navigation ranging signals are directly broadcast from LEO satellites, leveraging the high ground level of low-orbit signals to achieve enhanced positioning in environments with resistance to interference, obstruction, and complex environments. These systems also serve as a backup navigation, positioning, and timing method in the event of interference or denial of Beidou satellite navigation signals. This system will assist the country in building a comprehensive PNT system that features diverse information, integrated air-space-ground communication, and is resistant to interference, deception, robustness, and continuity.

[0003] The time unification system is the most critical part of the low-orbit navigation enhancement system. There is currently no relevant method to design a high-precision time synchronization system for low-orbit navigation enhancement. Summary of the Invention

[0004] In view of this, a first embodiment of the present invention provides a low-orbit satellite time synchronization method, comprising:

[0005] The onboard navigation receiver of the low-orbit satellite receives and interprets the signals sent by the Beidou navigation satellite, and outputs the onboard observation data to the ground data processing center;

[0006] The ground data processing center receives satellite observation data and IGS data and calculates precise correction data;

[0007] According to the precise correction data sent by the ground data processing center, satellite-ground time synchronization, inter-satellite time synchronization and time synchronization between ground stations are performed.

[0008] In a specific embodiment, the method further comprises:

[0009] The onboard receiver of the low-orbit satellite disciplines the small rubidium atomic clock.

[0010] In a specific embodiment, the taming includes:

[0011] The navigation receiver of the low-orbit satellite generates a 1PPS signal when tracking the BeiDou navigation satellite, and compares the signal with the 1PPS signal generated by the small rubidium atomic clock;

[0012] A control voltage for adjusting the frequency is generated according to the comparison result, so that the frequency accuracy output by the small rubidium atomic clock is consistent with the frequency of the second pulse signal of the Beidou navigation receiver.

[0013] In a specific embodiment, performing the time synchronization process between Beidou navigation satellites includes:

[0014] Calculating the time difference between the BeiDou navigation satellite and the low-orbit satellite based on the onboard observation data output by the onboard navigation receiver of the low-orbit satellite and the precise correction data and broadcast ephemeris data output by the ground data processing center;

[0015] Calculating the time difference between the Beidou navigation satellites based on the time difference between the Beidou navigation satellite and the low-orbit satellite;

[0016] Time synchronization processing is performed according to the time difference between the low-orbit satellites.

[0017] In a specific embodiment, the onboard observation data includes: pseudo-range and carrier phase between the onboard navigation receiver of the low-orbit satellite and the Beidou navigation satellite.

[0018] In a specific embodiment, the precise correction data includes precise ephemeris, precise clock error and real-time precise orbit determination of Beidou navigation satellites.

[0019] In a specific embodiment, the ground data processing centers exchange clock error data via a network;

[0020] The low-orbit satellites exchange clock error data via inter-satellite links;

[0021] The ground data processing center and the low-orbit satellite exchange clock error data via a satellite-to-ground link.

[0022] A second embodiment of the present invention provides a low-orbit satellite time synchronization system, comprising:

[0023] The onboard navigation receiver of the low-orbit satellite is used to receive and interpret the signals sent by the Beidou navigation satellite, and output the onboard observation data to the ground data processing center;

[0024] The ground data processing center is used to receive satellite observation data and IGS data, and calculate precise correction data to achieve satellite-ground time synchronization, inter-satellite time synchronization, and inter-ground station time synchronization.

[0025] The beneficial effects of the present invention are as follows:

[0026] The present invention proposes a low-orbit satellite time synchronization method and system, in which the onboard navigation receiver of the low-orbit satellite receives and solves the signals sent by the Beidou navigation satellite, and outputs the onboard observation data to transmit to the ground data processing center. The ground data processing center receives the onboard observation data and IGS data, calculates precise correction data, and performs corrections based on the correction data, thereby achieving satellite-to-ground time synchronization, inter-satellite time synchronization, and time synchronization between ground stations, with a synchronization accuracy of within 2ns. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A schematic flow chart showing a method for synchronizing low-orbit satellite time according to an embodiment of the present invention is shown;

[0029] Figure 2 A schematic diagram of satellite-ground time synchronization based on a real-time precise point positioning method according to an embodiment of the present invention is shown.

[0030] Figure 3 A principle block diagram of a GNSS real-time time transfer terminal according to an embodiment of the present invention is shown.

[0031] Figure 4 A functional block diagram of a taming system according to an embodiment of the present invention is shown.

[0032] Figure 5 A schematic diagram of a low-orbit satellite time synchronization system according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0033] To make the technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0034] like Figure 1 As shown, one embodiment of the present invention provides a low-orbit satellite time synchronization method, comprising:

[0035] The onboard navigation receiver of the low-orbit satellite receives and interprets the signals sent by the Beidou navigation satellite, and outputs the onboard observation data to the ground data processing center;

[0036] The satellite-borne navigation receiver captures, tracks, and resolves the signals at various frequencies of the Beidou navigation system, outputs satellite-borne observation data, and transmits it to the ground data processing center for processing via the satellite-to-ground data transmission link.

[0037] In an optional embodiment, the onboard observation data includes: pseudo-range and carrier phase between the onboard navigation receiver of the low-orbit satellite and the Beidou navigation satellite.

[0038] The ground data processing center receives satellite observation data and IGS (International GNSS Service, International GNSS (Global Navigation Satellite System) service) data and calculates precise correction data;

[0039] Using frequency observation data and real-time navigation ephemeris from ground-based data processing centers and satellite-based receivers, we achieve real-time precise orbit determination and clock estimation for BeiDou navigation satellites. Enhanced by onboard receiver observations, the combined orbit determination of the Earth-orbiting satellite constellation and BeiDou navigation satellites significantly improves the orbit accuracy of BeiDou navigation satellites.

[0040] The precise correction data includes precise ephemeris, precise clock error and real-time precise orbit determination of Beidou navigation satellites.

[0041] According to the precise correction data sent by the ground data processing center, satellite-ground time synchronization, inter-satellite time synchronization and time synchronization between ground stations are performed.

[0042] In a specific embodiment, performing the time synchronization process between Beidou navigation satellites includes:

[0043] Calculating the time difference between the BeiDou navigation satellite and the low-orbit satellite based on the onboard observation data output by the onboard navigation receiver of the low-orbit satellite and the precise correction data and broadcast ephemeris data output by the ground data processing center;

[0044] like Figure 2 As shown, taking the low-orbit satellites at points A and B as an example, the time differences between the Beidou navigation satellite and the low-orbit satellites at points A and B are:

[0045] ΔTa=Ta–T BDS

[0046] and

[0047] ΔTb=Tb-T BDS

[0048] Among them, Ta is the time of point A, Ta is the time of point B, T BDS The time is the Beidou satellite navigation system;

[0049] Then, the time difference between A and B between the low-orbit satellites can be obtained by subtracting the two results:

[0050] ΔTa-ΔTb=Ta-TBDS-(Tb-TBDS)=Ta-Tb

[0051] Time synchronization processing is performed according to the time difference between the low-orbit satellites.

[0052] It can be seen that in order to obtain the final time difference between stations A and B, it is necessary to know the test results of the two places at the same time, and to calculate the difference between the data of the two stations with the same epoch to obtain the real-time clock difference between the two stations.

[0053] In one embodiment, between ground monitoring stations, since each ground monitoring station needs to access the network to obtain real-time correction data, the network can also be used to transmit precise clock errors; between low-orbit satellites, real-time correction data and precise clock errors between two satellites can be transmitted through inter-satellite links; between satellites and the ground, precise clock errors are transmitted through satellite-to-ground links.

[0054] Real-time precise point positioning and time difference calculation for a single-station GNSS receiving terminal is based on real-time data processing and broadcasting by a ground-based data center. Therefore, for GNSS, the ground-based data processing center completes the generation and broadcasting of correction data, while the receiver only needs to address the data processing of local GNSS observations and the use of the broadcasted correction data.

[0055] Different from positioning, time transfer requires measuring the time difference between the local 1PPS signal and GNSS. Figure 3 This is a block diagram of the GNSS real-time time transfer terminal. The GNSS choke antenna effectively suppresses multipath noise and provides received satellite signals to the GNSS receiver module. The 10MHz local time frequency standard is provided to the GNSS receiver module via the frequency distribution amplifier unit as an external reference and a time base for the time interval measurement module. The time interval measurement module measures the time interval between the receiver's 1PPS output and the local 1PPS, compensating for the time difference in the PPP solution. The network communication module receives IGS real-time orbit and satellite clock correction data and exchanges clock differences between stations. The data processing unit decodes the real-time correction data, synchronizes the network real-time correction data with the broadcast ephemeris, and then compensates for it to complete the precise point positioning solution. All data processing is performed by software in the data processing module. During data processing, external input is required for various error correction parameters involved in the PPP solution.

[0056] In a specific embodiment, the method further comprises:

[0057] The onboard receiver of the low-orbit satellite disciplines the small rubidium atomic clock.

[0058] Specifically: a 1PPS signal generated by the navigation receiver of the low-orbit satellite when tracking the BeiDou navigation satellite is compared with the 1PPS signal generated by the small rubidium atomic clock;

[0059] A control voltage for adjusting the frequency is generated according to the comparison result, so that the frequency accuracy output by the small rubidium atomic clock is consistent with the frequency of the second pulse signal of the Beidou navigation receiver.

[0060] In this embodiment, if Figure 4 As shown, the onboard receiver of a low-orbit satellite can generate a precise 1PPS signal while tracking Beidou navigation satellites. This signal is then measured along with the 1PPS signal generated by a small rubidium atomic clock through frequency division. Through filtering and PID processing, a control voltage is generated to adjust the frequency, ensuring that the output frequency accuracy always tracks and locks to the Beidou navigation satellite's pulse-per-second signal, thereby improving the long-term accuracy of the small rubidium atomic clock's output frequency. Because the system continuously tracks and tames the satellite as long as the satellite remains locked, no metrological calibration is required.

[0061] The low-orbit satellite time synchronization method proposed in this embodiment mainly includes two aspects in terms of time base maintenance and system time synchronization: first, it has a good time and frequency base. The present invention is equipped with a miniaturized rubidium atomic clock with good short-term stability and supports GNSS second pulse training for frequency accuracy; second, time synchronization between satellites, between satellites and ground stations, and between ground stations is ensured through time synchronization and other means. Time synchronization between stations is the basis for time synchronization between satellites.

[0062] In terms of time reference, high-performance satellite-borne atomic clocks are not suitable for low-orbit satellites due to factors such as power consumption, size, weight, and cost. This patent proposes the use of miniaturized rubidium atomic clocks for time maintenance, providing a unified time and frequency reference signal for the entire satellite. To ensure high accuracy and time and frequency stability, it is necessary to calculate the low-orbit satellite clock error in real time or near real time, and use clock error training to maintain the low-orbit satellite time reference.

[0063] System time synchronization requires that the clocks of all components of the satellite navigation system have coordinated timing and rhythm. Currently, time synchronization for low-orbit navigation augmentation systems includes satellite-to-ground time synchronization, inter-satellite time synchronization, and time synchronization between ground stations. In this patent, both satellites and ground stations are time-synchronized via Beidou navigation satellites, and innovative real-time precise point positioning (PPP) is used for real-time time synchronization.

[0064] like Figure 5 As shown, another embodiment of the present invention provides a low-orbit satellite time synchronization system, comprising:

[0065] The onboard navigation receiver of the low-orbit satellite is used to receive and interpret the signals sent by the Beidou navigation satellite, and output the onboard observation data to the ground data processing center;

[0066] The ground data processing center is used to receive satellite observation data and IGS data, and calculate precise correction data to achieve satellite-ground time synchronization, inter-satellite time synchronization, and inter-ground station time synchronization.

[0067] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A low-orbit satellite time synchronization method, characterized in that: include: The onboard navigation receiver of the low-orbit satellite receives and interprets the signals sent by the Beidou navigation satellite, and outputs the onboard observation data to the ground data processing center; The ground data processing center receives satellite observation data and IGS data and calculates precise correction data; Perform satellite-ground time synchronization, inter-satellite time synchronization, and inter-ground station time synchronization according to the precise correction data sent by the ground data processing center; The method further comprises: The onboard receiver of the low-orbit satellite disciplines the small rubidium atomic clock; The taming includes: The navigation receiver of the low-orbit satellite generates a 1PPS signal when tracking the BeiDou navigation satellite, and compares the signal with the 1PPS signal generated by the small rubidium atomic clock; Generate a control voltage for adjusting the frequency according to the comparison result, so that the frequency accuracy output by the small rubidium atomic clock is consistent with the frequency of the second pulse signal of the Beidou navigation receiver; The low-orbit satellites exchange clock error data via inter-satellite links; The ground data processing center and the low-orbit satellite exchange clock error data via a satellite-to-ground link.

2. The method according to claim 1, characterized in that Performing the time synchronization process between Beidou navigation satellites includes: Calculating the time difference between the BeiDou navigation satellite and the low-orbit satellite based on the onboard observation data output by the onboard navigation receiver of the low-orbit satellite and the precise correction data and broadcast ephemeris data output by the ground data processing center; Calculating the time difference between the Beidou navigation satellites based on the time difference between the Beidou navigation satellite and the low-orbit satellite; Time synchronization processing is performed according to the time difference between the low-orbit satellites.

3. The method according to claim 1, characterized in that The onboard observation data includes: the pseudorange and carrier phase between the onboard navigation receiver of the low-orbit satellite and the Beidou navigation satellite.

4. The method according to claim 1, wherein The precise correction data includes precise ephemeris, precise clock error and real-time precise orbit determination of Beidou navigation satellites.

5. A low-orbit satellite time synchronization system using the low-orbit satellite time synchronization method according to any one of claims 1 to 4, characterized in that: include: The onboard navigation receiver of the low-orbit satellite is used to receive and interpret the signals sent by the Beidou navigation satellite, and output the onboard observation data to the ground data processing center; The ground data processing center is used to receive satellite observation data and IGS data, and calculate precise correction data to achieve satellite-ground time synchronization, inter-satellite time synchronization, and inter-ground station time synchronization.

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