Satellite-borne time-frequency transmission and synchronization method and system

Abstract

The invention provides a satellite-borne time-frequency transmission and synchronization method and system, and relates to the technical field of wireless communication. The method comprises the following steps: adjusting satellite clock frequencies of a plurality of satellites to be respectively phase-locked with a system clock frequency of a GNSS (Global Navigation Satellite System); the satellites comprise a master satellite and at least one slave satellite; the satellite clock frequency comprises a master satellite clock frequency and a slave satellite clock frequency; the system clock frequency, the master satellite clock frequency and the slave satellite clock frequency are frequencies of frequency signals generated by oscillators in time frequency modules of a GNSS system, a master satellite and a slave satellite respectively; all slave satellite clock frequencies are adjusted to be locked with the master satellite clock frequency in a phase mode, and satellite-borne time frequency transmission and synchronization are completed.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a satellite-borne time and frequency transmission and synchronization method and system. Background Art

[0002] Time synchronization and spatial synchronization are among the most critical issues facing distributed satellite systems, with time synchronization also serving as the foundation for spatial synchronization. Therefore, inter-satellite time synchronization is fundamental to the application of distributed satellite systems and critical to the effectiveness of system missions. With the continuous advancement of microsatellite technology, formation-flying small satellite constellations consisting of several or even dozens of small satellites have gained widespread attention and are playing an increasingly important role in communications, remote sensing, navigation, and electronic reconnaissance. Achieving inter-satellite relative ranging and establishing information exchange links are key to achieving coordinated control of formation-flying small satellite constellations and enhancing their autonomous survival and management capabilities. Inter-satellite time synchronization primarily involves the transmission and filtering of time reference information, as well as time comparison and adjustment. The specific application requirements for high-precision range measurement and time synchronization in small satellite SAR systems are: nanosecond-level time synchronization accuracy and 1cm relative range accuracy. Time synchronization accuracy directly impacts the performance of small satellite SAR collaboration. For example, low-precision time synchronization can reduce inter-satellite relative positioning accuracy and cause blur in the resulting composite image. Therefore, developing high-precision time synchronization solutions is a key technical issue that needs to be addressed.

[0003] In the prior art, such as the Chinese invention patent with publication number CN119922677A, publication 202410735568.1, it includes: receiving a modulated signal from a second wireless device, the modulated signal indicating information of a first PPS signal for time synchronization, and the first PPS signal is received by the second wireless device via a network protocol or GNSS receiver for time synchronization. The method also includes obtaining a second PPS signal by demodulating the received modulated signal. The method also includes determining the delay offset between the first PPS signal and the second PPS signal. In addition, the method also includes recovering the first PPS signal for time synchronization based on the second PPS signal and the delay offset. However, the above-mentioned comparative document does not disclose how to use the communication link established between satellites to detect the clock error of distributed aircraft in real time through high-precision clock error measurement technology, thereby improving the time-frequency transmission and synchronization capabilities of collaborative formation flight missions. Summary of the Invention

[0004] In order to solve the technical problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a satellite-borne time and frequency transmission and synchronization method and system, which utilizes the communication link built between satellites and uses high-precision clock error measurement technology to detect the clock errors of distributed aircraft in real time, thereby improving the time and frequency transmission and synchronization capabilities of collaborative formation flight missions.

[0005] To achieve the above-mentioned object, the present invention provides a satellite-borne time-frequency transfer and synchronization method, comprising:

[0006] S1. Adjust the satellite clock frequencies of multiple satellites to phase lock with the system clock frequency of the GNSS system respectively;

[0007] The satellites include a primary satellite and at least one secondary satellite;

[0008] The satellite clock frequency includes the master satellite clock frequency and the slave satellite clock frequency;

[0009] The system clock frequency, master satellite clock frequency and slave satellite clock frequency are the frequencies of the frequency signals generated by the oscillators in the time-frequency modules of the GNSS system, master satellite and slave satellite respectively;

[0010] S2. Adjust the clock frequencies of all slave satellites to phase-lock with the clock frequency of the master satellite, and complete the onboard time and frequency transfer and synchronization.

[0011] According to a technical solution of the present invention, the satellite clock frequencies of multiple satellites are adjusted to phase lock with the system clock frequency of the GNSS system. The specific process is as follows:

[0012] S11, obtaining a navigation signal;

[0013] S12. Calculate the clock difference and clock drift between the satellite and the GNSS system using the current satellite clock frequency, the TIC signal, and the navigation signal;

[0014] S13, performing a second-order Kalman filter process on the clock error and clock drift to obtain a phase difference, a corrected clock error, and a corrected clock drift;

[0015] S14. Calculating a frequency adjustment amount using the phase difference, the corrected clock error, and the corrected clock drift based on a frequency steering algorithm;

[0016] S15. Adjust the oscillator of the satellite's time-frequency module according to the frequency adjustment amount, output the adjusted frequency signal, and obtain the adjusted satellite clock frequency;

[0017] S17: Use the adjusted satellite clock frequency as the current satellite clock frequency, and repeat steps S11 to S16 until the current satellite clock frequency is phase-locked with the system clock frequency.

[0018] According to a technical solution of the present invention, the oscillator of the satellite is adjusted by the frequency adjustment amount, and the specific process is as follows:

[0019] Converting the frequency adjustment amount into a first adjustment voltage according to a preset first voltage control characteristic;

[0020] The first adjustment voltage is applied to an oscillator of the satellite.

[0021] According to a technical solution of the present invention, the clock frequencies of all slave satellites are adjusted to phase lock with the clock frequency of the master satellite. The specific process is as follows:

[0022] S21. The master satellite establishes a first ranging link from the master satellite to the slave satellite based on the master satellite clock frequency; the slave satellite establishes a second ranging link from the slave satellite to the master satellite based on the current slave satellite clock frequency;

[0023] S22. The master satellite measures a master satellite pseudorange observation value between the master satellite and the slave satellite through the first ranging link; and the slave satellite measures a slave satellite pseudorange observation value between the master satellite and the slave satellite through the second ranging link.

[0024] S23, comparing the master satellite pseudorange observation value with the slave satellite pseudorange observation value to calculate the clock error between the master satellite and the slave satellite;

[0025] S24, adjusting an oscillator in a time-frequency module of the slave satellite using the clock difference, so that the oscillator outputs an adjusted slave satellite clock frequency;

[0026] S26: Use the adjusted slave satellite clock frequency as the current slave satellite clock frequency, and repeat steps S21 to S25 until the current slave satellite clock frequency is phase-locked with the master satellite clock frequency.

[0027] According to a technical solution of the present invention, the oscillator of the time-frequency module of the slave satellite is adjusted by the clock error, and the specific steps are as follows:

[0028] Converting the clock difference into a second adjustment voltage according to a preset second voltage-controlled characteristic;

[0029] The second adjustment voltage is applied to the oscillator of the slave star.

[0030] The present invention provides a satellite-borne time-frequency transmission and synchronization system, comprising a plurality of time-frequency modules and a phase-locked module;

[0031] The multiple time-frequency modules include a time-frequency module in a master satellite and a time-frequency module in at least one slave satellite;

[0032] The master satellite's time-frequency module is used to phase-lock the master satellite's clock frequency with the GNSS system's system clock frequency by adjusting the frequency;

[0033] The slave satellite's time and frequency module is used to adjust the phase lock between the slave satellite's clock frequency and the GNSS system's system clock frequency;

[0034] Then, the slave satellite clock frequency is adjusted to phase-lock with the master satellite clock frequency to complete onboard time and frequency transmission and synchronization;

[0035] The system clock frequency, the master satellite clock frequency and the slave satellite clock frequency are the frequencies of the frequency signals generated by the oscillators in the time-frequency modules of the GNSS system, the master satellite and the slave satellite respectively.

[0036] According to a technical solution of the present invention, the time-frequency module includes:

[0037] An interface unit, used for obtaining navigation signals;

[0038] The baseband unit is configured to calculate the clock difference and clock drift between the satellite and the GNSS system using the current satellite clock frequency, the TIC signal, and the navigation signal;

[0039] A Kalman filter unit, configured to perform a second-order Kalman filter process on the clock error and clock drift to obtain a phase difference, a corrected clock error, and a corrected clock drift;

[0040] a frequency steering unit, configured to calculate a frequency adjustment amount using the phase difference, the corrected clock error, and the corrected clock drift based on a frequency steering algorithm;

[0041] an oscillator adjustment unit, configured to adjust the oscillator by the frequency adjustment amount;

[0042] an oscillator, configured to output an adjusted frequency signal to obtain an adjusted satellite clock frequency;

[0043] The adjusted satellite clock frequency is used as the current satellite clock frequency and input into the baseband unit.

[0044] According to a technical solution of the present invention, the oscillator adjustment unit includes a first digital-to-analog conversion unit;

[0045] a first digital-to-analog conversion unit, configured to convert the frequency adjustment amount into a first adjustment voltage according to a preset first voltage control characteristic;

[0046] And applying the first adjustment voltage to the oscillator of the satellite.

[0047] According to a technical solution of the present invention, it also includes:

[0048] The master satellite transmitting module is configured to establish a first ranging link from the master satellite to the slave satellite based on the master satellite clock frequency;

[0049] The slave satellite transmitting module is configured to establish a second ranging link from the slave satellite to the master satellite based on the current slave satellite clock frequency;

[0050] The master satellite receiving module is configured to measure and obtain a master satellite pseudorange observation value between the master satellite and the slave satellite through the first ranging link;

[0051] The slave satellite receiving module is configured to obtain a slave satellite pseudorange observation value between the master satellite and the slave satellite by measuring the slave satellite through the second ranging link;

[0052] The master satellite transmitting module is further used to send the master satellite pseudorange observation value to the slave satellite clock synchronization module;

[0053] A slave satellite clock synchronization module is used to compare the master satellite pseudorange observation value with the slave satellite pseudorange observation value to calculate the clock difference between the master satellite and the slave satellite;

[0054] And the oscillator in the time-frequency module of the slave satellite is adjusted by the clock difference, so that the oscillator outputs the adjusted slave satellite clock frequency.

[0055] According to a technical solution of the present invention, the slave clock synchronization module includes:

[0056] A clock error calculation unit is used to compare the pseudorange observation value of the master satellite with the pseudorange observation value of the slave satellite to calculate the clock error between the master satellite and the slave satellite;

[0057] A loop filter unit, configured to smooth the clock error;

[0058] A second digital-to-analog conversion unit, configured to convert the smoothed clock difference into a second adjustment voltage according to a preset second voltage control characteristic;

[0059] And applying the second adjustment voltage to the oscillator of the slave star.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1. A lightweight intersatellite link design method that integrates multiple functions such as intersatellite communication, ranging, and time synchronization is proposed. By utilizing the intersatellite communication link, the clock errors of distributed spacecraft are detected in real time through high-precision clock error measurement technology, forming a clock remote phase-locked synchronization loop. The clock is then adjusted on-orbit to achieve an intersatellite time synchronization accuracy of 5ns.

[0062] 2. It can provide distributed aircraft with an autonomous, real-time, continuous, high-precision communication and time service system that is independent of the outside world, thereby enhancing the system's rapid response capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0064] Figure 1 Schematically showing a structure of a time-frequency module in a satellite-borne time-frequency transmission and synchronization system according to an embodiment of the present invention;

[0065] Figure 2 Schematically showing the structure of an inter-satellite time and frequency synchronization module in a satellite-borne time and frequency transfer and synchronization system according to an embodiment of the present invention;

[0066] Figure 3 A schematic diagram illustrating the principles of GNSS training the satellite clocks of a master satellite and a slave satellite, and the master satellite training the slave satellite clock of the slave satellite, in a satellite-borne time and frequency transfer and synchronization method according to an embodiment of the present invention;

[0067] Figure 4 The diagram schematically shows a state transition diagram during a GNSS training process of satellite clocks of a master satellite and a slave satellite in a satellite-borne time and frequency transfer and synchronization method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0068] The description of the embodiments in this specification should be combined with the corresponding drawings, which should be considered a complete part of this specification. In the drawings, the shapes and thicknesses of the embodiments may be exaggerated and indicated for simplicity or convenience. Furthermore, the various structural components in the drawings will be described separately. It is worth noting that components not shown in the drawings or not described in words are known to those of ordinary skill in the art.

[0069] The description of the embodiments herein and any references to directions and orientations are for ease of description only and are not to be construed as limiting the scope of the present invention. The following description of the preferred embodiments may involve combinations of features, which may exist independently or in combination. The present invention is not specifically limited to the preferred embodiments. The scope of the present invention is defined by the claims.

[0070] like Figures 1 to 4 As shown, a satellite-borne time-frequency transfer and synchronization method of the present invention includes:

[0071] S1. Adjust the satellite clock frequencies of multiple satellites to phase lock with the system clock frequency of the GNSS system respectively;

[0072] Satellites include a primary satellite and at least one secondary satellite;

[0073] Satellite clock frequency includes master satellite clock frequency and slave satellite clock frequency;

[0074] The system clock frequency, master satellite clock frequency and slave satellite clock frequency are the frequencies of the frequency signals generated by the oscillators in the time-frequency modules of the GNSS system, master satellite and slave satellite respectively;

[0075] S2. Adjust the clock frequencies of all slave satellites to phase-lock with the clock frequency of the master satellite to complete onboard time and frequency transfer and synchronization.

[0076] In this embodiment, the GNSS system is a system used to calibrate and control the master and slave satellites in addition to the master and slave satellites, as follows:

[0077] Step S1 is the GNSS system's training process for the satellite clocks of the master and slave satellites, which can meet the GNSS system's absolute time synchronization, frequency accuracy, and long-term stability.

[0078] Step S2 is the process of taming the slave clock of the slave satellite by the master satellite, which can further meet the relative time synchronization between the satellites within the system.

[0079] In the first stage of this implementation, the master clock frequency of the master and slave satellites and the slave clock frequency of the slave satellite are phase-locked with the system clock frequency of the GNSS system respectively. Then, in the second stage, the slave clock frequency of the slave satellite is phase-locked with the master clock frequency of the master satellite to ensure high-precision synchronization between all relevant satellite clocks.

[0080] In the first phase, each satellite's clock is precisely aligned with global time, a step that significantly reduces errors caused by inherent frequency deviations, or drift, in the satellite clocks.

[0081] However, due to potential minor discrepancies caused by the different propagation paths from the GNSS system clock to each satellite, there is still a certain deviation between the slave satellite clock and the master satellite clock. Therefore, in the second phase, after ensuring that each satellite clock is synchronized with the GNSS system clock, the slave satellite clock frequency is phase-locked with the master satellite clock frequency to further reduce the relative clock deviation between satellites. This helps to eliminate potential minor discrepancies caused by the different propagation paths from the GNSS system clock to each satellite, thereby achieving higher-precision time synchronization.

[0082] In step S1, the satellite clock frequencies of the multiple satellites are adjusted to be phase-locked with the system clock frequency of the GNSS system. The specific process is as follows:

[0083] S11, obtaining a navigation signal;

[0084] S12. Calculate the clock difference and clock drift between the satellite and the GNSS system using the current satellite clock frequency, TIC signal, and navigation signal;

[0085] S13, performing second-order Kalman filtering on the clock error and clock drift to obtain a phase difference, a corrected clock error, and a corrected clock drift;

[0086] S14. Based on the frequency steering algorithm, a frequency adjustment amount is calculated using the phase difference, the corrected clock error, and the corrected clock drift;

[0087] S15. Adjust the oscillator of the satellite's time-frequency module by the frequency adjustment amount, output the adjusted frequency signal, and obtain the adjusted satellite clock frequency;

[0088] S17: Use the adjusted satellite clock frequency as the current satellite clock frequency, and repeat steps S11 to S16 until the current satellite clock frequency is phase-locked with the system clock frequency.

[0089] In this embodiment, if Figure 1 and Figure 3 As shown in FIG, specifically, the process of taming the local clock of the GNSS system, wherein the local clock refers to the satellite clock currently being synchronized.

[0090] (1) The satellite's time-frequency module provides a high-stability frequency source (frequency signal generated by an oscillator, 10.23 MHz) and a TIC signal (100 ms pulse);

[0091] (2) Receive navigation signals, use the local time and frequency source (i.e., the frequency signal generated by the time and frequency module, TIC signal, and 1PPS signal, etc.) as a reference, and use pseudorange and carrier phase measurement methods to calculate the clock difference and clock drift between the local and GNSS systems (accuracy controlled within 2ns);

[0092] (3) Sending clock error, clock drift and other information once per second for subsequent data processing;

[0093] (4) During the data processing process, the data is processed by a second-order Kalman filter to obtain a smooth phase difference, as well as an estimate of the current frequency difference and frequency drift (corrected value output by the second-order Kalman filter);

[0094] (5) The frequency steering algorithm calculates the frequency adjustment amount for the oscillator (high-voltage-controlled crystal oscillator) based on the phase difference, frequency difference, and frequency drift, and adjusts the oscillator based on the frequency adjustment amount. Ultimately, when the frequency signal (10.23MHz) output by the oscillator is phase-locked to the system clock frequency phase of the GNSS system, absolute time synchronization of 10ns can be achieved simultaneously.

[0095] (6) The oscillator outputs the (sinusoidal) frequency signal through frequency distribution amplification, square wave conversion, and clock generation modules, outputs pulse signals (1PPS and TIC signals), and provides a phase-locked 10.23MHz frequency source.

[0096] In step S15, the satellite's oscillator is adjusted by the frequency adjustment amount. The specific process is as follows:

[0097] Converting the frequency adjustment amount into a first adjustment voltage according to a preset first voltage control characteristic;

[0098] A first adjustment voltage is applied to an oscillator of the satellite.

[0099] In this embodiment, the above step (5) specifically calculates the frequency adjustment amount of the oscillator (high-voltage-controlled crystal oscillator) based on the phase difference, frequency difference and frequency drift through the frequency control algorithm, forms a first adjustment voltage after digital-to-analog conversion, and applies it to the oscillator.

[0100] The first voltage-controlled characteristic is the voltage-controlled characteristic of the satellite's oscillator. The frequency adjustment amount can be calculated through the oscillator's voltage-controlled characteristic to obtain the corresponding voltage increment, which is then added to the original control voltage of the oscillator to obtain the first adjustment voltage, which is applied to the satellite's oscillator.

[0101] In step S2, the clock frequencies of all slave satellites are adjusted to phase lock with the clock frequency of the master satellite. The specific process is as follows:

[0102] S21. The master satellite establishes a first ranging link from the master satellite to the slave satellite based on the master satellite clock frequency; the slave satellite establishes a second ranging link from the slave satellite to the master satellite based on the current slave satellite clock frequency;

[0103] S22. The master satellite measures a master satellite pseudorange observation value between the master satellite and the slave satellite through the first ranging link; the slave satellite measures a slave satellite pseudorange observation value between the master satellite and the slave satellite through the second ranging link;

[0104] S23, comparing the pseudorange observation value of the master satellite with the pseudorange observation value of the slave satellite, and calculating the clock difference between the master satellite and the slave satellite;

[0105] S24, adjusting the oscillator in the time-frequency module of the slave satellite by using the clock difference, so that the oscillator outputs the adjusted slave satellite clock frequency;

[0106] S26: Use the adjusted slave satellite clock frequency as the current slave satellite clock frequency, and repeat steps S21 to S25 until the current slave satellite clock frequency is phase-locked with the master satellite clock frequency.

[0107] In this embodiment, if Figure 2 and Figure 3 As shown, specifically, the master star tames the slave star's clock during the master star's taming process:

[0108] (1) Based on the master and slave satellite clocks being tamed by the GNSS system, when the master and slave satellites receive the inter-satellite time synchronization instruction (state switching instruction, switching from the state of the master and slave satellite clocks being tamed by the GNSS system to the state of the master satellite taming the slave satellite clock), the master satellite remains in the state of being tamed by the GNSS system, and the slave satellite is released from the state of being tamed by the GNSS system;

[0109] (2) The master satellite and the slave satellite respectively start the inter-satellite link transceiver channel based on the local time and frequency source, and use frequency division duplex (FDD) and code division multiple access (CDMA) to establish two bidirectional inter-satellite communication ranging links (the first ranging link and the second ranging link) between the master satellite and the slave satellite;

[0110] (3) The master satellite and the slave satellite each perform pseudo-range measurements and obtain ranging results that eliminate various errors introduced by free-space signal transmission;

[0111] (4) The pseudo-range observation value of the master satellite is transmitted to the slave satellite through the transmission of telegrams;

[0112] (5) After data demodulation, the slave satellite obtains the pseudo-range observation value of the master satellite, which is then compared with the previously cached pseudo-range observation value of the slave satellite to obtain the clock error between the master and slave satellites at that time;

[0113] (6) The oscillator of the time-frequency module of the slave satellite is continuously corrected through clock error so that it is synchronized with the output frequency of the oscillator of the master satellite and eventually reaches a stable state.

[0114] The above process uses inter-satellite two-way asynchronous transmission spread spectrum ranging, that is, two-way ranging technology to eliminate the influence of channel propagation delay on pseudo-range measurement, and improve the accuracy of pseudo-range measurement and clock error solution; through the integration of measurement, control and data transmission integrated channel technology, ranging, telemetry / remote control, data transmission and other functions are realized simultaneously on one channel

[0115] In step S24, the oscillator of the time-frequency module of the slave satellite is adjusted by the clock error. The specific steps are as follows:

[0116] Converting the clock difference into a second adjustment voltage according to a preset second voltage-controlled characteristic;

[0117] A second adjustment voltage is applied to the oscillator of the slave star.

[0118] In this embodiment, the above step (6) is specifically as follows:

[0119] The slave satellite outputs the smoothed clock error after filtering, and converts the clock error value into a voltage analog quantity through digital-to-analog conversion. The output control voltage (second adjustment voltage) continuously corrects the oscillation frequency of the slave satellite's oscillator so that it is synchronized with the output frequency of the master satellite's oscillator (master satellite clock frequency), and finally reaches a stable state, meeting the inter-satellite time synchronization accuracy of 5ns.

[0120] Among them, it is necessary to first convert the clock difference into a frequency difference, and then convert the frequency difference into a corresponding voltage increment through the second voltage-controlled characteristic (the voltage-controlled characteristic of the oscillator of the slave star). The voltage increment is added to the original control power supply to obtain a new control voltage, that is, the second adjustment voltage.

[0121] A satellite-borne time-frequency transmission and synchronization system includes multiple time-frequency modules and phase-locked modules;

[0122] The multiple time-frequency modules include a time-frequency module in a master satellite and a time-frequency module in at least one slave satellite;

[0123] The master satellite's time-frequency module is used to phase-lock the master satellite's clock frequency with the GNSS system's system clock frequency by adjusting the frequency;

[0124] The slave satellite's time and frequency module is used to adjust the phase lock between the slave satellite's clock frequency and the GNSS system's system clock frequency;

[0125] Then, the slave satellite clock frequency is adjusted to phase-lock with the master satellite clock frequency to complete onboard time and frequency transmission and synchronization;

[0126] The system clock frequency, the master satellite clock frequency and the slave satellite clock frequency are the frequencies of the frequency signals generated by the oscillators in the time-frequency modules of the GNSS system, the master satellite and the slave satellite respectively.

[0127] like Figure 1 As shown, the time-frequency module includes:

[0128] An interface unit, used for obtaining navigation signals;

[0129] The baseband unit is used to calculate the clock difference and drift between the satellite and the GNSS system using the current satellite clock frequency, TIC signal, and navigation signal.

[0130] A Kalman filter unit is used to perform second-order Kalman filtering on the clock error and clock drift to obtain the phase difference, the corrected clock error and the corrected clock drift;

[0131] A frequency steering unit is configured to calculate a frequency adjustment amount based on a frequency steering algorithm by using the phase difference, the corrected clock error, and the corrected clock drift;

[0132] an oscillator adjustment unit, configured to adjust the oscillator by a frequency adjustment amount;

[0133] an oscillator, configured to output an adjusted frequency signal to obtain an adjusted satellite clock frequency;

[0134] The adjusted satellite clock frequency is used as the current satellite clock frequency and input into the baseband unit.

[0135] In this implementation, the baseband unit is a minimal SOC system. By selecting a new software-defined radio architecture combining a baseband SOC and a radio frequency transceiver, the system's scalability is further enhanced. Compared to existing FPGA+CPU hardware architectures, this significantly reduces space and power consumption, further enhancing the system's sophistication.

[0136] In GNSS system discipline mode, the interface unit receives clock error and drift data from the orbit determination software in the navigation SOC chip's main core. Based on the data optimization results (accuracy-based), it uses the clock error and drift information output by the baseband unit as input data and passes it to the clock discipline FPGA. The Kalman filter unit filters and the frequency steering algorithm in the frequency steering unit calculates the frequency adjustment for the satellite's 10.23MHz oscillator (voltage-controlled ovenized crystal oscillator).

[0137] like Figure 4 As shown in Figure 1, the frequency steering process between the GNSS system and the master / slave satellite can be described by several different states. When a given condition is met, the system switches from one state to the next.

[0138] (1) When the satellite-borne time-frequency transmission and synchronization system is started, the time-frequency module is reset and enters the "oscillator preheating" state. In this state, a fixed voltage is applied to the oscillator to put the oscillator in the preheating state. After a period of time, the output frequency of the oscillator reaches a stable state. The basis for judging whether its preheating is completed is whether its frequency deviation is less than 2e -8 As the 10.23MHz and 1PPS signals from the time-frequency module stabilize, the synchronization module begins acquiring the GNSS system's frequency signal. Upon successful acquisition, it enters the tracking state until it outputs the time comparison results. Once the time difference measurement results from the equal time difference comparison module stabilize (without significant fluctuations), the onboard time-frequency transmission and synchronization system enters the "pre-synchronization" state.

[0139] (2) When entering the "pre-synchronization" state, there is a relatively large time difference between the master / slave satellite oscillators and the GNSS system time. Although the phase-locked loop algorithm used can lock within a large phase and frequency difference range, when the initial time difference is too large, it takes too long to directly use the phase-locking algorithm until it locks. Therefore, pre-synchronization of the time difference is required.

[0140] Presynchronization involves applying a coarse phase shift algorithm to the 1PPS signal, shifting its phase relative to the 10.23MHz signal. This coarse phase shift adjusts the phase of the 1PPS signal after it is divided down from the 10.23MHz signal. Therefore, coarse phase shifting can reduce the time difference to within ±50ns, significantly reducing the required lock time. Before presynchronization, the current time difference must be determined. If the current time difference is less than 300ns, presynchronization is not required, as the phase lock algorithm will already lock quickly. Presynchronization is only performed when the time difference exceeds 300ns.

[0141] (3) In the “phase-locked tracking” mode, the satellite-borne time-frequency transmission and synchronization system continuously adjusts the voltage of the voltage-controlled oscillator according to the current phase difference and frequency difference, and fine-tunes the frequency of the 10.23M frequency signal, thereby changing the phase of the 1PPS signal and achieving phase tracking of the system clock (atomic clock) of the remote GNSS system.

[0142] In this state, both the phase and frequency differences are controlled within specified limits, and the system achieves a locked state. During the continuous tracking process, the second-order Kalman filter detects gross errors or outliers that occur during the measurement process. Once measurement data is identified as an outlier, it is discarded and does not enter the frequency steering algorithm, thereby preventing it from affecting the oscillator output frequency. However, if an abnormal situation occurs, such as a significant jump in the phase or frequency difference, or if measurement data is interrupted, the onboard time and frequency transmission and synchronization system will enter a "hold" state.

[0143] (4) In the "hold" state, the system operates in an open loop and keeps the oscillator output frequency as stable as possible. The system no longer adjusts the oscillator frequency based on the time comparison results, but maintains the state before entering the "hold" state, and corrects the oscillator output frequency based on the parameters (such as frequency drift) of the local oscillator relative to the navigation system time calibrated during normal operation, so that it can maintain phase consistency with the remote atomic clock for as long as possible in the open loop state. When the time comparison data returns to normal and the phase difference and frequency difference reach a stable state, the system enters the "pre-synchronization" state again, estimates the current phase difference and frequency difference, and restarts a new round of tracking.

[0144] The oscillator adjustment unit includes a first digital-to-analog conversion unit;

[0145] A first digital-to-analog conversion unit, configured to convert the frequency adjustment amount into a first adjustment voltage according to a preset first voltage control characteristic;

[0146] And applying a first adjustment voltage to an oscillator of the satellite.

[0147] In this embodiment, the frequency adjustment amount is converted into a voltage increment based on a preset first voltage-controlled characteristic, and finally converted into a 20-bit integer, which is input into the first digital-to-analog conversion unit DAC. After digital-to-analog conversion, the analog voltage obtained is applied to the voltage-controlled end of the 10.23MHz oscillator to adjust the frequency of the oscillator, suppress the influence of environmental disturbances on the time difference between the local clock and the remote clock, and control the time difference within the indicator range.

[0148] like Figure 2 As shown, the satellite-borne time-frequency transmission and synchronization system also includes:

[0149] The master satellite transmitting module is used to establish the first ranging link from the master satellite to the slave satellite based on the master satellite clock frequency;

[0150] A slave satellite transmitting module is used to establish a second ranging link from the slave satellite to the master satellite based on the current slave satellite clock frequency;

[0151] A master satellite receiving module is used to measure and obtain a master satellite pseudo-range observation value between the master satellite and the slave satellite through a first ranging link;

[0152] The slave satellite receiving module is used to measure the slave satellite pseudo-range observation value between the master satellite and the slave satellite through the second ranging link;

[0153] The master satellite transmitting module is also used to send the master satellite pseudorange observation value to the slave satellite clock synchronization module;

[0154] The slave satellite clock synchronization module is used to compare the master satellite pseudorange observation value with the slave satellite pseudorange observation value to calculate the clock difference between the master and slave satellites;

[0155] And the oscillator in the time-frequency module of the slave satellite is adjusted by the clock difference, so that the oscillator outputs the adjusted slave satellite clock frequency.

[0156] In this implementation, the master and slave satellites communicate bidirectionally through free space. Each satellite contains a transmitter module and a receiver module, responsible for signal transmission and reception, respectively. An oscillator (voltage-controlled crystal, VCXO) provides a local time and frequency source.

[0157] Among them, the transmitting module on the master satellite side and the transmitting module on the slave satellite side are both baseband units in their respective time-frequency modules;

[0158] The launch module on the main satellite side is used to:

[0159] Perform telegram modulation and pseudo-code modulation, load the data information to be sent and the pseudo-random code sequence onto the carrier to form a modulated signal.

[0160] Carrier modulation is performed and the modulated signal is loaded onto the RF carrier for transmission.

[0161] The primary satellite's oscillator generates a 1pps signal as a time reference to ensure time synchronization during the modulation process. It also generates a TIC (Time Interval Counter) signal to measure signal transmission time and thus calculate pseudorange.

[0162] The receiving module on the main satellite side is used for:

[0163] Capture and track, perform preliminary identification and continuous tracking of received signals to maintain synchronization.

[0164] The pseudo-range observation value between the master satellite and the slave satellite is calculated by using pseudo-code ranging and smooth ranging technology combined with TIC signal transmission time.

[0165] Perform data demodulation to extract the original data information from the received signal.

[0166] The receiving module on the slave side is used for:

[0167] Capture and tracking, similar to the main satellite, identify and track the signals from the main satellite.

[0168] Ranging and data demodulation, distance measurement and data recovery are performed in the same way as the primary satellite.

[0169] Pseudo-code ranging and smooth ranging are used to calculate the pseudo-range observation value of the slave satellite between the master satellite and the slave satellite, and improve the ranging accuracy.

[0170] Clock error solution, based on the ranging results and timestamp information, calculates the clock error between the master satellite and the slave satellite.

[0171] The clock synchronization loop module includes:

[0172] Loop filtering: Filter the clock error solution results to remove noise interference.

[0173] DA conversion: Converts the filtered digital signal into an analog signal for adjusting the frequency of the oscillator.

[0174] The slave satellite's oscillator changes its output frequency according to the adjusted control voltage to achieve synchronization with the master satellite's clock.

[0175] The transmitter module on the satellite side is used to:

[0176] Perform telegram modulation and pseudo code modulation to generate the modulated signal sent from the satellite to the master satellite.

[0177] Carrier modulation: The modulated signal is loaded onto the RF carrier.

[0178] The 1pps signal generated from the satellite's oscillator provides a time reference to ensure time synchronization during the modulation process. It also generates a TIC signal to measure signal transmission time and calculate pseudorange.

[0179] The slave clock synchronization module includes:

[0180] The clock error calculation unit is used to compare the pseudo-range observation value of the master satellite with the pseudo-range observation value of the slave satellite to calculate the clock error between the master satellite and the slave satellite;

[0181] Loop filter unit, used to smooth the clock error;

[0182] A second digital-to-analog conversion unit, configured to convert the smoothed clock difference into a second adjustment voltage according to a preset second voltage control characteristic;

[0183] and applying a second adjustment voltage to the oscillator of the slave star.

[0184] The present invention provides a satellite-borne time-frequency transfer and synchronization method and system, the method comprising: adjusting the satellite clock frequencies of multiple satellites to phase-lock with the system clock frequency of a GNSS system; the satellites comprising a master satellite and at least one slave satellite; the satellite clock frequencies comprising a master satellite clock frequency and a slave satellite clock frequency; the system clock frequency, the master satellite clock frequency and the slave satellite clock frequency are respectively the frequencies of frequency signals generated by oscillators in time-frequency modules of the GNSS system, the master satellite and the slave satellite; adjusting the clock frequencies of all slave satellites to phase-lock with the master satellite clock frequency, thereby completing satellite-borne time-frequency transfer and synchronization.

[0185] Furthermore, it should be noted that the present invention may be provided as a method, apparatus, or computer program product. Thus, embodiments of the present invention may take the form of entirely hardware embodiments, entirely software embodiments, or embodiments combining software and hardware aspects. Furthermore, embodiments of the present invention may take the form of a computer program product embodied on one or more computer-usable storage media containing computer-usable program code.

[0186] The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of the methods, terminal devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, an embedded processor, or other programmable data processing terminal device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the process in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0187] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing terminal device to operate in a specific manner, so that the instructions stored in the computer readable memory produce a manufactured product including an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device, so that a series of operation steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing instructions for implementing the process in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0188] It should also be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or terminal device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or terminal device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or terminal device comprising the element.

[0189] Finally, it should be noted that the above is a preferred embodiment of the present invention. It should be noted that although the preferred embodiment of the present invention has been described, it is clear that those skilled in the art, once they understand the basic inventive concept of the present invention, can make various improvements and modifications without departing from the principles of the present invention. Such improvements and modifications should also be considered as within the scope of protection of the present invention. Therefore, the appended claims are intended to be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the embodiments of the present invention.

Claims

1. A satellite-borne time-frequency transfer and synchronization method, characterized in that: include: S1. Adjust the satellite clock frequencies of multiple satellites to phase lock with the system clock frequency of the GNSS system respectively; The satellites include a primary satellite and at least one secondary satellite; The satellite clock frequency includes the master satellite clock frequency and the slave satellite clock frequency; The system clock frequency, master satellite clock frequency and slave satellite clock frequency are the frequencies of the frequency signals generated by the oscillators in the time-frequency modules of the GNSS system, master satellite and slave satellite respectively; S2. Adjust the clock frequencies of all slave satellites to phase-lock with the clock frequency of the master satellite, and complete the onboard time and frequency transfer and synchronization.

2. The satellite-borne time-frequency transfer and synchronization method according to claim 1, characterized in that: Adjust the satellite clock frequencies of multiple satellites to phase lock with the system clock frequency of the GNSS system. The specific process is as follows: S11, obtaining a navigation signal; S12. Calculate the clock difference and clock drift between the satellite and the GNSS system using the current satellite clock frequency, the TIC signal, and the navigation signal; S13, performing a second-order Kalman filter process on the clock error and clock drift to obtain a phase difference, a corrected clock error, and a corrected clock drift; S14. Calculating a frequency adjustment amount using the phase difference, the corrected clock error, and the corrected clock drift based on a frequency steering algorithm; S15. Adjust the oscillator of the satellite's time-frequency module according to the frequency adjustment amount, output the adjusted frequency signal, and obtain the adjusted satellite clock frequency; S17: Use the adjusted satellite clock frequency as the current satellite clock frequency, and repeat steps S11 to S16 until the current satellite clock frequency is phase-locked with the system clock frequency.

3. The satellite-borne time-frequency transfer and synchronization method according to claim 2, characterized in that: The satellite's oscillator is adjusted by the frequency adjustment amount. The specific process is as follows: Converting the frequency adjustment amount into a first adjustment voltage according to a preset first voltage control characteristic; The first adjustment voltage is applied to an oscillator of the satellite.

4. The satellite-borne time-frequency transfer and synchronization method according to claim 2 or 3, characterized in that: Adjust the clock frequencies of all slave satellites to phase lock with the clock frequency of the master satellite. The specific process is as follows: S21. The master satellite establishes a first ranging link from the master satellite to the slave satellite based on the master satellite clock frequency; the slave satellite establishes a second ranging link from the slave satellite to the master satellite based on the current slave satellite clock frequency; S22. The master satellite measures, through the first ranging link, a master satellite pseudorange observation value between the master satellite and the slave satellite; The slave satellite measures and obtains a slave satellite pseudorange observation value between the master satellite and the slave satellite through the second ranging link; S23, comparing the master satellite pseudorange observation value with the slave satellite pseudorange observation value to calculate the clock error between the master satellite and the slave satellite; S24, adjusting an oscillator in a time-frequency module of the slave satellite using the clock difference, so that the oscillator outputs an adjusted slave satellite clock frequency; S26: Use the adjusted slave satellite clock frequency as the current slave satellite clock frequency, and repeat steps S21 to S25 until the current slave satellite clock frequency is phase-locked with the master satellite clock frequency.

5. The satellite-borne time-frequency transfer and synchronization method according to claim 4, characterized in that: The oscillator of the time-frequency module of the slave satellite is adjusted by the clock error. The specific steps are as follows: Converting the clock difference into a second adjustment voltage according to a preset second voltage-controlled characteristic; The second adjustment voltage is applied to the oscillator of the slave star.

6. A satellite-borne time-frequency transfer and synchronization system, characterized in that: Includes multiple time-frequency modules and phase-locked modules; The multiple time-frequency modules include a time-frequency module in a master satellite and a time-frequency module in at least one slave satellite; The master satellite's time-frequency module is used to phase-lock the master satellite's clock frequency with the GNSS system's system clock frequency by adjusting the frequency; The slave satellite's time and frequency module is used to adjust the phase lock between the slave satellite's clock frequency and the GNSS system's system clock frequency; Then, the slave satellite clock frequency is adjusted to phase-lock with the master satellite clock frequency to complete onboard time and frequency transmission and synchronization; The system clock frequency, the master satellite clock frequency and the slave satellite clock frequency are the frequencies of the frequency signals generated by the oscillators in the time-frequency modules of the GNSS system, the master satellite and the slave satellite respectively.

7. The satellite-borne time-frequency transmission and synchronization system according to claim 6, characterized in that: The time-frequency module includes: An interface unit, used for obtaining a navigation signal; The baseband unit is configured to calculate the clock difference and clock drift between the satellite and the GNSS system using the current satellite clock frequency, the TIC signal, and the navigation signal; A Kalman filter unit, configured to perform a second-order Kalman filter process on the clock error and clock drift to obtain a phase difference, a corrected clock error, and a corrected clock drift; a frequency steering unit, configured to calculate a frequency adjustment amount using the phase difference, the corrected clock error, and the corrected clock drift based on a frequency steering algorithm; an oscillator adjustment unit, configured to adjust the oscillator by the frequency adjustment amount; an oscillator, configured to output an adjusted frequency signal to obtain an adjusted satellite clock frequency; The adjusted satellite clock frequency is used as the current satellite clock frequency and input into the baseband unit.

8. The satellite-borne time-frequency transmission and synchronization system according to claim 7, characterized in that: The oscillator adjustment unit includes a first digital-to-analog conversion unit; a first digital-to-analog conversion unit, configured to convert the frequency adjustment amount into a first adjustment voltage according to a preset first voltage control characteristic; And applying the first adjustment voltage to the oscillator of the satellite.

9. The satellite-borne time-frequency transmission and synchronization system according to claim 7 or 8, characterized in that: Also includes: The master satellite transmitting module is configured to establish a first ranging link from the master satellite to the slave satellite based on the master satellite clock frequency; The slave satellite transmitting module is configured to establish a second ranging link from the slave satellite to the master satellite based on the current slave satellite clock frequency; The master satellite receiving module is configured to measure and obtain a master satellite pseudorange observation value between the master satellite and the slave satellite through the first ranging link; The slave satellite receiving module is configured to obtain a slave satellite pseudorange observation value between the master satellite and the slave satellite by measuring the slave satellite through the second ranging link; The master satellite transmitting module is further used to send the master satellite pseudorange observation value to the slave satellite clock synchronization module; A slave satellite clock synchronization module is used to compare the master satellite pseudorange observation value with the slave satellite pseudorange observation value to calculate the clock difference between the master satellite and the slave satellite; And the oscillator in the time-frequency module of the slave satellite is adjusted by the clock difference, so that the oscillator outputs the adjusted slave satellite clock frequency.

10. The satellite-borne time-frequency transmission and synchronization system according to claim 9, characterized in that: The slave clock synchronization module includes: A clock error calculation unit is used to compare the pseudorange observation value of the master satellite with the pseudorange observation value of the slave satellite to calculate the clock error between the master satellite and the slave satellite; A loop filter unit, configured to smooth the clock error; A second digital-to-analog conversion unit, configured to convert the smoothed clock difference into a second adjustment voltage according to a preset second voltage control characteristic; And applying the second adjustment voltage to the oscillator of the slave star.

Images