High-precision clock transfer control method based on ground station calibration

Abstract

The application provides a high-precision clock transmission control method based on ground station calibration, and relates to the technical field of time-frequency synchronization, and the method comprises the following steps: controlling a satellite and at least one ground station to simultaneously and mutually send distance measurement signals according to a preset time sequence, so as to construct a star-ground bidirectional symmetric transmission link and obtain original bidirectional pseudo-range measurement values containing uplink pseudo-range and downlink pseudo-range; based on the original bidirectional pseudo-range measurement values, controlling the ground station to perform a dynamic calibration process of local closed-loop calibration and multi-station mutual comparison, so as to obtain real-time device time delay calibration parameters; and dynamically compensating the time delay drift of the transmitting and receiving devices of the ground station through the real-time device time delay calibration parameters, so as to obtain bidirectional pseudo-range data compensated by the device time delay. The application realizes sub-nanosecond clock synchronization precision.

Description

Technical Field

[0001] This invention relates to the field of time and frequency synchronization technology, and in particular to a high-precision clock transmission control method based on ground station calibration. Background Technology

[0002] High-precision time transfer is a core foundational technology in fields such as satellite navigation, deep space communication, and scientific experiments. Existing mainstream technologies have the following limitations: satellite one-way time transmission (such as the GNSS common-view method) relies on ionospheric model correction, and residual errors result in an accuracy of only 1 to 10 nanoseconds, which is also susceptible to orbital errors. Although fiber optic transmission achieves picosecond-level stability, it requires a pre-set fixed link and cannot support dynamic targets. Satellite-to-ground laser transmission has high theoretical accuracy, but it is limited by atmospheric turbulence and weather, making it impractical. Although traditional two-way time and frequency transmission can eliminate common errors through path symmetry, it does not solve asymmetric errors such as equipment delay drift and motion delay, making it difficult to achieve a stable accuracy better than 1 nanosecond in practice.

[0003] International Atomic Time (TAI) is generated by a weighted average of global laboratory clocks, and its algorithm is insufficient for suppressing short-term noise. The Kalman filtering algorithm suffers from estimation error divergence, which affects the long-term stability of the time base. Therefore, a new transfer technology is needed that takes into account dynamic adaptability, multi-error suppression capability, and autonomous time maintenance accuracy. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a high-precision clock transmission control method based on ground station calibration, so as to achieve sub-nanosecond clock synchronization accuracy.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] Firstly, a high-precision clock transmission control method based on ground station calibration, the method comprising:

[0007] Step S1: Control the satellite and at least one ground station to simultaneously transmit ranging signals to each other according to a preset time sequence, so as to establish a two-way symmetrical transmission link between the satellite and the ground, and obtain the original two-way pseudorange measurement values ​​including uplink pseudorange and downlink pseudorange.

[0008] Step S2: Based on the original two-way pseudorange measurement values, control the ground station to perform a dynamic calibration process of local closed-loop calibration and multi-station comparison to obtain real-time equipment delay calibration parameters; use the real-time equipment delay calibration parameters to dynamically compensate for the delay drift of the ground station's transceiver equipment to obtain two-way pseudorange data after equipment delay compensation.

[0009] Step S3: Based on the two-way pseudorange data after equipment delay compensation, control the integrated error corrector to apply joint correction of multi-source space propagation errors, including ionospheric delay, tropospheric delay, Sagnac effect, antenna phase center offset and relativistic effect, so as to obtain two-way pseudorange data after space error correction.

[0010] Step S4: Based on the bidirectional pseudorange data corrected for spatial errors, and by performing a difference calculation through the path symmetry of the uplink pseudorange and downlink pseudorange, the clock difference calculation unit is controlled to calculate the high-precision clock difference sequence between the satellite clock and the ground station clock.

[0011] Step S5: Based on the high-precision clock difference sequence, the time scale generation unit executes a two-stage time scale generation process that includes overlapping Hadamard variance stability assessment and Kalman-weighted average fusion algorithm to generate and maintain a high-precision autonomous time base, and finally obtain a stable UTC time scale.

[0012] Furthermore, the dynamic calibration process of local closed-loop calibration and multi-station cross-comparison in step S2 includes:

[0013] Step S2.1: Control the internal signal generator of the ground station to periodically generate a self-test signal, and pass the self-test signal through its transmitting channel, coupler and receiving channel in sequence to form a local closed loop. By measuring the total time delay change of the closed loop, the baseband time delay jitter of the transmitting channel and the receiving channel and the time delay drift of the radio frequency device caused by temperature change are calculated in real time.

[0014] Step S2.2: Control at least three ground stations to send standard time comparison signals to each other via optical fiber or microwave link, obtain the original time difference measurement value between each station, and process the original time difference measurement value based on the least squares algorithm to separate the inherent equipment delay of each station and the signal transmission delay between stations, and generate the equipment delay difference calibration parameter between stations.

[0015] Step S2.3: The time delay drift amount and the inter-station equipment time delay difference calibration parameters are fused together to obtain the real-time equipment time delay calibration parameters output at a preset update cycle.

[0016] Furthermore, the dynamic calibration process in step S2 also includes a motion delay compensation step:

[0017] Step S2.4: During the time window for signal interaction between the satellite and the ground station, the displacement caused by the ground station's movement with the Earth's rotation is calculated in real time based on the satellite's precise orbit prediction data and the ground station's precise coordinates.

[0018] Step S2.5: Based on the displacement and signal propagation direction, dynamically calculate and compensate for the change in signal propagation time caused by the motion of the receiver. The compensation amount and the real-time equipment delay calibration parameters are applied together to compensate for the original bidirectional pseudorange measurement value.

[0019] Furthermore, the joint correction of multi-source spatial propagation error applied in step S3 includes:

[0020] Step S3.1: For the two-way pseudorange data after equipment delay compensation, perform ionospheric delay correction and tropospheric delay correction respectively; wherein, the ionospheric delay correction is performed using the ionospheric total electron content mapping function based on dual-frequency observation and the Klobuchar enhancement model, and the tropospheric delay correction is performed using the Saastamoinen model based on meteorological parameter input, to obtain two-way pseudorange data after ionospheric and tropospheric correction;

[0021] Step S3.2: Sagnac effect compensation is performed on the two-way pseudorange data that has been corrected by the ionosphere and troposphere. The compensation is achieved by converting the ground station position from the geocentric geofixed coordinate system to the geocentric inertial coordinate system in real time and calculating the geometric path difference of signal propagation based on the coordinate rotation angle, so as to obtain the two-way pseudorange data after Sagnac effect compensation.

[0022] Step S3.3: Further apply antenna phase center offset compensation and relativistic effect compensation to the two-way pseudorange data after Sagnac effect compensation; wherein, antenna phase center offset compensation is achieved by projecting the deviation vector of the antenna phase center in the satellite or ground station centroid coordinate system to the star-ground line of sight direction, and relativistic effect compensation includes the correction of the periodic clock error term caused by the satellite orbit eccentricity.

[0023] Step S3.4: Output the bidirectional pseudorange data after spatial error correction, which has been processed step by step through all the correction steps from S3.1 to S3.3.

[0024] Furthermore, step S4 specifically includes:

[0025] Step S4.1: The uplink pseudorange observations and downlink pseudorange observations in the two-way pseudorange data after spatial error correction are subtracted. By utilizing the path symmetry of the satellite-to-ground two-way link, the common effects of orbital error, tropospheric delay, and some ionospheric error are eliminated to obtain preliminary clock error data.

[0026] Step S4.2 introduces residual asymmetric error compensation processing into the preliminary clock difference data. The residual asymmetric error includes at least the equipment delay asymmetry remaining after dynamic calibration in step S2 and the spatial propagation error residual remaining after joint correction in step S3, so as to obtain refined clock difference data.

[0027] Step S4.3: Based on the refined clock difference data, a high-precision clock difference sequence is calculated in real time using the clock difference solution model.

[0028] Furthermore, the two-level timescale generation process in step S5 includes:

[0029] Step S5.1: After preprocessing the input high-precision clock difference sequence, the overlapping Hadamard variance algorithm is used to calculate the clock frequency stability within a specified smoothing time. Based on the frequency stability evaluation results, the clock difference sequence is filtered and optimized to obtain short-term stable clock difference data.

[0030] Step S5.2: Input the short-term stabilized clock bias data into the algorithm module that integrates Kalman filtering and weighted averaging for processing; wherein, Kalman filtering is used to make the optimal estimate of the clock bias state and suppress short-term noise, and the weighted averaging algorithm dynamically allocates the weights of each time period based on the evaluated clock stability to suppress the divergence of the long-term state estimate.

[0031] In step S5.3, the control algorithm module outputs a long-term stable and autonomously maintained UTC time scale, and feeds back the stability information of the output time scale to step S5.2, which is used to dynamically adjust the weighted average weight to form a closed-loop control.

[0032] Furthermore, the method also includes enhancement steps for specific application scenarios:

[0033] When deploying ground stations in densely populated urban areas with complex electromagnetic environments, the phased array antenna installed at the ground station is controlled to dynamically adjust the receiving beam direction to suppress multipath effects, and a space-time joint filtering algorithm is run synchronously. The space-time joint filtering algorithm uses adaptive filtering in the time domain to eliminate delayed reflection signals and forms beam nulls in the spatial domain in the direction of the identified main reflection path.

[0034] When deploying a single ground station on a dynamically unstable offshore mobile platform, the three-axis gyroscope stabilization platform installed on the platform is controlled to compensate for the displacement of the antenna phase center caused by changes in the platform's attitude in real time. It also dynamically corrects the changes in the antenna phase center height caused by changes in sea level by combining the tidal model. At the same time, by connecting to a two-way link with a geostationary orbit satellite, the position stability of the geostationary orbit satellite is used to assist in compensating for the platform's own position drift.

[0035] Secondly, a high-precision clock transmission control system based on ground station calibration includes:

[0036] The acquisition module is used to control the satellite and at least one ground station to simultaneously transmit ranging signals to each other according to a preset time sequence, so as to build a two-way symmetrical transmission link between the satellite and the ground, and to acquire the original two-way pseudorange measurement values ​​including uplink pseudorange and downlink pseudorange.

[0037] The calibration module is used to control the ground station to perform a dynamic calibration process of local closed-loop calibration and multi-station comparison based on the original two-way pseudorange measurement values, so as to obtain real-time equipment delay calibration parameters; and to dynamically compensate for the delay drift of the ground station's transceiver equipment through the real-time equipment delay calibration parameters, so as to obtain two-way pseudorange data after equipment delay compensation.

[0038] The correction module is used to control the integrated error corrector to apply joint corrections to multi-source space propagation errors, including ionospheric delay, tropospheric delay, Sagnac effect, antenna phase center offset and relativistic effect, based on the two-way pseudorange data after equipment delay compensation, so as to obtain two-way pseudorange data after space error correction.

[0039] The calculation module is used to calculate the high-precision clock difference sequence between the satellite clock and the ground station clock based on the bidirectional pseudorange data after spatial error correction and by performing the difference calculation through the path symmetry of the uplink pseudorange and downlink pseudorange.

[0040] The processing module is used to control the time scale generation unit to perform a two-stage time scale generation process based on a high-precision clock difference sequence. This process includes an overlap Hadamard variance stability assessment and a Kalman-weighted average fusion algorithm to generate and maintain a high-precision autonomous time base, ultimately resulting in a stable UTC time scale.

[0041] Thirdly, a computing device includes:

[0042] One or more processors;

[0043] A storage device for storing one or more programs that, when executed by one or more processors, cause the one or more processors to implement the method.

[0044] Fourthly, a computer-readable storage medium storing a program that, when executed by a processor, implements the method.

[0045] The present invention described above has the following advantageous technical effects:

[0046] This invention employs a three-level dynamic calibration process involving a two-way symmetrical transmission link between satellite and ground stations, local closed-loop calibration at ground stations, multi-station cross-comparison, and motion delay compensation. It also includes joint correction of multi-source spatial propagation errors such as ionospheric and tropospheric delays, and a two-level timescale generation algorithm that integrates overlapping Hadamard variance stability assessment and Kalman-weighted averaging. Furthermore, it incorporates enhancement schemes for special scenarios such as densely populated urban areas and mobile offshore platforms, including phased array antennas with joint space-time filtering, a three-axis gyroscope-stabilized platform, and tidal models with GEO satellite assistance. Therefore, it overcomes the technical problems of large residual errors in traditional satellite timing, inability of fiber optic transmission to support dynamic targets, insufficient practicality of laser transmission, difficulty in solving asymmetric errors such as equipment delay drift and motion delay in traditional two-way time and frequency transmission, as well as insufficient short-term noise suppression of time reference, easy divergence in long-term estimation, and poor adaptability to complex scenarios. It achieves sub-nanosecond-level clock synchronization accuracy, controls the residual effects of errors such as ionospheric dispersion to an extremely low level, and achieves a stable UTC time scale with an accuracy better than 25ns for 60 days of autonomous maintenance, and can adapt to a variety of complex application scenarios. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating a high-precision clock transmission control method based on ground station calibration provided in an embodiment of the present invention.

[0048] Figure 2 This is a schematic diagram of a high-precision clock transmission control system based on ground station calibration provided in an embodiment of the present invention. Detailed Implementation

[0049] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0050] like Figure 1 As shown, embodiments of the present invention propose a high-precision clock transmission control method based on ground station calibration, the method comprising the following steps:

[0051] Step S1: Control the satellite and at least one ground station to simultaneously transmit ranging signals to each other according to a preset time sequence, so as to establish a two-way symmetrical transmission link between the satellite and the ground, and obtain the original two-way pseudorange measurement values ​​including uplink pseudorange and downlink pseudorange.

[0052] Step S2: Based on the original two-way pseudorange measurement values, control the ground station to perform a dynamic calibration process of local closed-loop calibration and multi-station comparison to obtain real-time equipment delay calibration parameters; use the real-time equipment delay calibration parameters to dynamically compensate for the delay drift of the ground station's transceiver equipment to obtain two-way pseudorange data after equipment delay compensation.

[0053] Step S3: Based on the two-way pseudorange data after equipment delay compensation, control the integrated error corrector to apply joint correction of multi-source space propagation errors, including ionospheric delay, tropospheric delay, Sagnac effect, antenna phase center offset and relativistic effect, so as to obtain two-way pseudorange data after space error correction.

[0054] Step S4: Based on the bidirectional pseudorange data corrected for spatial errors, and by performing a difference calculation through the path symmetry of the uplink pseudorange and downlink pseudorange, the clock difference calculation unit is controlled to calculate the high-precision clock difference sequence between the satellite clock and the ground station clock.

[0055] Step S5: Based on the high-precision clock difference sequence, the time scale generation unit executes a two-stage time scale generation process that includes overlapping Hadamard variance stability assessment and Kalman-weighted average fusion algorithm to generate and maintain a high-precision autonomous time base, and finally obtain a stable UTC time scale.

[0056] In this embodiment of the invention, the invention overcomes the technical problems of traditional satellite timing, such as large residual errors, difficulty in accurately compensating for equipment delay drift and asymmetric errors, interference from multi-source space propagation errors, insufficient short-term noise suppression of time references, and easy divergence in long-term estimation, by employing a two-way symmetrical transmission link between satellite and ground, local closed-loop calibration at ground stations and dynamic calibration through multi-station comparison, joint correction of multi-source space propagation errors including ionospheric delay and tropospheric delay, clock error calculation based on path symmetry difference, and the generation of a two-level time scale that integrates overlapping Hadamard variance stability assessment and Kalman-weighted average. Thus, it achieves sub-nanosecond-level clock synchronization accuracy, controls the residual effects of key errors such as ionospheric dispersion to an extremely low level, generates and maintains a stable UTC time scale with excellent accuracy for 60 days, and improves the technical effect of time synchronization reliability and accuracy in cross-regional and complex scenarios.

[0057] In a preferred embodiment of the present invention, step S1 above may include:

[0058] Step S1 involves controlling the satellite and at least one ground station to simultaneously transmit ranging signals to each other according to a preset timing sequence, thereby establishing a two-way symmetrical transmission link between the satellite and the ground, and obtaining the original two-way pseudorange measurement values, including uplink pseudorange and downlink pseudorange. Specifically, this includes: fully calibrating the clocks of the satellite and the ground station to ensure that their time bases are consistent; then, clearly setting the preset timing sequence for signal transmission; and making detailed plans for key parameters such as the transmission time node and signal interval to ensure that the transmission actions of the satellite and the ground station are strictly synchronized. Following the pre-planned timing sequence, the satellite and at least one ground station simultaneously initiate ranging signal transmission operations. The satellite continuously transmits downlink ranging signals towards the ground station, while the ground station continuously transmits uplink ranging signals towards the satellite. This bidirectional synchronous transmission method establishes a two-way symmetrical transmission link between the satellite and the ground, ensuring symmetrical signal propagation paths. During signal transmission, the satellite receives the uplink ranging signals transmitted by the ground station in real time, while the ground station receives the downlink ranging signals transmitted by the satellite in real time. Both stations record the time of their respective signal transmission, the time of receiving the other's signal, and relevant status information during signal propagation, ensuring that all data related to signal transmission is fully captured. Finally, based on the complete transmission information recorded by both the satellite and the ground station, precise measurements and calculations determine the uplink pseudorange measurement value from the ground station to the satellite and the downlink pseudorange measurement value from the satellite to the ground station. These values ​​are then integrated to obtain the original bidirectional pseudorange measurement value, providing comprehensive and reliable basic data support for equipment delay compensation, multi-source spatial error correction, and high-precision clock error calculation.

[0059] In this embodiment of the invention, by employing the technical means of controlling the satellite and at least one ground station to simultaneously transmit ranging signals according to a preset timing sequence, constructing a two-way symmetrical transmission link between the satellite and the ground, and obtaining the original two-way pseudorange measurement values ​​containing uplink pseudorange and downlink pseudorange, the technical problems of traditional satellite one-way time synchronization relying on ionospheric model correction leading to large residual errors and susceptibility to orbital errors, as well as the difficulty in completely offsetting common errors due to insufficient link symmetry in traditional two-way time and frequency transmission, are overcome. Thus, the technical effect of initially eliminating common errors such as orbital errors and tropospheric delays through the symmetry of the satellite-ground link path is achieved, providing a basic condition for high-precision clock error calculation, and simultaneously obtaining complete and symmetrical original pseudorange data, providing reliable data support for equipment delay compensation and multi-source spatial error correction is achieved.

[0060] In a preferred embodiment of the present invention, the dynamic calibration process of local closed-loop calibration and multi-station cross-comparison in step S2 includes:

[0061] Step S2.1: The ground station's internal signal generator periodically generates a self-test signal, which is then sequentially transmitted through its transmitting channel, coupler, and receiving channel to form a local closed-loop circuit. By measuring the total time delay change of this closed-loop circuit, the baseband time delay jitter of the transmitting and receiving channels, as well as the time delay drift of the RF devices due to temperature changes, are calculated in real time. Specifically, this includes: configuring the parameters of the ground station's internal signal generator to define the generation period and signal characteristics of the self-test signal, ensuring that the signal accurately reflects the status of the equipment transmission link; then controlling the signal generator to continuously generate a stable self-test signal according to the set period, and sequentially transmitting the self-test signal to the ground station. The signal from the transmitting channel, after processing, is guided to the receiving channel via a coupler, forming a complete local closed-loop circuit. This ensures that the signal is transmitted only within the ground station and not transmitted outwards. During the self-test signal transmission process, a high-precision delay measurement device monitors the total delay change of the entire closed-loop circuit in real time, recording delay data at different times. Based on this recorded total delay change data, a specialized data analysis method is used to calculate the baseband delay jitter generated by the transmitting and receiving channels during signal transmission in real time. At the same time, the delay drift caused by changes in ambient temperature of the RF devices is accurately calculated, providing basic data for equipment delay compensation based on the characteristics of the equipment within a single station.

[0062] Step S2.2 involves controlling at least three ground stations to exchange standard time comparison signals via fiber optic or microwave links to obtain the original time difference measurements between each station. The original time difference measurements are then processed using a least squares algorithm to separate the inherent equipment delay of each station from the inter-station signal transmission delay, generating inter-station equipment delay difference calibration parameters. Specifically, this includes: deploying at least three ground stations, planning communication links between each ground station, selecting fiber optic or microwave as the carrier for inter-station signal transmission, ensuring the stability and reliability of the link transmission, and then controlling these three or more ground stations to continuously send standard time comparison signals to each other. Each ground station acts as a signal transmitter, sending signals to the other stations. The ground station sends signals and also receives signals from other ground stations. During the signal exchange, each ground station records the standard time comparison signals received from different stations in real time, accurately obtains the original time difference measurement values ​​between stations, ensures the integrity and accuracy of the data records, organizes all the collected original time difference measurement values, and uses the least squares algorithm to process the data in depth. Through algorithm calculation, the inherent equipment delay of each ground station is separated, and the transmission delay generated by the transmission of signals between stations on optical fiber or microwave links is distinguished. Finally, based on the separation results, an inter-station equipment delay difference calibration parameter that can reflect the equipment delay differences of each station is generated.

[0063] Step S2.3 involves fusing the delay drift quantity with the inter-station equipment delay difference calibration parameters to obtain real-time equipment delay calibration parameters output at a preset update cycle. Specifically, this includes: establishing a dedicated data fusion processing model; clarifying the fusion rules and weight allocation methods for the delay drift quantity calculated in step S2.1 and the inter-station equipment delay difference calibration parameters generated in step S2.2; ensuring effective combination of the two types of data; simultaneously inputting the delay drift quantity obtained in step S2.1 (reflecting delay changes within a single station) and the inter-station equipment delay difference calibration parameters obtained in step S2.2 (reflecting delay differences between multiple stations) into the data fusion processing model; synchronously analyzing, calculating, and integrating the two types of data through the model; eliminating data redundancy and conflicts; extracting key information that comprehensively reflects the delay status of ground station equipment; setting a reasonable preset update cycle; and outputting the fused results as real-time equipment delay calibration parameters according to the preset update cycle, ensuring timely updates of the calibration parameters; and providing accurate and real-time parameter support for dynamic equipment delay compensation of the original two-way pseudorange measurements.

[0064] In this embodiment of the invention, the local closed-loop calibration and multi-station mutual comparison dynamic calibration process in step S2 involves using a signal generator inside the ground station to periodically generate a self-test signal and forming a local closed-loop circuit through a transmit channel, coupler, and receive channel to calculate baseband delay jitter and RF device temperature drift. At least three ground stations are controlled to mutually transmit standard time comparison signals via fiber optic or microwave links, and the device delay and inter-station transmission delay are separated based on a least squares algorithm to generate inter-station device delay difference calibration parameters. These delay drift values ​​are then fused with the inter-station device delay difference calibration parameters to obtain a preset update cycle. The technical means of real-time equipment delay calibration parameters overcomes the technical problems of traditional clock transmission technology, such as the inability to capture baseband delay jitter and RF device temperature drift in real time, the difficulty in effectively separating the inherent delay of equipment between multiple stations from the signal transmission delay, which leads to inaccurate equipment delay calibration parameters and affects clock transmission accuracy. Thus, it achieves real-time and accurate acquisition of equipment delay calibration parameters, dynamically compensates for delay drift of ground station transceivers, provides reliable support for the acquisition of bidirectional pseudorange data after equipment delay compensation, improves the accuracy and timeliness of equipment delay compensation during clock transmission, and ensures the overall clock transmission accuracy.

[0065] In a preferred embodiment of the present invention, the dynamic calibration process in step S2 further includes a motion delay compensation step:

[0066] Step S2.4: Within the time window for signal interaction between the satellite and the ground station, based on the satellite's precise orbit prediction data and the ground station's precise coordinates, the displacement of the ground station due to the Earth's rotation is calculated in real time. This includes: collecting complete satellite precise orbit prediction data, ensuring that the data includes key orbital parameters such as the satellite's position and velocity at different times; simultaneously acquiring the ground station's precise coordinate information to ensure the accuracy of the coordinate data; defining the time window for signal interaction between the satellite and the ground station, which is the specific time period during which they mutually transmit and receive ranging signals; continuously tracking the real-time changes in the satellite's precise orbit prediction data within the time window; combining the ground station's precise coordinates with the Earth's rotational motion laws and related celestial mechanics principles to calculate the positional changes of the ground station due to the Earth's rotation in real time; and finally accurately calculating the displacement of the ground station during the signal interaction period, providing key data support for motion delay compensation.

[0067] Step S2.5: Based on the displacement and signal propagation direction, dynamically calculate and compensate for the change in signal propagation time caused by the motion of the receiver. The compensation amount, along with the real-time equipment delay calibration parameters, is applied to compensate for the original two-way pseudorange measurement values. Specifically, this includes: clarifying the specific direction of signal propagation between the satellite and the ground station, i.e., the transmission path direction of the signal from the transmitter to the receiver; analyzing the impact of receiver motion on signal propagation time based on the calculated ground station displacement and the determined signal propagation direction; and dynamically calculating the change in signal propagation time using a specialized motion delay analysis method. Based on the calculated change in signal propagation time, determine the corresponding motion delay compensation amount. Integrate the motion delay compensation amount with the real-time equipment delay calibration parameters and apply them together to the compensation process of the original two-way pseudorange measurement values. This simultaneously corrects the delay errors caused by equipment delay drift and receiver motion, thereby improving the accuracy of the two-way pseudorange data.

[0068] In this embodiment of the invention, the technique of calculating the displacement of the ground station due to the Earth's rotation in real time based on the satellite's precise orbit prediction data and the ground station's precise coordinates within the time window of signal interaction between the satellite and the ground station, and then dynamically calculating and compensating for the change in signal propagation time caused by the motion of the receiving end based on the displacement and the signal propagation direction, and applying the compensation amount together with the real-time equipment delay calibration parameters to compensate for the original two-way pseudorange measurement value, overcomes the technical problem that traditional two-way time-frequency transmission technology does not consider the displacement effect caused by the motion of the ground station, cannot compensate for the change in signal propagation time caused by the motion of the receiving end, and thus produces asymmetric errors that make it difficult to stably improve the clock transmission accuracy. This achieves the technical effect of accurately offsetting the interference of the receiving end's motion on signal propagation, reducing the pseudorange measurement error caused by motion delay, further optimizing the accuracy of the two-way pseudorange data after equipment delay compensation, laying a solid data foundation for multi-source spatial error correction and high-precision clock difference calculation, and helping the overall clock transmission system achieve sub-nanosecond level synchronization accuracy.

[0069] In a preferred embodiment of the present invention, the joint correction of multi-source spatial propagation error in step S3 includes:

[0070] Step S3.1 involves performing ionospheric and tropospheric time delay corrections on the two-way pseudorange data after equipment time delay compensation. Ionospheric time delay correction utilizes the ionospheric total electron content mapping function based on dual-frequency observations and the Klobuchar enhancement model, while tropospheric time delay correction uses the Saastamoinen model based on meteorological parameter inputs. This yields two-way pseudorange data after ionospheric and tropospheric corrections. Specifically, this includes: acquiring the two-way pseudorange data after equipment time delay compensation, which will serve as the basis for ionospheric and tropospheric time delay corrections. For ionospheric time delay correction, relevant observation data is first collected using dual-frequency observation equipment. The observation data is then preliminarily analyzed and processed using the ionospheric total electron content mapping function. Finally, the Klobuchar enhancement model is used to optimize and adjust the preliminary processing results, accurately offsetting the time delay interference caused by the ionosphere on signal propagation. To address tropospheric time delay correction, a comprehensive collection of meteorological parameters, including temperature, air pressure, and humidity, is first undertaken. These parameters are then accurately input into the Saastamoinen model. The model's calculations analyze the impact of the tropospheric environment on signal propagation time delay. Subsequently, targeted corrections are applied to the two-way pseudorange data based on the model's output. After completing ionospheric and tropospheric time delay corrections, the two correction results are integrated to obtain two-way pseudorange data corrected for both ionospheric and tropospheric delays.

[0071] Step S3.2 involves applying Sagnac effect compensation to the two-way pseudorange data corrected for ionospheric and tropospheric conditions. This compensation is achieved by real-time conversion of the ground station's position from the geocentric-fixed coordinate system to the geocentric inertial coordinate system, and by calculating the geometric path difference of signal propagation based on the coordinate rotation angle. Specifically, this includes: using the two-way pseudorange data corrected for ionospheric and tropospheric conditions as the processing object, firstly, obtaining the precise position information of the ground station in the geocentric-fixed coordinate system; then, initiating a real-time coordinate system conversion program to convert the ground station's position information from the geocentric-fixed coordinate system to the geocentric inertial coordinate system; during the coordinate system conversion process, accurately calculating the coordinate rotation angle; and based on this coordinate rotation angle, deeply analyzing the geometric path difference of signal propagation between the satellite and the ground station to clarify the impact of this path difference on signal propagation time. Based on the analysis results, Sagnac effect compensation is applied to the two-way pseudorange data to eliminate errors caused by coordinate system differences and geometric path changes, ultimately obtaining Sagnac effect-compensated two-way pseudorange data.

[0072] Step S3.3 involves further applying antenna phase center offset compensation and relativistic effect compensation to the two-way pseudorange data compensated for the Sagnac effect. Antenna phase center offset compensation is achieved by projecting the deviation vector of the antenna phase center in the satellite or ground station's centroid coordinate system onto the satellite-to-ground line-of-sight direction. Relativistic effect compensation includes correcting the periodic clock bias term caused by the satellite's orbital eccentricity. Specifically, this includes receiving the Sagnac-effect-compensated two-way pseudorange data and performing antenna phase center offset compensation and relativistic effect compensation. For antenna phase center offset compensation, the antenna phase center is first determined to be in the satellite or ground station's centroid coordinate system. The deviation vector in the ground station's centroid coordinate system is accurately projected onto the satellite-to-ground line-of-sight direction using a professional projection calculation method. Based on the projection results, the two-way pseudorange data is adjusted to offset the measurement error caused by the antenna phase center offset. For relativistic effect compensation, satellite orbit-related parameters are first collected to identify the periodic clock error term caused by the satellite orbit eccentricity. The degree of interference of this periodic clock error term with time synchronization accuracy is analyzed. Then, a targeted correction method is used to correct this clock error term, eliminating the adverse effects of relativistic effects. After completing the two compensation operations, the correspondingly processed two-way pseudorange data is obtained.

[0073] Step S3.4: The combined output is the spatially corrected two-way pseudorange data, processed step-by-step through all correction steps from S3.1 to S3.3. Specifically, this includes collecting the two-way pseudorange data corrected for ionospheric and tropospheric errors in step S3.1, the two-way pseudorange data compensated for the Sagnac effect in step S3.2, and the two-way pseudorange data compensated for antenna phase center offset and relativistic effects in step S3.3. These correction data from different stages are comprehensively integrated, and a consistency check is performed to confirm that all correction steps for multi-source spatial propagation errors have been fully executed, and that the correction results of each step meet the preset accuracy control requirements, with no omissions or anomalies. After integration and checking, the combined output is the spatially corrected two-way pseudorange data, providing high-quality data support for high-precision clock error calculation.

[0074] In this embodiment of the invention, the joint correction of multi-source space propagation errors in step S3 is achieved by first correcting ionospheric time delay using the ionospheric total electron content mapping function based on dual-frequency observations and the Klobuchar enhancement model, then correcting tropospheric time delay using the Saastamoinen model based on meteorological parameter inputs, then compensating for the Sagnac effect through real-time conversion from the geocentric Earth-fixed coordinate system to the geocentric inertial coordinate system and calculation of coordinate rotation angles, followed by antenna phase center offset compensation by projecting the deviation vector in the satellite or ground station centroid coordinate system to the star-ground line-of-sight direction, and relativistic effect compensation by correcting the periodic clock error term caused by the satellite orbital eccentricity. Finally, the combined output is... The step-by-step data correction technique overcomes the technical problem of traditional clock transmission technology, which lacks a systematic integration of multi-source spatial propagation error correction strategies. Errors such as ionospheric delay, tropospheric delay, and Sagnac effect cause low pseudorange measurement accuracy and fail to meet the requirements of high-precision clock synchronization. This technique controls the residual effects of various spatial propagation errors to an extremely low level. The residual effects of ionospheric delay, Sagnac effect, and antenna phase center offset are all less than 0.01 nanoseconds, and the residual effect of relativistic effects is less than 1 picosecond. This improves the accuracy and reliability of two-way pseudorange data, provides high-quality data support for high-precision clock difference calculation, and helps the overall clock transmission system achieve sub-nanosecond synchronization accuracy.

[0075] In a preferred embodiment of the present invention, step S4 specifically includes:

[0076] Step S4.1 involves calculating the difference between the uplink and downlink pseudorange observations in the spatially corrected two-way pseudorange data. By leveraging the path symmetry of the satellite-to-ground two-way link, the common effects of orbital errors, tropospheric delays, and some ionospheric errors are eliminated, resulting in preliminary clock bias data. Specifically, this includes: acquiring spatially corrected two-way pseudorange data. The two-way pseudorange data has undergone joint correction of multi-source space propagation errors, including ionospheric delay, tropospheric delay, Sagnac effect, antenna phase center offset, and relativistic effects, ensuring that most spatial error interference has been eliminated at the data foundation level. Uplink and downlink pseudorange observations are extracted from the two-way pseudorange data, clearly distinguishing the signal propagation paths corresponding to the two types of observations. Specifically, the uplink pseudorange observations correspond to the propagation path data of the signal transmitted from the ground station to the satellite, and the downlink pseudorange observations correspond to the propagation path data of the signal transmitted from the satellite to the ground station. By fully utilizing the path symmetry characteristics of the satellite-to-ground two-way link, the extracted uplink pseudorange observations and downlink pseudorange observations are subtracted. This calculation process effectively offsets common influencing factors such as orbital errors, tropospheric delays, and some ionospheric errors that occur during two-way signal propagation. These common influencing factors are not fully eliminated in traditional techniques, leading to a decrease in accuracy. This step weakens these interferences at their source by subtracting based on path symmetry, ultimately obtaining preliminary clock bias data to lay a solid foundation for improving clock bias accuracy.

[0077] Step S4.2 introduces residual asymmetric error compensation processing into the preliminary clock bias data. The residual asymmetric error includes at least the equipment delay asymmetry remaining after dynamic calibration in step S2 and the residual spatial propagation error after joint correction in step S3, to obtain refined clock bias data. Specifically, this includes: comprehensively identifying possible types of residual asymmetric errors; considering the error problems not addressed by traditional solutions in the background technology; clarifying that such residual asymmetric errors include at least the equipment delay asymmetry not completely eliminated after dynamic calibration in step S2, and the residual spatial propagation error after joint correction of multi-source spatial propagation errors in step S3, ensuring that no key residual errors are overlooked. For the identified residual asymmetric errors, a dedicated residual error compensation model is established. Based on the characteristics of various residual errors and their impact on clock accuracy, the compensation weight and specific calculation method for each error are reasonably determined to ensure the pertinence and effectiveness of the compensation model. The preliminary clock error data obtained in step S4.1 is input into the residual error compensation model, and the parts of the preliminary clock error data affected by residual asymmetric errors are adjusted and corrected one by one. Through precise compensation operations, the interference of residual asymmetric errors on clock accuracy is further weakened, solving the problem of excessive time synchronization residuals caused by the lack of compensation for such errors in traditional technologies. Finally, refined clock error data is obtained, improving the accuracy and reliability of clock error data.

[0078] Step S4.3: Based on the refined clock difference data, a high-precision clock difference sequence is calculated in real time using the clock difference solution model. Specifically, this includes: First, a comprehensive quality inspection is performed on the refined clock difference data obtained in step S4.2. Methods such as data integrity checks, outlier identification and removal are used to ensure that there are no missing values, abnormal fluctuation values ​​or other issues that affect the calculation results in the refined clock difference data, thus ensuring the high quality and high reliability of the input data. Based on the demand for sub-nanosecond-level high-precision clock synchronization in fields such as low-orbit navigation enhancement and marine seismic detection, a clock difference calculation model adapted to this high-precision requirement is selected. This model must be able to fully utilize the effective information of refined clock difference data and accurately calculate the difference between the satellite clock and the ground station clock. The refined clock difference data that has passed quality inspection is input into the selected clock difference calculation model, and the model is started to perform real-time calculation processing. Through continuous analysis, calculation and optimization of the data by the model, a high-precision clock difference sequence that can accurately reflect the real-time difference between the satellite clock and the ground station clock is obtained. The high-precision clock difference sequence provides accurate and reliable data input for generating a stable UTC time scale in step S5, effectively solving the problem that the time synchronization residual is too large in traditional technology and cannot meet the requirements of high-precision measurement and control.

[0079] In this embodiment of the invention, the method of first calculating the difference between the uplink and downlink pseudorange observations in the bidirectional pseudorange data after spatial error correction, utilizing the path symmetry of the satellite-to-ground bidirectional link to eliminate the common influence of orbital errors, tropospheric delays, and some ionospheric errors, and then introducing residual asymmetric error compensation processing, including the residual equipment delay asymmetry after dynamic calibration in step S2 and the residual space propagation error residual after joint correction in step S3, and finally calculating in real time based on the refined clock difference data through a clock difference calculation model, overcomes the technical problems of traditional clock transmission technology that fail to fully utilize the link path symmetry to eliminate common errors and fail to specifically compensate for residual asymmetric errors, resulting in low clock difference calculation accuracy and inability to meet the requirements of high-precision time synchronization. This effectively reduces the interference of various errors on clock difference calculation, generates a high-precision clock difference sequence, provides accurate data input for the subsequent two-level time scale generation process, and helps the overall clock transmission system achieve sub-nanosecond level synchronization accuracy.

[0080] In a preferred embodiment of the present invention, the two-level timescale generation process in step S5 includes:

[0081] Step S5.1 involves preprocessing the input high-precision clock difference sequence, then using the overlapping Hadamard variance algorithm to calculate the clock frequency stability within a specified smoothing time. Based on the frequency stability evaluation results, the clock difference sequence is filtered and optimized to obtain short-term stable clock difference data. Specifically, this includes: receiving the high-precision clock difference sequence calculated in step S4; addressing the issue of insufficient accuracy caused by inadequate data processing in traditional schemes in the background technology; performing comprehensive preprocessing on the sequence; outlier removal by identifying and removing deviation data caused by measurement anomalies through setting reasonable thresholds; median filtering to reduce the interference of random noise on the data; and data smoothing to eliminate high-frequency fluctuations in the data, ensuring the continuity and reliability of the clock difference sequence. After preprocessing, the overlapping Hadamard variance algorithm is introduced. The overlapping Hadamard variance algorithm can overcome the shortcomings of traditional algorithms in terms of sensitivity to frequency drift. It is specifically used to evaluate clock frequency stability. Based on the high-precision requirements of fields such as LEO navigation enhancement and marine seismic detection, a reasonable specified smoothing time is set. The overlapping Hadamard variance algorithm is used to calculate the clock frequency stability within this time range, accurately capturing the short-term variation characteristics of the clock frequency. Based on the calculated frequency stability evaluation results, the clock difference sequence is subjected to targeted filtering and optimization to retain the effective information in the sequence and filter out short-term noise and unstable components. Finally, short-term stable clock difference data is obtained, which provides high-quality basic data for long-term benchmark generation.

[0082] Step S5.2 involves inputting the short-term stabilized clock bias data into the algorithm module that integrates Kalman filtering and weighted averaging for processing. Kalman filtering is used to optimally estimate the clock bias state and suppress short-term noise. The weighted averaging algorithm dynamically allocates weights for each time period based on the evaluated clock stability to suppress divergence in long-term state estimation. Specifically, this includes: inputting the short-term stabilized clock bias data obtained in step S5.1 into the algorithm module that integrates Kalman filtering and weighted averaging. This algorithm module is specifically designed to address the problems of insufficient short-term noise suppression and easy divergence in long-term state estimation in traditional techniques. It activates the Kalman filtering function, which enables optimal estimation of the clock bias state by establishing a reasonable state equation. The algorithm employs a process and observation equation to track clock bias state changes in real time, effectively suppressing short-term noise interference with clock bias data to improve short-term stability. Simultaneously, a weighted average algorithm is run, dynamically assigning weights to different time periods of the clock bias sequence based on the clock frequency stability assessed in step S5.1. Periods with higher stability are assigned greater weights to highlight their contribution to the time base, while periods with lower stability are assigned smaller weights to reduce their impact on overall accuracy. This dynamic weight allocation effectively suppresses the divergence problem in long-term state estimation, ensuring the long-term stability of the time base. The two algorithms work together to deeply process short-term stable clock bias data, laying the foundation for a long-term stable time scale.

[0083] Step S5.3: The control algorithm module outputs a long-term stable and autonomously maintained UTC timescale, and feeds back the stability information of the output timescale to step S5.2. This is used to dynamically adjust the weighted average weights to form a closed-loop control. Specifically, this includes controlling the algorithm module that fuses Kalman filtering and weighted averaging to output a deeply processed timescale. This timescale possesses the characteristics of long-term stability and autonomous maintenance, meeting the requirements of sub-nanosecond high-precision time references in fields such as low-Earth orbit navigation enhancement and marine seismic detection—that is, a stable UTC timescale. Simultaneously, the stability information of this output timescale is collected in real time, including key indicators such as frequency stability and time deviation fluctuation range. This stability information is fed back to the algorithm module in step S5.2, resulting in a closed-loop control mechanism. Based on the feedback stability information, the algorithm module dynamically adjusts the weight allocation ratio in the weighted average algorithm. If the stability of the timescale decreases in a certain time period, the weight of that time period can be appropriately reduced; if the stability improves, the weight is increased accordingly, ensuring that the weighted average algorithm is always optimized based on the latest stability state. Through this continuous feedback adjustment, the processing effect of the algorithm module is further optimized, long-term state estimation divergence is suppressed, and the output UTC time scale can maintain high accuracy for a long time, thus completely solving the problem of insufficient time base stability and inability to meet the high-precision requirements of complex scenarios in traditional technologies.

[0084] In this embodiment of the invention, the two-level time scale generation process in step S5 of the invention uses a technical means to overcome the technical problems of insufficient short-term noise suppression and long-term state estimation divergence in traditional time base generation technologies, which are caused by the International Atomic Time algorithm's insufficient short-term noise suppression and the Kalman filter's long-term state estimation divergence. This results in poor short-term stability and insufficient long-term maintenance accuracy of the time base. The technical effect is to effectively improve the short-term stability of the clock frequency, suppress long-term state estimation divergence, generate and maintain a long-term stable and autonomously controllable UTC time scale, and achieve a clock frequency stability better than 25 nanoseconds for 60 days. This provides a solid time base support for the overall clock transmission system to achieve sub-nanosecond level synchronization accuracy.

[0085] In a preferred embodiment of the present invention, the method further includes enhancement steps for specific application scenarios:

[0086] When deploying ground stations in densely populated urban areas with complex electromagnetic environments, the phased array antenna installed at the ground station is dynamically adjusted to suppress multipath effects. A joint space-time filtering algorithm is run simultaneously. This algorithm uses adaptive filtering in the time domain to eliminate delayed reflections and forms beam nulls in the spatial domain along the identified main reflection paths. Specifically, this involves: conducting a comprehensive survey of the deployment environment in densely populated urban areas, thoroughly investigating the distribution of surrounding high-rise buildings, the location of electromagnetic interference sources, and possible signal reflection paths; establishing a complete environmental characteristic database; clarifying the main causes and impact range of multipath effects; and providing precise environmental basis for subsequent suppression measures. Subsequently, a phased array antenna adapted to the complex electromagnetic environment is installed at the ground station, and precise docking and debugging of the antenna and the ground station receiving system are completed to ensure the antenna can flexibly adjust its beam direction in response to control commands. During clock transmission, the transmission status of satellite signals and the interference intensity of multipath signals are monitored in real time. Based on the monitoring data, the receiving beam direction of the phased array antenna is dynamically adjusted to precisely compress the antenna's signal reception range to a specific narrow domain, reducing the access of reflected signals from non-target directions, thus initially suppressing multipath effects at the hardware level. Simultaneously, a space-time joint filtering algorithm is launched. In the time domain, adaptive filtering technology is used to continuously analyze the temporal characteristics of the received signal, accurately identify the difference between delayed reflection signals and direct signals, and eliminate the interference of delayed reflection signals on the original signal through algorithmic calculations. In the spatial domain, combined with the previously established environmental feature database, the specific directions of the main reflection paths are accurately identified. Beamforming technology is used to form deep beam nulls in these directions to weaken the intensity of the reflected signals and avoid them interfering with the effective signal. Through the coordinated efforts of hardware adjustments and algorithm optimization, the multipath effect in the complex electromagnetic environment of densely populated urban areas is comprehensively suppressed, ensuring the acquisition accuracy of two-way pseudorange data.

[0087] When deploying a single ground station on a dynamically unstable offshore mobile platform, a three-axis gyro stabilization platform installed on the platform is used to compensate for the displacement of the antenna phase center caused by changes in platform attitude in real time. It also dynamically corrects for changes in antenna phase center height caused by sea level variations using a tidal model. Simultaneously, by connecting to a two-way link with a geostationary satellite, the platform's position stability is utilized to assist in compensating for its own positional drift. Specifically, this involves a comprehensive analysis of the offshore mobile platform's motion characteristics, including the potential range of pitch, roll, and other attitude changes, as well as the frequency of motion. Based on these characteristics, a suitable three-axis gyro stabilization platform is equipped for the platform. This platform is rigidly connected to and precisely calibrated with the ground station's antenna system to ensure that the stabilization platform can perceive antenna attitude changes in real time. During clock transmission, the three-axis gyro stabilization platform continuously collects platform attitude change data and monitors the displacement of the antenna phase center in real time through its built-in sensing module. Based on the monitored displacement data, it quickly calculates the compensation amount and drives the actuator to adjust the antenna position in real time, offsetting the displacement effect of platform attitude changes on the antenna phase center and ensuring that the antenna remains in a stable signal receiving attitude. Simultaneously, tidal observation data and historical sea-level change records for the maritime area are collected. This data is input into the tidal model and combined with real-time monitored sea-level height data to dynamically calculate the antenna phase center height offset caused by sea-level changes. Based on the calculation results, the antenna height parameters are specifically corrected to eliminate measurement errors caused by sea-level fluctuations. Furthermore, the establishment and debugging of a two-way link between the ground station and the geostationary satellite are completed in advance to ensure the stability of link transmission and the real-time nature of data interaction. During clock transmission, the position signal from the geostationary satellite is continuously received. Leveraging its high position stability, the position drift data of the maritime mobile platform is compared and analyzed in real time to calculate the drift compensation. Precise compensation for the platform's own position drift is achieved through signal feedback from the two-way link. Additionally, the ground station equipment is sealed and protected against special environmental conditions such as salt spray corrosion and high humidity at sea, ensuring stable operation in complex marine environments. Through multi-dimensional collaboration of attitude compensation, altitude correction, position drift compensation, and environmental protection, the problem of decreased clock transmission accuracy caused by the dynamic instability of the maritime mobile platform is solved.

[0088] In this embodiment of the invention, the enhanced steps for special application scenarios utilize techniques such as dynamically adjusting the receiving beam direction of the phased array antenna and synchronously running a space-time joint filtering algorithm when deploying a ground station in densely populated urban areas, and controlling a three-axis gyroscope-stabilized platform to compensate for antenna phase center displacement in real time when deploying a single ground station on a maritime mobile platform, dynamically correcting antenna phase center height changes by combining a tidal model, and connecting to a geostationary orbit satellite bidirectional link to assist in compensating for platform position drift. Therefore, this overcomes the technical challenges of multipath interference in complex electromagnetic environments of densely populated urban areas and antenna phase center displacement and height changes and platform position drift caused by the dynamic instability of maritime mobile platforms. Consequently, it effectively suppresses interference and compensates for various deviations in these two complex and special scenarios, ensuring the stability and accuracy of clock transmission. This allows the high-precision clock transmission control method of the present invention to adapt to more complex application scenarios, thereby expanding the scope of its application.

[0089] like Figure 2 As shown, embodiments of the present invention also provide a high-precision clock transmission control system based on ground station calibration, comprising:

[0090] The acquisition module is used to control the satellite and at least one ground station to simultaneously transmit ranging signals to each other according to a preset time sequence, so as to build a two-way symmetrical transmission link between the satellite and the ground, and to acquire the original two-way pseudorange measurement values ​​including uplink pseudorange and downlink pseudorange.

[0091] The calibration module is used to control the ground station to perform a dynamic calibration process of local closed-loop calibration and multi-station comparison based on the original two-way pseudorange measurement values, so as to obtain real-time equipment delay calibration parameters; and to dynamically compensate for the delay drift of the ground station's transceiver equipment through the real-time equipment delay calibration parameters, so as to obtain two-way pseudorange data after equipment delay compensation.

[0092] The correction module is used to control the integrated error corrector to apply joint corrections to multi-source space propagation errors, including ionospheric delay, tropospheric delay, Sagnac effect, antenna phase center offset and relativistic effect, based on the two-way pseudorange data after equipment delay compensation, so as to obtain two-way pseudorange data after space error correction.

[0093] The calculation module is used to calculate the high-precision clock difference sequence between the satellite clock and the ground station clock based on the bidirectional pseudorange data after spatial error correction and by performing the difference calculation through the path symmetry of the uplink pseudorange and downlink pseudorange.

[0094] The processing module is used to control the time scale generation unit to perform a two-stage time scale generation process based on a high-precision clock difference sequence. This process includes an overlap Hadamard variance stability assessment and a Kalman-weighted average fusion algorithm to generate and maintain a high-precision autonomous time base, ultimately resulting in a stable UTC time scale.

[0095] In a preferred embodiment of the present invention, the present invention proposes a high-precision satellite-to-ground clock transmission method integrating real-time calibration by ground stations. This method solves the aforementioned problems through the following innovative design: a satellite-to-ground two-way collaborative architecture; simultaneous transmission of ranging signals between the satellite and the ground station to construct a symmetrical transmission link, based on uplink pseudorange... Downlink pseudorange Observation equation: ; ,in, It is the uplink pseudorange. The satellite's position vector represents its position in space. The position vector of a ground station represents its position in space. It is the speed of light in a vacuum. Satellite clock deviation refers to the time difference between the satellite clock and the ideal reference clock. Ground station clock deviation refers to the time difference between the ground station clock and the ideal reference clock. The random error of the uplink pseudorange is an error component that cannot be corrected by the model. The modelable error of the uplink pseudorange is the portion of the error that can be corrected using an error model. It is the downlink pseudorange. The random error of downlink pseudorange is similarly an error that cannot be modeled in the downlink. The modelable error of downlink pseudorange is similar to the error in the downlink that can be corrected by the model.

[0096] The clock error solution is obtained by subtracting the differences: ;in, To model the error, a design utilizes path symmetry to eliminate common terms such as orbital error and tropospheric delay, reducing ionospheric dispersion error to within 0.01 nanoseconds. The ground station dynamic calibration system employs a three-level calibration mechanism to address transmit / receive delay drift and multipath effects. Local closed-loop calibration involves the ground station periodically injecting self-test signals to measure baseband delay jitter and RF device temperature drift. Multi-station comparison is achieved by exchanging signals between at least three ground stations to separate equipment delay from transmission delay. Motion delay compensation dynamically calculates the receiver displacement during signal propagation based on satellite orbit prediction and ground station location, using the following correction formula. ,in, Motion delay compensation is the amount of time delay that needs to be corrected due to displacement of the receiver during signal propagation. The velocity vector at the receiving end. This is the satellite station vector.

[0097] The multi-error joint correction model specifically includes:

[0098] Table 1. Error types and corresponding correction strategies in the multi-error joint correction model.

[0099] ;

[0100] The time base autonomous maintenance algorithm adopts a two-level time scale generation mechanism. The short-term stability layer is based on the overlapping Hadamard variance to evaluate the stability of satellite clocks, and the calculation formula is as follows: The overlapping Hadamard variance is used to assess the stability of the satellite clock. It is the sampling interval of the clock difference sequence. The length of the clock bias sequence, i.e., the total number of satellite clock bias data points. For clock difference sequences, the time base self-maintenance algorithm overcomes the sensitivity of Allan variance to frequency drift, supports stability assessment from 1 to 100 days, and provides a long-term benchmark layer; it integrates Kalman filtering and weighted averaging algorithms, and suppresses state estimation divergence through noise variance constraints, achieving a 60-day self-maintenance accuracy better than 25 nanoseconds.

[0101] In a preferred embodiment of the present invention, specifically, the low-orbit satellite time transfer calibration is performed, initial configuration is established, three ground stations are deployed, and the satellite carries a pre-tuned rubidium clock. ,in, The initial nominal frequency of the satellite clock is the reference frequency before pre-adjustment; G is the gravitational constant; M is the mass of the central celestial body (here, the mass of the celestial body the satellite orbits in the satellite-Ground system); c is the speed of light in a vacuum; x is the distance from the satellite to the center of mass of the central celestial body, i.e., a parameter similar to the satellite's orbital radius; a is the semi-major axis of the satellite's orbit around the central celestial body (Earth), in meters; the signal exchange satellite transmits downlink signals at UTC 12:00:00, and ground station A synchronously transmits uplink signals; the satellite records the reception time difference. Dynamic correction, ionosphere: VTEC is calculated using a two-layer mapping function, with a correction of 3.2 ns. Performance verification: clock error residual is 0.32 ns, and stability reaches 4.2 × 10⁻¹⁴ after 72 hours. High-latitude winter calibration: special scenario, high latitude, temperature -25℃, satellite elevation angle 30°. Calibration strategy: local closed loop: temperature control cabin maintains ±0.1℃, time delay drift is suppressed to 0.08 ns / h. Multipath suppression: anti-icing coating antenna is activated, residual error is reduced to 0.08 ns. Error correction, Sagnac effect compensation: ECEF-ECI rotation angle correction is 1.7 arcseconds. Emergency time reference recovery: fault scenario, main atomic clock malfunction, time reference needs to be rebuilt within 60 minutes. Rapid response: three-station cross-comparison, real-time monitoring of overlap Hadamard variance, dynamic weight allocation of KPW algorithm to restore effect, temporary time scale UTC is generated in 40 minutes, stability: 2 × 10⁻¹³ after 1 hour.

[0102] Multipath suppression was implemented in densely populated urban areas. A ground station was deployed in the center of a megacity, surrounded by high-rise buildings over 80 meters tall. The elevation angle fluctuated between 15° and 35° when the satellite passed overhead. Multipath reflections caused the original pseudorange error to reach 1.2 ns. The implementation employed core patented technologies: hardware upgrades, including the installation of an 8-element phased array antenna and dynamic beam pointing adjustment to compress the signal reception range to a 5° cone angle; algorithm upgrades, including the operation of a space-time joint filtering system, employing a 128th-order LMS adaptive filter in the time domain to eliminate delayed reflections, and using beamforming technology in the spatial domain to generate a -30dB null in the main reflection direction; and environmental modeling pre-loading a building laser point cloud database to identify the main reflection paths of glass curtain walls and concrete walls. Single-station calibration was also implemented on a mobile offshore platform. An independent ground station was deployed on an oil drilling platform far from the coastline, facing challenges such as platform sway, salt spray corrosion, and lack of multi-station coordination. Key technology implementation paths: Mechanical disturbance rejection, employing a three-axis gyroscope-stabilized platform to compensate for platform pitch / roll motion in real time, reducing the conversion coefficient of tilt fluctuations into time delay to 0.016 ns / degree; Environmental adaptability, with a sealed temperature-controlled chamber filled with nitrogen, achieving a temperature control accuracy of ±0.5℃, reducing the time delay temperature drift coefficient from 2.1 ns / h to 0.3 ns / h; Single-site innovation, shortening the local closed-loop calibration cycle to 15 minutes, and dynamically correcting the antenna phase center height through a tidal model. It synchronously connects to the two-way link of GEO navigation satellites and uses their position stability to compensate for platform drift.

[0103] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-precision clock transmission control method based on ground station calibration, characterized in that, The method includes: Step S1: Control the satellite and at least one ground station to simultaneously transmit ranging signals to each other according to a preset time sequence, so as to establish a two-way symmetrical transmission link between the satellite and the ground, and obtain the original two-way pseudorange measurement values ​​including uplink pseudorange and downlink pseudorange. Step S2: Based on the original two-way pseudorange measurement values, control the ground station to perform a dynamic calibration process of local closed-loop calibration and multi-station comparison to obtain real-time equipment delay calibration parameters; use the real-time equipment delay calibration parameters to dynamically compensate for the delay drift of the ground station's transceiver equipment to obtain two-way pseudorange data after equipment delay compensation. Step S3: Based on the two-way pseudorange data after equipment delay compensation, control the integrated error corrector to apply joint correction of multi-source space propagation errors, including ionospheric delay, tropospheric delay, Sagnac effect, antenna phase center offset and relativistic effect, so as to obtain two-way pseudorange data after space error correction. Step S4: Based on the bidirectional pseudorange data corrected for spatial errors, and by performing a difference calculation through the path symmetry of the uplink pseudorange and downlink pseudorange, the clock difference calculation unit is controlled to calculate the high-precision clock difference sequence between the satellite clock and the ground station clock. Step S5: Based on the high-precision clock difference sequence, the timescale generation unit executes a two-stage timescale generation process, including overlapping Hadamard variance stability assessment and Kalman-weighted average fusion algorithm, to generate and maintain a high-precision autonomous time base, ultimately obtaining a stable UTC timescale, including: Step S5.1: After preprocessing the input high-precision clock difference sequence, the overlapping Hadamard variance algorithm is used to calculate the clock frequency stability within a specified smoothing time. Based on the frequency stability evaluation results, the clock difference sequence is filtered and optimized to obtain short-term stable clock difference data. Step S5.2: Input the short-term stabilized clock bias data into the algorithm module that integrates Kalman filtering and weighted averaging for processing; wherein, Kalman filtering is used to make the optimal estimate of the clock bias state and suppress short-term noise, and the weighted averaging algorithm dynamically allocates the weights of each time period based on the evaluated clock stability to suppress the divergence of the long-term state estimate. In step S5.3, the control algorithm module outputs a long-term stable and autonomously maintained UTC time scale, and feeds back the stability information of the output time scale to step S5.2, which is used to dynamically adjust the weighted average weight to form a closed-loop control.

2. The high-precision clock transmission control method based on ground station calibration according to claim 1, characterized in that, The dynamic calibration process of local closed-loop calibration and multi-station cross-comparison in step S2 includes: Step S2.1: Control the internal signal generator of the ground station to periodically generate a self-test signal, and pass the self-test signal through its transmitting channel, coupler and receiving channel in sequence to form a local closed loop. By measuring the total time delay change of the closed loop, the baseband time delay jitter of the transmitting channel and the receiving channel and the time delay drift of the radio frequency device caused by temperature change are calculated in real time. Step S2.2: Control at least three ground stations to send standard time comparison signals to each other via optical fiber or microwave link, obtain the original time difference measurement value between each station, and process the original time difference measurement value based on the least squares algorithm to separate the inherent equipment delay of each station and the signal transmission delay between stations, and generate the equipment delay difference calibration parameter between stations. Step S2.3: The time delay drift amount and the inter-station equipment time delay difference calibration parameters are fused together to obtain the real-time equipment time delay calibration parameters output at a preset update cycle.

3. The high-precision clock transmission control method based on ground station calibration according to claim 2, characterized in that, The dynamic calibration process in step S2 also includes a motion delay compensation step: Step S2.4: During the time window for signal interaction between the satellite and the ground station, the displacement caused by the ground station's movement with the Earth's rotation is calculated in real time based on the satellite's precise orbit prediction data and the ground station's precise coordinates. Step S2.5: Based on the displacement and signal propagation direction, dynamically calculate and compensate for the change in signal propagation time caused by the motion of the receiver. The compensation amount and the real-time equipment delay calibration parameters are applied together to compensate for the original bidirectional pseudorange measurement value.

4. The high-precision clock transmission control method based on ground station calibration according to claim 1, characterized in that, The joint correction of multi-source spatial propagation error applied in step S3 includes: Step S3.1: For the two-way pseudorange data after equipment delay compensation, perform ionospheric delay correction and tropospheric delay correction respectively; wherein, the ionospheric delay correction is performed using the ionospheric total electron content mapping function based on dual-frequency observation and the Klobuchar enhancement model, and the tropospheric delay correction is performed using the Saastamoinen model based on meteorological parameter input, to obtain two-way pseudorange data after ionospheric and tropospheric correction; Step S3.2: Sagnac effect compensation is performed on the two-way pseudorange data that has been corrected by the ionosphere and troposphere. The compensation is achieved by converting the ground station position from the geocentric geofixed coordinate system to the geocentric inertial coordinate system in real time and calculating the geometric path difference of signal propagation based on the coordinate rotation angle, so as to obtain the two-way pseudorange data after Sagnac effect compensation. Step S3.3: Further apply antenna phase center offset compensation and relativistic effect compensation to the two-way pseudorange data after Sagnac effect compensation; wherein, antenna phase center offset compensation is achieved by projecting the deviation vector of the antenna phase center in the satellite or ground station centroid coordinate system to the star-ground line of sight direction, and relativistic effect compensation includes the correction of the periodic clock error term caused by the satellite orbit eccentricity. Step S3.4: Output the bidirectional pseudorange data after spatial error correction, which has been processed step by step through all the correction steps from S3.1 to S3.

3.

5. The high-precision clock transmission control method based on ground station calibration according to claim 1 or 4, characterized in that, Step S4 specifically includes: Step S4.1: The uplink pseudorange observations and downlink pseudorange observations in the two-way pseudorange data after spatial error correction are subtracted. By utilizing the path symmetry of the satellite-to-ground two-way link, the common effects of orbital error, tropospheric delay, and some ionospheric error are eliminated to obtain preliminary clock error data. Step S4.2 introduces residual asymmetric error compensation processing into the preliminary clock difference data. The residual asymmetric error includes at least the equipment delay asymmetry remaining after dynamic calibration in step S2 and the spatial propagation error residual remaining after joint correction in step S3, so as to obtain refined clock difference data. Step S4.3: Based on the refined clock difference data, a high-precision clock difference sequence is calculated in real time using the clock difference solution model.

6. The high-precision clock transmission control method based on ground station calibration according to claim 1, characterized in that, The method also includes enhancement steps for specific application scenarios: When deploying ground stations in densely populated urban areas with complex electromagnetic environments, the phased array antenna installed at the ground station is controlled to dynamically adjust the receiving beam direction to suppress multipath effects, and a space-time joint filtering algorithm is run synchronously. The space-time joint filtering algorithm uses adaptive filtering in the time domain to eliminate delayed reflection signals and forms beam nulls in the spatial domain in the direction of the identified main reflection path. When deploying a single ground station on a dynamically unstable offshore mobile platform, the three-axis gyroscope stabilization platform installed on the platform is controlled to compensate for the displacement of the antenna phase center caused by changes in the platform's attitude in real time. It also dynamically corrects the changes in the antenna phase center height caused by changes in sea level by combining the tidal model. At the same time, by connecting to a two-way link with a geostationary orbit satellite, the position stability of the geostationary orbit satellite is used to assist in compensating for the platform's own position drift.

7. A high-precision clock transmission control system based on ground station calibration, wherein the system implements the method as described in any one of claims 1 to 6, characterized in that, include: The acquisition module is used to control the satellite and at least one ground station to simultaneously transmit ranging signals to each other according to a preset time sequence, so as to build a two-way symmetrical transmission link between the satellite and the ground, and to acquire the original two-way pseudorange measurement values ​​including uplink pseudorange and downlink pseudorange. The calibration module is used to control the ground station to perform a dynamic calibration process of local closed-loop calibration and multi-station comparison based on the original two-way pseudorange measurement values, so as to obtain real-time equipment delay calibration parameters. The delay drift of the ground station's transceiver equipment is dynamically compensated by real-time equipment delay calibration parameters to obtain two-way pseudorange data after equipment delay compensation. The correction module is used to control the integrated error corrector to apply joint corrections to multi-source space propagation errors, including ionospheric delay, tropospheric delay, Sagnac effect, antenna phase center offset and relativistic effect, based on the two-way pseudorange data after equipment delay compensation, so as to obtain two-way pseudorange data after space error correction. The calculation module is used to calculate the high-precision clock difference sequence between the satellite clock and the ground station clock based on the bidirectional pseudorange data after spatial error correction and by performing the difference calculation through the path symmetry of the uplink pseudorange and downlink pseudorange. The processing module is used to control the time scale generation unit to perform a two-stage time scale generation process based on a high-precision clock difference sequence. This process includes an overlap Hadamard variance stability assessment and a Kalman-weighted average fusion algorithm to generate and maintain a high-precision autonomous time base, ultimately resulting in a stable UTC time scale.

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