An apparatus and method for dynamic clock compensation in a time-transfer receiver.

Abstract

This invention provides a dynamic clock compensation device and method for a time-transfer receiver, comprising an adaptive amplification unit, a waveform shaping unit, an FPGA-based time-to-digital converter, and a data processing unit. The 1PPS signal generated by the GNSS receiver serves as the START signal, and the 1PPS signal from the external clock serves as the STOP signal. Both signals pass through the adaptive amplification unit and the waveform shaping unit, respectively. The shaped 1PPS signals are then sent to the FPGA-based time-to-digital converter to be converted into digital count values. These count values ​​are then sent to the data processing unit, which calculates the time difference between the two 1PPS signals based on the counting frequency. Finally, the time difference is multiplied by the speed of light to convert it into a distance value, which is then used to compensate for the pseudorange measured by the GNSS receiver.

Description

Technical Field

[0001] This invention belongs to the field of metrology, and specifically relates to a device and method for dynamic clock compensation of a time-transfer receiver, which is particularly suitable for improving the time synchronization accuracy and precision of pseudorange observation data. Background Technology

[0002] In satellite navigation, high-precision positioning, and time-frequency transfer systems, pseudorange measurement is an important ranging method. It calculates the time difference between the ground clock and the satellite clock by measuring the distance from the satellite to the receiver. The accuracy of the time difference measurement directly depends on the synchronization accuracy between the receiver clock and the external reference clock. Receivers typically use an internal crystal oscillator to generate a second pulse signal. However, due to the instability of the crystal oscillator, there is a frequency deviation between the receiver clock and the external reference clock. Therefore, in time-transfer receivers, an external frequency reference signal is generally used as the operating time base to generate the second pulse signal. However, there will be a time difference between the start time of the generated second pulse signal and the start time of the second pulse of the external reference clock. This error will cause deviations in the pseudorange measurement results of the receiver, thus affecting the accuracy of time-frequency comparison.

[0003] Currently, many high-precision time synchronization technologies rely on external reference clocks or satellite signals for clock calibration. However, traditional clock synchronization methods often fail to effectively address the discrepancy between the receiver's internal clock and the external reference clock's second pulse start time. Existing dynamic compensation techniques typically rely on long-term measurement data or external reference clocks, but still struggle to provide real-time, accurate dynamic clock compensation solutions, generally suffering from the following problems: first, insufficient accuracy, making sub-nanosecond error control difficult; second, lack of deep integration with GNSS pseudorange data, hindering dynamic correction of the observation data itself; and third, system response lag, failing to meet real-time requirements in dynamic scenarios. The calibration effect is particularly poor when the second pulse start time changes after each receiver restart. To improve pseudorange measurement accuracy, a new method is needed to address the real-time time difference between the receiver clock and the external reference clock, ensuring the accuracy of time-frequency measurement results.

[0004] Therefore, there is an urgent need for a device and method based on dynamic compensation of the time-transfer receiver clock, which can accurately compensate for the initial time error of the receiver's second pulse and ensure the accuracy of the pseudorange measurement results. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art and provide a device and method for dynamic clock compensation of a time-transfer receiver. It can use a precision time interval measuring device to measure and dynamically compensate for the internal time delay of the receiver in real time, so as to keep the external clock 1PPS synchronized with the GNSS receiver itself 1PPS.

[0006] This invention includes a time-transfer receiver clock dynamic compensation device, comprising an adaptive amplification unit, a waveform shaping unit, an FPGA-based time-to-digital converter, and a data processing unit. The 1PPS signal generated by the GNSS receiver serves as the START signal, and the 1PPS signal from the external clock serves as the STOP signal. Both signals pass through the adaptive amplification unit, which attenuates or amplifies the amplitude of the 1PPS signals to CMOS level. The waveform shaping unit eliminates the influence of the rising edge transition process of the 1PPS signals, reducing the rising edge time to less than 2ns. The two shaped 1PPS signals are then sent to the FPGA-based time-to-digital converter, which converts the time interval between the two signals into a digital count value. This count value is then sent to the data processing unit, which calculates the time difference between the two 1PPS signals based on the counting frequency. Finally, the time difference is multiplied by the speed of light to convert it into a distance value, which is then used to compensate for the pseudorange measured by the GNSS receiver.

[0007] Furthermore, the device also includes a multi-channel support module, which can simultaneously measure 1PPS time difference from multiple GNSS systems (such as GPS, BeiDou, GLONASS, Galileo);

[0008] Furthermore, the device also includes a sliding window filter and a Kalman filter for smoothing and dynamic modeling and prediction of the time difference sequence;

[0009] Furthermore, this device also includes: a RINEX format processing module, which automatically extracts pseudorange observations, performs error correction, and outputs in a compatible format;

[0010] Furthermore, this device also includes: an API interface or a serial communication module for real-time communication with a GNSS receiver or data processing system;

[0011] Furthermore, the device also includes an error source analysis module to distinguish whether the error originates from receiver local oscillator drift, external clock instability, or satellite signal propagation model deviation.

[0012] This invention also includes a method for dynamic clock compensation of a time-transfer receiver. The method includes using an external clock, a GNSS receiver, and the aforementioned dynamic clock compensation device. The external clock generates a 10MHz frequency signal and a 1PPS time signal. The 10MHz signal provides a frequency reference for both the GNSS receiver and the dynamic clock compensation device. After receiving the 10MHz signal, the GNSS receiver generates a 1PPS signal using this signal. Simultaneously, the GNSS receiver locks onto a satellite and uses the 1PPS signal to perform pseudorange measurement, generating a raw pseudorange observation. This raw pseudorange observation is sent to the dynamic clock compensation device. The dynamic clock compensation device receives the 1PPS signal generated by the GNSS receiver and the 1PPS signal from the external clock, measures the time interval Δt(t) between the two 1PPS signals, and subtracts Δt(t) from the raw pseudorange observation. c. Finally, the compensated pseudorange values ​​are stored as RINEX format data.

[0013] Furthermore, the time-transfer receiver clock dynamic compensation method also includes enabling dynamic filtering function, predicting the time difference trend through a sliding window filter or a Kalman filter, and dynamically estimating the future compensation amount.

[0014] Furthermore, the time-transfer receiver clock dynamic compensation method also includes synchronously outputting the compensated data to the back-end data processing system or GNSS positioning and calculation system via API or serial port.

[0015] Through the above technical solution, this application can achieve the following beneficial effects: it can significantly reduce the measurement error introduced by the 1PPS time difference; it introduces a high-precision TDC module, realizes nanosecond-level time resolution based on FPGA, and improves synchronization accuracy; it supports multi-system GNSS and multi-band extension, adapting to complex navigation environments; combined with sliding window and filtering algorithms, it can dynamically predict and fit the time difference change trend, improving robustness; the output conforms to the standard format, is compatible with the existing RINEX data processing system, and facilitates engineering applications; it adds an error source identification mechanism, which helps users optimize system configuration and compensation strategies; it can be expanded into an embedded module, adapting to scenarios such as UAVs, measurement equipment, and timing base stations, realizing low-cost integrated applications. By constructing a closed-loop link of time difference measurement—error conversion—pseudorange compensation—formatted storage, the measurement accuracy and synchronization performance of the GNSS receiver are effectively improved. Attached Figure Description

[0016] Figure 1 Schematic diagram of a clock dynamic compensation device for a time-transfer receiver;

[0017] Figure 2A schematic diagram of a dynamic clock compensation method for a time-transfer receiver;

[0018] Figure 3 A schematic diagram of a remote time comparison device for a time-transfer type receiver clock dynamic compensation device;

[0019] Figure 4 The results show the comparison between the time and frequency source of the Guizhou Provincial Institute of Metrology and Testing and the time difference of UTC (NIM). Detailed Implementation

[0020] The invention will now be further described with reference to the accompanying drawings:

[0021] Time-transfer receiver clock dynamic compensation device such as Figure 1 As shown by the dashed line, the time-transfer receiver clock dynamic compensation device includes a first adaptive amplification unit and a second adaptive amplification unit, a waveform shaping unit, an FPGA-based time-to-digital converter, and a data processing unit. The 1PPS signal generated by the GNSS receiver serves as the START signal, and the 1PPS signal from the external clock serves as the STOP signal. Both signals pass through the adaptive amplification unit, which attenuates or amplifies the amplitude of the 1PPS signal to CMOS level. The waveform shaping unit eliminates the influence of the rising edge transition process of the 1PPS signal, reducing the rising edge time to less than 2ns. The two shaped 1PPS signals are then sent to the FPGA-based time-to-digital converter, which converts the time interval between the two signals into a digital count value. This count value is then sent to the data processing unit, which calculates the time difference between the two 1PPS signals based on the counting frequency. Finally, the time difference is multiplied by the speed of light to convert it into a distance value, which is then used to compensate for the pseudorange measurement result of the GNSS receiver.

[0022] Dynamic clock compensation methods for time-transfer receivers, such as Figure 2As shown, it includes an external clock, a GNSS receiver, and a time-transfer receiver clock dynamic compensation device. The external clock generates a 10MHz frequency signal and a 1PPS time signal. The 10MHz signal provides a frequency reference for both the GNSS receiver and the time-transfer receiver clock dynamic compensation device. After receiving the 10MHz signal, the GNSS receiver uses it to generate a 1PPS signal. Simultaneously, the GNSS receiver locks onto a satellite and uses the 1PPS signal to perform pseudorange measurements, generating raw observations. These raw observations are then sent to the time-transfer receiver clock dynamic compensation device. The time-transfer receiver clock dynamic compensation device receives the 1PPS signal generated by the GNSS receiver and the 1PPS signal from the external clock, and measures the time interval Δt(t) between the two 1PPS signals. This time interval is a quantity that changes with time, i.e., the time difference that needs to be compensated. Since the raw observations generated by the GNSS receiver are stored as RINEX format data, the data value is pseudorange, which is the distance from the receiver antenna phase center to the GNSS satellite measured using pseudo-random codes. This includes the distance variation introduced by Δt(t). Therefore, the pseudorange value must be subtracted from Δt(t). c. Finally, the compensated pseudorange values ​​are stored as RINEX format data.

[0023] Furthermore, dynamic filtering can be enabled to predict the time difference trend through a sliding window filter or a Kalman filter, and to dynamically estimate the future compensation amount.

[0024] Furthermore, the compensated data can be synchronously output to the backend data processing system or GNSS positioning and calculation system via API or serial port.

[0025] The time-transfer receiver clock dynamic compensation method in this embodiment can be performed according to the following illustrated steps:

[0026] (1) Connect the 10MHz external clock to the GNSS receiver and the time transfer receiver clock dynamic compensation device respectively;

[0027] (2) Connect the 1PPS output from the GNSS receiver and the 1PPS output from the external clock to the time transfer receiver clock dynamic compensation device respectively.

[0028] (3) Connect the serial port output of the GNSS receiver to the serial port of the time transfer receiver clock dynamic compensation device for the transmission of raw observation data;

[0029] (4) Start the device and set the sampling interval to 1s, that is, measure one time difference data Δt(t) every 1s. At the same time, the GNSS receiver generates a set of pseudorange values ​​every 1s. This set of pseudorange values ​​includes pseudorange values ​​of different GNSS satellite systems and at different frequencies. Then, multiply the time difference data Δt(t) by the speed of light c to obtain the distance to be compensated. Then, subtract Δt(t) from all the pseudorange values ​​measured at the same time. c. Finally, the compensated pseudorange values ​​are stored as RINEX format data.

[0030] In this embodiment, actual verification testing was also conducted. A GNSS receiver with an embedded time-transfer receiver clock dynamic compensation device was used to transmit the atomic time standard UTC (NIM) of the National Institute of Metrology of China to the Guizhou Provincial Institute of Metrology and Testing, achieving remote time comparison. The specific method is as follows... Figure 3 As shown.

[0031] (1) Embed two sets of time-transfer receiver clock dynamic compensation devices into GNSS receiver 1 and GNSS receiver 2 respectively;

[0032] (2) Connect 1PPS and 10MHz of UTC(NIM) to GNSS receiver 1. The time transfer receiver clock dynamic compensation device can measure the time difference between 1PPS of UTC(NIM) and 1PPS of GNSS receiver itself, convert the time difference value into a distance value to compensate the pseudorange value measured by GNSS receiver 1, and save it as RINEX format data.

[0033] (3) Connect the 1PPS and 10MHz generated by the time frequency source of Guizhou Institute of Metrology and Testing to GNSS receiver 2. The time transfer receiver clock dynamic compensation device can measure the time difference between the 1PPS of the time frequency source and the 1PPS of the GNSS receiver itself, convert the time difference value into a distance value to compensate the pseudorange value measured by GNSS receiver 2, and save it as RINEX format data.

[0034] (4) The RINEX format data generated by the two GNSS receivers were converted into CGGTTS files using the software R2CGGTTS recommended by the International Bureau of Weights and Measures. Then, the difference was calculated to obtain the time difference between the time and frequency source of the Guizhou Provincial Institute of Metrology and Testing and the UTC (NIM) of the National Institute of Metrology, China. The comparison results are as follows: Figure 4 As shown, the average value of the comparison results is 0.43 ns, and the standard deviation is 0.89 ns, eliminating the dynamic error introduced by the asynchronous initial timing.

Claims

1. A time transfer receiver clock dynamic compensation device, comprising a first adaptive amplification unit, a second adaptive amplification unit, a first waveform shaping unit, a second waveform shaping unit, a FPGA-based time-to-digital conversion unit and a data processing unit, wherein the 1PPS signal generated by the GNSS receiver is taken as the START signal, and the 1PPS of the external clock is taken as the STOP signal, the 1PPS signal is attenuated or amplified to the CMOS level through the first and second adaptive amplification units respectively, the influence of the rising edge transition process of the 1PPS is eliminated through the first or second waveform shaping unit, the rising edge time is reduced, and the rising edge time is less than 2ns, the two paths of the shaped 1PPS are sent to the FPGA-based time-to-digital conversion unit, the two time intervals are converted into digital count values, the count values are sent to the data processing unit, the time difference of the two 1PPS signals is calculated according to the count frequency, and finally the time difference value is multiplied by the speed of light to convert into the value of distance, which is compensated into the pseudorange result measured by the GNSS receiver, the time transfer receiver clock dynamic compensation device further comprises: Multi-channel support module, which can measure the 1PPS time difference from multiple GNSS systems simultaneously; Error source analysis module, which can distinguish the error source from receiver local oscillator drift, external clock instability or satellite signal propagation model bias.

2. A time transfer receiver clock dynamic compensation apparatus as claimed in claim 1, the apparatus further comprising: Sliding window filter and Kalman filter, which can be used to smooth and dynamically model the time difference series.

3. The time transfer receiver clock dynamic compensation apparatus of claim 1, further comprising: RINEX format processing module, which can automatically extract pseudorange observations, correct errors and output compatible formats.

4. The time transfer receiver clock dynamic compensation apparatus of claim 1, the time transfer receiver clock dynamic compensation apparatus further comprising: API interface or serial communication module, which can be used for real-time communication with GNSS receivers or data processing systems.

5. A time transfer receiver clock dynamic compensation method based on the time transfer receiver clock dynamic compensation device of any one of claims 1-4, wherein the method uses an external clock, a GNSS receiver and the time transfer receiver clock dynamic compensation device, and comprises the following steps: (1) The external clock generates a 10MHz frequency signal and a time signal 1PPS, wherein the 10MHz signal provides a frequency reference for the GNSS receiver and a frequency reference for the time transfer receiver clock dynamic compensation device; (2) After receiving the 10MHz signal, the GNSS receiver generates a 1PPS signal using the 10MHz signal, locks the satellite and measures the pseudorange using the 1PPS, generates the original pseudorange observation and stores it as RINEX format data; (3) The original pseudorange observation is sent to the time transfer receiver clock dynamic compensation device, which receives the 1PPS signal generated by the GNSS receiver and the 1PPS signal from the external clock, measures the time interval Δt(t) between the two 1PPS signals, which is a time difference value that needs to be compensated; (4) The value of the RINEX format data obtained in step (2) is the pseudorange, i.e. the distance from the receiver antenna phase center to the GNSS satellite measured by the pseudorandom code, which is subtracted by Δt(t)·c, and the compensated pseudorange value is finally stored as RINEX format data.

6. The time transfer receiver clock dynamic compensation method of claim 5, further comprising enabling a dynamic filtering function to predict the time difference trend through a sliding window filter or a Kalman filter to dynamically estimate the future compensation amount.

7. The time transfer receiver clock dynamic compensation method of claim 6, further comprising synchronously outputting the compensated data to a backend data processing system or a GNSS positioning solution system through an API or a serial port.

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