Device and method for clock dynamic compensation of time transfer type receiver

Abstract

The invention provides a time transfer type receiver clock dynamic compensation device and a dynamic method. The time transfer type receiver clock dynamic compensation device comprises a self-adaptive amplification unit, a waveform shaping unit, an FPGA-based time digital conversion unit and a data processing unit. Wherein a 1PPS signal generated by the GNSS receiver is used as a START signal, a 1PPS of an external clock is used as a STOP signal, the signals respectively pass through the adaptive amplification unit and the waveform shaping unit, the two paths of shaped 1PPS are sent to the FPGA-based time digital conversion unit to be converted into a digital count value, the count value is sent to the data processing unit, and the data processing unit is used for processing the digital count value. And calculating a time difference value of the two paths of 1PPS signals according to the counting frequency, and finally multiplying the time difference value by the light velocity, converting the time difference value into a distance magnitude, and compensating a pseudo-range result measured by the GNSS receiver.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metrology, and particularly relates to a device and method for dynamic compensation of a time transfer type receiver clock, and is especially suitable for improving the time synchronization accuracy and precision of pseudo-range observation data. BACKGROUND

[0002] In satellite navigation, high-precision positioning and time-frequency transfer systems, pseudo-range measurement is an important ranging method, which calculates the distance information from the satellite to the receiver to calculate the time difference information between the ground clock and the satellite clock. The accuracy of time difference measurement directly depends on the synchronization accuracy between the receiver clock and the external reference clock. The receiver usually uses an internal crystal oscillator to generate a second pulse signal, but due to the instability of the crystal oscillator, there is a frequency deviation between the receiver clock and the external reference clock. Therefore, in a time transfer type receiver, an external frequency reference signal is usually used as a working time base to generate a second pulse signal, but there is a time difference between the starting time of the generated second pulse signal and the starting time of the second pulse of the external reference clock. This error will cause the pseudo-range result measured by the receiver to deviate, and thus affect 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 cannot effectively solve the problem of deviation in the starting time of the second pulse between the internal clock of the receiver and the external reference clock. Existing dynamic compensation technologies usually rely on long-term measurement data or external reference clocks, but still cannot provide real-time and accurate clock dynamic compensation schemes, and generally have the following problems: first, the precision is insufficient, and it is difficult to achieve sub-nanosecond error control; second, they are not deeply integrated with GNSS pseudo-range data, and cannot dynamically correct the observation data itself; third, the system response is lagging, and cannot meet the real-time requirements in dynamic scenarios. Especially when the starting point of the second pulse changes after each restart of the receiver, the calibration effect is not good. In order to improve the pseudo-range measurement accuracy, a new method is needed to solve the starting time difference between the receiver clock and the external reference clock in real time and ensure the accuracy of time-frequency measurement results.

[0004] Therefore, there is an urgent need for a device and method for dynamic compensation of a time transfer type receiver clock, which can accurately compensate for the initial time error of the receiver second pulse and ensure the accuracy of the pseudo-range measurement result. SUMMARY

[0005] The present application aims to solve the problems existing in the prior art, and provides a device and method for dynamic compensation of a time transfer type receiver clock, which can use a precise time interval measurement device to measure and dynamically compensate for the internal time delay of the receiver, and keep the external clock 1PPS synchronized with the GNSS receiver's own 1PPS.

[0006] The application comprises a time transfer type receiver clock dynamic compensation device, which comprises an adaptive amplification unit, a waveform shaping unit, a FPGA-based time-to-digital conversion unit and a data processing unit. 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, which are respectively passed through the adaptive amplification unit to attenuate or amplify the amplitude of the 1PPS signal to the CMOS level, and then passed through the waveform shaping unit to eliminate the influence of the rising edge transition process of the 1PPS and reduce the rising edge time, so that the rising edge time is less than 2ns. The two 1PPS signals after shaping are sent to the FPGA-based time-to-digital conversion unit, the two time intervals are converted into digital count values, and then the count values are sent to the data processing unit to calculate the time difference of the two 1PPS signals according to the count frequency. Finally, the time difference 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.

[0007] Further, the device further comprises a multi-channel support module, which can simultaneously measure the 1PPS time difference from multiple GNSS systems (such as GPS, Beidou, GLONASS and Galileo);

[0008] Further, the device further comprises a sliding window filter and Kalman filter, which are used for smoothing and dynamically modeling and predicting the time difference sequence;

[0009] Further, the device further comprises a RINEX format processing module, which automatically extracts the pseudorange observation value, performs error correction and outputs the compatible format;

[0010] Further, the device further comprises an API interface or serial communication module, which is used for real-time communication with the GNSS receiver or the data processing system;

[0011] Further, the device further comprises an error source analysis module, which distinguishes whether the error is caused by the receiver local oscillator drift, the external clock instability or the satellite signal propagation model deviation.

[0012] The application also comprises a time transfer type receiver clock dynamic compensation method, which comprises an external clock, a GNSS receiver and the time transfer type receiver clock dynamic compensation device. 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 the time transfer type receiver clock dynamic compensation device. The GNSS receiver generates a 1PPS signal by using the 10MHz signal after receiving the 10MHz signal. Meanwhile, the GNSS receiver locks a satellite and performs pseudorange measurement by using the 1PPS, thereby generating an original pseudorange observation. The original pseudorange observation is sent to the time transfer type receiver clock dynamic compensation device. The time transfer type receiver clock dynamic compensation device receives the 1PPS signal generated by the GNSS receiver and the 1PPS signal of the external clock, measures the time interval At(t) of the two 1PPS signals, and subtracts At(t) from the original pseudorange observation c. Finally, the compensated pseudorange value is stored as RINEX format data.

[0013] Further, the time transfer type receiver clock dynamic compensation method further comprises enabling a dynamic filtering function, predicting the time difference trend by a sliding window filter or a Kalman filter, and dynamically estimating the future compensation amount.

[0014] Further, the time transfer type receiver clock dynamic compensation method further comprises synchronously outputting the compensated data to a backend data processing system or a GNSS positioning solution system through an API or a serial port.

[0015] Through the above technical solution, the application can achieve the following beneficial effects: the measurement error introduced by the 1PPS time difference can be significantly reduced; a high-precision TDC module is introduced, and nanosecond-level time resolution is realized based on FPGA, thereby improving the synchronization accuracy; multi-system GNSS and multi-band extension are supported, and the application is suitable for complex navigation environments; the sliding window and filtering algorithm are combined to dynamically predict and fit the time difference trend, thereby improving the robustness; the output conforms to the standard format, is compatible with the existing RINEX data solution system, and is convenient for engineering application; an error source identification mechanism is added, which is helpful for users to optimize system configuration and compensation strategy; the application can be extended to an embedded module, which is suitable for scenarios such as unmanned aerial vehicles, measurement equipment and time service base stations, and realizes low-cost integrated application. By constructing a closed loop link of time difference measurement-error conversion-pseudorange compensation-format storage, the measurement accuracy and synchronization performance of the GNSS receiver are effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 FIG. 1 is a schematic diagram of a time transfer type receiver clock dynamic compensation device;

[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 2The shown. Including external clock, GNSS receiver and time transfer type receiver clock dynamic compensation device. External clock generates 10MHz frequency signal and time signal 1PPS, wherein the 10MHz signal provides frequency reference for GNSS receiver and time transfer type receiver clock dynamic compensation device, GNSS receiver receives 10MHz signal, uses the 10MHz signal to generate 1PPS signal, at the same time GNSS receiver locks satellite and uses the 1PPS to measure pseudorange, generates original observation, sends the original observation to time transfer type receiver clock dynamic compensation device, time transfer type receiver clock dynamic compensation device receives 1PPS signal generated by GNSS receiver and 1PPS signal of external clock, measures time interval Δt(t) of two 1PPS signals, which is a quantity changing with time, i.e. time difference value to be compensated. Since the original observation generated by GNSS receiver is RINEX format data when stored, the value of the data is pseudorange, i.e. the distance from the phase center of the receiver antenna to the GNSS satellite measured by the pseudo-random code, which contains the distance change introduced by Δt(t), therefore, the pseudorange value needs to be subtracted Δt(t) c. Finally, the compensated pseudorange value is stored as RINEX format data.

[0023] Further, dynamic filtering function can also be enabled, and the time difference trend is predicted by sliding window filter or Kalman filter to dynamically estimate the future compensation amount;

[0024] Further, the compensated data can be output to the backend data processing system or GNSS positioning solution system through API or serial port synchronization.

[0025] The time transfer type receiver clock dynamic compensation method of the embodiment can be performed according to the following steps:

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

[0027] (2) Connect the 1PPS output by the GNSS receiver and the 1PPS output by the external clock to the time transfer type 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 type receiver clock dynamic compensation device for transmission of original observation;

[0029] (4) Start the device, set the sampling interval to 1s, i.e. measure a time difference data Δt(t) every 1s, and the GNSS receiver generates a set of pseudorange values every 1s, which contains pseudorange values of different GNSS satellite systems and different frequency points. Then, the distance amount to be compensated is obtained by multiplying the time difference data Δt(t) by the speed of light c, and then subtracting Δt(t) from the set of pseudorange values measured at the same time c, and finally the compensated pseudorange values are stored as RINEX format data.

[0030] In this embodiment, actual verification tests are also carried out. The GNSS receiver embedded with the time transfer type receiver clock dynamic compensation device is used to transfer the atomic time scale UTC(NIM) of the National Metrology Reference of China Metrology Science and Technology Institute to the Guizhou Metrology and Test Institute, so as to realize remote time comparison. The specific mode is as shown in Figure 3 .

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

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

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

[0034] (4) Convert the RINEX format data generated by the two GNSS receivers into CGGTTS files by using the software R2CGGTTS recommended by the International Bureau, and then subtract them to obtain the time difference between the time and frequency source of Guizhou Metrology and Test Institute and the UTC(NIM) of China Metrology Science and Technology Institute. The comparison result is as shown in Figure 4 . The average value of the comparison result is 0.43ns, and the standard deviation is 0.89ns, which eliminates the dynamic error introduced due to different initial time synchronization.

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 a 1PPS signal generated by a GNSS receiver is taken as a START signal, a 1PPS of an external clock is taken as a STOP signal, the amplitudes of the 1PPS signals are attenuated or amplified to 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 so that the rising edge time is less than 2ns, the two 1PPS signals after shaping 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.

2. A time transfer receiver clock dynamic compensation apparatus as claimed in claim 1, the apparatus further comprising: A multi-channel support module can measure the 1PPS time difference from multiple GNSS systems at the same time.

3. A time transfer receiver clock dynamic compensation apparatus as claimed in claim 1, said apparatus further comprising: A sliding window filter and Kalman filter are used for smoothing and dynamic modeling and prediction of the time difference sequence.

4. The time transfer receiver clock dynamic compensation apparatus of claim 1, further comprising: A RINEX format processing module automatically extracts the pseudorange observation value, corrects the error and outputs the compatible format.

5. The apparatus of claim 1, further comprising: An API interface or serial communication module is used for real-time communication with the GNSS receiver or data processing system.

6. A time transfer receiver clock dynamic compensation apparatus as claimed in claim 1, said apparatus further comprising: An error source analysis module distinguishes whether the error is caused by the receiver local oscillator drift, external clock instability or satellite signal propagation model deviation.

7. A time transfer receiver clock dynamic compensation method based on the time transfer receiver clock dynamic compensation device of any one of claims 1-6, 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 to generate the original pseudorange observation, which is stored as RINEX format data; (3) The original pseudorange observation is 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 of the external clock, measures the time interval Δt(t) of 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 pseudo-range, that is, the distance from the phase center of the receiver antenna to the GNSS satellite measured by the pseudo-random code. The pseudo-range value is subtracted by Δt(t)·c, and finally the compensated pseudo-range value is stored as RINEX format data.

8. The time transfer type receiver clock dynamic compensation method according to claim 7, 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.

9. The time transfer type receiver clock dynamic compensation method according to claim 7, 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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