Time service and time keeping method based on satellite-borne GNSS high-precision real-time orbit determination

Abstract

The invention provides a time service and time keeping method based on satellite-borne GNSS high-precision real-time orbit determination, which has the function of resolving the clock error and clock drift of a receiver in real time, and can perform time model correction by using the clock error and clock drift, thereby finally realizing high-precision time service and time keeping functions. The method is characterized in that rough time information is extracted from a message of a navigation signal; performing high-precision orbit determination through a dual-frequency carrier phase, and resolving a clock error and clock drift in real time; calculating the hardware time delay of the whole signal link by using a high-precision hardware time delay estimation technology; real-time frequency modulation and phase modulation are carried out by using clock drift and clock difference information, and a high-precision time service technology is realized; after a navigation satellite signal is interrupted, a local time model is maintained and PPS (pulse per second) is output by utilizing orbit extrapolation, clock error and clock drift information and a time model, so that a high-precision time keeping function is realized; fusion and advantage complementation of the constant-temperature crystal oscillator and the GNSS receiver are realized, and the cost of high-precision time service is reduced.

Description

Technical Field

[0001] The present invention relates to the field of measurement and testing technology, and in particular to a time service and time keeping method based on high-precision real-time orbit determination of a satellite-borne GNSS. Background Art

[0002] With the development of GNSS, satellite-borne GNSS receivers have become an effective way to determine the orbit and time of various satellites with high precision. They can provide satellites with all-day, all-weather, high-precision position and time information, and have been widely used. As the aerospace field has higher and higher requirements for satellite position and velocity accuracy, the corresponding various payload tasks have also higher and higher requirements for time accuracy. Not only must they have high-precision timing functions, but they must also have the ability to keep time under conditions of navigation signal interruption to ensure that various tasks can be completed in different scenarios or satellite attitude conditions.

[0003] At present, high-precision timing on satellites mainly relies on GNSS and onboard atomic clocks, which are usually composed of independent single machines without deep integration. Commonly used onboard navigation receivers only provide position, speed, time and PPS information, and do not output frequency reference signals. Ordinary temperature-compensated crystal oscillators and constant temperature crystal oscillators are difficult to meet the requirements of onboard equipment or payloads for frequency signal stability and accuracy. Usually, they must be equipped with onboard atomic clocks. In addition, the PPS accuracy output by ordinary navigation receivers is usually about 100ns, which can no longer meet the current satellite payload's requirements for high-precision detection accuracy. At the same time, onboard atomic clocks are large in size and weight, consume a lot of power, and are very expensive, which greatly limits their application and correspondingly limits the payload detection accuracy of low-cost small satellites.

[0004] General satellite-borne navigation receivers usually use pseudo-range observations for positioning and orbit determination. The calculated position and velocity have low accuracy, and information such as clock error and clock drift cannot form a feedback loop for correcting PPS delay, resulting in low timing accuracy and large error fluctuations. At the same time, they also do not have high-precision phase-locking function. Even if they can output frequency reference signals, the accuracy and stability of the frequency reference signals are poor due to the limitations of the characteristics of the crystal oscillator itself.

[0005] To this end, it is necessary to improve the timing and timekeeping methods of GNSS receivers, integrate navigation and time and frequency into an integrated design, use high-precision orbit determination information to correct the frequency signal of ordinary constant temperature crystal oscillators through the DDS chip, and output high-precision PPS signals and high-stability frequency reference signals to meet the timing and timekeeping requirements of payloads and other satellite-borne equipment. Summary of the invention

[0006] The present invention is to solve the problem that time service and time keeping cannot be synchronized, and provides a time service and time keeping method based on high-precision real-time orbit determination of satellite-borne GNSS. It uses dual-frequency carrier phase observation values, combined with satellite dynamics models and constraint strategies, and a robust Kalman filter to achieve high-precision orbit determination and output position, speed, clock error and clock drift information. On this basis, high-precision clock error estimation technology and high-precision hardware delay correction technology are used to complete the high-precision time and frequency correction function, and realize the time service and time keeping method based on GNSS high-precision real-time orbit determination. The implementation method of the present invention has the function of real-time calculation of receiver clock error and clock drift, and can use clock error and clock drift to correct the time model, and finally realize high-precision time service and time keeping functions. Its important features are to extract rough time information from the navigation signal message; perform high-precision orbit determination through dual-frequency carrier phase, and solve clock error and clock drift in real time; use high-precision hardware delay estimation technology to calculate the hardware delay of the entire signal link; use clock drift and clock error information to perform real-time frequency and phase modulation to achieve high-precision timing technology; after the navigation satellite signal is interrupted, use orbit extrapolation and clock error and clock drift information and time model to maintain the local time model and output PPS (pulse per second) to achieve high-precision timekeeping function; realize the integration and complementary advantages of constant temperature crystal oscillators and GNSS receivers, and reduce the cost of high-precision timing.

[0007] The present invention provides a time service and time keeping method based on high-precision real-time orbit determination of satellite-borne GNSS, comprising the following steps:

[0008] S1. The onboard GNSS receiver filters, amplifies, down-converts and samples the received RF signal and then outputs it to the baseband signal processing module of the timing and timekeeping system. The baseband signal processing module captures, tracks and demodulates the message / observation of the signal and extracts the rough time information from the message of the navigation signal;

[0009] S2. After the onboard GNSS receiver is positioned, the navigation information processing module of the timing system performs carrier phase cycle slip detection, performs real-time orbit determination by filtering and resolving pseudo ambiguity, and reversely calculates clock error and clock drift in real time.

[0010] S3, the system control module of the timekeeping system calculates the hardware delay of the entire signal link and pre-stores it in the parameters of the onboard GNSS receiver, which can be extracted and corrected in real time;

[0011] S4, the frequency phase-locked unit of the timekeeping system corrects the frequency signal of the constant temperature crystal oscillator through the DDS chip of the frequency correction unit to output a frequency reference signal, and the baseband signal processing module outputs a PPS signal according to the frequency reference signal;

[0012] The system control module uses the clock difference information to perform whole-second phase modulation. When it is not in external clock mode, it uses the clock drift information to perform DDS frequency modulation and extracts the hardware delay for compensation and elimination, so that the frequency reference signal and the PPS signal are of the same source and in phase.

[0013] When the clock drift is less than the set threshold, the time model converges, the phase modulation stops, and only the clock drift information is used for frequency modulation;

[0014] When the clock drift information exceeds the set threshold, the clock drift information is first used for frequency modulation, and after the time model converges, the clock error is used for phase modulation.

[0015] When the navigation satellite signal is interrupted, the process goes to step S5;

[0016] S5. Using the orbit extrapolated position and velocity information, clock error, clock drift, time information of the interruption moment and the frequency signal of the constant temperature crystal oscillator, the local time model is maintained and the PPS and frequency signals are output. A timing and punctuality method based on high-precision real-time orbit determination of satellite-borne GNSS is completed.

[0017] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention is, as a preferred mode, in step S1, the default parameters of the baseband signal processing module are initialized, and it is determined whether there is time information in FLASH. If yes, it is initialized, and if not, it returns until there is time information in FLASH;

[0018] After initialization, determine whether the message correction has been passed. If not, use the navigation message bit information to perform a rough calibration of the time model, and continue to determine whether the message verification has been passed; if yes, directly determine whether the message verification has been passed;

[0019] If the message passes the telegram verification, it is determined whether the code time correction has been made. If the message fails the telegram verification, it is returned to determine whether the message correction has been made.

[0020] If the code time correction has not been performed, the time model is precisely calibrated by tracking the code phase of the loop, and then the orbit determination is judged to be converged; if the code time correction has been performed, the orbit determination is directly judged to be converged;

[0021] If the orbit determination converges, go to step S2 and use the orbit determination result to reversely calculate the clock drift and clock error information; if the orbit determination does not converge, determine whether the positioning is successful. If the positioning is successful, go to step S2 and calculate the clock error and clock drift information based on the least squares principle; if the positioning is unsuccessful, continue to perform the time model fine calibration.

[0022] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention, as a preferred embodiment, step S4 includes the following steps:

[0023] S41, the frequency phase-locked unit of the timekeeping system corrects the frequency signal of the constant temperature crystal oscillator through the DDS chip of the frequency correction unit to output a frequency reference signal, and the baseband signal processing module outputs a PPS signal according to the frequency reference signal;

[0024] The system control module uses the clock error information in the orbit determination information to adjust the clock count TIC inside the onboard GNSS receiver, so that the PPS signal generation time is aligned with the whole second of the navigation system time, completing the phase adjustment function;

[0025] S42, when the external clock mode is not in effect, the system control module uses the clock drift information to perform frequency modulation processing, corrects the frequency control word of the DDS chip, and assigns the frequency control word to the DDS chip through the FPGA;

[0026] S43, judging whether the adjustment of the clock source accuracy converges, if converged, stopping the phase adjustment operation, and using the orbit determination result to reversely calculate the clock error and clock drift information; if not converged, judging whether the positioning is successful, if successful, calculating the clock error and clock drift information based on the least squares principle, if unsuccessful, returning to step S42;

[0027] S44, during the operation of the onboard GNSS receiver, when the clock is stable within the threshold range and external factors change, frequency modulation is performed using the clock difference information without phase modulation to maintain the PPS signal output accuracy; when the clock source accuracy exceeds the set threshold, proceed to step S45;

[0028] S45, if the clock drift information exceeds the set threshold value, the clock drift information is first used for frequency modulation processing, and after convergence, the clock difference information is used for frequency modulation processing, and the process is repeated until the accuracy of the clock source reaches the set threshold value;

[0029] S46. After DDS frequency modulation processing, the frequency signal output by DA is filtered, amplified, phase-locked, etc. to obtain 10MHz and 62MHz frequency reference signals.

[0030] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention is, as a preferred embodiment, in step S41, the navigation system time is BDT or GPST;

[0031] In step S43, the method for determining whether the clock source accuracy adjustment has converged is: determining whether the clock drift value is less than a set threshold, if so, the clock source accuracy adjustment has converged;

[0032] In step S44, the external factor changes include changes in navigation satellites and changes in ambient temperature.

[0033] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention is, as a preferred embodiment, in step S43, the threshold value is 0.3m / s or 0.5m / s.

[0034] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention is, as a preferred embodiment, in step S2, a UD decomposition filtering algorithm is used for data processing, and an extended Kalman filter is used in combination with an orbital dynamics model and an observation model to filter and resolve pseudo ambiguity for real-time orbit determination.

[0035] The present invention discloses a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS. As a preferred embodiment, the timing and timekeeping system includes a baseband signal processing module, a navigation information processing module, and a system control module connected in sequence, a constant temperature crystal oscillator, a frequency correction unit, and a frequency phase-locked unit connected in sequence, the constant temperature crystal oscillator outputs a clock signal to the frequency correction unit, the system control module is connected to a DDS chip of the frequency correction unit, the output end of the frequency phase-locked unit is connected to a baseband signal processing module, and the baseband signal processing module receives 10MHz and 62MHz signals of the frequency phase-locked unit and outputs a PPS signal.

[0036] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention is, as a preferred embodiment, the frequency correction unit includes a connected DDS chip and a first filter, and the constant temperature crystal oscillator outputs a 10MHz clock signal to the DDS chip;

[0037] The frequency phase-locked unit includes a first-stage amplifier and a first splitter connected in sequence, a first phase-locked loop and a second phase-locked loop respectively connected to the output end of the first splitter, a second filter connected in sequence to the first phase-locked loop, a second-stage amplifier, a second splitter, and a third filter and a third-stage amplifier connected in sequence to the second phase-locked loop;

[0038] The output end of the first filter is connected to the first-stage amplifier, the second splitter outputs two 10MHz signals, one of which is output to the baseband signal processing module and the other is used as frequency reference information, and the third-stage amplifier outputs a 62MHz signal to the baseband signal processing module.

[0039] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention, as a preferred embodiment, the evaluation method of the timing and timekeeping system comprises the following steps:

[0040] SⅠ. Input the navigation signal into the GNSS receiver, input the PPS signal into the oscilloscope, input the 10MHz frequency reference information into the frequency measuring instrument, and save the positioning, orbit determination and time information after the GNSS receiver has determined the orbit and converged;

[0041] SⅡ, select the data file, and make a difference between the trajectory in the satellite navigation signal simulator and the positioning and orbit determination data output by the GNSS receiver to obtain the accuracy analysis result of positioning and orbit determination;

[0042] SⅢ, set the two channels of the oscilloscope, turn on the persistence mode, observe the PPS output by the GNSS receiver and the PPS output by the signal simulator through the interface, and compare them to obtain the timing accuracy;

[0043] SIV. Disconnect the navigation signal, start the orbit determination extrapolation mode of the GNSS receiver, wait for the first predetermined time, and observe the drift of the PPS of the GNSS receiver to obtain the timing accuracy;

[0044] SⅤ. Restore the navigation signal, wait for the GNSS receiver to converge on orbit determination, start the frequency measuring instrument, wait for a second predetermined time, and obtain the accuracy of the frequency reference signal through the interface of the frequency measuring instrument.

[0045] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention is, as a preferred embodiment, in step SIV, the first predetermined time is 30 minutes.

[0046] The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS described in the present invention is, as a preferred embodiment, in step SⅤ, the second predetermined time is 60 minutes.

[0047] The present invention has the following advantages:

[0048] (1) This method integrates navigation and time-frequency into an integrated design, realizing the integration of navigation and time-frequency functions. The high-precision orbit determination technology is used to correct the frequency signal of the ordinary constant temperature crystal oscillator through the DDS chip. It not only outputs positioning, orbit determination, orbit extrapolation and other information, but also outputs high-accuracy and high-stability PPS signals and frequency reference signals.

[0049] (2) This method uses the ionospheric combined residual method and the MW combined residual method to detect carrier phase cycle slips, and uses the UD decomposition filter algorithm for data processing to achieve a robust extended Kalman filter design. Combined with the orbital dynamics model and the observation model, the pseudo ambiguity is filtered and resolved, and finally a high-precision real-time orbit determination based on the GNSS dual-frequency carrier phase is achieved. The position accuracy of the GNSS receiver positioning is better than 10m, and the velocity accuracy is better than 0.1m / s; after the orbit determination converges, the real-time position accuracy is better than 0.5m, and the velocity accuracy is better than 0.002m / s. Both the position and velocity accuracy can be improved by more than 10 times;

[0050] (3) This method relies on the frequency reference unit module of the satellite receiver to process the clock signal of the constant temperature crystal oscillator and make corrections based on the real-time processing frequency deviation information; based on the frequency signal, the phase of the PPS is adjusted to compensate and eliminate the link delay, and the two are made co-source and co-phase. The accuracy and stability of the frequency reference signal before correction is usually 10 -7 ~10 -8 , after correction, can reach 10 -11 ~10 -12 ,The performance indicators have been improved by about 3 to 4 orders of magnitude;

[0051] (4) This method studies and proposes a method for estimating hardware delay errors in real time on orbit and based on ground post-processing, which greatly reduces the impact of hardware delay errors on PPS accuracy. At the same time, the frequency and phase modulation of the clock drift and clock error information obtained from orbit determination can further improve the stability and accuracy of the PPS signal and frequency reference signal. The uncorrected PPS accuracy is usually a few hundred ns, but after correction, it can be better than 10ns, which is more than ten times the accuracy. When using a constant temperature crystal oscillator alone, the 30-minute timekeeping accuracy is usually about 20us to 200us. After calibration with GNSS, the accuracy can be better than 1us. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a flow chart of a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS;

[0053] Figure 2 A schematic diagram of the timing and timekeeping system structure of a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS;

[0054] Figure 3a A schematic diagram of the positioning error of a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS;

[0055] Figure 3b A schematic diagram of positioning velocity error of a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS;

[0056] Figure 3c A schematic diagram of orbit determination position error of a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS;

[0057] Figure 3d A schematic diagram of orbit determination velocity error of a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS;

[0058] Figure 4 A schematic diagram of the accuracy measurement results of a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS;

[0059] Figure 5 This is a schematic diagram of the frequency signal accuracy measurement results of a timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS.

[0060] Reference numerals:

[0061] 1. Baseband signal processing module; 2. Navigation information processing module; 3. System control module; 4. Frequency phase-locked unit; 41. First stage amplifier; 42. First splitter; 43. First phase-locked loop; 44. Second phase-locked loop; 45. Second filter; 46. Second stage amplifier; 47. Second splitter; 48. Third filter; 49. Third stage amplifier; 5. Frequency correction unit; 6. Constant temperature crystal oscillator. DETAILED DESCRIPTION

[0062] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0063] Example 1

[0064] like Figures 1-2 As shown, a timing and punctuality method based on high-precision real-time orbit determination of satellite-borne GNSS, the satellite-borne GNSS receiver includes a baseband signal processing module 1, a navigation information processing module 2, a system control module 3, a frequency phase-locking unit 4, a frequency correction unit 5, a clock module 6 (constant temperature crystal oscillator), a power supply module, etc. Figure 2 shown.

[0065] The frequency phase-locked unit 4 includes a first-stage amplifier 41 and a first splitter 42 connected in sequence, a first phase-locked loop 43 and a second phase-locked loop 44 respectively connected to the output end of the first splitter 42, a second filter 45, a second-stage amplifier 46, a second splitter 47 connected in sequence to the first phase-locked loop 43, and a third filter 48 and a third-stage amplifier 49 connected in sequence to the second phase-locked loop 44;

[0066] The output end of the first filter is connected to the first stage amplifier 41 , the second splitter 47 outputs two 10 MHz signals, one of which is output to the baseband signal processing module 1 and the other is used as frequency reference information, and the third stage amplifier 49 outputs a 62 MHz signal to the baseband signal processing module 1 .

[0067] The present invention is to extract rough time information from the telegram of the navigation signal; to perform high-precision orbit determination through the dual-frequency carrier phase, and to solve the clock error and clock drift in real time; to calculate the hardware delay of the entire signal link by using the high-precision hardware delay estimation technology; to perform real-time frequency and phase modulation by using the clock drift and clock error information, and to realize the high-precision time service technology; after the navigation satellite signal is interrupted, the orbit extrapolation and the clock error and clock drift information and the time model can be used to maintain the local time model and output the PPS and frequency signal, so as to realize the high-precision timekeeping function.

[0068] This is achieved through the following steps:

[0069] S1: After filtering, amplifying, down-converting and sampling the RF signal, the satellite-borne GNSS receiver enters the baseband signal processing module 1 to capture, track and demodulate the signal and extract the rough time information from the navigation signal message;

[0070] S2: After the GNSS receiver is positioned, it performs carrier phase cycle slip detection, uses the UD decomposition filter algorithm for data processing, and uses a robust extended Kalman filter in combination with the orbit dynamics model and observation model to filter and resolve pseudo ambiguities, achieving high-precision real-time orbit determination based on the GNSS dual-frequency carrier phase, and real-time inverse calculation of clock error and clock drift;

[0071] S3: Use high-precision hardware delay estimation technology to calculate the hardware delay of the entire signal link, including channel link delay, temperature-related relative delay, and hardware delay related to device aging, which are pre-stored in the receiver parameters and extracted and corrected in real time;

[0072] S4: Use clock drift and clock difference information to perform real-time frequency and phase modulation to achieve high-precision timing technology and process reference Figure 1 , the specific steps are as follows:

[0073] S41: Use the clock error information in the orbit determination information to adjust the clock count TIC inside the receiver, so that the PPS generation time is aligned with the navigation system time (BDT or GPST) in full seconds, complete the phase adjustment function, and ensure the PPS output accuracy;

[0074] S42: using the clock drift information to perform frequency modulation processing to improve the accuracy of the local clock source; that is, using the clock drift information to correct the frequency control word of the DDS chip, assigning the frequency control word to the DDS chip through the FPGA, and improving the accuracy of the frequency reference signal output by the DDS;

[0075] S43: After the clock source accuracy adjustment converges, that is, when the calculated clock drift value is less than the set threshold (typical value is 0.3m / s or 0.5m / s), the phase adjustment operation is stopped, so that the phase stability among PPS, 10MHz and 62MHz can be ensured;

[0076] S44: During the operation of the receiver, after the clock is stable, when external factors (such as navigation satellites, ambient temperature, etc.) change, the clock drift information is used to perform frequency modulation without phase modulation to maintain the PPS output accuracy;

[0077] S45: If the accuracy of the clock source exceeds the set threshold, that is, the corresponding clock drift information exceeds the set threshold value, the clock drift information is first used for frequency modulation processing, and after convergence, the clock error information is used for phase modulation processing. In this way, repeated iterations can ensure the phase stability among PPS, 10MHz, and 62MHz, and can also ensure the PPS output accuracy;

[0078] S46: After DDS frequency modulation, the frequency signal output by DA is filtered, amplified, phase-locked, etc. to obtain high-accuracy and high-stability 10MHz and 62MHz frequency reference signals;

[0079] S5: If the navigation satellite signal is interrupted, the orbit extrapolated position and velocity information, clock error and drift information, time information of the interruption moment and the frequency signal of the constant temperature crystal oscillator can be used to maintain the local time model and output the PPS and frequency signal to achieve high-precision timekeeping function.

[0080] The present invention is further described below with specific numerical values. Taking GPS and BDS systems as examples, the onboard GNSS receiver is in dynamic mode, the GNSS signal simulator is set to dual-system dual-frequency mode (GPS L1, L2 and BDS B1I, B3I), the orbit altitude of the user receiver is 600km, the GNSS receiver and the test instrument are correctly connected, and the method provided by the present invention is used to evaluate the accuracy of orbit determination, timing and timekeeping. The specific steps are as follows:

[0081] Step I: Input the navigation signal into the GNSS receiver, input the PPS signal into the oscilloscope, input the 10MHz frequency reference signal into the frequency measuring instrument, and save the positioning, orbit determination and time information after the receiver has determined the orbit and converged;

[0082] Step II: Select the data file and make a difference between the trajectory in the satellite navigation signal simulator and the positioning and orbit determination data output by the GNSS receiver to obtain the accuracy analysis results of positioning and orbit determination, such as Figure 3a to 3d As shown;

[0083] Step III: Set the two channels of the oscilloscope, turn on the persistence mode, observe the PPS output by the receiver and the PPS output by the signal simulator through the interface, and compare the two to get the timing accuracy;

[0084] Step IV: Disconnect the navigation signal, start the orbit determination extrapolation mode of the GNSS receiver, wait for a predetermined time (for example, 30 minutes), and observe the drift of the receiver PPS to obtain the timing accuracy, such as Figure 4 As shown;

[0085] Step V: Restore the navigation signal, wait for the GNSS receiver to converge, start the frequency measurement instrument, wait for a predetermined time (e.g. 60 minutes), and obtain the accuracy of the frequency reference signal through the interface of the frequency measurement instrument, such as Figure 5 shown.

[0086] From the example Figure 3a to 3d As can be seen from Figures 4 and 5, the position and velocity accuracy of the satellite-borne high-precision GNSS receiver are 3.8m and 0.046m / s, respectively, and the position and velocity accuracy of orbit determination are 0.374m and 0.001m / s, respectively; the timing accuracy based on the satellite-borne GNSS high-precision real-time orbit determination is about 10ns, the 30-minute timekeeping accuracy is about 0.8us, and the accuracy of the frequency reference signal can reach 10 -11 ~10 -12 .

[0087] The present invention utilizes dual-frequency carrier phase observations, combined with satellite dynamics models and constraint strategies, and through a robust Kalman filter, achieves high-precision orbit determination and outputs position, velocity, clock error and clock drift information. On this basis, high-precision clock error estimation technology and high-precision hardware delay correction technology are used to complete the high-precision time and frequency correction function, and realize the timing and timekeeping method based on GNSS high-precision real-time orbit determination. The implementation method of the present invention has the function of real-time calculation of receiver clock error and clock drift, and can use clock error and clock drift to correct the time model, and finally achieve high-precision timing and timekeeping functions.

[0088] The present invention extracts rough time information from the telegram of the navigation signal, performs high-precision orbit determination through the dual-frequency carrier phase, and solves the clock error and clock drift in real time; uses the high-precision hardware delay estimation technology to calculate the hardware delay of the entire signal link and provide PPS delay correction information; uses the clock drift and clock error information to perform real-time frequency and phase modulation to achieve high-precision timing technology; when the navigation satellite signal is interrupted, uses orbit extrapolation and clock error and clock drift information and a time model to maintain the local time model and output PPS (pulse per second) to achieve a high-precision timekeeping function; realizes the integration and complementary advantages of a constant temperature crystal oscillator and a GNSS receiver, and reduces the cost of high-precision timing.

[0089] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS, characterized in that: The following steps are involved: S1, the satellite-borne GNSS receiver filters, amplifies, down-converts and samples the received radio frequency signal and then outputs it to the baseband signal processing module (1) of the timing and time keeping system. The baseband signal processing module (1) captures, tracks and demodulates the message / observation quantity of the signal and extracts the rough time information from the message of the navigation signal; S2, after the onboard GNSS receiver is positioned, the navigation information processing module (2) of the timing system performs carrier phase cycle slip detection, performs real-time orbit determination by filtering and resolving pseudo ambiguity, and performs real-time inverse calculation of clock error and clock drift; S3, the system control module (3) of the timekeeping system calculates the hardware delay of the entire signal link and pre-stores it in the parameters of the onboard GNSS receiver, which can be extracted and corrected in real time; S4, the frequency phase-locked unit (4) of the timekeeping system corrects the frequency signal of the constant temperature crystal oscillator (6) through the DDS chip of the frequency correction unit (5) to output a frequency reference signal, and the baseband signal processing (1) module outputs a PPS signal according to the frequency reference signal; The system control module (3) uses the clock difference information to perform whole second phase modulation processing, and when it is not in external clock mode, uses the clock drift information to perform DDS frequency modulation processing, and extracts the hardware delay to compensate and eliminate it, so that the frequency reference signal and the PPS signal are of the same source and in the same phase; When the clock drift is less than the set threshold, the time model converges, the phase modulation stops, and only the clock drift information is used for frequency modulation; When the clock drift information exceeds the set threshold, the clock drift information is first used for frequency modulation, and after the time model converges, the clock error is used for phase modulation. When the navigation satellite signal is interrupted, the process goes to step S5; S5. By utilizing the orbit extrapolated position and velocity information, clock error, clock drift, time information of the interruption moment and the frequency signal of the constant temperature crystal oscillator, the local time model is maintained and the PPS and frequency signal are output. A time synchronization and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS is completed.

2. The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 1, characterized in that: In step S1, the baseband signal processing module (1) initializes default parameters and determines whether there is time information in the FLASH. If yes, it initializes. If not, it returns until there is time information in the FLASH. After initialization, determine whether the message correction has been passed. If not, use the navigation message bit information to perform a rough calibration of the time model and continue to determine whether the message verification has been passed; If yes, it is directly determined whether it is verified by telegram; If the message passes the telegram verification, it is determined whether the code time correction has been made. If the message fails the telegram verification, it is returned to determine whether the message correction has been made. If the code time correction has not been performed, the time model is precisely calibrated by tracking the code phase of the loop, and then the orbit determination is judged to be converged; if the code time correction has been performed, the orbit determination is directly judged to be converged; If the orbit determination converges, proceed to step S2 to reversely calculate the clock drift and clock error information using the orbit determination result; If the orbit determination fails to converge, it is determined whether the positioning is successful. If the positioning is successful, the process proceeds to step S2 to calculate the clock error and clock drift information based on the least squares principle. If the positioning is unsuccessful, continue with the time model fine calibration.

3. The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 1, characterized in that: Step S4 includes the following steps: S41, the frequency phase-locked unit (4) of the timekeeping system corrects the frequency signal of the constant temperature crystal oscillator (6) through the DDS chip of the frequency correction unit (5) and outputs the frequency reference signal, and the baseband signal processing (1) module outputs the PPS signal according to the frequency reference signal; The system control module (3) uses the clock error information in the orbit determination information to adjust the clock count TIC inside the onboard GNSS receiver, so that the PPS signal generation time is aligned with the whole second time of the navigation system time, thereby completing the phase adjustment function; S42, when the external clock mode is not in effect, the system control module (3) uses the clock drift information to perform frequency modulation processing, corrects the frequency control word of the DDS chip, and assigns the frequency control word to the DDS chip through the FPGA; S43, judging whether the adjustment of the clock source accuracy converges, if converged, stopping the phase adjustment operation, and using the orbit determination result to reversely calculate the clock error and clock drift information; if not converged, judging whether the positioning is successful, if successful, calculating the clock error and clock drift information based on the least squares principle, if unsuccessful, returning to step S42; S44, when the clock of the satellite-borne GNSS receiver is stable within the threshold range and external factors change, frequency modulation is performed using the clock difference information without phase modulation to maintain the PPS signal output accuracy; when the clock source accuracy exceeds the set threshold, proceed to step S45; S45, if the clock drift information exceeds the set threshold value, the clock drift information is first used for frequency modulation processing, and after convergence, the clock difference information is used for frequency modulation processing, and the process is repeated until the accuracy of the clock source reaches the set threshold value; S46. After DDS frequency modulation processing, the frequency signal output by DA is filtered, amplified, phase-locked, etc. to obtain 10MHz and 62MHz frequency reference signals.

4. The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 1, characterized in that: In step S41, the navigation system time is BDT or GPST; In step S43, the method for determining whether the clock source accuracy adjustment has converged is: determining whether the clock drift value is less than a set threshold, if so, the clock source accuracy adjustment has converged; In step S44, the external factor changes include changes in navigation satellites and changes in ambient temperature.

5. The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 4, characterized in that: In step S43, the threshold is 0.3 m / s or 0.5 m / s.

6. The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 1, characterized in that: In step S2, the UD decomposition filter algorithm is used for data processing, and the extended Kalman filter is used in combination with the orbit dynamics model and the observation model to filter and resolve the pseudo ambiguity for real-time orbit determination.

7. The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 1, characterized in that: The timing and time keeping system comprises the baseband signal processing module (1), the navigation information processing module (2), and the system control module (3) which are connected in sequence, the constant temperature crystal oscillator (6), the frequency correction unit (5), and the frequency phase locking unit (4) which are connected in sequence, the constant temperature crystal oscillator (6) outputs a clock signal to the frequency correction unit (5), the system control module (3) is connected to the DDS chip of the frequency correction unit (5), the output end of the frequency phase locking unit (4) is connected to the baseband signal processing module (1), and the baseband signal processing module (1) receives 10 MHz and 62 MHz signals of the frequency phase locking unit (4) and outputs a PPS signal.

8. The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 7, characterized in that: The frequency correction unit (5) comprises the connected DDS chip and the first filter, and the constant temperature crystal oscillator (6) outputs a 10 MHz clock signal to the DDS chip; The frequency phase-locked unit (4) comprises a first-stage amplifier (41) and a first splitter (42) connected in sequence, a first phase-locked loop (43) and a second phase-locked loop (44) respectively connected to the output end of the first splitter (42), a second filter (45), a second-stage amplifier (46), and a second splitter (47) connected in sequence to the first phase-locked loop (43), and a third filter (48) and a third-stage amplifier (49) connected in sequence to the second phase-locked loop (44); The output end of the first filter is connected to the first-stage amplifier (41); the second splitter (47) outputs two 10 MHz signals, one of which is output to the baseband signal processing module (1) and the other is used as frequency reference information; and the third-stage amplifier (49) outputs a 62 MHz signal to the baseband signal processing module (1).

9. The timing and timekeeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 1, characterized in that: The evaluation method of the timing and time keeping system comprises the following steps: SⅠ. Input the navigation signal into the GNSS receiver, input the PPS signal into the oscilloscope, input the 10 MHz frequency reference information into the frequency measuring instrument, and save the positioning orbit determination and time information after the GNSS receiver determines the orbit and converges; SII, selecting a data file, subtracting the trajectory in the satellite navigation signal simulator from the positioning and orbit determination data output by the GNSS receiver to obtain an accuracy analysis result of positioning and orbit determination; SⅢ, set the two channels of the oscilloscope, turn on the persistence mode, observe the PPS output by the GNSS receiver and the PPS output by the signal simulator through the interface, and compare them to obtain the timing accuracy; SIV. disconnecting the navigation signal, the GNSS receiver starts the orbit determination extrapolation mode, waits for a first predetermined time, and observes the drift of the PPS of the GNSS receiver to obtain the timing accuracy; SⅤ. Restore the navigation signal, and after the orbit determination of the GNSS receiver converges, start the frequency measuring instrument, wait for a second predetermined time, and obtain the accuracy of the frequency reference signal through the interface of the frequency measuring instrument.

10. The timing and time keeping method based on high-precision real-time orbit determination of satellite-borne GNSS according to claim 9, characterized in that: In step SIV, the first predetermined time is 30 minutes; in step SV, the second predetermined time is 60 minutes.

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