Common view time synchronization method and system based on CPT atomic clock

Abstract

The embodiment of the invention discloses a common-view time synchronization method and system based on a CPT atomic clock. The method comprises the following steps: acquiring a first pulse per second signal of a first CPT atomic clock, a second pulse per second signal of a first receiver and a first delay time signal, and obtaining a first deviation signal according to the first pulse per second signal, the second pulse per second signal and the first delay time signal; acquiring a third second pulse signal of a second CPT atomic clock, and a fourth second pulse signal and a second delay time signal of a second receiver of the slave station, and obtaining a second deviation signal according to the third second pulse signal, the fourth second pulse signal and the second delay time signal; calculating the time correction of the substation according to the first deviation signal and the second deviation signal; performing common view time synchronization on the substations according to the time correction amount; performing common-view time synchronization on the master station according to the first deviation signal; and performing frequency synchronization on the first CPT atomic clock and the second CPT atomic clock by using a three-state clock model Kalman filter.

Description

Technical Field

[0001] The present invention relates to the technical field of time service. More specifically, it relates to a common-view time synchronization method and system based on a CPT atomic clock. Background Art

[0002] At present, the common-view time synchronization technology is mainly used to solve the high-precision time synchronization between different locations. In many fields, such as aerospace, communication networks, power systems, etc., high requirements are placed on the time synchronization accuracy. Traditional time synchronization technologies may be interfered by many factors such as distance, transmission medium, environment, etc., resulting in time errors. The common-view time synchronization technology uses satellite signals (such as GPS or Beidou) as a common reference, and realizes time comparison by observing the same satellite signal at different locations simultaneously.

[0003] Traditional common-view time synchronization technologies use crystal oscillators as clock sources. Since crystal oscillators are vulnerable to environmental influences and it is difficult to maintain high accuracy and long-term stability, generally, a method of taming the crystal oscillator is adopted to achieve time synchronization. Taming the clock (such as a crystal oscillator) through common-view comparison is a common time-frequency traceability method, with mature technology and wide application in the market. However, the emerging coherent population trapping atomic clock (CPT) not only has the same low power consumption as a crystal oscillator, but also has higher long-term stability and taming accuracy, is not easily affected by the environment, and is more suitable for occasions that require high-precision clocks such as portable devices and meeting power grid synchronization. Summary of the Invention

[0004] The purpose of the present invention is to provide a common-view time synchronization method and system based on a CPT atomic clock to solve at least one of the problems existing in the prior art.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The first aspect of the present invention provides a common-view time synchronization method based on a CPT atomic clock, and the method includes:

[0007] Obtain the first second pulse signal of the first CPT atomic clock at the master station, the second second pulse signal of the first receiver at the master station, and the first delay time signal from the common-view satellite to the master station, and obtain a first deviation signal according to the first second pulse signal, the second second pulse signal, and the first delay time signal;

[0008] Obtain the third second pulse signal of the second CPT atomic clock at the slave station, the fourth second pulse signal of the second receiver at the slave station, and the second delay time signal from the common-view satellite to the slave station, and obtain a second deviation signal according to the third second pulse signal, the fourth second pulse signal, and the second delay time signal;

[0009] Calculate the time correction amount of the slave station according to the first deviation signal and the second deviation signal;

[0010] Perform common-view time synchronization on the slave station according to the time correction amount;

[0011] Perform common-view time synchronization on the master station according to the first deviation signal;

[0012] Perform frequency synchronization on the first CPT atomic clock and the second CPT atomic clock by using a three-state clock model Kalman filter.

[0013] Optionally, the calculation formula for obtaining the first deviation signal according to the first second pulse signal, the second second pulse signal, and the first delay time signal is:

[0014] T a = t a -(t outA + d a )

[0015] In the formula, T a is the first deviation signal; t a is the first second pulse signal; t outA is the second second pulse signal; d a is the first delay time signal.

[0016] Optionally, the calculation formula for obtaining the second deviation signal according to the third second pulse signal, the fourth second pulse signal, and the second delay time signal is:

[0017] T b = t b -(t outB + d b )

[0018] In the formula, T b is the second deviation signal; t b is the third second pulse signal; t outB is the fourth second pulse signal; d b is the second delay time signal.

[0019] Optionally, the calculation formula for calculating the time correction amount of the slave station according to the first deviation signal and the second deviation signal is:

[0020] T ab = T a - T b

[0021] In the formula, T ab is the time correction amount.

[0022] Optionally, calculating the time correction amount of the sub-station according to the first deviation signal and the second deviation signal includes:

[0023] Using the time of the i-th common-view satellite obtained by calculation as an intermediate quantity, where i is an integer greater than or equal to 1;

[0024] Calculating the time correction amount of the sub-station according to the first deviation signal, the second deviation signal and the intermediate quantity.

[0025] Optionally, the calculation formula for calculating the time correction amount of the sub-station according to the first deviation signal, the second deviation signal and the intermediate quantity is:

[0026] T ab = T a - T b = (T a - t svi ) - (T b - t svi )

[0027] In the formula, t svi is the intermediate quantity; T a - t svi is the difference between the first deviation signal and the intermediate quantity; T b - t svi is the difference between the second deviation signal and the intermediate quantity.

[0028] Optionally, the calculation formula for the difference between the first deviation signal and the intermediate quantity is:

[0029]

[0030] In the formula, T a - T outA is the time difference between the first second pulse signal and the second second pulse signal; is the hardware error of the second second pulse signal of the first receiver, is the first average time value calculated by the first receiver; is the difference between the first average time value calculated by the first receiver and the actual time of the i-th common-view satellite; t' svι - t svi is the clock error of the i-th common-view satellite calculated by the first receiver.

[0031] Optionally, the calculation formula for the difference between the second deviation signal and the intermediate quantity is:

[0032]

[0033] In the formula, T b - T outB is the time difference between the third second pulse signal and the fourth second pulse signal; Hardware error of the fourth second pulse signal for the second receiver Second average time value calculated for the second receiver Difference between the second average time value calculated for the second receiver and the actual time of the i-th common-view satellite; t′ svι -t svi Clock error of the i-th common-view satellite calculated by the second receiver. The clock error of the i-th common-view satellite calculated by the second receiver is equal to the clock error of the i-th common-view satellite calculated by the first receiver.

[0034] Optionally, the clock error of the i-th common-view satellite calculated by the first receiver includes: ionospheric delay error, tropospheric delay error, multipath effect error, and system synchronization accuracy error.

[0035] The second aspect of the present invention provides a common-view time synchronization system based on a CPT atomic clock, which includes:

[0036] A first data processing unit, configured to obtain a first second pulse signal of a first CPT atomic clock of a master station, a second second pulse signal of a first receiver of the master station, and a first delay time signal of a common-view satellite to the master station, and obtain a first deviation signal according to the first second pulse signal, the second second pulse signal, and the first delay time signal;

[0037] A second data processing unit, configured to obtain a third second pulse signal of a second CPT atomic clock of a slave station, a fourth second pulse signal of a second receiver of the slave station, and a second delay time signal of a common-view satellite to the slave station, and obtain a second deviation signal according to the third second pulse signal, the fourth second pulse signal, and the second delay time signal;

[0038] A third data processing unit, configured to calculate a time correction amount of a sub-station according to the first deviation signal and the second deviation signal;

[0039] A first time synchronization unit, configured to perform common-view time synchronization on the sub-station according to the time correction amount;

[0040] A second time synchronization unit, configured to perform common-view time synchronization on the master station according to the first deviation signal;

[0041] A frequency synchronization unit, configured to perform frequency synchronization on the first CPT atomic clock and the second CPT atomic clock by using a three-state clock model Kalman filter.

[0042] The beneficial effects of the present invention are as follows:

[0043] The technical solution of the present invention uses a CPT chip atomic clock, which not only has the same low power consumption as a crystal oscillator, but also has higher long-term stability and taming accuracy, is not easily affected by the environment, reduces the influence of the path delay of satellite signals during transmission on the time synchronization accuracy, and is more suitable for occasions such as portable devices and meeting the needs of high-precision clocks for power grid synchronization. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0045] Figure 1 The flowchart showing the common-view time synchronization method based on a CPT atomic clock provided by an embodiment of the present invention is shown.

[0046] Figure 2 The schematic diagram showing the common-view time synchronization method based on a CPT atomic clock provided by an embodiment of the present invention is shown.

[0047] Figure 3 The data processing flowchart showing the common-view time synchronization method based on a CPT atomic clock provided by an embodiment of the present invention is shown. SPECIFIC EMBODIMENTS

[0048] To more clearly illustrate the present invention, the following further describes the present invention with reference to the embodiments and the drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0049] In the prior art, the common-view time synchronization steps include: assuming that satellite receivers are respectively placed at two known positions A and B, and observing the same satellite j at the same moment;

[0050] Further, the master station common-view device obtains the standard time t at the first moment at position A A , and calculates the first deviation data Δt at position A according to the description of the standard time t A and the common-view data t j , that is, the clock difference between clock A and satellite j, Δt jA = t jA - t j - t A .

[0051] Further, the slave station common-view device obtains the standard time t at the first moment at position B B , and calculates the first deviation data Δt at position B according to the description of the standard time t B and the common-view data t j , that is, the clock difference between clock B and satellite j, Δt jB , Δt jB = tj -t B 。

[0052] Furthermore, data measured at the same moment at two locations are integrated together through the network or short message, and the difference between the two equations can be used to obtain the clock difference between Station A and Station B, that is:

[0053] Δt jA -Δt jB =(t j -t A )-(t j -t B )=t B -t A

[0054] Furthermore, obtain the clock difference between Station A and Station B from the common view device, adjust the local clock difference according to the preset value taming model, and synchronize with the time of the master common view device.

[0055] It can be seen that the prior art does not consider the influence of the path delay of satellite signals during transmission on the time synchronization accuracy in practical applications.

[0056] In view of this, an embodiment of the present invention provides a common view time synchronization method based on a CPT atomic clock. As Figure 1 shown, the method includes: obtaining the first second pulse signal of the first CPT atomic clock of the master station, the second second pulse signal of the first receiver of the master station, and the first delay time signal from the common view satellite to the master station, and obtaining a first deviation signal according to the first second pulse signal, the second second pulse signal, and the first delay time signal; obtaining the third second pulse signal of the second CPT atomic clock of the slave station, the fourth second pulse signal of the second receiver of the slave station, and the second delay time signal from the common view satellite to the slave station, and obtaining a second deviation signal according to the third second pulse signal, the fourth second pulse signal, and the second delay time signal; calculating the time correction amount of the sub-station according to the first deviation signal and the second deviation signal; performing common view time synchronization on the sub-station according to the time correction amount; performing common view time synchronization on the master station according to the first deviation signal; and performing frequency synchronization on the first CPT atomic clock and the second CPT atomic clock by using a three-state clock model Kalman filter.

[0057] In a specific example, the CPT chip atomic clock is a low-power and high-precision clock. The CPT atomic clock is tamed by the GNSS signal to ensure the frequency accuracy of the CPT atomic clock. By performing common view observations on navigation satellites by the master common view device and the slave common view device, the original observation data at the same moment are respectively obtained to calculate the clock difference data between the reference source of the common view device and each satellite, and the clock difference comparison results calculated at the two locations are used to correct the output signal of the slave common view device to synchronize to the reference source of the master common view device, ensuring the synchronization accuracy of the signals at the two locations.

[0058] In this embodiment, the CPT chip atomic clock is used, which not only has the same low power consumption as the crystal oscillator, but also has higher long-term stability and taming accuracy, is not easily affected by the environment, reduces the influence of the path delay of satellite signals during transmission on the time synchronization accuracy, and is more suitable for occasions such as portable devices and meeting the needs of high-precision clocks for power grid synchronization.

[0059] In a possible implementation manner, the calculation formula for obtaining the first deviation signal based on the first second pulse signal, the second second pulse signal, and the first delay time signal is:

[0060] T a = t a -(t outA + d a )

[0061] In the formula, T a is the first deviation signal; t a is the first second pulse signal; t outA is the second second pulse signal; d a is the first delay time signal.

[0062] In a possible implementation manner, the calculation formula for obtaining the second deviation signal based on the third second pulse signal, the fourth second pulse signal, and the second delay time signal is:

[0063] T b = t b -(t outB + d b )

[0064] In the formula, T b is the second deviation signal; t b is the third second pulse signal; t outB is the fourth second pulse signal; d b is the second delay time signal.

[0065] In a possible implementation manner, the calculation formula for calculating the time correction amount of the sub-station based on the first deviation signal and the second deviation signal is:

[0066] T ab = T a - T b

[0067] In the formula, T ab is the time correction amount.

[0068] In a specific example, in practical applications, due to the path delay of satellite signals during transmission, the analysis of the common view principle is as follows:

[0069] Further, let the standard time of the first moment at location A be the first second pulse signal t a ; the standard time of the first moment at location B be the third second pulse signal t b ; the satellite time be the second second pulse signal t outA or the fourth second pulse signal t outB , and the second second pulse signal t outA is equal to the fourth second pulse signal t outB ; the path delay from the satellite to location A be the first delay time signal d a , and the path delay from the satellite to location B be the second delay time signal d b .

[0070] Further, the receivers at locations A and B receive the signals of the same satellite at the same moment, and send the second pulse representing the satellite time output by the receivers to the high-precision time interval measurement module, which is compared with the second pulse output by the local clock, and the time difference meter value between the receiver at location A and the same satellite is the first deviation signal T a , and the time difference meter value between the receiver at location B and the same satellite is the second deviation signal T b .

[0071] Further, T a =t a -(t outA +d a ), T b =t b -(t outB +d b ).

[0072] Further, the data of locations A and B are transmitted to the computers of each other through the communication network, where the first delay time signal d a and the second delay time signal d b can be obtained by calculating the satellite ephemeris.

[0073] Further, subtracting T a =t a -(t outA +d a ) and T b =t b -(t outB +d b ) can obtain the time difference between the two places, that is, the time correction amount T ab .

[0074] Further, T ab =T a -T b =(t a -t outA -da )-(t b -t outB -d b )

[0075] Furthermore, t outA =t outB , then there is T ab =T a -T b =(t a -t b )-(d a -d b ).

[0076] It can be seen that common view can eliminate the influence of the satellite clock and most of the path additional time delay effects, such as the effects of the ionosphere, troposphere, etc.

[0077] Furthermore, the frequency synchronization of the CPT atomic clock is completed based on the three-state clock model Kalman filter.

[0078] In a possible implementation, calculating the time correction amount of the sub-station according to the first deviation signal and the second deviation signal includes:

[0079] Using the moment of the i-th common view satellite obtained by calculation as an intermediate quantity, where i is an integer greater than or equal to 1; calculating the time correction amount of the sub-station according to the first deviation signal, the second deviation signal and the intermediate quantity.

[0080] In a possible implementation, the calculation formula for calculating the time correction amount of the sub-station according to the first deviation signal, the second deviation signal and the intermediate quantity is:

[0081] T ab =T a -T b =(T a -t svi )-(T b -t svi )

[0082] In the formula, t svi is the intermediate quantity; T a -t svi is the difference between the first deviation signal and the intermediate quantity; T b -t svi is the difference between the second deviation signal and the intermediate quantity.

[0083] In a possible implementation, the calculation formula for the difference between the first deviation signal and the intermediate quantity is:

[0084]

[0085] Wherein, T a -T outA is the time difference between the first one-second pulse signal and the second one-second pulse signal; is the hardware error of the second one-second pulse signal of the first receiver, is the first average time value calculated by the first receiver; is the difference between the first average time value calculated by the first receiver and the actual time of the i-th common-view satellite; t′ svl -t svi is the clock error of the i-th common-view satellite calculated by the first receiver.

[0086] In a possible implementation manner, the calculation formula for the difference between the second deviation signal and the intermediate quantity is:

[0087]

[0088] Wherein, T b -T outB is the time difference between the third one-second pulse signal and the fourth one-second pulse signal; is the hardware error of the fourth one-second pulse signal of the second receiver, is the second average time value calculated by the second receiver; is the difference between the second average time value calculated by the second receiver and the actual time of the i-th common-view satellite; t′ svι -t svi is the clock error of the i-th common-view satellite calculated by the second receiver, and the clock error of the i-th common-view satellite calculated by the second receiver is equal to the clock error of the i-th common-view satellite calculated by the first receiver.

[0089] In a specific example, the algorithm principle of Beidou multi-satellite common-view between places A and B is as Figure 2 shown, Figure 2 in which it is assumed that the satellites tracked by the receiver at place A are satellites numbered 1, 2, 3, 4, and 5; Figure 2 in which it is assumed that the satellites tracked by the receiver at place B are satellites numbered 3, 4, 5, and 6.

[0090] Furthermore, the satellites available for common-view between places A and B are satellites numbered 3, 4, and 5. The clock difference between the two places, that is, the time correction amount T ab =T a -T b is the quantity that needs to be solved and output by the common-view algorithm. The calculation method is as follows:

[0091] Furthermore, if the time t svi of the satellite numbered i calculated is used as the intermediate quantity, then there is:

[0092] T ab =Ta -T b = (T a -t svi ) - (T b -t svi )

[0093] Furthermore, after transforming this equation, at location A, we have:

[0094]

[0095] In the equation, T a -T outA is the time difference between the first-second pulse signal and the second-second pulse signal, that is, the time difference X between the 1PPS of the CPT atomic clock and the 1PPS of the receiver at location A, which can be directly measured; A ; is the hardware error of the second-second pulse signal of the first receiver, that is, the hardware error T of the 1PPS signal generated by the Beidou receiver, which can be calibrated in advance; xa ; is the first average time value calculated by the first receiver; is the difference between the first average time value calculated by the first receiver and the actual time of the i-th common-view satellite, that is, the difference between the average time of each effective Beidou satellite solved by the receiver and the satellite time of satellite number i, which can be obtained by calculating the carrier phase; t' svι -t svi is the clock error of the i-th common-view satellite calculated by the first receiver, that is, the clock error of satellite number i solved by the receiver.

[0096] Furthermore, at location B, we have:

[0097]

[0098] In the equation, T a -t svi and T b -t svi have similar meanings for each parameter.

[0099] Furthermore, is the average time value representing Beidou time calculated by the Beidou receiver at location A, is the average time value representing Beidou time calculated by the Beidou receiver at location B; T outA and T outB are the 1PPS pulse moments representing Beidou time actually output by the receiver at location A and the receiver at location B; T a and T b are the moments corresponding to the 1PPS pulse signals output by the CPT atomic clocks at location A and location B on the time axis respectively; t svi and t' svlThey are the time of the satellite numbered i calculated by the receiver and the actual time of the satellite numbered i respectively.

[0100] Furthermore, by measuring and calculating at two locations A and B, the clock differences between the described local CPT atomic clock and each satellite can be obtained. Then, the measurement and calculation results at the two locations are transmitted through the communication link, and the data at the two locations are subtracted to obtain:

[0101]

[0102] In summary, since the measurements at different locations are all referenced to the common satellite time t svi Therefore, through the mutual difference calculation, not only the magnitude transfer of the clock differences between the two locations is realized, but also the high-precision comparison of the clock differences between the two locations is realized. Due to the clock error t′ svl -t svi of the satellites of the receivers at the two locations is the same, the satellite common view method completely eliminates the satellite clock error. The clock error includes the mutual difference calculation of the ionospheric delay and the atmospheric delay at the two locations. Since the corrections at the two locations have a certain correlation, the delay errors due to the ionosphere and the atmosphere can be further reduced, and the common view synchronization accuracy can be improved. In addition, there are multiple Beidou satellites that can be in common view during the actual observation process. Therefore, it is necessary to average multiple common view results to obtain a more optimized measurement value, so as to achieve remote high-precision synchronization. In this embodiment, first, the clock differences of each satellite at the two locations are calculated, and then the average clock difference of all the common view satellites is calculated, which is the comparison result between the two locations.

[0103] In a specific example, the information table uploaded by the sub-station to the main station is shown in Table 1.

[0104] Table 1 Information table uploaded by the sub-station to the main station

[0105]

[0106]

[0107] In a specific example, the information table sent by the main station to the sub-station is shown in Table 2.

[0108] Table 2 Information table sent by the main station to the sub-station

[0109] Serial number Marker Number of bytes Description 1 Frame header 4 bytes Command number 2 Sub-station number 1 byte Sub-station number corrected by the master station 3 Clock difference correction amount 6 bytes Time difference correction value between the master station and the sub-station (unit: 0.1 ns) 4 Common-view satellite number 1×12 bytes Satellite numbers commonly viewed by the sub-station and the master station 5 Elevation angle of the common-view satellite 1×12 bytes Elevation angle of the common-view satellite at the sub-station 6 Status 1 byte Operating status of the sub-station 7 CK 1 byte Check byte 8 Frame tail 4 bytes Command number

[0110] In a specific example, in addition to calculating the error of the geometric distance from the satellite position to the receiver, according to the principle of multi-star common view of Beidou, where t′ svl -t sviThe error between the satellite time of the i-th satellite calculated by the receiver and the actual satellite time of the satellite numbered i is mainly affected by the ionospheric delay error and the tropospheric model mismatch. Therefore, the synchronization accuracy error of Beidou multi-satellite common view is mainly affected by the geometric time delay calculation error caused by the satellite ephemeris error, the ionospheric delay correction model error, the atmospheric delay correction model error, the multipath error caused by the receiving antenna, and the error caused by the device itself synchronization.

[0111] In a possible implementation, the clock error of the i-th common-view satellite calculated by the first receiver includes: ionospheric delay error, tropospheric delay error, multipath effect error, and system synchronization accuracy error.

[0112] In a specific example, the clock error also includes the geometric time delay calculation error. The geometric time delay is the geometric distance time delay from the satellite position to the ground station receiver position. To calculate the geometric time delay, the receiver position and the satellite position coordinates must be known. The receiver position can be obtained through accurate measurement, and the satellite position is calculated according to the satellite ephemeris. The satellite ephemeris is information describing the satellite's motion orbit, and a set of satellite ephemerides corresponds to the orbit parameters at a certain moment. The Beidou satellite ephemeris is divided into broadcast ephemeris and precise ephemeris. In this example, the broadcast ephemeris is used to calculate the satellite position.

[0113] Furthermore, the geometric time delay calculation error mainly includes two aspects: one is the error caused by the broadcast ephemeris, and the other is the error caused by the receiver position.

[0114] In a specific example, the clock error also includes the broadcast ephemeris error. Since the broadcast ephemeris is a predicted ephemeris and cannot fully reflect the magnitudes and variation laws of various perturbation factors acting on the satellite, there are errors in the predicted data. The root mean square error of the satellite position accuracy σR calculated therefrom is about 20m - 40m. The inter-station synchronization error caused thereby can be estimated by the following formula:

[0115]

[0116] In the formula, σ eph is the mean square error caused by the broadcast ephemeris; d is the inter-station distance, here taking 200km; D1 is the distance from the Beidou satellite to the common-view station, here taking 20000km; σR is the satellite position accuracy, here taking 60m; c is the speed of light.

[0117] Furthermore, the mean square error σ eph caused by the broadcast ephemeris is obtained therefrom ≤ 0.8ns, and this error is inherent in the system and cannot be canceled.

[0118] In a specific example, the clock error also includes the receiver position error. The receiver position affects the inter-station time synchronization accuracy, and this influence mainly depends on the relative measurement accuracy of the two station locations. Given the high positioning accuracy of high-precision satellite receivers, through the high-precision positioning function, a positioning accuracy of about 0.1 decimeter is achieved. The error introduced by its radial component is relatively small, and the mean square error σ rec ≤0.1 ns.

[0119] Furthermore, the clock error caused by the position accuracy of the receiver can be reduced by accurately measuring the station location or selecting a high-precision Beidou receiver.

[0120] In a specific example, the clock error also includes the ionospheric delay error. The ionosphere is the atmosphere with a height between 50 km and 1000 km. Due to the strong radiation of the sun, some gas molecules in the ionosphere will be ionized to form a large number of free electrons and positive ions. When an electromagnetic wave signal passes through the ionosphere, the propagation speed will change. Therefore, the product of the signal propagation time and the propagation speed in vacuum is not equal to the actual propagation distance of the signal, resulting in a ranging error, which is called the ionospheric delay error.

[0121] Furthermore, to reduce this error, this example adopts the "Klobuchar" model correction method, which is a calculation model uniformly adopted by various international time and frequency transfer research institutions. According to the ionospheric delay correction parameters provided by the navigation message (including α0, α1, α2, α3 and β0, βl, β2, β3), as well as the longitude and latitude of the Beidou receiver antenna, the elevation angle of the satellite, the azimuth angle, and the GPS time of the receiver (GPSTime), calculate according to the following model:

[0122]

[0123] AMP is the amplitude of the cosine curve; F is the ionospheric tilt factor; F iono is the ionospheric vertical delay correction, in seconds; x is the phase of the ionospheric delay;

[0124] In the formula,

[0125] α n is the ionospheric correction model coefficient; is the geodetic latitude of the ionospheric pierce point;

[0126]

[0127] t is the local time at the intersection point (pierce point M) of the line connecting the receiver and the satellite with the ionosphere (the value range is 0 to 86400), in seconds; PER is the period of the cosine curve;

[0128]

[0129] β n is the ionospheric correction model coefficient;

[0130] F = 1.0 + 16.0×(0.53 - E) 3 ;

[0131] E is the satellite elevation angle;

[0132] φ m = φ i + 0.064×cos(λ i - 1.617);

[0133] φ m is the geomagnetic latitude of the piercing point; φ i is the geographic latitude of the piercing point; λ i is the geographic longitude of the piercing point;

[0134]

[0135] λ u is the user's geographic longitude; ψ is the geocentric angle; φ u is the user's geographic latitude; A is the satellite elevation angle;

[0136]

[0137] E is the satellite elevation angle;

[0138] t = 4.32 * 10 4 λ i + GPStime;

[0139] t is the local time of the piercing point, in seconds; GPSTime is the GPS time of the receiver;

[0140]

[0141] i is the number of days;

[0142] Furthermore, in the formula, i is an integer, making the result satisfy 0 ≤ t ≤ 86400; α n and β n are obtained from the satellite's navigation message. The elevation angle E, azimuth angle A1, user geographic latitude data φ u , user geographic longitude data λ u , system time GPSTime are generated by the receiver processing the satellite signals. Since the ionospheric delay correction model is basically an empirical estimation formula, and a set of coefficients α n and β n, so correcting with the above model can eliminate about 60% of the ionospheric delay. The mean square error σ of correcting the ionospheric time delay with this model ion ≤4 ns.

[0143] Furthermore, the calculation and correction of the ionospheric delay are realized inside the device by using the "klobuchar" model correction algorithm and the time delay correction control circuit.

[0144] Furthermore, by using a dual-frequency receiver, the calculation accuracy of the ionosphere is better than σ ion ≤1 ns.

[0145] In a specific example, the clock error also includes the tropospheric delay error. The troposphere is the atmosphere with a height lower than 40 km. When electromagnetic waves pass through the troposphere, the propagation speed will change, resulting in propagation delay. For the L band of the Beidou signal, the time delay of the troposphere is independent of the frequency. In this example, the "Hopfield" model is used for correction.

[0146] Furthermore, the path length difference caused by the tropospheric delay, that is, the path length corresponding to the additional time delay is

[0147]

[0148] In the formula, n is the refractive index; ds is the total tropospheric delay; ΔS 对流层 is the path length difference caused by the tropospheric delay.

[0149] Furthermore, for the time delay model of the troposphere, in the case of no real-time meteorological data, the mean square error σ of the delay introduced by observing satellite data at high elevation angles atm ≤1 ns.

[0150] Furthermore, the calculation and correction of the tropospheric delay are realized inside the device by using the "Hopfield" model correction algorithm and the time delay correction control circuit.

[0151] In a specific example, the clock error also includes the error introduced by the multipath effect. Multipath is one of the main error sources encountered in the receiver measurement process. The generation of multipath is related to the antenna site and the surrounding environment. For the two stations participating in the common view comparison, their surrounding environments, as well as the elevation angles and azimuth angles relative to the satellite are all different, so the multipath effects are completely uncorrelated.

[0152] Furthermore, anti-multipath methods mostly use anti-multipath interference antennas, select receivers with good performance, and increase the elevation angle of the observed satellite, which can further reduce the multipath effect. In this example, a high-precision satellite receiver and an anti-multipath interference antenna are used. Through actual tests, the mean square error σ introduced by the multipath effect path ≤0.5 ns.

[0153] In a specific example, a three-state clock model Kalman filter is adopted for the frequency synchronization of the CPT atomic clock. By using the three state parameters of the clock, namely phase, frequency, and frequency drift, a Kalman prediction equation is established to achieve the calibration and synchronization of the frequency accuracy of the CPT atomic clock by the Beidou system. The specific method is as follows:

[0154] Furthermore, the output model of the CPT atomic clock can be described as:

[0155]

[0156] where V(t) is the output voltage at time t; V0 is the nominal peak voltage; ξ(t) is the amplitude offset; is the phase deviation; f r is the nominal frequency.

[0157] Furthermore, the instantaneous frequency is:

[0158]

[0159] where f(t) is the instantaneous frequency; is the change in phase; dt is the change in time;

[0160] Furthermore, the relative frequency offset is:

[0161]

[0162] where y(t) is the relative frequency offset; Δf is the absolute frequency deviation; dx(t) is the change in relative time deviation;

[0163] Furthermore, the formula can be derived as:

[0164]

[0165] where x(t) is the relative time deviation; x0 is the initial time deviation; y0 is the initial frequency deviation; D is the daily aging rate; ε(t) is the random deviation, which is the comprehensive result of the linear addition of five mutually independent noises.

[0166] Furthermore, the power spectral density model formula of the five noises is:

[0167] S y (f) = h2f 2 + h1f + h0 + h -1 f -1 + h -2 f -2

[0168] where S y(f) is; f is the Fourier frequency; h2 is white phase modulation noise; f 2 is the square of the Fourier frequency; h1 is flicker phase modulation noise; h0 is white frequency modulation noise; h -1 is flicker frequency modulation noise; f -1 is the -1 power of the Fourier frequency; h -2 is random walk frequency modulation noise; f -2 is the -2 power of the Fourier frequency;

[0169] where 0 < f ≤ f h ; f h is the upper cut-off frequency; h α is a constant characterizing the strength of various noises. α corresponds to different noise types. α = 2 corresponds to white phase modulation noise, α = 1 corresponds to flicker phase modulation noise, α = 0 corresponds to white frequency modulation noise, α = -1 corresponds to flicker frequency modulation noise, and α = -2 corresponds to random walk frequency modulation noise.

[0170] Furthermore, the best fitting method for white phase modulation noise, white frequency modulation noise, and random walk frequency modulation noise is Kalman filter estimation. Taking the phase deviation, frequency deviation, and daily aging rate D as the three state variables of the clock, establishing a Kalman state matrix, the frequency deviation can be estimated with high precision, and then the frequency can be tamed and locked through a control algorithm.

[0171] Another embodiment of the present invention provides a common-view time synchronization system based on a CPT atomic clock. The system includes: a first data processing unit for obtaining the first second pulse signal of the first CPT atomic clock of the master station, the second second pulse signal of the first receiver of the master station, and the first delay time signal from the common-view satellite to the master station, and obtaining a first deviation signal according to the first second pulse signal, the second second pulse signal, and the first delay time signal; a second data processing unit for obtaining the third second pulse signal of the second CPT atomic clock of the slave station, the fourth second pulse signal of the second receiver of the slave station, and the second delay time signal from the common-view satellite to the slave station, and obtaining a second deviation signal according to the third second pulse signal, the fourth second pulse signal, and the second delay time signal; a third data processing unit for calculating the time correction amount of the sub-station according to the first deviation signal and the second deviation signal; a first time synchronization unit for performing common-view time synchronization on the sub-station according to the time correction amount; a second time synchronization unit for performing common-view time synchronization on the master station according to the first deviation signal; and a frequency synchronization unit for performing frequency synchronization on the first CPT atomic clock and the second CPT atomic clock by using a three-state clock model Kalman filter.

[0172] In a specific example, the common-view time synchronization consists of a master station, multiple sub-stations, and a communication link configured with a common-view time synchronization device. The common-view data processing flow between the master and sub-stations is asFigure 3 As shown in:

[0173] Furthermore, the master sub-station selects the optimal satellite for data acquisition and performs fitting processing on the data.

[0174] Furthermore, after the data fitting is completed, the sub-station uploads the fitting data of its own station to the master station.

[0175] Furthermore, after the master station receives the data of all stations, it performs data screening.

[0176] Furthermore, after the data screening is completed, the time correction amount of each sub-station is calculated based on the common-view satellite as the standard and sent to each sub-station respectively.

[0177] Furthermore, after each sub-station receives the correction data, it accurately shifts and synchronizes its own local seconds, and finally completes the output of the common-view seconds of the sub-station.

[0178] Furthermore, the master station measures the time difference between the local second (atomic clock second) and the receiver reference second in real time and sends it to the time difference compensation unit, and finally completes the close tracking of the local second and the reference second and generates the common-view second of the master station.

[0179] In a specific example, the common-view time synchronization device based on the CPT atomic clock includes a CPT chip atomic clock, a full-frequency antenna, a high-precision satellite receiver, and a Beidou common-view module.

[0180] Furthermore, the high-precision satellite receiver is responsible for obtaining the satellite navigation message settlement of the current observation and obtaining the original observation data.

[0181] Furthermore, the Beidou common-view module is responsible for analyzing the data to calculate the clock difference data between the local time and each satellite, and performing time difference comparison with the common-view device of the master station through the network or short message, calculating the time difference value between the two places. After the local common-view device obtains the time difference, it corrects the internal time to complete the time synchronization with the common-view device of the master station.

[0182] This device has a smaller volume, lower power consumption, higher accuracy and long-term stability.

[0183] This embodiment uses a CPT chip atomic clock, which not only has the same low power consumption as the crystal oscillator, but also has higher long-term stability and disciplining accuracy, is not easily affected by the environment, reduces the influence of the path delay of the satellite signal in transmission on the time synchronization accuracy, and is more suitable for occasions such as portable devices and meeting the needs of high-precision clocks such as power grid synchronization.

[0184] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A common-view time synchronization method based on a CPT atomic clock, characterized in that, The method includes: Obtaining a first second pulse signal of a first CPT atomic clock of a master station, a second second pulse signal of a first receiver of the master station, and a first delay time signal from a common-view satellite to the master station, and obtaining a first deviation signal according to the first second pulse signal, the second second pulse signal, and the first delay time signal; Obtaining a third second pulse signal of a second CPT atomic clock of a slave station, a fourth second pulse signal of a second receiver of the slave station, and a second delay time signal from the common-view satellite to the slave station, and obtaining a second deviation signal according to the third second pulse signal, the fourth second pulse signal, and the second delay time signal; Calculating a time correction amount of a sub-station according to the first deviation signal and the second deviation signal; Performing common-view time synchronization on the sub-station according to the time correction amount; Performing common-view time synchronization on the master station according to the first deviation signal; Performing frequency synchronization on the first CPT atomic clock and the second CPT atomic clock by using a three-state clock model Kalman filter.

2. The common-view time synchronization method based on a CPT atomic clock according to claim 1, wherein The calculation formula for obtaining the first deviation signal according to the first second pulse signal, the second second pulse signal, and the first delay time signal is: T a = t a -(t outA + d a ) Wherein, T a is the first deviation signal; t a is the first one-second pulse signal; t outA is the second one-second pulse signal; d a is the first delay time signal.

3. The common-view time synchronization method based on a CPT atomic clock according to claim 2, wherein The calculation formula for obtaining the second deviation signal according to the third second pulse signal, the fourth second pulse signal, and the second delay time signal is: T b = t b -(t outB + d b ) Wherein, T b is the second deviation signal; t b is the third second pulse signal; t outB is the fourth second pulse signal; d b is the second delay time signal.

4. The common-view time synchronization method based on a CPT atomic clock according to claim 3, wherein The calculation formula for calculating the time correction amount of the sub-station according to the first deviation signal and the second deviation signal is: T ab = T a -T b where T ab is the time correction amount.

5. The common-view time synchronization method based on a CPT atomic clock according to claim 4, wherein Calculating the time correction amount of the sub-station according to the first deviation signal and the second deviation signal includes: Using the moment of the i-th common-view satellite obtained by calculation as an intermediate quantity, where i is an integer greater than or equal to 1; Calculating the time correction amount of the sub-station according to the first deviation signal, the second deviation signal, and the intermediate quantity.

6. The common-view time synchronization method based on a CPT atomic clock according to claim 5, wherein The calculation formula for calculating the time correction amount of the sub-station according to the first deviation signal, the second deviation signal, and the intermediate quantity is: T ab = T a -T b =(T a -t svi )-(T b -t svi ) where t svi is an intermediate quantity; T a - t svi is the difference between the first deviation signal and the intermediate quantity; T b -t svi is the difference between the second deviation signal and the intermediate quantity.

7. The common-view time synchronization method based on a CPT atomic clock according to claim 6, wherein The calculation formula for the difference between the first deviation signal and the intermediate quantity is: Where, T a -T outA is the time difference between the first second pulse signal and the second second pulse signal; is the hardware error of the second second pulse signal of the first receiver, is the first average time value calculated by the first receiver; is the difference between the first average time value calculated by the first receiver and the actual time of the i-th common-view satellite; t′ svl -t svi Clock error of the i-th common-view satellite calculated for the first receiver.

8. The common-view time synchronization method based on a CPT atomic clock according to claim 7, wherein The calculation formula for the difference between the second deviation signal and the intermediate quantity is: where T b -T outB is the time difference between the third-second pulse signal and the fourth-second pulse signal; is the hardware error of the fourth-second pulse signal of the second receiver, is the second average time value calculated by the second receiver; is the difference between the second average time value calculated by the second receiver and the actual time of the i-th common-view satellite; t′ svι -t svi The clock error of the i-th common-view satellite calculated for the second receiver, where the clock error of the i-th common-view satellite calculated for the second receiver is equal to the clock error of the i-th common-view satellite calculated for the first receiver.

9. The common-view time synchronization method based on a CPT atomic clock according to claim 8, wherein The clock error of the i-th common-view satellite calculated by the first receiver includes: ionospheric delay error, tropospheric delay error, multipath effect error, and system synchronization accuracy error.

10. A common-view time synchronization system based on a CPT atomic clock, characterized in that, The system includes: The first data processing unit is configured to obtain the first second pulse signal of the first CPT atomic clock of the master station, the second second pulse signal of the first receiver of the master station, and the first delay time signal from the common-view satellite to the master station, and obtain a first deviation signal according to the first second pulse signal, the second second pulse signal, and the first delay time signal; The second data processing unit is configured to obtain the third second pulse signal of the second CPT atomic clock of the slave station, the fourth second pulse signal of the second receiver of the slave station, and the second delay time signal from the common-view satellite to the slave station, and obtain a second deviation signal according to the third second pulse signal, the fourth second pulse signal, and the second delay time signal; The third data processing unit is configured to calculate the time correction amount of the sub-station according to the first deviation signal and the second deviation signal; The first time synchronization unit is configured to perform common-view time synchronization on the sub-station according to the time correction amount; The second time synchronization unit is configured to perform common-view time synchronization on the master station according to the first deviation signal; The frequency synchronization unit is configured to perform frequency synchronization on the first CPT atomic clock and the second CPT atomic clock by using a three-state clock model Kalman filter.

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