A wide-area time transfer method that does not rely on the Internet

Abstract

The present invention provides a wide-area time transfer method that does not rely on the Internet, including: receivers of a user station and a reference station, both for decoding Galileo E6B signals to obtain GNSS observations, broadcast ephemeris and HAS corrections, and then recovering satellite precise orbits; using satellite precise orbits in combination with GNSS observations to perform PPP Kalman filtering to obtain receiver clock errors; a receiver of the reference station, for broadcasting the reference station receiver clock error; a receiver of the user station, for calculating the time difference between the reference station receiver clock error and the user station receiver clock error, and using the time difference to regulate the frequency source of the user station, so that it keeps time synchronization with the frequency source of the reference station. The present invention broadcasts the reference station receiver clock error to the satellite through a Beidou short message, which belongs to real-time transmission without a network and does not rely on a network terminal, thereby improving the flexibility of PPP services and expanding the scope of PPP time services.

Description

Technical Field

[0001] The present invention belongs to the technical field of GNSS time transfer, and in particular relates to a wide area time transfer method that does not rely on the Internet. Background Art

[0002] PPP (precise point positioning) technology has been widely used in the field of time transfer due to its advantages of large range, long distance and high precision. Time is a physical quantity that passes by. Rapidly obtaining high-precision time information is of great significance to national defense construction and people's livelihood. The emergence of real-time PPP technology makes it possible to transmit time information without delay. The base station and user station restore the real-time received broadcast ephemeris and the correction number of the broadcast ephemeris into precise ephemeris, and respectively calculate the local clock difference based on PPP technology. After data exchange, time transfer is realized. It can be seen that the current PPP time transfer technology is highly dependent on the network and has many application scenarios, which affects the flexibility of PPP time service. Beidou PPP-B2b service broadcasts broadcast ephemeris correction numbers through Beidou-3 geostationary orbit satellites, avoiding network transmission risks, but PPP-B2b currently only provides services in Asia and the Pacific coastal areas, limiting the universality of PPP time service.

[0003] In January 2023, Galileo HAS (high accuracy service) provided broadcast ephemeris corrections to global users through E6B signals and the Internet. It is the first GNSS (Global Navigation Satellite System) to provide free high-precision positioning services worldwide, following the centimeter-level augmentation service of Japan's Quasi-Zenith Satellite System and the regional precise point positioning service PPP-B2b of China's BeiDou Satellite Navigation System.

[0004] The short message communication function is a special service of the Beidou satellite navigation system. It provides regional short message communication services for China and surrounding areas through GEO (Geostationary Orbit) satellites, and provides global short message communication services for global users through medium earth orbit satellites and inclined earth orbit satellites.

[0005] The patent document of the prior art (CN115085849A) provides a Beidou PPP-B2b precise timing method and device that does not rely on the Internet. The server is connected to a standard time source, the user station is connected to a user's local time source, and the short message terminal of the server establishes a communication link with the short message terminal of the user station. Real-time PPP time transfer is achieved through the Beidou-3 precise point positioning service and the Beidou short message service. The user station can achieve sub-nanosecond timing or time synchronization that does not rely on the Internet. Due to the limited scope of PPP-B2b services, it can only be applied to users in the Asia-Pacific region. Therefore, the prior art cannot solve the time transfer service for global users without a network. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a wide area time transfer method that does not rely on the Internet. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] A method for wide-area time transfer that does not rely on the Internet includes:

[0008] The receivers of the user station and the base station are used to:

[0009] Receive Galileo E6B signals and decode them to obtain GNSS observations, broadcast ephemeris and HAS corrections;

[0010] Recover satellite precise orbits using broadcast ephemeris and HAS corrections;

[0011] The receiver clock error is obtained by using the satellite precise orbit combined with the GNSS observation value and the receiver hardware delay to perform PPP Kalman filtering. The user station corresponds to the user station receiver clock error, and the reference station corresponds to the reference station receiver clock error.

[0012] The base station receiver is used to:

[0013] According to the agreed method, the base station receiver clock difference is broadcasted through the Beidou global short message receiving terminal;

[0014] A receiver at a user station for:

[0015] The base station receiver clock difference is received by the Beidou global short message receiving terminal, and the time difference between it and the user station receiver clock difference is calculated to obtain the time difference result;

[0016] The time difference result is used to adjust the frequency source of the user station so that it maintains time synchronization with the frequency source of the reference station.

[0017] Beneficial effects:

[0018] The invention provides a wide-area time transfer method that does not rely on the Internet, including: a receiver of a user station and a receiver of a reference station, both used to: receive Galileo E6B signals, and decode them to obtain GNSS observation values, broadcast ephemeris and HAS corrections; use the broadcast ephemeris and HAS corrections to restore the satellite precise orbit; use the satellite precise orbit in combination with the GNSS observation value and the receiver hardware delay to perform PPP Kalman filtering to obtain the receiver clock difference; the receiver of the reference station is used to: broadcast the reference station receiver clock difference according to the agreed method; the receiver of the user station is used to: receive the reference station receiver clock difference, and calculate the time difference between it and the user station receiver clock difference to obtain the time difference result; use the time difference result to regulate the frequency source of the user station so that it keeps time synchronization with the frequency source of the reference station. The invention broadcasts the reference station receiver clock difference to the satellite through Beidou short messages, which belongs to real-time transmission without network and does not rely on the network end, thereby improving the flexibility of PPP services and expanding the scope of PPP time services.

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow chart of a wide area time transfer method that does not rely on the Internet provided by the present invention;

[0021] Figure 2 It is a terminal detail schematic diagram of a wide area time transfer method independent of the Internet provided by the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0023] Combination Figure 1 and Figure 2 The present invention provides a wide area time transfer method that does not rely on the Internet, comprising:

[0024] The receivers of the user station and the base station are used to:

[0025] S1, receives Galileo E6B signals and decodes them to obtain GNSS observations, broadcast ephemeris and HAS corrections;

[0026] Among them, the HAS correction number includes the satellite's orbit correction number, the first ephemeris age and the clock correction number; the broadcast ephemeris includes the second ephemeris age; this step can obtain the HAS correction number through RS (Reed-Solomon) decoding.

[0027] refer to Figure 2As shown, the receiver of the user station and the receiver of the reference station in the present invention receive Galileo E6B signals from multiple MEO (Middle Earth Orbit) satellites.

[0028] S2, using broadcast ephemeris and HAS corrections to recover the satellite's precise orbit;

[0029] This step converts the satellite's orbit correction number from the satellite coordinate system to the Earth-centered Earth-fixed coordinate system, and after the conversion is completed, corrects it to the broadcast ephemeris of the corresponding time to obtain the satellite's orbit correction number in the Earth-centered Earth-fixed coordinate system; the first ephemeris age is matched with the second ephemeris age, and if the two are consistent, the satellite's orbit correction number is superimposed on the satellite orbit calculated using the broadcast ephemeris to restore the satellite's precise orbit.

[0030] The satellite orbit correction number is the tangential, radial and normal vectors in the satellite orbit coordinate system. The satellite orbit correction number in the geocentric earth-fixed coordinate system can be obtained by converting the coordinates and correcting them to the broadcast ephemeris at the corresponding time. The satellite orbit correction number in the geocentric earth-fixed coordinate system is expressed as:

[0031] (1);

[0032] In the formula, Satellite in Earth-centered Earth-fixed coordinate system The orbit correction number, is the correction vector in the satellite orbit coordinate system, , , is the unit vector of the HAS correction number in the tangential, radial and normal directions, For satellite The orbit correction number is the velocity vector in the Earth-centered Earth-fixed coordinate system, For satellite The coordinate vector of the orbit correction number in the satellite coordinate system, with the superscript Indicates satellite;

[0033] When the ephemeris age (IODnav) in the broadcast HAS correction number matches the ephemeris age (IODE) in the broadcast ephemeris, it indicates that the time is consistent. The orbit correction number of the satellite in the Earth-centered Earth-fixed coordinate system can be superimposed on the satellite orbit calculated by the broadcast ephemeris to restore the satellite precise orbit. The satellite precise orbit is expressed by the formula:

[0034] (2);

[0035] In the formula, For satellite The precise orbit of satellites, Satellites calculated using broadcast ephemeris satellite orbit.

[0036] S3, using the satellite precise orbit combined with GNSS observations and receiver hardware delay to perform PPP Kalman filtering to obtain the receiver clock error; where the user station corresponds to the user station receiver clock error, and the reference station corresponds to the reference station receiver clock error;

[0037] In an optional embodiment of the present invention, S3 includes:

[0038] S31, extrapolating the clock correction number to the time of the nearest neighbor broadcast ephemeris using an extrapolation formula to obtain a transformed clock correction number;

[0039] Among them, the extrapolation formula is expressed as:

[0040] (3);

[0041] In the formula, for Time Satellite The clock difference, for The clock difference, for The speed of the clock, for The clock of time drifts, For the current moment, is the start time of broadcast ephemeris;

[0042] S32, adding the transformed clock correction number to the satellite clock error calculated using the broadcast ephemeris to restore the satellite precise clock error; the satellite precise clock error is expressed by the formula:

[0043] (4);

[0044] In the formula, For satellite The satellite clock error is Satellites calculated using broadcast ephemeris The satellite clock error is is the clock correction after transformation, is the speed of light in a vacuum.

[0045] S33, obtaining initial pseudorange and carrier phase observation equations, and eliminating ionospheric errors in the initial pseudorange and carrier phase observation equations to obtain final pseudorange and carrier phase observation equations;

[0046] Taking into account the user clock error, satellite clock error, tropospheric and ionospheric delays, and ignoring the influence of solid tide, ocean tide, earth rotation correction and phase entanglement, the initial pseudorange and carrier phase observation equations are expressed as follows:

[0047] (5);

[0048] In the formula, Observe satellites for user stations or base stations The obtained frequency The raw pseudorange in meters at From user station or base station to satellite The geometric distance is the user station receiver clock error or the reference station receiver clock error, For satellite The tropospheric delay, From user station or base station to satellite At frequency The ionospheric delay in meters at for The observation noise is Observe satellites for user stations or base stations The obtained frequency The phase observation in meters at For the frequency The wavelength at Observe satellites for user stations or base stations The obtained frequency The phase observation in cycles, Observe satellites for user stations or base stations At frequency The fuzziness at for The observation noise of

[0049] The dual-frequency ionospheric elimination combination can eliminate more than 90% of the ionospheric errors in the signal propagation path. Therefore, after eliminating the ionospheric errors, the final pseudorange and carrier phase observation equations are expressed as follows:

[0050] ;

[0051] In the formula, To eliminate Pseudorange after accounting for ionospheric errors, For satellite At frequency 1, Observe satellites for user stations or base stations The pseudorange obtained at frequency point 1 is For satellite At frequency 2, Observe satellites for user stations or base stations The pseudorange obtained at frequency 2 is: To eliminate The observation noise after ionospheric errors, To eliminate The phase observation after ionospheric error, Observe satellites for user stations or base stations The phase at frequency 1 is obtained. Observe satellites for user stations or base stations The phase at frequency 2 is obtained, To eliminate The wavelength after ionospheric errors, To eliminate The ambiguity after accounting for ionospheric errors, To eliminate Observation noise after ionospheric errors.

[0052] S34, substitute the recovered satellite precise clock error into the final pseudorange and carrier phase observation equation, and use Kalman filter to calculate the real-time vector by ephemeris; the real-time vector is expressed by the formula:

[0053] (7);

[0054] In the formula, For The real-time vector at the moment, is the ambiguity of the first satellite after eliminating the ionospheric error, with the superscript Indicates the transpose of a vector, the superscript For satellite.

[0055] S35, extracting the receiver clock error from the real-time vector.

[0056] In this step, the base station receiver clock error is expressed as , the user station receiver clock error is expressed as .

[0057] The base station receiver is used to:

[0058] S4, broadcast the base station receiver clock difference through the Beidou global short message receiving terminal in accordance with the agreed method;

[0059] refer to Figure 2 As shown, the receiver of the reference station of the present invention broadcasts the reference station receiver clock difference to the GEO satellite through the Beidou global short message receiving terminal.

[0060] A receiver at a user station for:

[0061] S5, receiving the base station receiver clock difference through the Beidou global short message receiving terminal, and calculating the time difference between the base station receiver clock difference and the user station receiver clock difference to obtain the time difference result;

[0062] The user station and the base station are equipped with Beidou global short message receiving terminals. The base station terminal is broadcast through the Beidou global short message communication service in an agreed manner. The user station receives the base station receiver clock difference through the Beidou global short message communication service. After differential processing, the receiver hardware delay is deducted to obtain the time difference result between the user station and the base station. The time difference result is expressed by the formula:

[0063] (8);

[0064] In the formula, The time difference result is is the base station receiver clock error, is the hardware delay of the base station, is the user station receiver clock error, The hardware delay of the user station.

[0065] S6, using the time difference result to adjust the frequency source of the user station so that it maintains time synchronization with the frequency source of the reference station.

[0066] Among them, the base station is connected to the world standard time or atomic clock.

[0067] This step adjusts the frequency source of the user end according to the time difference result to keep it in time synchronization with the reference station and generate a high-precision time and frequency signal. When the reference station is connected to the world standard time UTC maintained by various timing laboratories, the user station can achieve traceability; when the reference station is connected to a high-performance atomic clock, the user station can achieve time transfer.

[0068] The invention provides a wide-area time transfer method that does not rely on the Internet, including: a receiver of a user station and a receiver of a reference station, both used to: receive Galileo E6B signals, and decode them to obtain GNSS observation values, broadcast ephemeris and HAS corrections; use the broadcast ephemeris and HAS corrections to restore the satellite precise orbit; use the satellite precise orbit in combination with the GNSS observation value and the receiver hardware delay to perform PPP Kalman filtering to obtain the receiver clock difference; the receiver of the reference station is used to: broadcast the reference station receiver clock difference according to the agreed method; the receiver of the user station is used to: receive the reference station receiver clock difference, and calculate the time difference between it and the user station receiver clock difference to obtain the time difference result; use the time difference result to regulate the frequency source of the user station so that it keeps time synchronization with the frequency source of the reference station. The invention broadcasts the reference station receiver clock difference to the satellite through Beidou short messages, which belongs to real-time transmission without network and does not rely on the network end, thereby improving the flexibility of PPP services and expanding the scope of PPP time services.

[0069] It is worth noting that the terms "first" and "second" in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0070] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art may understand and implement other variations of the disclosed embodiments by reviewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality of components or steps.

[0071] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A wide area time transfer method that does not rely on the Internet, characterized in that: include: The receivers of the user station and the base station are used to: Receive Galileo E6B signals and decode them to obtain GNSS observations, broadcast ephemeris and HAS corrections; Restoring the satellite precise orbit using the broadcast ephemeris and HAS corrections; The PPP Kalman filter is used to solve the receiver clock error by combining the satellite precise orbit with the GNSS observation value and the receiver hardware delay; wherein the user station corresponds to the user station receiver clock error, and the reference station corresponds to the reference station receiver clock error; The receiver of the reference station is used for: According to the agreed method, the base station receiver clock difference is broadcasted through the Beidou global short message receiving terminal; The receiver of the user station is used for: Receive the reference station receiver clock difference through the Beidou global short message receiving terminal, and calculate the time difference between the reference station receiver clock difference and the user station receiver clock difference to obtain a time difference result; Using the time difference result, regulating the frequency source of the user station to keep time synchronization with the frequency source of the reference station; The HAS corrections include the satellite's orbit correction, the first ephemeris age and the clock correction; the broadcast ephemeris includes the second ephemeris age; the satellite's orbit correction is the tangential, radial and normal vectors in the satellite orbit coordinate system.

2. The method for wide area time transfer independent of the Internet according to claim 1, characterized in that: The method of restoring the satellite precise orbit by using the broadcast ephemeris and HAS corrections comprises: The orbit correction number of the satellite is converted from the satellite coordinate system to the earth-centered earth-fixed coordinate system, and after the conversion is completed, it is corrected to the broadcast ephemeris of the corresponding time to obtain the orbit correction number of the satellite in the earth-centered earth-fixed coordinate system; The first ephemeris age is matched with the second ephemeris age. If the two are consistent, the orbit correction number of the satellite in the Earth-centered Earth-fixed coordinate system is superimposed on the satellite orbit calculated using the broadcast ephemeris to restore the satellite precise orbit.

3. The method for wide-area time transfer independent of the Internet according to claim 2, characterized in that: The orbit correction number of the satellite in the Earth-centered Earth-fixed coordinate system is expressed as: Where δXk is the orbit correction of satellite k in the Earth-centered Earth-fixed coordinate system, δO is the correction vector in the satellite orbit coordinate system, er, ea, ec are the unit vectors of HAS corrections in the tangential, radial, and normal directions, is the velocity vector of the orbit correction of satellite k in the Earth-centered Earth-fixed coordinate system, xk is the coordinate vector of the orbit correction of satellite k in the satellite coordinate system, and the superscript k represents the satellite; The satellite precise orbit is expressed by the formula: In the formula, is the precise satellite orbit of satellite k, is the satellite orbit of satellite k calculated using the broadcast ephemeris.

4. The method for wide area time transfer independent of the Internet according to claim 3, characterized in that: The method of using the satellite precise orbit in combination with the GNSS observation value and the receiver hardware delay to perform PPP Kalman filtering to obtain the receiver clock error includes: Extrapolating the clock correction number to the time of the nearest neighbor broadcast ephemeris using an extrapolation formula to obtain a transformed clock correction number; Adding the transformed clock correction number to the satellite clock error calculated using the broadcast ephemeris to restore the satellite precise clock error; Acquire initial pseudorange and carrier phase observation equations, and eliminate ionospheric errors in the initial pseudorange and carrier phase observation equations to obtain final pseudorange and carrier phase observation equations; Substitute the recovered satellite precise clock error into the final pseudorange and carrier phase observation equations, and use Kalman filter to calculate the real-time vector on a per-satellite basis. A receiver clock error is extracted from the real-time vector.

5. The method for wide area time transfer independent of the Internet according to claim 4, characterized in that: The extrapolation formula is expressed as: ΔCk=C0+C1· ( t-t0 ) +C2· ( t-t0 ) 2(3); Where ΔCk is the clock error of satellite k at time t, C0 is the clock error at time t0, C1 is the clock speed at time t0, C2 is the clock drift at time t0, t is the current time, and t0 is the start time of broadcast ephemeris; The satellite precise clock error is expressed by the formula: Where dtk is the satellite precise clock error of satellite k, is the satellite clock error of satellite k calculated using the broadcast ephemeris, is the clock correction number after transformation, and c is the speed of light in vacuum.

6. The method for wide area time transfer independent of the Internet according to claim 5, characterized in that: The initial pseudorange and carrier phase observation equations are expressed as follows: Where Pik is the original pseudorange in meters at frequency point i obtained by the user station or reference station observing satellite k, ρk is the geometric distance from the user station or reference station to satellite k, dtr is the receiver clock error of the user station or the reference station, Tk is the tropospheric delay of satellite k, is the ionospheric delay from the user station or reference station to satellite k at frequency i in meters, is Pik’s observation noise, is the phase observation value in meters at frequency point i obtained by the user station or the base station observing satellite k, λi is the wavelength at frequency point i, is the phase observation value in cycles at frequency point i obtained by the user station or the base station observing satellite k, is the ambiguity of satellite k at frequency i observed by the user station or the reference station, for The observation noise of The final pseudorange and carrier phase observation equations are expressed as follows: In the formula, To eliminate the pseudorange of the ionospheric error in Pik, f1 is the frequency of satellite k at frequency point 1, P1k is the pseudorange at frequency point 1 obtained by the user station or the base station observing satellite k, f2 is the frequency of satellite k at frequency point 2, is the pseudorange at frequency point 2 obtained by the user station or the base station observing satellite k, To eliminate The observation noise after ionospheric errors, To eliminate The phase observation after ionospheric error, is the phase at frequency point 1 obtained by the user station or the base station observing satellite k, is the phase at frequency 2 obtained by the user station or the base station observing satellite k, λIF is the wavelength after eliminating the ionospheric error in λi, To eliminate The ambiguity after accounting for ionospheric errors, To eliminate Observation noise after ionospheric errors.

7. The method for wide area time transfer independent of the Internet according to claim 6, characterized in that: The real-time vector is expressed by the formula: Where X(t) is the real-time vector at time t, is the ambiguity of the first satellite after eliminating the ionospheric error. The superscript T represents the vector transpose.

8. The method for wide area time transfer independent of the Internet according to claim 6, characterized in that: The time difference result is expressed by the formula: dt r _diff=[dt r (base)-delay(base)]-[dt r (user)-delay(user)](8); Where, dtr_diff is the time difference result, dtr(base) is the base station receiver clock difference, delay(base) is the base station hardware delay, dtr(user) is the user station receiver clock difference, and delay(user) is the user station hardware delay.

9. The method for wide area time transfer independent of the Internet according to claim 1, characterized in that: The reference station is connected to the world standard time or an atomic clock.

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