Sub-nanosecond time service method based on satellite-based augmented seamless connection

Abstract

The present invention provides a sub-nanosecond time service method based on satellite-based augmentation and seamless connection, using a receiver to respectively receive PPP-B2b signals, HAS signals, dual-frequency observation data and broadcast ephemeris; using broadcast ephemeris to calculate preliminary satellite orbits and preliminary satellite clock errors, and using correction numbers in PPP-B2b signals and HAS signals to correct them; based on the two corrected precise satellite orbits and two precise satellite clock errors, using dual-frequency observation data to perform PPP solutions to obtain two final receiver clock errors; and after the user terminal completes the switching, the receiver clock error is updated according to the difference between the two final receiver clock errors. When the PPP-B2b signal can be received, the present invention mainly uses the PPP-B2b service for high-precision time synchronization, and when the PPP-B2b signal cannot be received, uses the HAS service for high-precision time synchronization, so as to achieve global seamless time service.

Description

Technical Field

[0001] The invention belongs to the field of radio navigation timing, and in particular relates to a sub-nanosecond time service method based on satellite-based enhanced seamless connection. Background Art

[0002] The completion of my country's Beidou global network has provided a new opportunity for the positioning, navigation and timing (PNT) of the Global Navigation Satellite System (GNSS). Satellite timing methods based on Beidou / GNSS provide key support for global time services, and have a profound impact on many fields such as navigation, communication, scientific research and daily life. High-precision timing ensures the accuracy and consistency between different devices, and provides a basic guarantee for the operation of various complex systems. High-precision timing is listed as one of the main services of each navigation system. The timing service based on Precise Point Positioning (PPP) technology is an emerging sub-nanosecond time transfer method. At present, more than 50 of the more than 80 timing laboratories registered with the International Bureau of Weights and Measures use this method to achieve local coordinated universal time UTC(k) (k is the abbreviation of timing laboratory) accurate traceability to coordinated universal time UTC.

[0003] In order to achieve high-precision satellite-based augmented PNT services, my country provides PPP-B2b signals covering the Asia-Pacific region, providing users in the Asia-Pacific region with precise orbit, clock and code deviation correction information free of charge, and can achieve satellite-based augmented sub-nanosecond time synchronization based on this service. Similar to my country's Beidou PPP-B2b signal, the Galileo satellite navigation system has also provided free high-precision service (High Accuracy Service, HAS) signals to the world in recent years, which plays an important role in achieving high-precision time synchronization and satellite timing.

[0004] Beidou PPP-B2b is suitable for high-precision PNT services, especially high-precision positioning and navigation applications in environments without ground communications. The availability of PPP-B2b satellite-based augmentation services in China and surrounding areas has reached more than 95%, but due to regional restrictions, it is not conducive to the global promotion and use of Beidou. Galileo HAS supports sub-nanosecond timing of the Global Positioning System (GPS) and the Galileo Satellite Navigation System (Galileo), but does not support Beidou's localization needs. In the case of PPP-B2b and HAS signal loss or user switching, the user's switching time is long, resulting in errors in the receiver clock error benchmark, causing confusion in user-side timing. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a sub-nanosecond time service method based on satellite-based enhanced seamless connection. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] A sub-nanosecond time service method based on satellite-based enhanced seamless connection is applied to a user end, and the user end includes a receiver. The sub-nanosecond time service method based on satellite-based enhanced seamless connection includes:

[0007] S100, using a receiver to respectively receive a PPP-B2b signal, a HAS signal, dual-frequency observation data, and a broadcast ephemeris; the PPP-B2b signal and the HAS signal both include correction numbers, and the correction numbers include a satellite orbit correction number and a satellite clock correction number;

[0008] S200, calculating a preliminary satellite orbit and a preliminary satellite clock error of the satellite using the broadcast ephemeris;

[0009] S300, using the correction numbers in the PPP-B2b signal and the HAS signal, respectively correct the preliminary satellite orbit and the preliminary satellite clock error to obtain two precise satellite orbits and two precise satellite clock errors;

[0010] S400, based on two precise satellite orbits and two precise satellite clock errors, dual-frequency observation data are used to perform PPP solution to obtain two receiver clock errors at each moment, and wait for the two receiver clock errors to converge to obtain two final receiver clock errors;

[0011] S500, calculating the difference between two final receiver clock errors;

[0012] S600, when the user terminal needs to switch to a new satellite, the user terminal performs the switch, and after the switch is completed, the receiver clock difference is updated according to the difference.

[0013] Beneficial effects:

[0014] The present invention provides a sub-nanosecond time service method based on satellite-based augmentation seamless connection, using a receiver to respectively receive PPP-B2b signals, HAS signals, dual-frequency observation data and broadcast ephemeris; using broadcast ephemeris to calculate the preliminary satellite orbit and preliminary satellite clock error of the satellite; using the correction numbers in the PPP-B2b signal and the HAS signal, respectively correcting the preliminary satellite orbit and preliminary satellite clock error to obtain two precise satellite orbits and two precise satellite clock errors; based on the two precise satellite orbits and the two precise satellite clock errors, using dual-frequency observation data to perform PPP solution to obtain two receiver clock errors at each moment, and waiting for the two receiver clock errors to converge, and finally obtaining the two receiver clock errors; calculating the difference between the two receiver clock errors; switching when the user terminal needs to switch to a new satellite, and updating the receiver clock error according to the difference after the switching is completed. The present invention uses the PPP-B2b service as the main service for high-precision time service when the PPP-B2b signal can be received, and uses the HAS service for high-precision time service when the PPP-B2b signal cannot be received, so as to realize global seamless time service.

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of a sub-nanosecond time service method based on satellite-based enhanced seamless connection provided by the present invention;

[0017] Figure 2 It is a schematic diagram of the overall process of a sub-nanosecond time service method based on satellite-based enhanced seamless connection provided by the present invention;

[0018] Figure 3a and Figure 3b It is a comparison diagram of receiver clock errors calculated using PPP-B2b and HAS signals provided by the present invention;

[0019] Figure 4 It is a schematic diagram of the effect of using PPP-B2b and HAS to solve the second-stable Allan variance of the receiver clock error provided by the present invention;

[0020] Figure 5 It is a schematic diagram of the effect of the second-steady Allan variance of the difference between the receiver clock difference calculated by PPP-B2b and HAS provided by the present invention;

[0021] Figure 6 It is a comparison diagram of the receiver clock difference sequence before and after the repair 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] The present invention solves the technical problems existing in the prior art, and adopts a high-precision time synchronization scheme and clock difference switching method that integrates Beidou PPP-B2b and Galileo HAS. When the PPP-B2b signal can be received, the PPP-B2b service is used as the main service for high-precision time service, and when the PPP-B2b signal cannot be received, the HAS service is used for high-precision time service. The present invention combines the two, and carefully designs a new time synchronization scheme and a receiver clock difference monitoring method, so that seamless receiver clock difference switching can be achieved when the signal is lost or the user needs to switch. First, the PPP-B2b and HAS signals are received by the receiver respectively, and the corresponding correction numbers can be obtained by decoding the telegram. The correction numbers are used to correct the broadcast ephemeris to obtain precise orbit and clock difference data, and then the receiver pseudorange and carrier observation data are combined to implement the precise single point positioning algorithm to respectively solve the PPP-B2b and HAS high-precision receiver clock differences, and the receiver clock difference monitoring method is used to calculate the clock difference jump value when switching is required, and the calculated clock difference is corrected by the numerical value in the subsequent. The present invention is based on the sub-nanosecond time service that integrates Beidou PPP-B2b and Galileo HAS services, which can fully utilize the advantages of both to provide stable sub-nanosecond time transmission and realize more stable and reliable time services worldwide.

[0024] Combination Figure 1 and Figure 2 The present invention provides a sub-nanosecond time service method based on satellite-based enhanced seamless connection, which is applied to a user terminal, and the user terminal includes a receiver. The sub-nanosecond time service method based on satellite-based enhanced seamless connection includes:

[0025] S100, using a receiver to respectively receive PPP-B2b signals, HAS signals, dual-frequency observation data and broadcast ephemeris; both the PPP-B2b signal and the HAS signal include correction numbers, the correction numbers include satellite orbit correction numbers and satellite clock correction numbers; the dual-frequency observation data includes pseudoranges of two frequencies and carrier phase observation data.

[0026] S200, calculating a preliminary satellite orbit and a preliminary satellite clock error of the satellite using the broadcast ephemeris;

[0027] S300, using the correction numbers in the PPP-B2b signal and the HAS signal, respectively correct the preliminary satellite orbit and the preliminary satellite clock error to obtain two precise satellite orbits and two precise satellite clock errors;

[0028] S400, based on two precise satellite orbits and two precise satellite clock errors, dual-frequency observation data are used to perform PPP solution to obtain two receiver clock errors at each moment, and wait for the two receiver clock errors to converge to obtain two final receiver clock errors;

[0029] After obtaining the precise satellite orbit and clock error in this step, the PPP solution using dual-frequency observation data can obtain precise estimated parameters, including receiver position, receiver clock error, zenith tropospheric wet delay, and phase ambiguity.

[0030] S500, calculating the difference between two final receiver clock errors;

[0031] S600, when the user terminal needs to switch to a new satellite, the user terminal performs the switch, and after the switch is completed, the receiver clock difference is updated according to the difference.

[0032] The situations where the user terminal needs to switch to a new satellite include the user terminal actively requesting to switch, the user terminal losing the PPP-B2b signal, or the HAS signal and the receiver clock error being abnormal.

[0033] The present invention provides a sub-nanosecond time service method based on satellite-based augmentation seamless connection, using a receiver to respectively receive PPP-B2b signals, HAS signals, dual-frequency observation data and broadcast ephemeris; using broadcast ephemeris to calculate the preliminary satellite orbit and preliminary satellite clock error of the satellite; using the correction numbers in the PPP-B2b signal and the HAS signal, respectively correcting the preliminary satellite orbit and preliminary satellite clock error to obtain two precise satellite orbits and two precise satellite clock errors; based on the two precise satellite orbits and the two precise satellite clock errors, using dual-frequency observation data to perform PPP solution to obtain two receiver clock errors at each moment, and waiting for the two receiver clock errors to converge to obtain two final receiver clock errors; calculating the difference between the two final receiver clock errors; switching when the user terminal needs to switch to a new satellite, and updating the receiver clock error according to the difference after the switching is completed. The present invention uses the PPP-B2b service as the main service for high-precision time service when the PPP-B2b signal can be received, and uses the HAS service for high-precision time service when the PPP-B2b signal cannot be received, so as to realize global seamless time service.

[0034] As an optional implementation manner of the present invention, S300 includes:

[0035] S310, converting the satellite orbit correction numbers of the PPP-B2b signal and the HAS signal from the satellite body coordinate system to the Earth-centered Earth-fixed coordinate system, and obtaining a first satellite orbit correction number corresponding to the PPP-B2b signal and a second satellite orbit correction number corresponding to the HAS signal in the Earth-centered Earth-fixed coordinate system;

[0036] S320, inputting the first satellite orbit correction number in the Earth-centered Earth-fixed coordinate system and the preliminary satellite orbit into an orbit correction formula to correct the preliminary satellite orbit to obtain a first precise satellite orbit;

[0037] S330, inputting the second satellite orbit correction number in the Earth-centered Earth-fixed coordinate system and the preliminary satellite orbit into an orbit correction formula to correct the preliminary satellite orbit to obtain a second precise satellite orbit;

[0038] The orbit correction formula is expressed as:

[0039] (1);

[0040] In the formula, is the first precise satellite orbit or the second precise satellite orbit, For the initial satellite orbit, is the first satellite orbit correction number or the second satellite orbit correction number corresponding to the Earth-centered Earth-fixed coordinate system;

[0041] (2);

[0042] (3);

[0043] (4);

[0044] (5);

[0045] In the formula, is the first satellite orbit correction number or the second satellite orbit correction number in the radial direction The rotation vector of is the first satellite orbit correction number or the second satellite orbit correction number in the tangential direction The rotation vector of is the first satellite orbit correction number or the second satellite orbit correction number in the normal direction The rotation vector of The information decoded in the radial direction , Tangential and normal The orbit correction vector of is the satellite velocity vector calculated using the broadcast ephemeris.

[0046] S340, inputting the first satellite clock error correction number and the preliminary satellite clock error included in the PPP-B2b signal into a clock error correction formula to correct the preliminary satellite clock error to obtain a first precise satellite clock error;

[0047] S350, input the second satellite clock error correction number and the preliminary satellite clock error contained in the HAS signal into the clock error correction formula to correct the preliminary satellite clock error and obtain the second precise satellite clock error.

[0048] The clock error correction formula is expressed as:

[0049] (6);

[0050] In the formula, is the first precise satellite clock error or the second precise satellite clock error, is the initial satellite clock error, is the corresponding first satellite clock correction number or second satellite clock correction number, is the speed of light in a vacuum.

[0051] As an optional implementation manner of the present invention, S400 includes:

[0052] S410, performing ionosphere-free combination of pseudorange and carrier phase observation data of two frequency points to obtain pseudorange observation data and carrier phase observation data with first-order ionospheric delay eliminated;

[0053] The pseudo-range observation data and carrier phase observation data that eliminate the first-order term of ionospheric delay are expressed by the following formulas:

[0054] (7);

[0055] (8);

[0056] (9);

[0057] (10);

[0058] In the formula, To eliminate the pseudorange observation value of the first-order term of ionospheric delay, For receiver Observation satellites received The pseudorange observation value at frequency 1, For receiver Observation satellites received The pseudorange observation value at frequency 2, For satellite To Receiver The geometric distance between For receivers without ionospheric delay The receiver clock error is Satellites without ionospheric delay The satellite clock error is For satellite The altitude angle is The tropospheric projection function at time , is the tropospheric delay without ionospheric delay, For receiver and satellite The uncorrected pseudorange hardware delay, for The noise term, To eliminate the carrier phase observation value of the first-order term of ionospheric delay, For receiver Observation satellites received The carrier phase observation at frequency 1, For receiver Observation satellites received The carrier phase observation at frequency 2, is the floating point ambiguity without ionospheric delay, For receiver and satellite The uncorrected phase hardware delay on for The noise term, superscript represents the parameter for eliminating ionospheric delay, and Indicates an intermediate parameter and has no meaning. is frequency 1, is frequency 2.

[0059] S420, based on two precise satellite orbits and two precise satellite clock errors, PPP solution is performed using pseudorange observation data and carrier phase observation data that eliminate the first-order term of ionospheric delay to obtain two receiver clock errors at each moment;

[0060] S430, repeat S420 to continue PPP solution until the two receiver clock errors converge, and obtain two final receiver clock errors.

[0061] In an optional implementation manner of the present invention, after S500, the sub-nanosecond time service method based on satellite-based enhanced seamless connection further includes:

[0062] a. Calculate the second-steady Allan variance of the difference between the two final receiver clock errors respectively;

[0063] b, 3 times of the Allan variance of the second stability is used as the threshold;

[0064] c. Calculate the jump value of the difference by using the difference between the two final receiver clock errors;

[0065] d. Determine whether the jump value is greater than the threshold. If so, it is confirmed that the difference jumps. If not, no jump occurs.

[0066] e. When the difference jumps, confirm that the receiver clock error is abnormal.

[0067] This implementation uses 3 times the second-steady Allan variance as a threshold to determine whether the clock error difference has jumped. The specific formula is as follows:

[0068] (11);

[0069] In the formula, is the difference between the two final receiver clock errors, in seconds, is the jump value, is the second-stable Allan variance of the difference between the two receiver clock errors.

[0070] As an optional implementation manner of the present invention, S600 includes:

[0071] S610, when the user terminal needs to switch to a new satellite, switching is performed;

[0072] S620, after the switching is completed, the receiver clock difference on the receiver is subtracted from the difference value to obtain an updated receiver clock difference.

[0073] Combination Figure 1 and Figure 2 , if the currently calculated receiver clock error is It is the receiver clock error calculated using the PPP-B2b signal. , then the receiver clock error is As the benchmark, When the PPP-B2b signal is lost or the user switches to HAS, the jump value is calculated , and record the jump value Subsequent receiver clock error , which can be calculated by HAS, the new receiver clock error , In order to utilize the receiver clock difference calculated by the HAS signal, PPP-B2b switches to HAS and uses the new receiver clock difference as the reference for timing.

[0074] In order to realize high-precision time service applications in different regions around the world, the present invention designs a global seamless sub-nanosecond time service method that combines PPP-B2b and HAS services. This method can combine the advantages of the two services, and realize seamless time service when the PPP-B2b signal is lost or the user switches to HAS. When switching the clock difference, the method of the present invention is used to detect the clock jump, and the detection value is used to correct the new receiver clock difference reference, so as to achieve stable and continuous high-precision time service.

[0075] In order to verify the present invention, the SEPT POLARX5TR receiver built on March 30, 2024 (the 90th day of 2024) was selected, and the XUPT1 and XUPT2 stations with external passive VCH-1008 hydrogen clocks were used to verify the switching process after the PPP-B2b and HAS clock errors converged. The data of the two stations were downsampled from the original 1 second sampling rate to 30 seconds. XUPT1 used PPP-B2b to solve the receiver clock error. , XUPT2 uses HAS’s GPS to calculate the receiver clock error , respectively solve the Allan variance second-stable value for a period of time after convergence, and use the method of the present invention to switch the receiver clock difference at the switching moment. Figure 3a and Figure 3b A comparison of the receiver clock errors calculated using PPP-B2b and HAS clock error solutions was plotted, and it was found that the clock error trends calculated by PPP-B2b (Beidou) and HAS (GPS) were similar, and the difference fluctuated within 4 nanoseconds. Figure 4 The second-stable Allan variance of the clock errors solved by PPP-B2b (Beidou) and HAS (GPS) was plotted, and it was found that the 30-fold second-stable Allan variance was 0.00120 ns and 0.00075 ns. It can be inferred that the time for the second-stable Allan variance to stabilize is about 0.04 ns and 0.03 ns.

[0076] When the receiver clock error calculated by PPP-B2b (Beidou) is switched to HAS (GPS) clock error at 12:00 on March 30, 2024, the clock error sequence of PPP-B2b (Beidou) and HAS (GPS) is subtracted, and then the clock error difference is calculated. The modified second-stable Allan variance is Figure 5 As shown, the 30-fold second-stable Allan variance is found to be 0.0011 ns. It can be inferred that the second-stable variance stabilization time is about When the clock difference is greater than The clock difference between PPP-B2b (Beidou) and HAS (GPS) receivers is recorded at the switching time. From the clock difference comparison diagram between PPP-B2b and HAS receivers, it can be seen that the absolute value of the clock difference jump at 12:00 (90.5 days) is 107.25 ns, which is greater than 0.1 ns. The clock difference sequence after switching is as follows: Figure 6 As shown, it can be seen that when not repaired, the clock error will jump at a certain moment due to signal loss, but after being repaired using the present invention, the clock error sequence can run continuously and achieve long-term stable time service.

[0077] The present invention uses two SEPT POLARX5TR receiver boards connected to the same passive VCH-1008 hydrogen clock to simultaneously receive PPP-B2b, HAS signals, Beidou / GNSS pseudoranges and carrier observations. Based on the seamless clock switching algorithm proposed by the present invention, combined with PPP-B2b and HAS satellite-based augmentation services, it is verified that in the scenario where PPP-B2b and HAS signals are missing or users need to switch, stable sub-nanosecond time service applications can still be provided.

[0078] 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.

[0079] 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.

[0080] 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 protection scope of the present invention.

Claims

1. A sub-nanosecond time service method based on satellite-based enhanced seamless connection, characterized in that: Applied to a user terminal, the user terminal includes a receiver, and the sub-nanosecond time service method based on satellite-based enhanced seamless connection includes: S100, using the receiver to respectively receive a PPP-B2b signal, a HAS signal, dual-frequency observation data and a broadcast ephemeris; the PPP-B2b signal and the HAS signal both include correction numbers, and the correction numbers include a satellite orbit correction number and a satellite clock correction number; S200, calculating a preliminary satellite orbit and a preliminary satellite clock error of the satellite using the broadcast ephemeris; S300, using the correction numbers in the PPP-B2b signal and the HAS signal, respectively correct the preliminary satellite orbit and the preliminary satellite clock error to obtain two precise satellite orbits and two precise satellite clock errors; S400, based on the two precise satellite orbits and the two precise satellite clock errors, using the dual-frequency observation data to perform PPP solution to obtain two receiver clock errors at each moment, and waiting for the two receiver clock errors to converge to obtain two final receiver clock errors; S500, calculating the difference between two final receiver clock errors; S600, when the user terminal needs to switch to a new satellite, switching is performed, and after the switching is completed, the receiver clock error is updated according to the difference; the dual-frequency observation data includes pseudoranges and carrier phase observation data of two frequencies; S400 includes: S410, performing ionosphere-free combination of pseudorange and carrier phase observation data of two frequency points to obtain pseudorange observation data and carrier phase observation data with first-order ionospheric delay eliminated; S420, based on the two precise satellite orbits and the two precise satellite clock errors, PPP solution is performed using the pseudorange observation data and the carrier phase observation data that eliminate the first-order term of ionospheric delay to obtain two receiver clock errors at each moment; S430, repeat S420 to continue PPP solution until the two receiver clock errors converge, and obtain two final receiver clock errors.

2. The sub-nanosecond time service method based on satellite-based enhanced seamless connection according to claim 1, characterized in that: S300 includes: S310, converting the satellite orbit correction numbers of the PPP-B2b signal and the HAS signal from the satellite body coordinate system to the Earth-centered Earth-fixed coordinate system, and obtaining a first satellite orbit correction number corresponding to the PPP-B2b signal and a second satellite orbit correction number corresponding to the HAS signal in the Earth-centered Earth-fixed coordinate system; S320, inputting the first satellite orbit correction number in the Earth-centered Earth-fixed coordinate system and the preliminary satellite orbit into an orbit correction formula to correct the preliminary satellite orbit to obtain a first precise satellite orbit; S330, inputting the second satellite orbit correction number in the Earth-centered Earth-fixed coordinate system and the preliminary satellite orbit into the orbit correction formula to correct the preliminary satellite orbit to obtain a second precise satellite orbit; S340, inputting the first satellite clock error correction number included in the PPP-B2b signal and the preliminary satellite clock error into a clock error correction formula to correct the preliminary satellite clock error to obtain a first precise satellite clock error; S350, inputting the second satellite clock error correction number contained in the HAS signal and the preliminary satellite clock error into the clock error correction formula to correct the preliminary satellite clock error to obtain a second precise satellite clock error.

3. The sub-nanosecond time service method based on satellite-based enhanced seamless connection according to claim 2, characterized in that: The orbit correction formula is expressed as: Xo=X-δo (1); Where Xo is the first precise satellite orbit or the second precise satellite orbit, X is the preliminary satellite orbit, and δo is the first satellite orbit correction or the second satellite orbit correction in the corresponding Earth-centered Earth-fixed coordinate system; In the formula, is the rotation vector of the first satellite orbit correction number or the second satellite orbit correction number in the radial direction rd, is the rotation vector of the first satellite orbit correction number or the second satellite orbit correction number in the tangent direction a, is the rotation vector of the first satellite orbit correction number or the second satellite orbit correction number in the normal direction h, δx is the orbit correction vector in the radial direction rd, tangential direction a and normal direction h obtained by information decoding, is the satellite velocity vector calculated using the broadcast ephemeris.

4. The sub-nanosecond time service method based on satellite-based enhanced seamless connection according to claim 3 is characterized in that: The clock error correction formula is expressed as: Where ts is the first precise satellite clock error or the second precise satellite clock error, tb is the preliminary satellite clock error, C0 is the corresponding first satellite clock error correction or the second satellite clock error correction, and c is the speed of light in vacuum.

5. The sub-nanosecond time service method based on satellite-based enhanced seamless connection according to claim 1, characterized in that: The pseudo-range observation data and carrier phase observation data that eliminate the first-order term of ionospheric delay in S410 are expressed by the following formulas: Where PIF is the pseudorange observation value after eliminating the first-order term of ionospheric delay, is the pseudorange observation value of the observation satellite s at frequency 1 received by the receiver r, is the pseudorange observation value of the observation satellite s at frequency 2 received by the receiver r, is the geometric distance between satellite s and receiver r, dt IF , r is the receiver clock error of receiver r without ionospheric delay, is the satellite clock error of satellite s without ionospheric delay, M(θ) is the tropospheric projection function when the altitude angle of satellite s is θ, TIF is the tropospheric delay without ionospheric delay, d is the uncorrected pseudorange hardware delay on receiver r and satellite s, is the noise term of PIF, LIF is the carrier phase observation value after eliminating the first-order term of ionospheric delay, is the carrier phase observation value of the observation satellite s at frequency 1 received by the receiver r, is the carrier phase observation value of the observation satellite s at frequency 2 received by the receiver r, is the floating point ambiguity without ionospheric delay, D is the uncorrected phase hardware delay between receiver r and satellite s, is the noise term of LIF, the subscript IF represents the parameter for eliminating ionospheric delay, α and β represent intermediate parameters and have no meaning, f1 is frequency 1, f2 is frequency 2, and c is the speed of light in vacuum.

6. The sub-nanosecond time service method based on satellite-based enhanced seamless connection according to claim 1, characterized in that: After S500, the sub-nanosecond time service method based on satellite-based enhanced seamless connection further includes: a, respectively calculating the second-steady Allan variance of the difference between the two final receiver clock errors; b, 3 times of the Allan variance of the second stability is used as the threshold; c. using the difference between the two final receiver clock errors to calculate a jump value of the difference; d. Determine whether the jump value is greater than the threshold value. If so, confirm that the difference value jumps. If not, no jump occurs. e. When the difference jumps, it is confirmed that the receiver clock error is abnormal.

7. The sub-nanosecond time service method based on satellite-based enhanced seamless connection according to claim 1, characterized in that: The situations where the user end needs to switch to a new satellite include the user end actively requesting to switch, the user end losing the PPP-B2b signal, or the HAS signal and the receiver clock error being abnormal.

8. The sub-nanosecond time service method based on satellite-based enhanced seamless connection according to claim 1, characterized in that: S600 includes: S610, when the user terminal needs to switch to a new satellite, switching is performed; S620: After the switching is completed, the difference is subtracted from the receiver clock difference on the receiver to obtain an updated receiver clock difference.

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