LU102875B1 - Method and system for synchronizing time among low earth orbit satellites - Google Patents

Method and system for synchronizing time among low earth orbit satellites Download PDF

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LU102875B1
LU102875B1 LU102875A LU102875A LU102875B1 LU 102875 B1 LU102875 B1 LU 102875B1 LU 102875 A LU102875 A LU 102875A LU 102875 A LU102875 A LU 102875A LU 102875 B1 LU102875 B1 LU 102875B1
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satellite
leo
inter
time synchronization
model
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LU102875A
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German (de)
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Furong Hou
Xia Xiao
Junqiang Han
Siyao Wang
Rui Zhang
Rui Tu
Lihong Fan
Pengfei Zhang
Xiaochun Lu
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Nat Time Service Ct Cas
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
    • G01S19/256—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to timing, e.g. time of week, code phase, timing offset
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
    • G01S19/05—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing aiding data
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/14—Receivers specially adapted for specific applications
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
    • G01S19/258—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
    • G—PHYSICS
    • G04—HOROLOGY
    • G04R—RADIO-CONTROLLED TIME-PIECES
    • G04R40/00—Correcting the clock frequency
    • G04R40/06—Correcting the clock frequency by computing the time value implied by the radio signal
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)
  • Radio Relay Systems (AREA)

Abstract

The present disclosure provides a method for synchronizing time among low earth orbit (LEO) satellites, including: providing on the ground with multiple ground common-clock tracking stations, each of which tracks multiple LEO satellites, and acquiring LEO satellite observation data of each of the multiple ground common-clock tracking stations and a satellite-borne global navigation satellite system (GNSS) observation data of each of the multiple LEO satellites; establishing, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on a ground common-clock tracking station to serve as a first LEO inter-satellite time synchronization model; establishing, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS to serve as a second LEO inter-satellite time synchronization model; combinedly solving the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain clock offsets of the multiple LEO satellites relative to the ground; and performing a subtraction operation on a clock offset of each LEO satellite to implement time synchronization among the multiple LEO satellites.

Description

METHOD AND SYSTEM FOR SYNCHRONIZING TIME AMONG LOW EARTH HU102875
ORBIT SATELLITES TECHNICAL FIELD
[01] The present disclosure relates to the field of time synchronization of satellites, and in particular, to a method and system for synchronizing time among low earth orbit (LEO) satellites.
BACKGROUND ART
[02] LEO satellites at an altitude of less than 1,000 km play an important role in many aspects for their special applications and scientific research needs. In recent years, with the rapid development of commercial LEO constellations such as Hongyan and Hongyun, enhanced navigation and positioning services provided based on LEO constellations have become hotspots researched in home and abroad. To provide the highly precise, quick and continuous navigation and positioning services based on the LEO constellations, higher requirements are imposed on the precision of time synchronization among LEO satellites. Conventional LEO satellites are mostly synchronized in time by calculating clock offsets of the LEO satellites during orbital determination with a dynamical method or a satellite-borne global navigation satellite system (GNSS) method. Through double integration on an acceleration, the dynamical method is mainly intended to obtain orbital parameters and clock offset parameters of the LEO satellites from a least squares model and a dynamical model in combination with initial epoch positions and initial velocities of the LEO satellites, thereby further implementing the time synchronization among the LEO satellites. The GNSS method is intended to use precise point positioning (PPP) technology or pseudo-range single point positioning technology to calculate three-dimensional (3D) positions and clock offsets of the LEO satellites by GNSS receiver of the LEO satellites at one epoch. However, the above two methods are implemented by taking the clock offset parameters of the LEO satellites as white noise for estimation, resulting in strengths of the clock offset parameters of the satellites in a mathematical model are weak to further restrict the precision of time synchronization among the LEO satellites. Therefore, how to enhance strengths of the clock offsets of the LEO satellites in a model and improve the precision of time synchronization among present LEO satellites is a scientific problem to be solved urgently in navigation and positioning applications of the LEO satellites.
SUMMARY
[03] An object of the present disclosure is to provide a method and system for synchronizing 1 time among LEO satellites, and to provide highly precise and highly stable time synchronization 102875 information of the LEO satellites.
[04] To implement the above object, the present disclosure provides the following solutions:
[05] A method for synchronizing time among LEO satellites includes:
[06] providing on the ground with multiple ground common-clock tracking stations, each of which tracks multiple LEO satellites, and acquiring LEO satellite observation data of each of multiple ground common-clock tracking stations and satellite-borne global navigation satellite system (GNSS) observation data of each of multiple LEO satellites, where the LEO satellite observation data includes: a LEO satellite pseudo-range observed by the ground common-clock tracking station, carrier phase observation data observed by the ground common-clock tracking station and a geocentric coordinate of the ground common-clock tracking station; and the satellite-borne GNSS observation data includes: a satellite-borne GNSS pseudo-range observed by a LEO satellite-borne GNSS receiver, and a satellite-borne carrier phase observation data observed by the LEO satellite-borne GNSS receiver;
[07] establishing, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on the ground common-clock tracking station to serve as a first LEO inter-satellite time synchronization model;
[08] establishing, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS to serve as a second LEO inter-satellite time synchronization model;
[09] combinedly solving the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain clock offsets of multiple LEO satellites relative to the ground; and
[10] performing a subtraction operation on a clock offset of each LEO satellite to implement time synchronization among the multiple LEO satellites.
[11] In some embodiments, the first LEO inter-satellite time synchronization model may include a first LEO inter-satellite time synchronization functional model and a first random model;
[12] the first LEO inter-satellite time synchronization functional model may be a LEO inter-satellite time synchronization functional model based on the ground common-clock tracking station, and the first LEO inter-satellite time synchronization functional model may be: PL (U)=Al x, +17, dt, dt], +E] R (U)= Aa ART + dt TU +N] +e)
[13] dt, = dt is) == dt, : and
[14] the first random model may be a LEO measurement random model of the ground 2 common-clock tracking station, and the first random model may be: HU102875 7 ~ N(o, 5%)
[15] Es ~ N(0, 0)
[16] where, i represents a serial number of the ground common-clock tracking station, J represents a serial number of the LEO satellite, k represents a serial number of an epoch, U represents an identifier of the LEO satellite, Bi (U) is a pseudo-range of a J th LEO satellite observed by an Ith ground common-clock tracking station at a kth moment, di (U) is a carrier phase measurement of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, 7 is a mapping function of a tropospheric delay at the k th moment, is a zenith tropospheric delay at the k th moment, iy is a receiver clock offset parameter of the ‘th ground common-clock tracking station at the k th moment, das is a receiver clock offset parameter of a first ground common-clock tracking station at the k th moment, d'a is a receiver clock offset parameter of a second ground common-clock tracking station at the kth moment, yma is a receiver clock offset parameter of an th ground common-clock tracking station at the k th moment, di x is a clock offset parameter of the / th LEO satellite at the kth moment, N} is a carrier phase ambiguity parameter between the “th ground common-clock tracking station and the J th LEO satellite, ir is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Fh is carrier phase measurement noise of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Krk is an orbital vector of the /th LEO satellite at the Æ th moment, Al is a coefficient vector established with a coordinate of the ! th ground common-clock tracking station and a coordinate of the Jth LEO satellite at the Æ th moment, * is an orbital vector of the LEO satellite at the Æ th moment, £ is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the LEO satellite observed by the ground common-clock tracking station, £5 is carrier phase measurement noise of the LEO satellite observed by the ground common-clock tracking station, Op WU) is a pseudo-range measurement noise value of the LEO satellite, and To ) is a carrier phase measurement noise value of the LEO satellite.
[17] In some embodiments, the second LEO inter-satellite time synchronization model may include a second LEO inter-satellite time synchronization functional model and a second random model: 3
[18] the second LEO inter-satellite time synchronization functional model may be a LEO 27 inter-satellite time synchronization functional model based on the satellite-borne GNSS, and the second LEO inter-satellite time synchronization functional model may be: Pia (G)= Al x, + Tir +d, TU + ep,
[19] A (G)= A} x PTT Hdi dig +N; +e, sand
[20] the second random model may be a satellite-borne GNSS random model, and the second random model may be: 211 Ep ~ N (0,050) Es ~ N (0,040)
[22] where, the ! is a serial number of a LEO satellite-borne GNSS satellite, G is an identifier of the LEO satellite-borne GNSS satellite, Bu (G) is a pseudo-range of a GNSS satellite observed by a J th LEO satellite-borne GNSS receiver at the th moment, ba (G) is a carrier phase measurement observed by the Jth LEO satellite-borne GNSS receiver at the k th moment, di, is a clock offset parameter of an th GNSS satellite at the kth moment, ua is a clock offset parameter of a Jth LEO satellite at the kth moment, Ar is a coefficient vector established with a coordinate of the /th LEO satellite and a coordinate of the lth LEO satellite-borne GNSS at the Æ th moment, £ is pseudo-range measurement noise of the GNSS satellite observed by the LEO satellite-borne GNSS receiver, £5 is carrier phase measurement noise observed by the LEO satellite-borne GNSS receiver, Op © is a pseudo-range measurement noise value of the GNSS satellite, and O4) is a carrier phase measurement noise value of the GNSS satellite.
[23] In some embodiments, the combinedly solving the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain clock offsets of multiple LEO satellites relative to the ground, may specifically include:
[24] combining the first LEO inter-satellite time synchronization functional model and the second LEO inter-satellite time synchronization functional model to obtain a satellite-ground combined LEO inter-satellite time synchronization functional model;
[25] determining a proportion of the first random model and a proportion of the second random model with an empirical weight method or a Helmert variance component method, and performing weighting on the first random model and the second random model after the determining to establish a comprehensive random model;
[26] combining the satellite-ground combined LEO inter-satellite time synchronization functional model and the comprehensive random model to obtain a satellite-ground combined 4
LEO inter-satellite time synchronization normal equation; and HU102675
[27] solving the satellite-ground combined LEO inter-satellite time synchronization normal equation to obtain the clock offset of each LEO satellite relative to the ground.
[28] In some embodiments, before the establishing, according to the LEO satellite observation data, the LEO inter-satellite time synchronization model based on the ground common-clock tracking station, the method may further include:
[29] correcting a tropospheric error, an ionospheric error, a tidal error and a relativistic effect error of the LEO satellite observation data; and
[30] correcting a tropospheric error, an ionospheric error, a relativistic effect error and an antenna phase center offset of the satellite-borne GNSS observation data.
[31] The present disclosure further provides a system for synchronizing time among LEO satellites, the system includes:
[32] a LEO satellite observation data acquisition module, configured to acquire LEO satellite observation data of each ground common-clock tracking station;
[33] a satellite-borne GNSS observation data acquisition module, configured to acquire satellite-borne GNSS observation data of each LEO satellite;
[34] a first LEO inter-satellite time synchronization model establishment module, configured to establish, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on the ground common-clock tracking station, the LEO inter-satellite time synchronization model based on the ground common-clock tracking station being a first LEO inter-satellite time synchronization model;
[35] a second LEO inter-satellite time synchronization model establishment module, configured to establish, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS, the LEO inter-satellite time synchronization model based on the satellite-borne GNSS being a second LEO inter-satellite time synchronization model;
[36] a combined solving module, configured to combinedly solve the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain a clock offset of each LEO satellite relative to the ground; and
[37] a subtraction operation module, configured to perform a subtraction operation on the clock offset of each LEO satellite to implement time synchronization among the LEO satellites.
[38] In some embodiments, the first LEO inter-satellite time synchronization model establishment module may include a first LEO inter-satellite time synchronization functional model and a first random model;
[39] the first LEO inter-satellite time synchronization functional model may be a LEO inter-satellite time synchronization functional model based on the ground common-clock 7975 tracking station, and the first LEO inter-satellite time synchronization functional model may be: PL (U)=Al x, +17, +t, —dt} HE, “ (U)= A} x, +T, 7, + dia dt}, + N} + Ei.
[40] din) = dt 2) a A iyi : and
[41] the first random model may be a LEO measurement random model of the ground common-clock tracking station, and the first random model may be:
[42] 7 “oe Es ~ N(o, 0)
[43] where, i represents a serial number of the ground common-clock tracking station, J represents a serial number of the LEO satellite, k represents a serial number of an epoch, U represents an identifier of the LEO satellite, Bi (U) is a pseudo-range of a J th LEO satellite observed by an Ith ground common-clock tracking station at a kth moment, dix (U) is a carrier phase measurement of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, 7 is a mapping function of a tropospheric delay at the k th moment, is a zenith tropospheric delay at the k th moment, iy is a receiver clock offset parameter of the ‘th ground common-clock tracking station at the k th moment, a. is a receiver clock offset parameter of a first ground common-clock tracking station at the k th moment, da is a receiver clock offset parameter of a second ground common-clock tracking station at the kth moment, yma is a receiver clock offset parameter of an "th ground common-clock tracking station at the k th moment, dx is a clock offset parameter of the / th LEO satellite at the kth moment, N} is a carrier phase ambiguity parameter between the “th ground common-clock tracking station and the J th LEO satellite, ir is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Fh is carrier phase measurement noise of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Xi is an orbital vector of the / th LEO satellite at the Æ th moment, Al is a coefficient vector established with a coordinate of the ! th ground common-clock tracking station and a coordinate of the Jth LEO satellite at the Æ th moment, * is an orbital vector of the LEO satellite at the Æ th moment, , is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the LEO satellite observed by the ground common-clock tracking station, £5 is carrier phase measurement noise 6 eo LU102875 of the LEO satellite observed by the ground common-clock tracking station, "W) is a pseudo-range measurement noise value of the LEO satellite, and To ) is a carrier phase measurement noise value of the LEO satellite.
[44] In some embodiments, the second LEO inter-satellite time synchronization model establishment module may include a second LEO inter-satellite time synchronization functional model and a second random model;
[45] the second LEO inter-satellite time synchronization functional model may be a LEO inter-satellite time synchronization functional model based on the satellite-borne GNSS, and the second LEO inter-satellite time synchronization functional model may be: P(G)=A x, + TT +dty — dr, +e, 146] A (G)= A} x PTT Hdi dig +N; +e, sand
[47] the second random model may be a satellite-borne GNSS random model, and the second random model may be: 45] gp ~N (0.03) Es ~ N (0,040)
[49] where, the ! is a serial number of a LEO satellite-borne GNSS satellite, G is an identifier of the LEO satellite-borne GNSS satellite, Bu (6) is a pseudo-range of a GNSS satellite observed by a J th LEO satellite-borne GNSS receiver at the th moment, ba (G) is a carrier phase measurement observed by the Jth LEO satellite-borne GNSS receiver at the k th moment, di, is a clock offset parameter of an th GNSS satellite at the kth moment, ua is a clock offset parameter of a Jth LEO satellite at the kth moment, Ar is a coefficient vector established with a coordinate of the /th LEO satellite and a coordinate of the lth LEO satellite-borne GNSS at the Æ th moment, £ is pseudo-range measurement noise of the GNSS satellite observed by the LEO satellite-borne GNSS receiver, £5 is carrier phase measurement noise observed by the LEO satellite-borne GNSS receiver, Op © is a pseudo-range measurement noise value of the GNSS satellite, and Tie is a carrier phase measurement noise value of the GNSS satellite.
[50] In some embodiments, the combined solving module may include:
[51] a functional module combining submodule, configured to combine the first LEO inter-satellite time synchronization functional model and the second LEO inter-satellite time synchronization functional model to obtain a satellite-ground combined LEO inter-satellite time synchronization functional model;
[52] a random module establishment submodule, configured to determine a proportion of the 7 first random model and a proportion of the second random model with an empirical weight 102875 method or a Helmert variance component method, and performing weighting on the first random model and the second random model after determining the proportions to establish a comprehensive random model;
[53] an equation establishment submodule, configured to combine the satellite-ground joint LEO inter-satellite time synchronization functional model and the comprehensive random model to obtain a satellite-ground combined LEO inter-satellite time synchronization normal equation; and
[54] an equation solving submodule, configured to solve the LEO inter-satellite time synchronization normal equation to obtain the clock offset of each LEO satellite relative to the ground.
[55] In some embodiments, the system may further include:
[56] a LEO satellite observation data correction module, configured to correct a tropospheric error, an ionospheric error, a tidal error and a relativistic effect error of the LEO satellite observation data; and
[57] a satellite-borne GNSS observation data correction module, configured to correct a tropospheric error, an ionospheric error, a relativistic effect error and an antenna phase center offset of the satellite-borne GNSS observation data.
[58] According to specific embodiments provided in the present disclosure, the present disclosure discloses the following technical effects:
[59] The present disclosure provides a method for synchronizing time among LEO satellites, the method includes: providing on the ground with multiple ground common-clock tracking stations, each of which tracks multiple LEO satellites, and acquiring LEO satellite observation data of each of the multiple ground common-clock tracking stations and a satellite-borne GNSS observation data of each of the multiple LEO satellites, where the LEO satellite observation data includes: a LEO satellite pseudo-range observed by the ground common-clock tracking station, carrier phase observation data observed by the ground common-clock tracking station and a geocentric coordinate of the ground common-clock tracking station; and the satellite-borne GNSS observation data includes: a satellite-borne GNSS pseudo-range observed by a LEO satellite-borne GNSS receiver, and a satellite-borne carrier phase observation data observed by the LEO satellite-borne GNSS receiver; establishing, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on the ground common-clock tracking station to serve as a first LEO inter-satellite time synchronization model; establishing, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS to serve as a second LEO inter-satellite 8 time synchronization model; combinedly solving the first LEO inter-satellite time 102875 synchronization model and the second LEO inter-satellite time synchronization model to obtain clock offsets of the multiple LEO satellites relative to the ground; and performing a subtraction operation on a clock offset of each LEO satellite to implement time synchronization among the multiple LEO satellites.
[60] The present disclosure further provides a system for synchronizing time among LEO satellites, the system includes: a LEO satellite observation data acquisition module, configured to acquire LEO satellite observation data of each ground common-clock tracking station; a satellite-borne GNSS observation data acquisition module, configured to acquire satellite-borne GNSS observation data of each LEO satellite; a first LEO inter-satellite time synchronization model establishment module, configured to establish, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on the ground common-clock tracking station, the LEO inter-satellite time synchronization model based on the ground common-clock tracking station being a first LEO inter-satellite time synchronization model; a second LEO inter-satellite time synchronization model establishment module, configured to establish, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS, the LEO inter-satellite time synchronization model based on the satellite-borne GNSS being a second LEO inter-satellite time synchronization model; a combined solving module, configured to combinedly solve the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain a clock offset of each LEO satellite relative to the ground; and a subtraction operation module, configured to perform a subtraction operation on the clock offset of each LEO satellite to implement time synchronization among the LEO satellites.
[61] The LEO satellite time synchronization based on the ground common-clock tracking station and the LEO time synchronization based on the satellite-borne GNSS are complementary to each other, so the present disclosure provides highly precise and highly stable time synchronization information of the LEO satellites.
BRIEF DESCRIPTION OF THE DRAWINGS
[62] To describe the technical solutions in the embodiments of the present disclosure or in the prior art more clearly, accompanying drawings required for the embodiments are briefly described below. Apparently, the accompanying drawings in the following description show merely some embodiments of the present disclosure, and a person of ordinary skill in the art may still derive other accompanying drawings from these accompanying drawings without creative efforts.
9
[63] FIG 1 is a flow chart of a method for synchronizing time among LEO satellites 102875 according to the present disclosure.
[64] FIG 2 is a structural block diagram of a method for synchronizing time among LEO satellites according to the present disclosure.
[65] FIG. 3 is a schematic structural view of a LEO inter-satellite time synchronization functional model according to the present disclosure.
[66] FIG 4 is flow chart for estimating a time parameter among LEO satellites according to the present disclosure.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[67] The technical solutions of the embodiments of the present disclosure are clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are merely a part rather than all of the embodiments of the present disclosure. All of other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.
[68] An object of the present disclosure is to provide a method and system for synchronizing time among low earth orbit (LEO) satellites, which provides highly precise and highly stable time synchronization information of the LEO satellites by combining LEO satellite observation data of a ground common-clock tracking station and satellite-borne global navigation satellite system (GNSS) observation data for processing.
[69] To make the above-mentioned object, features, and advantages of the present disclosure clearer and more comprehensible, the present disclosure will be further described in detail below with reference to the accompanying drawings and specific implementations.
[70] A method for synchronizing time among LEO satellites includes: providing multiple ground common-clock tracking stations on the ground, tracking multiple LEO satellites by each ground common-clock tracking station, acquiring LEO satellite observation data of each ground common-clock tracking station and satellite-borne GNSS observation data of each LEO satellite, where the LEO satellite observation data includes: a LEO satellite pseudo-range observed by the ground common-clock tracking station, carrier phase observation data observed by the ground common-clock tracking station and a geocentric coordinate of the ground common-clock tracking station. and the satellite-borne GNSS observation data includes: a satellite-borne GNSS pseudo-range observed by a LEO satellite-borne GNSS receiver, and a satellite-borne carrier phase observation data observed by the LEO satellite-borne GNSS receiver; establishing, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on the ground common-clock tracking station to serve as a first LEO inter-satellite time 102875 synchronization model; establishing, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS to serve as a second LEO inter-satellite time synchronization model; jointly solving the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain clock offsets of multiple LEO satellites relative to the ground; and performing a subtraction operation on a clock offset of each LEO satellite to implement time synchronization among the LEO satellites.
[71] The ground common-clock tracking stations are provided on the ground. Each station is provided with a high-precision hydrogen atomic clock. The hydrogen atomic clock of each station is calibrated in time and frequency with a fiber-based time transfer technology to keep the ground common-clock tracking stations synchronous in time. Meanwhile, GNSS geodetic surveying is used to measure the geocentric coordinate of each ground common-clock tracking station.
[72] The first LEO inter-satellite time synchronization model includes a first LEO inter-satellite time synchronization functional model and a first random model; the first LEO inter-satellite time synchronization functional model is a LEO inter-satellite time synchronization functional model based on the ground common-clock tracking station, and the first LEO inter-satellite time synchronization functional model may be: Pi (U)=Alx + Tr +d, TUE +e), R (U)=Al x ART Hd TU +N] +e) dt, = din) ST dt, . and the first random model is a LEO measurement random model of the ground common-clock tracking station, and the first random model may be: gp ~ N (0,05) Ei N (0,04) ; where, ! represents a serial number of the ground common-clock tracking station, and may be written as {= iLi2..m , J represents a serial number of the LEO satellite, and may be written as J=J172...jn , k represents a serial number of an epoch, U represents an identifier of the LEO satellite, Ex (U) is a pseudo-range of a Jth LEO satellite observed by an ‘th ground common-clock tracking station at a k th moment, Pix (U) is a carrier phase measurement of the / th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, 7 is a mapping function of a tropospheric delay at the k th moment, is a zenith tropospheric delay at the k th moment, iy is a receiver clock offset parameter of the Ith 11 dt. LU102875 ground common-clock tracking station at the kth moment, Wk is a receiver clock offset parameter of a first ground common-clock tracking station at the k th moment, das is a receiver clock offset parameter of a second ground common-clock tracking station at the k th moment, im. is a receiver clock offset parameter of an 7 th ground common-clock tracking station at the K th moment, Mo x is a clock offset parameter of the J th LEO satellite at the K th moment, N} is a carrier phase ambiguity parameter between the ‘th ground common-clock tracking station and the J th LEO satellite, En is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Zh is carrier phase measurement noise of the /th LEO satellite observed by the ith ground common-clock tracking station at the k th moment, Yi is an orbital vector of the /th LEO satellite at the kth moment, Ak is a coefficient vector established with a coordinate of the ith ground common-clock tracking station and a coordinate of the J th LEO satellite at the Æ th moment, *% is an orbital vector of the LEO satellite at the * th moment, , is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the LEO satellite observed by the ground common-clock tracking station, & is carrier phase measurement noise 2 of the LEO satellite observed by the ground common-clock tracking station, Tru) is a pseudo-range measurement noise value of the LEO satellite, and Ta ) is a carrier phase measurement noise value of the LEO satellite.
[73] Ak may be calculated with the following Equation: Al, = x. A) ; lox =) (x) where, the numerator is a vector, the denominator is a quadratic sum of the vector and is a distance, and thus A is a coefficient vector. X, is a positional parameter among the ground common-clock tracking stations.
[74] The second LEO inter-satellite time synchronization model includes a second LEO inter-satellite time synchronization functional model and a second random model; the second LEO inter-satellite time synchronization functional model is a LEO inter-satellite time synchronization functional model based on the satellite-borne GNSS, and the second LEO inter-satellite time synchronization functional model may be: PL (G)=Al x HT +d —dt, +85, i (G)=A) x PTT +d, —di +N +g 12 and the second random model is a satellite-borne GNSS random model, and the second random 102875 model may be: gp ~ N (0,070) Es ~ N (0,00) ; where, the ! is a serial number of a LEO satellite-borne GNSS satellite, G is an identifier of the LEO satellite-borne GNSS satellite, Bu (6) is a pseudo-range of a GNSS satellite observed by a Jth LEO satellite-borne GNSS receiver at the Æ th moment, ba (6) is a carrier phase measurement observed by the J th LEO satellite-borne GNSS receiver at the À th moment, di, is a clock offset parameter of an lth GNSS satellite at the “th moment, yj) is a clock offset parameter of a Jth LEO satellite at the Æ th moment, A is a coefficient vector established with a coordinate of the /th LEO satellite and a coordinate of the !th LEO satellite-borne GNSS at the Æ th moment, £ is pseudo-range measurement noise of the GNSS satellite observed by the LEO satellite-borne GNSS receiver, es is carrier phase measurement noise observed by the LEO satellite-borne GNSS receiver, 7 ©) is a pseudo-range measurement noise value of the GNSS satellite, and Tso is a carrier phase measurement noise value of the GNSS satellite.
[75] As the LEO satellite run at a speed faster than the ground common-clock tracking station, a valid transiting time window of the LEO satellite is determined with Kalman filtering and may be calculated with an adaptive optimal combination method under a condition where the LEO satellite can be observed by the ground common-clock tracking station.
[76] Combinedly solving the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain the clock offsets of the multiple LEO satellites relative to the ground specifically includes: combining the first LEO inter-satellite time synchronization functional model and the second LEO inter-satellite time synchronization functional model to obtain a satellite-ground combined LEO inter-satellite time synchronization functional model; determining a proportion of the first random model and a proportion of the second random model with an empirical weight method or a Helmert variance component method, and performing weighting on the first random model and second random model after the determining proportions to establish a comprehensive random model; combining the satellite-ground joint LEO inter-satellite time synchronization functional model and the comprehensive random model to obtain a satellite-ground combined LEO inter-satellite time synchronization normal equation; and solving the satellite-ground combined LEO inter-satellite time synchronization normal equation to obtain the clock offset of each LEO satellite relative to 13 the ground. HU102675
[77] The empirical weight is determined based on noise levels of different measurements, and is typically Opa) =0.3m Oya) =0.003m Opp) = 0-1m and CHO) =0.001m
[78] Before establishing, according to the LEO satellite observation data, the LEO inter-satellite time synchronization model based on the ground common-clock tracking station, the method further includes: correcting a tropospheric error, an ionospheric error, a tidal error and a relativistic effect error of the LEO satellite observation data; and correcting a tropospheric error, an ionospheric error, a relativistic effect error and an antenna phase center offset of the satellite-borne GNSS observation data.
[79] The LEO satellite observation data of the ground common-clock tracking station and the satellite-borne GNSS data are preprocessed to obtain preprocessed data. The data preprocessing includes: data check, outlier detection and removal, and carrier phase cycle-slip detection.
[80] The present disclosure further provides a system for synchronizing time among LEO satellites, the system includes: a LEO satellite observation data acquisition module, configured to acquire LEO satellite observation data of each ground common-clock tracking station; a satellite-borne GNSS observation data acquisition module, configured to acquire satellite-borne GNSS observation data of each LEO satellite; a first LEO inter-satellite time synchronization model establishment module, configured to establish, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on the ground common-clock tracking station, the LEO inter-satellite time synchronization model based on the ground common-clock tracking station being a first LEO inter-satellite time synchronization model; a second LEO inter-satellite time synchronization model establishment module, configured to establish, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS, the LEO inter-satellite time synchronization model based on the satellite-borne GNSS being a second LEO inter-satellite time synchronization model; a combined solving module, configured to combinedly solve the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain a clock offset of each LEO satellite relative to the ground; and a subtraction operation module, configured to perform a subtraction operation on the clock offset of each LEO satellite to implement time synchronization among the LEO satellites.
[81] The first LEO inter-satellite time synchronization model establishment module includes a first LEO inter-satellite time synchronization functional model and a first random model; the first LEO inter-satellite time synchronization functional model is a LEO inter-satellite time synchronization functional model based on the ground common-clock tracking station, and the first LEO inter-satellite time synchronization functional model may be: 14
PL (U)=Aj,x, + Tz, +t, — dif, +e] HUT02875 R (U)=Al x ART Hd TU +N] +e) dis = di) TT dim) ; and the first random model is a LEO measurement random model of the ground common-clock tracking station, and the first random model may be: gp ~ N (0,07) Es ~ N (0,05) ; where, ! represents a serial number of the ground common-clock tracking station, and may be written as | =iLi2..im , J represents a serial number of the LEO satellite, and may be written as J=J172...jn , k represents a serial number of an epoch, U represents an identifier of the LEO satellite, BL (U) is a pseudo-range of a Jth LEO satellite observed by an ‘th ground common-clock tracking station at a k th moment, di (U) is a carrier phase measurement of the /th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, 7 is a mapping function of a tropospheric delay at the k th moment, is a zenith tropospheric delay at the k th moment, ann is a receiver clock offset parameter of the ‘th ground common-clock tracking station at the k th moment, ya is a receiver clock offset parameter of a first ground common-clock tracking station at the k th moment, das is a receiver clock offset parameter of a second ground common-clock tracking station at the k th moment, im. is a receiver clock offset parameter of an 7 th ground common-clock tracking station at the K th moment, dx is a clock offset parameter of the J th LEO satellite at the K th moment, N} is a carrier phase ambiguity parameter between the / th ground common-clock tracking station and the J th LEO satellite, En is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Eh is carrier phase measurement noise of the /th LEO satellite observed by the th ground common-clock tracking station at the Kth moment, Xi x is an orbital vector of the /th LEO satellite at the Kth moment, Ak is a coefficient vector established with a coordinate of the ‘th ground common-clock tracking station and a coordinate of the J th LEO satellite at the th moment, *% is an orbital vector of the LEO satellite at the * th moment, £ is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the LEO satellite observed by the ground common-clock tracking station, & is carrier phase measurement noise of the LEO satellite observed by the ground common-clock tracking station, Op WU) is a po LU102875 pseudo-range measurement noise value of the LEO satellite, and “) is a carrier phase measurement noise value of the LEO satellite. P(U) represents the LEO satellite pseudo-range observed by the LEO satellite tracking station, (U) represents an measurement of a carrier phase dual-frequency ionospheric-free combination observed by the LEO satellite tracking station, A represents a coefficient vector of the orbital vector * of the LEO satellite, 7 represents a mapping function of a tropospheric delay, 7 represents a zenith tropospheric delay parameter, di represents a clock offset parameter of the ground receiver, diy represents a clock offset parameter of the LEO satellite, N} represents an ambiguity parameter, and € represents noise of the measurement.
[82] The zenith tropospheric delay is estimated as a constant or manifested as a random walk process. The clock offset of the LEO satellite is estimated epoch by epoch as white noise. The phase ambiguity is estimated as a constant in case of no cycle slips during continuous measurement.
[83] The second LEO inter-satellite time synchronization model establishment module includes a second LEO inter-satellite time synchronization functional model and a second random model; the second LEO inter-satellite time synchronization functional model is a LEO inter-satellite time synchronization functional model based on the satellite-borne GNSS, and the second LEO inter-satellite time synchronization functional model may be: PG) =A) x + Tir Ft TU +e, A (G)= Aj x + Tz, Hip TA + Nj +g; and the second random model is a satellite-borne GNSS random model, and the second random model may be: Ep ~ N(0.07) Es ~ N (0,040) ; where, the ! is a serial number of a LEO satellite-borne GNSS satellite, G is an identifier of the LEO satellite-borne GNSS satellite, Bu (G) is a pseudo-range of a GNSS satellite observed by a Jth LEO satellite-borne GNSS receiver at the Æ th moment, ba (6) is a carrier phase measurement observed by the J th LEO satellite-borne GNSS receiver at the À th moment, di, is a clock offset parameter of an lth GNSS satellite at the Æ th moment, du a is a clock offset parameter of a Jth LEO satellite at the Æ th moment, Ar is a coefficient vector established with a coordinate of the /th LEO satellite and a coordinate of the !th LEO satellite-borne GNSS at the X th moment, £ is pseudo-range measurement noise of the GNSS satellite observed by the LEO satellite-borne GNSS receiver, £ is carrier phase measurement 16 po LU102875 noise observed by the LEO satellite-borne GNSS receiver, (©) is a pseudo-range measurement noise value of the GNSS satellite, and io) is a carrier phase measurement noise value of the GNSS satellite. P(G) represents the pseudo-range of the GNSS satellite observed by the LEO satellite-borne GNSS receiver, 4(G) represents an measurement of a carrier phase dual-frequency ionospheric-free combination observed by the LEO satellite-borne GNSS receiver, df represents a clock offset parameter of the GNSS satellite, and diy represents a clock offset parameter of the LEO satellite.
[84] The coordinate of the GNSS satellite and the clock offset of the GNSS satellite are provided by the international GNSS service (IGS) analytic center, the zenith tropospheric delay is estimated as a constant or manifested as a random walk process, and the clock offset of the LEO satellite is estimated epoch by epoch as Gaussian white noise.
[85] The combined solving module includes: a functional module combining submodule, configured to combine the first LEO inter-satellite time synchronization functional model and the second LEO inter-satellite time synchronization functional model to obtain a satellite-ground combined LEO inter-satellite time synchronization functional model; the combined solving module further includes a random module establishment submodule, configured to determine a proportion of the first random model and a proportion of the second random model with an empirical weight method or a Helmert variance component method, and performing weighting on the first random model and the second random model after determining the proportions to establish a comprehensive random model; the combined solving module further includes an equation establishment submodule, configured to combine the satellite-ground joint LEO inter-satellite time synchronization functional model and the comprehensive random model to obtain a satellite-ground combined LEO inter-satellite time synchronization normal equation; and the combined solving module further includes an equation solving submodule, configured to solve the satellite-ground combined LEO inter-satellite time synchronization normal equation to obtain the clock offset of each LEO satellite relative to the ground.
[86] The system further includes: a LEO satellite observation data correction module, configured to correct a tropospheric error, an ionospheric error, a tidal error and a relativistic effect error of the LEO satellite observation data: and a satellite-borne GNSS observation data correction module, configured to correct a tropospheric error, an ionospheric error, a relativistic effect error and an antenna phase center offset of the satellite-borne GNSS observation data.
[87] In Step 1, at least four ground common-clock tracking stations are deployed on the ground at a distance of not less than 100 km, a high-precision hydrogen atomic clock is provided for each station, and the high-precision hydrogen atomic clock of each station is calibrated in 17 time and frequency with a fiber-based time transfer technology to keep the ground 102875 common-clock tracking stations synchronous in time. Each tracking station is positioned at a high precision with GNSS positioning to acquire a high-precision coordinate of the ground common-clock tracking station in a geocentric coordinate system, such that position parameters X, and time parameters of the ground common-clock tracking stations are determined; and, a geocentric coordinate of each ground common-clock tracking station is measured with GNSS geodetic surveying.
[88] In Step 2, a LEO satellite pseudo-range and carrier phase observation data of the ground common-clock tracking station as well as the geocentric coordinate of the tracking station are acquired, and a satellite-borne GNSS pseudo-range, carrier phase observation data, a GNSS precise satellite orbit and a satellite clock offset are acquired.
[89] In Step 3, as shown in FIG. 2, the LEO satellite observation data of the ground tracking station and the satellite-borne GNSS data are processed in parallel by a data reprocessing module, which has functions such as data check, outlier detection and removal, and carrier phase cycle-slip detection, to obtain clean data. Errors of the LEO observation data of the ground tracking station, such as a tropospheric error, an ionospheric error, a tidal error and a relativistic effect error, are corrected; and a tropospheric error, an ionospheric error, a relativistic effect error and an antenna phase center offset of the satellite-borne GNSS observation data are corrected. Then, a LEO inter-satellite time synchronization functional model based on the ground common-clock tracking station and a LEO inter-satellite time synchronization functional model based on a satellite-borne GNSS are respectively formed, thereby a satellite-ground combined LEO inter-satellite time synchronization functional model is further formed.
[90] In Step 4, as shown in FIG. 3, a satellite-ground combined LEO inter-satellite time synchronization normal equation of the LEO satellite is further calculated with an empirical weight in combination with a LEO satellite time synchronization random model based on the ground common-clock tracking station and a LEO satellite time synchronization random model based on the satellite-borne GNSS, and a clock offset parameter of the LEO satellite is estimated with a Markov white noise process; and a time scale of the LEO satellite is established with the clock offset parameter of each satellite, thereby implementing time synchronization among the LEO satellites.
[91] The present disclosure provides a method and system for determining and predicting a real-time clock offset of a navigation satellite and an LEO satellite, which parallelly estimate real-time clock offsets of the medium-earth and high-earth orbit navigation satellites and the LEO satellite based on the ground multi-mode GNSS data and the satellite-borne GNSS measurement, and perform an ultra-short-term real-time precise clock offset prediction to 18 improve the precision of estimation and prediction of the real-time precise clock offsets for the 102875 medium-earth and high-earth orbit navigation satellites and the LEO satellite.
[92] The present disclosure has the following beneficial effects:
[93] First, the LEO satellite time synchronization based on the ground common-clock tracking station and the LEO time synchronization based on the satellite-borne GNSS are complementary to each other, so the present disclosure provides highly precise and highly stable time synchronization information of the LEO satellites.
[94] By combinedly processing the LEO satellite observation data of the high-precision ground common-clock tracking station and the satellite-borne GNSS observation data, the present disclosure makes up the defects of no restriction in a short term and easy drift in a long term in the existing satellite-borne GNSS time transfer technology, makes two technical means complementary to each other, and can output both highly precise orbit information and clock offset information of the LEO satellites, and thus can be directly applied to time synchronization of the LEO satellites.
[95] Second, the present disclosure effectively utilizes LEO observation information of the ground common-clock tracking station to provide a new way for the time synchronization among the LEO satellites.
[96] As timing systems of the ground common-clock tracking stations are not unified, for the existing LEO satellite time synchronization, the receiver clock offset and the LEO satellite clock offset in the ground common-clock tracking station are hard to be separated. By applying the observation information of the ground common-clock tracking station to the time synchronization of the LEO satellites, the present disclosure can effectively improve the precision of estimation on the LEO satellite clock offset, provides a new way for acquisition of the LEO satellite clock offset parameter, and thus is of great significance to research on the time synchronization among the LEO satellites.
[97] Third, the present disclosure effectively reduces noise of the LEO satellite clock offset parameter acquired by the satellite-borne GNSS, and accelerates a convergence speed in calculation of a time parameter among the LEO satellites.
[98] By fusing the highly reliable LEO observation data of the ground common-clock tracking station into the time synchronization among the LEO satellites, the present disclosure can restrict the strength of the satellite-borne GNSS to solve the LEO satellite clock offset, and accelerate the convergence speed.
[99] Each embodiment of the present disclosure is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts between the embodiments may refer to each other. Since the system disclosed in the 19 embodiments corresponds to the method disclosed in the embodiments, the description i 102875 relatively simple, and reference can be made to the method description.
[100] In this specification, several specific embodiments are applied for illustration of the principles and implementations of the present disclosure. The description of the foregoing embodiments is used to help illustrate the method of the present disclosure and the core ideas thereof. In addition, those of ordinary skill in the art can make various modifications in terms of specific implementations and the scope of application in accordance with the ideas of the present disclosure. In conclusion, the content of this specification shall not be construed as a limitation to the present disclosure.

Claims (10)

WHAT IS CLAIMED IS: HU102875
1. A method for synchronizing time among low earth orbit (LEO) satellites, comprising: providing on the ground with a plurality of ground common-clock tracking stations, each of which tracks a plurality of LEO satellites, and acquiring LEO satellite observation data of each of the plurality of ground common-clock tracking stations and satellite-borne global navigation satellite system (GNSS) observation data of each of the plurality of LEO satellites, wherein the LEO satellite observation data comprises: a LEO satellite pseudo-range observed by the ground common-clock tracking station, carrier phase observation data observed by the ground common-clock tracking station and a geocentric coordinate of the ground common-clock tracking station; and the satellite-borne GNSS observation data comprises: a satellite-borne GNSS pseudo-range observed by a LEO satellite-borne GNSS receiver, and a satellite-borne carrier phase observation data observed by the LEO satellite-borne GNSS receiver; establishing, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on the ground common-clock tracking station to serve as a first LEO inter-satellite time synchronization model; establishing, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS to serve as a second LEO inter-satellite time synchronization model; combinedly solving the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain clock offsets of the plurality of LEO satellites relative to the ground; and performing a subtraction operation on a clock offset of each LEO satellite to implement time synchronization among the plurality of LEO satellites.
2. The method for synchronizing time among LEO satellites according to claim 1, wherein the first LEO inter-satellite time synchronization model comprises a first LEO inter-satellite time synchronization functional model and a first random model; the first LEO inter-satellite time synchronization functional model is a LEO inter-satellite time synchronization functional model based on the ground common-clock tracking station, and the first LEO inter-satellite time synchronization functional model is: Pi (U)=Al x, +17, + dt, di +e, R (U)=Al x ART Hd TU +N] +e) dt = din) == dt, : and the first random model is a LEO measurement random model of the ground common-clock 21 tracking station, and the first random model is: HU102875 gp ~ N(o, or) Es ~ N(o, or) wherein, ! represents a serial number of the ground common-clock tracking station, J represents a serial number of the LEO satellite, k represents a serial number of an epoch, U represents an identifier of the LEO satellite, Bi (U) is a pseudo-range of a J th LEO satellite observed by an Ith ground common-clock tracking station at a kth moment, di (U) is a carrier phase measurement of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, 7 is a mapping function of a tropospheric delay at the k th moment, is a zenith tropospheric delay at the k th moment, iy is a receiver clock offset parameter of the ‘th ground common-clock tracking station at the k th moment, das is a receiver clock offset parameter of a first ground common-clock tracking station at the k th moment, d'a is a receiver clock offset parameter of a second ground common-clock tracking station at the kth moment, yma is a receiver clock offset parameter of an th ground common-clock tracking station at the k th moment, di x is a clock offset parameter of the / th LEO satellite at the kth moment, N} is a carrier phase ambiguity parameter between the “th ground common-clock tracking station and the J th LEO satellite, ir is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Fh is carrier phase measurement noise of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Krk is an orbital vector of the /th LEO satellite at the Æ th moment, Al is a coefficient vector established with a coordinate of the ! th ground common-clock tracking station and a coordinate of the Jth LEO satellite at the Æ th moment, * is an orbital vector of the LEO satellite at the Æ th moment, £ is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the LEO satellite observed by the ground common-clock tracking station, £5 is carrier phase measurement noise of the LEO satellite observed by the ground common-clock tracking station, Op WU) is a pseudo-range measurement noise value of the LEO satellite, and To ) is a carrier phase measurement noise value of the LEO satellite.
3. The method for synchronizing time among LEO satellites according to claim 2, wherein the second LEO inter-satellite time synchronization model comprises a second LEO 22 inter-satellite time synchronization functional model and a second random model; HU102675 the second LEO inter-satellite time synchronization functional model is a LEO inter-satellite time synchronization functional model based on the satellite-borne GNSS, and the second LEO inter-satellite time synchronization functional model is: P (G)=A x +T,7, +d —dt, + Ep, i (G)=Aj x + Tz, +d), —dt, +N +e) and the second random model is a satellite-borne GNSS random model, and the second random model is: gy ~ N(o, oc) Es ~ N(o, Oc) wherein, the ! is a serial number of a LEO satellite-borne GNSS satellite, G is an identifier of the LEO satellite-borne GNSS satellite, Bis (G) is a pseudo-range of a GNSS satellite observed by a J th LEO satellite-borne GNSS receiver at the À th moment, 4 k (6) is a carrier phase measurement observed by the Jth LEO satellite-borne GNSS receiver at the th moment, di; is a clock offset parameter of an Ith GNSS satellite at the kth moment, dos is a clock offset parameter of a J th LEO satellite at the kth moment, Ar is a coefficient vector established with a coordinate of the / th LEO satellite and a coordinate of the !th LEO satellite-borne GNSS at the * th moment, £ is pseudo-range measurement noise of the GNSS satellite observed by the LEO satellite-borne GNSS receiver, £ is carrier phase measurement noise observed by the LEO satellite-borne GNSS receiver, Op (©) is a pseudo-range measurement noise value of the GNSS satellite, and Tie is a carrier phase measurement noise value of the GNSS satellite.
4. The method for synchronizing time among LEO satellites according to claim 3, wherein the combinedly solving the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain clock offsets of the plurality LEO satellites relative to the ground, comprises: combining the first LEO inter-satellite time synchronization functional model and the second LEO inter-satellite time synchronization functional model to obtain a satellite-ground combined LEO inter-satellite time synchronization functional model; determining a proportion of the first random model and a proportion of the second random model with an empirical weight method or a Helmert variance component method, and performing weighting on the first random model and the second random model after the 23 determining to obtain a comprehensive random model; HU102875 combining the satellite-ground combined LEO inter-satellite time synchronization functional model and the comprehensive random model to obtain a satellite-ground combined LEO inter-satellite time synchronization normal equation; and solving the satellite-ground combined LEO inter-satellite time synchronization normal equation to obtain the clock offset of each LEO satellite relative to the ground.
5. The method for synchronizing time among LEO satellites according to claim 1, before the establishing, according to the LEO satellite observation data, the LEO inter-satellite time synchronization model based on the ground common-clock tracking station, further comprising: correcting a tropospheric error, an ionospheric error, a tidal error and a relativistic effect error of the LEO satellite observation data; and correcting a tropospheric error, an ionospheric error, a relativistic effect error and an antenna phase center offset of the satellite-borne GNSS observation data.
6. A system for synchronizing time among low earth orbit (LEO) satellites, comprising: a LEO satellite observation data acquisition module, configured to acquire LEO satellite observation data of each ground common-clock tracking station; a satellite-borne global navigation satellite system (GNSS) observation data acquisition module, configured to acquire satellite-borne GNSS observation data of each LEO satellite; a first LEO inter-satellite time synchronization model establishment module, configured to establish, according to the LEO satellite observation data, a LEO inter-satellite time synchronization model based on the ground common-clock tracking station, the LEO inter-satellite time synchronization model based on the ground common-clock tracking station being a first LEO inter-satellite time synchronization model; a second LEO inter-satellite time synchronization model establishment module, configured to establish, according to the satellite-borne GNSS observation data, a LEO inter-satellite time synchronization model based on a satellite-borne GNSS, the LEO inter-satellite time synchronization model based on the satellite-borne GNSS being a second LEO inter-satellite time synchronization model; a combined solving module, configured to combinedly solve the first LEO inter-satellite time synchronization model and the second LEO inter-satellite time synchronization model to obtain a clock offset of each LEO satellite relative to the ground; and a subtraction operation module, configured to perform a subtraction operation on the clock offset of each LEO satellite to implement time synchronization among the LEO satellites.
24
7. The system for synchronizing time among LEO satellites according to claim 6, wherein the first LEO inter-satellite time synchronization model establishment module comprises a first LEO inter-satellite time synchronization functional model and a first random model; the first LEO inter-satellite time synchronization functional model is a LEO inter-satellite time synchronization functional model based on the ground common-clock tracking station, and the first LEO inter-satellite time synchronization functional model is: Pi (U)=Al x, +17, + dt, di +e, R (U)=Al x, +T 7 dt, di +N] +e] dt = din) ST dt, and the first random model is: gp ~ N(o, ow) Es ~ N(o, ow) wherein, ! represents a serial number of the ground common-clock tracking station, J represents a serial number of the LEO satellite, k represents a serial number of an epoch, U represents an identifier of the LEO satellite, Pi (U) is a pseudo-range of a J th LEO satellite observed by an ‘th ground common-clock tracking station at a k th moment, dix (U) is a carrier phase measurement of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, 7 is a mapping function of a tropospheric delay at the k th moment, is a zenith tropospheric delay at the k th moment, ann is a receiver clock offset parameter of the !th ground common-clock tracking station at the k th moment, i is a receiver clock offset parameter of a first ground common-clock tracking station at the k th moment, 2) is a receiver clock offset parameter of a second ground common-clock tracking station at the kth moment, im. is a receiver clock offset parameter of an th ground common-clock tracking station at the k th moment, dix is a clock offset parameter of the / th LEO satellite at the K th moment, N} is a carrier phase ambiguity parameter between the ‘th ground common-clock tracking station and the J th LEO satellite, En, is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Eh is carrier phase measurement noise of the J th LEO satellite observed by the ‘th ground common-clock tracking station at the k th moment, Krk is an orbital vector of the /th LEO satellite at the “th moment, Aix is a coefficient vector established with a coordinate of the ‘th ground common-clock tracking station and a coordinate of the Jth LEO satellite at the k ES moment, “ is an orbital vector of the LEO satellite at the Æ th moment, £ is pseudo-range measurement noise of a dual-frequency ionospheric-free combination of the LEO satellite observed by the ground common-clock tracking station, £5 is carrier phase measurement noise of the LEO satellite observed by the ground common-clock tracking station, Op WU) is a pseudo-range measurement noise value of the LEO satellite, and To ) is a carrier phase measurement noise value of the LEO satellite.
8. The system for synchronizing time among LEO satellites according to claim 7, wherein the second LEO inter-satellite time synchronization model establishment module comprises a second LEO inter-satellite time synchronization functional model and a second random model; the second LEO inter-satellite time synchronization functional model is: Pl (G)=A x PTT +d, 7 9 + Ep, (G)=A x +T 7, +dt —dt, +N; +8; and the second random model is: gy ~ N(o, oc) Es ~ N(o, oc) wherein, the ! is a serial number of a LEO satellite-borne GNSS satellite, G is an identifier of the LEO satellite-borne GNSS satellite, Bis (G) is a pseudo-range of a GNSS satellite observed by a J th LEO satellite-borne GNSS receiver at the À th moment, 4 k (6) is a carrier phase measurement observed by the Jth LEO satellite-borne GNSS receiver at the th moment, di; is a clock offset parameter of an Ith GNSS satellite at the th moment, dos is a clock offset parameter of a J th LEO satellite at the kth moment, Ar is a coefficient vector established with a coordinate of the / th LEO satellite and a coordinate of the !th LEO satellite-borne GNSS at the Æ th moment, £ is pseudo-range measurement noise of the GNSS satellite observed by the LEO satellite-borne GNSS receiver, es is carrier phase measurement noise observed by the LEO satellite-borne GNSS receiver, Op (©) is a pseudo-range measurement noise value of the GNSS satellite, and Tso is a carrier phase measurement noise value of the GNSS satellite.
9. The system for synchronizing time among LEO satellites according to claim 8, wherein the combined solving module comprises: 26 a functional module combining submodule, configured to combine the first LEO 07975 inter-satellite time synchronization functional model and the second LEO inter-satellite time synchronization functional model to obtain a satellite-ground combined LEO inter-satellite time synchronization functional model; a random module establishment submodule, configured to determine a proportion of the first random model and a proportion of the second random model with an empirical weight method or a Helmert variance component method, and performing weighting on the first random model and the second random model after determining the proportions to establish a comprehensive random model; an equation establishment submodule, configured to combine the satellite-ground joint LEO inter-satellite time synchronization functional model and the comprehensive random model to obtain a satellite-ground combined LEO inter-satellite time synchronization normal equation; and an equation solving submodule, configured to solve the satellite-ground combined LEO inter-satellite time synchronization normal equation to obtain the clock offset of each LEO satellite relative to the ground.
10. The system for synchronizing time among LEO satellites according to claim 6, further comprising: a LEO satellite observation data correction module, configured to correct a tropospheric error, an ionospheric error, a tidal error and a relativistic effect error of the LEO satellite observation data; and a satellite-borne GNSS observation data correction module, configured to correct a tropospheric error, an ionospheric error, a relativistic effect error and an antenna phase center offset of the satellite-borne GNSS observation data.
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