Composite satellite time service system and composite satellite-ground time synchronization method

Abstract

The invention discloses a composite satellite time service system and a composite satellite-ground time synchronization method, and belongs to the technical field of time synchronization. The composite satellite time service system comprises a satellite, and a central station and a user station which are in communication connection with the satellite; the central station spontaneously receives the long forwarding ranging signal and the main forwarding ranging signal, and measures a long forwarding ranging value and a main forwarding ranging value; the satellite is used for sending a pseudo-range ranging signal to the user station; the user station is used for receiving the pseudo-range ranging signal and synchronously measuring the pseudo-range ranging signal to correspondingly obtain a slave pseudo-range ranging value, and the computing device sends the pseudo-range ranging signal to the user station based on the slave pseudo-range ranging value and the long forwarding ranging value. The main forwarding ranging value determines the total number of ionospheric electrons on the ranging signal path between the satellite and the subscriber station, the total number of ionospheric electrons on the ranging signal path between the satellite and the central station, and the relative clock error between the subscriber station and the satellite.

Description

Technical Field

[0001] This invention relates to the field of space technology, and more specifically to a composite satellite timing system.

[0002] This invention also relates to a composite satellite-to-ground time synchronization method. Background Technology

[0003] my country's satellite navigation system has evolved to include two basic systems: the BeiDou-2 Positioning System and the BeiDou Navigation Satellite System. The BeiDou-2 Positioning System is my country's first-generation satellite navigation system. This system typically consists of two satellites and provides positioning, velocity measurement, communication, and time synchronization functions; it is often referred to as a two-satellite positioning system. The BeiDou satellite navigation system has undergone development from a regional satellite navigation system to a global satellite navigation system, and currently, my country provides satellite navigation services globally.

[0004] The BeiDou dual-satellite positioning system, also known as the Radio Determination Satellite System, is a system in which a central station transmits signals, and through the radio propagation time between satellites and users, it can determine the user's coordinates, speed, direction, and other information, and can also transmit brief messages. It is abbreviated as RDSS system.

[0005] A key characteristic of the RDSS system is that the satellite does not have an onboard atomic clock; it only has transponders, which transmit signals to achieve system functionality. The user and satellite sides use the L and S bands, while the central station and satellite sides use the C band. The central station transmits ranging signals, which are relayed by the satellite and then by the user's response. The central station then receives the returned signals, obtaining the ranging value through a self-transmitting and self-receiving method. Because the satellite ephemeris and the central station's coordinates are known, the spatial distance between the central station and the satellite can be obtained. Subtracting the spatial distance and other influencing factors from the measured value yields the distance between the satellite and the user station, which is then used to calculate the user's coordinates for positioning.

[0006] In addition to positioning, the RDSS system also provides time synchronization services. It offers two types: one-way and two-way time synchronization, with accuracies of approximately 100ns and 10ns respectively.

[0007] A key feature of the BeiDou Navigation Satellite System is that its satellites carry onboard atomic clocks. The satellites directly broadcast pseudorange ranging signals to users, who then receive, measure, and process these signals to achieve positioning and time synchronization. Typical time synchronization accuracy is around 30 nanoseconds.

[0008] The BeiDou dual-satellite positioning system and the BeiDou satellite navigation system are two independent systems. How to organically integrate the two and give full play to their role is an important issue. Summary of the Invention

[0009] The purpose of this invention is to address the aforementioned problems by proposing a novel positioning and timing system that integrates the BeiDou dual-satellite positioning system and the BeiDou satellite navigation system. The integrated system can provide high-precision timing and positioning services.

[0010] The technical solution adopted in this invention is as follows:

[0011] A composite satellite timing system includes a central station and a user station that are respectively connected to a satellite for communication, and the central station, the satellite and the user station communicate with each other via long-range relay ranging signals;

[0012] When there is a primary relay ranging signal in communication between the satellite and the central station, and a secondary pseudorange ranging signal in communication between the satellite and the user station;

[0013] Similarly, when there is a relay ranging signal in communication between the satellite and the user station, there is a primary pseudorange ranging signal in communication between the satellite and the central station;

[0014] The main pseudorange ranging signal is played by the satellite and received and measured by the central station;

[0015] The pseudorange ranging signal is played by the satellite and received and measured by the user station;

[0016] The main relay ranging signal includes a main uplink signal and a main downlink signal. The central station broadcasts the main uplink signal and receives the main downlink signal. The satellite receives the main uplink signal and forwards it to form the main downlink signal.

[0017] The relay ranging signal includes an uplink signal and a downlink signal. The user station broadcasts the uplink signal and receives the downlink signal. The satellite receives the uplink signal and forwards it to form the downlink signal.

[0018] The long-transfer ranging signal includes a first uplink signal broadcast by the central station, a first downlink signal formed by the satellite receiving and forwarding the first uplink signal, a second uplink signal formed by the user station receiving and forwarding the first downlink signal, and a second downlink signal formed by the satellite receiving the second uplink signal and forwarding it to the central station.

[0019] A composite satellite timing system includes a central station and a user station that are respectively connected to a satellite for communication, and the central station, the satellite and the user station communicate with each other via long-range relay ranging signals;

[0020] When the system does not have a primary relay ranging signal, the communication between the satellite and the user station is via a secondary pseudorange ranging signal;

[0021] Similarly, when the system does not have a slave relay ranging signal, the communication between the satellite and the central station has a primary pseudorange ranging signal;

[0022] The main pseudorange ranging signal is played by the satellite and received and measured by the central station;

[0023] The pseudorange ranging signal is played by the satellite and received and measured by the user station;

[0024] The main relay ranging signal includes a main uplink signal and a main downlink signal. The central station broadcasts the main uplink signal and receives the main downlink signal. The satellite receives the main uplink signal and forwards it to form the main downlink signal.

[0025] The relay ranging signal includes an uplink signal and a downlink signal. The user station broadcasts the uplink signal and receives the downlink signal. The satellite receives the uplink signal and forwards it to form the downlink signal.

[0026] The long-transfer ranging signal includes a first uplink signal broadcast by the central station, a first downlink signal formed by the satellite receiving and forwarding the first uplink signal, a second uplink signal formed by the user station receiving and forwarding the first downlink signal, and a second downlink signal formed by the satellite receiving the second uplink signal and forwarding it to the central station.

[0027] Furthermore, the satellite includes:

[0028] Pseudorange broadcasting equipment generates and broadcasts the main pseudorange ranging signal or the slave pseudorange ranging signal;

[0029] The repeater forwards a received first uplink signal into a first downlink signal and a received second uplink signal into a second downlink signal; it forwards the received primary uplink signal to the central station; and it forwards the received secondary uplink signal to the user station.

[0030] The satellite time and frequency equipment provides time and frequency signals to the transponder and pseudorange broadcasting equipment;

[0031] The central station includes:

[0032] A long-transfer ranging device is used to broadcast the first uplink signal, receive and measure the second downlink signal to obtain a long-transfer ranging value;

[0033] The main forwarding ranging device is used to generate and broadcast the main uplink signal, and to receive and measure the main downlink signal to obtain the main forwarding ranging value;

[0034] When the system does not contain a primary forwarding ranging signal, i.e., no primary forwarding ranging device is set up, the central station adds a primary pseudorange ranging device to receive and measure the primary pseudorange ranging signal to obtain the primary pseudorange ranging value.

[0035] At least one primary time-frequency device is used to provide time-frequency signals to the long-transfer ranging device, the primary transfer ranging device, or the primary pseudorange ranging device.

[0036] The user station includes:

[0037] A response device, configured to receive the first downlink signal and forward it into the second uplink signal;

[0038] The forwarding ranging device is used to generate and broadcast the forwarding uplink signal, and to receive and measure the forwarding downlink signal to obtain the forwarding ranging value;

[0039] Similarly, when the system does not contain a forwarding ranging signal, that is, the user station does not have a forwarding ranging device, the user station adds a pseudorange ranging device to receive and measure the pseudorange ranging signal to obtain the pseudorange ranging value.

[0040] At least one time-frequency device is used to provide time-frequency signals to a response device, a relay ranging device, or a pseudorange ranging device.

[0041] Furthermore, the primary relay ranging device and the long relay ranging device are set to zero baseline, or the primary pseudorange ranging device and the long relay ranging device are set to zero baseline; the response device and the secondary pseudorange ranging device are set to zero baseline, or the response device and the secondary pseudorange relay ranging device are set to zero baseline.

[0042] Furthermore, the system also includes:

[0043] The computing device is communicatively connected to the central station and the user station respectively. The computing device receives long-range relay ranging values, primary relay ranging values, and secondary pseudorange ranging values, and calculates the total number of primary ionospheric electrons, the total number of secondary ionospheric electrons, and the relative clock difference between the user station and the satellite based on the long-range relay ranging values, primary relay ranging values, and secondary pseudorange ranging values.

[0044] Similarly, the computing device receives long-range relay ranging values, slave relay ranging values, and main pseudorange ranging values, and calculates the total number of electrons in the main ionosphere, the total number of electrons in the slave ionosphere, and the relative clock difference between the central station and the satellite based on the long-range relay ranging values, slave relay ranging values, and main pseudorange ranging values.

[0045] When no main relay ranging signal is set, the relative clock difference between the user station and the satellite and the total number of electrons in the ionosphere between the user station and the satellite are determined based on the pseudorange ranging value, the long relay ranging value, and the known ionospheric delay, tropospheric delay, and spatial distance between the central station and the satellite.

[0046] When there is at least one primary relay ranging signal, the relative clock difference between the user station and the satellite and the total number of electrons in the ionosphere between the user station and the satellite are determined based on the pseudorange ranging value, the long relay ranging value, the primary relay ranging value, and the known ionospheric delay between the central station and the satellite.

[0047] Similarly, when no relay ranging signal is set, the relative clock difference between the central station and the satellite and the total number of electrons in the ionosphere between the central station and the satellite are determined based on the main pseudorange ranging value, the long relay ranging value, and the known ionospheric delay, tropospheric delay, and spatial distance between the user station and the satellite.

[0048] When there is at least one primary relay ranging signal, the relative clock difference between the central station and the satellite and the total number of electrons in the ionosphere between the central station and the satellite are determined based on the pseudorange ranging value, the long relay ranging value, the primary relay ranging value, and the known ionospheric delay between the user station and the satellite.

[0049] This invention also provides a composite satellite-to-ground time synchronization method, employing the aforementioned composite satellite timing system. The method is executed by a computing device and includes:

[0050] The system communicates with the central station to obtain h primary forwarding ranging values ​​and s long forwarding ranging values, and communicates with the user station to obtain m secondary pseudorange ranging values. The s long forwarding ranging values ​​and h primary forwarding ranging values ​​are obtained by the central station measuring the long forwarding ranging signal and the primary forwarding ranging signal, and the m secondary pseudorange ranging values ​​are obtained by the user station measuring the secondary pseudorange ranging signal. h, s, and m are all positive integers, and m + h + s ≥ 5.

[0051] The computing device determines the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite based on the m pseudorange ranging values, the h main transponder ranging values, and the s long transponder ranging values;

[0052] Wherein, the total number of electrons in the main ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the central station and the satellite, and the total number of electrons in the secondary ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the user station and the satellite.

[0053] Further, based on the m pseudorange ranging values, the h main transponder ranging values, and the s long transponder ranging values, the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite are determined, including:

[0054] m pseudorange values ​​are corrected to obtain m corrected pseudorange values.

[0055] The h primary forwarding ranging values ​​are corrected to obtain h corrected primary forwarding ranging values;

[0056] The s long forwarding ranging values ​​are corrected to obtain s corrected long forwarding ranging values;

[0057] The relative clock difference between the user station and the satellite is determined by using the total number of electrons in the main ionosphere, any corrected pseudorange ranging value, any corrected main transponder ranging value, and any corrected long transponder ranging value.

[0058] Alternatively, the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite can be determined based on the m corrected pseudorange ranging values, the h corrected primary relay ranging values, and the s corrected long relay ranging values.

[0059] Further, based on the m corrected pseudorange ranging values, the h corrected primary transponder ranging values, and the s corrected long transponder ranging values, the total number of primary ionospheric electrons, the total number of secondary ionospheric electrons, and the relative clock difference between the user station and the satellite are determined, including:

[0060] The correction is performed mathematically on the pseudorange ranging value, the corrected main forwarding ranging value, and the corrected long forwarding ranging value to obtain the difference matrix;

[0061] Based on the difference matrix and the carrier frequencies of the pseudorange ranging signal, the main relay ranging signal, and the long relay ranging signal, a matrix equation is constructed with the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite as unknowns:

[0062]

[0063] Solving the matrix equation yields the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite.

[0064] In the formula, δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt u (n) represents the clock difference between the user station and the system time at time n, in seconds; c represents the speed of light, in meters per second; TEC z(n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter (TEC). u (n) represents the total number of electrons from the ionosphere on the ranging signal path between the satellite and the user station at time n, in electrons per square meter. G represents the coefficient matrix, which is at least a 3×3 matrix, and b represents the difference matrix, which is at least a 3×1 matrix.

[0065] Further, the relative clock difference between the user station and the satellite is determined based on the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, any of the corrected secondary pseudorange ranging values, any of the corrected primary transponder ranging values, and any of the corrected long transponder ranging values, including:

[0066] The relative clock difference between the user station and the satellite is obtained by processing the pseudorange ranging value, the primary relay ranging value, and the secondary relay ranging value with any correction. The relative clock difference is expressed as follows:

[0067]

[0068] Furthermore, the average relative clock difference between the user station and the satellite is obtained by averaging the relative clock differences between the user station and the satellite determined based on the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, multiple corrected secondary pseudorange ranging values, multiple corrected main transponder ranging values, and multiple corrected long transponder ranging values.

[0069] In the formula, δt u (n) represents the clock difference between the user station and the system time at time n, in seconds; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; L on,k,a (n) represents the corrected long-range relay ranging value with number k at time n, in meters; L z,j,a (n) represents the corrected primary relay ranging value with number j at time n, in meters; ρ u,i,a (n) represents the corrected pseudorange value numbered i at time n, in meters; u,i (n) represents the ionospheric delay of the pseudorange ranging signal numbered i at time n, in meters; xu,j (n),I xd,j (n) represents the ionospheric delay of the main uplink signal and the ionospheric delay of the main downlink signal of the main relay ranging signal numbered j at time n, in meters; zu,k (n),I zd,k (n) represents the ionospheric delay of the first uplink signal and the ionospheric delay of the second downlink signal for the long-transfer ranging value numbered k at time n, in meters; uu,k (n),Iud,k (n) represents the ionospheric delay of the second uplink signal and the ionospheric delay of the first downlink signal for the long-transfer ranging value numbered k at time n, in meters; Q ion Represents the ionospheric time delay factor; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter; TEC u (n) represents the total number of electrons from the ionosphere along the ranging signal path between the satellite and the user station at time n, in electrons per square meter; f u,i (n) represents the carrier frequency of the pseudorange ranging signal numbered i at time n, in Hertz; f xu,j (n),f xd,j (n) represents the carrier frequencies of the primary uplink and primary downlink signals of the primary relay ranging signal numbered j at time n, in Hertz; f zu,k (n),f zd,k (n) represents the carrier frequencies of the first uplink and second downlink signals of the long-transfer ranging signal numbered k at time n, in Hertz; f uu,k (n),f ud,k (n) represents the carrier frequencies of the second uplink signal and the first downlink signal of the long-transfer ranging signal numbered k at time n, in Hertz.

[0070] Further, determining the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere using the m corrected pseudorange ranging values, h corrected main transponder ranging values, and s corrected long transponder ranging values ​​includes:

[0071] When m≥1, s≥3, h≥1, the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere are calculated based on at least three corrected long-forward ranging values ​​corresponding to at least three long-forward ranging signals.

[0072] When m≥2, s≥1, and h≥2, the total number of electrons in the main ionosphere is determined using at least two corrected main forward ranging values, and the total number of electrons in the secondary ionosphere is determined using at least two corrected pseudorange ranging values.

[0073] When m≥2, s≥2, and h≥1, the total number of electrons in the ionosphere is determined using at least two corrected pseudorange ranging values, and then the total number of electrons in the main ionosphere is determined using the total number of electrons in the ionosphere and at least two corrected long-range ranging values.

[0074] When m≥1, s≥2, and h≥2, the total number of electrons in the main ionosphere is determined using at least two corrected main forwarding ranging values, and then the total number of electrons in the secondary ionosphere is determined using the total number of electrons in the main ionosphere and at least two corrected long forwarding ranging values.

[0075] A composite satellite-to-ground time synchronization method, employing the aforementioned composite satellite timing system, wherein the method is executed by a computing device, includes:

[0076] The system communicates with the central station to acquire m primary pseudorange ranging values ​​and s long forwarding ranging values, and communicates with the user station to acquire h secondary forwarding ranging values. The long forwarding ranging values ​​and primary pseudorange ranging values ​​are obtained by the central station measuring the long forwarding ranging signal and the primary pseudorange ranging signal, respectively. The h secondary forwarding ranging values ​​are obtained by the user station measuring h secondary forwarding ranging signals. Here, m, h, and s are all positive integers, and m + s + h ≥ 5.

[0077] The computing device determines the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite based on the m primary pseudorange ranging values, the h secondary relay ranging values, and the s long relay ranging values.

[0078] Further, the correction is performed based on the m primary pseudorange ranging values, the h secondary forwarding ranging values, and the s long forwarding ranging values, including:

[0079] The m principal pseudorange values ​​are corrected to obtain m corrected principal pseudorange values.

[0080] The h forwarding ranging values ​​are corrected to obtain h corrected forwarding ranging values;

[0081] The s long forwarding ranging values ​​are corrected to obtain s corrected long forwarding ranging values;

[0082] The relative clock difference between the central station and the satellite is determined by using the total number of electrons in the main ionosphere, any corrected main pseudorange ranging value, any corrected secondary relay ranging value, and any corrected long relay ranging value.

[0083] Alternatively, the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite can be determined based on the m primary pseudorange ranging values, the h secondary relay ranging values, and the s long relay ranging values.

[0084] Further, based on the m corrected primary pseudorange ranging values, the h corrected secondary transponder ranging values, and the s corrected long transponder ranging values, the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite are determined, including:

[0085] The modified primary pseudorange ranging value, the modified secondary forwarding ranging value, and the modified long forwarding ranging value are mathematically processed to obtain a difference matrix;

[0086] Based on the difference matrix and the carrier frequencies of the primary pseudorange ranging signal, the secondary relay ranging signal, and the long relay ranging signal, a matrix equation is constructed with the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite as unknowns:

[0087]

[0088] Solving the matrix equation yields the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite.

[0089] In the formula, δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter (TEC). u (n) represents the total number of electrons from the ionosphere on the ranging signal path between the satellite and the user station at time n, in electrons per square meter. G represents the coefficient matrix, which is at least a 3×3 matrix, and b represents the difference matrix, which is at least a 3×1 matrix.

[0090] Further, the relative clock difference between the central station and the satellite is determined based on the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, any of the corrected main pseudorange ranging values, any of the corrected secondary transponder ranging values, and any of the corrected long transponder ranging values, including:

[0091] The relative clock difference between the central station and the satellite is obtained by processing any of the corrected master-slave pseudorange ranging values, any corrected slave relay ranging values, and any corrected long relay ranging values. The clock difference is expressed as follows:

[0092]

[0093] Alternatively, the average relative clock difference between the central station and the satellite can be obtained by averaging the relative clock differences between the central station and the satellite determined based on the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, multiple corrected main pseudorange ranging values, multiple corrected secondary relay ranging values, and multiple corrected long relay ranging values.

[0094] In the formula, δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; L on,k,a(n) represents the corrected long-range relay ranging value with number k at time n, in meters; L u,j,a (n) represents the corrected relay ranging value with number j at time n, in meters; ρ z,i,a (n) represents the corrected pseudorange value numbered i at time n, in meters; z,i (n) represents the ionospheric delay of the primary pseudorange ranging signal numbered i at time n, in meters; yu,j (n),I yd,j (n) represents the ionospheric delay of the uplink signal and the downlink signal at time n, with the number j, in meters; zu,k (n),I zd,k (n) represents the ionospheric delay of the first uplink signal and the ionospheric delay of the second downlink signal for the long-transfer ranging value numbered k at time n, in meters; uu,k (n),I ud,k (n) represents the ionospheric delay of the second uplink signal and the ionospheric delay of the first downlink signal for the long-transfer ranging value numbered k at time n, in meters; Q ion Represents the ionospheric time delay factor; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter; TEC u (n) represents the total number of electrons from the ionosphere along the ranging signal path between the satellite and the user station at time n, in electrons per square meter; f z,i (n) represents the carrier frequency of the primary pseudorange ranging signal numbered i at time n, in Hertz; f yu,j (n),f yd,j (n) represents the carrier frequencies of the uplink and downlink signals of the slave relay ranging signal numbered j at time n, in Hertz; f zu,k (n),f zd,k (n) represents the carrier frequencies of the first uplink and second downlink signals of the long-transfer ranging signal numbered k at time n, in Hertz; f uu,k (n),f ud,k (n) represents the carrier frequencies of the second uplink signal and the first downlink signal of the long-transfer ranging signal numbered k at time n, in Hertz;

[0095] Further, determining the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere using the m corrected primary pseudorange ranging values, h corrected secondary transponder ranging values, and s corrected long transponder ranging values ​​includes:

[0096] When m≥1, s≥3, h≥1, the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere are calculated based on at least three corrected long-forward ranging values ​​corresponding to at least three long-forward ranging signals.

[0097] When m≥2, s≥1, and h≥2, the total number of electrons in the main ionosphere is determined using at least two corrected main pseudorange values, and the total number of electrons in the secondary ionosphere is determined using at least two corrected secondary range values.

[0098] When m≥2, s≥2, and h≥1, the total number of electrons in the main ionosphere is determined using at least two corrected main pseudorange values, and then the total number of electrons in the secondary ionosphere is determined using the total number of electrons in the main ionosphere and at least two corrected long-range ranging values.

[0099] When m≥1, s≥2, and h≥2, the total number of electrons in the ionosphere is determined using at least two corrected long-range ranging values, and then the total number of electrons in the main ionosphere is determined using the total number of electrons in the ionosphere and at least two corrected long-range ranging values.

[0100] A method for merging satellite-to-ground time synchronization, employing the aforementioned composite satellite timing system, wherein the method is executed by a computing device, includes:

[0101] There are h primary relay ranging signals between the central station and the satellite, m secondary pseudorange ranging signals between the satellite and the user station, and s long relay ranging signals between the central station, the satellite, and the user station. m secondary pseudorange ranging values ​​are obtained through the secondary pseudorange ranging device, s long relay ranging values ​​are obtained through the long relay ranging device, and h primary relay ranging values ​​are obtained through the primary relay ranging device. h is an integer greater than or equal to 0, s and m are both positive integers, and m+s≥3.

[0102] When h = 0, the relative clock difference between the user station and the satellite and the total number of electrons in the ionosphere between the user station and the satellite are determined based on m pseudorange ranging values, s long-transfer ranging values, the known total number of electrons in the main ionosphere between the central station and the satellite, the tropospheric delay, and the spatial distance.

[0103] When h≥1, the relative clock difference between the user station and the satellite and the total number of electrons in the secondary ionosphere between the user station and the satellite are determined based on m pseudorange ranging values, s long-transfer ranging values, h main-transfer ranging values, and the known total number of electrons in the primary ionosphere between the central station and the satellite.

[0104] Furthermore, based on m pseudorange ranging values, s long-transfer ranging values, and h main-transfer ranging values, the relative clock difference between the user station and the satellite and the total number of electrons in the ionosphere between the user station and the satellite are determined, including:

[0105] m pseudorange values ​​are corrected to obtain m corrected pseudorange values;

[0106] S corrected long forwarding ranging values ​​are obtained by correcting the s long forwarding ranging values;

[0107] The h primary forwarding ranging values ​​are corrected to obtain h corrected primary forwarding ranging values;

[0108] When h = 0, the equivalent long-transfer ranging value is obtained by using the known ionospheric delay, tropospheric delay and spatial distance between the central station and the satellite, based on the corrected long-transfer ranging value.

[0109] When h≥1, the equivalent slave relay ranging value is obtained by using the known ionospheric delay between the central station and the satellite, based on the corrected long relay ranging value and the corrected main relay ranging value.

[0110] The relative clock difference between the user station and the satellite is determined using the total number of electrons in the ionosphere, any equivalent relay ranging value, and any corrected pseudorange ranging value.

[0111] Alternatively, the relative clock difference between the user station and the satellite and the total number of electrons from the ionosphere can be determined based on s equivalent forwarding ranging values ​​and m corrected pseudorange ranging values.

[0112] Further, based on s equivalent relay ranging values ​​and m corrected pseudorange ranging values, the relative clock difference between the user station and the satellite and the total number of electrons from the ionosphere are determined, including:

[0113] The equivalent forwarding ranging value and the corrected pseudorange ranging value are mathematically processed to obtain the difference matrix;

[0114] Based on the difference matrix and the carrier frequencies of the pseudorange ranging signal and the equivalent relay ranging signal, a matrix equation is constructed with the total number of electrons in the ionosphere and the relative clock difference between the user station and the satellite as unknowns:

[0115]

[0116] Solving the matrix equation yields the total number of electrons from the ionosphere and the relative clock difference between the user station and the satellite;

[0117] In the formula, δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt u (n) represents the clock difference between the user station and the system time at time n, in seconds; c represents the speed of light, in meters per second; TEC u (n) represents the total number of electrons in the ionosphere along the ranging signal path between the satellite and the user station at time n, in units of electrons per square meter. G represents the coefficient matrix, which is at least a 2×2 matrix, and b represents the difference matrix, which is at least a 2×1 matrix.

[0118] Further, determining the relative clock difference between the user station and the satellite based on the total number of electrons from the ionosphere, any of the corrected pseudorange ranging values, and any of the equivalent relay ranging values ​​includes:

[0119] The relative clock difference between the user station and the satellite is obtained by processing the pseudorange ranging value and the equivalent forwarding ranging value of any correction, respectively. The relative clock difference is expressed as:

[0120]

[0121] Alternatively, the average relative clock difference between the user station and the satellite can be obtained by averaging the relative clock differences between the user station and the satellite determined from the total number of electrons in the ionosphere, multiple corrected pseudorange ranging values, and multiple equivalent relay ranging values.

[0122] In the formula, δt u (n) represents the clock difference between the user station and the system time at time n, in seconds; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; L eq,u,k,a (n) represents the equivalent relay ranging value with number k at time n, in meters, where k is a positive integer; ρ u,i,a (n) represents the corrected pseudorange value with ID i at time n, in meters, where i is a positive integer; u,i (n) represents the ionospheric delay of the pseudorange ranging signal numbered i at time n, in meters; uu,k (n),I ud,k (n) represents the equivalent uplink and downlink ionospheric delays of the relay ranging value at time n, with the number k, in meters; Q ion Represents the ionospheric time delay factor; c represents the speed of light, in meters per second; TEC u (n) represents the total number of electrons from the ionosphere along the ranging signal path between the satellite and the user station at time n, in electrons per square meter; f u,i (n) represents the carrier frequency of the pseudorange ranging signal numbered i at time n, in Hertz; f uu,k (n),f ud,k (n) represents the carrier frequencies of the uplink and downlink signals of the equivalent relay ranging signal numbered k at time n, in Hertz;

[0123] Further, determining the total number of electrons from the ionosphere using the m corrected pseudorange distance values ​​includes:

[0124] When m≥2, the total number of electrons in the ionosphere is determined using at least two corrected pseudorange distance measurements.

[0125] A composite satellite-to-ground time synchronization method, employing the aforementioned composite satellite timing system, wherein the method is executed by a computing device, includes:

[0126] There are h slave relay ranging signals between the central station and the satellite, m primary pseudorange ranging signals between the satellite and the central station, and s long relay ranging signals between the central station, the satellite, and the user station. The central station obtains m primary pseudorange ranging values ​​through the primary pseudorange ranging device, the long relay ranging device obtains s long relay ranging values, and the slave relay ranging device obtains h slave relay ranging values. Here, h is an integer greater than or equal to 0, s and m are both positive integers, and m + s ≥ 3.

[0127] When h = 0, based on m main pseudorange ranging values, s long relay ranging values, and the known ionospheric delay, tropospheric delay, and spatial distance between the user station and the satellite, the relative clock difference between the central station and the satellite and the total number of electrons in the main ionosphere between the central station and the satellite are determined.

[0128] When h≥1, the relative clock difference between the central station and the satellite and the total number of primary ionospheric electrons between the central station and the satellite are determined based on m primary pseudorange ranging values, s long-transfer ranging values, h secondary-transfer ranging values, and the known ionospheric delay between the user station and the satellite.

[0129] The total number of electrons in the main ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the central station and the satellite.

[0130] Furthermore, based on m primary pseudorange ranging values, s long-transfer ranging values, and h from the transfer ranging values, the relative clock difference between the central station and the satellite and the total number of primary ionospheric electrons between the central station and the satellite are determined, including:

[0131] m primary pseudorange values ​​are corrected to obtain m corrected primary pseudorange values;

[0132] S corrected long forwarding ranging values ​​are obtained by correcting the s long forwarding ranging values;

[0133] h forwarding ranging values ​​are corrected to obtain h corrected forwarding ranging values;

[0134] When h = 0, the equivalent main transponder ranging value is obtained by using the known total number of electrons from the ionosphere, tropospheric time delay, and spatial distance between the user station and the satellite, based on the corrected long transponder ranging value.

[0135] When h≥1, the equivalent primary transponder ranging value is obtained by using the known total number of electrons from the ionosphere between the user station and the satellite, based on the corrected long transponder ranging value and the corrected secondary transponder ranging value.

[0136] The relative clock difference between the central station and the satellite is determined using the total number of electrons in the main ionosphere, any equivalent main relay ranging value, and any corrected main pseudorange ranging value.

[0137] Alternatively, the relative clock difference and the total number of electrons in the main ionosphere between the central station and the satellite can be determined based on s equivalent main relay ranging values ​​and m corrected main pseudorange ranging values.

[0138] Furthermore, based on s equivalent primary relay ranging values ​​and m corrected primary pseudorange ranging values, the relative clock difference between the central station and the satellite and the total number of electrons in the primary ionosphere are determined, including:

[0139] The equivalent primary forwarding ranging value and the corrected primary pseudorange ranging value are mathematically processed to obtain the difference matrix;

[0140] Based on the difference matrix, the carrier frequencies of the main pseudorange ranging signal and the equivalent main relay ranging signal, a matrix equation is constructed with the total number of electrons in the main ionosphere and the relative clock difference between the central station and the satellite as unknowns:

[0141]

[0142] Solving the matrix equation yields the total number of electrons in the main ionosphere and the relative clock difference between the central station and the satellite;

[0143] In the formula, δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter. G represents the coefficient matrix, which is at least a 2×2 matrix, and b represents the difference matrix, which is at least a 2×1 matrix.

[0144] Further, determining the relative clock difference between the central station and the satellite based on the total number of electrons in the main ionosphere, any of the corrected main pseudorange ranging values, and any of the equivalent main transponder ranging values ​​includes:

[0145] By processing any of the corrected primary pseudorange ranging values ​​and any of the corrected equivalent primary relay ranging values, the relative clock difference between the central station and the satellite is obtained, and the relative clock difference is expressed as:

[0146]

[0147] Alternatively, the average relative clock difference between the central station and the satellite can be obtained by averaging the relative clock differences between the central station and the satellite determined based on the total number of electrons in the main ionosphere, multiple corrected main pseudorange ranging values, and multiple equivalent main transponder ranging values.

[0148] In the formula, δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; L eq,z,k,a (n) represents the equivalent primary relay ranging value numbered k at time n, in meters; ρ z,i,a (n) represents the corrected principal pseudorange value numbered i at time n, in meters; z,i (n) represents the ionospheric delay of the primary pseudorange ranging signal numbered i at time n, in meters; zu,k (n),I zd,k (n) represents the uplink and downlink ionospheric delays of the equivalent primary relay ranging value at time n, numbered k, in meters; Q ion Represents the ionospheric time delay factor; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter; f z,i (n) represents the carrier frequency of the primary pseudorange ranging signal numbered i at time n, in Hertz; f zu,k (n),f zd,k (n) represents the carrier frequencies of the uplink and downlink signals of the equivalent primary relay ranging signal numbered k at time n, in Hertz;

[0149] Further, determining the total number of electrons from the ionosphere using the m corrected pseudorange distance values ​​includes:

[0150] When m≥2, the total number of electrons in the main ionosphere is determined using at least two corrected main pseudorange measurements.

[0151] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0152] This application provides a composite satellite timing system and method that creatively integrates the BeiDou dual-satellite positioning system and the BeiDou satellite navigation system, significantly improving the satellite timing accuracy compared to either the BeiDou dual-satellite positioning system or the BeiDou satellite navigation system alone. It can obtain not only the total number of electrons in the primary ionosphere and the total number of electrons in the secondary ionosphere, but also the relative clock difference between the user station and the satellite, or the relative clock difference between the central station and the satellite. It boasts advantages such as high timing accuracy and strong real-time performance. Attached Figure Description

[0153] Figure 1 A schematic diagram of a first typical embodiment of the second composite satellite timing system provided by the present invention;

[0154] Figure 2 A schematic diagram of a second typical embodiment of the second composite satellite timing system provided by the present invention;

[0155] Figure 3 A schematic diagram of a third typical embodiment of the second composite satellite timing system provided by the present invention;

[0156] Figure 4 A schematic diagram of a fourth typical embodiment of the second composite satellite timing system provided by the present invention;

[0157] Figure 5 This is a diagram illustrating the equipment composition of a second composite satellite timing system provided in an embodiment of the present invention.

[0158] Figure 6 This is a diagram showing the equipment composition of a fourth composite satellite timing system provided in an embodiment of the present invention. Detailed Implementation

[0159] The present invention will now be described in detail with reference to the accompanying drawings.

[0160] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0161] The formula parameters appearing in this invention are explained as follows:

[0162] ρ u,i (n) represents the pseudorange value of number i at time n, in meters; ρ u,i,a (n) represents the corrected pseudorange value numbered i at time n, in meters; R true,u,i (n) represents the actual spatial distance traversed by the pseudorange ranging signal numbered i at time n, in meters; u,i (n) represents the ionospheric delay of the pseudorange ranging signal numbered i at time n, in meters (T). duiliu,u,i (n) represents the tropospheric time delay of the pseudorange ranging signal numbered i at time n, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt u(n) represents the clock difference between the user station and the system time at time n, in seconds; sagnac uu (n) represents the Sagnac effect delay of the pseudorange ranging signal at time n, in meters; X u.i (n) represents the hardware delay of the pseudorange ranging signal numbered i at time n, in meters. The hardware delay of the pseudorange ranging signal includes the transmission delay of the satellite for the pseudorange ranging signal numbered i and the reception delay of the user station for the pseudorange ranging signal numbered i.

[0163] L z,j (n) represents the primary relay ranging value numbered j at time n, in meters; L z,j,a (n) represents the corrected primary relay ranging value with number j at time n, in meters; R true,xu,j (n), R true,xd,j (n) represents the actual spatial distance traversed by the main uplink and main downlink signals of the main relay ranging signal numbered j at time n, in meters; xu,j (n), I xd,j (n) represents the ionospheric delay of the main uplink and main downlink signals of the main relay ranging signal numbered j at time n, in meters (T). duiliu,xu,j (n), T duiliu,xd,j (n) represents the tropospheric delay of the main uplink and main downlink signals of the main relay ranging signal numbered j at time n, in meters; Y z,j (n) represents the hardware device delay of the primary relay ranging signal numbered j at time n, in meters. The hardware device delay of the primary relay ranging signal includes the transmission delay of the primary uplink signal of the primary relay ranging signal numbered j by the central station, the forwarding delay of the primary downlink signal of the primary relay ranging signal numbered j generated by the satellite, and the reception delay of the primary downlink signal of the primary relay ranging signal numbered j by the central station.

[0164] L on,k (n) represents the long-range ranging value with ID k at time n, in meters; L on,k,a (n) represents the corrected long-range relay ranging value with number k at time n, in meters; R true,zu,k (n), R true,zd,k (n) represents the actual spatial distance traversed by the first uplink and second downlink signals between the central station and the satellite in the long-transfer ranging signal numbered k at time n, in meters; zu,k (n), I zd,k (n) represents the ionospheric delay of the first uplink and second downlink signals between the central station and the satellite in the long-range ranging signal numbered k at time n, in meters (T). duiliu,zu,k(n), T duiliu,zd,k (n) represents the tropospheric delay between the first uplink and second downlink signals between the central station and the satellite in the long-transfer ranging signal numbered k at time n, in meters; R true,uu,k (n), R true,ud,k (n) represents the true spatial distance traversed by the first downlink and second uplink signals between the user station and the satellite in the long-transfer ranging signal numbered k at time n, in meters; uu,k (n), I ud,k (n) represents the ionospheric delay of the first downlink and second uplink signals between the user station and the satellite in the long-transfer ranging signal numbered k at time n, in meters (T). duiliu,uu,k (n), T duiliu,ud,k (n) represents the tropospheric delay between the user station and the satellite in the long-transfer ranging signal numbered k at time n, in meters; Y on,k (n) represents the hardware device delay of the long-transfer ranging signal numbered k at time n, in meters. The hardware device delay includes the transmission and reception delay of the central station for the first uplink signal and the second downlink signal in the long-transfer ranging signal numbered k, the transmission and reception delay of the user station for the second uplink signal and the first downlink signal in the long-transfer ranging signal numbered k, and the forwarding delay of the satellite and the user station for the long-transfer ranging signal numbered k.

[0165] ρ z,i (n) represents the main pseudorange value numbered i at time n, in meters; ρ z,i,a (n) represents the corrected principal pseudorange value numbered i at time n, in meters; R true,z,i (n) represents the actual spatial distance traversed by the primary pseudorange ranging signal numbered i at time n, in meters; z,i (n) represents the ionospheric delay of the primary pseudorange ranging signal numbered i at time n, in meters (T). duiliu,z,i (n) represents the tropospheric delay of the primary pseudorange ranging signal numbered i at time n, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; sagnac zz (n) represents the Sagnac effect delay of the main pseudorange ranging signal at time n, in meters; X z.i(n) represents the hardware delay of the primary pseudorange ranging signal numbered i at time n, in meters. The hardware delay of the pseudorange ranging signal includes the transmission delay of the satellite for the primary pseudorange ranging signal numbered i and the reception delay of the central station for the primary pseudorange ranging signal numbered i.

[0166] L u,j (n) represents the ranging value of the relay with ID j at time n, in meters; L u,j,a (n) represents the corrected relay ranging value with number j at time n, in meters; R true,yu,j (n), R true,yd,j (n) represents the actual spatial distance traversed by the uplink and downlink signals of the relay ranging signal numbered j at time n, in meters; yu,j (n), I yd,j (n) represents the ionospheric delay of the uplink and downlink signals of the slave relay ranging signal numbered j at time n, in meters (T). duiliu,yu,j (n), T duiliu,yd,j (n) represents the tropospheric delay of the uplink and downlink signals of the relay ranging signal numbered j at time n, in meters; Y u,j (n) represents the hardware device delay of the slave-forwarded ranging signal numbered j at time n, in meters. The hardware device delay of the slave-forwarded ranging signal includes the transmission delay of the slave-forwarded ranging device for the slave uplink signal of the slave-forwarded ranging signal numbered j, the forwarding delay of the satellite generating the slave downlink signal of the slave-forwarded ranging signal numbered j, and the reception delay of the slave-forwarded ranging device receiving the slave downlink signal of the slave-forwarded ranging signal numbered j.

[0167] L eq,u,s,a (n) represents the equivalent relay ranging value with number s at time n, in meters; L eq,z,s,a (n) represents the equivalent primary relay ranging value numbered s at time n, in meters; f z,i (n) represents the carrier frequency of the primary pseudorange ranging signal numbered i at time n, in Hertz; f u,i (n) represents the carrier frequency of the pseudorange ranging signal numbered i at time n, in Hertz; f xu,j (n),f xd,j (n) represents the carrier frequencies of the primary uplink and primary downlink signals of the primary relay ranging signal numbered j at time n, in Hertz; f yu,j (n),f yd,j (n) represents the carrier frequencies of the upstream and downstream signals of the slave ranging signal numbered j at time n, in Hertz; f zu,k (n),fzd,k (n) represents the carrier frequencies of the first uplink and second downlink signals of the long-transfer ranging signal numbered k at time n, in Hertz; f uu,k (n),f ud,k (n) represents the carrier frequencies of the second uplink and first downlink signals of the long-transfer ranging signal numbered k at time n, in Hertz;

[0168] i, j, and k are all positive integers.

[0169] When satellites and ground stations communicate via radio, the radio signals experience time delays as they pass through the atmosphere, including ionospheric and tropospheric delays. When the carrier frequency is less than 30 GHz, the tropospheric delay is considered equal to the radio signal delay. However, the ionospheric delay is inversely proportional to the square of the carrier frequency and directly proportional to the total number of electrons in the ionosphere along the transmission path. The mathematical expression for the time delay of a radio signal crossing the ionosphere can be:

[0170]

[0171] In the formula, dI is the time delay of the radio frequency signal (i.e., the radio signal) when it travels through the ionospheric path of the satellite-to-ground connection (unit: meters); f is the carrier frequency of the radio signal (unit: Hertz); TEC is the total number of electrons in the ionosphere along the path between the satellite and the ground station (unit: electrons / square meter).

[0172] Special note: Q ion The ionospheric time delay coefficient is published by certain international organizations. With in-depth research on ionospheric time delay, the coefficient has become increasingly accurate. Previously, the ionospheric time delay coefficient was 40.28, 40.30, and currently it is 40.309. More precise coefficients may be available in the future. This application does not impose any specific limitations on the ionospheric time delay coefficient and uses the latest published value. In this embodiment, Q... ion The value is 40.309.

[0173] Obtaining ionospheric TEC values ​​has wide applications not only in satellite navigation but also in satellite communication and satellite remote sensing.

[0174] Ionospheric delay is a major positioning error term in satellite navigation and positioning, and also has a significant impact on satellite communication and satellite remote sensing. To address the above problems, embodiments of the present invention provide a composite satellite timing system.

[0175] The composite satellite timing system and related methods provided in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0176] The system time mentioned in this invention refers to the time during which a system is generated and maintained. For example, the system comprised of satellites, a central station, user stations, and computing equipment as described in this invention. In practical applications, BeiDou time is often used as the reference time and system time; the clock difference between different devices is the clock difference of each device relative to this BeiDou reference time.

[0177] Based on my country's existing dual-satellite positioning system and BeiDou satellite navigation system, this invention creatively integrates the two by relaying ranging signals, and presents a composite satellite timing system.

[0178] The present invention provides four types of composite satellite timing systems, each including a central station, user stations, and satellites. The four types of composite satellite timing systems are as follows:

[0179] The first scenario: There is no primary relay ranging signal or at least one primary relay ranging signal between the central station and the satellite; there are at least two secondary pseudorange ranging signals between the satellite and the user station; and there is at least one long relay ranging signal between the central station, the satellite, and the user. Alternatively, there is no primary relay ranging signal or at least one primary relay ranging signal between the central station and the satellite; there is at least one secondary pseudorange ranging signal between the satellite and the user station; and there are at least two long relay ranging signals between the central station, the satellite, and the user. The secondary pseudorange ranging value, long relay ranging value, and primary relay ranging value are obtained by measuring the secondary pseudorange ranging signal, the long relay ranging signal, and the primary relay ranging signal, respectively.

[0180] When there is no primary relay ranging signal between the central station and the satellite, if the spatial distance, tropospheric delay, and ionospheric delay between the central station and the satellite are known, these known quantities can be subtracted from the long-transfer ranging value to obtain the equivalent secondary relay ranging value between the satellite and the user station. Based on the equivalent secondary relay ranging value and the secondary pseudorange ranging value, the total number of electrons in the ionosphere between the satellite and the user station, and the relative clock difference between the user station and the satellite, can be obtained.

[0181] The spatial distance between the central station and the satellite can be calculated based on the satellite ephemeris and the coordinates of the central station. The tropospheric delay can be estimated based on the tropospheric model, while the ionospheric delay can be obtained using data provided by a third party or based on at least two pseudorange ranging signals broadcast by the satellite.

[0182] When there is at least one primary relay ranging signal between the central station and the satellite, and the total number of electrons in the primary ionosphere is known, the equivalent secondary relay ranging value is obtained based on the long relay ranging value, the primary relay ranging value, and the known total number of electrons in the primary ionosphere. Then, the total number of electrons in the secondary ionosphere and the relative clock difference between the user station and the satellite are obtained by combining the secondary pseudorange ranging value.

[0183] The second scenario involves h primary relay ranging signals between the central station and the satellite, at least m secondary pseudorange ranging signals between the satellite and the user station, and at least s long relay ranging signals between the central station, the satellite, and the user station, where m, s, and h are all positive integers, and m + s + h ≥ 5. The secondary pseudorange ranging value, long relay ranging value, and primary relay ranging value are obtained by measuring the secondary pseudorange ranging signal, the long relay ranging signal, and the primary relay ranging signal, respectively. The computing equipment calculates the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite based on the m secondary pseudorange ranging values, the s long relay ranging values, and the h primary relay ranging values.

[0184] The third scenario: There is no secondary ranging signal or at least one secondary ranging signal between the user station and the satellite; there are at least two primary pseudorange ranging signals between the satellite and the central station; and there is at least one long-transfer ranging signal between the central station, the satellite, and the user. Alternatively, there is no secondary ranging signal or at least one secondary ranging signal between the user station and the satellite; there is at least one primary pseudorange ranging signal between the satellite and the central station; and there are at least two long-transfer ranging signals between the central station, the satellite, and the user. The primary pseudorange ranging value, long-transfer ranging value, and secondary ranging value are obtained by measuring the primary pseudorange ranging signal, the long-transfer ranging signal, and the secondary ranging signal, respectively.

[0185] When there is no relay ranging signal between the user station and the satellite, if the spatial distance, tropospheric delay, and ionospheric delay between the user station and the satellite are known, these known quantities can be subtracted from the long relay ranging value to obtain the equivalent primary relay ranging value between the satellite and the central station. Based on the equivalent primary relay ranging value and the primary pseudorange ranging value, the total number of primary ionospheric electrons between the satellite and the central station and the relative clock difference between the central station and the satellite can be obtained.

[0186] The spatial distance between the user station and the satellite can be calculated based on the satellite ephemeris and the user station coordinates. The tropospheric delay can be estimated based on the tropospheric model, while the ionospheric delay can be obtained using data provided by a third party or based on at least two pseudorange ranging signals broadcast by the satellite.

[0187] When there is at least one slave relay ranging signal between the user station and the satellite, and the total number of electrons in the ionosphere is known, the equivalent master relay ranging value is obtained based on the long relay ranging value, the slave relay ranging value, and the known total number of electrons in the ionosphere. Then, the total number of electrons in the main ionosphere and the relative clock difference between the central station and the satellite are obtained by combining the master pseudorange ranging value.

[0188] The fourth method involves m primary pseudorange ranging signals between the central station and the satellite, at least h secondary ranging signals between the satellite and the user station, and at least s long-range ranging signals between the central station, the satellite, and the user station. Here, m, s, and h are all positive integers, and m + s + h ≥ 5. The primary pseudorange ranging value, long-range ranging value, and secondary ranging value are obtained by measuring the primary pseudorange ranging signal, the long-range ranging value, and the secondary ranging value, respectively. The calculation equipment uses the m primary pseudorange ranging values, the s long-range ranging values, and the h secondary ranging values ​​to calculate the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite.

[0189] When the number of primary relay ranging signals in the first type of composite satellite timing system is greater than or equal to 2, it evolves into the second type of composite satellite timing system.

[0190] When the number of relayed ranging signals in the third type of composite satellite timing system is greater than or equal to 2, it evolves into the fourth type of composite satellite timing system.

[0191] Both the primary pseudorange and the secondary pseudorange signals are signals broadcast by the satellite, but they are measured by the central station and the user station, respectively. The clock difference of the obtained pseudorange values ​​has different physical meanings. Other parameters such as spatial distance, tropospheric delay, ionospheric delay, and the Sagnac effect have similar physical meanings.

[0192] Therefore, for the sake of simplicity, the pseudorange signal will sometimes be referred to as either the primary pseudorange signal or the secondary pseudorange signal. The pseudorange value will refer to either the primary or secondary pseudorange value.

[0193] The same applies to relayed ranging signals; sometimes, relayed ranging signals refer to either the primary relayed ranging signal or the secondary relayed ranging signal. Relayed ranging values ​​refer to either the primary relayed ranging value or the secondary relayed ranging value.

[0194] It is worth noting that in the embodiments of this application, the computing device may be integrated into the central station, or integrated into the user station, or it may be independent of the central station and the user station, or it may be distributed in the central station and the user station to perform computing, or it may be a separate device.

[0195] Since the function of the computing device is to perform calculations based on pseudorange ranging values, long-range relay ranging values, and relay ranging values, which is not the core function of this application, this application focuses on describing the composite satellite timing system and various calculation methods.

[0196] For the second scenario: there are h primary relay ranging signals between the central station and the satellite, at least m secondary pseudorange ranging signals between the satellite and the user station, and at least s long relay ranging signals between the central station, the satellite, and the user station, where m, h, and s are all positive integers, and m + s + h ≥ 5. This scenario has four typical implementations, all of which can use the method of this application to obtain the total number of primary ionospheric electrons, the total number of secondary ionospheric electrons, and the relative clock difference between the user station and the satellite. The second scenario can be further divided into the following four typical implementations:

[0197] First typical embodiment: As shown in 1, there is one pseudorange ranging signal between the satellite and the user station, one main relay ranging signal between the satellite and the central station, and three long relay ranging signals between the central station, the satellite, and the user station. At this time, m=1, s=3, and h=1.

[0198] Second typical embodiment: such as Figure 2 As shown, there are two pseudorange ranging signals between the satellite and the user station, two main relay ranging signals between the satellite and the central station, and one long relay ranging signal between the central station, the satellite, and the user station. At this time, m = 2, s = 1, and h = 2.

[0199] Third typical embodiment: such as Figure 3 As shown, there is one pseudorange ranging signal between the satellite and the user station, two main relay ranging signals between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. At this time, m = 1, s = 2, and h = 2.

[0200] Fourth typical embodiment: such as Figure 4 As shown, there are two pseudorange ranging signals between the satellite and the user station, one main relay ranging signal between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. At this time, m = 2, s = 2, and h = 1.

[0201] For the fourth scenario: there are m primary pseudorange ranging signals between the central station and the satellite, at least h secondary ranging signals between the satellite and the user station, and at least s long-range ranging signals between the central station, the satellite, and the user, where m, h, and s are all positive integers, and m + s + h ≥ 5. This scenario has four typical implementations, all of which can use the method of this application to obtain the total number of primary ionospheric electrons, the total number of secondary ionospheric electrons, and the relative clock difference between the central station and the satellite. The fourth scenario can be further divided into the following four typical implementations:

[0202] First typical embodiment: There is one primary pseudorange ranging signal between the satellite and the central station, one secondary relay ranging signal between the satellite and the user station, and three long relay ranging signals between the central station, the satellite, and the user station. In this case, m=1, s=3, and h=1.

[0203] Second typical embodiment: There are two primary pseudorange ranging signals between the satellite and the central station, two secondary relay ranging signals between the satellite and the user station, and one long relay ranging signal between the central station, the satellite, and the user station. In this case, m=2, s=1, and h=2.

[0204] The third typical embodiment: There is one primary pseudorange ranging signal between the satellite and the central station, two secondary relay ranging signals between the satellite and the user station, and two long relay ranging signals between the central station, the satellite, and the user station. In this case, m=1, s=2, and h=2.

[0205] Fourth typical embodiment: There are two primary pseudorange ranging signals between the satellite and the central station, one secondary relay ranging signal between the satellite and the user station, and two long relay ranging signals between the central station, the satellite, and the user station. In this case, m=2, s=2, and h=1.

[0206] In an exemplary embodiment, the composite satellite timing system includes a central station 200, a satellite 100, and a user station 300, as well as computing devices. A long-range relay ranging signal exists between the central station 200, the satellite 100, and the user station 300. This long-range relay ranging signal consists of a first uplink signal broadcast by the central station 200, a first downlink signal formed by the satellite 100 receiving and relaying the first uplink signal, a second uplink signal formed by the user station 300 receiving and relaying the first downlink signal, and a second downlink signal received by the satellite 100 and relayed to the central station 200. Two self-transmitting and self-receiving main relay ranging signals exist between the central station and the satellite. The satellite 100 broadcasts a pseudorange ranging signal to the user station 300, which receives and measures the pseudorange ranging signal to obtain the pseudorange ranging value.

[0207] It should be noted that the pseudorange ranging signal, long-transfer ranging signal, and forward ranging signal described in this exemplary embodiment refer to the signal obtained by modulating a ranging code signal into a carrier signal. In some specific embodiments, the ranging code can be a pseudo code, a weil code, an M code, etc., and this application does not make any special limitation on which ranging code is specifically selected. Furthermore, it is understood that all pseudorange ranging signals, long-transfer ranging signals, and forward ranging signals described in the embodiments of this application are spread spectrum signals. When multiple spread spectrum signals are transmitted and received, the relationship between the carrier frequency and the ranging code is processed according to spread spectrum communication technology and code division multiple access communication technology, which will not be elaborated here.

[0208] Since pseudorange ranging signals, long-running ranging signals, and repeating ranging signals are all spread spectrum signals, they are collectively referred to as ranging signals for the sake of simplicity and convenience.

[0209] The specific structures of the satellite 100, central station 200, and user station 300 in this exemplary embodiment will be further described below with reference to the accompanying drawings.

[0210] The composite satellite timing system provided in this application can be applied to aerospace systems, for example, using satellites as navigation satellites, communication satellites, remote sensing satellites, or meteorological satellites. Furthermore, when this system is used to provide timing services to user stations, the user stations can be base stations in the mobile communication field.

[0211] In the second embodiment, the device composition is as follows: Figure 5 As shown, satellite 100 may include transponder 101, pseudorange broadcasting device 102, and satellite time and frequency device 103. Satellite time and frequency device 103 can provide time and frequency signals for transponder and pseudorange broadcasting device 102. Transponder 101 can forward uplink signals of several received forwarding ranging signals into downlink signals of forwarding ranging signals. It can also forward the first uplink signal of a long forwarding ranging signal into a first downlink signal and forward the second uplink signal into a second downlink signal.

[0212] The repeater 101 is mainly used to perform frequency conversion and power amplification on the acquired uplink signal before forwarding it.

[0213] The pseudorange broadcasting device 102 is used to generate pseudorange ranging signals. The user station receives the pseudorange ranging signal, which is called the slave pseudorange ranging signal, and the central station receives the pseudorange ranging signal, which is called the master pseudorange ranging signal.

[0214] It should be understood that the transponder 101, pseudorange broadcasting device 102, and satellite time and frequency device 103 described in this embodiment can be set independently or integrated into a hardware device, that is, implemented through an integrated hardware device. All of these fall within the protection scope of this application.

[0215] The central station 200 may include a main time-frequency device 203, a main relay ranging device 201, and a long relay ranging device 202 that establish communication connections with each other. The main relay ranging device 201 broadcasts the main uplink signal and receives the main downlink signal to measure and obtain the main relay ranging value; the long relay ranging device 201 broadcasts the first uplink signal and receives the second downlink signal relayed by the satellite to measure and obtain the long relay ranging value.

[0216] The main time-frequency device 203 can provide time-frequency signals to the main relay ranging device 201 and the long relay ranging device 202.

[0217] The central station's main relay ranging device 201 may include a modulator, mixer, demodulator, antenna, and data acquisition unit. The modulator generates an intermediate frequency spread spectrum signal; the mixer mixes the intermediate frequency spread spectrum signal to a radio frequency (RF) signal; the antenna transmits the RF signal to the satellite and receives the RF signal relayed by the satellite; the antenna receives the RF signal and mixes it to an intermediate frequency signal by the mixer; the demodulator demodulates the intermediate frequency signal and obtains the main relay ranging value through ranging code correlation calculation; and the data acquisition unit records and stores the main relay ranging value.

[0218] Furthermore, it should be noted that the main time-frequency device 203, the main relay ranging device 201, and the long relay ranging device 202 can be set up independently or integrated, and these all fall within the protection scope of this invention.

[0219] User station 300 may include time and frequency device 303, pseudorange ranging device 302, response device 301, and computing device 304, wherein computing device 304 integrates the computing device of the composite satellite timing system provided in this application into the user station, and the computing device described thereafter refers to computing device 304 integrated into the user station.

[0220] The pseudorange measuring device 302 is used to receive and measure the pseudorange measuring signal to obtain the pseudorange measuring value.

[0221] The time-frequency device 303 can provide time-frequency signals to the pseudorange ranging device 302 and the response device.

[0222] The computing device 304 is connected to the pseudorange ranging device 302 and the central station to obtain the pseudorange ranging value, the long-transfer ranging value and the main-transfer ranging value, and executes the method provided by the present invention to obtain the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite.

[0223] Furthermore, it should be noted that the pseudorange ranging device 302, the time and frequency device 303, the response device 301, and the computing device 304 included in the user station 300 can be set up independently or integrated, and all of these fall within the protection scope of this application.

[0224] The pseudorange ranging device 302 includes a receiving antenna and a receiver, wherein the receiving antenna receives the pseudorange ranging signal and performs the measurement.

[0225] In this exemplary embodiment, the pseudorange ranging device 302 and the response device 301 are set to zero baseline.

[0226] In the fourth embodiment, the device composition is as follows: Figure 6 As shown, the satellite equipment composition is the same in both cases. The only difference is the composition of the central station. Figure 5 The central station main relay ranging equipment 201 was changed to Figure 6The central station's main pseudorange ranging device 211, and the composition of the user station are simply... Figure 5 The pseudorange ranging device 302 was changed to Figure 6 The ranging device 312 is used for forwarding.

[0227] It is worth noting that the zero baseline setting mentioned in this application does not mean that the distance between the pseudorange ranging device 302 and the response device 301 is zero. Rather, it means that the distance between them is set to ensure that the spatial paths traversed by each pseudorange ranging signal, the first downlink signal, and the second uplink signal are approximately the same. For example, as the distance between the pseudorange ranging device 302 and the response device 301 becomes smaller and smaller, and they can be integrated into a single device, the approximation gradually becomes identical, with the same satellite-to-ground spatial distance, the same tropospheric time delay, and the same total number of ionospheric electrons.

[0228] In this embodiment, at least one time-frequency device is used for both the pseudorange measuring device 302 and the response device 301. One time-frequency device provides a time-frequency signal to the pseudorange measuring device 302, while the remaining time-frequency devices provide time-frequency signals to the response device 301. In practical use, the preset time interval can be set to 1 second, with the pseudorange measuring device 302 performing synchronous measurements at the rising or falling edge of its own 1PPS (1 Pulse Per Second) signal. The response device 301 operates under its own time-frequency signal. Preferably, it is generally recommended to use a single clock, meaning that the pseudorange measuring device 302 and the response device 301 operate using a common time-frequency signal.

[0229] The main relay ranging device 201 and the long relay ranging device 202 of the central station are also set to zero baseline, because the pseudorange ranging device and the response device of the same user station are set to zero baseline.

[0230] Figure 6 In the process, the main pseudorange ranging device 201 and the long relay ranging device 202 of the central station are set to zero baseline, and the slave relay ranging device and the response device of the user station are set to zero baseline.

[0231] The transponder 101 generates satellite forwarding delay during the signal forwarding process. The satellite forwarding delay includes the forwarding delay of the ranging signal and the forwarding delay of the long-term ranging signal through the satellite 100.

[0232] It is worth noting that, in this embodiment, during communication between the central station 200 and the satellite 100, the satellite 100 can first transmit its forwarding delay to the central station 200 by adding a communication signal, thereby enabling the central station 200 to obtain the forwarding delay of the satellite 100. Then, the central station 200 uses the long-range ranging signal to transmit the aforementioned satellite forwarding delay to the user station 300, or broadcasts the satellite forwarding delay to the central station and the user station through the pseudorange ranging signal broadcast by the satellite.

[0233] In this embodiment, the central station 200 has central station equipment delay, which includes the transmission and reception delay of the main relay ranging device 201, the transmission and reception delay of the long relay ranging device 202, or the reception delay of the central station main pseudorange ranging device.

[0234] In this embodiment, the user station 300 has device delays, including reception delays for receiving pseudorange ranging signals from pseudorange ranging device 302, forwarding delays for responding device to receive a first downlink signal and forward it as a second uplink signal, or transmission and reception delays from forwarding ranging device.

[0235] The carrier frequencies of all pseudorange ranging signals, all long-transit ranging signals, and all transit ranging signals are frequency-hopped on the time axis according to a preset frequency hopping pattern, which can improve the anti-interference capability and anti-interception capability of the signals.

[0236] Of course, the carrier frequency of each signal in all pseudorange ranging signals, all long-running ranging signals, and all-running ranging signals can remain unchanged for a long time, that is, the time interval between two frequency hopping is infinite.

[0237] The composite satellite timing system provided in this embodiment also has a satellite-to-ground communication function. The satellite 100 uses an additional communication signal to interact with the central station. The additional communication signal can be a remote control and telemetry signal.

[0238] It should be noted that in this embodiment, when calculating the relative clock difference between the user station and the satellite or the relative clock difference between the central station and the satellite, the corresponding Sagnac effect delay needs to be obtained. When calculating the clock difference, the Sagnac effect delay requires the coordinates of the user station and the satellite or the coordinates of the central station and the satellite. The coordinates of the satellite can be obtained from known satellite ephemeris, and the coordinates of the user station or the central station can be obtained from existing positioning methods. In this way, the coordinate information required by the method of this application embodiment is obtained, and then the Sagnac effect delay is obtained.

[0239] Furthermore, unless otherwise specified, this embodiment can obtain the relativistic delay of the satellite based on the satellite's ephemeris and motion velocity, or it can refer to the existing BeiDou satellite clock method to perform relativistic delay correction.

[0240] When using the forwarding ranging expression to characterize the forwarding ranging value, there is no Sagnac effect delay in the forwarding ranging expression because the Sagnac effect delay of the uplink signal and the Sagnac effect delay of the downlink signal have opposite signs, and the difference in their absolute values ​​is very small. Therefore, these two Sagnac effect delays can be approximately canceled out, so the Sagnac effect delay term is not reflected in the forwarding ranging expression.

[0241] When using the long-transfer ranging expression to characterize the long-transfer ranging value, there is no Sagnac effect delay in the long-transfer ranging expression because the Sagnac effect delay of the uplink signal and the Sagnac effect delay of the downlink signal have opposite signs, and the difference in their absolute values ​​is very small. Therefore, these two Sagnac effect delays can be approximately canceled out, so the Sagnac effect delay term is not reflected in the long-transfer ranging expression.

[0242] Of course, in other embodiments, the Sagnac effect delay can also be considered, that is, the Sagnac effect delay of the uplink signal and the Sagnac effect delay of the downlink signal are added to the forwarding ranging expression, so as to obtain better measurement accuracy of the forwarding ranging value. These are all within the protection scope of this application.

[0243] In this application, pseudorange ranging signals, long-transfer ranging signals, and relay ranging signals all need to pass through the troposphere and ionosphere when traversing the atmosphere. The ionosphere is a diffuse medium, meaning that the time delay generated by the ionosphere for radio frequency signals with different carrier frequencies varies depending on the carrier frequency. In contrast, the troposphere is a non-diffuse medium, meaning that the troposphere generates the same time delay for radio frequency signals with different carrier frequencies.

[0244] Because the primary and secondary uplink signals of the main and secondary relay ranging signals traverse the common path between the satellite and the central station, and both the primary relay ranging device 201 and the secondary relay ranging device 202 are configured with zero baselines. Both the primary and secondary relay ranging signals are transmitted and received by the central station itself, and there is a certain time difference between transmission and reception. Within a short period, such as a few seconds, the ionosphere is stable, and the total number of electrons in the ionosphere remains almost constant. It can be calculated that the round-trip time of radio frequency signals between almost all spacecraft and ground stations currently does not exceed a few seconds, fully meeting the requirements. Combining the spatial relationship of zero baseline settings and the short time difference, the spatial paths traversed by the primary and secondary relay ranging signals are exactly the same, as shown in the following equation:

[0245]

[0246]

[0247] In this embodiment, the pseudorange ranging device 302 and the response device 301 are set to zero baseline. The first downlink signal and the second uplink signal in the pseudorange ranging signal and the long-transfer ranging signal also have a similar spatial path relationship as described above, as follows:

[0248] R true,u,1 (n)=R true,u,2 (n)=R true,uu,1 (n)=R true,ud,1 (n)=R true,uu,2 (n)=R true,ud,2 (n)(12)

[0249] T duiliu,u,1 (n)=T duiliu,u,2 (n)=T duiliu,uu,1 (n)=T duiliu,ud,1 (n)=T duiliu,uu,2 (n)=T duiliu,ud,2 (n)(13)

[0250] Similarly, in this embodiment, the main pseudorange ranging device 211 and the long-transfer ranging device 202 are set to zero baseline. The spatial distances on the transmission paths of the first uplink signal and the second downlink signal in the main pseudorange ranging signal and the long-transfer ranging signal are equal, and the tropospheric delays are also equal.

[0251] The forward ranging device 312 and the response device 301 are set to zero baseline. The spatial distances on the transmission paths of the second uplink signal and the first downlink signal in the forward ranging signal and the long forward ranging signal are equal, and the tropospheric delays are also equal.

[0252] It should be noted that since the central station and user stations measure the long-range relay ranging value, the primary relay ranging value, and the secondary pseudorange ranging value under their respective clock signals, the central station and user stations need to meet the coarse synchronization requirement in time, which is generally required to be on the order of milliseconds. It can be considered that the central station and user stations are measuring synchronously before executing the method of this application.

[0253] Based on the above embodiments, this embodiment also provides a composite satellite-to-ground time synchronization method, which is applied to the composite satellite timing system described in any of the above embodiments. The method is executed by a computing device and is applicable to a second type of composite satellite timing system.

[0254] The composite satellite-to-ground time synchronization method may include the following steps:

[0255] S200. Based on the communication results with the central station, obtain h primary forwarding ranging values ​​and s long forwarding ranging values ​​measured by the central station, and obtain m secondary pseudorange ranging values ​​based on the communication results with the user station; where m, h, and s are all positive integers, and m+s+h≥5;

[0256] S210. Each of the primary forwarding ranging values ​​is represented by a forwarding ranging expression, each of the long forwarding ranging values ​​is represented by a long forwarding ranging expression, and each of the secondary pseudorange ranging values ​​is represented by a pseudorange ranging expression.

[0257] S220. Based on the s long-transfer ranging values, the h primary transfer ranging values, and the m secondary pseudorange ranging values, determine the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite.

[0258] The maximum envelope of the four typical systems in the second scenario consists of three long-range forwarding ranging values ​​+ two primary forwarding ranging values ​​+ two secondary pseudorange ranging values. The calculation is explained based on the required measurement values ​​for each of the four typical systems.

[0259] In S200, the main relay ranging value and long relay ranging value obtained from the central station are obtained, and the pseudorange ranging value is obtained by communicating with the user station; in S210, the computing device can characterize the main relay ranging value by the following formula (14), the long relay ranging value by the following formula (15), and the pseudorange ranging value by the following formula (16):

[0260] L z,j (n)=R true,xu,j (n)+R true,xd,j (n)+I xu,j (n)+I xd,j (n)+T duiliu,xu,j (n)+T duiliu,xd,j (n)+Y z,j (n)(14)

[0261] In the formula, j = 1, 2, ..., h, where j and h are positive integers;

[0262]

[0263] In the formula, k = 1, 2, ..., s, where k and s are positive integers;

[0264] ρ u,i (n)=R true,u,i (n)+I u,i (n)+T duiliu,u,i (n)+sagnac uu (n)+X u,i (n)+c·(δt u (n)-δt s (n)) (16)

[0265] In the formula, i = 1, 2, ..., m, where i and m are positive integers;

[0266] As analyzed above, the computing device further obtains the specific first primary forwarding ranging value and the second primary forwarding ranging value based on formula (14), as shown in formulas (17) and (18):

[0267] L z,1 (n)=R true,xu,1 (n)+R true,xd,1 (n)+I xu,1 (n)+I xd,1 (n)+T duiliu,xu,1 (n)+T duiliu,xd,1 (n)+Y z,1 (n) (17)

[0268] L z,2 (n)=R true,xu,2 (n)+R true,xd,2 (n)+I xu,2 (n)+I xd,2 (n)+T duiliu,xu,2 (n)+T duiliu,xd,2 (n)+Y z,2 (n) (18)

[0269] Similarly, the computing device obtains the specific first long forwarding ranging value, the second long forwarding ranging value and the third long forwarding ranging value according to formula (15), as shown in formulas (19), (20) and (21);

[0270]

[0271]

[0272]

[0273] Similarly, the computing device obtains the specific first pseudorange measurement value and the second pseudorange measurement value according to formula (16), as shown in formulas (22) and (23);

[0274] ρ u,1 (n)=R true,u,1 (n)+I u,1 (n)+T duiliu,u,1 (n)+sagnac uu (n)+X u,1 (n)+c·(δt u (n)-δt s (n))(22)

[0275] ρ u,2 (n)=R true,u,2 (n)+I u,2 (n)+T duiliu,u,2 (n)+sagnac uu(n)+X u,2 (n)+c·(δt u (n)-δt s (n))(23)

[0276] The first primary forwarding ranging value, the second primary forwarding ranging value, the first long forwarding ranging value, the second long forwarding ranging value, and the third long forwarding ranging value are corrected respectively to obtain the first corrected primary forwarding ranging value and the second corrected primary forwarding ranging value as shown in formulas (24) and (25), and the first corrected long forwarding ranging value, the second corrected long forwarding ranging value, and the third corrected long forwarding ranging value as shown in formulas (26), (27), and (28).

[0277] L z,1,a (n)=L z,1 (n)-Y z,1 (n)=R true,xu,1 (n)+R true,xd,1 (n)+I xu,1 (n)+I xd,1 (n)+T duiliu,xu,1 (n)+T duiliu,xd,1 (n) (24)

[0278] L z,2,a (n)=L z,2 (n)-Y z,2 (n)=R true,xu,2 (n)+R true,xd,2 (n)+I xu,2 (n)+I xd,2 (n)+T duiliu,xu,2 (n)+T duiliu,xd,2 (n) (25)

[0279]

[0280]

[0281]

[0282] The first and second pseudorange measurements are corrected to obtain the first and second corrected pseudorange measurements as shown in formulas (29) and (30):

[0283]

[0284]

[0285] This embodiment provides two methods to determine the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite. The first method uses a matrix approach to jointly solve for the three unknowns; the second method first calculates the total number of electrons in the secondary ionosphere between the user station and the satellite and the total number of electrons in the main ionosphere between the central station and the satellite, and then calculates the relative clock difference between the user station and the satellite. These two calculation methods are explained in detail below.

[0286] (1) Matrix method

[0287] In the matrix method, the computing device utilizes the zero-baseline setting relationship between the response device and the pseudorange ranging device in the user station, and the zero-baseline setting relationship between the main relay ranging device and the long relay ranging device in the central station. It processes m corrected pseudorange ranging values, h corrected main relay ranging values, and s corrected long relay ranging values ​​to form a matrix equation as shown in formula (1):

[0288]

[0289] The solution to the above matrix equation (1) is expression (31).

[0290]

[0291] In the formula, matrix G has at least 3 rows and 3 columns, with the first column consisting entirely of 1s; matrix b has at least 3 rows and 1 column.

[0292] The computing device obtains the corresponding matrix G and matrix b for the specific system according to the four typical embodiments of the second case, and then substitutes the specific matrix into formula (31) to solve for the unknown. The calculation process of the four typical embodiments of the second case is described below.

[0293] First typical embodiment: such as Figure 1 As shown, there is one pseudorange ranging signal between the satellite and the user station, one main relay ranging signal between the satellite and the central station, and three long relay ranging signals between the central station, the satellite, and the user station. At this time, m = 1, s = 3, and h = 1.

[0294] The carrier frequencies of the three long-range relay ranging signals are different from the carrier frequencies of one pseudorange ranging signal and one main relay ranging signal; thus, matrices G and b are obtained.

[0295]

[0296]

[0297] Second typical embodiment: such as Figure 2As shown, there are two pseudorange ranging signals between the satellite and the user station, two main relay ranging signals between the satellite and the central station, and one long relay ranging signal between the central station, the satellite, and the user station. At this time, m = 2, s = 1, and h = 2.

[0298] The carrier frequencies of the two pseudorange ranging signals and the carrier frequency of the one long-relay ranging signal are different. This yields matrices G and b.

[0299]

[0300]

[0301] Third typical embodiment: such as Figure 3 As shown, there is one pseudorange ranging signal between the satellite and the user station, two main relay ranging signals between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. At this time, m = 1, s = 2, and h = 2.

[0302] The carrier frequencies of the one pseudorange ranging signal, the two long-transfer ranging signals, and the two main-transfer ranging signals are all different. This yields matrices G and b.

[0303]

[0304]

[0305] Fourth typical embodiment: such as Figure 4 As shown, there are two pseudorange ranging signals between the satellite and the user station, one main relay ranging signal between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. At this time, m = 2, s = 2, and h = 1.

[0306] The carrier frequencies of the two pseudorange ranging signals, the two long-transfer ranging signals, and the main-transfer ranging signal are all different. This yields matrices G and b.

[0307]

[0308]

[0309] (2) Sequential method

[0310] The sequential method involves the computing device first calculating the total number of electrons in the ionosphere between the user station and the satellite, and the total number of electrons in the main ionosphere between the central station and the satellite. Then, using the total number of electrons in the main ionosphere, the total number of electrons in the ionosphere, and any corrected pseudorange ranging value, any corrected main transponder ranging value, and any corrected long transponder ranging value, the relative clock difference between the user station and the satellite is calculated. Here, the first corrected pseudorange ranging value, the first corrected main transponder ranging value, and the first corrected long transponder ranging value are selected respectively for calculation, as shown in formula (40).

[0311]

[0312] The specific calculation methods for the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere will still be explained separately for the two composite satellite timing systems:

[0313] First typical embodiment: There is one pseudorange ranging signal between the satellite and the user station, one main relay ranging signal between the satellite and the central station, and three long relay ranging signals between the central station, the satellite, and the user station. The total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere are calculated using the three long relay ranging values. At this time, m=1, s=3, and h=1.

[0314] The carrier frequencies of the three long-transfer ranging signals are different from the carrier frequencies of one pseudorange ranging signal and one main-transfer ranging signal.

[0315] A matrix equation is constructed using three corrected long-range ranging values ​​to calculate the total number of electrons in the primary ionosphere and the secondary ionosphere. Then, the relative clock difference between the user station and the satellite is determined using the total number of electrons in the primary and secondary ionospheres, any corrected long-range ranging value, any corrected primary ranging value, and any corrected secondary pseudorange ranging value.

[0316] Construct a matrix equation (41) with the unknowns being the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere;

[0317]

[0318] The solution to matrix equation (41) is given by formula (42).

[0319]

[0320] in,

[0321]

[0322]

[0323] Second typical embodiment: such as Figure 2As shown, there are two pseudorange ranging signals between the satellite and the user station, two main relay ranging signals between the satellite and the central station, and one long relay ranging signal between the central station, the satellite, and the user station. The total number of electrons in the ionosphere is calculated using the two pseudorange ranging values, and the total number of electrons in the main ionosphere is calculated using the two main relay ranging values. At this time, m=2, s=1, and h=2.

[0324] The carrier frequencies of the two pseudorange ranging signals and the carrier frequency of the one long-forward ranging signal are different.

[0325] The total number of electrons in the ionosphere is calculated from the pseudorange measurement value using two corrections, and is obtained using the following formula (45):

[0326]

[0327] The total number of electrons in the main ionosphere is calculated using two corrected main transponder ranging values, and is obtained using the following formula (46):

[0328]

[0329] The third typical embodiment: There is one pseudorange ranging signal between the satellite and the user station, two main relay ranging signals between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. The total number of electrons in the main ionosphere is calculated using the two main relay ranging values, and then the total number of electrons in the secondary ionosphere is calculated using the two long relay ranging values ​​and the total number of electrons in the main ionosphere. In this case, m=1, s=2, and h=2.

[0330] The carrier frequencies of the one pseudorange ranging signal, the two long-relay ranging signals, and the two main-relay ranging signals are all different.

[0331] First, the total number of electrons in the main ionosphere is calculated using two corrected main forwarding ranging values, as shown in formula (46);

[0332] The total number of electrons in the ionosphere is calculated based on two corrected long-range ranging values ​​and the already calculated total number of electrons in the main ionosphere, according to the following formula (47).

[0333]

[0334] Fourth typical embodiment: such as Figure 4As shown, there are two pseudorange ranging signals between the satellite and the user station, one main relay ranging signal between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. The total number of electrons in the ionosphere is calculated using the two pseudorange ranging values, and then the total number of electrons in the main ionosphere is calculated using the two long relay ranging values ​​and the total number of electrons in the ionosphere. At this time, m=2, s=2, and h=1.

[0335] The carrier frequencies of the two pseudorange ranging signals, the two long-relay ranging signals, and the main relay ranging signal are all different.

[0336] First, the total number of electrons in the ionosphere is calculated from the pseudorange measurement value using two corrections, as shown in formula (45);

[0337] The total number of electrons in the main ionosphere is calculated based on two corrected long-range ranging values ​​and the already calculated total number of electrons in the ionosphere, according to the following formula (48).

[0338]

[0339] Based on the above embodiments, this embodiment also provides a composite satellite-to-ground time synchronization method for the first composite satellite timing system, which is executed by a computing device.

[0340] The first type of composite satellite time synchronization system: It uses either no master relay ranging signal or one master relay ranging signal. The composite satellite-to-ground time synchronization method of this first type of system calculates the total number of electrons in the ionosphere and the relative clock difference between the user station and the satellite based on equivalent slave relay ranging values ​​and slave pseudorange ranging values. This method can calculate the equivalent slave relay ranging value based on the long relay ranging value, whether there is no master relay ranging signal or at least one master relay ranging signal.

[0341] The composite satellite-to-ground time synchronization method may include the following steps:

[0342] S100: Based on the communication results with the central station, obtain h primary forwarding ranging values ​​and s long forwarding ranging values ​​measured by the central station, and obtain m secondary pseudorange ranging values ​​based on the communication results with the user station; where h is an integer greater than or equal to 0, m and s are both positive integers, and m+s≥3;

[0343] S110. Each of the primary forwarding ranging values ​​is represented by a forwarding ranging expression, each of the long forwarding ranging values ​​is represented by a long forwarding ranging expression, and each of the secondary pseudorange ranging values ​​is represented by a pseudorange ranging expression.

[0344] S120. Based on the s long forwarding ranging values, the h primary forwarding ranging values ​​are used to determine s equivalent secondary forwarding ranging values;

[0345] S130. Determine the total number of electrons in the ionosphere and the relative clock difference between the user station and the satellite based on the s equivalent relay ranging values ​​and the m pseudorange ranging values.

[0346] In step S100, there are two cases, as follows:

[0347] Scenario 1: When there is no primary relay ranging signal between the central station and the satellite, there are at least two secondary pseudorange ranging signals between the satellite and the user station, and at least one long relay ranging signal between the central station, the satellite, and the user; or, when there is no primary relay ranging signal between the central station and the satellite, there is at least one secondary pseudorange ranging signal between the satellite and the user station, and at least two long relay ranging signals between the central station, the satellite, and the user; measure the secondary pseudorange ranging signal and the long relay ranging signal to obtain the secondary pseudorange ranging value and the long relay ranging value, respectively.

[0348] When the coordinates of the central station and the satellite ephemeris are known, the spatial distance between the central station and the satellite can be calculated. The tropospheric delay between the central station and the satellite is estimated using the tropospheric delay model, and the ionospheric delay between the central station and the satellite is estimated using the ionospheric model, or the ionospheric delay is obtained based on the known total number of electrons in the main ionosphere. Then, based on the known spatial distance, tropospheric delay, and ionospheric delay, the equivalent relay ranging value between the satellite and the user station is obtained, as shown in formulas (49) and (50).

[0349]

[0350]

[0351] Case 2: When there is at least one primary relay ranging signal between the central station and the satellite, at least two secondary pseudorange ranging signals between the satellite and the user station, and at least one long relay ranging signal between the central station, the satellite, and the user; or, when there is at least one primary relay ranging signal between the central station and the satellite, at least one secondary pseudorange ranging signal between the satellite and the user station, and at least two long relay ranging signals between the central station, the satellite, and the user; measure the secondary pseudorange ranging signal, the long relay ranging signal, and the primary relay ranging signal to obtain the secondary pseudorange ranging value, the long relay ranging value, and the primary relay ranging value, respectively. When the total number of electrons in the primary ionosphere between the central station and the satellite is known, the derivation process of the equivalent secondary relay ranging value is shown in (51):

[0352]

[0353] L eq,u,1 (n) is the transition value of the first equivalent forwarding ranging value. Based on this transition value, the final first equivalent forwarding ranging value L is obtained. eq,u,1,a (n) and the second equivalent forwarding ranging value Leq,u,2,a (n).

[0354] The ionospheric delay between the satellite and the central station in formula (51) is shown in formulas (52) to (55).

[0355]

[0356]

[0357]

[0358]

[0359] Finally, the two equivalent forwarding ranging values ​​obtained according to formula (51) are shown in formulas (56) and (57):

[0360]

[0361]

[0362] in,

[0363]

[0364]

[0365] In practice, because the pseudorange ranging signal broadcast by the satellite is a broadcast signal, the central station can also receive the pseudorange ranging signal broadcast by the satellite. When there are at least two pseudorange ranging signals, the central station can obtain two pseudorange ranging values. Based on these pseudorange ranging values, the total number of electrons in the main ionosphere can be calculated.

[0366] When there are two primary relay ranging signals between the satellite and the central station, two primary relay ranging values ​​can be obtained, as well as the total number of electrons in the main ionosphere.

[0367] Regardless of whether there is a primary relay ranging signal between the central station and the satellite, an equivalent secondary relay ranging value can be obtained. Then, the equivalent secondary relay ranging value and the secondary pseudorange ranging value are used to calculate the total number of electrons in the ionosphere and the relative clock difference between the user station and the satellite.

[0368] The equivalent number of forwarding ranging values ​​is equal to the number of long forwarding ranging values.

[0369] In step S130, when there are two long-range transponder ranging values ​​and one pseudorange ranging value, the relative clock error between the user station and the satellite and the total number of electrons in the ionosphere are jointly solved using two equivalent transponder ranging values ​​and one corrected pseudorange ranging value. A matrix equation is constructed with the relative clock error between the user station and the satellite and the total number of electrons in the ionosphere as unknowns:

[0370]

[0371] The solution to the above matrix equation (5) is expression (60).

[0372]

[0373] Where G and b are respectively shown in formulas (61) and (62):

[0374]

[0375]

[0376] In step S130, when there is one long-range transponder ranging value and two pseudorange ranging values, an equivalent transponder ranging value and two corrected pseudorange ranging values ​​are used to jointly solve for the relative clock error between the user station and the satellite and the total number of electrons in the ionosphere. A matrix equation is constructed with the relative clock error between the user station and the satellite and the total number of electrons in the ionosphere as unknowns:

[0377]

[0378] The solution to the above matrix equation (5) is expression (63).

[0379]

[0380] Wherein, G and b are shown in formulas (64) and (65) respectively:

[0381]

[0382]

[0383] In addition to the matrix method described above, a sequential method can also be used to calculate the relative clock difference between the user station and the satellite. The specific calculation method is as follows: Select any equivalent transponder ranging value and any pseudorange ranging value, along with the known total number of electrons in the ionosphere, to calculate the relative clock difference between the user station and the satellite. According to formula (6), the first corrected pseudorange ranging value and the first equivalent transponder ranging value are selected for calculation. The relative clock difference between the user station and the satellite is obtained as shown in formula (66).

[0384]

[0385] Based on the above embodiments, this embodiment also provides a composite satellite-to-ground time synchronization method for a fourth type of composite satellite timing system, which is executed by a computing device.

[0386] The composite satellite-to-ground time synchronization method may include the following steps:

[0387] S400. Based on the communication results with the central station, obtain m primary pseudorange ranging values ​​and s long forwarding ranging values ​​measured by the central station, and obtain h secondary forwarding ranging values ​​based on the communication results with the user station; where m, h, and s are all positive integers, and m+s+h≥5;

[0388] S410. Each of the slave forwarding ranging values ​​is represented by a forwarding ranging expression, each of the long forwarding ranging values ​​is represented by a long forwarding ranging expression, and each of the master pseudorange ranging values ​​is represented by a pseudorange ranging expression.

[0389] S420. Based on the s long-range relay ranging values, the h slave relay ranging values, and the m main pseudorange ranging values, determine the total number of electrons in the main ionosphere, the total number of electrons in the slave ionosphere, and the relative clock difference between the central station and the satellite.

[0390] The maximum envelope of the four typical embodiments of the fourth type of composite satellite timing system is three long-transfer ranging values ​​+ two primary pseudorange ranging values ​​+ two secondary transfer ranging values. The calculation is explained based on the required measurement values ​​of the four typical systems.

[0391] In S400, the main pseudorange and long-range ranging values ​​obtained from the central station are obtained, and the slave ranging value is obtained by communicating with the user station. In S410, the computing device can characterize the slave ranging value by the following formula (70), characterize the main pseudorange value by the following formula (71), and characterize the long-range ranging value by the following formula (15).

[0392] L u,j (n)=R true,yu,j (n)+R true,yd,j (n)+I yu,j (n)+I yd,j (n)+T duiliu,yu,j (n)+T duiliu,yd,j (n)+Y u,j (n)(70)

[0393] In the formula, j = 1, 2, ..., h, where j and h are positive integers;

[0394] ρ z,i (n)=R true,z,i (n)+I z,i (n)+T duiliu,z,i (n)+sagnac zz (n)+X z,i (n)+c·(δt z (n)-δt s (n))(71)

[0395] In the formula, i = 1, 2, ..., m, where i and m are positive integers;

[0396] As analyzed above, the computing device further obtains the specific first and second slave forwarding ranging values ​​based on formula (70), as shown in formulas (72) and (73):

[0397] L u,1 (n)=R true,yu,1 (n)+R true,yd,1 (n)+I yu,1 (n)+I yd,1 (n)+T duiliu,yu,1 (n)+T duiliu,yd,1 (n)+Y u,1 (n) (72)

[0398] L u,2 (n)=R true,yu,2 (n)+R true,yd,2 (n)+I yu,2 (n)+I yd,2 (n)+T duiliu,yu,2 (n)+T duiliu,yd,2 (n)+Y u,2 (n) (73)

[0399] Similarly, the computing device obtains the specific first primary pseudorange measurement value and the second primary pseudorange measurement value according to formula (71), as shown in formulas (74) and (75);

[0400] ρ z,1 (n)=R true,z,1 (n)+I z,1 (n)+T duiliu,z,1 (n)+sagnac zz (n)+X z,1 (n)+c·(δt z (n)-δt s (n)) (74)

[0401] ρ z,2 (n)=R true,z,2 (n)+I z,2 (n)+T duiliu,z,2 (n)+sagnac zz (n)+X z,2 (n)+c·(δt z (n)-δt s (n)) (75)

[0402] The first primary forwarding ranging value and the second primary forwarding ranging value are corrected respectively to obtain the first corrected secondary forwarding ranging value and the second corrected secondary forwarding ranging value as shown in formulas (76) and (77).

[0403] L u,1,a (n)=L u,1 (n)-Y u,1 (n)=R true,yu,1 (n)+R true,yd,1 (n)+I yu,1 (n)+I yd,1 (n)+T duiliu,yu,1 (n)+T duiliu,yd,1 (n) (76)

[0404] L u,2,a (n)=L u,2 (n)-Y u,2 (n)=R true,yu,2 (n)+R true,yd,2 (n)+I yu,2 (n)+I yd,2 (n)+T duiliu,yu,2 (n)+T duiliu,yd,2 (n) (77)

[0405] The three corrected long-range ranging values ​​still use the first corrected long-range ranging value, the second corrected long-range ranging value, and the third corrected long-range ranging value as shown in formulas (26), (27), and (28).

[0406] The first and second principal pseudorange values ​​are corrected to obtain the first and second corrected principal pseudorange values ​​as shown in formulas (78) and (79):

[0407]

[0408]

[0409] This embodiment provides two methods for determining the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite, based on four typical embodiments of the fourth type of composite satellite timing system. The first method uses a matrix approach to jointly solve for the three unknowns; the second method first calculates the total number of electrons in the secondary ionosphere between the user station and the satellite, and the total number of electrons in the primary ionosphere between the central station and the satellite, and then calculates the relative clock difference between the central station and the satellite. These two calculation methods are explained in detail below.

[0410] (1) Matrix method

[0411] In the matrix method, the computing device utilizes the zero-baseline setting relationship between the response device and the slave pseudorange ranging device in the user station, and the zero-baseline setting relationship between the central station forwarding ranging device and the long forwarding ranging device in the central station. It processes m corrected primary pseudorange ranging values, h corrected slave forwarding ranging values, and s corrected long forwarding ranging values ​​to form a matrix equation as shown in formula (3):

[0412]

[0413] The solution to the above matrix equation (3) is expression (80).

[0414]

[0415] In the formula, matrix G has at least 3 rows and 3 columns, with the first column consisting entirely of 1s; matrix b has at least 3 rows and 1 column.

[0416] The computing device obtains the corresponding matrix G and matrix b for the specific system according to the four typical embodiments of the second case, and then substitutes the specific matrices into formula (80) to solve for the unknowns. The calculation process of the four typical embodiments of the second case is described below.

[0417] First typical embodiment: There is one secondary relay ranging signal between the satellite and the user station, one primary pseudorange ranging signal between the satellite and the central station, and three long relay ranging signals between the central station, the satellite, and the user station. In this case, m=1, s=3, and h=1.

[0418] The carrier frequencies of the three long-pass ranging signals are different from the carrier frequencies of one main pseudorange ranging signal and one slave ranging signal; thus, matrices G and b are obtained.

[0419]

[0420]

[0421] Second typical embodiment: There are two secondary relay ranging signals between the satellite and the user station, two primary pseudorange ranging signals between the satellite and the central station, and one long relay ranging signal between the central station, the satellite, and the user station. In this case, m=2, s=1, and h=2.

[0422] The carrier frequencies of the two primary pseudorange ranging signals, the carrier frequency of the one long-pass ranging signal, and the carrier frequencies of the two secondary-pass ranging signals are all different. This yields matrices G and b.

[0423]

[0424]

[0425] The third typical embodiment: There are two secondary relay ranging signals between the satellite and the user station, one primary pseudorange ranging signal between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. In this case, m=1, s=2, and h=2.

[0426] The carrier frequencies of the two follower ranging signals, the two long-follower ranging signals, and the main pseudorange ranging signal are all different. This yields matrices G and b.

[0427]

[0428]

[0429] Fourth typical embodiment: There is one secondary relay ranging signal between the satellite and the user station, two primary pseudorange ranging signals between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. In this case, m=2, s=2, and h=1.

[0430] The carrier frequencies of the one forwarding ranging signal, the two long forwarding ranging signals, and the two main pseudorange ranging signals are all different. This yields matrices G and b.

[0431]

[0432]

[0433] (2) Sequential method

[0434] The second method is to first calculate the total number of electrons in the ionosphere between the user station and the satellite, and the total number of electrons in the main ionosphere between the central station and the satellite using the total number of electrons in the main ionosphere, the total number of electrons in the ionosphere, and any corrected main pseudorange ranging value, any corrected secondary relay ranging value, and any corrected long relay ranging value to calculate the relative clock difference between the central station and the satellite. Here, the first corrected main pseudorange ranging value, the first corrected secondary relay ranging value, and the first corrected long relay ranging value are selected respectively to perform the calculation, as shown in formula (89).

[0435]

[0436] The specific calculation methods for the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere will still be explained separately for the four typical systems:

[0437] First typical embodiment: There is one secondary relay ranging signal between the satellite and the user station, one primary pseudorange ranging signal between the satellite and the central station, and three long relay ranging signals between the central station, the satellite, and the user station. In this case, m=1, s=3, and h=1.

[0438] The total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere are still obtained using formulas (41), (42), (43), and (44);

[0439] Second typical embodiment: There are two secondary relay ranging signals between the satellite and the user station, two primary pseudorange ranging signals between the satellite and the central station, and one long relay ranging signal between the central station, the satellite, and the user station. In this case, m=2, s=1, and h=2.

[0440] The carrier frequencies of the two forwarded ranging signals and the one forwarded ranging signal are different. The carrier frequencies of the two main pseudorange ranging signals are also different.

[0441] The total number of electrons in the main ionosphere is calculated using two corrected main pseudorange measurements, and is obtained using the following formula (90):

[0442]

[0443] The total number of electrons in the ionosphere is calculated from the transponder ranging value using two corrections, and is obtained using the following formula (91):

[0444]

[0445] The third typical embodiment: There are two secondary relay ranging signals between the satellite and the user station, one primary pseudorange ranging signal between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. In this case, m=1, s=2, and h=2.

[0446] The carrier frequencies of the two slave relay ranging signals, the two long relay ranging signals, and the main pseudorange ranging signal are all different. First, the total number of electrons in the ionosphere is calculated using the two corrected slave relay ranging values, as shown in formula (91);

[0447] The total number of electrons in the main ionosphere is calculated based on two corrected long-range ranging values ​​and the already calculated total number of electrons in the ionosphere, and can be calculated according to formula (48).

[0448] Fourth typical embodiment: There is one secondary relay ranging signal between the satellite and the user station, two primary pseudorange ranging signals between the satellite and the central station, and two long relay ranging signals between the central station, the satellite, and the user station. In this case, m=2, s=2, and h=1.

[0449] The carrier frequencies of the one forwarding ranging signal, the two long forwarding ranging signals, and the two main pseudorange ranging signals are all different.

[0450] First, the total number of electrons in the main ionosphere is calculated using two corrected main pseudorange measurements, as shown in formula (90);

[0451] The total number of electrons in the ionosphere is calculated based on two corrected long-range ranging values ​​and the already calculated total number of electrons in the main ionosphere, and can be calculated according to formula (47).

[0452] Based on the above embodiments, this embodiment also provides a composite satellite-to-ground time synchronization method for a third type of composite satellite timing system, which is executed by a computing device.

[0453] The third type of composite satellite timing system: This system uses either no slave relay ranging signal or one slave relay ranging signal. The composite satellite-to-ground time synchronization method of this third type of system calculates the total number of electrons in the main ionosphere and the relative clock difference between the central station and the satellite based on the equivalent primary relay ranging value and the primary pseudorange ranging value. This method can calculate the equivalent primary relay ranging value based on the long relay ranging value, whether there is no slave relay ranging signal or at least one slave relay ranging signal.

[0454] The composite satellite-to-ground time synchronization method may include the following steps:

[0455] S300: Based on the communication results with the central station, obtain s long forwarding ranging values ​​and m primary pseudorange ranging values ​​measured by the central station, and obtain h secondary forwarding ranging values ​​based on the communication results with the user station; where h is an integer greater than or equal to 0, m and s are both positive integers, and m+s≥3;

[0456] S310. Each of the slave forwarding ranging values ​​is represented by a forwarding ranging expression, each of the long forwarding ranging values ​​is represented by a long forwarding ranging expression, and each of the master pseudorange ranging values ​​is represented by a pseudorange ranging expression.

[0457] S320. Based on the s long forwarding ranging values, the h slave forwarding ranging values ​​are used to determine s equivalent primary forwarding ranging values;

[0458] S330. Based on the s equivalent primary relay ranging values ​​and the m primary pseudorange ranging values, determine the total number of electrons in the primary ionosphere and the relative clock difference between the central station and the satellite.

[0459] In step S300, there are two cases, as follows:

[0460] Scenario 1: When there is no relay ranging signal between the user station and the satellite, there are at least two primary pseudorange ranging signals between the satellite and the central station, and at least one long relay ranging signal between the central station, the satellite, and the user; or, when there is no relay ranging signal between the user station and the satellite, there is at least one primary pseudorange ranging signal between the satellite and the user station, and at least two long relay ranging signals between the central station, the satellite, and the user; measure the primary pseudorange ranging signal and the long relay ranging signal to obtain the primary pseudorange ranging value and the long relay ranging value, respectively.

[0461] When the coordinates of the user station and the satellite ephemeris are known, the spatial distance between the user station and the satellite can be calculated. The tropospheric delay between the user station and the satellite is estimated using the tropospheric delay model, and the ionospheric delay between the user station and the satellite is estimated using the ionospheric model, or the ionospheric delay is obtained from the known total number of electrons in the ionosphere. Then, based on the known spatial distance, tropospheric delay, and ionospheric delay, the equivalent primary relay ranging value between the satellite and the central station is obtained, as shown in formulas (92) and (93).

[0462]

[0463]

[0464] Case 2: When there is at least one slave relay ranging signal between the user station and the satellite, at least two main pseudorange ranging signals between the satellite and the central station, and at least one long relay ranging signal between the central station, the satellite, and the user; or, when there is at least one slave relay ranging signal between the user station and the satellite, at least one main pseudorange ranging signal between the satellite and the user station, and at least two long relay ranging signals between the central station, the satellite, and the user; measure the main pseudorange ranging signal, the long relay ranging signal, and the slave relay ranging signal to obtain the main pseudorange ranging value, the long relay ranging value, and the slave relay ranging value, respectively. When the total number of electrons in the ionosphere between the user station and the satellite is known, the derivation process of the equivalent main relay ranging value is shown in (94):

[0465]

[0466] L eq,z,1 (n) is the transition value of the first equivalent primary forwarding ranging value. The final first equivalent primary forwarding ranging value L is obtained based on this transition value. eq,z,1,a (n) and the second equivalent main forwarding ranging value L eq,z,2,a (n).

[0467] The ionospheric delay between the satellite and the user station in formula (94) is shown in formulas (95) to (98).

[0468]

[0469]

[0470]

[0471]

[0472] Finally, the two equivalent main relay ranging values ​​obtained according to formula (94) are shown in formulas (99) and (100):

[0473]

[0474]

[0475] in,

[0476]

[0477]

[0478] In practice, because the main pseudorange ranging signal broadcast by the satellite is a broadcast signal, the user station can also receive the main pseudorange ranging signal broadcast by the satellite. When there are at least two main pseudorange ranging signals, the user station can obtain two main pseudorange ranging values. Based on these main pseudorange ranging values, the total number of electrons in the ionosphere can be calculated.

[0479] When there are two relay ranging signals between the satellite and the station, two relay ranging values ​​can be obtained, as well as the total number of electrons in the ionosphere.

[0480] Regardless of whether there is a relay ranging signal between the user station and the satellite, the equivalent primary relay ranging value can be obtained. Then, the equivalent primary relay ranging value and the primary pseudorange ranging value are used to calculate the total number of electrons in the primary ionosphere and the relative clock difference between the central station and the satellite.

[0481] The number of equivalent primary forwarding ranging values ​​is equal to the number of long forwarding ranging values.

[0482] In step S330, when there are two long-range transponder ranging values ​​and one main pseudorange ranging value, the relative clock difference between the central station and the satellite and the total number of electrons in the main ionosphere are jointly solved using two equivalent main transponder ranging values ​​and one corrected main pseudorange ranging value. A matrix equation is constructed with the relative clock difference between the central station and the satellite and the total number of electrons in the main ionosphere as unknowns:

[0483]

[0484] The solution to the above matrix equation (7) is expression (103).

[0485]

[0486] Where G and b are respectively shown in formulas (104) and (105):

[0487]

[0488]

[0489] In step S330, when there is one long-range transponder ranging value and two main pseudorange ranging values, an equivalent main transponder ranging value and two corrected main pseudorange ranging values ​​are used to jointly solve for the relative clock error between the central station and the satellite and the total number of electrons in the main ionosphere. A matrix equation is constructed with the relative clock error between the central station and the satellite and the total number of electrons in the main ionosphere as unknowns:

[0490]

[0491] The solution to the above matrix equation (7) is expression (106).

[0492]

[0493] Wherein, G and b are shown in formulas (107) and (108) respectively:

[0494]

[0495]

[0496] In addition to the matrix method described above, a sequential method can also be used to calculate the relative clock difference between the central station and the satellite. The specific calculation method is as follows: Select any equivalent primary transponder ranging value and any primary pseudorange ranging value, along with the known total number of electrons in the primary ionosphere, to calculate the relative clock difference between the user station and the satellite. According to formula (8), and here, the first corrected primary pseudorange ranging value and the first equivalent primary transponder ranging value are selected respectively for calculation. The relative clock difference between the central station and the satellite is obtained as shown in formula (109).

[0497]

[0498] Based on the above embodiments, this embodiment also provides an inter-station time synchronization method, which can be executed by a user station. This exemplary embodiment is only illustrated by example of the method being executed by a user station. The method may include:

[0499] Communicate with the target user station to exchange data; or, exchange data with the target user control station via the communication link to obtain the clock difference of the target user station relative to the system time.

[0500] After determining the relative clock difference between the user station and the system time, the user station can transmit data with the target user station through the communication link. Multiple user stations can exchange their relative clock differences with the system time through the communication link to achieve time synchronization between multiple user stations. For details, please refer to the satellite common-view time comparison technology, which will not be elaborated here.

[0501] In summary, it can be seen that the composite satellite timing system and method provided in this application can integrate my country's dual-satellite positioning system and BeiDou satellite navigation system to obtain high-precision clock error, which is more accurate than the timing service provided by the dual-satellite positioning system and BeiDou satellite navigation system alone.

[0502] The composite satellite timing system and method provided in this embodiment have the following characteristics:

[0503] 1. This application can independently obtain the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere without requiring the total number of electrons in the ionosphere provided by a third party. It has the advantages of high real-time performance and independence from third-party total number of electrons in the ionosphere.

[0504] 2. By applying this method, existing satellite navigation industry resources can be utilized, which can reduce the complexity and cost of user stations.

[0505] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A composite satellite timing system, the system comprising a central station and user stations respectively connected to a satellite for communication, characterized in that, The communication between the central station, the satellite, and the user station uses long-range relay ranging signals. When there is a primary relay ranging signal in communication between the satellite and the central station, and a secondary pseudorange ranging signal in communication between the satellite and the user station; Similarly, when there is a relay ranging signal in communication between the satellite and the user station, there is a primary pseudorange ranging signal in communication between the satellite and the central station; The main pseudorange ranging signal is played by the satellite and received and measured by the central station; The pseudorange ranging signal is played by the satellite and received and measured by the user station; The main relay ranging signal includes a main uplink signal and a main downlink signal. The central station broadcasts the main uplink signal and receives the main downlink signal. The satellite receives the main uplink signal and forwards it to form the main downlink signal. The relay ranging signal includes an uplink signal and a downlink signal. The user station broadcasts the uplink signal and receives the downlink signal. The satellite receives the uplink signal and forwards it to form the downlink signal. The long-transfer ranging signal includes a first uplink signal broadcast by the central station, a first downlink signal formed by the satellite receiving and forwarding the first uplink signal, a second uplink signal formed by the user station receiving and forwarding the first downlink signal, and a second downlink signal formed by the satellite receiving the second uplink signal and forwarding it to the central station.

2. A composite satellite timing system, the system comprising a central station and user stations respectively connected to a satellite for communication, characterized in that, The communication between the central station, the satellite, and the user station uses long-range relay ranging signals. When the system does not have a primary relay ranging signal, the communication between the satellite and the user station is via a secondary pseudorange ranging signal; Similarly, when the system does not have a slave relay ranging signal, the communication between the satellite and the central station has a primary pseudorange ranging signal; The main pseudorange ranging signal is played by the satellite and received and measured by the central station; The pseudorange ranging signal is played by the satellite and received and measured by the user station; The main relay ranging signal includes a main uplink signal and a main downlink signal. The central station broadcasts the main uplink signal and receives the main downlink signal. The satellite receives the main uplink signal and forwards it to form the main downlink signal. The relay ranging signal includes an uplink signal and a downlink signal. The user station broadcasts the uplink signal and receives the downlink signal. The satellite receives the uplink signal and forwards it to form the downlink signal. The long-transfer ranging signal includes a first uplink signal broadcast by the central station, a first downlink signal formed by the satellite receiving and forwarding the first uplink signal, a second uplink signal formed by the user station receiving and forwarding the first downlink signal, and a second downlink signal formed by the satellite receiving the second uplink signal and forwarding it to the central station.

3. A composite satellite timing system according to claim 1 or 2, characterized in that, The satellites include: The pseudorange broadcasting device generates and broadcasts the primary pseudorange ranging signal or the secondary pseudorange ranging signal. The repeater forwards the received first uplink signal into the first downlink signal, and the received second uplink signal into the second downlink signal; it forwards the received primary uplink signal to the central station; and it forwards the received secondary uplink signal to the user station. The satellite time and frequency equipment provides time and frequency signals to the transponder and pseudorange broadcasting equipment; The central station includes: A long-transfer ranging device is used to broadcast the first uplink signal, receive and measure the second downlink signal to obtain a long-transfer ranging value; The main forwarding ranging device is used to generate and broadcast the main uplink signal, and to receive and measure the main downlink signal to obtain the main forwarding ranging value; When the system does not contain a primary forwarding ranging signal, i.e., no primary forwarding ranging device is set up, the central station is replaced with a primary pseudorange ranging device to receive and measure the primary pseudorange ranging signal to obtain the primary pseudorange ranging value. At least one primary time-frequency device is used to provide time-frequency signals to the long-transfer ranging device, the primary transfer ranging device, or the primary pseudorange ranging device. The user station includes: A response device, configured to receive the first downlink signal and forward it into the second uplink signal; The forwarding ranging device is used to generate and broadcast the forwarding uplink signal, and to receive and measure the forwarding downlink signal to obtain the forwarding ranging value; Similarly, when the system does not contain a forwarding ranging signal, that is, the user station does not have a forwarding ranging device, the user station is instead equipped with a pseudorange ranging device to receive and measure the pseudorange ranging signal to obtain the pseudorange ranging value. At least one time-frequency device is used to provide time-frequency signals to a response device, a relay ranging device, or a pseudorange ranging device.

4. A composite satellite timing system according to claim 3, characterized in that, The primary relay ranging device and the long relay ranging device are set to zero baseline, or the primary pseudorange ranging device and the long relay ranging device are set to zero baseline; the response device and the secondary relay ranging device are set to zero baseline, or the response device and the secondary pseudorange relay ranging device are set to zero baseline.

5. A composite satellite timing system according to claim 3, characterized in that, The system also includes: The computing device is communicatively connected to both the central station and the user station. The computing device receives the long-range relay ranging value, the primary relay ranging value, and the secondary pseudorange ranging value, and calculates the total number of primary ionospheric electrons between the central station and the satellite, the total number of secondary ionospheric electrons between the user station and the satellite, and the relative clock difference between the user station and the satellite based on the long-range relay ranging value, the primary relay ranging value, and the secondary pseudorange ranging value. Similarly, the computing device receives the long-range relay ranging value, the secondary relay ranging value, and the primary pseudorange ranging value, and calculates the total number of primary ionospheric electrons between the central station and the satellite, the total number of secondary ionospheric electrons between the user station and the satellite, and the relative clock difference between the central station and the satellite based on the long-range relay ranging value, the secondary relay ranging value, and the primary pseudorange ranging value. When no primary relay ranging signal is set, the relative clock difference between the user station and the satellite and the total number of electrons in the ionosphere between the user station and the satellite are determined based on the pseudorange ranging value, the long relay ranging value, and the known ionospheric delay, tropospheric delay, and spatial distance between the central station and the satellite. When there is at least one primary relay ranging signal, the relative clock difference between the user station and the satellite and the total number of electrons in the ionosphere between the user station and the satellite are determined based on the pseudorange ranging value, the long relay ranging value, the primary relay ranging value, and the known ionospheric delay between the central station and the satellite. Similarly, when the relay ranging signal is not set, the relative clock difference between the central station and the satellite and the total number of electrons in the main ionosphere between the central station and the satellite are determined based on the main pseudorange ranging value, the long relay ranging value, and the known ionospheric delay, tropospheric delay, and spatial distance between the user station and the satellite. When there is at least one relay ranging signal, the relative clock difference between the central station and the satellite and the total number of primary ionospheric electrons between the central station and the satellite are determined based on the primary pseudorange ranging value, the long relay ranging value, the slave relay ranging value, and the known ionospheric delay between the user station and the satellite.

6. A composite satellite-to-ground time synchronization method, characterized in that, The composite satellite timing system according to any one of claims 1, 3, 4, and 5, wherein the method is executed by a computing device, includes: The system communicates with the central station to obtain h primary forwarding ranging values ​​and s long forwarding ranging values, and communicates with the user station to obtain m secondary pseudorange ranging values. The s long forwarding ranging values ​​and the h primary forwarding ranging values ​​are obtained by the central station measuring the long forwarding ranging signal and the primary forwarding ranging signal, and the m secondary pseudorange ranging values ​​are obtained by the user station measuring the secondary pseudorange ranging signal. h, s, and m are all positive integers, and m + h + s ≥ 5. The computing device determines the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite based on the m pseudorange ranging values, the h primary relay ranging values, and the s long relay ranging values; Wherein, the total number of electrons in the main ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the central station and the satellite, and the total number of electrons in the secondary ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the user station and the satellite.

7. The composite satellite-to-ground time synchronization method according to claim 6, characterized in that, The determination of the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite based on the m pseudorange ranging values, the h primary transponder ranging values, and the s long transponder ranging values ​​includes: The m pseudorange values ​​are corrected to obtain m corrected pseudorange values; The h primary forwarding ranging values ​​are corrected to obtain h corrected primary forwarding ranging values; The s long forwarding ranging values ​​are corrected to obtain s corrected long forwarding ranging values; The relative clock difference between the user station and the satellite is determined by using the total number of electrons in the main ionosphere, any corrected pseudorange ranging value, any corrected main transponder ranging value, and any corrected long transponder ranging value. Alternatively, the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite can be determined based on the m corrected pseudorange ranging values, the h corrected primary relay ranging values, and the s corrected long relay ranging values.

8. The composite satellite-to-ground time synchronization method according to claim 7, characterized in that: Based on the m corrected pseudorange ranging values, the h corrected primary transponder ranging values, and the s corrected long transponder ranging values, the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite are determined, including: The correction is performed mathematically on the pseudorange ranging value, the corrected main forwarding ranging value, and the corrected long forwarding ranging value to obtain the difference matrix; Based on the difference matrix and the carrier frequencies of the pseudorange ranging signal, the main relay ranging signal, and the long relay ranging signal, a matrix equation is constructed with the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite as unknowns: Solving the matrix equation yields the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the user station and the satellite. In the formula, δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt u (n) represents the clock difference between the user station and the system time at time n, in seconds; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter (TEC). u (n) represents the total number of electrons from the ionosphere on the ranging signal path between the satellite and the user station at time n, in electrons per square meter. G represents the coefficient matrix, which is at least a 3×3 matrix, and b represents the difference matrix, which is at least a 3×1 matrix.

9. The composite satellite-to-ground time synchronization method according to claim 7, characterized in that, The relative clock difference between the user station and the satellite is determined based on the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, any of the corrected secondary pseudorange ranging values, any of the corrected primary transponder ranging values, and any of the corrected long transponder ranging values, including: The corrected pseudorange ranging value, the corrected primary relay ranging value, and the corrected long relay ranging value are processed to obtain the relative clock difference between the user station and the satellite. The relative clock difference is expressed as follows: Alternatively, the average relative clock difference between the user station and the satellite can be obtained by averaging the relative clock differences between the user station and the satellite determined based on the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, multiple corrected pseudorange ranging values, multiple corrected main relay ranging values, and multiple corrected long relay ranging values. In the formula, δt u (n) represents the clock difference between the user station and the system time at time n, in seconds; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; L on,k,a (n) represents the corrected long-range relay ranging value with number k at time n, in meters; L z,j,a (n) represents the corrected primary relay ranging value with number j at time n, in meters; ρ u,i,a (n) represents the corrected pseudorange value numbered i at time n, in meters; u,i (n) represents the ionospheric delay of the pseudorange ranging signal numbered i at time n, in meters; xu,j (n),I xd,j (n) represents the ionospheric delay of the main uplink signal and the ionospheric delay of the main downlink signal of the main relay ranging signal numbered j at time n, in meters; zu,k (n),I zd,k (n) represents the ionospheric delay of the first uplink signal and the ionospheric delay of the second downlink signal for the long-transfer ranging value numbered k at time n, in meters; uu,k (n),I ud,k (n) represents the ionospheric delay of the second uplink signal and the ionospheric delay of the first downlink signal for the long-transfer ranging value numbered k at time n, in meters; Q ion Represents the ionospheric time delay factor; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter; TEC u (n) represents the total number of electrons from the ionosphere along the ranging signal path between the satellite and the user station at time n, in electrons per square meter; f u,i (n) represents the carrier frequency of the pseudorange ranging signal numbered i at time n, in Hertz; f xu,j (n),f xd,j (n) represents the carrier frequencies of the primary uplink and primary downlink signals of the primary relay ranging signal numbered j at time n, in Hertz; f zu,k (n),f zd,k (n) represents the carrier frequencies of the first uplink and second downlink signals of the long-transfer ranging signal numbered k at time n, in Hertz; f uu,k (n),f ud,k (n) represents the carrier frequencies of the second uplink signal and the first downlink signal of the long-transfer ranging signal numbered k at time n, in Hertz.

10. A composite satellite-to-ground time synchronization method according to claim 9, characterized in that, The determination of the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere using the m corrected pseudorange ranging values, the h corrected main transponder ranging values, and the s corrected long transponder ranging values ​​includes: When m≥1, s≥3, and h≥1, the total number of electrons in the primary ionosphere and the total number of electrons in the secondary ionosphere are calculated based on at least three corrected long-forward ranging values ​​corresponding to at least three long-forward ranging signals. When m≥2, s≥1, and h≥2, the total number of electrons in the main ionosphere is determined using at least two corrected main forwarding ranging values, and the total number of electrons in the secondary ionosphere is determined using at least two corrected pseudorange ranging values. When m≥2, s≥2, and h≥1, the total number of electrons in the ionosphere is determined using at least two corrected pseudorange ranging values, and then the total number of electrons in the main ionosphere is determined using the total number of electrons in the ionosphere and at least two corrected long-range ranging values. When m≥1, s≥2, and h≥2, the total number of electrons in the main ionosphere is determined using at least two corrected main forwarding ranging values, and then the total number of electrons in the secondary ionosphere is determined using the total number of electrons in the main ionosphere and at least two corrected long forwarding ranging values.

11. A composite satellite-to-ground time synchronization method, characterized in that, The composite satellite timing system according to any one of claims 1, 3, 4, and 5, wherein the method is executed by a computing device, includes: The system communicates with the central station to obtain m primary pseudorange ranging values ​​and s long forwarding ranging values, and communicates with the user station to obtain h secondary forwarding ranging values. The m primary pseudorange ranging values ​​and the s long forwarding ranging values ​​are obtained by the central station measuring the primary pseudorange ranging signal and the long forwarding ranging signal, and the h secondary forwarding ranging values ​​are obtained by the user station measuring the h secondary forwarding ranging signals. Here, m, h, and s are all positive integers, and m+s+h≥5. The computing device determines the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite based on the m primary pseudorange ranging values, the h secondary relay ranging values, and the s long relay ranging values; Wherein, the total number of electrons in the main ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the central station and the satellite, and the total number of electrons in the secondary ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the user station and the satellite.

12. The composite satellite-to-ground time synchronization method according to claim 11, characterized in that, The total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite are determined based on the m primary pseudorange ranging values, the h secondary transponder ranging values, and the s long transponder ranging values, including: The m principal pseudorange values ​​are corrected to obtain m corrected principal pseudorange values. The h forwarding ranging values ​​are corrected to obtain h corrected forwarding ranging values; The s long forwarding ranging values ​​are corrected to obtain s corrected long forwarding ranging values; The relative clock difference between the central station and the satellite is determined by using the total number of electrons in the main ionosphere, any corrected main pseudorange ranging value, any corrected secondary relay ranging value, and any corrected long relay ranging value. Alternatively, the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite can be determined based on the m primary pseudorange ranging values, the h secondary relay ranging values, and the s long relay ranging values.

13. A composite satellite-to-ground time synchronization method according to claim 12, characterized in that, The total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite are determined based on the m corrected primary pseudorange ranging values, the h corrected secondary transponder ranging values, and the s corrected long transponder ranging values, including: The modified primary pseudorange ranging value, the modified secondary forwarding ranging value, and the modified long forwarding ranging value are mathematically processed to obtain a difference matrix; Based on the difference matrix and the carrier frequencies of the primary pseudorange ranging signal, the secondary relay ranging signal, and the long relay ranging signal, a matrix equation is constructed with the total number of electrons in the primary ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite as unknowns: Solving the matrix equation yields the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, and the relative clock difference between the central station and the satellite. In the formula, δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter (TEC). u (n) represents the total number of electrons in the ionosphere along the ranging signal path between the satellite and the user station at time n, in units of electrons per square meter. G represents the coefficient matrix, which is at least a 3×3 matrix, and b represents the difference matrix, which is at least a 3×1 matrix.

14. The composite satellite-to-ground time synchronization method according to claim 12, characterized in that, The relative clock difference between the central station and the satellite is determined based on the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, any of the corrected main pseudorange ranging values, any of the corrected secondary transponder ranging values, and any of the corrected long transponder ranging values, including: By processing any of the corrected primary pseudorange ranging values, any of the corrected secondary relay ranging values, and any of the corrected long relay ranging values, the relative clock difference between the central station and the satellite is obtained. The relative clock difference is expressed as: Alternatively, the average relative clock difference between the central station and the satellite can be obtained by averaging the relative clock differences between the central station and the satellite determined based on the total number of electrons in the main ionosphere, the total number of electrons in the secondary ionosphere, multiple corrected main pseudorange ranging values, multiple corrected secondary relay ranging values, and multiple corrected long relay ranging values; In the formula, δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; L on,k,a (n) represents the corrected long-range relay ranging value with number k at time n, in meters; L u,j,a (n) represents the corrected relay ranging value with number j at time n, in meters; ρ z,i,a (n) represents the corrected principal pseudorange value numbered i at time n, in meters; z,i (n) represents the ionospheric delay of the primary pseudorange ranging signal numbered i at time n, in meters; yu,j (n),I yd,j (n) represents the ionospheric delay of the uplink signal and the downlink signal at time n, with the number j, in meters; zu,k (n),I zd,k (n) represents the ionospheric delay of the first uplink signal and the ionospheric delay of the second downlink signal for the long-transfer ranging value numbered k at time n, in meters; uu,k (n),I ud,k (n) represents the ionospheric delay of the second uplink signal and the ionospheric delay of the first downlink signal for the long-transfer ranging value numbered k at time n, in meters; Q ion Represents the ionospheric time delay factor; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter; TEC u (n) represents the total number of electrons from the ionosphere along the ranging signal path between the satellite and the user station at time n, in electrons per square meter; f z,i (n) represents the carrier frequency of the primary pseudorange ranging signal numbered i at time n, in Hertz; f yu,j (n),f yd,j (n) represents the carrier frequencies of the uplink and downlink signals of the slave relay ranging signal numbered j at time n, in Hertz; f zu,k (n),f zd,k (n) represents the carrier frequencies of the first uplink and second downlink signals of the long-transfer ranging signal numbered k at time n, in Hertz; f uu,k (n),f ud,k (n) represents the carrier frequencies of the second uplink signal and the first downlink signal of the long-transfer ranging signal numbered k at time n, in Hertz.

15. A composite satellite-to-ground time synchronization method according to claim 14, characterized in that, Determining the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere using the m corrected main pseudorange ranging values, the h corrected secondary transponder ranging values, and the s corrected long transponder ranging values ​​includes: When m≥1, s≥3, and h≥1, the total number of electrons in the main ionosphere and the total number of electrons in the secondary ionosphere are calculated based on at least three corrected long-forward ranging values ​​corresponding to at least three long-forward ranging signals. When m≥2, s≥1, and h≥2, the total number of electrons in the main ionosphere is determined using at least two corrected main pseudorange ranging values, and the total number of electrons in the secondary ionosphere is determined using at least two corrected secondary ranging values. When m≥2, s≥2, and h≥1, the total number of electrons in the main ionosphere is determined using at least two corrected main pseudorange values, and then the total number of electrons in the secondary ionosphere is determined using the total number of electrons in the main ionosphere and at least two corrected long-range ranging values. When m≥1, s≥2, and h≥2, the total number of electrons in the ionosphere is determined using at least two corrected long-range ranging values, and then the total number of electrons in the main ionosphere is determined using the total number of electrons in the ionosphere and at least two corrected long-range ranging values.

16. A composite satellite-to-ground time synchronization method, characterized in that, The composite satellite timing system according to any one of claims 1 to 5, wherein the method is executed by a computing device, includes: There are h primary relay ranging signals between the central station and the satellite, m secondary pseudorange ranging signals between the satellite and the user station, and s long relay ranging signals between the central station, the satellite, and the user station. m secondary pseudorange ranging values ​​are obtained through the secondary pseudorange ranging device, s long relay ranging values ​​are obtained through the long relay ranging device, and h primary relay ranging values ​​are obtained through the primary relay ranging device. h is an integer greater than or equal to 0, s and m are both positive integers, and m+s≥3. When h = 0, the relative clock difference between the user station and the satellite and the total number of electrons in the ionosphere between the user station and the satellite are determined based on m pseudorange ranging values, s long-transfer ranging values, the known total number of electrons in the main ionosphere between the central station and the satellite, the tropospheric delay, and the spatial distance. When h≥1, the relative clock difference between the user station and the satellite and the total number of electrons in the ionosphere are determined based on m pseudorange ranging values, s long-transfer ranging values, h main-transfer ranging values, and the known total number of electrons in the main ionosphere between the central station and the satellite. Wherein, the total number of electrons from the ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the user station and the satellite.

17. A composite satellite-to-ground time synchronization method according to claim 16, characterized in that, Based on m pseudorange ranging values, s long-transfer ranging values, and h main-transfer ranging values, the relative clock difference between the user station and the satellite and the total number of electrons from the ionosphere are determined, including: The m pseudorange values ​​are corrected to obtain m corrected pseudorange values. The s long forwarding ranging values ​​are corrected to obtain s corrected long forwarding ranging values; The h primary forwarding ranging values ​​are corrected to obtain h corrected primary forwarding ranging values; When h=0, the equivalent long-transfer ranging value is obtained by using the known total number of electrons in the main ionosphere, tropospheric time delay, and spatial distance between the central station and the satellite, based on the corrected long-transfer ranging value. When h≥1, the equivalent secondary relay ranging value is obtained by using the known total number of electrons in the main ionosphere between the central station and the satellite, based on the corrected long relay ranging value and the corrected main relay ranging value. The relative clock difference between the user station and the satellite is determined using the total number of electrons in the ionosphere, any equivalent relay ranging value, and any corrected pseudorange ranging value. Alternatively, the relative clock difference between the user station and the satellite and the total number of electrons from the ionosphere can be determined based on s equivalent forwarding ranging values ​​and m corrected pseudorange ranging values.

18. A composite satellite-to-ground time synchronization method according to claim 17, characterized in that: The relative clock difference between the user station and the satellite and the total number of electrons from the ionosphere are determined based on s equivalent relay ranging values ​​and m corrected pseudorange ranging values, including: The equivalent forwarding ranging value and the corrected pseudorange ranging value are mathematically processed to obtain the difference matrix; Based on the difference matrix and the carrier frequencies of the pseudorange ranging signal and the equivalent relay ranging signal, a matrix equation is constructed with the total number of electrons in the ionosphere and the relative clock difference between the user station and the satellite as unknowns: Solving the matrix equation yields the total number of electrons from the ionosphere and the relative clock difference between the user station and the satellite; In the formula, δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt u (n) represents the clock difference between the user station and the system time at time n, in seconds; c represents the speed of light, in meters per second; TEC u (n) represents the total number of electrons from the ionosphere on the ranging signal path between the satellite and the user station at time n, in electrons per square meter. G represents the coefficient matrix, which is at least a 2×2 matrix, and b represents the difference matrix, which is at least a 2×1 matrix.

19. A composite satellite-to-ground time synchronization method according to claim 17, characterized in that, Determining the relative clock difference between the user station and the satellite based on the total number of electrons from the ionosphere, any of the corrected pseudorange ranging values, and any of the equivalent relay ranging values ​​includes: The relative clock difference between the user station and the satellite is obtained by processing the pseudorange ranging value and the equivalent forwarding ranging value of any correction, respectively. The relative clock difference is expressed as: Alternatively, the average relative clock difference between the user station and the satellite can be obtained by averaging the relative clock differences between the user station and the satellite determined from the total number of electrons in the ionosphere, multiple corrected pseudorange ranging values, and multiple equivalent relay ranging values; In the formula, δt u (n) represents the clock difference between the user station and the system time at time n, in seconds; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; L eq,u,k,a (n) represents the equivalent pseudorange measurement value with ID k at time n, in meters, where k is a positive integer; ρ u,i,a (n) represents the corrected pseudorange value with ID i at time n, in meters, where i is a positive integer; u,i (n) represents the ionospheric delay of the pseudorange ranging signal numbered i at time n, in meters; uu,k (n),I ud,k (n) represents the equivalent uplink and downlink ionospheric delays of the relay ranging value at time n, with the number k, in meters; Q ion Represents the ionospheric time delay factor; c represents the speed of light, in meters per second; TEC u (n) represents the total number of electrons from the ionosphere along the ranging signal path between the satellite and the user station at time n, in electrons per square meter; f u,i (n) represents the carrier frequency of the pseudorange ranging signal numbered i at time n, in Hertz; f uu,k (n),f ud,k (n) represents the carrier frequencies of the uplink and downlink signals of the equivalent slave relay ranging signal numbered k at time n, in Hertz.

20. A composite satellite-to-ground time synchronization method according to claim 19, characterized in that, Determining the total number of electrons from the ionosphere using the m corrected pseudorange distance measurements includes: When m≥2, the total number of electrons in the ionosphere is determined using at least two corrected pseudorange distance measurements.

21. A composite satellite-to-ground time synchronization method, characterized in that, The composite satellite timing system according to any one of claims 1 to 5, wherein the method is executed by a computing device, includes: There are h slave relay ranging signals between the central station and the satellite, m primary pseudorange ranging signals between the satellite and the central station, and s long relay ranging signals between the central station, the satellite, and the user station. The central station, the satellite, and the user station obtain m primary pseudorange ranging values ​​through the primary pseudorange ranging device, s long relay ranging values ​​through the long relay ranging device, and h slave relay ranging values ​​through the slave relay ranging device. Here, h is an integer greater than or equal to 0, s and m are both positive integers, and m + s ≥ 3. When h = 0, the relative clock difference between the central station and the satellite and the total number of primary ionospheric electrons between the central station and the satellite are determined based on m primary pseudorange ranging values, s long-transfer ranging values, the known total number of electrons in the ionosphere between the user station and the satellite, the tropospheric delay, and the spatial distance. When h≥1, the relative clock difference between the central station and the satellite and the total number of primary ionospheric electrons are determined based on m primary pseudorange ranging values, s long-transfer ranging values, h secondary transfer ranging values, and the known total number of secondary ionospheric electrons between the user station and the satellite. The total number of electrons in the main ionosphere is the total number of electrons in the ionosphere along the ranging signal path between the central station and the satellite.

22. The composite satellite-to-ground time synchronization method according to claim 21, characterized in that, Based on m primary pseudorange ranging values, s long-transfer ranging values, and h secondary transfer ranging values, the relative clock difference between the central station and the satellite and the total number of electrons in the main ionosphere are determined, including: The m principal pseudorange values ​​are corrected to obtain m corrected principal pseudorange values; The s long forwarding ranging values ​​are corrected to obtain s corrected long forwarding ranging values; The h forwarding ranging values ​​are corrected to obtain h corrected forwarding ranging values; When h = 0, the equivalent main transponder ranging value is obtained by using the known total number of electrons from the ionosphere, tropospheric time delay, and spatial distance between the user station and the satellite, based on the corrected long transponder ranging value. When h≥1, the equivalent primary transponder ranging value is obtained by using the known total number of electrons from the ionosphere between the user station and the satellite, based on the corrected long transponder ranging value and the corrected secondary transponder ranging value. The relative clock difference between the central station and the satellite is determined using the total number of electrons in the main ionosphere, any equivalent main relay ranging value, and any corrected main pseudorange ranging value. Alternatively, the relative clock difference and the total number of electrons in the main ionosphere between the central station and the satellite can be determined based on s equivalent main relay ranging values ​​and m corrected main pseudorange ranging values.

23. The composite satellite-to-ground time synchronization method according to claim 22, characterized in that: Based on s equivalent primary relay ranging values ​​and m corrected primary pseudorange ranging values, the relative clock difference between the central station and the satellite and the total number of electrons in the primary ionosphere are determined, including: The equivalent primary forwarding ranging value and the corrected primary pseudorange ranging value are mathematically processed to obtain the difference matrix; Based on the difference matrix, the carrier frequencies of the main pseudorange ranging signal and the equivalent main relay ranging signal, a matrix equation is constructed with the total number of electrons in the main ionosphere and the relative clock difference between the central station and the satellite as unknowns: Solving the matrix equation yields the total number of electrons in the main ionosphere and the relative clock difference between the central station and the satellite; In the formula, δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter. G represents the coefficient matrix, which is at least a 2×2 matrix, and b represents the difference matrix, which is at least a 2×1 matrix.

24. The composite satellite-to-ground time synchronization method according to claim 22, characterized in that, The relative clock difference between the central station and the satellite is determined based on the total number of electrons in the main ionosphere, any of the corrected main pseudorange ranging values, and any of the equivalent main transponder ranging values, including: By processing any of the corrected primary pseudorange ranging values ​​and any of the corrected equivalent primary relay ranging values, the relative clock difference between the central station and the satellite is obtained, and the relative clock difference is expressed as: Alternatively, the average relative clock difference between the central station and the satellite can be obtained by averaging the relative clock differences between the central station and the satellite determined based on the total number of electrons in the main ionosphere, multiple corrected main pseudorange ranging values, and multiple equivalent main transponder ranging values. In the formula, δt z (n) represents the clock difference between the central station and the system time at time n, in seconds; δt s (n) represents the clock difference of the satellite relative to the system time at time n, in seconds; L eq,z,k,a (n) represents the equivalent principal pseudorange value numbered k at time n, in meters, where k is a positive integer; ρ z,i,a (n) represents the corrected principal pseudorange value numbered i at time n, in meters, where i is a positive integer; z,i (n) represents the ionospheric delay of the primary pseudorange ranging signal numbered i at time n, in meters; zu,k (n),I zd,k (n) represents the uplink and downlink ionospheric delays of the equivalent primary relay ranging value at time n, numbered k, in meters; Q ion Represents the ionospheric time delay factor; c represents the speed of light, in meters per second; TEC z (n) represents the total number of electrons in the main ionosphere along the ranging signal path between the satellite and the central station at time n, in electrons per square meter; f z,i (n) represents the carrier frequency of the primary pseudorange ranging signal numbered i at time n, in Hertz; f zu,k (n),f zd,k (n) represents the carrier frequencies of the uplink and downlink signals of the equivalent primary relay ranging signal numbered k at time n, in Hertz.

25. A composite satellite-to-ground time synchronization method according to claim 24, characterized in that, Determining the total number of electrons in the main ionosphere using the m corrected principal pseudorange measurements includes: When m≥2, the total number of electrons in the main ionosphere is determined using at least two corrected main pseudorange measurements.

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