Dual-frequency time synchronization system, time synchronization method and navigation application thereof

Abstract

The application discloses a dual-frequency time synchronization system, a time synchronization method and navigation application thereof, and belongs to the technical field of time synchronization. In the application, a pseudo-range ranging signal and a relay ranging signal exist between a first device and a second device; a pseudo-range ranging value is determined based on the pseudo-range ranging signal and is characterized by a pseudo-range ranging expression; a relay ranging value is determined based on the relay ranging signal and is characterized by a relay ranging expression, wherein the relay ranging signal comprises an uplink signal broadcast to the first device and a downlink signal relayed by the first device; and a clock difference between the first device and the second device is determined based on the relay ranging value characterized by the relay ranging expression, the pseudo-range ranging value characterized by the pseudo-range ranging expression, and a corresponding relationship of ionospheric delays of two carrier frequencies.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese Patent Application No. 202411068713.1, filed August 6, 2024, entitled “A Dual-Frequency Time Synchronization System and Time Synchronization Method,” the entire contents of which are incorporated herein by reference in their entirety. SUMMARY FIG. 1 TECHNICAL FIELD

[0003] The present application relates to the field of space technology, in particular to a dual-frequency time synchronization system, a time synchronization method and navigation application thereof. BACKGROUND

[0004] Currently, the future-oriented 6G communication is being developed vigorously. Compared with the previous mobile communication technology, the biggest feature of 6G communication is to add satellite communication part, which organically integrates satellite communication and ground mobile communication to form a ubiquitous communication network with global coverage. Among them, the satellite communication part uses some technologies in the field of ground mobile communication technology, so that the satellite communication has the same technical characteristics as the ground mobile communication, such as the need for high-precision time synchronization function, and the time synchronization requirement is in the order of nanoseconds. The typical feature of 6G-oriented satellite communication is dominated by low-orbit satellites, such as domestic Internet communication constellation and foreign Starlink satellite constellation. These low-orbit satellite communication constellations need a large number of satellites to support, and how to meet the time synchronization requirement with low cost and high performance is an urgent demand. In other aerospace systems such as navigation satellites, communication satellites, remote sensing satellites, etc., high-precision satellite-ground time synchronization is also required.

[0005] The typical method to realize high-precision satellite-ground time synchronization at present is the two-way pseudo-range measurement method and laser measurement method. The two-way pseudo-range measurement method is a powerful technical means to solve the satellite-ground time synchronization in the 6G system. The two-way pseudo-range measurement method has been widely used in satellite navigation systems due to its high time synchronization accuracy. The working principle of the two-way pseudo-range measurement method is that the satellite and the earth station both transmit pseudo-range measurement signals under the control of local clocks, and the receivers of the satellite and the earth station receive the measurement signals transmitted by each other. Then, the two parties measure the pseudo-range measurement values of each other, and then exchange the pseudo-range measurement values through communication means. By comparing the two pseudo-code measurement values, the clock difference between the satellite and the earth station can be obtained. The obtained clock difference contains ionospheric time delay residual error. If it is necessary to further overcome the influence of ionospheric time delay error, ionospheric model correction or third-party provided ionospheric total electron content correction is needed.

[0006] The reason why the two-way pseudo-range measurement method has high time synchronization accuracy is that the signal propagation paths between the satellite and the earth station are the same, which have the same space distance between the satellite and the earth station and the same tropospheric time delay, but the ionospheric time delay is different. Therefore, the clock difference between the satellite and the earth station is the difference between the measured pseudo-ranges divided by the speed of light or the difference between the time instants of the respective time scales detected by the satellite and the earth station.

[0007] In the two-way pseudo-range ranging measurement method, the ground station and the satellite each use one carrier frequency, a total of two carrier frequency radio signals, which first requires that the satellite and the ground station satisfy the rough time synchronization requirement, otherwise the error caused by the unequal space distance will be brought; at the same time, the satellite or the ground station has the corresponding pseudo-range ranging device. The traditional two-way pseudo-range measurement method is used in the L, S frequency band, and the L, S frequency band has concentrated a large number of satellite communication and satellite navigation services. If the radio signals of the L, S frequency band are used again, the mutual interference and other problems will be brought. At present, industry experts are actively developing high-frequency two-way pseudo-range time comparison methods, and the satellite-ground time synchronization method suitable for high-frequency bands is still under study.

[0008] In order to realize the satellite-ground time synchronization, a laser method can also be used. Laser can be regarded as a radio signal with very high frequency. When the laser signal penetrates the ionosphere, the time delay is very small and can be ignored. The satellite and the ground station both use laser devices instead of radio transmitters or receivers, which has the disadvantages of high cost and limited application. When using laser, there is the disadvantage of being greatly affected by the weather. In rainy, snowy, cloudy and other weather conditions, the laser method cannot be used, and can only be used in sunny weather. Therefore, although the laser method can achieve very good time synchronization performance, it is restricted by the high cost and the great influence of the weather, and it is difficult to be used universally.

[0009] The above-mentioned various methods require the satellite or the ground receiver to receive signals and measure them. For the receiving party, the signal transmission between the satellite and the ground involves the ionosphere and the troposphere of the far-end atmosphere, the multipath effect and the electromagnetic environment of the near-end. The far-end and the near-end are collectively referred to as the environmental section. Among them, the atmospheric influence is comprehensive and fundamental, and it is a worldwide problem. In addition to the environmental section, the above-mentioned methods have the problems of a large number of observation devices, large time synchronization error, initial time synchronization accuracy, satellite orbit determination accuracy, and user coordinate accuracy, which affect the time synchronization accuracy of the two-way pseudo-range measurement method.

[0010] The above-mentioned content is only used to assist in understanding the technical solutions of the present application, and does not represent the acknowledgement of the above-mentioned content as prior art. SUMMARY

[0011] The main purpose of the present application is to provide a dual-frequency time synchronization system, a time synchronization method and a navigation application thereof, which aims to solve the problems of low clock difference accuracy, poor real-time performance and high cost in the existing two-way pseudo-range ranging method, and to provide a low-cost and high-performance time synchronization solution for satellite communication of the 6G system.

[0012] To achieve the above object, the application provides a dual-frequency time synchronization system, comprising a first device and a second device connected in communication; there is one pseudorange ranging signal and one retransmission ranging signal between the first device and the second device; wherein the pseudorange ranging signal is broadcast by the first device and received by the second device, or broadcast by the second device and received by the first device; the retransmission ranging signal is composed of an uplink signal and a downlink signal, the second device broadcasts the uplink signal and receives the downlink signal, the first device receives the uplink signal and retransmits to form the downlink signal; the carrier frequency of the uplink signal, the carrier frequency of the downlink signal and the carrier frequency of the pseudorange ranging signal satisfy a preset carrier frequency relationship.

[0013] In addition, to achieve the above object, the application also provides a time synchronization method, applied to the dual-frequency time synchronization system described in any embodiment of the application, the method is executed by a computing device, the method comprises: when the pseudorange ranging signal is broadcast by the second device and received by the first device, communicating with the first device to obtain one pseudorange ranging value measured by the first device, and communicating with the second device to obtain one retransmission ranging value measured by the second device; when the pseudorange ranging signal is broadcast by the first device and received by the second device, communicating with the second device to obtain one pseudorange ranging value and one retransmission ranging value measured by the second device; wherein the carrier frequency corresponding to the one retransmission ranging value and the carrier frequency corresponding to the one pseudorange ranging value satisfy a preset carrier frequency relationship; the pseudorange ranging value is represented by a pseudorange ranging expression and the retransmission ranging value is represented by a retransmission ranging expression; the relative clock difference between the first device and the second device is determined based on the pseudorange ranging value represented by the pseudorange ranging expression, the retransmission ranging value represented by the retransmission ranging expression and the preset carrier frequency relationship.

[0014] In addition, to achieve the above object, the application also provides a space distance determination method between satellite and ground, applied to the dual-frequency time synchronization system described in any embodiment of the application, the method is executed by a computing device, the method comprises: determining the troposphere delay on the ranging signal path between the first device and the second device based on a preset troposphere model; determining the ionosphere delay on the ranging signal path between the first device and the second device based on an ionosphere model or the total electron content of ionosphere provided by a third party; determining the relative space distance shown in the following formula (10) by using the following formula (3') based on the determined troposphere delay, ionosphere delay, relative clock difference and corrected pseudorange ranging value, wherein the relative space distance is the space distance between the first device and the second device:

[0015]

[0016] Alternatively, based on the determined tropospheric delay, ionospheric delay and the corrected round-trip ranging value, a relative spatial distance shown in the following formula (11) is determined by using the following formula (4'):

[0017] R true,z1u (n)=L z1,m (n)-T duiliu,z1u (n)-(I z1u (n)+I z1d (n)) / 2 (11);

[0018] Alternatively, the formula (10) and the formula (11) are weighted and averaged to obtain a weighted and averaged relative spatial distance, wherein the sum of the weighting coefficients is equal to 1.

[0019] In addition, to achieve the above object, the application further provides a satellite navigation system, comprising: the double-frequency time synchronization system according to any one of the embodiments of the application, wherein the first device is a satellite, the second device is an earth station, and the number of the satellites is greater than or equal to 2; a plurality of third devices, each of which is in communication connection with the satellite; wherein the earth station obtains the orbit parameters of the corresponding satellite based on the data transmission results of each satellite, and determines the coordinate information of the earth station based on the orbit parameters of each satellite and the relative spatial distance between the earth station and the satellite; part of the third devices constitute a satellite orbit determination system, which is used for orbit monitoring and processing of the satellite to obtain the satellite orbit parameters; and part of the third devices constitute a satellite-ground time synchronization system, which is used for time monitoring of each satellite.

[0020] In addition, to achieve the above object, the application further provides an inter-station time synchronization system, comprising: the satellite navigation system according to any one of the embodiments of the application; wherein when the earth station is at least two, at least two of the earth stations realize time synchronization with each other by exchanging data through communication.

[0021] In addition, to achieve the above object, the application further provides an inter-station time synchronization system, comprising: the double-frequency time synchronization system according to any one of the embodiments of the application; wherein when the first device or the second device is at least two, at least two of the first devices or the second devices realize time synchronization with each other by exchanging data through communication.

[0022] Further, to achieve the above object, the application further provides a satellite positioning method applied to the satellite navigation system according to any of the embodiments of the application, wherein the method is executed by the earth station, and the method comprises: obtaining orbit parameters of each satellite, wherein the orbit parameters of the satellite are determined by an orbit determination system; determining coordinate information of the corresponding satellite based on the orbit parameters; obtaining relative spatial distances between the earth station and each satellite; and determining coordinate information of the earth station based on the orbit parameters of each satellite and the relative spatial distances between the earth station and each satellite.

[0023] The double-frequency time synchronization system provided by the application comprises a first device and a second device. The first device broadcasts a pseudo-range measurement signal to the second device, and the second device sends an uplink signal to the first device. The first device performs frequency conversion and power amplification on the uplink signal to obtain a downlink signal after obtaining the uplink signal, and forwards the downlink signal to the second device. The carrier frequencies of the uplink signal, the downlink signal and the pseudo-range measurement signal have a preset carrier frequency relationship. In this way, the second device can determine the clock difference between the first device and the second device by performing mathematical operations on the preset carrier frequency relationship between the carrier frequencies of the three signals without knowing the exact time delay error caused by the atmosphere. When the double-frequency time synchronization system is applied to the field of satellite navigation, compared with the prior art, the double-frequency time synchronization system of the application can improve the accuracy of the determined clock difference, improve the navigation accuracy and has the advantages of strong real-time performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 2 FIG. 1 is a structural schematic diagram of a double-frequency time synchronization system according to an embodiment of the application;

[0025] FIG. 3 FIG. 2 is a structural block diagram of a satellite and an earth station according to an embodiment of the application;

[0026] FIG. 4 FIG. 3 is a structural block diagram of a satellite and an earth station according to another embodiment of the application;

[0027] FIG. 5 FIG. 4 is a flowchart of a time synchronization method according to an embodiment of the application;

[0028] FIG. 6 FIG. 5 is a flowchart of a method for determining a spatial distance between a satellite and an earth station according to an embodiment of the application;

[0029] FIG. 7 FIG. 6 is a structural schematic diagram of a satellite navigation system according to an embodiment of the application;

[0030] FIG. 1 FIG. 7 is a flowchart of a satellite positioning method according to an embodiment of the application.

[0031] The objectives, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below with reference to the drawings in the present application. Obviously, the described embodiments are only a part of, rather than all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort should fall within the protection scope of the present application. It should be understood that the specific embodiments described herein are only used to explain the present application, and should not be used to limit the present application.

[0033] Firstly, the meanings of the parameters involved in the present exemplary embodiments are described as follows:

[0034] ρ z1z,m (n) represents the corrected pseudo-range measurement value at the nth moment, in units of meters; ρ z1z (n) represents the pseudo-range measurement value at the nth moment, in units of meters; R true,z1z (n) represents the real space distance passed by the pseudo-range measurement signal at the nth moment, in units of meters; I z1z (n) represents the ionospheric delay of the pseudo-range measurement signal at the nth moment, in units of meters; T duiliu,z1z (n) represents the tropospheric delay of the pseudo-range measurement signal at the nth moment, in units of meters; c represents the speed of light, in units of meters / second; δt s (n) represents the clock difference of the first device relative to the system time at the nth moment, in units of seconds; δt z (n) represents the clock difference of the second device relative to the system time at the nth moment, in units of seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudo-range measurement signal at the nth moment, in units of meters; X z1 (n) represents the pseudo-range measurement signal hardware device delay at the nth moment, in units of meters, which includes the transmission delay of the pseudo-range measurement signal and the reception delay of the pseudo-range measurement signal;

[0035] L z1,m (n) represents the corrected forward measurement value at the nth moment, in units of meters; L z1 (n) represents the forward measurement value at the nth moment, in units of meters; R true,z1u (n) represents the real space distance passed by the uplink signal at the nth moment, in units of meters; R true,z1d (n) represents the real space distance passed by the downlink signal at the nth moment, in units of meters; I z1u(n) ionospheric delay of the uplink signal at the nth moment, unit: meter; I z1d (n) ionospheric delay of the downlink signal at the nth moment, unit: meter; T duiliu,z1u (n) tropospheric delay of the uplink signal at the nth moment, unit: meter; T duiliu,z1d (n) tropospheric delay of the downlink signal at the nth moment, unit: meter; Y z1 (n) hardware device delay of the retransmission ranging signal at the nth moment, the hardware device delay of the retransmission ranging signal includes the transmission delay of the uplink signal, the retransmission delay of the first device generating the downlink signal, and the reception delay of the downlink signal, unit: meter.

[0036] Q ion represents an ionospheric delay coefficient, TEC(n) represents the total number of electrons in the ionosphere on the ranging signal path between the first device and the second device at the nth moment; f z1u (n) carrier frequency of the uplink signal at the nth moment, unit: hertz; f z1d (n) carrier frequency of the downlink signal at the nth moment, unit: hertz; f z1z (n) carrier frequency of the pseudo-range ranging signal at the nth moment, unit: hertz.

[0037] It is particularly pointed out that: Q ion is an ionospheric delay coefficient, which is published by some international institutions. With the deepening of the research on ionospheric delay, the ionospheric delay coefficient is more and more accurate. The ionospheric delay coefficient was once 40.28, 40.30, and is currently 40.309. In the future, there may be more accurate ionospheric delay coefficients. The ionospheric delay coefficient is not particularly limited in the present application, and the latest published value is taken. In the present embodiment, Q ion is 40.309.

[0038] The present application creatively applies the carrier frequencies of the retransmission ranging signal and the pseudo-range ranging signal, and proposes a dual-frequency time synchronization system and method.

[0039] Meanwhile, on the basis of the dual-frequency time synchronization system and method, a satellite navigation system is proposed by combination. The biggest feature of the satellite navigation system compared with the existing Beidou satellite navigation system is that the user clock difference is obtained first, and then the three-dimensional coordinates of the earth station are calculated by using the spatial geometric distance between the earth station and the satellite, unlike the Beidou satellite navigation system that calculates the three-dimensional coordinates and the user clock difference. The satellite navigation system provided by the present application can realize time service and positioning service only by using two satellites, and has the characteristics of small investment and excellent performance.

[0040] The system time described in the present application refers to the time generated and maintained by a certain system, such as the system composed of the first device and the second device in the present application. In actual application, the Beidou time in China is often used as the reference time and the system time, and the clock difference of different devices is the clock difference of different devices relative to the Beidou reference time.

[0041] The computing device of the present application can respectively communicate with the first device and the second device to obtain the pseudo-range measurement value and the retransmission measurement value.

[0042] When the first device broadcasts the pseudo-range measurement signal, the second device receives the pseudo-range measurement signal and measures to obtain the pseudo-range measurement value, and the second device spontaneously transmits and receives the retransmission measurement signal and measures to obtain the retransmission measurement value. At this time, the computing device communicates with the second device to obtain the pseudo-range measurement value and the retransmission measurement value.

[0043] When the second device broadcasts the pseudo-range measurement signal, the first device receives the pseudo-range measurement signal and measures to obtain the pseudo-range measurement value, and the second device spontaneously transmits and receives the retransmission measurement signal and measures to obtain the retransmission measurement value. At this time, the computing device communicates with the second device to obtain the retransmission measurement value, and communicates with the first device to obtain the pseudo-range measurement value.

[0044] After the computing device obtains the pseudo-range measurement value and the retransmission measurement value, the method of the present application is executed to calculate the relative clock difference, that is, the clock difference between the first device and the second device.

[0045] It is worth noting that in the present exemplary embodiment, the computing device can be integrated into the first device, or integrated into the second device, or independent of the first device and the second device, that is, an independent device.

[0046] The core function of the present application is that the retransmission measurement signal and the pseudo-range measurement signal between the first device and the second device are each one, and one pseudo-range measurement value and one retransmission measurement value are obtained, and the clock difference between the first device and the second device is calculated according to the pseudo-range measurement value, the retransmission measurement value, and the corresponding preset carrier frequency relationship.

[0047] Therefore, the present application focuses on the signal structure of the first device, the second device, and the signal structure between the two, as well as the calculation method for obtaining the relative clock difference and the calculation method for obtaining the relative spatial distance.

[0048] First, the dual-frequency time synchronization system is described, and then the satellite navigation system is described.

[0049] In the dual-frequency time synchronization system described in the present application, there is one pseudo-range measurement signal and one retransmission measurement signal between the first device and the second device.

[0050] The forward ranging signal is composed of an uplink signal and a downlink signal, the second device broadcasts the uplink signal, the first device receives the uplink signal and forwards to form the downlink signal, and the second device receives the downlink signal; the pseudo-range ranging signal is broadcast by the first device and received by the second device, or broadcast by the second device and received by the first device.

[0051] The pseudo-range ranging signal and the forward ranging signal are both spread spectrum signals.

[0052] It is worth noting that in the present exemplary embodiment, the pseudo-range ranging signal can be broadcast by the first device and received by the second device, or it can also be broadcast by the second device and received by the first device.

[0053] When the pseudo-range ranging signal is broadcast by the second device, the uplink signal broadcast by the forward ranging device in the second device can be used as the pseudo-range ranging signal. After the uplink signal reaches the first device, it is divided into two parts, one part is used as the pseudo-range ranging signal, and the other part of the signal is forwarded by the forwarder to form the downlink signal.

[0054] When the pseudo-range ranging signal is broadcast by the first device and received by the second device, the forward ranging signal is broadcast and received by the second device. In this working condition, the forward ranging signal and the pseudo-range ranging signal are both received and measured by the second device, and the second device performs synchronous measurement to obtain the pseudo-range ranging value and the forward ranging value.

[0055] It should be noted that when the pseudo-range ranging signal is broadcast by the second device and received by the first device, the forward ranging signal is broadcast and received by the second device. The forward ranging signal and the pseudo-range ranging signal are respectively received and measured by the second device and the first device, and cannot be strictly synchronously measured. The first device and the second device need to have a rough time synchronization condition (the same is true for the two-way pseudo-range measurement method, the satellite and the ground station each measure the pseudo-range ranging signal sent by the other party, and the satellite and the ground station need to have a rough time synchronization requirement). At this time, the pseudo-range value measured by the first device and the forward ranging value measured by the second measuring device can be regarded as synchronous measurement, and then the clock difference is calculated using the method of the present application.

[0056] In addition, whether the pseudo-range ranging signal is measured by the second device or the first device corresponds to two different types of systems. The signal structure, system composition, and processing method of the two different types of systems are the same except for the direction of the pseudo-range ranging signal transmission and the pseudo-range measuring device. Therefore, for the sake of simplicity and clarity, only the case where the first device broadcasts the pseudo-range ranging signal is exemplarily described below.

[0057] There is one pseudo-range ranging signal and one retransmission ranging signal between the first device and the second device; the pseudo-range ranging signal is broadcast by the first device and received by the second device; the retransmission ranging signal includes uplink signals broadcast by the second device and downlink signals received by the second device, and the downlink signals are obtained by the first device retransmitting the uplink signals; the carrier frequency of the one pseudo-range ranging signal (including the carrier frequency of the uplink signals and the carrier frequency of the downlink signals) and the carrier frequency of the one retransmission ranging signal satisfy a preset carrier frequency relationship.

[0058] In other embodiments, the first device and the second device can also be located on the same side of the ionosphere, for example, both on the ground or both in space, at this time, the ionosphere delay is 0. When the first device and the second device are located in space, at this time, the ranging signal does not pass through the atmosphere, and there is no troposphere delay and ionosphere delay, and the pseudo-range ranging signal has a sagnac delay effect; when the first device and the second device are located in low altitude or even on the ground, the ranging signal experienced by the path also has no ionosphere delay, and the ionosphere delay is 0, at this time, the sagnac delay effect of the pseudo-range ranging signal can be ignored. For these cases, the clock difference between the first device and the second device can also be determined by the time synchronization method provided in the embodiments of the present application.

[0059] The dual-frequency time synchronization system provided in the embodiments of the present application can be applied to a space system, and typically can be a time synchronization system composed of an earth station and a satellite (such as satellite navigation, satellite communication, satellite remote sensing, satellite reconnaissance, and meteorological satellite, etc.), that is, a star-ground time synchronization system, in which the clock difference between the satellite and the earth station is monitored by the earth station. In addition to the star-ground time synchronization system, the embodiments of the present application can also be applied to time synchronization between ground stations.

[0060] The first device can be a satellite, and the second device can be an earth station, when the device is integrated in the earth station, that is, the clock difference between the satellite and the earth station and the relative spatial distance are determined by the earth station, so that the satellite can be synchronized with the clock of the earth station. Of course, in other embodiments, the first device can also be an earth station, and the second device can be a satellite.

[0061] In addition, the first device can also be a high-orbit device, and the second device can be a low-orbit device, or the first device and the second device can both be low-orbit devices, as long as the two devices are located on both sides of the ionosphere, or one device is located in the ionosphere and the other device is located outside the ionosphere, or both devices are located in the ionosphere.

[0062] FIG. 1 A structural schematic diagram of the dual-frequency time synchronization system according to an embodiment of the present application is shown in FIG. 1. FIG. 2As shown, the dual-frequency time synchronization system can include a first device 100 and a second device 200 connected in communication; the first device 100 forwards a downlink signal to the second device 200 based on a received uplink signal, and broadcasts a pseudo-range measurement signal to the second device 200, wherein the uplink signal and the downlink signal formed by the first device 100 forwarding constitute a forwarding measurement signal; the second device 200 is configured to broadcast an uplink signal to the first device 100, receive a pseudo-range measurement signal and a downlink signal, and correspondingly obtain a forwarding measurement value and a pseudo-range measurement value by synchronously measuring the forwarding measurement signal and the pseudo-range measurement signal. The carrier frequency of the uplink signal, the carrier frequency of the downlink signal and the carrier frequency of the pseudo-range measurement signal satisfy a preset carrier frequency relationship.

[0063] In the following, without special instructions, the first device 100 is taken as a satellite and the second device 200 is taken as an earth station for example.

[0064] It is worth noting that in the present exemplary embodiment, if the telemetry signal is a spread spectrum system, the telemetry signal sent by the telemetry unit in the satellite can be used as the pseudo-range measurement signal.

[0065] The dual-frequency time synchronization system provided by the present application can be used for the satellite to send a pseudo-range measurement signal to the earth station, the earth station to send an uplink signal to the satellite, the satellite to obtain the uplink signal, to forward the uplink signal to obtain a downlink signal, and to send the downlink signal to the earth station, and the carrier frequency of the uplink signal, the carrier frequency of the downlink signal and the carrier frequency of the pseudo-range measurement signal satisfy a preset carrier frequency relationship. In this way, the earth station can determine the clock difference between the satellite and the earth station by mathematical operation based on the preset carrier frequency relationship without knowing the exact atmospheric delay error caused by the atmosphere, and when the dual-frequency time synchronization system is applied to satellite navigation, compared with the prior art, the dual-frequency time synchronization system of the present application can overcome the ionospheric delay, overcome the error influence of the tropospheric delay, eliminate the relative spatial distance, improve the accuracy of the determined clock difference, has the advantages of simplifying the satellite payload and reducing the cost of the satellite.

[0066] In the present exemplary embodiment, the forwarding measurement signal and the pseudo-range measurement signal are both spread spectrum signals, and the spread spectrum technology, carrier frequency multiplexing technology and code division multiple access technology are used for corresponding processing in signal transmission, forwarding and receiving processing.

[0067] In the present exemplary embodiment, the earth station sends an uplink signal to the satellite based on its own clock system, i.e., using local time as a reference, the satellite obtains the uplink signal, forwards the uplink signal to obtain a downlink signal, and forwards the downlink signal after frequency conversion to the earth station. It can be seen that the carrier frequencies of the uplink signal and the downlink signal are different in the present exemplary embodiment.

[0068] The uplink signal and the downlink signal relayed by the satellite constitute the relay ranging signal, which the earth station uses to determine the relay ranging value. In addition, the satellite also transmits a pseudorange ranging signal to the earth station based on its own clock system, i.e., local time. The earth station receives and demodulates the pseudorange ranging signal to obtain the pseudorange ranging value. Therefore, the earth station can calculate the relative clock difference and relative spatial distance based on the determined relay ranging value, pseudorange ranging value, and a preset frequency relationship. Here, the relative clock difference is the clock difference between the satellite and the earth station, and the relative spatial distance is the satellite-to-ground spatial distance between the satellite and the earth station.

[0069] It should be noted that the pseudorange ranging signal and the forwarding ranging signal described in this exemplary embodiment refer to the modulated signals obtained by modulating the ranging code signal into the carrier signal. The ranging codes used in the pseudorange ranging signal and the forwarding ranging signal can be the same or different, and the ranging code of the uplink signal in the forwarding ranging signal is the same as the ranging code of the downlink signal. In some specific embodiments, the ranging code can be obtained by loading protocol data through pseudocode, Weil code, M code, etc. This application does not make any special limitation on which ranging code is specifically selected. It is also understood that the forwarding ranging signal and the pseudorange ranging signal 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.

[0070] For details on the process of determining the clock difference between the satellite and the earth station, please refer to the description of the subsequent method embodiments, which will not be elaborated here.

[0071] FIG. 2 Here is a structural block diagram of a satellite and earth station according to one embodiment of this application, such as FIG. 3 As shown, in an exemplary embodiment, the satellite may include a transponder 101, a pseudorange generator 102, and a first time-frequency device 103. The pseudorange generator 102 generates and broadcasts pseudorange ranging signals; the transponder 101 receives uplink signals, performs frequency conversion and power amplification on the uplink signals, and then forwards downlink signals to the second device 200; the first time-frequency device 103 provides clock signals for the transponder 101 and the pseudorange generator 102.

[0072] It should be understood that the repeater 101 and pseudorange generator 102 described in this exemplary embodiment can be set independently or integrated into a hardware device, that is, the functions of the repeater 101 and pseudorange generator 102 can be implemented through an integrated hardware device, or the repeater 101, pseudorange generator 102 and first time-frequency device 103 can be integrated. All of these are within the protection scope of this application.

[0073] It should be noted that in the example embodiment, the pseudo-range generating device 102 and the transponder 101 are communicatively connected, i.e., they can communicate with each other. They can communicate directly with each other or through a third device. These are all within the protection scope of the present application.

[0074] Since the computing device is only used to implement the computing function, it can be independently arranged or integrated into the first device 100 or the second device 200, which does not affect the implementation of the scheme of the present application. Therefore, the example embodiment is exemplarily described by taking the case that the computing device is integrated into the second device 200. Based on this, the earth station can include a transponder ranging device 201, a second pseudo-range ranging device 202, a second time-frequency device 203, and a computing device 204. The second pseudo-range ranging device 202 processes the received pseudo-range ranging signal to obtain a pseudo-range ranging value. The transponder ranging device 201 generates and broadcasts an uplink signal, and receives a downlink signal and determines a transponder ranging value based on the downlink signal. The computing device 204 is communicatively connected to the second pseudo-range ranging device 202 and the transponder ranging device 201. The computing device 204 receives the pseudo-range ranging value and the transponder ranging value, and determines the clock difference between the satellite and the earth station based on the pseudo-range ranging value, the transponder ranging value, and a preset carrier frequency relationship, and determines the relative spatial distance based on the pseudo-range ranging value and the transponder ranging value. The second time-frequency device 203 provides a clock signal for the transponder ranging device 201 and the second pseudo-range ranging device 202.

[0075] In addition, it should be noted that the second pseudo-range ranging device 202 and the transponder ranging device 201 in the example embodiment can be independently arranged or integrated into one hardware device, i.e., one hardware device implements the functions of the second pseudo-range ranging device 202 and the transponder ranging device 201, or the second pseudo-range ranging device 202, the transponder ranging device 201, and the second time-frequency device 203 are integrated. These are all within the protection scope of the present application.

[0076] FIG. 3 For the structural block diagram of the satellite and the earth station according to another embodiment of the present application, as described above, the pseudo-range ranging signal can also be broadcast by the second device 200 and received by the first device 100. In this case, as shown in FIG. 4, the second device 200 includes a second pseudo-range ranging device 202, a second time-frequency device 203, and a computing device 204. The second pseudo-range ranging device 202 processes the received pseudo-range ranging signal to obtain a pseudo-range ranging value. The computing device 204 is communicatively connected to the second pseudo-range ranging device 202. The computing device 204 receives the pseudo-range ranging value and determines the clock difference between the satellite and the earth station based on the pseudo-range ranging value and a preset carrier frequency relationship, and determines the relative spatial distance based on the pseudo-range ranging value. The second time-frequency device 203 provides a clock signal for the second pseudo-range ranging device 202. FIG. 2As shown, the first device 100 comprises a first time-frequency device 103, a transponder 101 and a first pseudorange ranging device 104; the first time-frequency device 103 is configured to provide time-frequency signals to the transponder 101 and the first pseudorange ranging device 104; the transponder 101 is configured to receive uplink signals, perform frequency conversion and power amplification on the uplink signals respectively, and then forward the downlink signals to the second device 200; the first pseudorange ranging device 104 is in communication connection with the transponder 101, and is configured to receive and measure pseudorange ranging signals to obtain pseudorange ranging values; the second device 200 comprises a second time-frequency device 203 and a transponder ranging device 201; the second time-frequency device 203 is configured to provide time-frequency signals to the transponder ranging device 201 at least; the transponder ranging device 201 is configured to generate and broadcast uplink signals, and receive downlink signals, and determine transponder ranging values based on the transponder ranging signals; wherein the uplink signals broadcasted by the transponder ranging device 201 serve as the pseudorange ranging signals; wherein the first pseudorange ranging device 104 is integrated with or separately arranged from the first time-frequency device 103 and the transponder 101, and the second pseudorange ranging device 202 is integrated with or separately arranged from the second time-frequency device 203 and the transponder ranging device 201.

[0077] The computing device 204 is in communication connection with the first device 100 and the second device 200, and is configured to receive the pseudorange ranging values and the transponder ranging values, determine relative spatial distances and clock differences between the first device 100 and the second device 200 based on the transponder ranging values and the pseudorange ranging values. In this case, the transmission delay of the transponder ranging device 201 can be measured in advance, so that the delay is pre-set in the computing device 204, and the computing device 204 directly uses the delay in subsequent calculations. Because the first device 100 and the second device 200 only differ in the broadcasting mode of the pseudorange ranging signals in this working condition, the specific functions of the functional components are similar to those shown in the structure of the first device 100 and the second device 200. FIG. 2 The structure is similar to that shown in FIG. 1 The specific structure of the first device 100 and the second device 200 will be further introduced below taking the system structure shown in

[0078] In the exemplary embodiments, the transponder ranging device 201 can comprise a modulator, a mixer, a demodulator, an antenna, a data collector, etc., the modulator generates intermediate frequency spread spectrum signals; the mixer mixes the intermediate frequency spread spectrum signals into radio frequency signals, the antenna sends the radio frequency signals to the satellite, and receives the radio frequency signals forwarded by the satellite, the antenna receives the radio frequency signals and mixes them into intermediate frequency signals by the mixer; the demodulator demodulates the intermediate frequency signals to obtain the transponder ranging values through ranging code correlation operation; and the data collector records and stores the transponder ranging values. The second pseudorange ranging device 202 can comprise a demodulator, a receiving antenna, a data collector, etc., the receiving antenna receives the pseudorange ranging signals of the satellite and generates the pseudorange ranging values by the second pseudorange ranging device 202.

[0079] It is worth noting that in the present exemplary embodiment, the second pseudorange ranging device 202 and the repeater ranging device 201 are arranged with a zero baseline.

[0080] It is worth noting that the zero baseline arrangement in the present application does not mean that the distance between the second pseudorange ranging device 202 and the repeater ranging device 201 is 0, but that the distance between them is arranged to satisfy the condition that the space paths experienced by the repeater ranging signal and the pseudorange ranging signal are approximately the same. When the distance between the second pseudorange ranging device 202 and the repeater ranging device 201 becomes smaller and smaller, and they can be integrated into one device, the approximately same gradually becomes the same, and they have the same relative spatial distance, the same troposphere delay, and the same ionosphere total electron content.

[0081] At this time, the two signals of the pseudorange ranging signal and the repeater ranging signal have the same transmission path, so the atmosphere has the same effect on the repeater ranging signal and the pseudorange ranging signal, i.e., the repeater ranging signal and the pseudorange ranging signal have the same ionosphere path and troposphere path. Therefore, the clock difference between the satellite and the earth station can be calculated by using the preset carrier frequency relationship between the uplink signal, the downlink signal, and the carrier frequency of the pseudorange ranging signal to partially eliminate the effect of the atmosphere error.

[0082] In the exemplary embodiment, the second pseudorange ranging device 202 and the repeater ranging device 201 use the same time-frequency device, so that the second pseudorange ranging device 202 and the repeater ranging device 201 measure the pseudorange ranging value and the repeater ranging value at the same time. It is worth noting that the same time-frequency device in the present exemplary embodiment can include two clocks (crystal oscillator or atomic clock) or one clock (crystal oscillator or atomic clock). When the time-frequency device includes two clocks (crystal oscillator or atomic clock), one clock provides a clock signal for the second pseudorange ranging device 202, and the other clock provides a clock signal for the repeater ranging device 201. In actual use, the preset time interval can be set as needed, for example, it can be set to 1s, and the second pseudorange ranging device 202 and the repeater ranging device 201 measure at the rising edge or falling edge of the respective 1PPS (1 Pulse Per Second, second pulse) signal. As a preferred, it is generally recommended to use one clock to perform synchronous measurement of the pseudorange ranging signal and the repeater ranging signal at the rising edge or falling edge of the same 1PPS signal.

[0083] The repeater 101 has a repeater delay when performing signal forwarding, which refers to the time delay generated in the process of converting the uplink signal received by the satellite into a downlink signal.

[0084] The pseudorange ranging signal transmission delay refers to the time delay generated in the process of generating and transmitting the pseudorange ranging signal by the satellite pseudorange generating device 102.

[0085] Specifically, the repeater 101 is in communication connection with the pseudo-range generating device 102, so that the repeater delay can be sent to the pseudo-range generating device 102. The pseudo-range generating device 102 can load the obtained repeater delay and pseudo-range ranging signal transmission delay into the pseudo-range ranging signal, so that after the pseudo-range ranging signal is sent to the earth station, the repeater delay and the pseudo-range ranging signal transmission delay can be obtained after the second pseudo-range ranging device 202 in the earth station demodulates the pseudo-range ranging signal. Alternatively, because the repeater delay and the pseudo-range ranging signal transmission delay change little or are known, i.e., the repeater delay and the pseudo-range ranging signal transmission delay can be regarded as known quantities, so in actual use, the repeater delay and the pseudo-range ranging signal transmission delay can also be preset in the processing device 204.

[0086] By loading the repeater delay and the pseudo-range ranging signal transmission delay into the pseudo-range ranging signal to be transmitted to the earth station, the repeater delay and the pseudo-range ranging signal transmission delay are completely transmitted by using the existing signals between the satellite and the earth station, without the need to additionally set up a communication link, so as not to additionally occupy communication resources, and the communication cost can be greatly reduced, and the frequency resources can be saved.

[0087] It is worth noting that the above embodiment is only described by taking the signals owned by the earth station and the satellite (the pseudo-range ranging signal broadcast by the pseudo-range generating device 102) as an example to transmit the repeater delay and the pseudo-range ranging signal transmission delay.

[0088] The second pseudo-range ranging device 202 of the earth station has a pseudo-range receiving delay, which refers to the delay generated by the second pseudo-range ranging device 202 in the process of receiving the pseudo-range ranging signal sent by the satellite and generating the pseudo-range ranging value.

[0089] The repeater ranging device 201 of the earth station has a transmission delay and a receiving delay. The transmission delay refers to the delay from the generation of the uplink signal to the emission of the uplink signal from the antenna; and the receiving delay refers to the delay of receiving the downlink signal and generating the repeater ranging value.

[0090] In some other embodiments of the present application, the repeater delay and the pseudo-range ranging signal transmission delay can also be transmitted between the earth station and the satellite by using an additional communication signal, for example, a telemetry unit can be arranged in the satellite, and the repeater delay and the pseudo-range ranging signal transmission delay can be transmitted by the telemetry signal broadcast by the telemetry unit, or the repeater delay and the pseudo-range ranging signal transmission delay can be transmitted to the earth station by a user-defined other communication link signal. The present application does not specially limit the specific signal by which the repeater delay and the pseudo-range ranging signal transmission delay are transmitted.

[0091] In the example embodiment, the preset carrier frequency relationship refers to a frequency relationship satisfied among the carrier frequency of the uplink signal, the carrier frequency of the downlink signal and the carrier frequency of the pseudo-range measurement signal. In a specific embodiment, the carrier frequency of the uplink signal, the carrier frequency of the downlink signal and the carrier frequency of the pseudo-range measurement signal satisfy the preset carrier frequency relationship shown in the following formula (f1) or formula (f2):

[0092] f z1u (n)≠f z1d (n)=f z1z (n) (f1);

[0093] f z1d (n)≠f z1u (n)=f z1z (n) (f2);

[0094] It should be understood that in a specific implementation, the carrier frequency of a signal can have a certain frequency value fluctuation due to objective reasons or other factors. After the carrier frequencies of the signals are determined using the signal frequency relationship shown in the formula (f1) or (f2), in actual application, the actual frequency can have a small fluctuation on the basis of the theoretical carrier frequency determined (for example, frequency error caused by clock manufacturing, etc.), which is within the protection scope of the present application.

[0095] Further, in some embodiments, the carrier frequencies of the uplink signal, the downlink signal and the pseudo-range measurement signal perform frequency hopping according to a preset frequency hopping pattern on the time axis, that is, the uplink signal, the downlink signal and the pseudo-range measurement signal at different time do not use the same fixed frequency, but use different frequency signals at different time. In this way, the signal is frequency-hopped, which can improve the anti-interference and anti-interception of the signal.

[0096] It should be noted that regardless of how the frequency hopping is performed, the carrier frequencies of the pseudo-range measurement signal, the uplink signal and the downlink signal still need to satisfy the preset carrier frequency relationship.

[0097] Of course, the carrier frequencies of the uplink signal, the downlink signal and the pseudo-range measurement signal can also remain unchanged for a long time, that is, the time interval between adjacent two frequency hopping is infinite.

[0098] In the example embodiment, the dual-frequency time synchronization system provided by the embodiment of the application also has a communication function. The first device 100 uses the uplink signal and the pseudo-range measurement signal to perform data transmission with the second device 200, or uses an added communication signal to perform data transmission with the second device 200. Specifically, the satellite divides the uplink signal of the retransmission measurement signal into two parts, one part is retransmitted downward to the earth station, and the other part is received by the satellite to realize communication, or an additional communication signal is added to realize data transmission between the satellite and the earth station.

[0099] In the example embodiment, as shown in FIG. 4 The satellite can also send the retransmission delay and the pseudo-range measurement signal transmission delay to the earth station through an added communication signal, that is, in addition to the uplink signal link, the downlink signal link and the pseudo-range measurement signal link between the satellite and the earth station, the satellite also has an added communication link (including the communication link uplink signal fu and the communication link downlink signal fd), and the satellite transmits the retransmission delay and the pseudo-range measurement signal transmission delay to the earth station through the added communication link. The added communication signal can be a remote control and telemetry signal.

[0100] As can be seen, the satellite can transmit the retransmission delay and the pseudo-range measurement signal transmission delay to the earth station in various ways, and the specific transmission method of the retransmission delay and the pseudo-range measurement signal transmission delay is not specially limited in the application.

[0101] In the pseudo-range measurement value, the Sagnac effect delay of the satellite needs to be obtained, and the Sagnac effect delay needs the coordinates of the earth station and the satellite. The coordinates of the satellite can be obtained by the known satellite ephemeris, and the coordinates of the earth station can be obtained by the existing positioning method. Thus, the coordinate information required by the method of the embodiment of the application is obtained, and the Sagnac effect delay is obtained.

[0102] In the pseudo-range measurement value, the relativistic delay effect term does not appear. This is because in practice, the satellite in space has a time-frequency device to provide time and frequency. According to the knowledge of relativity, it is easy to know that the clock on the satellite will produce a corresponding relativistic effect delay due to the relativistic effect. For the relativistic effect delay of the satellite clock, the existing method can be used to solve, such as the satellite clock has been adjusted before being launched into space. The adjusted satellite clock is the same as the clock on the ground and has no relativistic effect delay. For details, refer to the practice of the Beidou navigation satellite clock in terms of relativity.

[0103] In the case of using the expression of the forward ranging to represent the forward ranging value, the Sagnac delay is not included in the expression of the forward ranging, because the Sagnac delay of the uplink signal and the Sagnac delay of the downlink signal are opposite in sign and have a very small difference in absolute value, so the two Sagnac delays can be approximately cancelled out, and thus the Sagnac delay term is not included in the expression of the forward ranging. Of course, in some other embodiments of the present application, the Sagnac delays can also be considered, i.e., the Sagnac delay of the uplink signal and the Sagnac delay of the downlink signal are added in the expression of the forward ranging, so as to achieve better measurement accuracy of the forward ranging value, which is within the protection scope of the present application.

[0104] In addition, the device delay used in the embodiments of the present method and the way of obtaining the same can refer to the description of the system embodiments above, and will not be repeated here.

[0105] When the pseudo-range ranging signal is broadcast by the second device and received by the first device, the first device receives the pseudo-range ranging signal broadcast by the second device and measures to obtain the pseudo-range ranging value. The second device broadcasts the uplink signal and receives the downlink signal formed by the first device, and the second device measures the downlink signal to obtain the forward ranging value.

[0106] In addition, when the pseudo-range ranging signal is broadcast by the first device and received by the second device, the second device obtains the forward ranging value and the pseudo-range ranging value by performing the following processes:

[0107] Broadcasting the uplink signal to the first device;

[0108] Obtaining the downlink signal based on the uplink signal broadcast by the first device, wherein the uplink signal and the downlink signal constitute the forward ranging signal;

[0109] Obtaining the pseudo-range ranging signal broadcast by the first device;

[0110] Synchronously measuring the forward ranging signal and the pseudo-range ranging signal to obtain the pseudo-range ranging value and the forward ranging value.

[0111] On the basis of the above embodiments, the embodiments of the present application further provide a time synchronization method, which can be applied to the dual-frequency time synchronization system of any of the above embodiments. The method can be executed by a computing device, and when the computing device is integrated into a ground station, the method is executed by the ground station.

[0112] FIG. 4 As shown in the flowchart of the time synchronization method according to an embodiment of the present application, the time synchronization method can include the following steps: FIG. 5

[0113] ​S100, when the pseudo-range measurement signal is broadcast by the second device and received by the first device, obtaining, through communication with the first device, a pseudo-range measurement value measured by the first device, and obtaining, through communication with the second device, a retransmission range value measured by the second device;

[0114] when the pseudo-range measurement signal is broadcast by the first device and received by the second device, obtaining, through communication with the second device, a pseudo-range measurement value measured by the second device and a retransmission range value measured by the second device;

[0115] wherein the preset carrier frequency relationship is satisfied between the carrier frequency corresponding to the one retransmission range value and the carrier frequency corresponding to the one pseudo-range measurement value;

[0116] S110, respectively using a pseudo-range measurement expression to represent the pseudo-range measurement value and using a retransmission range expression to represent the retransmission range value;

[0117] S120, determining a relative clock difference based on the pseudo-range measurement value represented by the pseudo-range measurement expression, the retransmission range value represented by the retransmission range expression, and the preset carrier frequency relationship, wherein the relative clock difference is a clock difference between the first device and the second device.

[0118] The following will continue to take the first device as a satellite and the second device as an earth station as an example to specifically describe the method.

[0119] wherein the earth station can obtain a pseudo-range measurement signal in the communication process with the satellite, demodulate the pseudo-range measurement signal to obtain a time delay when the pseudo-range measurement signal is transmitted, the pseudo-range measurement signal is transmitted by the satellite to the earth station, and the earth station receives and demodulates the pseudo-range measurement signal to determine a pseudo-range measurement value.

[0120] The earth station can also obtain a retransmission range signal by self-transmission and self-reception in the communication process with the satellite, and then measure a retransmission range value.

[0121] It should be noted that the Sagnac effect time delay in the pseudo-range measurement expression and the retransmission range expression in the present application has been explained in the foregoing and can be taken as a known value, and the star-ground space distance, the troposphere time delay, the ionosphere time delay, the clock difference of the satellite relative to the system time, and the clock difference of the earth station relative to the system time are unknowns. The method of the present application calculates the clock difference between the satellite and the earth station according to the measured pseudo-range measurement value and the retransmission range value.

[0122] It should be noted that the dual-frequency time synchronization system and method proposed in the present application can be used to solve the clock difference of the satellite relative to the system time when the clock difference of the earth station relative to the system time is known, and can be used to solve the clock difference of the earth station relative to the system time when the clock difference of the satellite relative to the system time is known.

[0123] The pseudo-range measurement signal and the retransmission measurement signal pass through the same atmospheric layer path, and the ionosphere total electron content experienced by the measurement signal is the same. The ionosphere is a dispersive medium, that is, the ionosphere produces different time delays for radio frequency signals of different carrier frequencies. The troposphere is a non-dispersive medium, that is, the troposphere produces the same time delay for radio frequency signals of different carrier frequencies.

[0124] Because of the zero baseline setting between the second pseudo-range measurement device 202 and the retransmission measurement device 201, the pseudo-range measurement signal and the downlink signal pass through the same space path, and the time when the uplink signal passes through the ionosphere and the time when the downlink signal passes through the ionosphere after being retransmitted by the satellite are different, with a certain time difference. In a relatively short time (such as a few seconds), the ionosphere is stable, and the ionosphere total electron content is almost unchanged. It can be calculated that the round-trip time of the radio frequency signal between almost all spacecraft and the ground station at present will not exceed a few seconds, which fully meets the conditions. In combination with the zero baseline setting space relationship and the time relationship that the time difference is very short, the space paths passed through by the retransmission measurement signal and the pseudo-range measurement signal are completely the same. Because of the zero baseline setting between the second pseudo-range measurement device 202 and the retransmission measurement device 201, the space paths passed through by the pseudo-range measurement signal and the retransmission measurement signal are completely the same, so there are equations (19) and (20):

[0125] R true,z1z (n)=R true,z1u (n)=R true,z1d (n) (19);

[0126] T duiliu,z1z (n)=T duiliu,z1u (n)=T duiliu,z1d (n) (20);

[0127] When the pseudo-range measurement signal is broadcast by the second device, the uplink signal of the pseudo-range measurement signal and the retransmission measurement signal pass through the same space path, and the retransmitter and the first pseudo-range measurement device also have the formula of the above zero baseline setting relationship.

[0128] When the first device and the second device are both located on the ground, at this time there is no ionosphere in the path passed through by the pseudo-range measurement signal and the retransmission measurement signal, and there are still the relationship formulas of the above equations (19) and (20).

[0129] In some embodiments, after step S100, the time synchronization method can further include the following step: correcting the retransmission measurement value and the pseudo-range measurement value using a pseudo-range smoothing algorithm. Specifically, the pseudo-range measurement value and the retransmission measurement value are corrected using the pseudo-range smoothing algorithm, so that the noise of the pseudo-range measurement value and the retransmission measurement value can be reduced, which is beneficial to improving the accuracy of the finally determined clock difference. The specific content of the pseudo-range smoothing algorithm is not repeated here.

[0130] In some embodiments, the preset time delay parameter term included in the pseudo-range measurement expression includes at least tropospheric delay, ionospheric delay, Sagnac effect delay, real space distance between the satellite and the earth station, and clock difference. In some other embodiments, the preset time delay parameter term can further include hardware device delay.

[0131] In step S110, after the pseudo-range measurement value and the retransmission measurement value are measured, the corresponding measurement expression is further used to characterize, i.e., to obtain a mathematical expression of the pseudo-range measurement value and a mathematical expression of the retransmission measurement value, so that in subsequent steps, the mathematical expressions are used for mathematical processing to eliminate error terms common to both, and finally the clock difference between the satellite and the earth station is obtained.

[0132] In the present exemplary embodiment, the pseudo-range measurement value can be characterized by using the pseudo-range measurement expression shown in the following formula (3) by the computing device:

[0133] ρ z1z (n) = R true,z1z (n) + I z1z (n) + T duiliu,z1z (n) ± c · (δt z (n) - δt s (n)) ± sagnac zz (n) + X z1 (n) (3).

[0134] And the retransmission measurement value can be characterized by using the retransmission measurement expression shown in the following formula (4): z1 (n) = R true,z1u (n) + R true,z1d (n) + I z1u (n) + I z1d (n) + T duiliu,z1u (n) + T duiliu,z1d (n) + Y z1 (n) (4).

[0135] It is worth noting that ± c · (δt z (n) - δt s (n)) in the pseudo-range measurement value formula (3) corresponds to the satellite broadcasting the pseudo-range measurement signal and the earth station receiving the measurement when + c · (δt z (n) - δt s (n) is taken; and corresponds to the earth station broadcasting the pseudo-range measurement signal and the satellite receiving the measurement when - c · (δt z (n) - δt s (n) is taken.

[0136] ± sagncazz (n), when taking +sagnca zz (n), when taking -sagnca zz (n), when taking -sagnca

[0137] Because the directions of the pseudo-range signals are different, in addition to the signs of the clock differences between the satellite and the earth station being opposite, the signs of the Sagnac effects are opposite, the rest are the same. Therefore, when the satellite broadcasts the pseudo-range signal, the pseudo-range measurement formula is as follows formula (f3); when the earth station broadcasts the pseudo-range signal, the pseudo-range measurement formula is as follows formula (S3):

[0138] ρ z1z (n) = R true,z1z (n) + I z1z (n) + T duiliu,z1z (n) + c·(δt z (n) - δt s (n) + sagnac zz (n) + X z1 (n) (f3)

[0139] ρ z1z (n) = R true,z1z (n) + I z1z (n) + T duiliu,z1z (n) - c·(δt z (n) - δt s (n) - sagnac zz (n) + X z1 (n) (S3)

[0140] When the first device and the second device are located at low altitude or on the ground, there is no ionospheric delay term in the pseudo-range measurement value formula (3), no tropospheric delay, and the Sagnac term can also be without the Sagnac term because the distance between the first device and the second device is relatively close.

[0141] As described above, the ionospheric delay term is included in the pseudo-range signal, and the ionospheric delay term is also included in the relay signal. In this application, the computing device can eliminate or reduce the linear combination result of the ionospheric delay of the uplink signal, the ionospheric delay of the downlink signal, and the ionospheric delay of the pseudo-range signal based on the preset carrier frequency relationship, so as to finally eliminate the ionospheric delay error in the process of calculating the relative clock difference (i.e. the clock difference between the satellite and the earth station).

[0142] Because the zero baseline setting relationship between the repeater ranging device of the earth station and the second pseudo ranging device, the ionosphere paths crossed by the repeater ranging signal and the pseudo ranging signal are the same, but the ionosphere total electron number TEC(n) is unknown.

[0143] In the present exemplary embodiment, the carrier frequency of the uplink signal, the carrier frequency of the downlink signal and the carrier frequency of the pseudo ranging signal satisfy the preset carrier frequency relationship shown in formula (f1) or formula (f2):

[0144] f z1u (n)≠f z1d (n)=f z1z (n) (f1);

[0145] f z1d (n)≠f z1u (n)=f z1z (n) (f2);

[0146] When the carrier frequencies of the signals between the earth station and the satellite satisfy the preset carrier frequency relationship shown in the above formula (f1) or (f2), the ionosphere delay parameters are associated in the corresponding carrier frequency terms based on the preset carrier frequency relationship between the carrier frequency of the uplink signal, the carrier frequency of the downlink signal and the carrier frequency of the pseudo ranging signal, to obtain the ionosphere delay corresponding relationship between the ionosphere delay of the uplink signal, the ionosphere delay of the downlink signal and the ionosphere delay of the pseudo ranging signal, wherein the ionosphere delay parameters include the ionosphere total electron number TEC(n) and the ionosphere delay coefficient on the ranging signal path of the satellite and the earth station, and the following formula (1) and formula (1') are obtained:

[0147]

[0148]

[0149] Equivalent transformation is performed on the formula (1) or formula (1'), to obtain the ionosphere delay corresponding relationship between the ionosphere delay of the uplink signal, the ionosphere delay of the downlink signal and the ionosphere delay of the pseudo ranging signal shown in formula (2) or formula (2'):

[0150] I z1z (n)-(I z1u (n)+I z1d (n)) / 2=(I z1d (n)-I z1u (n)) / 2≠0 (2);

[0151] I z1z (n)-(I z1u (n)+I z1d(n)) / 2 = (I z1u (n) - I z1d (n)) / 2 ≠ 0 (2');

[0152] In this way, the computing device can determine the clock difference between the satellite and the earth station based on the obtained ionospheric delay correspondence relationship and partially eliminate the ionospheric delay.

[0153] In some embodiments, step S120 can specifically include the following process:

[0154] S121, correcting the pseudo-range measurement value represented by the pseudo-range measurement expression to obtain a corrected pseudo-range measurement value;

[0155] S122, correcting the retransmission measurement value represented by the retransmission measurement expression to obtain a corrected retransmission measurement value;

[0156] S123, determining the relative clock difference based on the corrected pseudo-range measurement value, the corrected retransmission measurement value, and the preset carrier frequency relationship.

[0157] Specifically, step S121 is to correct the above formula (3) to obtain a corrected pseudo-range measurement value as shown in the following formula (3'):

[0158]

[0159] Further, when the satellite broadcasts the pseudo-range measurement signal, the pseudo-range measurement formula is specifically as follows formula (f3):

[0160] ρ z1z (n) = R true,z1z (n) + I z1z (n) + T duiliu,z1z (n) + c · (δt z (n) - δt s (n) ) + sagnac zz (n) + X z1 (n) (f3) ;

[0161] When the earth station broadcasts the pseudo-range measurement signal, the pseudo-range measurement formula is specifically as follows formula (S3): ρ z1z (n) = R true,z1z (n) + I z1z (n) + T duiliu,z1z (n) - c · (δt z (n) - δt s (n) ) - sagnac zz (n) + X z1 (n) (S3) ;

[0162] Therefore, in step S121, when the satellite broadcasts the pseudo-range measurement signal, the computing device modifies the formula (f3) to obtain the following formula (f3'), i.e., further specifies the formula (3') as the formula (f3'):

[0163]

[0164] When the satellite broadcasts the pseudo-range measurement signal, the computing device modifies the formula (f3) to obtain the following formula (f3'), i.e., further specifies the formula (3') as the formula (f3'):

[0165]

[0166] In step S122, the computing device transforms the relay measurement value shown in the formula (4) obtained in the above steps to obtain a modified relay measurement value, i.e., obtains the modified relay measurement value shown in the following formula (4'):

[0167]

[0168] After obtaining the ionospheric delay corresponding relationship of the above three signals, in step S123, the computing device further processes the modified pseudo-range measurement value represented by the formula (f3') and the modified relay measurement value represented by the formula (4') obtained by the above steps to obtain the relative clock difference, i.e., the clock difference between the satellite and the earth station.

[0169] In the exemplary embodiment, step S123 can specifically include the following steps:

[0170] S1231, mathematically processing the modified pseudo-range measurement value and the modified relay measurement value to obtain an expression containing the relative clock difference;

[0171] S1232, determining the clock difference between the first device and the second device by using the expression containing the relative clock difference and the preset carrier frequency relationship.

[0172] Because the directions of the pseudo-range measurement signals are different, in addition to the signs of the clock difference between the satellite and the earth station being opposite and the signs of the Sagnac effect being opposite, the rest are the same. The following continues to take the satellite broadcasting the pseudo-range measurement signal as an example to describe the method of the present application, i.e., expands the description of the pseudo-range measurement formula (f3) and the modified pseudo-range measurement formula (f3') corresponding to the pseudo-range measurement signal broadcast by the satellite.

[0173] The computing device further processes the modified pseudo-range measurement value represented by the formula (f3') and the modified relay measurement value represented by the formula (4') to obtain the relative clock difference;

[0174] Specifically, the computing device can utilize the modified relay measurement value Lz1,m (n) and the modified pseudo-range measurement value p z1z,m (n) to obtain an expression containing the relative clock difference as shown in equation (5) below:

[0175]

[0176] On this basis, the computing device uses the above equations (19), (20) to substitute into equation (5) to obtain the relative clock difference as shown in equation (6) below:

[0177]

[0178] As can be seen from equation (6), after the above step processing, the relative clock difference obtained eliminates the tropospheric delay parameter term and the relative spatial distance term, and at this time still contains the ionospheric delay combination term.

[0179] It has been described above that when the signal between the earth station and the satellite has a preset carrier frequency relationship as shown in equation (f1) or (f2) above, and further has an ionospheric delay corresponding relationship as shown in equation (2) or (2'), the computing device uses the ionospheric delay corresponding relationship as shown in equation (2) or (2') to partially eliminate the ionospheric delay term in equation (6) to obtain the relative clock difference as shown in equation (7) or (7') below:

[0180] δt z (n) - δt s (n) + 0.5 · (I z1d - I z1u ) / c = (p z1z,m (n) - L z1,m (n)) / c (7);

[0181] δt z (n) - δt s (n) + 0.5 · (I z1u - I z1d ) / c = (p z1z,m (n) - L z1,m (n)) / c (7');

[0182] Equation (7) or (7') shows that the finally calculated relative clock difference still contains a part of ionospheric delay residual error. If the ionospheric delay residual is to be further eliminated, the ionospheric delay correction method needs to be used, such as using ionospheric model correction or third-party provided ionospheric total electron number correction.

[0183] Because the ionospheric delay I z1z , I z1u , I z1dis unknown, as an error, the ionospheric delay residual in formula (7) or (7') is as an error, and thus the relative clock difference finally calculated is shown in formula (8):

[0184] (δt z (n)-δt s (n)) c = (p z1z,m (n)-L z1,m (n)) / c (8);

[0185] The relative clock difference obtained by formula (8) contains the ionospheric residual error part.

[0186] From formula (7) or (7'), and formula (8), it can be seen that when the first device and the second device are located at low altitude or on the ground, because there is no ionospheric delay term, the obtained relative clock difference has no ionospheric residual error, and the obtained is the accurate clock difference.

[0187] In some embodiments, after step S110, the time synchronization method can further include the following step: correcting the relay ranging value and the pseudo-range ranging value using a pseudo-range smoothing algorithm. Accordingly, in step S120, the relative clock difference can be calculated using the relay ranging value and the pseudo-range ranging value corrected by the pseudo-range smoothing algorithm. It can be understood that correcting the pseudo-range ranging value and the relay ranging value using the pseudo-range smoothing algorithm can reduce the noise of the pseudo-range ranging value and the relay ranging value, and is beneficial to improve the accuracy of the finally determined clock difference. The specific content of the pseudo-range smoothing algorithm will not be repeated here.

[0188] According to formula (8), when the clock difference δt z of the earth station relative to the system time is a known quantity, the clock difference δt s of the satellite relative to the system time can be easily obtained; conversely, when the clock difference δt s of the satellite relative to the system time is a known quantity, the clock difference δt z of the earth station relative to the system time can be easily obtained; when the clock difference of the earth station relative to the system time and the clock difference of the satellite relative to the system time are both unknown, the relative clock difference is obtained.

[0189] The computing device determines the relative clock difference (δt z (n)-δt s (n)) cAfterwards, data transmission can be performed with the satellite based on the uplink signal and the pseudo-range measurement signal, or data transmission can be performed with the satellite based on an additional communication signal, which can be a satellite remote control signal or a telemetry signal. The satellite obtains the relative clock difference based on the data transmission result. After obtaining the relative clock difference, the satellite further synchronizes its clock with the time of the earth station. These all belong to the protection scope of the present application.

[0190] The specific impact value of the ionospheric residual in formula (8) can be further illustrated by specific examples. When the carrier frequency of the uplink signal and the carrier frequency of the downlink signal use the L frequency band, such as f z1z = 1200 MHz, f z1u = 1600 MHz, and TEC = 50e16 electrons per square meter, the ionospheric residual is:

[0191] 0.5(I z1z -I z1u ) = 3.06 m, which is converted into time as 10.2 ns, and the obtained ionospheric residual is still relatively large.

[0192] When the carrier frequency of the uplink signal and the carrier frequency of the downlink signal use the Cn frequency band (5010-5030 MHz), which is a new frequency band allocated to satellite navigation by the International Telecommunication Union. For example, f z1z = 5015 MHz, f z1u = 5025 MHz, and TEC = 50e16, the ionospheric residual is:

[0193] 0.5(I z1z -I z1u ) = 0.0016 m, which is converted into time as 0.0053 ns.

[0194] It can be seen that when the Cn frequency band is used, the ionospheric residual is very small; when the Ku, Ka, Q, and V frequency bands are used, the ionospheric residual is still very small. Therefore, when the Cn, Ku, Ka, Q, and V frequency bands are used, and other random errors and the like are considered, sub-nanosecond level time synchronization accuracy can be completely achieved.

[0195] In addition, when the carrier frequency of the pseudo-range measurement signal and the carrier frequency of the retransmission measurement signal perform frequency hopping according to a frequency hopping pattern, the frequency after frequency hopping still satisfies the preset carrier frequency relationship, and the above-mentioned satellite-earth clock difference calculation method is still used to calculate the clock difference and transmit the calculated clock difference to the satellite, and the specific calculation steps are not described again.

[0196] In addition, on the basis of the above-mentioned embodiments, the present application further provides a satellite-earth spatial distance determination method, which can be executed by a computing device, FIG. 5As shown in a flowchart of a satellite-earth space distance determination method according to an embodiment of the present application, FIG. 6 the method can specifically include the following steps:

[0197] S200, determining tropospheric delay on a ranging signal path between the first device and the second device based on a preset tropospheric model;

[0198] S210, determining ionospheric delay on the ranging signal path between the first device and the second device based on an ionospheric model or total electron content of ionosphere provided by a third party;

[0199] S220, determining relative space distance shown in the following formula (10) by using the following formula (3') based on the determined tropospheric delay, ionospheric delay, relative clock difference and corrected pseudorange ranging value, wherein the relative space distance is satellite-earth space distance between the first device and the second device:

[0200]

[0201]

[0202] Taking satellite broadcast pseudorange ranging signal as an example, in this step, the computing device is to determine satellite-earth space distance, i.e. relative space distance, between the satellite and the earth station in the case of satellite broadcast pseudorange ranging signal in this embodiment by using the following formula (f3') in combination with formula (10), as shown in formula (10-1):

[0203]

[0204]

[0205] R true,z1z (n) = p z1z,m (n) - I z1z (n) - T duiliu,z1z (n) - c · (δt z (n) - δt s (n) c (10-1);

[0206] Alternatively, the relative space distance shown in the following formula (11) is determined by using the following formula (4') based on the determined tropospheric delay, ionospheric delay and corrected retransmission ranging value:

[0207]

[0208] R true,z1u (n) = L z1,m (n) - T duiliu,z1u (n) - (Iz1u (n)+I z1d (n)) / 2 (11);

[0209] Wherein, the relative clock difference, the corrected pseudo-range measurement value, the corrected retransmission measurement value can be determined according to the time synchronization method described in any of the above embodiments.

[0210] Or, the formula (10-1) and the formula (11) are weighted average, and the weighted average satellite and earth station between the space distance, that is, the relative spatial distance, wherein the sum of the weighting coefficients is equal to 1.

[0211] Wherein, in step S210, ionospheric delay can be obtained using 8-parameter Klobuchar model, or using 14-parameter Klobuchar model, or also through the third party to get ionospheric TEC value, then the computing device can calculate the ionospheric delay of each signal based on the following formula (15), (16), (17):

[0212]

[0213]

[0214]

[0215] Wherein, the tropospheric delay T between the earth station and the satellite can be corrected using a preset model, and the tropospheric delay calculation needs to use meteorological parameters, in the absence of real-time meteorological parameters, a simple model related only to satellite elevation angle can be used for calculation, as shown in formula (T1):

[0216] T=2.47 / (sinθ+0.0121) (T1);

[0217] In the formula: T represents the tropospheric delay, unit: meter; θ represents the satellite elevation angle, unit: radian.

[0218] At present, there are relatively many models for calculating tropospheric delay based on meteorological parameters, and the difference between them decreases with the satellite elevation angle, about several millimeters to several centimeters, which is higher than the accuracy calculated by such a simple model.

[0219] Common models for determining tropospheric delay correction include Saastamoinen model, hopfield model, etc. Research shows that when the elevation angle is greater than or equal to 15°, the results obtained by different models are in good agreement, and the model can be arbitrarily selected. However, when the elevation of the station is very large, the tropospheric delay in the zenith direction calculated by the two models can be different by tens of centimeters. After comparison with the actual meteorological data, it is recommended to use Saastamoinen model.

[0220] After obtaining the tropospheric delay and the ionospheric delay, the computing device can further obtain the relative spatial distance by using formula (10-1), or by using formula (11), or by using formula (10-1) and formula (11) for weighted calculation, and the related calculation process is not described here.

[0221] On the basis of the above-mentioned embodiments, the application further provides a satellite navigation system, which is based on the above-mentioned dual-frequency time synchronization system and method, increases the operation and control system, and increases the number of satellites to form a complete and simplest satellite navigation system.

[0222] Specifically, the satellite navigation system includes the dual-frequency time synchronization system described in any of the above-mentioned embodiments, and in the dual-frequency time synchronization system, the first device is specifically a satellite, the second device is specifically an earth station, and the number of satellites is greater than or equal to 2, and the satellite broadcasts a pseudo-range ranging signal. The earth station obtains the orbit parameters of the corresponding satellite based on the data transmission result with each satellite, and determines the coordinate information of itself based on the orbit parameters of each satellite and the relative spatial distance between the earth station and the satellite.

[0223] The satellite navigation system further includes a plurality of third devices, which are in communication connection with the satellites. Part of the third devices constitute a satellite orbit determination system for orbit monitoring and processing of the satellites to obtain satellite orbit parameters; and part of the third devices constitute a satellite-earth time synchronization system for time monitoring of each of the satellites to keep the time of each satellite synchronized with the operation and control system. The operation and control system herein refers to a system composed of the satellite orbit determination system and the satellite-earth time synchronization system.

[0224] The satellite navigation system is as shown in FIG. 7 In the satellite navigation system, at least two satellites are provided, and the orbit determination system can adopt an existing Beidou orbit determination method.

[0225] The third device in the satellite-earth time synchronization system has the hardware composition and signal structure of the dual-frequency time synchronization system between the satellite and the third device. The computing device can be integrated in the third device to execute the time synchronization method of the application. At this time, the time of the third device in the satellite-earth time synchronization system is taken as the system time, and the relative time of the satellite to the system is taken as an unknown quantity. The clock difference of the satellite relative to the system time is obtained by the method of the application to realize the time synchronization of the satellite and the operation and control system. The satellite further broadcasts a pseudo-range ranging signal with known time to the outside. At this time, the time of the satellite relative to the system is known, and the time of the earth station relative to the system is unknown. The clock difference of the earth station relative to the system time is obtained by the dual-frequency time synchronization system and method of the application to realize the satellite time service function. At this time, the earth station can not interact with the satellite for clock difference data after obtaining the clock difference of the earth station relative to the system time.

[0226] Of course, the star-ground time synchronization system can also use other existing star-ground time synchronization technologies, such as a two-way pseudo-range measurement method. Using these methods can also achieve star-ground time synchronization.

[0227] After the time synchronization of the earth station is implemented, the relative spatial distance between the earth station and the satellite is obtained, and according to the satellite ephemeris and the relative spatial distance, if the satellite navigation system has only two satellites, the user needs to configure an altimeter to obtain the user elevation, and then the Beidou double-star positioning principle can be referred to to obtain the earth station coordinates; when the satellite has three or more satellites, the earth station does not need to configure an altimeter, and through the relative spatial distance with the three satellites and the satellite ephemeris, the earth station coordinate information can be obtained.

[0228] On the basis of the above embodiments, the embodiments of the present application also provide an inter-station time synchronization system, which comprises the satellite navigation system described in any of the above embodiments; wherein when the earth stations are at least two, the at least two earth stations realize time synchronization with each other through communication and data exchange.

[0229] Alternatively, the inter-station time synchronization system comprises the double-frequency time synchronization system described in any of the above embodiments; wherein when the first device or the second device is at least two, the at least two first devices or second devices realize time synchronization with each other through communication and data exchange.

[0230] On the basis of the above embodiments, the embodiments of the present application also provide an inter-station time synchronization method, which can be applied to the double-frequency time synchronization system described in the above embodiments or also can be applied to the satellite navigation system described in the above embodiments. The method can comprise:

[0231] directly communicating with a target earth station to exchange data and obtain the clock difference of the target earth station;

[0232] calculating according to the clock difference of the earth station itself and the clock difference of the target earth station to determine the time difference between the two.

[0233] After the clock difference of the earth station relative to the system time is determined, the earth station can perform data transmission with the target earth station based on the communication link, and multiple earth stations realize time synchronization among the multiple earth stations through communication and exchange of the clock difference of each earth station relative to the system time, which is similar to the common-view method, and will not be described here.

[0234] On the basis of the above embodiments, the embodiments of the present application also provide a satellite positioning method, which can be applied to the satellite navigation system described above, FIG. 7 A flowchart of the satellite positioning method according to an embodiment of the present application, which can be executed by an earth station that needs to be positioned, such as ​As shown, the satellite positioning method can include the following steps:

[0235] S610, acquiring orbit parameters of each satellite, wherein the orbit parameters of the satellite are determined by an orbit determination system;

[0236] S620, determining coordinates of the corresponding satellite based on the orbit parameters;

[0237] S630, acquiring relative spatial distances between the satellite and each satellite;

[0238] S640, determining coordinate information of the satellite based on the orbit parameters of each satellite and the relative spatial distances between the satellite and each satellite.

[0239] In step S610, the orbit parameters of the satellite are satellite ephemeris, and the orbit parameters of the satellite are determined according to an existing satellite orbit determination method, such as a Beidou navigation satellite orbit determination method, so that the earth station acquires the orbit parameters of the corresponding satellite based on the data transmission results (such as receiving a pseudo-range ranging signal) with each satellite.

[0240] In step S620, the earth station calculates the satellite coordinates at the current ranging moment according to the acquired orbit parameters of the satellite.

[0241] In step S630, the earth station can determine the relative spatial distances between the satellite and each satellite by using any of the above-mentioned satellite-ground spatial distance determination methods performed by the earth station.

[0242] In step S640, the earth station calculates the coordinate information of the satellite based on the coordinate information of each satellite and the relative spatial distances between the satellite and each satellite, that is, the satellite positioning of the satellite is realized.

[0243] It is worth noting that in the present exemplary embodiment, the number of satellites needs to be greater than or equal to 2, and specifically, when the number of satellites is greater than or equal to 2, the earth station can select at least two satellites from all the satellites and calculate the coordinate information of the satellite by referring to the existing Beidou double-satellite positioning method.

[0244] In summary, it can be seen that the dual-frequency time synchronization system and method provided by the present application creatively changes one pseudo-range ranging signal in the two-way pseudo-range measurement method into a retransmission ranging signal, integrates it with another pseudo-range ranging signal, still uses two carrier frequencies, can obtain the same satellite-ground time synchronization performance as the two-way pseudo-range measurement method, can obtain a more accurate satellite-ground spatial distance, and can reduce the cost. The dual-frequency time synchronization system and method provided by the present application has the following advantages:

[0245] 1. Compared with the two-way pseudo-range measurement method, the system requirements and cost are reduced;

[0246] 2. Compared with the existing two-way pseudorange measurement method, in the embodiments of this application, the satellite does not need a pseudorange measurement device, which can reduce the complexity of the satellite payload and reduce the cost of the satellite.

[0247] 3. Compared with the two-way pseudorange measurement method, this method completely overcomes the influence of tropospheric time delay and partially eliminates ionospheric time delay, thus achieving better satellite-to-ground time synchronization accuracy.

[0248] 4. Given the current scarcity of L and S band resources, satellite communication and satellite navigation are developing towards higher frequency bands. If the carrier frequency used in this application is a high frequency band, such as Cn, Ka, Q, V, etc., it can achieve sub-nanosecond time synchronization accuracy.

[0249] 5. Because the earth station only needs to receive signals from one satellite, it can use a directional antenna to reduce multipath effects, thereby achieving better ranging accuracy and better time synchronization accuracy.

[0250] 6. This method not only overcomes the effects of atmospheric time delay, but also the effects of multipath effects, and overcomes the environmental segment effects at the near and far ends between the satellite and the earth station;

[0251] 8. This application can obtain relatively accurate satellite-to-ground spatial distances, providing support for subsequent satellite orbit determination and user positioning;

[0252] 9. This method fully meets the requirements of high performance and low cost of satellite-to-ground time synchronization in 6G communication systems. It reduces costs by reducing carrier frequency costs and optimizing satellite payloads. It can even directly use spread spectrum remote control and telemetry signals to achieve satellite-to-ground time synchronization, making it more cost-effective.

[0253] 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 dual-frequency time synchronization system, characterized in that, It includes a first device and a second device that are connected in communication, and a computing device that is connected in communication with the first device and the second device respectively. There is one pseudorange ranging signal and one forwarded ranging signal between the first device and the second device; Wherein, the pseudorange ranging signal is broadcast by the first device and received by the second device, or broadcast by the second device and received by the first device; The forwarding ranging signal consists of an uplink signal and a downlink signal. The second device broadcasts the uplink signal and receives the downlink signal, and the first device receives the uplink signal and forwards it to form the downlink signal. The computing device receives pseudorange ranging values ​​and forwarding ranging values, and determines a relative clock difference based on the relationship between the pseudorange ranging values, the forwarding ranging values, and a preset carrier frequency. The relative clock difference is the clock difference between the first device and the second device. The pseudorange ranging value is obtained by the first device or the second device measuring the pseudorange ranging signal, and the forwarding ranging value is obtained by the second device measuring the forwarding ranging signal. The carrier frequency of the uplink signal, the carrier frequency of the downlink signal, and the carrier frequency of the pseudorange ranging signal satisfy the preset carrier frequency relationship shown in formula (f1) or formula (f2): f z1u (n)≠f z1d (n)=f z1z (n)(f1); f z1d (n)≠f z1u (n)=f z1z (n)(f2); In the formula: f z1u (n) represents the carrier frequency of the uplink signal at time n, in Hertz; f z1d (n) represents the carrier frequency of the downlink signal at time n, in Hertz; f z1z (n) represents the carrier frequency of the pseudorange ranging signal at time n, in Hertz.

2. The dual-frequency time synchronization system according to claim 1, characterized in that, Both the forwarding ranging signal and the pseudorange ranging signal are spread spectrum signals. The first device and / or the second device use spread spectrum technology, carrier frequency reuse technology and code division multiple access technology for corresponding processing in signal transmission, forwarding and reception processing.

3. The dual-frequency time synchronization system according to claim 1, characterized in that, The carrier frequency of the uplink signal, the carrier frequency of the downlink signal, and the carrier frequency of the pseudorange ranging signal are frequency-hopping on the time axis according to a preset frequency-hopping pattern, and satisfy the preset carrier frequency relationship.

4. The dual-frequency time synchronization system according to claim 1, characterized in that, The first device includes a first time-frequency device, a transponder, and a pseudorange generator; the second device includes a second time-frequency device, a transponder ranging device, and a second pseudorange ranging device. The first time-frequency device is used to provide time-frequency signals to the transponder and the pseudorange generator; The repeater is used to receive the uplink signal, perform frequency conversion and power amplification on the uplink signal, and then forward the downlink signal to the second device. The pseudorange generator is communicatively connected to the repeater, and the pseudorange generator is used to generate and broadcast the pseudorange ranging signal. The second time-frequency device is used to provide time-frequency signals to the relay ranging device and the second pseudorange ranging device; The second pseudorange measuring device is used to receive the pseudorange measuring signal and process it to obtain the pseudorange measuring value; The forwarding ranging device is used to generate and broadcast the uplink signal, and to receive and measure the downlink signal to obtain the forwarding ranging value; The first time-frequency device, the repeater, and the pseudorange generator are integrated or separate, and / or the second time-frequency device, the repeater ranging device, and the second pseudorange ranging device are integrated or separate. or, The first device includes a first time-frequency device, a transponder, and a first pseudorange ranging device; the second device includes a second time-frequency device and a transponder ranging device. The first time-frequency device is used to provide time-frequency signals to the transponder and the first pseudorange ranging device; The repeater is used to receive the uplink signal, perform frequency conversion and power amplification on the uplink signal, and then forward the downlink signal to the second device. The first pseudorange ranging device is communicatively connected to the transponder and is used to receive and measure the pseudorange ranging signal to obtain the pseudorange ranging value. The second time-frequency device is used to provide time-frequency signals to the relay ranging device; The forwarding ranging device is used to generate and broadcast the uplink signal, and to receive and measure the downlink signal to obtain the forwarding ranging value, wherein a portion of the uplink signal broadcast by the forwarding ranging device is used as the pseudorange ranging signal; The first time-frequency device, the repeater, and the first pseudorange ranging device are integrated or separate, and / or the second time-frequency device and the repeater ranging device are integrated or separate.

5. The dual-frequency time synchronization system according to claim 4, characterized in that, The second pseudorange ranging device and the repeater ranging device are set to zero baseline; the first pseudorange ranging device or the pseudorange generating device and the repeater are set to zero baseline.

6. The dual-frequency time synchronization system according to claim 4, characterized in that, The first device uses at least one of the first time-frequency devices, and the second device uses at least one of the second time-frequency devices.

7. The dual-frequency time synchronization system according to claim 1, characterized in that, The computing device may be located in the first device, in the second device, or exist independently. When the computing device is installed on the first device or the second device, the first device uses an additional communication signal to transmit data with the second device. When the computing device is set up independently, the computing device communicates with the first device and the second device; The computing device determines the relative spatial distance based on the forwarding ranging value and / or the pseudorange ranging value, wherein the relative spatial distance is the satellite-to-ground spatial distance between the first device and the second device.

8. The dual-frequency time synchronization system according to claim 4, characterized in that, The repeater has a forwarding delay, and the pseudorange generating device has a transmission delay; both the first pseudorange ranging device and the second pseudorange ranging device have a receiving delay, and the forwarding ranging device has both a transmission delay and a receiving delay; The computing device acquires the forwarding delay of the repeater, the transmission delay of the pseudorange generator, the reception delay of the first pseudorange ranging device or the second pseudorange ranging device, and the transmission and reception delay of the forwarding ranging device.

9. A time synchronization method, characterized in that, Applied to the dual-frequency time synchronization system according to any one of claims 1-8, the method is executed by a computing device, and the method includes: When the pseudorange ranging signal is broadcast by the second device and received by the first device, it communicates with the first device to obtain a pseudorange ranging value measured by the first device, and communicates with the second device to obtain a forwarding ranging value measured by the second device. When the pseudorange ranging signal is broadcast by the first device and received by the second device, the device communicates with the second device to obtain one pseudorange ranging value and one forwarding ranging value measured by the second device; wherein, the carrier frequency corresponding to the one forwarding ranging value and the carrier frequency corresponding to the one pseudorange ranging value satisfy a preset carrier frequency relationship; The pseudorange value is represented by a pseudorange ranging expression and the forwarding ranging value is represented by a forwarding ranging expression, respectively. The relative clock bias is determined based on the pseudorange ranging value represented by the pseudorange ranging expression, the forwarding ranging value represented by the forwarding ranging expression, and the preset carrier frequency relationship, wherein the relative clock bias is the clock bias between the first device and the second device.

10. The time synchronization method according to claim 9, characterized in that, The steps of characterizing the pseudorange value using a pseudorange ranging expression and characterizing the forwarding ranging value using a forwarding ranging expression include: The pseudorange value is characterized by the pseudorange measurement expression shown in the following formula (3): ρ z1z (n)=R true,z1z (n)+I z1z (n)+T duiliu,z1z (n)±c·(δt z (n)-δt s (n))±sagnac zz (n)+X z1 (n)(3); The forwarding ranging value is characterized by the forwarding ranging expression shown in the following formula (4): L z1 (n)=R true,z1u (n)+R true,z1d (n)+I z1u (n)+I z1d (n)+T duiliu,z1u (n)+T duiliu,z1d (n)+Y z1 (n)(4); In the formula: L z1 (n) represents the forwarding ranging value at time n, in meters; R true,z1u (n) represents the actual spatial distance traversed by the uplink signal at time n, in meters; R true,z1d (n) represents the actual spatial distance traversed by the downlink signal at time n, in meters; z1u (n) represents the ionospheric delay of the uplink signal at time n, in meters; z1d (n) represents the ionospheric delay of the downlink signal at time n, in meters (T). duiliu,z1u (n) represents the tropospheric delay of the uplink signal at time n, in meters (T). duiliu,z1d (n) represents the tropospheric delay of the downlink signal at time n, in meters; Y z1 (n) represents the hardware device delay for forwarding the ranging signal at time n, wherein the hardware device delay for forwarding the ranging signal includes the transmission delay of the uplink signal, the forwarding delay of the downlink signal generated by the first device, and the reception delay of the downlink signal, in meters; ρ z1z (n) represents the pseudorange value at time n, in meters; R true,z1z (n) represents the actual spatial distance traversed by the pseudorange ranging signal at time n, in meters; z1z (n) represents the ionospheric delay of the pseudorange ranging signal at time n, in meters (T). duiliu,z1z (n) represents the tropospheric delay of the pseudorange ranging signal at time n, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference of the first device relative to the system time at time n, in seconds; δt z (n) represents the clock difference of the second device relative to the system time at time n, in seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudorange ranging signal at time n, in meters; X z1 (n) represents the hardware delay of the pseudorange ranging signal at time n, in meters. The hardware delay of the pseudorange ranging signal includes the transmission delay of the pseudorange ranging signal and the reception delay of the pseudorange ranging signal.

11. The time synchronization method according to claim 9, characterized in that, The determination of the relative clock bias based on the pseudorange ranging value represented by the pseudorange ranging expression, the forwarding ranging value represented by the forwarding ranging expression, and the preset carrier frequency relationship includes: The pseudorange measurement value represented by the pseudorange measurement expression is corrected to obtain the corrected pseudorange measurement value. The forwarding ranging value represented by the forwarding ranging expression is corrected to obtain the corrected forwarding ranging value; The relative clock bias is determined based on the relationship between the corrected pseudorange ranging value, the corrected forwarding ranging value, and the preset carrier frequency.

12. The time synchronization method according to claim 11, characterized in that, The step of correcting the pseudorange value represented by the pseudorange measurement expression to obtain the corrected pseudorange value includes: The corrected pseudorange distance value shown in formula (3') is obtained by modifying formula (3') as follows: ρ z1z (n)=R true,z1z (n)+I z1z (n)+T duiliu,z1z (n)±c·(δt z (n)-δt s (n))±sagnac zz (n)+X z1 (n)(3); The step of correcting the forwarding ranging value represented by the forwarding ranging expression to obtain the corrected forwarding ranging value includes: The corrected forwarding ranging value shown in formula (4') is obtained by transforming formula (4') as follows: L z1 (n)=R true,z1u (n)+R true,z1d (n)+I z1u (n)+I z1d (n)+T duiliu,z1u (n)+T duiliu,z1d (n)+Y z1 (n)(4); In the formula: L z1,m (n) represents the corrected forwarding ranging value at time n, in meters; L z1 (n) represents the forwarding ranging value at time n, in meters; R true,z1u (n) represents the actual spatial distance traversed by the uplink signal at time n, in meters; R true,z1d (n) represents the actual spatial distance traversed by the downlink signal at time n, in meters; z1u (n) represents the ionospheric delay of the uplink signal at time n, in meters; z1d (n) represents the ionospheric delay of the downlink signal at time n, in meters (T). duiliu,z1u (n) represents the tropospheric delay of the uplink signal at time n, in meters (T). duiliu,z1d (n) represents the tropospheric delay of the downlink signal at time n, in meters; Y z1 (n) represents the hardware device delay for forwarding the ranging signal at time n, wherein the hardware device delay for forwarding the ranging signal includes the transmission delay of the uplink signal, the forwarding delay of the downlink signal generated by the first device, and the reception delay of the downlink signal, in meters; ρ z1z,m (n) represents the corrected pseudorange value at time n, in meters; ρ z1z (n) represents the pseudorange value at time n, in meters; R true,z1z (n) represents the actual spatial distance traversed by the pseudorange ranging signal at time n, in meters; z1z (n) represents the ionospheric delay of the pseudorange ranging signal at time n, in meters (T). duiliu,z1z (n) represents the tropospheric delay of the pseudorange ranging signal at time n, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference of the first device relative to the system time at time n, in seconds; δt z (n) represents the clock difference of the second device relative to the system time at time n, in seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudorange ranging signal at time n, in meters; X z1 (n) represents the hardware delay of the pseudorange ranging signal at time n, in meters. The hardware delay of the pseudorange ranging signal includes the transmission delay of the pseudorange ranging signal and the reception delay of the pseudorange ranging signal.

13. The time synchronization method according to claim 11, characterized in that, The determination of relative clock bias based on the corrected pseudorange ranging value, the corrected forwarding ranging value, and the preset carrier frequency relationship includes: The corrected pseudorange and the corrected forwarding range are mathematically processed to obtain an expression that includes the relative clock bias. The clock difference between the first device and the second device is determined using an expression that includes the relative clock difference and the preset carrier frequency relationship.

14. The time synchronization method according to claim 13, characterized in that, The second device has its forwarding ranging device and the second pseudorange ranging device set to zero baseline, or the first device has its transponder and the first pseudorange ranging device set to zero baseline; the step of mathematically processing the corrected pseudorange ranging value and the corrected forwarding ranging value to obtain an expression containing the relative clock difference includes: Using the zero baseline setting relationship, the relative clock bias is determined based on the corrected pseudorange ranging value, the corrected forwarding ranging value, and the preset carrier frequency relationship, as shown in the following formula (8): ±(δt z (n)-δt s (n)) c =(ρ z1z,m (n)-L z1,m (n)) / c (8); In the formula: L z1,m (n) represents the corrected forwarding ranging value at time n, in meters; ρ z1z,m (n) represents the corrected pseudorange value at time n, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference of the first device relative to the system time at time n, in seconds; δt z (n) represents the clock difference of the second device relative to the system time at time n, in seconds.

15. The time synchronization method according to claim 9, characterized in that, After determining the relative clock difference, the method further includes: Communicate with the first device or the second device to transmit the determined relative clock difference to the first device or the second device, thereby achieving time synchronization between the first device and the second device; Wherein, when the clock difference of the first device relative to the system time is known, the second device determines its own clock difference relative to the system time based on the relative clock difference; When the clock difference of the second device relative to the system time is known, the first device determines its own clock difference relative to the system time based on the aforementioned relative clock difference.

16. A method for determining the distance between a satellite and the Earth, characterized in that, Applied to the dual-frequency time synchronization system according to any one of claims 1-8, the method is executed by a computing device, and the method includes: The tropospheric delay on the ranging signal path between the first and second devices is determined based on a preset tropospheric model. The ionospheric delay on the ranging signal path between the first and second devices is determined based on the ionospheric model or the total number of ionospheric electrons provided by a third party. Based on the determined tropospheric delay, ionospheric delay, relative clock error, and corrected pseudorange distance, the relative spatial distance shown in formula (10) is determined using formula (3'): Alternatively, based on the determined tropospheric delay, ionospheric delay, and corrected forwarding ranging values, the relative spatial distance shown in formula (11) can be determined using formula (4'): R true,z1u (n)=L z1,m (n)-T duiliu,z1u (n)-(I z1u (n)+I z1d (n)) / 2(11); Alternatively, a weighted average can be taken from formula (10) and formula (11) to obtain the relative spatial distance after weighted average, wherein the sum of the weighting coefficients is equal to 1; Wherein, the relative spatial distance is the satellite-to-ground spatial distance between the first device and the second device, and the relative clock difference is determined according to any one of claims 9-15 of the time synchronization method; L z1,m (n) represents the corrected forwarding ranging value at time n, in meters; L z1 (n) represents the forwarding ranging value at time n, in meters; R true,z1u (n) represents the actual spatial distance traversed by the uplink signal between the first and second devices at time n, in meters; R true,z1d (n) represents the actual spatial distance traversed by the downlink signal between the first and second devices at time n, in meters; z1u (n) represents the ionospheric delay of the uplink signal at time n, in meters; z1d (n) represents the ionospheric delay of the downlink signal at time n, in meters (T). duiliu,z1u (n) represents the tropospheric delay of the uplink signal at time n, in meters (T). duiliu,z1d (n) represents the tropospheric delay of the downlink signal at time n, in meters; Y z1 (n) represents the hardware device delay for forwarding the ranging signal at time n, wherein the hardware device delay for forwarding the ranging signal includes the transmission delay of the uplink signal, the forwarding delay of the downlink signal generated by the first device, and the reception delay of the downlink signal, in meters; ρ z1z,m (n) represents the corrected pseudorange value at time n, in meters; ρ z1z (n) represents the pseudorange value at time n, in meters; R true,z1z (n) represents the actual spatial distance traversed by the pseudorange ranging signal at time n, in meters; z1z (n) represents the ionospheric delay of the pseudorange ranging signal at time n, in meters (T). duiliu,z1z (n) represents the tropospheric delay of the pseudorange ranging signal at time n, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference of the first device relative to the system time at time n, in seconds; δt z (n) represents the clock difference of the second device relative to the system time at time n, in seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudorange ranging signal at time n, in meters; X z1 (n) represents the hardware delay of the pseudorange ranging signal at time n, in meters. The hardware delay of the pseudorange ranging signal includes the transmission delay of the pseudorange ranging signal and the reception delay of the pseudorange ranging signal.

17. A satellite navigation system, characterized in that, include: The dual-frequency time synchronization system according to any one of claims 1-8, wherein the first device is a satellite, the second device is an earth station, and the number of the satellites is greater than or equal to 2; Multiple third-party devices are all connected to the satellite in communication. The earth station obtains the orbital parameters of the corresponding satellites based on the data transmission results with each satellite, and determines its own coordinate information based on the orbital parameters of each satellite and the relative spatial distance between the earth station and the satellite. Some of the third devices constitute a satellite orbit determination system, used for orbit monitoring and processing of the satellite to obtain satellite orbit parameters; Some of the third devices constitute a satellite-to-ground time synchronization system for time monitoring of each of the satellites.

18. The satellite navigation system according to claim 17, characterized in that, The signal structure between the third device in the satellite-to-ground time synchronization system and the satellite is the same as the signal structure in the dual-frequency time synchronization system.

19. An inter-station time synchronization system, characterized in that, include: The satellite navigation system as described in claim 17 or 18; When there are at least two earth stations, the at least two earth stations achieve time synchronization with each other by exchanging data through communication.

20. An inter-station time synchronization system, characterized in that, include: The dual-frequency time synchronization system according to any one of claims 1-8; Where there are at least two first devices or second devices, the at least two first devices or second devices achieve time synchronization with each other by exchanging data through communication.

21. A satellite positioning method, characterized in that, Applied to the satellite navigation system of claim 17 or 18, the method is performed by an earth station, and the method includes: The orbital parameters of each satellite are obtained, wherein the orbital parameters of the satellite are determined by the orbit determination system; The coordinate information of the corresponding satellite is determined based on the orbital parameters; To obtain the relative spatial distance between itself and each satellite; Based on the orbital parameters of each satellite and the relative spatial distance between them, the coordinate information of the satellite is determined.

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