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

Abstract

The invention discloses a double-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 forwarding ranging signal exist between a first device and a second device; determining a pseudo-range ranging value based on the pseudo-range ranging signal and representing the pseudo-range ranging value by a pseudo-range ranging expression; determining a forwarding ranging value based on a forwarding ranging signal and representing the forwarding ranging value by using a forwarding ranging expression, the forwarding ranging signal comprising an uplink signal broadcasted to the first device and a downlink signal forwarded by the first device; and determining the clock error between the first device and the second device based on the forwarding ranging value represented by the forwarding ranging expression, the pseudo-range ranging value represented by the pseudo-range ranging expression and the ionosphere time delay corresponding relation of the two carrier frequencies.

Description

[0001] Cross-references

[0002] The present disclosure claims an application numbered 202411068713.1 filed on August 6, 2024 and entitled "A Dual-Frequency Timer The entire contents of the Chinese patent application are obtained through The references are incorporated herein in their entirety. Technical Field

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

[0004] At present, the future-oriented 6G communication is being developed in full swing. Compared with previous mobile communication technologies, the biggest feature of 6G communication is the addition of satellite communication, which organically integrates satellite communication and ground mobile communication to form a ubiquitous communication network with full coverage. The satellite communication part uses some technologies in the field of ground mobile communication technology, which makes satellite communication have the same technical characteristics as ground mobile communication, such as the need for high-precision time synchronization, which requires time synchronization at the level of several nanoseconds. The typical feature of 6G-oriented satellite communication is that low-orbit satellites are dominant, such as the domestic Internet communication constellation and the foreign Starlink satellite constellation. These low-orbit satellite communication constellations require a large number of satellites to support them, and how to meet the time synchronization requirements at low cost and high performance is an urgent need. Other aerospace systems such as navigation satellites, communication satellites, and remote sensing satellites also require high-precision satellite-ground time synchronization requirements.

[0005] At present, the typical methods for achieving high-precision satellite-ground time synchronization are two-way pseudorange measurement method, laser measurement method, etc. The application of two-way pseudorange measurement is a powerful technical means to solve the satellite-ground time synchronization in 6G system. The two-way pseudorange measurement method has been widely used in satellite navigation system due to its high time synchronization accuracy. The working principle of the two-way pseudorange measurement method is that both the satellite and the earth station transmit pseudorange ranging signals with their own independent clock face time under the control of the local clock. After the receivers of the satellite and the earth station receive the ranging signals transmitted by each other, the two sides measure each other to obtain their own pseudorange ranging values, and then exchange the pseudorange ranging values ​​through communication means. By comparing these two pseudocode ranging values, the clock difference between the satellite and the earth station can be obtained, and the obtained clock difference contains the ionospheric delay residual. If it is necessary to further overcome the influence of the ionospheric delay error, it is necessary to use ionospheric mode correction or use a third party to provide the total number of ionospheric electrons for correction.

[0006] The reason why the two-way pseudorange measurement method has high time synchronization accuracy is that it is based on the same signal propagation path between the satellite and the earth, with the same satellite-to-earth spatial distance and tropospheric delay, but different ionospheric delay. Therefore, the clock difference between the satellite and the earth station is the difference in the measured pseudoranges divided by the speed of light or the difference in the time when the satellite and the earth station detect the corresponding time scales.

[0007] In the two-way pseudorange measurement method, the ground station and the satellite each use a carrier frequency, a total of two carrier frequency radio frequency signals. This method first requires that the satellite and the ground station meet rough time synchronization requirements, otherwise it will cause errors caused by unequal spatial distances; at the same time, the satellite or ground station is required to have corresponding pseudorange measurement equipment. Traditional two-way pseudorange measurement methods are all used in the L and S frequency bands, and the L and S frequency bands have concentrated a large number of satellite communications and satellite navigation services. If the radio signals of the L and S frequency bands are used again, it will cause mutual interference and other problems. Currently, industry experts are actively developing two-way pseudorange time comparison methods for high-frequency bands, and satellite-ground time synchronization methods that are suitable for high-frequency bands are still under research;

[0008] In order to achieve satellite-ground time synchronization, laser methods can also be used. Laser can be regarded as a very high-frequency radio signal. When the laser signal passes through the ionosphere, the time delay is very small and can be ignored. Both satellites and ground stations use laser devices instead of radio transmitters or receivers, which have the disadvantages of high cost and limited application. When using lasers, there is a disadvantage of being greatly affected by the weather. The laser method cannot be used under weather conditions such as rainy days, snowy days, and cloudy days. It can only be used in clear weather. Therefore, although the laser method can achieve excellent time synchronization performance, it is restricted by the disadvantages of high cost and being greatly affected by the weather, making it difficult to be widely used.

[0009] The above methods require satellites or ground receivers to receive signals and perform measurements. When the signals are transmitted between the satellite and the ground, for the receiver, it involves the influence of the ionosphere and troposphere of the atmosphere at the far end, and the multipath effect and electromagnetic environment at the near end. The far end and the near end are collectively referred to as environmental segment influences. Among them, the atmospheric influence is comprehensive and basic, and it is a global problem. In addition to the environmental segment influence, the above methods have the problems of a large number of observation devices, large time synchronization errors, initial time synchronization accuracy, satellite orbit determination accuracy, and user coordinate accuracy, resulting in poor time synchronization accuracy obtained by the two-way pseudorange measurement method.

[0010] The above contents are only used to assist in understanding the technical solution of the present application and do not constitute an admission that the above contents are prior art. Summary of the invention

[0011] The main purpose of this application is to provide a dual-frequency time synchronization system, a time synchronization method and its navigation application, aiming to solve the problems of low clock error accuracy, poor real-time performance and high cost in the existing two-way pseudo-range measurement method, and to provide a low-cost, high-performance time synchronization solution for satellite communications of 6G systems.

[0012] To achieve the above-mentioned purpose, the present application provides a dual-frequency time synchronization system, comprising a first device and a second device in communication connection; there is one pseudo-range ranging signal and one forwarding ranging signal between the first device and the second device; wherein 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; the forwarding 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 forwards it 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 pseudo-range ranging signal satisfy a preset carrier frequency relationship.

[0013] In addition, to achieve the above-mentioned purpose, the present application also provides a time synchronization method, which is applied to the dual-frequency time synchronization system described in any embodiment of the present application, and 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, 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 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, communicating 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; respectively using a pseudorange ranging expression to characterize the pseudorange ranging value and using a forwarding ranging expression to characterize the forwarding ranging value; determining a relative clock difference 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 difference is the clock difference between the first device and the second device.

[0014] In addition, to achieve the above-mentioned purpose, the present application also provides a method for determining the satellite-ground space distance, which is applied to the dual-frequency time synchronization system described in any embodiment of the present application, and the method is executed by a computing device, and the method includes: determining the tropospheric delay on the ranging signal path between the first device and the second device based on a preset tropospheric model; determining the ionospheric delay on the ranging signal path between the first device and the second device based on the ionospheric model or the total number of ionospheric electrons provided by a third party; based on the determined tropospheric delay, the ionospheric delay, the relative clock error and the corrected pseudorange measurement value, using the following formula (3') to determine the relative space distance shown in the following formula (10), wherein the relative space distance is the satellite-ground space distance between the first device and the second device:

[0015]

[0016]

[0017] Alternatively, based on the determined tropospheric delay, ionospheric delay and corrected forward ranging value, the relative spatial distance shown in the following formula (11) is determined using the following formula (4'):

[0018] R true,z1u (n) = L z1,m (n)-T duiliu,z1u (n)-(I z1u (n)+I z1d (n)) / 2(11);

[0019] Alternatively, performing weighted averaging on the formula (10) and the formula (11) to obtain a weighted average relative spatial distance, wherein the sum of the weighted coefficients is equal to 1;

[0020] In addition, to achieve the above-mentioned purpose, the present application also provides a satellite navigation system, including: the dual-frequency time synchronization system described in any embodiment of the present 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; multiple third devices, all of which are communicatively connected to the satellite; wherein the earth station obtains the orbital parameters of the corresponding satellite 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, which is used to monitor and process the orbit of the satellite to obtain satellite orbit parameters; some of the third devices constitute a satellite-to-ground time synchronization system, which is used to monitor the time of each satellite.

[0021] In addition, to achieve the above-mentioned purpose, the present application also provides an inter-station time synchronization system, including: the satellite navigation system described in any embodiment of the present application; wherein, when there are at least two earth stations, at least two of the earth stations achieve time synchronization with each other by exchanging data through communication.

[0022] In addition, to achieve the above-mentioned purpose, the present application also provides an inter-station time synchronization system, including: the dual-frequency time synchronization system described in any embodiment of the present application; wherein, when there are at least two first devices or second devices, at least two of the first devices or second devices achieve time synchronization with each other by exchanging data through communication.

[0023] In addition, to achieve the above-mentioned purpose, the present application also provides a satellite positioning method, which is applied to the satellite navigation system described in any embodiment of the present application, and the method is executed by an earth station, and the method includes: obtaining the orbital parameters of each satellite, wherein the orbital parameters of the satellite are determined by an orbit determination system; determining the coordinate information of the corresponding satellite based on the orbital parameters; obtaining the relative spatial distance between itself and each satellite; and determining its own coordinate information based on the orbital parameters of each satellite and the relative spatial distance between itself and each satellite.

[0024] The dual-frequency time synchronization system provided by the present application, the first device broadcasts a pseudo-range measurement signal to the second device, the second device sends an uplink signal to the first device, the first device performs frequency conversion and power amplification processing on the uplink signal after acquiring the uplink signal to obtain a downlink signal and forwards the downlink signal to the second device, and the carrier frequencies of the uplink signal, the downlink signal and the pseudo-range measurement signal have a preset carrier frequency relationship, so that the second device can determine the clock difference between the first device and the second device by performing mathematical operations based on the preset carrier frequency relationship between the carrier frequencies of the three signals without knowing the exact delay error caused by the influence of the atmosphere. When the dual-frequency time synchronization system is applied to the field of satellite navigation, compared with the prior art, the error influence of the tropospheric delay of the dual-frequency time synchronization system of the present application can improve the accuracy of the determined clock difference, improve the navigation accuracy and have the advantages of strong real-time performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a dual-frequency time synchronization system according to an implementation mode of the present application;

[0026] Figure 2 A structural block diagram of a satellite and an earth station according to an implementation manner of the present application;

[0027] Figure 3 is a structural block diagram of a satellite and an earth station according to another implementation manner of the present application;

[0028] Figure 4 A flowchart of a time synchronization method according to an implementation of the present application;

[0029] Figure 5 This is a flow chart of a method for determining the satellite-to-earth space distance according to an embodiment of the present application;

[0030] Figure 6 is a schematic structural diagram of a satellite navigation system according to an implementation mode of the present application;

[0031] Figure 7 The present invention is a flowchart of a satellite positioning method according to one embodiment of the present application.

[0032] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below in conjunction with the drawings in the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0034] The meanings of various parameters involved in this exemplary embodiment are first explained as follows:

[0035] ρ z1z,m (n) represents the corrected pseudo-range measurement value at the nth moment, in meters; ρ z1z (n) represents the pseudo-range measurement value at the nth moment, in meters; R true,z1z (n) represents the real space distance that the pseudo-range measurement signal has passed at the nth moment, in meters; z1z (n) represents the ionospheric delay of the pseudo-range measurement signal at the nth moment, in meters; T duiliu,z1z (n) represents the tropospheric delay of the pseudo-range measurement signal at the nth moment, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference between the first device and the system time at the nth moment, in seconds; δt z (n) represents the clock difference between the second device and the system time at the nth moment, in seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudo-range measurement signal at the nth moment, in meters; X z1 (n) represents the pseudo-range measurement signal hardware device delay at the nth moment, in meters, wherein the pseudo-range measurement signal hardware device delay includes the pseudo-range measurement signal transmission delay and the pseudo-range measurement signal reception delay;

[0036] L z1,m (n) represents the corrected forwarding ranging value at the nth moment, in meters; L z1 (n) represents the forwarding ranging value at the nth moment, in meters; R true,z1u (n) represents the real spatial distance that the uplink signal travels at the nth moment, in meters; R true,z1d (n) represents the real spatial distance traveled by the downlink signal at the nth moment, in meters; I z1u(n) represents the ionospheric delay of the uplink signal at the nth moment, in meters; I z1d (n) represents the ionospheric delay of the downlink signal at the nth moment, in meters; T duiliu,z1u (n) represents the tropospheric delay of the uplink signal at the nth moment, in meters; T duiliu,z1d (n) represents the tropospheric delay of the downlink signal at the nth moment, in meters; Y z1 (n) represents the hardware device delay of forwarding the ranging signal at the nth moment, and the hardware device delay of forwarding the ranging signal includes the transmission delay of the uplink signal, the forwarding delay of the first device generating the downlink signal, and the receiving delay of the downlink signal, and the unit is meter.

[0037] Q ion represents the ionospheric delay coefficient, TEC(n) represents the total number of ionospheric electrons on the ranging signal path between the first device and the second device at the nth moment; f z1u (n) represents the carrier frequency of the uplink signal at the nth moment, in Hertz; f z1d (n) represents the carrier frequency of the downlink signal at the nth moment, in Hertz; f z1z (n) represents the carrier frequency of the pseudo-range measurement signal at the nth moment, in Hertz.

[0038] Special mention: Q ion is the ionospheric delay coefficient, which is published by some international organizations. With the in-depth study of ionospheric delay, the ionospheric delay coefficient is becoming more and more accurate. The ionospheric delay coefficient used to be 40.28, 40.30, and is currently 40.309. There may be more accurate ionospheric delay coefficients in the future. This application does not specifically limit the ionospheric delay coefficient, and takes the latest published value. In this embodiment, Q ion The value is 40.309.

[0039] The present application proposes a dual-frequency time synchronization system and method thereof by creatively applying the carrier frequencies of forwarding ranging signals and pseudo-ranging signals.

[0040] At the same time, based on the dual-frequency time synchronization system and its method, a satellite navigation system is proposed through combination. Compared with the existing Beidou satellite navigation system, the biggest feature of this satellite navigation system is that it first obtains the user clock difference, and then uses the spatial geometric distance between the earth station and the satellite to calculate the three-dimensional coordinates of the earth station, instead of calculating the three-dimensional coordinates and user clock difference like the Beidou satellite navigation system. The satellite navigation system provided by this application only needs two satellites at a minimum to realize timing and positioning services, and has the characteristics of small investment and excellent performance.

[0041] The system time described in this 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 of this application. In practical applications, my country's Beidou time is often used as the reference time and system time, and the clock difference of different devices is the clock difference of different devices relative to this Beidou reference time.

[0042] The computing device of the present application can communicate with the first device and the second device respectively to obtain a pseudorange measurement value and a forwarding range measurement value.

[0043] When the first device broadcasts a pseudo-range measurement signal, the second device receives the pseudo-range measurement signal and measures a pseudo-range measurement value, and the second device sends and receives a forwarding ranging signal and measures a forwarding ranging value. At this time, the computing device communicates with the second device to obtain a pseudo-range measurement value and a forwarding ranging value;

[0044] When the second device broadcasts a pseudorange ranging signal, the first device receives the pseudorange ranging signal and measures a pseudorange ranging value, and the second device sends and receives a forwarding ranging signal and measures a forwarding ranging value. At this time, the computing device communicates with the second device to obtain the forwarding ranging value, and communicates with the first device to obtain the pseudorange ranging value.

[0045] After the computing device obtains the pseudorange measurement value and the forwarded range measurement value, it executes the method of the present application to calculate the relative clock difference, that is, the clock difference between the first device and the second device.

[0046] It is worth noting that in this exemplary embodiment, the computing device may be integrated into the first device; or integrated into the second device; or may be independent of the first device and the second device, that is, an independent device.

[0047] The core function of the present application is to forward a ranging signal and a pseudo-range ranging signal between the first device and the second device, and obtain a corresponding pseudo-range ranging value and a forwarding ranging value, and calculate the clock difference between the first device and the second device according to the relationship between the pseudo-range ranging value, the forwarding ranging value and the corresponding preset carrier frequency.

[0048] Therefore, this application focuses on explaining the first device, the second device and the signal structure therebetween, as well as a calculation method for obtaining a relative clock difference and a calculation method for a relative spatial distance.

[0049] The following first describes the dual-frequency time synchronization system, and then describes the satellite navigation system.

[0050] In the dual-frequency time synchronization system described in the present application, there is a pseudo-range measurement signal and a forwarding range measurement signal between the first device and the second device;

[0051] Among them, the forwarded 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 it to form a 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.

[0052] Among them, both the pseudo-range ranging signal and the forwarding ranging signal are spread spectrum signals.

[0053] It should be noted that, in this exemplary embodiment, the pseudorange measurement signal may be broadcast by the first device and received by the second device, or may be broadcast by the second device and received by the first device.

[0054] When the pseudo-range measurement signal is broadcast by the second device, the uplink signal broadcast by the forwarding ranging device in the second device can be used as the pseudo-range measurement signal. After the uplink signal reaches the first device, it is split into two, one as the pseudo-range measurement signal, and the other signal is forwarded by the repeater into a downlink signal.

[0055] When the pseudo-range measurement signal is broadcast by the first device and received by the second device, the forwarded ranging signal is sent and received by the second device. Under this condition, both the forwarded ranging signal and the pseudo-range measurement signal are received and measured by the second device, and the second device performs synchronous measurement to obtain the pseudo-range measurement value and the forwarded ranging value;

[0056] It should be noted that when the pseudorange ranging signal is broadcast by the second device and received by the first device, the forwarded ranging signal is spontaneously sent and received by the second device, and the forwarded ranging signal and the pseudorange ranging signal are received and measured by the second device and the first device respectively, and strict synchronous measurement cannot be achieved. The first device and the second device need to have rough time synchronization conditions (the same is true for the two-way pseudorange measurement method. The satellite and the ground station each measure the pseudorange ranging signal sent by the other party, and the satellite and the ground station need to have rough time synchronization requirements). At this time, the pseudorange value measured by the first device and the forwarded ranging value obtained by the second measurement device can be regarded as synchronous measurement, and then the clock difference is calculated using the method of the present application.

[0057] In addition, two different types of systems are generated depending on whether the pseudo-range measurement signal is measured by the second device or the first device. The two different types of systems have the same signal structure, system composition, and processing method except for the different pseudo-range measurement signal transmission directions and pseudo-range measurement devices. Therefore, for the sake of simplicity and clarity, the following is an exemplary description of the case where the first device broadcasts the pseudo-range measurement signal.

[0058] There is one pseudo-range ranging signal and one forwarded ranging signal between the first device and the second device; wherein the pseudo-range ranging signal is broadcast by the first device and received by the second device; the forwarded ranging signal includes an uplink signal broadcast by the second device and a received downlink signal, and the downlink signal is obtained by forwarding the uplink signal by the first device; the carrier frequency of the one pseudo-range ranging signal (including the carrier frequency of the uplink signal and the carrier frequency of the downlink signal) and the carrier frequency of the one forwarded ranging signal satisfy a preset carrier frequency relationship.

[0059] In other embodiments, the first device and the second device may also be located on the same side of the ionosphere, for example, both are located on the ground, or both are located in space, in which case the ionospheric delay is 0. When the first device and the second device are located in space, the ranging signal does not pass through the atmosphere, and naturally there is no tropospheric delay and ionospheric delay, and the pseudo-range ranging signal has a sagnac delay effect; when the first device and the second device are located at low altitude or even on the ground, the path experienced by the ranging signal also has no ionospheric delay, and the ionospheric delay is 0, and the sagnac delay effect of the pseudo-range ranging signal can be ignored. For these situations, 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.

[0060] The dual-frequency time synchronization system provided in the embodiment of the present application can be applied to aerospace systems, typically 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 satellites, etc.), that is, a satellite-to-ground time synchronization system, in which the earth station monitors the clock difference between the satellite and the earth station. In addition to the satellite-to-ground time synchronization system, the embodiment of the present application can also be applied to time synchronization between ground stations.

[0061] The first device may be, for example, a satellite, and the second device may be, for example, an earth station. When the computing device is integrated into the earth station, the earth station determines the clock difference and relative spatial distance between the satellite and 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 may also be an earth station, and the second device may be a satellite.

[0062] In addition, the first device can also be a high-orbit device and the second device can be a low-orbit device, or both the first device and the second device can 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.

[0063] Figure 1 FIG. 1 is a schematic diagram of a dual-frequency time synchronization system according to an embodiment of the present application. Figure 1As shown, the dual-frequency time synchronization system may include a first device 100 and a second device 200 in communication connection; the first device 100 forwards a downlink signal to the second device 200 based on the received uplink signal, and broadcasts a pseudo-range ranging signal to the second device 200, wherein the uplink signal and the downlink signal formed by forwarding by the first device 100 constitute a forwarding ranging signal; the second device 200 is used to broadcast an uplink signal to the first device 100, receive a pseudo-range ranging signal and a downlink signal, and synchronously measure the forwarding ranging signal and the pseudo-range ranging signal to obtain a forwarding ranging value and a pseudo-range ranging value. Among them, the carrier frequency of the uplink signal, the carrier frequency of the downlink signal, and the carrier frequency of the pseudo-range ranging signal satisfy a preset carrier frequency relationship.

[0064] Unless otherwise specified, the following description will be given by taking the first device 100 as a satellite and the second device 200 as an earth station as an example.

[0065] It is worth noting that, in this 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 a pseudo-range measurement signal.

[0066] In the dual-frequency time synchronization system provided by the embodiment of the present application, the satellite sends a pseudo-range measurement signal to the earth station, the earth station sends an uplink signal to the satellite, and after acquiring the uplink signal, the satellite forwards the uplink signal to obtain a downlink signal and sends the downlink signal to the earth station. There is a 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-range measurement signal. In this way, the earth station performs mathematical operations based on the preset carrier frequency relationship and can determine the clock difference between the satellite and the earth station without knowing the exact atmospheric delay error caused by the influence of the atmosphere. 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 partially overcomes the ionospheric delay, overcomes the error influence of the tropospheric delay, eliminates the relative spatial distance, can improve the accuracy of the determined clock difference, and has the advantages of simplifying the satellite payload and reducing the satellite cost.

[0067] In this exemplary embodiment, both the forwarded ranging signal and the pseudo-ranging signal are spread spectrum signals, and the spread spectrum technology, carrier frequency multiplexing technology and code division multiple access technology are used for corresponding processing in the signal transmission, forwarding and reception processing.

[0068] In this exemplary embodiment, the earth station sends an uplink signal to the satellite based on its own clock system, that is, based on the local time. After acquiring the uplink signal, the satellite forwards the uplink signal to obtain a downlink signal, and forwards the frequency-converted downlink signal to the earth station. It can be seen that the carrier frequencies of the uplink signal and the downlink signal in this exemplary embodiment are different.

[0069] The uplink signal and the downlink signal forwarded by the satellite constitute a forwarding ranging signal, and the earth station can determine the forwarding ranging value based on the forwarding ranging signal. In addition, the satellite also sends a pseudo-range ranging signal to the earth station based on its own clock system, that is, local time. The earth station receives and demodulates the pseudo-range ranging signal to obtain the pseudo-range ranging value, so that the earth station can calculate the relative clock error and relative space distance based on the determined forwarding ranging value and pseudo-range ranging value and the preset frequency relationship. The relative clock error mentioned here is the clock error between the satellite and the earth station, and the relative space distance is the satellite-to-earth space distance between the satellite and the earth station.

[0070] It should be noted that the pseudo-range ranging signal and forwarding ranging signal described in this exemplary embodiment refer to the modulated signal obtained after modulating the ranging code signal in the carrier signal. The ranging codes used in the pseudo-range ranging signal and the forwarding ranging signal may 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 such as pseudo-code, weil code, M code, etc., and this application does not specifically limit the specific selection of the ranging code. It can also be understood that the forwarding ranging signal and pseudo-range ranging signal described in the embodiment of the present application are both spread spectrum signals. When multiple spread spectrum signals are received and transmitted, the relationship between the carrier frequency and the ranging code is processed in accordance with the spread spectrum communication technology and the code division multiple access communication technology, which will not be repeated here.

[0071] The specific process of the earth station determining the clock difference between the satellite and the earth station can be found in the introduction of the subsequent method embodiments, which will not be expanded here.

[0072] Figure 2 is a structural block diagram of a satellite and an earth station according to an implementation mode of the present application, such as Figure 2 As shown, in an exemplary embodiment, the satellite may include a transponder 101, a pseudorange generating device 102, and a first time and frequency device 103. The pseudorange generating device 102 generates and broadcasts a pseudorange ranging signal; the transponder 101 receives an uplink signal, performs frequency conversion processing and power amplification on the uplink signal, and then forwards the downlink signal to the second device 200; the first time and frequency device 103 provides a clock signal for the transponder 101 and the pseudorange generating device 102.

[0073] It should be understood that the repeater 101 and the pseudorange generating device 102 described in this exemplary embodiment can be set independently, or can also be integrated in one hardware device, that is, the functions of the repeater 101 and the pseudorange generating device 102 are realized by an integrated hardware device, or the repeater 101, the pseudorange generating device 102 and the first time-frequency device 103 are integrated, all of which belong to the protection scope of the present application.

[0074] It should be noted that in this exemplary embodiment, the pseudorange generating device 102 and the repeater 101 are communicatively connected, that is, the two can realize communication interaction. They can communicate with each other directly, or they can be connected to a third-party device to realize communication interaction. All of the above belong to the protection scope of this application.

[0075] Because the computing device is only used to implement the computing function, its independent setting or integration into the first device 100 or the second device 200 does not affect the implementation of the solution of the present application. Therefore, this exemplary embodiment takes the computing device integrated into the second device 200 as an example for exemplary description. Based on this, the earth station may include a forwarding ranging device 201, a second pseudo-range ranging device 202, a second time-frequency device 203 and a computing device 204, wherein the second pseudo-range ranging device 202 processes the received pseudo-range ranging signal to obtain a pseudo-range ranging value; the forwarding ranging device 201 generates and broadcasts an uplink signal, and receives a downlink signal and determines a forwarding ranging value based on the downlink signal. The computing device 204 is respectively connected to the second pseudo-range measuring device 202 and the forwarding ranging device 201 for communication. The computing device 204 receives the pseudo-range measuring value and the forwarding ranging value, and determines the clock difference between the satellite and the earth station based on the relationship between the pseudo-range measuring value, the forwarding ranging value, and the preset carrier frequency, and determines the relative spatial distance based on the pseudo-range measuring value and the forwarding ranging value; the second time and frequency device 203 provides a clock signal for the forwarding ranging device 201 and the second pseudo-range measuring device 202.

[0076] In addition, it should be noted that the second pseudo-range ranging device 202 and the forwarding ranging device 201 in this exemplary embodiment can be independently configured, or can be integrated into one hardware device, that is, one hardware device implements the functions of the second pseudo-range ranging device 202 and the forwarding ranging device 201, or the second pseudo-range ranging device 202, the forwarding ranging device 201 and the second time-frequency device 203 are integrated, all of which belong to the protection scope of the present application.

[0077] Figure 3 is a structural block diagram of a satellite and an earth station according to another embodiment of the present application. As described above, the pseudo-range measurement signal can also be broadcast by the second device 200 and received by the first device 100. In this case, Figure 3As shown, the first device 100 includes a first time-frequency device 103, a repeater 101 and a first pseudo-range measuring device 104; the first time-frequency device 103 is used to provide a time-frequency signal to the repeater 101 and the first pseudo-range measuring device 104; the repeater 101 is used to receive an uplink signal, perform frequency conversion processing and power amplification on the uplink signal, and then forward the downlink signal to the second device 200; the first pseudo-range measuring device 104 is connected to the repeater 101 for communication, and the first pseudo-range measuring device 104 is used to receive and measure the pseudo-range measuring signal to obtain a pseudo-range measuring value; the second device 200 includes a second time-frequency device 203 and the forwarding ranging device 201; the second time-frequency device 203 is at least used to provide a time-frequency signal to the forwarding ranging device 201; the forwarding ranging device 201 is used to generate and broadcast an uplink signal, receive a downlink signal, and determine a forwarding ranging value based on the forwarding ranging signal; wherein the uplink signal broadcast by the forwarding ranging device 201 is used as a pseudo-range ranging signal; wherein the first pseudo-range ranging device 104 is integrated with or separately arranged with the first time-frequency device 103 and the repeater 101, and the second pseudo-range ranging device 202 is integrated with or separately arranged with the second time-frequency device 203 and the forwarding ranging device 201.

[0078] The computing device 204 is in communication connection with the first device 100 and the second device 200. The computing device 204 receives the pseudo-range measurement value and the forwarding measurement value, and determines the relative spatial distance and the clock difference between the first device 100 and the second device 200 based on the forwarding measurement value and the pseudo-range measurement value. In this case, the transmission delay of the forwarding measurement 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 in this working condition have corresponding differences in system structure only due to the different broadcasting methods of the pseudo-range measurement signal, the specific functions of each functional component are different. Figure 2 The structure shown is similar. Figure 2 The system structure shown is taken as an example to further introduce the specific structures of the first device 100 and the second device 200.

[0079] In an exemplary embodiment, the forwarding ranging device 201 may include a modulator, a mixer, a demodulator, an antenna, a data collector, etc. The modulator generates an intermediate frequency spread spectrum signal; the mixer mixes the intermediate frequency spread spectrum signal into a radio frequency signal, the antenna sends the radio frequency signal to the satellite, and receives the radio frequency signal forwarded by the satellite, the antenna receives the radio frequency signal and is mixed into an intermediate frequency signal by the mixer; the demodulator demodulates the intermediate frequency signal and obtains the forwarding ranging value through ranging code correlation operation; the data collector records and stores the forwarding ranging value. The second pseudo-range ranging device 202 may include a demodulator, a receiving antenna, a data collector, etc. The receiving antenna receives the pseudo-range ranging signal of the satellite and the second pseudo-range ranging device 202 generates a pseudo-range ranging value.

[0080] It should be noted that, in this exemplary embodiment, a zero baseline is set between the second pseudo-range measuring device 202 and the forwarding ranging device 201 .

[0081] It is worth pointing out that the zero baseline setting mentioned in the present application does not mean that the distance between the second pseudo-range ranging device 202 and the forwarding ranging device 201 is 0, but that the distance setting between them must satisfy that the spatial paths experienced by the forwarding ranging signal and the pseudo-range ranging signal are approximately the same. When the distance between the second pseudo-range ranging device 202 and the forwarding ranging device 201 becomes smaller and smaller, and can be integrated into one device, the approximately same gradually becomes the same, with the same relative spatial distance, the same tropospheric delay, and the same total number of ionospheric electrons.

[0082] At this time, the pseudorange ranging signal and the forwarded ranging signal have the same transmission path, so the atmosphere has the same influence on the forwarded ranging signal and the pseudorange ranging signal, that is, the forwarded ranging signal and the pseudorange ranging signal have the same ionospheric path and tropospheric path. Therefore, the preset carrier frequency relationship between the carrier frequencies of the uplink signal, the downlink signal and the pseudorange ranging signal can be used to partially eliminate the influence of the atmospheric error and calculate the clock difference between the satellite and the earth station.

[0083] In an exemplary embodiment, the second pseudo-range measuring device 202 and the forwarding ranging device 201 use the same time-frequency device, so that the second pseudo-range measuring device 202 and the forwarding ranging device 201 perform measurements at the same time to obtain the pseudo-range ranging value and the forwarding ranging value at the same time. It is worth noting that the same time-frequency device in this exemplary embodiment may include two clocks (crystal oscillators or atomic clocks) or one clock (crystal oscillator or atomic clock). When the time-frequency device includes two clocks (crystal oscillators or atomic clocks), one clock provides a clock signal for the second pseudo-range measuring device 202, and the other clock provides a clock signal for the forwarding ranging device 201. In actual use, the preset time interval can be set as needed, for example, it can be set to 1s here, and the second pseudo-range measuring device 202 and the forwarding ranging device 201 measure at the rising edge or falling edge of their respective 1PPS (1Pulse PerSecond, pulse per second) signals. Preferably, it is generally recommended to use one clock to perform synchronous measurement of the pseudo-range measurement signal and the forwarded ranging signal at the rising edge or falling edge of the same 1PPS signal.

[0084] There is a forwarding delay when the repeater 101 forwards the signal. The forwarding delay refers to the delay generated in the process of forwarding the uplink signal to obtain the downlink signal after the satellite receives the uplink signal sent by the earth station.

[0085] The pseudo-range measurement signal transmission delay refers to the delay generated by the satellite pseudo-range generation device 102 in the process of generating and transmitting the pseudo-range measurement signal.

[0086] Specifically, the repeater 101 is connected in communication with the pseudorange generating device 102, so that the forwarding delay can be sent to the pseudorange generating device 102. The pseudorange generating device 102 can load the acquired forwarding delay and pseudorange ranging signal transmission delay into the pseudorange ranging signal, so that after sending the pseudorange ranging signal to the earth station, the second pseudorange ranging device 202 in the earth station can obtain the forwarding delay and pseudorange ranging signal transmission delay of the repeater 101 after demodulating the pseudorange ranging signal. Alternatively, because the change amount of the forwarding delay and the pseudorange ranging signal transmission delay is very small or known, the forwarding delay and the pseudorange ranging signal transmission delay can be regarded as known quantities, so that in actual use, the forwarding delay and the pseudorange ranging signal transmission delay can also be preset in the processing device 204.

[0087] By loading the forwarding delay and the pseudorange measurement signal transmission delay into the pseudorange measurement signal and transmitting it to the earth station, the existing signals between the satellite and the earth station are fully utilized to transmit the forwarding delay and the pseudorange measurement signal transmission delay. There is no need to set up additional communication links, so no additional communication resources are occupied, which can greatly reduce communication costs and save frequency resources.

[0088] It is worth noting that the above embodiment is described only by taking the earth station and the satellite's own signal (the pseudo-range measurement signal broadcast by the pseudo-range generation device 102) to transmit the forwarding delay and the pseudo-range measurement signal transmission delay as an example.

[0089] The second pseudorange measuring device 202 of the earth station has a pseudorange receiving delay, which refers to the delay generated in the process of the second pseudorange measuring device 202 receiving the pseudorange measuring signal sent by the satellite and generating a pseudorange measuring value.

[0090] The forwarding 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 transmission of the antenna; the receiving delay refers to the delay from receiving the downlink signal to generating the forwarding ranging value.

[0091] In other embodiments of the present application, additional communication signals may be used between the earth station and the satellite to transmit the forwarding delay and the pseudo-range measurement signal transmission delay. For example, a telemetry unit may be provided in the satellite, and the forwarding delay and the pseudo-range measurement signal transmission delay may be transmitted by the telemetry signal broadcast by the telemetry unit, or the forwarding delay and the pseudo-range measurement signal transmission delay may be transmitted to the earth station by other user-defined communication link signals. The present application does not specifically limit the specific signal used to transmit the forwarding delay and the pseudo-range measurement signal transmission delay.

[0092] In this exemplary embodiment, the preset carrier frequency relationship refers to the frequency relationship satisfied between the carrier frequency of the uplink signal, the carrier frequency of the downlink signal, and the carrier frequency of the pseudo-range ranging 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 ranging signal satisfy the preset carrier frequency relationship shown in the following formula (f1) or formula (f2):

[0093] f z1u (n)≠f z1d (n) = f z1z (n) (f1);

[0094] f z1d (n)≠f z1u (n) = f z1z (n) (f2);

[0095] It should be understood that in a specific implementation, the carrier frequency of the signal may fluctuate to a certain frequency value due to objective reasons or other factors. After the carrier frequency of each signal is determined using the signal frequency relationship shown in formula (f1) or (f2), in actual applications, the actual frequency may fluctuate slightly on the basis of the theoretical design frequency due to equipment reasons (for example, frequency errors caused by clock manufacturing reasons, etc.), which all fall within the scope of protection of this application.

[0096] Furthermore, in some embodiments, the carrier frequency of the uplink signal, the carrier frequency of the downlink signal, and the carrier frequency of the pseudorange measurement signal are frequency-hopped on the time axis according to a preset frequency-hopping pattern, that is, the uplink signal, the downlink signal, and the pseudorange measurement signal at different times do not use the same fixed frequency, but use signals of different frequencies at different times. Frequency hopping the signal in this way can improve the signal's anti-interference ability and enhance the signal's anti-interception ability.

[0097] It is worth noting that no matter 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.

[0098] Of course, the carrier frequency of the uplink signal, the carrier frequency of the downlink signal and the carrier frequency of the pseudo-range measurement signal may also remain unchanged for a long time, that is, the time interval between two adjacent frequency hops is infinite.

[0099] In an exemplary embodiment, the dual-frequency time synchronization system provided in the embodiment of the present application also has a communication function, and the first device 100 uses an uplink signal and a pseudo-range ranging signal to transmit data with the second device 200, or uses an additional communication signal to transmit data with the second device 200. Specifically, after receiving the uplink signal of the forwarding ranging signal, the satellite is divided into two, one is forwarded downlink to the earth station, and the other 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.

[0100] In an exemplary embodiment, if Figure 1 As shown, the satellite can also send the forwarding delay and the pseudo-range measurement signal transmission delay to the earth station by adding a communication signal, that is, in addition to the uplink signal link, the downlink signal link and the pseudo-range measurement signal link, there is an additional communication link (including the communication link uplink signal fu and the communication link downlink signal fd) between the satellite and the earth station. The satellite transmits the forwarding delay and the pseudo-range measurement signal transmission delay to the earth station through the additional communication link, wherein the additional communication signal can be a remote control and telemetry signal.

[0101] It can be seen that the satellite can transmit the forwarding delay and the pseudo-range measurement signal transmission delay to the earth station in a variety of ways. The present application does not specifically limit the specific transmission method of the forwarding delay and the pseudo-range measurement signal transmission delay.

[0102] In the pseudorange measurement value, it is necessary to obtain the Sagnac effect delay of the satellite, and the Sagnac effect delay requires the coordinates of the earth station and the satellite. The coordinates of the satellite can be obtained through the known satellite ephemeris, and the coordinates of the earth station can be obtained through the existing positioning method. In this way, the coordinate information required by the method of the embodiment of the present application is obtained, and then the Sagnac effect delay is obtained.

[0103] There is no relativistic delay effect term in the pseudo-range measurement value. This is because in reality, satellites in space have time and frequency equipment to provide time and frequency. According to the knowledge of relativity, it is easy to know that the clock on the satellite will produce corresponding relativistic effect delay due to relativity. The relativistic effect delay of the satellite clock can be solved using existing methods. For example, the satellite clock has been adjusted before going into space. After adjustment, the satellite clock has no relativistic effect delay like the clock on the ground. For details, please refer to the Beidou navigation satellite clock's approach to relativity.

[0104] When the forwarding ranging expression is used to characterize the forwarding ranging value, there is no Sagnac effect delay in the forwarding ranging expression because the Sagnac effect delay of the uplink signal is opposite to the Sagnac effect delay of the downlink signal, and the absolute value difference between the two is very small, so the two Sagnac effect delays can be approximately offset, so that the Sagnac effect delay term is not reflected in the forwarding ranging expression. Of course, in some other embodiments of the present application, the Sagnac effect delay can also be considered, that is, the Sagnac effect delay of the uplink signal and the Sagnac effect delay of the downlink signal are added to the forwarding ranging expression, so as to obtain better measurement accuracy of the forwarding ranging value, which all belong to the protection scope of the present application.

[0105] In addition, for the device delay and its acquisition method used in the embodiment of the present method, reference can be made to the introduction of the above-mentioned system embodiment, which will not be repeated here.

[0106] When the pseudo-range measurement signal is broadcast by the second device and received by the first device, the first device receives the pseudo-range measurement signal broadcast by the second device and measures to obtain the pseudo-range measurement value. The second device broadcasts an uplink signal and receives a downlink signal forwarded by the first device, and the second device measures the downlink signal to obtain the forwarded ranging value.

[0107] In addition, when the pseudo-range measurement signal is broadcast by the first device and received by the second device, the second device obtains the forwarded ranging value and the pseudo-range measurement value by performing the following process:

[0108] broadcasting an uplink signal to the first device;

[0109] Acquire a downlink signal forwarded by the first device based on the uplink signal, wherein the uplink signal and the downlink signal constitute a forwarding ranging signal;

[0110] Acquire a pseudorange measurement signal broadcast by the first device;

[0111] The forwarding ranging signal and the pseudo-range ranging signal are synchronously measured to obtain a pseudo-range ranging value and a forwarding ranging value.

[0112] Based on the above embodiments, the embodiments of the present application also provide a time synchronization method, which can be applied to the dual-frequency time synchronization system described in any of the above embodiments. The method can be executed by a computing device. When the computing device is integrated in an earth station, the method is executed by the earth station.

[0113] Figure 4 is a flow chart of a time synchronization method according to an implementation mode of the present application, such as Figure 4 As shown, the time synchronization method may include the following steps:

[0114] S100: when the pseudorange ranging signal is broadcast by the second device and received by the first device, communicate with the first device to obtain a pseudorange ranging value measured by the first device, and communicate with the second device to obtain a forwarding ranging value measured by the second device;

[0115] 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 forwarded ranging value measured by the second device;

[0116] The carrier frequency corresponding to the one forwarded ranging value and the carrier frequency corresponding to the one pseudorange ranging value satisfy a preset carrier frequency relationship;

[0117] S110, using a pseudorange measurement expression to represent the pseudorange measurement value and using a forwarding ranging expression to represent the forwarding ranging value;

[0118] S120. Determine a relative clock error 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 error is the clock error between the first device and the second device.

[0119] The method will be specifically described below by taking the first device as a satellite and the second device as an earth station as an example.

[0120] Among them, the earth station can obtain the pseudo-range measurement signal during the communication process with the satellite, demodulate the pseudo-range measurement signal to obtain the pseudo-range measurement signal transmission delay, the pseudo-range measurement signal is sent by the satellite to the earth station, and the earth station receives and demodulates the pseudo-range measurement signal to determine the pseudo-range measurement value.

[0121] During the communication process with the satellite, the earth station can also spontaneously send and receive forwarding ranging signals, and then measure the forwarding ranging values.

[0122] It should be noted that the Sagnac effect delay in the pseudo-range measurement expression and the forwarding ranging expression of the present application has been explained in the previous text and can be used as a known value, while the satellite-to-ground space distance, tropospheric delay, ionospheric delay, satellite clock error relative to system time, and earth station clock error relative to system time are unknown. The present application method calculates the clock error between the satellite and the earth station based on the measured pseudo-range measurement value and the forwarding ranging value.

[0123] It should be noted that the dual-frequency time synchronization system and method proposed in the present application can not only 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, but also 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.

[0124] The pseudo-range ranging signal and the forwarding ranging signal traverse exactly the same atmospheric path, and the total number of ionospheric electrons experienced by the ranging signal is exactly the same. The ionosphere is a diffuse medium, that is, the time delay produced by the ionosphere for RF signals of different carrier frequencies varies depending on the carrier frequency, while the troposphere is a non-dispersive medium, that is, the troposphere produces the same time delay for RF signals of different carrier frequencies.

[0125] Because a zero baseline is set between the second pseudo-range ranging device 202 and the forwarding ranging device 201, the pseudo-range ranging signal and the downlink signal traverse the same space path, but the time when the uplink signal crosses the ionosphere is different from the time when the downlink signal crosses the ionosphere after being forwarded by the satellite, and there is a certain time difference. In a relatively short period of time (such as a few seconds), the ionosphere is stable and the total number of electrons in the ionosphere remains almost unchanged. It can be calculated that the round-trip time of the radio frequency signal between almost all spacecraft and ground stations will not exceed a few seconds, which fully meets the conditions. Combined with the spatial relationship of the zero baseline setting and the time relationship with a very short time difference, the spatial paths traversed by the forwarding ranging signal and the pseudo-range ranging signal are exactly the same. Because a zero baseline is set between the second pseudo-range ranging device 202 and the forwarding ranging device 201, the pseudo-range ranging signal and the forwarding ranging signal traverse exactly the same space path, so there are equations (19), (20):

[0126] R true,z1z (n) = R true,z1u (n) = R true,z1d (n) (19);

[0127] T duiliu,z1z (n) = T duiliu,z1u (n) = T duiliu,z1d (n) (20);

[0128] When the pseudo-range ranging signal is broadcast by the second device, the pseudo-range ranging signal and the uplink signal of the forwarded ranging signal traverse the same spatial path, and the forwarder and the first pseudo-range ranging device also have the above formula for setting the zero baseline.

[0129] When both the first device and the second device are located on the ground, and there is no ionosphere on the path traversed by the pseudo-range measurement signal and the forwarded ranging signal, the relationship between the above formula (19) and formula (20) still holds.

[0130] In some embodiments, after step S100, the time synchronization method may further include the following steps: using a pseudorange smoothing algorithm to correct the forwarding ranging value and the pseudorange ranging value. Specifically, the pseudorange ranging value and the forwarding ranging value are corrected using the pseudorange smoothing algorithm, so that the noise of the pseudorange ranging value and the forwarding ranging value can be reduced, which is conducive to improving the accuracy of the clock difference finally determined. The specific content of the pseudorange smoothing algorithm is not repeated here.

[0131] In some embodiments, the pseudo-range measurement expression includes preset delay parameter items, and the preset delay parameter items include at least tropospheric delay, ionospheric delay, Sagnac effect delay, real space distance between the satellite and the earth station, and clock error. In some other embodiments, the preset delay parameter items may also include hardware device delay.

[0132] In step S110, after the pseudorange measurement value and the forwarding ranging value are measured, they are further characterized by using corresponding ranging expressions, that is, mathematical expressions of the pseudorange measurement value and the forwarding ranging value are obtained, so that the mathematical expressions are used for mathematical processing in subsequent steps to eliminate the common error terms in the two, and finally the clock difference between the satellite and the earth station is obtained.

[0133] In this exemplary embodiment, the computing device may specifically use the pseudorange measurement expression shown in the following formula (3) to represent the pseudorange measurement value:

[0134] 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);

[0135] And, the forwarding ranging value is represented by the forwarding ranging 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);

[0136] It is worth noting that: ±c·(δt z (n)-δt s (n)), when taking +c·(δt z (n)-δt s (n)), the corresponding satellite broadcasts the pseudo-range measurement signal, and the earth station receives and measures it; when -c·(δt z (n)-δt s (n)), the corresponding earth station broadcasts a pseudo-range measurement signal, and the satellite receives and measures;

[0137] ±sagnca in pseudorange measurement formula (3)zz (n), when taking + sagnca zz (n) corresponds to the Sagnac effect when the satellite broadcasts the pseudo-range measurement signal. When -sagnac zz (n), corresponds to the Sagnac effect of the pseudo-range ranging signal broadcast by the earth station. It can be seen that when the pseudo-range ranging signals are in opposite directions, the absolute value of the Sagnac effect is the same, but the sign is opposite.

[0138] Because the directions of pseudo-range measurement signals are different, except for the opposite signs of the clock error and Sagnac effect between the satellite and the earth station, the rest are the same. Therefore, when the satellite broadcasts the pseudo-range measurement signal, the pseudo-range measurement formula is as follows (f3); when the earth station broadcasts the pseudo-range measurement signal, the pseudo-range measurement formula is as follows (S3):

[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)(f3);

[0140] 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);

[0141] When the first device and the second device are located at low altitude or on the ground, there is no ionospheric delay term and tropospheric delay term in the pseudorange measurement value formula (3), and there may be no sagnac term because the distance between the first device and the second device is relatively close.

[0142] As described above, the pseudorange ranging signal includes an ionospheric delay term, and the forwarded ranging signal also includes an ionospheric delay term. In the present application, the computing device can eliminate or reduce the linear combination result of the ionospheric delay between the uplink signal, the downlink signal, and the ionospheric delay of the pseudorange ranging signal based on a preset carrier frequency relationship, so as to ultimately 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).

[0143] Because of the zero baseline setting of the earth station's repeater ranging device and the second pseudo-range ranging device, the repeater ranging signal and the pseudo-range ranging signal have the same ionospheric path, but the total ionospheric electron number TEC(n) is unknown.

[0144] In this exemplary embodiment, 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):

[0145] f z1u (n)≠f z1d (n) = f z1z (n) (f1);

[0146] f z1d (n)≠f z1u (n) = f z1z (n) (f2);

[0147] When the carrier frequency of the signal between the earth station and the satellite satisfies the preset carrier frequency relationship shown in the above formula (f1) or (f2), the ionospheric delay parameters are respectively associated in the corresponding carrier frequency items 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-range ranging signal, and the ionospheric delay correspondence between the ionospheric delay of the uplink signal, the ionospheric delay of the downlink signal and the ionospheric delay of the pseudo-range ranging signal is obtained, wherein the ionospheric delay parameter includes the ionospheric total electron number TEC(n) and the ionospheric delay coefficient on the ranging signal path of the satellite and the earth station, so the following formulas (1) and (1') are obtained:

[0148]

[0149]

[0150] By performing an equivalent transformation on formula (1) or formula (1'), the corresponding relationship between the ionospheric delay of the uplink signal, the ionospheric delay of the downlink signal and the ionospheric delay of the pseudo-range ranging signal is obtained as shown in formula (2) or formula (2'):

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

[0152] I z1z (n)-(I z1u (n)+I z1d(n)) / 2=(I z1u (n)-I z1d (n)) / 2≠0 (2');

[0153] In this way, the computing device can partially eliminate the ionospheric delay based on the obtained ionospheric delay correspondence to determine the clock difference between the satellite and the earth station.

[0154] In some embodiments, step S120 may specifically include the following process:

[0155] S121, correcting the pseudorange measurement value represented by the pseudorange measurement expression to obtain a corrected pseudorange measurement value;

[0156] S122, correcting the forwarding ranging value represented by the forwarding ranging expression to obtain a corrected forwarding ranging value;

[0157] S123: Determine a relative clock error based on the relationship between the corrected pseudorange ranging value, the corrected forward ranging value and the preset carrier frequency.

[0158] Specifically, step S121 is to correct the above formula (3) to obtain the corrected pseudorange measurement value shown in the following formula (3'):

[0159]

[0160] Furthermore, when the satellite broadcasts a pseudo-range measurement signal, the pseudo-range measurement formula is specifically the following formula (f3):

[0161] 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);

[0162] When the earth station broadcasts a pseudo-range measurement signal, the pseudo-range measurement formula is specifically as follows (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);

[0163] Therefore, in step S121, when the satellite broadcasts the pseudo-range measurement signal, the computing device needs to modify formula (f3) to obtain the following formula (f3'), that is, the above formula (3') is further clarified as formula (f3'):

[0164]

[0165] When the earth station broadcasts a pseudo-range measurement signal, the calculation device needs to modify formula (S3) to obtain the following formula (S3'), that is, the above formula (3') is further clarified as formula (s3'):

[0166]

[0167] Step S122 is to transform the forwarding ranging value shown in formula (4) obtained in the above step to obtain a corrected forwarding ranging value, that is, to obtain a corrected forwarding ranging value shown in the following formula (4'):

[0168]

[0169] After obtaining the corresponding relationship between the ionospheric time delays of the above three signals, in step S123, the computing device further processes the corrected pseudorange measurement value represented by formula (f3') and the corrected forwarding measurement value represented by formula (4') obtained in the above steps to obtain the relative clock error, that is, the clock error between the satellite and the earth station.

[0170] In an exemplary embodiment, step S123 may specifically include the following steps:

[0171] S1231, performing mathematical processing on the corrected pseudorange ranging value and the corrected forwarding ranging value to obtain an expression including a relative clock error;

[0172] S1232. Determine the clock difference between the first device and the second device using an expression containing the relative clock difference and the preset carrier frequency relationship.

[0173] Because the directions of the pseudo-range ranging signals are different, except for the opposite signs of the clock difference between the satellite and the earth station and the opposite signs of the Sagnac effect, the rest are the same. The following continues to use the satellite broadcasting pseudo-range ranging signal as an example to illustrate the method of the present application, that is, to use the pseudo-range ranging formula (f3) and the corrected pseudo-range ranging formula (f3') corresponding to the satellite broadcasting pseudo-range ranging signal to expand the explanation.

[0174] The computing device further processes the corrected pseudorange measurement value represented by formula (f3') and the corrected forwarding measurement value represented by formula (4') to obtain a relative clock error;

[0175] Specifically, the computing device may use the modified forwarding ranging value Lz1,m (n) and the corrected pseudorange value ρ z1z,m (n) The difference calculation is performed to obtain the expression including the relative clock error as shown in the following formula (5):

[0176]

[0177] On this basis, the computing device uses the above equations (19) and (20) and substitutes them into formula (5) to obtain the relative clock error shown in the following formula (6):

[0178]

[0179] It can be seen from formula (6) that after the above steps, the relative clock error obtained eliminates the tropospheric delay parameter term and the relative spatial distance term, but still contains the ionospheric delay combination term.

[0180] As described above, when the signal between the earth station and the satellite has a preset carrier frequency relationship as shown in the above formula (f1) or (f2), and then has an ionospheric delay corresponding relationship as shown in formula (2) or (2'), the computing device partially eliminates the ionospheric delay term in the formula (6) using the ionospheric delay corresponding relationship shown in formula (2) or (2'), and obtains the relative clock error shown in the following formula (7) or (7'):

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

[0182] δt z (n)-δt s (n)+0.5·(I z1u -I z1d ) / c=(ρ z1z,m (n)-L z1,m (n)) / c (7');

[0183] Formula (7) or (7') shows that the final calculated relative clock error still contains a part of the ionospheric delay residual error. If the ionospheric delay residual is to be further eliminated, it is necessary to use the ionospheric delay correction method, such as using the ionospheric model correction or the ionospheric total electron number correction provided by a third party.

[0184] Because the ionospheric delay I z1z ,I z1u ,I z1dis unknown and exists as an error. The ionospheric delay residual in formula (7) or (7') exists as an error. Therefore, the relative clock error finally calculated is shown in formula (8):

[0185] (δt z (n)-δt s (n)) c =(ρ z1z,m (n)-L z1,m (n)) / c (8);

[0186] The relative clock error obtained by formula (8) includes the ionospheric residual error.

[0187] 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 relative clock error obtained has no ionospheric residual, and the obtained clock error is an accurate clock error.

[0188] In some embodiments, after step S110, the time synchronization method may further include the following steps: using a pseudorange smoothing algorithm to correct the forwarding ranging value and the pseudorange ranging value. Accordingly, in step S120, the forwarding ranging value and the pseudorange ranging value corrected by the pseudorange smoothing algorithm may be used to calculate the relative clock error. It is understandable that using the pseudorange smoothing algorithm to correct the pseudorange ranging value and the forwarding ranging value may reduce the noise of the pseudorange ranging value and the forwarding ranging value, which is beneficial to improving the accuracy of the clock error finally determined. The specific content of the pseudorange smoothing algorithm will not be repeated here.

[0189] According to formula (8), when the clock difference δt of the earth station relative to the system time is z When the satellite clock error δt relative to the system time is known, it is easy to obtain s On the contrary, when the satellite clock difference δt relative to the system time is s When the time is known, the clock difference δt of the earth station relative to the system time can be easily obtained. z ; 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.

[0190] The computing device determines the relative clock error (δt z (n)-δt s (n)) cAfter that, data can be transmitted with the satellite based on the uplink signal and the pseudo-range measurement signal, or based on the additional communication signal. The additional communication signal 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 uses the relative clock difference to synchronize its own clock with the time of the earth station. All of these belong to the protection scope of this application.

[0191] The specific impact value of the ionospheric residual in formula (8) can be further explained by a specific example. When the carrier frequency of the uplink signal and the carrier frequency of the downlink signal use the L band, such as f z1z =1200MHz, f z1u =1600MHz, TEC = 50e16 electrons / square meter, then the ionospheric residual is:

[0192] 0.5(I z1z -I z1u )=3.06m, which is converted into time as 10.2ns. The obtained ionospheric residual is still relatively large.

[0193] When the carrier frequency of the uplink signal and the carrier frequency of the downlink signal use the Cn frequency band (5010MHz-5030MHz), this frequency band is a new frequency band allocated by the International Telecommunication Union for satellite navigation. z1z =5015MHz, f z1u =5025MHz, TEC = 50e16, then the ionospheric residual is:

[0194] 0.5(I z1z -I z1u ) = 0.0016m, which is converted to time as 0.0053ns;

[0195] It can be seen that when using the Cn frequency band, the ionospheric residual is very small; when using the Ku, Ka, Q, V frequency bands, the ionospheric residual is still very small. Therefore, when using the Cn, Ku, Ka, Q, V and other frequency bands, considering other factors such as random errors, it is entirely possible to achieve sub-nanosecond time synchronization accuracy.

[0196] In addition, when the carrier frequency of the pseudorange ranging signal and the carrier frequency of the forwarded ranging signal perform frequency hopping according to the frequency hopping pattern, the frequency after the frequency hopping still satisfies the preset carrier frequency relationship, and the above-mentioned satellite-ground time synchronization method is still used to calculate the satellite-ground clock difference, and the calculated clock difference is transmitted to the satellite, and the specific calculation steps are not repeated.

[0197] In addition, based on the above embodiment, the embodiment of the present application further provides a method for determining the space distance between the satellite and the earth. The method for determining the space distance between the satellite and the earth can be executed by a computing device. Figure 5FIG. 1 is a flow chart of a method for determining the satellite-to-earth space distance according to an embodiment of the present application. Figure 5 As shown, the method may specifically include the following steps:

[0198] S200, determining a tropospheric delay on a ranging signal path between a first device and a second device based on a preset tropospheric model;

[0199] S210, determining an ionospheric delay on a ranging signal path between the first device and the second device based on an ionospheric model or a total number of ionospheric electrons provided by a third party;

[0200] S220. Based on the determined tropospheric delay, ionospheric delay, relative clock error, and corrected pseudorange measurement value, determine the relative space distance shown in the following formula (10) using the following formula (3'), wherein the relative space distance is the satellite-to-ground space distance between the first device and the second device:

[0201]

[0202]

[0203] Taking the satellite broadcasting pseudo-range ranging signal as an example, in this step, the computing device is to use the following formula (f3') and, in combination with formula (10), determine the satellite-to-earth space distance, i.e., the relative space distance, between the satellite and the earth station when the satellite broadcasts the pseudo-range ranging signal in this embodiment, as shown in formula (10-1):

[0204]

[0205]

[0206] R true,z1z (n) = ρ z1z,m (n)-I z1z (n)-T duiliu,z1z (n)-c·(δt z (n)-δt s (n)) c (10-1);

[0207] Alternatively, based on the determined tropospheric delay, ionospheric delay and corrected forward ranging value, the relative spatial distance shown in the following formula (11) is determined using the following formula (4'):

[0208]

[0209] R true,z1u (n) = L z1,m (n)-T duiliu,z1u (n)-(Iz1u (n)+I z1d (n)) / 2(11);

[0210] Among them, the relative clock error, the corrected pseudorange ranging value, and the corrected forwarding ranging value can be determined according to the time synchronization method described in any of the above embodiments.

[0211] Alternatively, a weighted average is performed on the formula (10-1) and the formula (11) to obtain a weighted average of the satellite-to-earth space distance between the satellite and the earth station, that is, a relative space distance, where the sum of the weighted coefficients is equal to 1.

[0212] In step S210, the ionospheric delay can be obtained using an 8-parameter Klobuchar model, or using a 14-parameter Klobuchar model, or the ionospheric TEC value can be obtained through a third party. Then, the calculation device can calculate the ionospheric delay of each signal based on the following formulas (15), (16), and (17):

[0213]

[0214]

[0215]

[0216] The tropospheric delay T between the earth station and the satellite can be corrected using a preset model. The calculation of the tropospheric delay requires the help of meteorological parameters. In the absence of real-time meteorological parameters, a simple model related only to the satellite elevation angle can be used for calculation, as shown in formula (T1):

[0217] T=2.47 / (sinθ+0.0121) (T1);

[0218] Where: T is the tropospheric delay, unit: meter; θ is the satellite elevation angle, unit: radian.

[0219] There are relatively many models for calculating tropospheric delay based on meteorological parameters. The differences between them decrease with the satellite elevation angle by about a few millimeters to a few centimeters, which is more accurate than that calculated by this simple model.

[0220] Common models for determining tropospheric delay correction include the Saastamoinen model and the Hopfield model. Studies have shown that when the altitude angle is greater than or equal to 15°, the results obtained by different models are in good agreement, and the model can be selected arbitrarily. However, when the value of the station elevation is large, the tropospheric delay in the zenith direction calculated by the two models can differ by tens of centimeters. After comparison with the measured meteorological data, it is recommended to use the Saastamoinen model.

[0221] After obtaining the tropospheric delay and the ionospheric delay, the computing device can further use formula (10-1), or use formula (11), or use formula (10-1) and formula (11) to perform weighted calculation to obtain the relative spatial distance. The relevant calculation process will not be repeated here.

[0222] Based on the above embodiments, the present application also provides a satellite navigation system, which is based on the above dual-frequency time synchronization system and method, adds an operation and control system, and increases the number of satellites to form a complete and simplest satellite navigation system.

[0223] Specifically, the satellite navigation system includes the dual-frequency time synchronization system described in any of the above 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 measurement signal. The earth station obtains the orbital parameters of the corresponding satellite 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.

[0224] The satellite navigation system also includes a plurality of third devices, which are connected to the satellite for communication. Some of the third devices constitute a satellite orbit determination system, which is used to monitor and process the orbit of the satellite to obtain satellite orbit parameters; some of the third devices constitute a satellite-to-ground time synchronization system, which is used to monitor the time of each satellite and keep the time of each satellite synchronized with the operation and control system. The operation and control system mentioned here refers to a system composed of a satellite orbit determination system and a satellite-to-ground time synchronization system.

[0225] The satellite navigation system Figure 6 As shown, in the satellite navigation system, there are at least two satellites. In the satellite navigation system, the orbit determination system can adopt the existing Beidou orbit determination method.

[0226] The third device in the satellite-to-ground time synchronization system has the hardware composition and signal structure of the dual-frequency time synchronization system with the satellite. The computing device can be integrated into the third device to execute the time synchronization method of the present application. At this time, the time of the third device in the satellite-to-ground time synchronization system is used as the system time, and the satellite relative to the system time is used as an unknown number. The clock difference of the satellite relative to the system time is obtained through the method of the present application to achieve time synchronization between the satellite and the operation and control system. The satellite then broadcasts a pseudo-range measurement signal with a 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. Through the dual-frequency time synchronization system and method of the present application, the clock difference of the earth station relative to the system time is obtained to achieve the satellite timing function. At this time, after the earth station obtains its own clock difference relative to the system time, it does not need to interact with the satellite for clock difference data.

[0227] Of course, the satellite-ground time synchronization system can also use other existing satellite-ground time synchronization technologies, such as a two-way pseudo-range measurement method, etc. Satellite-ground time synchronization can be achieved using these methods.

[0228] After time synchronization is achieved at the earth station, the relative spatial distance between the earth station and the satellite is obtained. Based on 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 refer to the Beidou dual-star positioning principle to obtain the earth station coordinates; when there are three or more satellites, the earth station does not need to be configured with an altimeter, and the earth station coordinate information can be obtained through the relative spatial distance with three satellites and the satellite ephemeris.

[0229] Based on the above embodiments, an embodiment of the present application also provides an inter-station time synchronization system, which includes: the satellite navigation system described in any of the above embodiments; wherein, when there are at least two earth stations, at least two of the earth stations achieve time synchronization with each other by exchanging data through communication.

[0230] Alternatively, the inter-station time synchronization system includes: the dual-frequency time synchronization system described in any of the above embodiments; wherein, when there are at least two first devices or second devices, at least two of the first devices or second devices achieve time synchronization with each other by exchanging data through communication.

[0231] Based on the above embodiment, the embodiment of the present application further provides an inter-station time synchronization method, which can be applied to the dual-frequency time synchronization system described in the above embodiment or to the satellite navigation system described in the above embodiment. The method may include:

[0232] Directly communicate with the target earth station to exchange data and obtain the clock difference of the target earth station;

[0233] The time difference between the two is determined by calculating the clock difference of the earth station itself and the clock difference of the target earth station.

[0234] Among them, after determining the clock difference of the earth station relative to the system time, the earth station can transmit data with the target earth station based on the communication link. Multiple earth stations exchange the clock differences of each earth station relative to the system time through communication, thereby realizing time synchronization between multiple earth stations, which is similar to the common view method and will not be repeated here.

[0235] On the basis of the above-mentioned embodiment, the embodiment of the present application further provides a satellite positioning method, which can be applied to the above-mentioned satellite navigation system. Figure 7 FIG. 1 is a flow chart of a satellite positioning method according to an embodiment of the present application. The method can be executed by an earth station that needs to be positioned, such as Figure 7As shown, the satellite positioning method may include the following steps:

[0236] S610, acquiring orbital parameters of each satellite, wherein the orbital parameters of the satellite are determined by an orbit determination system;

[0237] S620, determining the coordinates of the corresponding satellite based on the orbital parameters;

[0238] S630, obtaining the relative spatial distance between itself and each satellite;

[0239] S640: Determine its own coordinate information based on the orbital parameters of each of the satellites and the relative spatial distance between the satellites.

[0240] Among them, in step S610, the orbital parameters of the satellite are satellite ephemeris, and the orbital parameters of the satellite are determined according to existing satellite orbit determination methods, such as the orbit determination method of Beidou navigation satellites, so that the earth station obtains the orbital parameters of the corresponding satellite based on the data transmission results with each satellite (for example, by receiving pseudorange measurement signals).

[0241] In step S620, the earth station calculates the satellite coordinates at the current ranging time according to the acquired orbital parameters of the satellite.

[0242] In step S630, the earth station may determine the relative spatial distance between itself and each satellite by using any of the satellite-to-earth spatial distance determination methods executed by the earth station.

[0243] In step S640, the earth station calculates its own coordinate information based on the coordinate information of each satellite and the relative spatial distance between itself and each satellite, that is, realizes satellite positioning of itself.

[0244] It is worth noting that in this exemplary embodiment, the number of satellites needs to be greater than or equal to 2. Specifically, when the number of satellites is greater than or equal to 2, the earth station can select at least two satellites from all satellites and calculate its own coordinate information with reference to the existing Beidou dual-star positioning method.

[0245] In summary, it can be seen that the dual-frequency time synchronization system and method provided in the embodiment of the present application creatively transforms one pseudo-range measurement signal in the two-way pseudo-range measurement method into a forwarding ranging signal, and integrates it with another pseudo-range measurement signal, and still uses two carrier frequencies, which can not only obtain the same satellite-to-ground time synchronization performance as the two-way pseudo-range measurement method, but also obtain a more accurate satellite-to-ground spatial distance, and at the same time reduce costs. The dual-frequency time synchronization system and method provided in the embodiment of the present application have the following advantages:

[0246] 1. Compared with the two-way pseudo-range measurement method, it reduces system requirements and costs;

[0247] 2. Compared with the existing two-way pseudo-range measurement method, for satellites, in the embodiments of the present application, the satellites do not need pseudo-range measurement equipment, which can reduce the complexity of satellite payloads and reduce satellite costs;

[0248] 3. Compared with the two-way pseudo-range measurement method, this method completely overcomes the influence of the tropospheric delay of the atmosphere and partially eliminates the ionospheric delay, thereby achieving better satellite-ground time synchronization accuracy;

[0249] 4. At present, under the circumstance that the resources of L and S frequency bands are very tight, satellite communications, satellite navigation, etc. are all developing towards high frequency bands. If the carrier frequency used in this application is a high frequency band, such as Cn, Ka, Q, V and other frequency bands, sub-nanosecond time synchronization accuracy can be achieved;

[0250] 5. Because the earth station only needs to receive one satellite signal, the earth station can use a directional antenna to reduce the multipath effect, thereby achieving better ranging accuracy and better time synchronization accuracy;

[0251] 6. This method not only overcomes the influence of atmospheric delay, but also overcomes the influence of multipath effect and the influence of near-end and far-end environmental segments between satellite and earth station;

[0252] 8. This application can obtain a relatively accurate satellite-to-ground space distance, providing support for subsequent satellite orbit determination and user positioning;

[0253] 9. This method fully meets the requirements of 6G communication systems for high-performance, low-cost satellite-ground time synchronization, reduces cost requirements from two aspects: carrier frequency cost and satellite payload optimization, and even directly uses remote control and telemetry signals of the spread spectrum system to achieve satellite-ground time synchronization, which is more cost-effective.

[0254] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A dual-frequency time synchronization system, characterized in that: comprising a first device and a second device in communication connection; There is one pseudo-range measurement signal and one forwarding range measurement signal between the first device and the second device; The pseudo-range measurement signal is broadcast by the first device and received by the second device, or is broadcast by the second device and received by the first device; The forwarded ranging signal is composed 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 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.

2. The dual-frequency time synchronization system according to claim 1, characterized in that: The forwarded ranging signal and the pseudo-ranging signal are both spread spectrum signals, and the first device and / or the second device use spread spectrum technology, carrier frequency multiplexing technology and code division multiple access technology to perform 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 pseudo-range 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); Where: f z1u (n) represents the carrier frequency of the uplink signal at the nth moment, in Hertz; f z1d (n) represents the carrier frequency of the downlink signal at the nth moment, in Hertz; f z1z (n) represents the carrier frequency of the pseudo-range measurement signal at the nth moment, in Hertz.

4. 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 pseudo-range measurement signal are frequency-hopped according to a preset frequency-hopping pattern on the time axis and satisfy the preset carrier frequency relationship.

5. The dual-frequency time synchronization system according to claim 1, characterized in that: The first device includes a first time-frequency device, a repeater, and a pseudo-range generating device, and the second device includes a second time-frequency device, a repeater ranging device, and a second pseudo-range ranging device; The first time-frequency device is used to provide a time-frequency signal to the repeater and the pseudorange generating 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 pseudorange generating device is communicatively connected with the repeater, and the pseudorange generating device is used to generate and broadcast the pseudorange ranging signal; The second time-frequency device is used to provide a time-frequency signal to the forwarding ranging device and the second pseudo-range ranging device; The second pseudo-range measuring device is used to receive the pseudo-range measuring signal and process it to obtain a pseudo-range measuring value; The forwarding ranging device is used to generate and broadcast the uplink signal, and receive and measure the downlink signal to obtain a forwarding ranging value; Wherein, the first time-frequency device, the repeater and the pseudo-range generating device are integrated or separately arranged, and / or the second time-frequency device, the repeater ranging device and the second pseudo-range ranging device are integrated or separately arranged; or, The first device includes a first time-frequency device, a repeater, and a first pseudo-range measuring device, and the second device includes a second time-frequency device and a repeater ranging device; The first time-frequency device is used to provide a time-frequency signal to the repeater and the first pseudo-range measuring 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 pseudo-range measuring device is communicatively connected to the repeater, and is used to receive and measure the pseudo-range measuring signal to obtain a pseudo-range measuring value; The second time-frequency device is used to provide a time-frequency signal to the forwarding ranging device; The forwarding ranging device is used to generate and broadcast the uplink signal, and receive and measure the downlink signal to obtain a forwarding ranging value, wherein part of the uplink signal broadcast by the forwarding ranging device is used as the pseudo-range ranging signal; The first time-frequency device, the repeater and the first pseudo-range measuring device are integrated or separately arranged, and / or the second time-frequency device and the repeater ranging device are integrated or separately arranged.

6. The dual-frequency time synchronization system according to claim 5, characterized in that: The second pseudo-range measuring device and the repeater ranging device are set with a zero baseline; the first pseudo-range measuring device or the pseudo-range generating device and the repeater are set with a zero baseline.

7. The dual-frequency time synchronization system according to claim 5, 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.

8. The dual-frequency time synchronization system according to claim 1, characterized in that: The system further comprises: A computing device, wherein the computing device is arranged in the first device or in the second device or exists independently; When the computing device is arranged on the first device or the second device, the first device performs data transmission with the second device by using an additional communication signal; When the computing device is independently arranged, the computing device communicates with the first device and the second device; The computing device receives a pseudorange measurement value and a forwarding ranging value, determines a relative spatial distance based on the forwarding ranging value and / or the pseudorange measurement value, and determines a relative clock error based on the relationship between the pseudorange measurement value, the forwarding ranging value and a preset carrier frequency, wherein the relative clock error is a clock error between the first device and the second device, the relative spatial distance is a satellite-to-ground spatial distance between the first device and the second device, the pseudorange measurement value is obtained by measuring the pseudorange measurement signal by the first device or the second device, and the forwarding ranging value is obtained by measuring the forwarding ranging signal by the second device.

9. The dual-frequency time synchronization system according to claim 5, characterized in that: The system further comprises: A computing device, respectively connected to the first device and the second device for communication; Among them, the repeater has a forwarding delay, and the pseudo-range generating device has a transmission delay; the first pseudo-range ranging device and the second pseudo-range ranging device both have a receiving delay, and the forwarding ranging device has a transmission delay and a receiving delay; The calculation device obtains the forwarding delay of the repeater, the transmission delay of the pseudorange generating device, the receiving delay of the first pseudorange ranging device or the second pseudorange ranging device, and the transmission delay and the receiving delay of the forwarding ranging device.

10. A time synchronization method, characterized in that: Applied to the dual-frequency time synchronization system according to any one of claims 1 to 9, the method is executed by a computing device, and 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 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, communicate 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; Using a pseudorange measurement expression to represent the pseudorange measurement value and using a forwarding measurement expression to represent the forwarding measurement value respectively; A relative clock error 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 error is the clock error between the first device and the second device.

11. The time synchronization method according to claim 10, characterized in that: The using a pseudorange ranging expression to represent the pseudorange ranging value and using a forward ranging expression to represent the forward ranging value respectively include: The pseudorange measurement value is represented 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 represented 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); Where: L z1 (n) represents the forwarding ranging value at the nth moment, in meters; R true,z1u (n) represents the real spatial distance that the uplink signal travels at the nth moment, in meters; R true,z1d (n) represents the real spatial distance traveled by the downlink signal at the nth moment, in meters; I z1u (n) represents the ionospheric delay of the uplink signal at the nth moment, in meters; I z1d (n) represents the ionospheric delay of the downlink signal at the nth moment, in meters; T duiliu,z1u (n) represents the tropospheric delay of the uplink signal at the nth moment, in meters; T duiliu,z1d (n) represents the tropospheric delay of the downlink signal at the nth moment, in meters; Y z1 (n) represents the hardware device delay of forwarding the ranging signal at the nth moment, wherein the hardware device delay of 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 pseudo-range measurement value at the nth moment, in meters; R true,z1z (n) represents the real space distance that the pseudo-range measurement signal has passed at the nth moment, in meters; z1z (n) represents the ionospheric delay of the pseudo-range measurement signal at the nth moment, in meters; T duiliu,z1z (n) represents the tropospheric delay of the pseudo-range measurement signal at the nth moment, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference between the first device and the system time at the nth moment, in seconds; δt z (n) represents the clock difference between the second device and the system time at the nth moment, in seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudo-range measurement signal at the nth moment, in meters; X z1 (n) represents the pseudo-range measurement signal hardware device delay at the nth moment, in meters. The pseudo-range measurement signal hardware device delay includes the pseudo-range measurement signal transmission delay and the pseudo-range measurement signal reception delay.

12. The time synchronization method according to claim 10, characterized in that: The determining of the relative clock error based on the relationship between the pseudorange measurement value represented by the pseudorange measurement expression, the forwarding ranging value represented by the forwarding ranging expression, and the preset carrier frequency includes: Correcting the pseudorange measurement value represented by the pseudorange measurement expression to obtain a corrected pseudorange measurement value; Correcting the forwarding ranging value represented by the forwarding ranging expression to obtain a corrected forwarding ranging value; A relative clock error is determined based on the relationship between the corrected pseudorange ranging value, the corrected forward ranging value and the preset carrier frequency.

13. The time synchronization method according to claim 12, characterized in that: The step of correcting the pseudorange measurement value represented by the pseudorange measurement expression to obtain a corrected pseudorange measurement value includes: The following formula (3) is corrected to obtain the corrected pseudorange measurement value shown in 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 step of correcting the forwarding ranging value represented by the forwarding ranging expression to obtain a corrected forwarding ranging value includes: The following formula (4) is transformed to obtain the corrected forwarding ranging value shown in 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); Where: L z1,m (n) represents the corrected forwarding ranging value at the nth moment, in meters; L z1 (n) represents the forwarding ranging value at the nth moment, in meters; R true,z1u (n) represents the real spatial distance that the uplink signal travels at the nth moment, in meters; R true,z1d (n) represents the real spatial distance traveled by the downlink signal at the nth moment, in meters; I z1u (n) represents the ionospheric delay of the uplink signal at the nth moment, in meters; I z1d (n) represents the ionospheric delay of the downlink signal at the nth moment, in meters; T duiliu,z1u (n) represents the tropospheric delay of the uplink signal at the nth moment, in meters; T duiliu,z1d (n) represents the tropospheric delay of the downlink signal at the nth moment, in meters; Y z1 (n) represents the hardware device delay of forwarding the ranging signal at the nth moment, wherein the hardware device delay of 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 pseudo-range measurement value at the nth moment, in meters; ρ z1z (n) represents the pseudo-range measurement value at the nth moment, in meters; R true,z1z (n) represents the real space distance that the pseudo-range measurement signal has passed at the nth moment, in meters; z1z (n) represents the ionospheric delay of the pseudo-range measurement signal at the nth moment, in meters; T duiliu,z1z (n) represents the tropospheric delay of the pseudo-range measurement signal at the nth moment, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference between the first device and the system time at the nth moment, in seconds; δt z (n) represents the clock difference between the second device and the system time at the nth moment, in seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudo-range measurement signal at the nth moment, in meters; X z1 (n) represents the pseudo-range measurement signal hardware device delay at the nth moment, in meters. The pseudo-range measurement signal hardware device delay includes the pseudo-range measurement signal transmission delay and the pseudo-range measurement signal reception delay.

14. The time synchronization method according to claim 12, characterized in that: The determining the relative clock error based on the relationship between the corrected pseudorange ranging value, the corrected forward ranging value and the preset carrier frequency includes: Mathematically processing the corrected pseudorange measurement value and the corrected forwarded measurement value to obtain an expression including a relative clock error; The clock difference between the first device and the second device is determined using an expression including the relative clock difference and the preset carrier frequency relationship.

15. The time synchronization method according to claim 14, characterized in that: The forwarding ranging device and the second pseudo-range ranging device in the second device are set to a zero baseline, or the forwarder and the first pseudo-range ranging device in the first device are set to a zero baseline; the corrected pseudo-range ranging value and the corrected forwarding ranging value are mathematically processed to obtain an expression containing a relative clock error, including: By using the zero baseline setting relationship, the relative clock error shown in the following formula (8) is determined based on the relationship between the corrected pseudorange ranging value, the corrected forward ranging value and the preset carrier frequency: ±(δt z (n)-δt s (n)) c =(ρ z1z,m (n)-L z1,m (n)) / c (8); Where: L z1,m (n) represents the corrected forwarding ranging value at the nth moment, in meters; ρ z1z,m (n) represents the corrected pseudo-range measurement value at the nth moment, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference between the first device and the system time at the nth moment, in seconds; δt z (n) represents the clock difference between the second device and the system time at the nth moment, in seconds.

16. The time synchronization method according to claim 10, characterized in that: After determining the relative clock error, the method further includes: Communicate with the first device or the second device, and transmit the determined relative clock difference to the first device or the second device to achieve 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 according to 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 relative clock difference.

17. 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 to 9, the method is executed by a computing device, and the method comprises: Determine the tropospheric delay on the ranging signal path between the first device and the second device based on a preset tropospheric model; Determine the ionospheric delay on the ranging signal path between the first device and the second device based on the ionospheric model or the total number of ionospheric electrons provided by a third party; Based on the determined tropospheric delay, the ionospheric delay, the relative clock error and the corrected pseudorange measurement value, the relative spatial distance shown in the following formula (10) is determined using the following formula (3'): Alternatively, based on the determined tropospheric delay, ionospheric delay and corrected forward ranging value, the relative spatial distance shown in the following formula (11) is determined using the following formula (4'): R true,z1u (n)=L z1,m (n)-T duiliu,z1u (n)-(I z1u (n)+I z1d (n)) / 2 (11); Alternatively, performing weighted averaging on the formula (10) and the formula (11) to obtain a weighted average relative spatial distance, wherein the sum of the weighted coefficients is equal to 1; The relative spatial distance is the space distance between the first device and the second device, and the relative clock difference is determined according to the time synchronization method according to any one of claims 10 to 16; L z1,m (n) represents the corrected forwarding ranging value at the nth moment, in meters; L z1 (n) represents the forwarding ranging value at the nth moment, in meters; R true,z1u (n) represents the actual spatial distance that the uplink signal between the first device and the second device passes at the nth moment, in meters; R true,z1d (n) represents the actual spatial distance that the downlink signal between the first device and the second device passes at the nth moment, in meters; z1u (n) represents the ionospheric delay of the uplink signal at the nth moment, in meters; I z1d (n) represents the ionospheric delay of the downlink signal at the nth moment, in meters; T duiliu,z1u (n) represents the tropospheric delay of the uplink signal at the nth moment, in meters; T duiliu,z1d (n) represents the tropospheric delay of the downlink signal at the nth moment, in meters; Y z1 (n) represents the hardware device delay of forwarding the ranging signal at the nth moment, wherein the hardware device delay of 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 pseudo-range measurement value at the nth moment, in meters; ρ z1z (n) represents the pseudo-range measurement value at the nth moment, in meters; R true,z1z (n) represents the real space distance that the pseudo-range measurement signal has passed at the nth moment, in meters; z1z (n) represents the ionospheric delay of the pseudo-range measurement signal at the nth moment, in meters; T duiliu,z1z (n) represents the tropospheric delay of the pseudo-range measurement signal at the nth moment, in meters; c represents the speed of light, in meters per second; δt s (n) represents the clock difference between the first device and the system time at the nth moment, in seconds; δt z (n) represents the clock difference between the second device and the system time at the nth moment, in seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudo-range measurement signal at the nth moment, in meters; X z1 (n) represents the pseudo-range measurement signal hardware device delay at the nth moment, in meters. The pseudo-range measurement signal hardware device delay includes the pseudo-range measurement signal transmission delay and the pseudo-range measurement signal reception delay.

18. A satellite navigation system, characterized in that: include: The dual-frequency time synchronization system according to any one of claims 1 to 9, 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, all of which are communicatively connected to the satellite; The earth station obtains the orbital parameters of the corresponding satellite 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; Part of the third device constitutes a satellite orbit determination system, which is used to monitor and process the orbit of the satellite to obtain satellite orbit parameters; Part of the third devices constitutes a satellite-ground time synchronization system for performing time monitoring on each of the satellites.

19. The satellite navigation system according to claim 18, 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.

20. An inter-station time synchronization system, characterized in that: include: The satellite navigation system according to claim 18 or 19; Wherein, when there are at least two earth stations, at least two earth stations achieve time synchronization with each other by exchanging data through communication.

21. An inter-station time synchronization system, characterized in that: include: The dual-frequency time synchronization system according to any one of claims 1 to 9; When there are at least two first devices or second devices, at least two first devices or second devices achieve time synchronization with each other by exchanging data through communication.

22. A satellite positioning method, characterized in that: Applied to the satellite navigation system of claim 18 or 19, the method is performed by an earth station, and the method comprises: Acquiring orbital parameters of each satellite, wherein the orbital parameters of the satellite are determined by an orbit determination system; Determining coordinate information of a corresponding satellite based on the orbital parameters; Get the relative spatial distance between itself and each satellite; Based on the orbital parameters of each of the satellites and the relative spatial distance between each of the satellites, its own coordinate information is determined.

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