Ionospheric delay monitoring system and method, and ionospheric delay monitoring and time synchronization system and method

Abstract

The present application relates to the technical field of ionospheric delay monitoring, and discloses an ionospheric delay monitoring system and method, and an ionospheric delay monitoring and time synchronization system and method. The ionospheric delay monitoring system comprises a first device and a second device which are communicatively connected to each other; there are at least two paths of relayed ranging signals between the first device and the second device, each relayed ranging signal comprises at least three different carrier frequencies, and the relayed ranging signal comprises an uplink signal and a downlink signal; and the second device is configured to transmit the uplink signal, the first device is configured to receive the uplink signal and forward the uplink signal into the downlink signal, and the second device is configured to receive the downlink signal.

Description

Ionospheric delay monitoring system, ionospheric delay monitoring and time synchronization system, and method

[0001] Cross-reference to related applications

[0002] This application is based on

[0003] The application number is 202411245725.7, the application date is September 6, 2024, and the application title is "An Ionospheric Time Delay Monitoring and Orbit Determination System and Related Methods".

[0004] The application number is 202410661194.3, the application date is May 27, 2024, and the application title is "An Ionospheric Time Delay Monitoring and Orbit Determination System and Related Methods".

[0005] The application number is 202411429579.3, the application date is October 14, 2024, and the application title is "An Ionospheric Delay Monitoring and Time Synchronization System, Method and Application".

[0006] Chinese patent application number 202411068715.0, filed on August 6, 2024, entitled "An Ionospheric Delay Monitoring and Time Synchronization System and Method", has been filed.

[0007] The applicant claims priority to the Chinese patent application, the entire contents of which are incorporated herein by reference. Technical Field

[0008] This application relates to the field of space technology, and in particular to an ionospheric time delay monitoring system, an ionospheric time delay monitoring and time synchronization system and method. Background Technology

[0009] Ionospheric delay is a major positioning error term in satellite navigation and positioning, and it also has a significant impact on satellite communication and satellite remote sensing. Currently, ionospheric delay monitoring commonly uses multi-frequency ranging signals broadcast by navigation satellites. Two different ranging signals are selected for pseudorange measurement, and then the dual-frequency method is used to calculate the ionospheric TEC value (total number of electrons in the ionosphere).

[0010] In related technologies, when satellites and ground stations conduct radio communication, the radio signals experience time delays as they pass through the atmosphere, including ionospheric and tropospheric delays. When the signal carrier frequency is less than 30 GHz, the tropospheric delay is considered equal to the radio signal delay. However, the ionospheric delay is inversely proportional to the square of the carrier frequency and directly proportional to the total number of electrons in the ionosphere along the transmission path. The mathematical expression for the time delay caused by a radio signal crossing the ionosphere can be: dI = Q × TEC / (f * f);

[0011] Where: dI is the time delay (in meters) of the radio frequency signal (i.e., radio signal) as it traverses the ionospheric path of the satellite-to-ground connection; f is the carrier frequency of the radio signal (in Hertz); TEC is the total number of electrons in the ionosphere along the path between the satellite and the ground station (in electrons per square meter); and Q is the ionospheric time delay coefficient.

[0012] The International GPS Service (IGS) uses a large network of ground stations to observe dual-frequency pseudoranges, calculates the TEC values ​​of different ionospheric puncture points, and forms global ionospheric data for use by a wide range of users.

[0013] When using ionospheric data provided by IGS, users need to download the ionospheric delay for the corresponding time period from the IGS website, which involves time lag and even the risk of not being able to obtain the data. When using a dual-frequency method to obtain ionospheric delay, the satellite needs to add a payload to broadcast multi-frequency ranging signals, increasing the satellite payload complexity and satellite development costs.

[0014] The above content is only used to help understand the technical solution of this application and does not represent an admission that the above content is prior art. Summary of the Invention

[0015] This application combines the characteristics of satellite transponders with the technical characteristics of spread spectrum signals. Leveraging the ability of a satellite transponder to forward one signal into at least two, and the ability of at least two spread spectrum signals to reuse carrier frequencies, it creatively proposes a system and method for determining the total number of electrons in the ionosphere using transponding ranging signals. The main objective of this application is to provide an ionospheric delay monitoring system, aiming to solve the problems of poor real-time performance, high cost, and time lag in existing ionospheric delay monitoring technologies.

[0016] To achieve the above objectives, this application provides an ionospheric delay monitoring system, including a first device and a second device connected by communication; there are at least two forwarded ranging signals between the first device and the second device, and the forwarded ranging signals have at least three different carrier frequencies; the forwarded ranging signals include uplink signals and downlink signals; the second device is used to broadcast the uplink signals, the first device is used to receive the uplink signals and forward them as downlink signals, and the second device is used to receive the downlink signals.

[0017] Furthermore, to achieve the above objectives, this application also provides an ionospheric delay monitoring method, applied to the ionospheric delay monitoring system described in any embodiment of this application. The method is executed by a second device, and includes: broadcasting at least one uplink signal to a first device; acquiring at least two downlink signals forwarded by the first device based on the at least one uplink signal; wherein the at least one uplink signal and the at least two downlink signals constitute at least two forwarding ranging signals; synchronously measuring each of the forwarding ranging signals to obtain x forwarding ranging values, and selecting y forwarding ranging values ​​from the x forwarding ranging values; or, selecting y forwarding ranging signals from the x forwarding ranging signals for synchronous measurement to obtain y forwarding ranging values. The following steps are taken: 1. Transmitting ranging values; where x is a positive integer greater than or equal to 2, and 2 ≤ y ≤ x; 2. Representing each of the forwarding ranging values ​​using a forwarding ranging expression; 3. Dividing the y forwarding ranging values ​​into two groups, one group containing m forwarding ranging values ​​and the other group containing h forwarding ranging values, where 2 ≤ y ≤ x, m + h = y, and y, m, and h are all positive integers; 4. Calculating the average of the two groups of forwarding ranging values ​​represented by each forwarding ranging expression to obtain a first corrected average forwarding ranging value and a second corrected average forwarding ranging value; 5. Determining the total number of ionospheric electrons on the ranging signal path between the first device and the second device based on the first corrected average forwarding ranging value and the second corrected average forwarding ranging value.

[0018] The ionospheric delay monitoring method provided in this application involves a second device broadcasting two uplink signals to a first device, and the first device forwarding two downlink signals to the second device from the two uplink signals. The second device can then measure the first forwarded ranging signal to obtain a first forwarded ranging value and measure the second forwarded ranging signal to obtain a second forwarded ranging value. Furthermore, the second device uses a forwarded ranging expression to characterize both the first and second forwarded ranging values. Thus, the total number of ionospheric electrons along the ranging signal path between the first and second devices can be calculated using the two forwarded ranging values ​​characterized by these two expressions.

[0019] To achieve the above objectives, this application also provides an ionospheric delay monitoring and time synchronization system, including a first device and a second device connected in communication, and a computing device connected in communication with the first device and the second device respectively; there are m pseudorange ranging signals and h forwarded ranging signals between the first device and the second device, and the pseudorange ranging signals and the forwarded ranging signals have at least three different carrier frequencies; wherein, m+h≥3, and m and h are both positive integers greater than or equal to 1; and the pseudorange ranging signals and the forwarded ranging signals have at least three different carrier frequencies; wherein, the pseudorange ranging signals are broadcast by the first device and received by the second device, or broadcast by the second device and received by the first device; the forwarded ranging signals consist of uplink signals and downlink signals, the second device broadcasts the uplink signals, the first device receives the uplink signals and forwards them to form the downlink signals, and the second device receives the downlink signals.

[0020] Furthermore, to achieve the above objectives, this application also provides an ionospheric delay monitoring and time synchronization method, applied to the ionospheric delay monitoring and time synchronization system described in any embodiment of this application. The method is executed by a computing device and includes: when the pseudorange ranging signal is broadcast by a second device and received by a first device, obtaining m pseudorange ranging values ​​measured by the first device based on the communication results with the first device, and obtaining h forwarding ranging values ​​measured by the second device based on the communication results with the second device; when the pseudorange ranging signal is broadcast by the first device and received by the second device, obtaining h forwarding ranging values ​​and m pseudorange ranging values ​​measured by the second device based on the communication results with the second device; wherein, m+h≥3, and m and h are both positive integers; representing each pseudorange ranging value using a pseudorange ranging expression and representing each forwarding ranging value using a forwarding ranging expression; determining the total number of ionospheric electrons on the ranging signal path between the first device and the second device and the clock difference between the first device and the second device based on the m pseudorange ranging values ​​and the h forwarding ranging values.

[0021] The ionospheric delay monitoring and time synchronization system provided in this application allows the second device to determine not only the clock difference between the first and second devices, but also the ionospheric delay along the ranging signal path between them. When this time synchronization system is applied to satellite navigation, compared to existing technologies, it overcomes the errors caused by ionospheric and tropospheric delays, improves the accuracy of the determined clock difference, enhances navigation accuracy, and offers the advantage of strong real-time performance. Attached Figure Description

[0022] Figure 1 is a schematic diagram of the structure of the ionospheric time delay monitoring system according to an embodiment of this application;

[0023] Figure 2 is a structural block diagram of a first device and a second device according to one embodiment of this application;

[0024] Figure 3 is a schematic diagram of an ionospheric delay monitoring and time synchronization system according to one embodiment of this application;

[0025] Figure 4 is a structural block diagram of a satellite and a user station according to one embodiment of this application;

[0026] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] This application creatively proposes a system and calculation method for obtaining the total number of electrons in the ionosphere by organically integrating the relay ranging signal and the satellite transponder of the first device. To achieve the function of this application, the second device broadcasts at least one uplink signal, the satellite transponder forwards the at least one uplink signal into at least two downlink signals with different carrier frequencies, the second device measures the at least two relay ranging signals to obtain at least two relay ranging values, and uses the at least two relay ranging values ​​to calculate the total number of electrons in the ionosphere.

[0029] The parameters involved in the embodiments of this application are explained in a unified manner below:

[0030] m represents the number of forwarded ranging values ​​in the first group; k represents the number of forwarded ranging values ​​in the first group; h represents the number of forwarded ranging values ​​in the second group; j represents the number of forwarded ranging values ​​in the second group; y represents the total number of forwarded ranging values ​​selected; x represents the total number of forwarded ranging signals or forwarded ranging values.

[0031] dL(n) represents the forwarding ranging difference, in meters; L 1,mean (n) represents the first corrected average forwarding ranging value, in meters; L 2,mean (n) represents the second corrected average forwarding ranging value, in meters; L zi (n) represents the forwarding ranging value of number i at time n, in meters; R true,ziu (n) represents the actual spatial distance traversed by the uplink signal numbered i at time n, i.e., the satellite-to-ground spatial distance, in meters; R true,zid(n) represents the actual spatial distance traversed by the downlink signal numbered i at time n, i.e., the satellite-to-ground spatial distance, in meters; ziu (n) represents the ionospheric delay of the uplink signal numbered i at time n, in meters; zid (n) represents the ionospheric delay of the downlink signal numbered i at time n, in meters (T). duiliu,ziu (n) represents the tropospheric delay of the uplink signal numbered i at time n, in meters. ； T duiliu,zid (n) represents the tropospheric delay of the downlink signal numbered i at time n, in meters; Y i (n) represents the hardware device delay of forwarding the ranging signal numbered i at time n, in meters. The hardware device delay includes the transmission delay of the second device for the uplink signal numbered i, the forwarding delay of the first device when forwarding the downlink signal numbered i, and the reception delay of the second device when receiving the downlink signal numbered i.

[0032] L z1 (n), L z2 ( n R represents the relay ranging value numbered 1 and 2 at time n, in meters; true,z1u ( n ), R true,z2u (n) represents the actual spatial distance traversed by the uplink signals numbered 1 and 2 at time n, i.e., the satellite-to-ground spatial distance, in meters; R true,z1d (n), R true,z2d (n) represents the actual spatial distance traversed by downlink signals numbered 1 and 2 at time n, i.e., the satellite-to-ground spatial distance, in meters; z1u (n), I z2u (n) represents the ionospheric delay of the uplink signals numbered 1 and 2 at time n, in meters; z1d (n), I z2d (n) represents the ionospheric delay of the downlink signals numbered k and j at time n, in meters (T). duiliu,z1u (n), T duiliu,z2u (n) represents the tropospheric delay of the uplink signals numbered 1 and 2 at time n, in meters (T). duiliu,z1d (n) 、 T duiliu,z2dY1(n) represents the tropospheric delay of downlink signals numbered 1 and 2 at time n, in meters; Y2(n) represents the hardware device delay of forwarding ranging signals numbered 1 and 2 at time n, in meters. The hardware device delay includes the transmission delay of the second device for the uplink signals numbered 1 and 2, the forwarding delay of the first device when forwarding the downlink signals numbered 1 and 2, and the reception delay of the second device when receiving the downlink signals numbered 1 and 2.

[0033] Q ion The ionospheric delay coefficient is represented by TEC(n), which represents the total number of electrons in the ionosphere along the ranging signal path between the first and second devices at time n, in electrons per square meter.

[0034] f zku (n) represents the carrier frequency of the uplink signal numbered k at time n, in Hertz; f zkd (n) represents the carrier frequency of the downlink signal numbered k at time n, in Hertz; f zju (n) represents the carrier frequency of the uplink signal numbered j at time n, in Hertz; f zjd (n) represents the carrier frequency of the downlink signal numbered j at time n, in Hertz;

[0035] f z1u (n) represents the carrier frequency of the uplink signal numbered 1 at time n, in Hertz; f z1d (n) represents the carrier frequency of the downlink signal numbered 1 at time n, in Hertz; f z2u (n) represents the carrier frequency of the uplink signal numbered 2 at time n, in Hertz; f z2d (n) represents the carrier frequency of the downlink signal numbered 2 at time n, in Hertz;

[0036] Special note: Q ion The ionospheric time delay coefficient is published by certain international organizations. With in-depth research on ionospheric time delay, the coefficient has become increasingly accurate. Previously, the ionospheric time delay coefficient was 40.28, 40.30, and currently it is 40.309. More precise coefficients may be available in the future. This application does not impose any specific limitations on the ionospheric time delay coefficient and uses the latest published value. In this embodiment, Q... ion The value is 40.309.

[0037] ρ z,1,a (n), ρ z,2,a (n) represents the first and second corrected pseudorange values ​​at time n, in meters; ρ z,1 (n), ρ z,2(n) represents the first and second pseudorange values ​​at time n, in meters; R true,z,1 (n), R true,z,2 (n) represents the actual spatial distance traversed by the first and second pseudorange ranging signals at time n, in meters; z,1 (n), I z,2 (n) represents the ionospheric delay of the first and second pseudorange ranging signals at time n, in meters (T). duiliu,z,1 (n), T duiliu,z,2 (n) represents the tropospheric delay of the first and second pseudorange ranging signals at time n, in meters; X z,1 (n), X z,2 ( n The denoted δt represents the hardware delay of the first and second pseudorange ranging signals at time n, in meters. This hardware delay includes the transmission delay and reception delay of both the first and second pseudorange ranging signals. s (n) represents the clock difference of the first device relative to the system time at time n, in seconds; δt z (n) represents the clock difference of the second device relative to the system time at time n, in seconds; sagnac zz (n) represents the Sagnac effect delay of the pseudorange ranging signal at time n, in meters;

[0038] L z,1,a (n), L z,2,a (n) represent the first and second corrected forwarding ranging values ​​at time n, respectively, in meters; L z,1 (n), L z,2 (n) represent the first and second relay ranging values ​​at time n, respectively, in meters; R true,zu,1 (n), R true,zu,2 (n) represents the actual spatial distance traversed by the uplink signals of the first and second forwarding ranging signals at time n, respectively, in meters; R true,zd,1 (n), R true,zd,2 (n) represents the actual spatial distance traversed by the downlink signals of the first and second relay ranging signals at time n, respectively, in meters; I zu,1 (n), I zu,1 (n) represents the ionospheric delay of the uplink signals of the first and second relay ranging signals at time n, respectively, in meters; I zd,1 ( n ), I zd,1(n) represents the ionospheric delay of the downlink signals of the first and second relay ranging signals at time n, respectively, in meters (T). duiliu,zu,1 (n), T duiliu,zu,2 (n) represents the tropospheric delay of the uplink signals of the first and second relay ranging signals at time n, respectively, in meters (T). duiliu,zd,1 (n), T duiliu,zd,2 (n) represents the tropospheric delay of the downlink signals of the first and second relay ranging signals at time n, respectively, in meters; Y z,1 (n), Y z,2 (n) represents the hardware device delay of the first forwarded ranging signal and the second forwarded ranging signal at time n, respectively, in meters. The hardware device delay of the forwarded ranging signal includes the transmission delay of the uplink signal of the first forwarded ranging signal and the second forwarded ranging signal, the forwarding delay of the downlink signal of the first forwarded ranging signal and the second forwarded ranging signal, and the reception delay of the downlink signal of the first forwarded ranging signal and the second forwarded ranging signal.

[0039] dL m2 (n) represents the forwarding ranging difference at time n, in meters;

[0040] f z,1 (n), f z,2 (n) represents the carrier frequencies of the first and second pseudorange ranging signals at time n, in Hertz; f zu,1 (n), f zu,2 ( n f represents the carrier frequency of the uplink signal of the first and second forwarding ranging signals at time n, respectively, in Hertz; zd,1 (n), f zd,2 (n) represents the carrier frequency of the downlink signal of the first forwarding ranging signal and the second forwarding ranging signal at time n, respectively, in Hertz.

[0041] Furthermore, it should be noted that in this embodiment, since only two forwarding ranging signals are used for illustration, it can be understood that after dividing the two forwarding ranging values ​​into two groups, each group contains one forwarding ranging value. Then, the forwarding ranging values ​​of each group are averaged to obtain the first corrected average forwarding ranging value and the second corrected average forwarding ranging value.

[0042] To illustrate the method provided in this application more clearly and generally, this application uses two forwarding ranging signals with different carrier frequencies. Two forwarding ranging values ​​are selected from these signals for calculation as an example. In this case, x = 2, y = 2, m = 1, h = 1, x = y = m + h, as shown in Figure 1. Two forwarding ranging values ​​are obtained by synchronous measurement, thereby illustrating the specific implementation of the method in this application.

[0043] The ionospheric time delay monitoring system and related methods provided in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0044] Figure 1 is a schematic diagram of the structure of the ionospheric delay monitoring system according to an embodiment of this application. As shown in Figure 1, the system includes a first device 100 and a second device 200 connected in communication. The ionospheric delay monitoring system provided in this embodiment will be described in detail below.

[0045] The first device 100 forwards a first downlink signal to the second device 200 based on the received first uplink signal, and forwards a second downlink signal to the second device 200 based on the received second uplink signal. The first uplink signal and the first downlink signal constitute a first forwarding ranging signal, and the second uplink signal and the second downlink signal constitute a second forwarding ranging signal.

[0046] The second device 200 is used to broadcast a first uplink signal and a second uplink signal to the first device 100, receive a first downlink signal and a second downlink signal, and simultaneously measure the first and second relay ranging signals to obtain the first and second relay ranging values, as well as the total number of ionospheric electrons along the ranging signal path between the first device 100 and the second device 200 based on the first and second relay ranging values. For example, the first device may be a satellite, and the second device may be a monitoring station.

[0047] The ionospheric delay monitoring system provided in this application can be applied to aerospace systems, such as satellite navigation, satellite communication, satellite remote sensing, satellite reconnaissance, and meteorological satellites. This application embodiment uses the example of a second device determining the total number of ionospheric electrons along the ranging signal path for illustrative purposes only.

[0048] Specifically, this embodiment provides several signal transmission methods between the first device 100 and the second device 200. The first method is shown in Figure 1: the second device 200 broadcasts two uplink signals to the first device 100, and the first device 100 forwards two downlink signals to the second device 200. The second method is: the second device 200 broadcasts one uplink signal to the first device 100, and the first device 100 forwards it as two downlink signals with different carrier frequencies. The third method is: the two uplink signals broadcast by the second device 200 to the first device 100 have different carrier frequencies, and the first device forwards them using carrier frequency multiplexing technology as two downlink signals with the same carrier frequency.

[0049] In the aforementioned signal transmission methods, the ionospheric delay monitoring system has two forwarding ranging signals and two corresponding forwarding ranging values, thus allowing the determination of the total number of ionospheric electrons along the ranging signal path. The following description uses the example shown in Figure 1, where the second device 200 broadcasts two uplink signals to the first device and the first device 100 forwards two downlink signals to the second device, to illustrate the ionospheric delay monitoring system of this application.

[0050] In this embodiment, the first device 100 forwards the two received uplink signals into two downlink signals to the second device 200, thereby enabling the second device 200 to determine the total number of ionospheric electrons along the ranging signal path between the first device 100 and the second device 200 based on the two forwarded ranging signals. In this exemplary embodiment, since the first device 100 does not need to broadcast pseudorange ranging signals, there is no need to include a device for transmitting pseudorange ranging signals in the first device 100, thus simplifying the structure of the first device 100 and reducing its equipment cost. The monitoring system provided in this application embodiment can obtain the total number of ionospheric electrons in real time, achieving complete autonomous control and independence from constraints from other organizations.

[0051] In this exemplary embodiment, the second device 200 can send a first uplink signal and a second uplink signal to the first device 100 based on its own time-frequency system, i.e., local time. After acquiring the first uplink signal and the second uplink signal, the first device 100 performs frequency conversion processing and power amplification on the first uplink signal and the second uplink signal to obtain a first downlink signal and a second downlink signal with different carrier frequencies. Further, the first device 100 then forwards the first downlink signal and the second downlink signal to the second device 200.

[0052] The first uplink signal and the first downlink signal constitute the first forwarding ranging signal, and the second uplink signal and the second downlink signal constitute the second forwarding ranging signal. The second device 200 measures the first forwarding ranging signal to obtain the first forwarding ranging value, and measures the second forwarding ranging signal to obtain the second forwarding ranging value.

[0053] After obtaining the first and second relay ranging values, the second device 200 uses relay ranging expressions to characterize the first and second relay ranging values, respectively. Then, the total number of ionospheric electrons along the ranging signal path between the second device 200 and the first device 100 can be obtained through mathematical calculations using the two relay ranging expressions.

[0054] Furthermore, it is worth noting that the second device 200 in this embodiment can be one or more. When there are multiple second devices 200, each of the multiple second devices 200 can determine the total number of ionospheric electrons on the ranging signal path between itself and the first device 100.

[0055] In some implementations, the carrier frequency of the first uplink signal, the carrier frequency of the first downlink signal, the carrier frequency of the second uplink signal, and the carrier frequency of the second downlink signal are frequency-hopped on the time axis according to a preset frequency-hopping pattern.

[0056] Specifically, the carrier frequencies of the first uplink signal and the second uplink signal at different times, and the first downlink signal and the second downlink signal, are not the same fixed frequency, but different frequencies are used at different times. Therefore, frequency hopping can improve the signal's anti-interference ability and enhance its anti-interception ability.

[0057] Of course, the carrier frequency of the first uplink signal, the carrier frequency of the first downlink signal, the carrier frequency of the second uplink signal, and the carrier frequency of the second downlink signal can also remain unchanged for a long time, that is, the time interval between the two frequency hopping is infinite.

[0058] Additionally, it should be noted that the forwarding ranging signal described in the embodiments of this application refers to the modulated signal obtained by modulating a ranging code signal onto a carrier signal. In some specific embodiments, the ranging code can be a pseudo-code, a weil code, an M code, etc., and this application does not impose any special limitation on the specific ranging code used. Furthermore, it is understood that the forwarding ranging signal described in the embodiments of this application is a spread spectrum signal. When multiple spread spectrum signals are transmitted and received, the relationship between the carrier frequency and the ranging code is processed according to spread spectrum communication technology and code division multiple access communication technology, which will not be elaborated here.

[0059] For details regarding the process by which the second device 200 determines the total number of ionospheric electrons along the ranging signal path between itself and the first device 100, please refer to the description of the subsequent method embodiments, which will not be elaborated here.

[0060] Figure 2 is a structural block diagram of a first device and a second device according to one embodiment of the present application. As shown in Figure 2, in some embodiments, the first device 100 may include a repeater 101 and a first time-frequency device 103, wherein the first time-frequency device 103 provides a time-frequency signal to the repeater 101, and the repeater 101 can be used to receive a first uplink signal and a second uplink signal, and after performing frequency conversion processing and power amplification on the first uplink signal, forward a first downlink signal to the second device 200, and after performing frequency conversion processing and power amplification on the second uplink signal, forward a second downlink signal to the second device 200.

[0061] Referring again to FIG2, in some embodiments, the second device 200 may include a forwarding ranging device 201, a processing device 202, and a second time-frequency device 203.

[0062] It should be noted that the second device 200 may include one or more forwarding ranging devices 201. Taking two forwarding ranging devices 201 as an example, in this embodiment, the two forwarding ranging devices 201 can be set independently or integrated into one hardware device, that is, one hardware device can implement the functions of two forwarding ranging devices 201. These are all within the protection scope of this application. Furthermore, it can be understood that the second device 200 shown in Figure 2 includes forwarding ranging devices 201, processing devices 202, and a second time-frequency device 203, which are modules divided according to function. Specifically, in hardware implementation, they can be implemented separately or integrated into one device; these are all within the protection scope of this application.

[0063] In an exemplary embodiment, the forwarding ranging device 201 may include a modulator, a mixer, a demodulator, an antenna, a data acquisition unit, etc. The modulator generates an intermediate frequency (IF) ranging code spread spectrum signal; the mixer mixes the IF ranging code spread spectrum signal to a radio frequency (RF) signal; the antenna transmits the RF signal to the first device 100 and receives the RF signal forwarded by the first device 100, which is then mixed to an IF signal by the mixer; the demodulator demodulates the received IF signal and obtains the forwarding ranging value through relevant mathematical operations; the data acquisition unit records and stores the forwarding ranging value. The forwarding ranging device 201 generates and broadcasts a first uplink signal and a second uplink signal; and receives a first downlink signal and a second downlink signal; the forwarding ranging device 201 determines a first forwarding ranging value based on the first forwarding ranging signal and a second forwarding ranging value based on the second forwarding ranging signal. The processing device 202 is communicatively connected to the relay ranging device 201. The processing device 202 receives the first relay ranging value and the second relay ranging value, and determines the total number of electrons in the ionosphere based on the first and second relay ranging values. The second time-frequency device 203 can provide time-frequency signals to the relay ranging device 201.

[0064] In some embodiments, the second device 200 includes at least two forwarding ranging devices 201; when there are two forwarding ranging devices 201, one forwarding ranging device 201 receives a first downlink signal and determines a first forwarding ranging value based on the first forwarding ranging signal, and the other forwarding ranging device 201 receives a second downlink signal and determines a second forwarding ranging value based on the second forwarding ranging signal, and the two forwarding ranging devices are set to zero baseline.

[0065] It is worth noting that in this embodiment, when the second device 200 includes two forwarding ranging devices 201, the two forwarding ranging devices 201 are set to zero baseline. This ensures that the first forwarding ranging signal and the second forwarding ranging signal have the same transmission path, that is, the two forwarding ranging signals have the same atmospheric path.

[0066] It is worth noting that the zero baseline setting mentioned in this application does not mean that the distance between two relay ranging devices is zero. Rather, it means that the distance between the two relay ranging devices is set such that the uplink signals transmitted and the downlink signals received by each relay ranging device follow approximately the same spatial path. As the distance between the two relay ranging devices decreases, eventually becoming one device, the approximation gradually becomes identical, resulting in the same tropospheric delay and the same total number of ionospheric electrons. This application can calculate this total number of ionospheric electrons. Of course, when there are multiple relay ranging devices, a zero baseline setting is applied across all of them.

[0067] In some embodiments, when the second device 200 includes two relay ranging devices 201, the two relay ranging devices 201 use at least one time-frequency system. When the two relay ranging devices 201 use the same time-frequency system, the two relay ranging devices 201 perform measurements at the same time to obtain two relay ranging values ​​at the same time.

[0068] It is worth noting that at least one time-frequency system in the embodiments of this application may include multiple clocks (crystal oscillators or atomic clocks) or a single clock (crystal oscillator or atomic clock). Generally, using a single clock is recommended. When the time-frequency system includes multiple clocks (crystal oscillators or atomic clocks), the multiple clocks provide time-frequency signals to the multiple relay ranging devices 201 respectively. In practical use, the preset time interval can be set to, for example, 1 second, and the two relay ranging devices 201 perform measurements at the rising or falling edge of their respective 1PPS (1 Pulse Per Second) signals. Preferably, it is generally recommended to use a single clock to synchronously measure the relay ranging signals at the rising or falling edge of the same 1PPS signal.

[0069] In some embodiments, the repeater 101 of the first device 100 has a forwarding delay, and the forwarding ranging device 201 of the second device 200 has a transmission delay and a reception delay; wherein, the forwarding delay is transmitted through an additional communication link, or the processing device 202 has a preset forwarding delay, transmission delay and reception delay.

[0070] It should be noted that the forwarding delay of repeater 101 refers to the delay generated when the first device 100 receives the first uplink signal and the second uplink signal sent by the second device 200 and forwards the first uplink signal and the second uplink signal to obtain the corresponding first downlink signal and the second downlink signal.

[0071] Furthermore, the transmission delay of the relay ranging device 201 refers to the delay incurred by the relay ranging device 201 during the process of sending the first uplink signal and the second uplink signal to the first device 100. The reception delay of the relay ranging device 201 refers to the delay incurred by the relay ranging device 201 during the process of receiving the first downlink signal and the second downlink signal sent by the first device 100.

[0072] In this exemplary embodiment, the forwarding delay of the repeater 101 can be transmitted between the second device 200 and the first device 100 via an additional communication link. For example, the first device 100 may be equipped with a telemetry unit, and the forwarding delay of the repeater 101 can be transmitted through telemetry signals broadcast by the telemetry unit; or, the forwarding delay of the repeater 101 can be transmitted to the second device 200 through other user-defined communication link signals. This application does not specifically limit which signal is used to transmit the forwarding delay of the repeater 101. Alternatively, since the variation in the forwarding delay of the repeater 101 is very small and known, the known forwarding delay of the repeater 101 can be treated as a constant, and thus, in actual use, the forwarding delay can also be preset in the processing device 202 of the second device 200.

[0073] In some embodiments, the ionospheric delay monitoring system may further include a central station, which is communicatively connected to the second device. The central station can acquire monitoring parameters of the second device based on the communication results with the second device. Specifically, the central station may be located on the ground or integrated into the first device. The second device and the central station can communicate directly; for example, in a city, the second device and the central station can communicate directly via a 4G or 5G network. Alternatively, the second device can also communicate with the central station through the first device. For example, at sea or in a desert, both the central station and the second device can communicate directly through the first device, thus enabling communication between the second device and the central station through the first device.

[0074] The second device 200 in this embodiment can be a base station, radar, etc. Furthermore, the number of second devices 200 in this embodiment can be one or more (for example, at least one second device includes monitoring station 1 to monitoring station n, where n is an integer greater than or equal to 1). For example, by deploying multiple second devices 200 covering the globe, the entire country, or different cities, each second device 200 can monitor the ionospheric delay within its coverage area. Each second device 200 communicates with a central station to send the ionospheric delay of its respective monitoring area to the central station, thereby allowing the central station to obtain the ionospheric delay at different locations globally or nationwide. When performing navigation or remote sensing monitoring, the corresponding equipment manufacturers or users can obtain the corresponding ionospheric delay based on their own regional location for position correction, improving navigation and positioning accuracy.

[0075] Based on the above embodiments, this application also provides an ionospheric delay monitoring method. The ionospheric delay monitoring method provided in this application determines the total number of ionospheric electrons on the ranging signal path between the first device and the second device by forwarding ranging signals through two channels. This ionospheric delay monitoring method can be applied to the ionospheric delay monitoring system described in any of the above embodiments, and the ionospheric delay monitoring method can be executed by the second device.

[0076] The method for calculating the total number of electrons in the ionosphere provided in this application involves y transponder ranging values, where y is at least 2 and at most x. These y transponder ranging values ​​are divided into two groups: one group has m transponder ranging values, and the other group has h transponder ranging values, where y = m + h. Each group of transponder ranging values ​​is first averaged to obtain a corrected average transponder ranging value. The difference between the two corrected average transponder ranging values ​​is then calculated to obtain the total number of electrons in the ionosphere.

[0077] To illustrate the use of this method, here x=2, y=2, m=1, h=1, and there are two average forwarding ranging values. These two values ​​are selected for calculation and divided into two groups. The first group has only one forwarding ranging value, and the corrected average is the value itself minus the hardware latency. The second group also has only one forwarding ranging value, and the corrected average is the value itself minus the hardware latency. Then, the total number of electrons in the ionosphere is calculated based on the two corrected average forwarding ranging values.

[0078] It should be noted that because the ranging relay equipment is set to zero baseline, the two ranging relay signals traverse the same atmospheric layers, resulting in identical satellite-to-ground spatial distances and identical tropospheric delays. Ionospheric delays differ due to the different carrier frequencies. That is, the tropospheric delays of the two ranging relay signals are identical, therefore equations (11) and (12) hold: R true,z1u (n)=R true,z2u (n)=R true,z1d (n)=Rtrue,z2d (n) (11); T duiliu,z1u (n)=T duiliu,z2u (n)=T duiliu,z1d (n)=T duiliu,z2d (n) (12);

[0079] When there are x forwarded ranging signals, the uplink and downlink signals of the x forwarded ranging signals experience equal spatial distances and equal tropospheric delays.

[0080] It should also be noted that in this embodiment, both the tropospheric delay and the ionospheric delay are unknowns. When calculating the total number of ionospheric electrons on the ranging signal path, the tropospheric delay is eliminated due to the zero baseline setting.

[0081] In some embodiments, the ionospheric time delay monitoring method may include the following steps:

[0082] Step 910: Broadcast at least one uplink signal to the first device;

[0083] Step 920: Obtain at least two downlink signals forwarded by the first device based on the at least one uplink signal; wherein the at least one uplink signal and the at least two downlink signals constitute at least two forwarding ranging signals;

[0084] Step 930: Synchronously measure each of the aforementioned forwarding ranging signals to obtain x forwarding ranging values, and select y forwarding ranging values ​​from the x forwarding ranging values; or, select y forwarding ranging signals from the x forwarding ranging signals for synchronous measurement to obtain y forwarding ranging values; where x is a positive integer greater than or equal to 2, and 2≤y≤x;

[0085] Step 940: Characterize each of the forwarding ranging values ​​using the forwarding ranging expression;

[0086] Step 950: Divide the y forwarding ranging values ​​into two groups, one group including m forwarding ranging values ​​and the other group including h forwarding ranging values, where 2≤y≤x, m+h=y, m and h are both greater than or equal to 1, and y, m and h are all positive integers;

[0087] Step 960: Calculate the mean of the two sets of forwarding ranging values ​​represented by each forwarding ranging expression to obtain the first corrected average forwarding ranging value and the second corrected average forwarding ranging value;

[0088] Step 970: Determine the total number of ionospheric electrons on the ranging signal path between the first device and the second device based on the first corrected average forwarding ranging value and the second corrected average forwarding ranging value.

[0089] Among them, the carrier frequencies of the first uplink signal, the first downlink signal, the second uplink signal, and the second downlink signal in the two forwarding ranging signals are different from each other or partially the same.

[0090] For example, the carrier frequencies of the first uplink signal and the second uplink signal are the same, while the carrier frequencies of the first downlink signal and the second downlink signal are different. Alternatively, the carrier frequencies of the first downlink signal and the second downlink signal are the same, while the carrier frequencies of the first uplink signal and the second uplink signal are different.

[0091] In step 930, two forwarding ranging values ​​(y = 2) are obtained. The second device measures the first forwarding ranging signal to obtain the first forwarding ranging value, and measures the second forwarding ranging signal to obtain the second forwarding ranging value. After obtaining the two forwarding ranging values, in step 940, the second device can use the forwarding ranging expression to represent the first forwarding ranging value and the forwarding ranging expression to represent the second forwarding ranging value.

[0092] In an exemplary embodiment, the second device can obtain the formula expression for the first and second forwarding ranging values ​​of this embodiment based on the forwarding ranging value numbered i among the y forwarding ranging values ​​shown in formula (1), where i is 1 and 2 respectively. zi (n)=R true,ziu (n)+R true,zid (n)+I ziu (n)+I zid (n)+T duiliu,ziu (n)+T duiliu,zid (n)+Y i (n) (1);

[0093] The second device can characterize the first forwarding ranging value using the forwarding ranging expression shown in formula (1-1): 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)+Y1(n) (1-1);

[0094] The second forwarding ranging value is characterized by the forwarding ranging expression shown in formula (1-2) below: L z2 (n)=R true,z2u (n)+R true,z2d (n)+I z2u (n)+I z2d (n)+Tduiliu,z2u (n)+T duiliu,z2d (n)+Y2(n) (1-2);

[0095] It is worth noting that in the embodiments of this application, when using the forwarding ranging expression to characterize the forwarding ranging value, the forwarding ranging expression does not include the Sagnac effect delay. This is because the Sagnac effect delay of the uplink signal and the Sagnac effect delay of the downlink signal have opposite signs, and their absolute values ​​differ very little. Therefore, these two Sagnac effect delays can be approximately canceled out, and thus the Sagnac effect delay term is not reflected in the forwarding ranging expression. Of course, in other embodiments of this 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 can be added to the forwarding ranging expression to achieve better ionospheric delay monitoring accuracy. These are all within the protection scope of this application.

[0096] In this embodiment of the application, the second device can obtain the total number of ionospheric electrons between the first device and the second device by performing mathematical calculations in subsequent steps using the forwarding ranging values ​​represented by the two forwarding ranging expressions.

[0097] As mentioned above, the first and second forward ranging signals contain the same tropospheric delay. Therefore, in subsequent steps, the second device uses the two forward ranging values ​​to determine the total number of ionospheric electrons between the first and second devices.

[0098] Steps 950 and 960 involve grouping the two forwarding ranging values ​​obtained in the preceding steps and calculating the corrected average forwarding ranging value represented by the forwarding ranging expression. For example, when x = 2, which represents the first forwarding ranging value and the second forwarding ranging value, in this step, all forwarding ranging values ​​are selected, x = y = 2. The first forwarding ranging value can be divided into the first group, and the first corrected average forwarding ranging value can be calculated. The second forwarding ranging value can be divided into the second group, and the second corrected average forwarding ranging value can be calculated.

[0099] In an exemplary embodiment, when calculating the total number of electrons in the ionosphere using two relay ranging signals, step 960 may specifically include the following process:

[0100] Step 960: Since this application embodiment uses two forwarding ranging values ​​as an example for illustration, the two forwarding ranging values ​​are divided into two groups, with one forwarding ranging value in each group. Therefore, the first corrected average forwarding ranging value calculated using formula (2) is as shown in formula (2-1):

[0101] At this point, m = 1. L 1,mean (n)=L z1(n)-Y1(n)=R true,z1u (n)+R true,z1d (n)+I z1u (n)+I z1d (n)+T duiliu,z1u (n)+T duiliu,z1d (n) (2-1);

[0102] The second average forwarding ranging value calculated using formula (3) is shown in formula (3-1):

[0103] At this point, h = 1, y = 2. L 2,mean (n)=L z2 (n)-Y2(n)=R true,z2u (n)+R true,z2d (n)+I z2u (n)+I z2d (n)+T duiliu,z2u (n)+T duiliu,z2d (n) (3-1);

[0104] Step 970 may specifically include the following process:

[0105] Step 971: Determine the forwarding ranging difference using the first corrected average forwarding ranging value and the second corrected average forwarding ranging value.

[0106] Step 972: Determine the total number of ionospheric electrons on the ranging signal paths of the first and second devices based on the forwarding ranging difference.

[0107] In an exemplary embodiment, when calculating the total number of electrons in the ionosphere using two relay ranging signals, step 970 may specifically include the following process:

[0108] The forwarding ranging difference is determined using the first corrected average forwarding ranging value and the second corrected average forwarding ranging value;

[0109] The total number of ionospheric electrons on the ranging signal paths of the first device and the second device is determined based on the aforementioned forwarding ranging difference; wherein, the second device calculates the difference between the first corrected average forwarding ranging value and the second corrected average forwarding ranging value according to the formula (5) for calculating the forwarding ranging difference, and at the same time uses the zero baseline setting relationship of the forwarding ranging device shown in formulas (11) and (12) to obtain the forwarding ranging difference of this embodiment as shown in the following formula (5-1):

[0110] Then, the second device can determine the total number of ionospheric electrons on the ranging signal path between the first device and the second device, as shown in formula (6-1), based on the carrier frequency of each signal in the forwarding ranging signal, the preset ionospheric delay coefficient, and formula (6):

[0111] In this embodiment, when the ionospheric delay monitoring method is applied to the communication system described in the above embodiment, after the second device determines the total number of electrons in the ionosphere, the second device can interact with the central station based on the communication link, so that the central station can obtain the total number of electrons in the ionosphere of each second device. By summarizing the total number of electrons in the ionosphere of each second device and publishing it, the central station can improve the positioning and navigation accuracy of the first device.

[0112] Global Navigation Satellite Systems (GNSS) are currently the mainstream satellite navigation systems, with international systems including China's BeiDou, the United States' GPS, Europe's Galileo, and Russia's GLONASS. A satellite navigation system is a very large and complex system, involving three main parts: operation and control, satellites, and users. It involves time synchronization between operation and control stations and satellites, time synchronization between operation and control stations, satellite orbit determination technology, and user positioning and timing applications. The operation and control part monitors the satellite's atomic clock time to ensure accuracy and reliability, and also determines the satellite's orbit and provides ephemeris for user use. The satellite part is the carrier that directly provides services to users, broadcasting three pseudorange signals containing satellite ephemeris messages. Users obtain pseudorange values ​​by measuring the pseudorange signals and use these pseudorange values ​​and satellite ephemeris to achieve positioning and timing. The operation and control part of the satellite navigation system monitors satellite orbits and time to ensure long-term reliable operation, with time synchronization between the navigation satellite time and the operation and control system being a key focus. Besides navigation satellites, other space systems such as communication satellites and remote sensing satellites also require high-precision space-to-ground time synchronization. The key to the positioning accuracy of navigation satellite systems lies in determining the clock bias and its variation in the onboard atomic clock. Currently, the main methods for determining satellite clock bias are as follows:

[0113] 1. Single-path ranging method: This method uses the measured pseudorange value and the distance between the satellite and the geostationary station obtained from orbital positioning. Subtracting the distance value from the pseudorange value yields the satellite clock difference. This method requires knowledge of precise ionospheric delay, tropospheric delay, and other parameters. 2. GPS reverse positioning method: The basic principle of this method is as follows: Four time-synchronized ground stations simultaneously receive pseudorange signals from a satellite, obtaining four pseudorange observations. The satellite's position coordinates and the clock difference between the satellite and the ground stations are calculated using the GPS positioning equation. The time synchronization accuracy obtained by this method is highly dependent on the geometric distribution of the stations and the time synchronization accuracy between stations. It also requires overcoming the tropospheric delay of the signal. 3. Two-way pseudorange measurement method: The working principle of two-way pseudorange time synchronization is based on the fact that the signal propagation paths between the satellite and the ground are exactly the same, with the same tropospheric delay, but different ionospheric delays. Therefore, the clock difference is the difference in the measured pseudoranges divided by the speed of light c, or the difference in the time of the corresponding time marker detected by the satellite and the ground. The process involves both the satellite and the ground station transmitting signals under the control of their respective local clocks using their independent clock faces. After receiving the signals transmitted by the other, the receivers at the satellite and the ground station complete the pseudorange measurement with their local clocks. By comparing these two pseudorange values, the clock difference between the satellite and the ground station can be obtained. The obtained clock difference includes the ionospheric delay residual.

[0114] All of the above methods require satellite or ground receivers to receive and measure signals. When signals are transmitted between the satellite and ground ends, the receiver is affected by the ionosphere and troposphere at the far end, and multipath effects and electromagnetic environment at the near end. These far-end and near-end effects are collectively referred to as environmental segment effects. The tropospheric delay has the same delay for radio frequency signals of different carrier frequencies and can be estimated using models. However, the ionospheric delay varies with the carrier frequency and is a very common error factor, comprehensive, fundamental, and a global challenge. Besides environmental segment effects, the above methods also suffer from drawbacks such as the large number of observation devices, time synchronization errors being affected by satellite orbit determination accuracy and user coordinate accuracy, resulting in relatively poor time synchronization accuracy.

[0115] In some embodiments, in order to solve the above-mentioned technical problems, this application creatively proposes an ionospheric delay monitoring and time synchronization system and method that can obtain both the total number of electrons in the ionosphere and high-precision clock difference by organically integrating the forwarding ranging signal and the pseudorange ranging signal.

[0116] The system time mentioned in this application refers to the time during which a system generates and maintains itself, such as the system composed of the first and second devices in this application. In practical applications, the Chinese 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.

[0117] The ionospheric delay monitoring and time synchronization system provided in this application includes a first device and a second device connected in communication, and a computing device connected in communication with both the first device and the second device. The computing device can communicate with both the first device and the second device to obtain pseudorange ranging values ​​and forwarding ranging values.

[0118] When the first device broadcasts a pseudorange ranging signal, the second device receives the pseudorange ranging signal and measures the pseudorange ranging value. The second device also transmits and receives the ranging signal to obtain the transmitted ranging value. At this time, the computing device communicates with the second device to obtain the pseudorange ranging value and the transmitted ranging value. When the second device broadcasts a pseudorange ranging signal, the first device receives the pseudorange ranging signal and measures the pseudorange ranging value. The second device also transmits and receives the ranging signal to obtain the transmitted ranging value. At this time, the computing device communicates with the second device to obtain the transmitted ranging value and with the first device to obtain the pseudorange ranging value.

[0119] After obtaining the pseudorange and relay range values, the computing device executes the method of this application to calculate the total number of ionospheric electrons between the first device and the second device and the clock difference between the first device and the second device.

[0120] It is worth noting that in the embodiments of this application, the computing device may be integrated into the first device; or integrated into the second device; or it may be independent of the first device and the second device, that is, it may be an independent device.

[0121] The core function of this application is that the sum of the number of forwarded ranging signals and pseudorange ranging signals between the first device and the second device is greater than or equal to 3, corresponding to the pseudorange ranging value and the forwarded ranging value, the sum of which is greater than or equal to 3. Based on the pseudorange ranging value and the forwarded ranging value, the total number of ionospheric electrons between the first device and the second device and the clock difference between the first device and the second device are calculated. Therefore, this application focuses on describing the first device, the second device, and the signal structure between them, as well as the calculation methods for the total number of ionospheric electrons and the clock difference.

[0122] The following section will first describe the ionospheric delay monitoring and time synchronization system.

[0123] In this application, there are pseudo-range ranging signals and forwarded ranging signals between the first device and the second device. The sum of the number of pseudo-range ranging signals and the number of forwarded ranging signals is greater than or equal to 3, and the pseudo-range ranging signals and forwarded ranging signals have at least three different carrier frequencies.

[0124] The forwarded ranging signal consists 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 the downlink signal, and the second device receives the downlink signal. The pseudorange ranging signal is broadcast by the first device and received by the second device, or broadcast by the second device and received by the first device. Both the pseudorange ranging signal and the forwarded ranging signal are spread spectrum signals.

[0125] As described above, in the embodiments of this application, the pseudorange ranging signal can be broadcast by the first device and received by the second device, or it can be broadcast by the second device and received by the first device.

[0126] When the pseudorange ranging signal is broadcast by the second device, the uplink signal broadcast by the relay ranging device in the second device can be used as the pseudorange ranging signal. After the uplink signal reaches the first device, it is split into multiple signals, one of which is used as the pseudorange ranging signal, and the remaining signals are forwarded by the transponder. Alternatively, the uplink signal broadcast by the relay ranging device in the second device can be directly received by the first pseudorange ranging device of the satellite without being forwarded as a downlink signal by the transponder.

[0127] When the pseudorange signal is broadcast by the first device and received by the second device, the forwarding range signal is transmitted and received by the second device. Both the forwarding range signal and the pseudorange signal are received and measured by the second device, and the pseudorange value and the forwarding range value can be measured synchronously.

[0128] It should be noted that when the pseudorange ranging signal is broadcast by the second device and received by the first device, the relay ranging signal is transmitted and received by the second device itself. The relay ranging signal and the pseudorange ranging signal are received and measured by the second device and measured by the first device, respectively. It is impossible to achieve strict synchronous measurement. The first device and the second device need to have a rough time synchronization condition (the same is true for the two-way pseudorange measurement method, where the satellite and the ground station measure the pseudorange ranging signal sent by the other, which requires a rough time synchronization requirement between the satellite and the ground station). In this case, the pseudorange value measured by the first device and the relay ranging value obtained by the second measuring device can be regarded as synchronous measurement and calculated using the method of this application.

[0129] Furthermore, whether the pseudorange ranging signal is measured by the second device or the first device corresponds to two different types of systems. These two types of systems are identical in signal structure, system composition, and processing methods, except for the different directions of pseudorange ranging signal transmission and the pseudorange measuring equipment. Therefore, for the sake of simplicity, the following explanation will only focus on the case where the pseudorange ranging signal is broadcast by the first device.

[0130] When the first device broadcasts a pseudorange ranging signal, the number of pseudorange ranging signals is set to m, and the number of forwarded ranging signals is set to h, where m+h≥3. There are two simplest systems that satisfy this condition, referred to as the first simplest system and the second simplest system, respectively.

[0131] The first simplified system consists of a first device broadcasting two pseudorange ranging signals to a second device, and a relay ranging signal between the first and second devices. The downlink signal of the relay ranging signal can be multiplexed or not multiplexed with the carrier frequency of any one of the pseudorange ranging signals. The second simplified system consists of a first device broadcasting one pseudorange ranging signal to a second device, and two relay ranging signals between the first and second devices. The carrier frequency of the pseudorange ranging signal can be multiplexed or not multiplexed with the carrier frequency of any one of the downlink signals of the two relay ranging signals. In other words, the carrier frequencies of the two downlink signals of the two relay ranging signals and the carrier frequency of the pseudorange ranging signal can be multiplexed or not multiplexed.

[0132] The two simplest systems described above yield two pseudorange values ​​and two relay range values, respectively. The total number of ionospheric electrons between the first and second devices can be obtained using either the two pseudorange values ​​or the two relay range values. Therefore, the clock difference between the first and second devices can be obtained using the method provided in this application.

[0133] Adding one relay ranging signal to the first simplified system and one pseudorange ranging signal to the second system transforms both simplified systems into systems with the same two pseudorange ranging signals and two relay ranging signals. When both simplified systems have two pseudorange ranging signals and two relay ranging signals, they are completely identical, and the corresponding calculation methods are also the same. Furthermore, when there are even more pseudorange ranging signals and relay ranging signals, they constitute a single system.

[0134] Furthermore, the process of calculating the total number of ionospheric electrons using two pseudorange values ​​in the first simplified system has been described in related technologies. The process of calculating the clock difference after obtaining the total number of ionospheric electrons is similar to that in the second simplified system. Therefore, to more clearly and generally illustrate the method provided in this application, the process of calculating the total number of ionospheric electrons in the first simplified system will not be repeated here. Instead, the second simplified system will be used as an example for illustrative purposes, where the carrier frequencies of the signals are different, and two relay ranging values ​​and one pseudorange ranging value are obtained through synchronous measurement. This will illustrate the specific implementation of the method in this application. In this case, m = 1, h = 2.

[0135] Because of the preciousness of radio spectrum resources, time synchronization can be achieved using the least amount of carrier frequency resources when m=1, h=2, or m=2, h=1, which is cost-effective. Therefore, this case is used for explanation.

[0136] For ease of explanation, the uplink signals of the two forwarded ranging signals in the second simplified system are referred to as the first uplink signal and the second uplink signal, respectively; the downlink signals of the two forwarded ranging signals are referred to as the first downlink signal and the second downlink signal, respectively; and the pseudorange ranging signal is referred to as the first pseudorange ranging signal. Furthermore, the example of a computing device integrated into the second device is used for illustration. Since the computing device is integrated into the second device, i.e., the computing device is part of the second device, the functions implemented by the computing device will be described as part of the functions of the second device in the following descriptions unless otherwise specified.

[0137] Figure 3 is a schematic diagram of an ionospheric delay monitoring and time synchronization system according to an embodiment of this application. The system includes a first device 100 and a second device 200 connected by communication. The first device 100 forwards a first downlink signal and a second downlink signal to the second device 200 based on received first uplink and second uplink signals, and broadcasts a first pseudorange ranging signal to the second device 200. The first uplink signal and the first downlink signal constitute a first forwarded ranging signal, and the second uplink signal and the second downlink signal constitute a second forwarded ranging signal. The second device 200 is used to broadcast the first uplink signal and the second uplink signal to the first device 100, receive the first pseudorange ranging signal and the first downlink signal and the second downlink signal, and simultaneously measure the first forwarding ranging signal, the second forwarding ranging signal and the first pseudorange ranging signal to obtain the first forwarding ranging value, the second forwarding ranging value and the first pseudorange ranging value, and determine the total number of ionospheric electrons on the ranging signal path between the first device 100 and the second device 200 and the clock difference between the first device 100 and the second device 200 based on the first pseudorange ranging value, the first forwarding ranging value and the second forwarding ranging value.

[0138] As shown in Figure 3, fu and fd represent the satellite-to-ground communication link added between the user station and the satellite, which can be a remote control and telemetry signal.

[0139] In this embodiment, the first device 100 can be, for example, a satellite, and the second device 200 can be, for example, a user station. When the computing device is integrated into the user station, the user station determines the clock difference between the satellite and the user station, and the total number of ionospheric electrons on the ranging signal path between the satellite and the user station, so that the satellite can synchronize with the clock of the user station. Of course, in other embodiments, the first device 100 can also be a user station, and the second device 200 can be a satellite. Furthermore, the first device 100 described in this embodiment can also be a high-orbit device, and the second device 200 can be a low-orbit device, or both the first device 100 and the second device 200 can be low-orbit devices, as long as the two devices are located on opposite sides of the ionosphere, or one device is located inside the ionosphere and the other device is located outside the ionosphere, or both devices are located inside the ionosphere.

[0140] Of course, in other embodiments, the first device 100 and the second device 200 may both be located on the same side of the ionosphere, for example, both on the ground or both in space. In this case, the ionospheric delay is 0, and the clock difference between the first device 100 and the second device 200 can be determined by the time synchronization method described in the embodiments of this application.

[0141] This application embodiment only uses the example of the first device 100 being a satellite and the second device 200 being a user station for illustrative purposes. The time synchronization system provided in this application embodiment can be applied to aerospace systems, typically a space-to-ground system consisting of a user station and a satellite, where the user station monitors the clock difference between the satellite and the user station, as well as the ionospheric delay on the ranging signal path. Specific applications of the space-to-ground time synchronization system may include, for example, satellite navigation, satellite communication, satellite remote sensing, satellite reconnaissance, and meteorological satellites.

[0142] In this exemplary embodiment, the user station sends uplink signals (including a first uplink signal and a second uplink signal) to the satellite based on its own clock system, i.e., local time. After the satellite receives the uplink signal, it forwards the uplink signal to obtain downlink signals (i.e., the first downlink signal and the second downlink signal), and forwards the frequency-converted downlink signals to the user station.

[0143] The uplink signal and the downlink signal relayed by the satellite constitute the relay ranging signal. The user station can determine the relay ranging value based on this signal. For example, the first uplink signal and the first downlink signal constitute the first relay ranging signal, and the second uplink signal and the second downlink signal constitute the second relay ranging signal. The user station can determine the first relay ranging value based on the first signal and the second relay ranging value based on the second signal. In addition, the satellite also transmits pseudorange ranging signals to the user station based on its own clock system, i.e., local time. The user station receives and demodulates the pseudorange ranging signals to obtain the pseudorange ranging value. Therefore, the user station can calculate the clock difference between the satellite and the user station, and the total number of ionospheric electrons along the ranging signal paths of the user station and the satellite, based on the determined relay ranging value and pseudorange ranging value.

[0144] Furthermore, in this exemplary embodiment, the second device 200 synchronously measures one pseudorange ranging signal and two forward ranging signals at a preset time interval to obtain one pseudorange ranging value and two forward ranging values.

[0145] The pseudorange ranging signal and the forwarding ranging signal described in the embodiments of this application are both spread spectrum signals, and are processed according to spread spectrum communication technology, carrier frequency reuse technology and code division multiple access communication technology, which will not be elaborated here. For the sake of brevity and convenience, the forwarding ranging signal and the pseudorange ranging signal are collectively referred to as ranging signals.

[0146] The specific structures of the satellites and user stations in the embodiments of this application will be further described below.

[0147] Figure 4 is a structural block diagram of a satellite and a user station according to one embodiment of this application. Figure 4 shows the internal structure of the system when the pseudorange ranging signal is broadcast by the first device. As shown in Figure 4, in an exemplary embodiment, the satellite may include a transponder 101, a pseudorange generating device 102, and a first time-frequency device 103 connected in communication. The transponder 101 is used to receive a first uplink signal and a second uplink signal, perform frequency conversion processing and power amplification on the first uplink signal, and then forward a first downlink signal to the user station. The transponder 102 is also used to perform frequency conversion processing and power amplification on the second uplink signal and then forward a second downlink signal to the user station. The pseudorange generating device 102 is connected in communication with the transponder 101 and is used to generate and broadcast the first pseudorange ranging signal. The first time-frequency device 103 provides time-frequency signals to the transponder 101 and the pseudorange generating device 102.

[0148] It should be understood that the repeater 101 and pseudorange generator 102 described in the embodiments of this application can be set independently or integrated into a hardware device, that is, the functions of the repeater 101 and pseudorange generator 102 can be implemented through an integrated hardware device, or the repeater 101, pseudorange generator 102 and first time-frequency device 103 can be integrated. All of these are within the protection scope of this application.

[0149] It should be noted that in the embodiments of this application, the pseudorange generating device 102 and the repeater 101 are connected in a communication manner, that is, the two can achieve communication interaction. This can be that the two communicate directly, or that both are connected to a third-party device to achieve communication interaction. All of the above are within the protection scope of this application.

[0150] As shown in Figure 4, the user station may include a second pseudorange ranging device 202, a relay ranging device 201, a second time-frequency device 203, and a computing device 204. The second time-frequency device 203 provides time-frequency signals to the relay ranging device 201 and the second pseudorange ranging device 202.

[0151] The second pseudorange ranging device 202 processes the received first pseudorange ranging signal to obtain a first pseudorange ranging value; the forwarding ranging device 201 generates and broadcasts a first uplink signal and a second uplink signal, and receives a first downlink signal and a second downlink signal, and determines a first forwarding ranging value based on the first forwarding ranging signal and a second forwarding ranging value based on the second forwarding ranging signal; the computing device 204 receives the first pseudorange ranging value, the first forwarding ranging value, and the second forwarding ranging value through communication, and corrects them to obtain a first corrected pseudorange ranging value, a first corrected forwarding ranging value, and a second corrected forwarding ranging value. The system determines the total number of ionospheric electrons on the ranging signal path using the first corrected forwarding ranging value and the second corrected forwarding ranging value; and determines the clock difference between the first device 100 and the second device 200 based on the total number of ionospheric electrons, any corrected forwarding ranging value, and any corrected pseudorange ranging value; or, determines the total number of ionospheric electrons on the ranging signal path between the first device 100 and the second device 200 and the clock difference between the first device 100 and the second device 200 based on the first corrected forwarding ranging value, the second corrected forwarding ranging value, and the first corrected pseudorange ranging value.

[0152] Furthermore, it should be noted that the second pseudorange ranging device 202 and the forwarding ranging device 201 in the embodiments of this application can be set independently, or they can be integrated into a hardware device, that is, the functions of the second pseudorange ranging device 202 and the forwarding ranging device 201 can be implemented by a single hardware device, or the second pseudorange ranging device 202, the forwarding ranging device 201 and the second time-frequency device 203 can be integrated. All of these are within the protection scope of this application.

[0153] As described above, the pseudorange ranging signal can also be broadcast by a second device and received by a first device. In this case, the first device includes a first time-frequency device, a repeater, and a first pseudorange ranging device. The first time-frequency device is used to provide time-frequency signals to the repeater and the first pseudorange ranging device. The repeater is used to receive the uplink signal, perform frequency conversion and power amplification on the uplink signal, and then forward the downlink signal to the second device. The first pseudorange ranging device is communicatively connected to the repeater and is used to receive and measure the pseudorange ranging signal. The second device includes a second time-frequency device and a forwarding ranging device. The second time-frequency device is used to provide time-frequency signals to the forwarding ranging device. The forwarding ranging device is used to generate and broadcast the uplink signal, receive the downlink signal, and determine the forwarding ranging value based on the forwarding ranging signal, wherein a portion of the uplink signal broadcast by the forwarding ranging device is used as the pseudorange ranging signal. Furthermore, the first time-frequency device, the repeater, and the first pseudorange ranging device are integrated or separate, and / or the second time-frequency device and the repeater ranging device are integrated or separate.

[0154] In this case, the transmission delay of the relay ranging device can be measured in advance, and this delay can be pre-loaded into the computing device, which can then directly use this delay in subsequent calculations. Because the only difference between the first and second devices in this operating condition is the different methods of broadcasting the pseudorange ranging signal, resulting in corresponding differences in system structure, the specific functions of each component are similar to the structure shown in Figure 4. The specific structures of the first and second devices will be further described below using the system structure shown in Figure 4 as an example.

[0155] In an exemplary embodiment, the transponder ranging device 201 may include a modulator, a mixer, a demodulator, an antenna, a data acquisition unit, etc. The modulator generates an intermediate frequency (IF) spread spectrum signal; the mixer mixes the IF spread spectrum signal to a radio frequency (RF) signal; the antenna transmits the RF signal to the satellite and receives the RF signal transponded by the satellite; the antenna receives the RF signal and mixes it to an IF signal by the mixer; the demodulator demodulates the IF signal and obtains the transponder ranging value through ranging code correlation operations; the data acquisition unit records and stores the transponder ranging value. The second pseudorange ranging device 202 may include a demodulator, a receiving antenna, a data acquisition unit, etc. The receiving antenna receives the pseudorange ranging signal from the satellite and the second pseudorange ranging device 202 generates a pseudorange ranging value.

[0156] It is worth noting that in this embodiment of the application, a zero baseline is set between the second pseudorange ranging device 202 and the forwarding ranging device 201.

[0157] It is worth noting that the zero baseline setting mentioned in this application does not mean that the distance between the second pseudorange ranging device 202 and the relay ranging device 201 is zero. Rather, it means that the distance between them is set to ensure that the spatial paths traversed by each relay ranging signal and pseudorange ranging signal are approximately the same. As the distance between the second pseudorange ranging device 202 and the relay ranging device 201 becomes smaller and smaller, and they can be integrated into a single device, the approximation gradually becomes identical, resulting in the same tropospheric delay and the same total number of ionospheric electrons.

[0158] At this point, the first pseudorange ranging signal and the first and second relay ranging signals have the same transmission path. Thus, the atmosphere has the same path influence on the first pseudorange ranging signal and the first and second relay ranging signals. That is, the first pseudorange ranging signal and the first and second relay ranging signals have the same ionospheric and tropospheric paths, thereby eliminating the tropospheric delay in one pseudorange ranging signal and two relay ranging signals. Then, the total number of ionospheric electrons between the satellite and the user station can be specifically calculated using the ionospheric delay.

[0159] In an exemplary embodiment, the second device is the user station of this embodiment. The user station uses at least one second time-frequency device 203. Specifically, the second pseudorange ranging device 202 and the relay ranging device 201 of the user station use at least one second time-frequency device 203. It is worth noting that the at least one time-frequency system described in this application embodiment may include multiple clocks (crystal oscillators or atomic clocks) or one clock (crystal oscillator or atomic clock). When multiple clocks are included, one clock provides a clock signal for the second pseudorange ranging device 202, and the remaining clocks provide clock signals for the relay ranging device 201. In actual use, the preset time interval can be set to, for example, 1 second. The second pseudorange ranging device 202 and the relay ranging device 201 perform measurements at the rising or falling edge of their respective 1PPS (1 Pulse Per Second) signals. Preferably, it is generally recommended to use one clock to perform synchronous measurements of the pseudorange ranging signal and the relay ranging signal at the rising or falling edge of the same 1PPS signal. The first device is similar, with at least one first time-frequency device 103. When there are multiple time-frequency devices, one time-frequency device provides a time-frequency signal to the transponder 101, and another time-frequency device provides a time-frequency signal to the pseudorange generator 102 or the pseudorange measuring device.

[0160] The repeater 101 has a forwarding delay, and the pseudorange generator 102 has a transmission delay; the second pseudorange ranging device 202 has a receiving delay, and the repeater ranging device 201 has both a transmission delay and a receiving delay; wherein, the first pseudorange ranging signal carries the forwarding delay of the repeater 101 and the transmission delay of the pseudorange generator 102, or, the computing device 204 presets the forwarding delay of the repeater 101 and the transmission delay of the pseudorange generator 102.

[0161] The forwarding delay of transponder 101 refers to the delay incurred by the satellite in the process of forwarding the first uplink signal and the second uplink signal after receiving them from the user station to obtain the first downlink signal and the second downlink signal. The transmission delay of pseudorange generator 102 refers to the delay incurred by pseudorange generator 102 in the process of generating and transmitting the first pseudorange ranging signal.

[0162] The receiving delay of the second pseudorange ranging device 202 at the user station refers to the delay generated during the process of receiving the pseudorange ranging signal sent by the satellite and generating the pseudorange ranging value.

[0163] The user station's relay ranging device 201 has transmission delay and reception delay. Transmission delay refers to the delay from the generation of the uplink signal to its transmission by the antenna; reception delay refers to the delay in receiving the downlink signal and generating the relay ranging value.

[0164] It is worth noting that, in this exemplary embodiment, the satellite can transmit the relay delay of the transponder ranging signal and the transmission delay of the pseudorange ranging signal to the user station via any pseudorange ranging signal. Alternatively, the user station and the satellite can also use additional communication signals to transmit the relay delay of the transponder 101 and the transmission delay of the pseudorange ranging signal. For example, the satellite may be equipped with a telemetry unit, which can transmit the relay delay of the transponder 101 and the transmission delay of the pseudorange ranging signal via telemetry signals broadcast by the telemetry unit. Alternatively, the relay delay of the transponder 101 and the transmission delay of the pseudorange ranging signal can be transmitted to the user station via other user-defined communication signals. This application does not specifically limit the type of signal used to transmit the relay delay of the transponder 101 and the transmission delay of the pseudorange ranging signal.

[0165] Alternatively, since the changes in the signal forwarding delay of the transponder 101 and the transmission delay of the pseudorange ranging signal are very small or known, the signal forwarding delay of the transponder 101 and the transmission delay of the pseudorange ranging signal can be treated as known quantities. Therefore, in actual use, the signal forwarding delay of the transponder 101 and the transmission delay of the pseudorange ranging signal can be preset in the computing device 204.

[0166] By loading the forwarding delay and pseudorange ranging signal transmission delay into any pseudorange ranging signal and transmitting it to the user station, the existing signals between the satellite and the user station are fully utilized to transmit the forwarding delay and pseudorange ranging signal transmission delay. No additional communication signals are required, thus avoiding the occupation of additional communication resources, which can greatly reduce communication costs and save frequency resources.

[0167] In some embodiments, the user station and the satellite may have only one relay ranging signal and two pseudorange ranging signals; or, the user station and the satellite may have two relay ranging signals and one pseudorange ranging signal; or, the user station and the satellite may have one relay ranging signal and three pseudorange ranging signals; or, the user station and the satellite may have three relay ranging signals and one pseudorange ranging signal.

[0168] Furthermore, in this embodiment, the signal structure can be further simplified by multiplexing the carrier frequency of the signal. The example of the signal structure between the user station and the satellite will continue to be used for illustration. Alternatively, when there are two forwarding ranging signals and one pseudorange ranging signal between the user station and the satellite, the carrier frequency of the first downlink signal, the second downlink signal, and the pseudorange ranging signal can be multiplexed; this is the carrier frequency multiplexing mode of the second simplest system. Alternatively, when there are two forwarding ranging signals and one pseudorange ranging signal between the user station and the satellite, the carrier frequency of either the first downlink signal or the second downlink signal is multiplexed with the pseudorange ranging signal. Alternatively, when there are two forwarding ranging signals and two pseudorange ranging signals between the user station and the satellite, the carrier frequency of the first pseudorange ranging signal is multiplexed with the first downlink signal, and the carrier frequency of the second pseudorange ranging signal is multiplexed with the second downlink signal.

[0169] It should be understood that the above embodiments illustrate the signal structure between the user station and the satellite. In actual use, there may be other forms of signal structure and signal carrier frequency reuse, which will not be elaborated here.

[0170] Furthermore, in some embodiments, the carrier frequency of the forwarding ranging signal and the carrier frequency of the pseudorange ranging signal are both frequency-hopped according to a preset frequency-hopping pattern. Such frequency hopping can improve the signal's anti-interference capability and enhance its anti-interception capability.

[0171] In an exemplary embodiment, the ionospheric delay monitoring and time synchronization system provided in this application also has a communication function. The satellite uses a first uplink signal or a second uplink signal, as well as a first pseudorange ranging signal, to transmit data with the user station, or uses an additional communication signal to transmit data with the user station. Specifically, after receiving an uplink signal from any one of the forwarding ranging signals, the satellite splits it into two: one forwards downlink to the user station, and the other receives data uploaded by the user station. The satellite then uses any pseudorange ranging signal to transmit the data downlink to the user station, thereby realizing satellite-to-ground communication. Alternatively, an additional communication signal can be added to achieve data transmission between the satellite and the user station.

[0172] In an exemplary embodiment, the satellite can also send forwarding delay and pseudorange ranging signal transmission delay to the user station through an additional communication link. That is, in addition to the uplink signal link, downlink signal link, and pseudorange ranging signal link, the satellite and the user station also have an additional communication link (including the communication link uplink signal fu and the communication link downlink signal fd). The satellite transmits forwarding delay and pseudorange ranging signal transmission delay to the user station through this additional communication link.

[0173] As can be seen, satellites can transmit forwarding delay and pseudorange ranging signal transmission delay to user stations in various ways. This application does not impose any special restrictions on the specific transmission methods of forwarding delay and pseudorange ranging signal transmission delay.

[0174] In pseudorange ranging values, it is necessary to obtain the Sagnac effect delay of the satellite. The Sagnac effect delay requires the coordinates of the user station and the satellite. The coordinates of the satellite can be obtained from known satellite ephemeris, and the coordinates of the user station can be obtained from existing positioning methods. Thus, the coordinate information required by the method of this application embodiment is obtained, and the Sagnac effect delay is obtained.

[0175] No relativistic time delay term appears in the pseudorange measurement values. This is because, in reality, satellites in space have time and frequency systems to provide time and frequency. Based on relativity, it's easy to know that satellite clocks experience relativistic time delays due to relativity. Existing methods can be used to address this relativistic time delay in satellite clocks. For example, the satellite clock may have been adjusted before launch; after adjustment, it will have no relativistic time delay, just like clocks on the ground. For specific examples, refer to the relativistic practices of the BeiDou navigation satellite clock.

[0176] When the pseudorange signal is broadcast by the second device and received by the first device, based on the above embodiments, this application embodiment also provides a method for determining the pseudorange value, which is applied to the ionospheric delay monitoring and time synchronization system described in any of the above embodiments. The method for determining the pseudorange value is executed by the first device.

[0177] The method for determining the pseudorange value is as follows: receive m pseudorange signals broadcast by the second device; synchronously measure each pseudorange signal to obtain m pseudorange values, where m is a positive integer.

[0178] When the pseudorange ranging signal is broadcast by the first device and received by the second device, based on the above embodiments, this application also provides a method for determining the ranging value, applied to the ionospheric delay monitoring and time synchronization system described in any of the above embodiments. This method for determining the ranging value is executed by the second device. The method for determining the pseudorange ranging value is as follows:

[0179] Broadcast at least one uplink signal to the first device;

[0180] The first device acquires at least one downlink signal forwarded based on the at least one uplink signal, wherein the at least one uplink signal and the at least one downlink signal constitute h forwarding ranging signals;

[0181] Acquire m pseudorange ranging signals broadcast by the first device;

[0182] The forwarding ranging signal and the pseudo-range ranging signal are measured synchronously to obtain h forwarding ranging values ​​and m pseudo-range ranging values;

[0183] Where m+h≥3, and m and h are both positive integers.

[0184] It is particularly worth noting that when the pseudorange ranging signal is broadcast by the second device and received by the first device, or when the pseudorange ranging signal is broadcast by the first device and received by the second device, all h forwarded ranging values ​​need to be measured by the second device, and all of them must satisfy m+h≥3.

[0185] The above describes the specific process by which the system determines the pseudorange and forwarding range values ​​under two different pseudorange signal transmission methods. Regardless of the method, after obtaining the pseudorange and forwarding range values, the computing device acquires these values ​​through communication with the first and second devices, and further calculates the total number of ionospheric electrons and clock bias.

[0186] Based on the above embodiments, this application also provides an ionospheric delay monitoring and time synchronization method, which can be applied to the ionospheric delay monitoring and time synchronization system described in any of the above embodiments. For details regarding the device delays used in this method embodiment and their acquisition methods, please refer to the description of the above system embodiments; further details will not be repeated here. The method will now be described in detail.

[0187] In some embodiments, this application provides an ionospheric delay monitoring and time synchronization method, which is executed by a computing device and may include the following steps:

[0188] S110. When the pseudorange ranging signal is broadcast by the second device and received by the first device, m pseudorange ranging values ​​measured by the first device are obtained based on the communication results with the first device, and h forwarding ranging values ​​measured by the second device are obtained based on the communication results with the second device.

[0189] When the pseudorange ranging signal is broadcast by the first device and received by the second device, h forwarding ranging values ​​and m pseudorange ranging values ​​measured by the second device are obtained based on the communication results with the second device; where m+h≥3, and m and h are both positive integers;

[0190] S120. Each pseudorange value is represented by a pseudorange ranging expression and each forwarding ranging value is represented by a forwarding ranging expression.

[0191] S130. Based on the m pseudorange ranging values ​​and the h forward ranging values, determine the total number of ionospheric electrons on the ranging signal path between the device and the first device, as well as the clock difference between the device and the first device.

[0192] Specifically, step S130 can be: selecting a0 (2≤a≤m) from m pseudorange ranging values ​​and selecting β (1≤β≤h) from h forwarding ranging values ​​to determine the total number of ionospheric electrons on the ranging signal path between the device and the first device, as well as the clock difference between the device and the first device; or, selecting λ (1≤λ≤m) from m pseudorange ranging values ​​and selecting θ (2≤θ≤h) from h forwarding ranging values ​​to determine the total number of ionospheric electrons on the ranging signal path between the device and the first device, as well as the clock difference between the device and the first device.

[0193] This application includes two simplified systems and their corresponding methods. The first simplified system has two pseudorange values ​​and one transponder ranging value. The total number of ionospheric electrons can be calculated based on the two common pseudorange values, and then the clock error can be calculated based on any pseudorange value and any transponder ranging value. The second simplified system has one pseudorange value and two transponder ranging values. The total number of ionospheric electrons can be calculated based on the two transponder ranging values, and then the clock error can be calculated based on any pseudorange value and any transponder ranging value. Since there are only two unknowns, namely the total number of ionospheric electrons and the clock error between the satellite and the user station, both simplified systems can form a 2×2 matrix when calculated using the matrix method. When the matrix is ​​invertible, the two unknowns can be obtained, and the calculation methods are similar.

[0194] Therefore, to concisely and clearly explain the method of this application, only the calculation method corresponding to the second simplified system is used as an example. In this second simplified system, the pseudorange ranging signal can be specifically defined as the first pseudorange ranging signal, the uplink signal can be specifically defined as the first uplink signal and the second uplink signal, the downlink signal can be specifically defined as the first downlink signal and the second downlink signal, and correspondingly, the forwarding ranging signal can be specifically defined as the first forwarding ranging signal and the second forwarding ranging signal. At this time, m = 1, h = 2; for this specific case, λ = 1, θ = 2; the above method can be specifically defined as the following steps:

[0195] S110. When the pseudorange ranging signal is broadcast by the second device and received by the first device, one pseudorange ranging value measured by the first device is obtained based on the communication result with the first device, and two forwarding ranging values ​​measured by the second device are obtained based on the communication result with the second device.

[0196] When the pseudorange ranging signal is broadcast by the first device and received by the second device, one pseudorange ranging value and two forwarding ranging values ​​measured by the second device are obtained based on the communication results with the second device.

[0197] S120. The first pseudorange value is represented by a pseudorange ranging expression, and the first forwarding ranging value and the second forwarding ranging value are represented by a forwarding ranging expression, respectively.

[0198] S130. Based on the first pseudorange ranging value represented by the pseudorange ranging expression, the first forwarding ranging value represented by the forwarding ranging expression, and the second forwarding ranging value, determine the total number of ionospheric electrons on the ranging signal path between the first device and the second device, as well as the clock difference between the first device and the second device.

[0199] The following section will continue to explain this method using the example of the first device being the satellite and the second device being the user station.

[0200] It should be noted that the Sagnac effect delay in the pseudorange and transponder ranging expressions of this application has been explained previously and can be considered a known value. However, the tropospheric delay, ionospheric delay, and the clock difference between the satellite and the system time or the user station and the system time are unknowns. This application uses the above method to calculate the clock difference between the satellite and the user station, as well as the total number of ionospheric electrons along the ranging signal path, based on the measured pseudorange and transponder ranging values.

[0201] It should be noted that the ionospheric monitoring and time synchronization system and method proposed in this application can solve for the clock difference of the satellite relative to the system time when the clock difference of the user station relative to the system time is known, and can also solve for the clock difference of the user station relative to the system time when the clock difference of the satellite relative to the system time is known.

[0202] Both pseudorange ranging signals and relay ranging signals traverse the atmosphere, which includes the troposphere and ionosphere. The ionosphere is a diffuse medium, and the time delay it produces for radio frequency signals with different carrier frequencies varies depending on the carrier frequency. In contrast, the troposphere is a non-diffuse medium, and it produces the same time delay for radio frequency signals with different carrier frequencies.

[0203] Because the second pseudorange ranging device 202 and the relay ranging device 201 are set with a zero baseline, the pseudorange ranging signal and the relay ranging signal traverse the exact same atmospheric path, and the total number of electrons in the ionosphere experienced by the ranging signal is exactly the same. The pseudorange ranging signal and the downlink signal traverse the same spatial path, but the time when the uplink signal crosses the ionosphere is different from the time when the downlink signal after being relayed by the satellite crosses the ionosphere, 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 is almost unchanged. It can be calculated that the round-trip time of radio frequency signals between almost all spacecraft and user stations will not exceed a few seconds, which fully meets the conditions. Combining the spatial relationship of the zero baseline setting and the time relationship of the very short time difference, the spatial paths traversed by the relay ranging signal and the pseudorange ranging signal are exactly the same, so the following equations (56) and (57) are given: R true,z,1 (n)=R true,z,2 (n)=R true,zu,1 (n)=R true,zd,1 (n)=R true,zu,2 (n)=R true,zd,2 (n) (56); T duiliu,z,1 (n)=T duiliu,z,2 (n)=T duiliu,zu,1 (n)=T duiliu,zd,1 (n)=T duiliu,zu,2 (n)=T duiliu,zd,2 (n) (57);

[0204] When the pseudorange signal is broadcast by the second device, the pseudorange signal and the uplink signal of the forwarded ranging signal traverse the same spatial path and also have the formula for the zero baseline setting relationship mentioned above.

[0205] In some embodiments, after step S120, the ionospheric delay monitoring and time synchronization method may further include the following step: correcting the first forwarding ranging value, the second forwarding ranging value, and the first pseudorange ranging value using a pseudorange smoothing algorithm. Specifically, correcting the pseudorange ranging value and the forwarding ranging value using a pseudorange smoothing algorithm can reduce the noise of the pseudorange ranging value and the forwarding ranging value, which is beneficial to improving the accuracy of the finally determined clock error. The specific details of the pseudorange smoothing algorithm will not be elaborated here.

[0206] Before introducing the specific method, it is important to note that in the pseudorange measurement formula (z1), ±c·(δt) z (n)-δt s (n)), when +c·(δt) z (n)-δt s When (n)), the first device broadcasts the pseudorange ranging signal, and the second device receives the measurement; when -c·(δt) is taken... z (n)-δts When (n) is reached, the second device broadcasts the pseudorange ranging signal and the first device receives the measurement.

[0207] ±sagnca in the pseudorange measurement formula (z1) zz (n), when taking +sagnca zz When (n), it corresponds to the Sagnac effect when the first device broadcasts the pseudorange ranging signal. When -sagnac is taken... zz When (n), this corresponds to the Sagnac effect of the pseudorange ranging signal broadcast by the second device. It can be seen that when the directions of the pseudorange ranging signals are opposite, the absolute values ​​of the Sagnac effect are the same, but the signs are opposite.

[0208] Because the pseudorange signals have different directions, they are identical except for the clock difference signs and the Sagnac effect signs being opposite between the first and second devices. Therefore, when the first device broadcasts the pseudorange signal, the pseudorange formula is as follows (fz1); when the second device broadcasts the pseudorange signal, the pseudorange formula is as follows (sz1): ρ z,i (n)=R true,z,i (n)+I z,i (n)+T duiliu,z,i (n)+c·(δt z (n)-δt s (n))+sagnac zz (n)+X z,i (n) (fz1); ρ z,i (n)=R true,z,i (n)+I z,i (n)+T duiliu,z,i (n)-c·(δt z (n)-δt s (n))-sagnac zz (n)+X z,i (n) (sz1);

[0209] The corresponding formulas for corrected pseudorange measurements are (fz1') and (sz1'):

[0210] The method of this application will be explained below using the example of the first device broadcasting a pseudorange ranging signal, that is, using the pseudorange ranging formula (fz1) and the corrected pseudorange ranging formula (fz1') corresponding to the pseudorange ranging signal broadcast by the first device.

[0211] In an exemplary embodiment, in step S120, the computing device may specifically use the pseudorange ranging expression shown in the following formula (fz1) to characterize the pseudorange ranging value numbered i: ρ z,i(n)=R true,z,i (n)+I z,i (n)+T duiliu,z,i (n)+c·(δt z (n)-δt s (n))+sagnac zz (n)+X z,i (n) (fz1);

[0212] Where i = 1, 2, ..., m, i is a positive integer;

[0213] The first pseudorange measurement value obtained is shown in the following formula (fz1-1): ρ z,1 (n)=R true,z,1 (n)+I z,1 (n)+T duiliu,z,1 (n)+c·(δt z (n)-δt s (n))+sagnac zz (n)+X z,1 (n) (fz1-1);

[0214] The forwarding ranging value numbered j is characterized by the following formula (z2): L z,j (n)=R true,zu,j (n)+R true,zd,j (n)+I zu,j (n)+I zd,j (n)+T duiliu,zu,j (n)+T duiliu,zd,j (n)+Y z,j (n) (z2);

[0215] Where j = 1, 2, ..., h, j is a positive integer;

[0216] The obtained first and second forwarding ranging values ​​are shown in formulas (z2-1) and (z2-2) respectively: L z,1 (n)=R true,zu,1 (n)+R true,zd,1 (n)+I zu,1 (n)+I zd,1 (n)+T duiliu,zu,1 (n)+T duiliu,zd,1 (n)+Y z,1 (n) (z2-1); L z,2 (n)=R true,zu,2 (n)+R true,zd,2 (n)+I zu,2 (n)+I zd,2 (n)+T duiliu,zu,2(n)+T duiliu,zd,2 (n)+Y z,2 (n) (z2-2);

[0217] In an exemplary embodiment, in step S130, the computing device first corrects the transponder ranging value and the pseudorange ranging value to obtain corrected transponder ranging values ​​and corrected pseudorange ranging values, and then uses the corrected transponder ranging values ​​and corrected pseudorange ranging values ​​to determine the total number of ionospheric electrons and the clock difference between the satellite and the user station. Specifically, the process of correcting the transponder ranging value and the pseudorange ranging value may include the following steps:

[0218] S1301, Correct the first forwarding ranging value to obtain a first corrected forwarding ranging value, and correct the second forwarding ranging value to obtain a second corrected forwarding ranging value;

[0219] S1302, Correct the first pseudorange measurement value to obtain a first corrected pseudorange measurement value;

[0220] S1303. Determine the forwarding ranging difference using the first corrected forwarding ranging value and the second corrected forwarding ranging value.

[0221] In step S1301, the computing device can correct the pseudorange value numbered i, represented by the pseudorange measurement expression shown in formula (fz1), according to formula (fz1') to obtain the corrected pseudorange value (fz1'-1) numbered i:

[0222] Where i = 1, 2, ..., m, i is a positive integer;

[0223] The specific first corrected pseudorange distance measurement value is obtained as shown in formula (fz1'-1):

[0224] The computing device corrects the forwarding ranging value with number j, represented by the forwarding ranging expression shown in formula (z2), to obtain the corrected forwarding ranging value with number j:

[0225] Where j = 1, 2, ..., h, j is a positive integer;

[0226] The obtained first and second corrected forwarding ranging values ​​are shown in the following formulas (z2'-1) and (z2'-2):

[0227] Then in step S1303, the computing device uses the first corrected forwarding ranging value and the second corrected forwarding ranging value to determine the forwarding ranging difference.

[0228] Specifically, the computing device can calculate the difference between the first corrected forwarding ranging value shown in formula (z2'-1) and the second corrected forwarding ranging value shown in formula (z2'-2) to obtain the forwarding ranging difference value shown in formula (u7-1);

[0229] Furthermore, the computing device can specifically perform the following steps to determine the total number of ionospheric electrons along the ranging signal path between the satellite and the user station:

[0230] S1304. Determine the total number of ionospheric electrons on the ranging signal path between the first device and the second device based on the forwarding ranging difference.

[0231] The computing device can use the relay ranging difference, the carrier frequency of each signal in the relay ranging signal, and the preset ionospheric delay coefficient to determine the total number of ionospheric electrons on the ranging signal path between the satellite and the user station, as shown in the following formula (u7-1):

[0232] Then, the computing device can determine the ionospheric delay of the pseudorange ranging signal and the relay ranging signal using the following formulas (u60) to (u64):

[0233] After obtaining the ionospheric delay of each signal, in step S130, the computing device can determine the clock difference between the satellite and the user station based on any relay ranging value and any pseudorange ranging value.

[0234] In one embodiment of this application, a computing device can determine the clock difference between the first device and the second device based on the total number of electrons in the ionosphere, any corrected transponder ranging value, and any corrected pseudorange ranging value. This process may include the following steps:

[0235] S1311. Perform mathematical processing on any corrected pseudorange ranging value and any corrected forwarding ranging value to obtain an expression that includes the clock difference between the first device and the second device;

[0236] S1312. Determine the clock difference between the satellite and the user station using an expression that includes the clock difference.

[0237] Specifically, after obtaining the aforementioned corrected pseudorange ranging value and corrected forwarding ranging value, the expression representing the first corrected pseudorange ranging value and the expression representing the first corrected forwarding ranging value are mathematically processed to obtain an expression containing the clock difference between the satellite and the user station; or, the expression representing the first corrected pseudorange ranging value and the expression representing the second corrected forwarding ranging value are mathematically processed to obtain an expression containing the clock difference between the satellite and the user station. That is, the computing device can use any corrected pseudorange ranging value and any corrected forwarding ranging value to calculate the clock difference between the satellite and the user station.

[0238] Specifically, in step S1311, the computing device can use the first corrected pseudorange ranging value shown in formula (fz1'-1) and the first corrected forwarding ranging value and the second corrected forwarding ranging value shown in formulas (z2'-1) and (z2'-2) to perform a difference calculation. Utilizing the zero-baseline setting relationship between the forwarding ranging device and the second pseudorange ranging device, as shown in formulas (56) and (57), the following expressions containing the clock difference between the first device and the second device are obtained according to formula (u10): (u10-1) and (u10-2)

[0239] Based on the clock difference expressions shown in formulas (u10-1) to (u10-2), the clock difference between the first and second devices, as shown in formulas (z3-1) to (z3-2), is obtained:

[0240] Of course, in other embodiments, the computing device can also use the above formulas (z3-1) to (z3-2) to perform averaging to obtain the averaged clock difference between the satellite and the user station.

[0241] Obviously, a smaller clock error can be obtained between the satellite and the user station after weighted averaging, which will not be elaborated here.

[0242] In another alternative embodiment of this application, the total number of ionospheric electrons on the ranging signal path between the satellite and the user station and the clock difference between the satellite and the user station can also be obtained by executing a system of simultaneous equations and solving matrix equations.

[0243] At this time, m = 1, h = 2; λ = 1; θ = 2;

[0244] The computing device determines the total number of ionospheric electrons on the ranging signal path between the first device and the second device, and the clock difference between the first device and the second device, based on the first corrected forwarding ranging value, the second corrected forwarding ranging value, and the first corrected pseudorange ranging value.

[0245] Specifically, as mentioned above, based on formulas (u10-1) to (u10-2), we obtain formulas (u20) to (u21):

[0246] Generally, each of the λ corrected pseudorange values ​​is subtracted from the θ corrected forwarding values, resulting in λ·θ subtraction formulas, and thus a (λ·θ)×2 matrix G. u The matrix b is a (λ·θ)×1 matrix where the first column is all 1s. u .

[0247] Thus, the computing device can use the formulas (u20) to (u21) to construct the following matrix equation (u18-1) with the unknowns being the clock difference between the satellite and the user station and the total number of ionospheric electrons on the ranging signal path between the satellite and the user station:

[0248] In the matrix equation (u18-1),

[0249] Special note here: Matrix G u1 elements and matrix b u1 The elements must be based on the corrected pseudorange ranging value, and the corrected forwarding ranging value and its corresponding carrier frequency must correspond one-to-one.

[0250] The solution to the above matrix equation (u18-1) is expressed as (u19-1).

[0251] In obtaining c·(δt) z (n)-δt s After obtaining the value of (n), dividing it by the speed of light c will give the clock difference δt between the satellite and the user station. z (n)-δt s (n).

[0252] In the above formula (u19-1), the matrix For matrix G u1 The transpose of column vector b u1 Given this, the computing device can calculate the clock difference between the satellite and the user station, as well as the total number of electrons in the ionosphere, TEC(n), according to formula (u19-1).

[0253] It is worth noting that formula (u19-1) shows the expression for determining the clock difference between the satellite and the user station when there is one pseudorange ranging signal and two relay ranging signals. When the carrier frequencies of the signals are the same, matrix G... u Column vector b u The formula (u19) also changes accordingly, thus making it universal.

[0254] Furthermore, because the value of TEC(n) is relatively large, in actual calculations, we can set TEC(n) = x(n) × TECU, where TECU = 10. 16 Unit: electrons per square meter (e1 / m) 2 At this time, matrix G u1 Change to G u1m :

[0255] Solve matrix equations The result is obtained as shown in formula (u19'-1):

[0256] It should be understood that when the system is the first simplest system, α = 2, β = 1, and matrix G... z ,b z Specifically, the following matrix G z1 ,b z1 :

[0257] The total number of ionospheric electrons on the ranging signal path between the first and second devices and the clock difference between the first and second devices can be solved using formula (z19). For details, please refer to the solution process of the second simplest system mentioned above, which will not be repeated here.

[0258] When the first simplified system adds one relay ranging signal and the second system adds one pseudorange ranging signal, the two simplified systems become systems with the same two pseudorange ranging signals and two relay ranging signals. When the number of pseudorange ranging signals and relay ranging signals in the two simplified systems are both two, the two systems are completely identical. At this point, the carrier frequencies are different, and the corresponding calculation methods are also the same. In this case, the total number of ionospheric electrons can be obtained using either the two relay ranging values ​​or the two pseudorange ranging values. Then, using any corrected relay ranging value, any corrected pseudorange ranging value, and the known total number of ionospheric electrons, the clock difference between the first and second devices can be obtained.

[0259] When solving using simultaneous equations, the corresponding matrices Gu and bu are Gu2 and bu2, respectively:

[0260] Then, by using formula (u19-2), the total number of ionospheric electrons between the ranging signals and the clock difference between the first and second devices can be obtained.

[0261] In obtaining c·(δt) z (n)-δt s After obtaining the value of (n), dividing it by the speed of light c will give the clock difference δt between the satellite and the user station.z (n)-δt s (n). Among them, after obtaining the clock difference between the satellite and the user station, the satellite further uses the clock difference to synchronize its own clock with the system clock.

[0262] After calculating the clock difference between the satellite and the user station, when the clock difference δt of the user station relative to the system time... z When (n) is a known quantity, the clock difference δt between the satellite and the system time can be easily obtained. s (n), such as the time of the ground control station of the Beidou satellite navigation system is known, the clock difference between the control station and the satellite is calculated by applying the method of this application, and then the satellite clock difference is obtained;

[0263] Conversely, when the clock difference δt between the satellite and the system time is used... s When (n) is a known quantity, the clock difference δt between the user station and the system time can be easily obtained. z (n), at which point the satellite can provide time services to the user station;

[0264] When both the clock difference of the user station relative to the system time and the clock difference of the satellite relative to the system time are unknown, the clock difference between the satellite and the user station is obtained.

[0265] In an exemplary embodiment, after determining the clock difference between the satellite and the user station, the computing device can communicate with a first device and a second device to transmit the determined clock difference between the first device and the second device to the first device and / or the second device, thereby achieving time synchronization between the first device and the second device. For example, the computing device transmits data with the satellite, and the satellite obtains the clock difference between the satellite and the user station based on the data transmission result, and synchronizes its own clock with the user station's time based on the clock difference between the satellite and the user station.

[0266] Alternatively, the user station may not exchange clock difference data with the satellite.

[0267] In summary, it can be seen that the ionospheric delay monitoring and time synchronization system and related methods provided in this application creatively fuse at least one pseudorange ranging signal and at least two relay ranging signals, achieving both high satellite-to-ground time synchronization performance and accurate total ionospheric electron count. Furthermore, this ionospheric delay monitoring and time synchronization system and method... The ionospheric delay monitoring and time synchronization system and related methods provided in this application have the following characteristics: 1. This application can independently obtain the total number of ionospheric electrons along the ranging signal path without requiring ionospheric electron count data provided by a third party, and can also provide ionospheric electron count data to other users; 2. Compared with the two-way pseudorange measurement method, this method does not require coarse satellite-to-ground synchronization, reducing system requirements and overcoming the influence of atmospheric delay, including tropospheric and ionospheric delay, thereby achieving higher satellite-to-ground time synchronization accuracy, reaching sub-nanosecond levels; 3. Applying this method, for satellites, compared with the existing two-way pseudorange measurement method, the satellites in this application embodiment do not need pseudorange measurement equipment, thus reducing satellite payload complexity and satellite cost; 4. Because the user station only needs to receive a signal from one satellite, the user station can use a directional antenna to reduce multipath effects, thereby achieving better ranging accuracy.

[0268] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. An ionospheric delay monitoring system comprising a first device and a second device connected in communication; at least two relay ranging signals are transmitted between the first device and the second device, the relay ranging signals having at least three different carrier frequencies; the relay ranging signals comprising uplink signals and downlink signals; the second device is configured to broadcast the uplink signals; the first device is configured to receive the uplink signals and relay the uplink signals as downlink signals; and the second device is configured to receive the downlink signals.

2. The system of claim 1, wherein, the first device comprises a first time-frequency device and a relay; and the second device comprises a second time-frequency device, a relay ranging device and a processing device; the first time-frequency device is configured to provide time-frequency signals to the relay; the relay is configured to receive the uplink signals, convert the uplink signals to different frequencies, amplify the power of the uplink signals and relay the downlink signals to the second device; the second time-frequency device is configured to provide time-frequency signals to the relay ranging device and / or the processing device; the relay ranging device is configured to generate and broadcast the uplink signals, receive the downlink signals and synchronously measure at least two of the relay ranging signals to obtain at least two of the relay ranging values; the processing device is connected in communication with the relay ranging device, and the processing device is configured to obtain the at least two relay ranging values and determine the total electron content of the ionosphere along the path of the ranging signals between the first device and the second device based on the relay ranging values; wherein the satellite time-frequency device and the relay are integrated or separate; and the second time-frequency device, the relay ranging device and the processing device are integrated or separate.

3. The system of claim 2, wherein, the second device comprises one or more relay ranging devices, and when the relay ranging devices are multiple, the multiple relay ranging devices are set in zero baseline.

4. The system of any one of claims 1 to 3, wherein, the system further comprises a central station connected in communication with the second device, and the central station is configured to obtain monitoring parameters of the second device based on the communication results of the second device; the central station is directly connected in communication with the second device; or the central station is connected in communication with the second device through the first device; when the central station is connected in communication with the second device through the first device, the central station has a main feeder link with the first device, and the second device has a slave feeder link with the first device; the main feeder link comprises a main feeder link uplink signal and a main feeder link downlink signal, the slave feeder link comprises a slave feeder link uplink signal and a slave feeder link downlink signal, the main feeder link uplink signal and the slave feeder link downlink signal form a forward communication link, and the slave feeder link uplink signal and the main feeder link downlink signal form a return communication link; wherein the second device is connected in communication with the central station through the forward communication link and the return communication link, or the second device is directly connected in communication with the central station.

5. An ionospheric delay monitoring method applied to the ionospheric delay monitoring system of any one of claims 1 to 5, the method being performed by the second device, the method comprising: at least one uplink signal is broadcast to the first device; acquire at least two downlink signals which are relayed by the first device based on the at least one uplink signal; wherein the at least one uplink signal and the at least two downlink signals constitute at least two relay ranging signals; synchronously measure each of the relay ranging signals to obtain x relay ranging values, and select y relay ranging values from the x relay ranging values, or select y relay ranging signals from the x relay ranging signals to obtain y relay ranging values by synchronous measurement; wherein x is a positive integer greater than or equal to 2, and 2≤y≤x; respectively use a relay ranging expression to represent each of the relay ranging values; divide the y relay ranging values into two groups, one group including m relay ranging values and the other group including h relay ranging values, wherein 2≤y≤x, m+h=y, m and h are both greater than or equal to 1, and y, m and h are all positive integers; respectively perform mean value calculation on the two groups of relay ranging values represented by the relay ranging expressions to obtain a first corrected average relay ranging value and a second corrected average relay ranging value; determine the total electron number of the ionosphere on the ranging signal path between the first device and the second device based on the first corrected average relay ranging value and the second corrected average relay ranging value.

6. The method of claim 5, wherein, The determination of the total electron number of the ionosphere on the ranging signal path between the first device and the second device based on the first corrected average relay ranging value and the second corrected average relay ranging value comprises: determining a relay ranging difference value by using the first corrected average relay ranging value and the second corrected average relay ranging value; and determining the total electron number of the ionosphere on the ranging signal path between the first device and the second device based on the relay ranging difference value.

7. The method of claim 6, wherein, The determination of the total electron number of the ionosphere on the ranging signal path between the first device and the second device based on the relay ranging difference value comprises: determining the total electron number of the ionosphere on the ranging signal path between the first device and the second device based on the carrier frequency of each signal in the relay ranging signal, a preset ionosphere time delay coefficient, and the relay ranging difference value.

8. The method of any one of claims 5 to 7, wherein, The mean value calculation on the two groups of relay ranging values represented by the relay ranging expressions to obtain the first corrected average relay ranging value and the second corrected average relay ranging value comprises: performing average calculation on the m relay ranging values in the first group to obtain the first corrected average relay ranging value; and performing average calculation on the h relay ranging values in the second group to obtain the second corrected average relay ranging value. The determination of the relay ranging difference value by using the first corrected average relay ranging value and the second corrected average relay ranging value comprises: determining the relay ranging difference value based on the first corrected average relay ranging value and the second corrected average relay ranging value.

9. The method of any one of claims 5 to 7, wherein, After the total electron number of the ionosphere on the ranging signal path between the first device and the second device is determined, the method further comprises: performing data interaction with a center station based on a communication link, wherein the center station acquires the total electron number of the ionosphere on the ranging signal path between the first device and the second device based on a data interaction result, and the communication link comprises a forward communication link and a return communication link.

10. An ionospheric delay monitoring and time synchronization system, the system comprising a first device and a second device communicatively connected, and a computing device communicatively connected with the first device and the second device respectively; there are m ranging signals of pseudo-range and h ranging signals of retransmission between the first device and the second device, and the ranging signals of pseudo-range and the ranging signals of retransmission have at least three different carrier frequencies; wherein, m+h≥3, m, h are positive integers greater than or equal to 1; the pseudo-range ranging signal is broadcasted by the first device and received by the second device, or broadcasted by the second device and received by the first device; The repeating ranging signal comprises an uplink signal and a downlink signal, the second device broadcasts the uplink signal, the first device receives the uplink signal and forms the downlink signal by repeating, and the second device receives the downlink signal.

11. The system of claim 10, wherein, The first device comprises a first time-frequency device, a repeater and a pseudo-range generating device, and the second device comprises a second time-frequency device, a repeating ranging device and a second pseudo-range ranging device; the first time-frequency device is configured to provide time-frequency signals to the repeater and the pseudo-range generating device; the repeater is configured 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 pseudo-range generating device is in communication connection with the repeater, and the pseudo-range generating device is configured to generate and broadcast the pseudo-range ranging signal; the second time-frequency device is configured to provide time-frequency signals to the repeating ranging device and the second pseudo-range ranging device; the second pseudo-range ranging device is configured to receive the pseudo-range ranging signal and process the pseudo-range ranging signal to obtain a pseudo-range ranging value; the repeating ranging device is configured to generate and broadcast the uplink signal, and receive the downlink signal and determine a repeating ranging value based on the repeating ranging signal; 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 repeating ranging device and the second pseudo-range ranging device are integrated or separately arranged. Alternatively, the first device comprises a first time-frequency device, a repeater and a first pseudo-range ranging device, and the second device comprises a second time-frequency device and a repeating ranging device; the first time-frequency device is configured to provide time-frequency signals to the repeater and the first pseudo-range ranging device; the repeater is configured 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 ranging device is in communication connection with the repeater, and the first pseudo-range ranging device is configured to receive and measure the pseudo-range ranging signal; the second time-frequency device is configured to provide time-frequency signals to the repeating ranging device; the repeating ranging device is configured to generate and broadcast the uplink signal, and receive the downlink signal and determine a repeating ranging value based on the repeating ranging signal, wherein part of the uplink signal broadcasted by the repeating ranging device serves as the pseudo-range ranging signal; wherein the first time-frequency device, the repeater and the first pseudo-range ranging device are integrated or separately arranged, and / or the second time-frequency device and the repeating ranging device are integrated or separately arranged.

12. The system of claim 11, wherein, The second pseudo-range ranging device and the repeating ranging device are zero-baseline arranged; the repeater and the first pseudo-range ranging device or the pseudo-range generating device are zero-baseline arranged.

13. The system of claim 11 or 12, wherein, 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.

14. The system of any one of claims 11 to 13, wherein the computing device is disposed in the first device, or in the second device, or independently; in the case that the computing device is disposed in the first device or the second device, the first device transmits data to the second device by using a communication signal; in the case that the computing device is independently disposed, the computing device respectively communicates with the first device and the second device; The computing device is configured to receive the pseudo-range measurement and the forward-range measurement, and to determine the clock difference between the first device and the second device based on the forward-range measurement, total electron content on a path of a ranging signal between the first device and the second device, and the forward-range measurement. in the case that the ionospheric total electron content and the clock difference are determined, the sum of the number of the pseudo-range measurement values and the re-transmitted range measurement values is greater than or equal to 3.

15. An ionospheric delay monitoring and time synchronization method applied to the system of any one of claims 11 to 14, the method being performed by a computing device, the method comprising: in the case that the pseudo-range measurement signal is broadcast by the second device and received by the first device, based on the communication result with the first device, m pseudo-range measurement values measured by the first device are obtained, and based on the communication result with the second device, h re-transmitted range measurement values measured by the second device are obtained; in the case that the pseudo-range measurement signal is broadcast by the first device and received by the second device, based on the communication result with the second device, m pseudo-range measurement values and h re-transmitted range measurement values measured by the second device are obtained; wherein m+h≥3, and m and h are positive integers; each of the pseudo-range measurement values is respectively represented by a pseudo-range measurement expression, and each of the re-transmitted range measurement values is represented by a re-transmitted range measurement expression; based on the m pseudo-range measurement values represented by the pseudo-range measurement expression and the h re-transmitted range measurement values represented by the re-transmitted range measurement expression, the ionospheric total electron content on the ranging signal path between the first device and the second device and the clock difference between the first device and the second device are determined.

16. The method of claim 15, wherein, the respective representation of each of the pseudo-range measurement values by the pseudo-range measurement expression and the respective representation of each of the re-transmitted range measurement values by the re-transmitted range measurement expression comprises: the pseudo-range measurement value numbered i is represented by a pseudo-range measurement expression shown in the following formula (z1): ρ z,i (n) = R true,z,i (n) + I z,i (n) + T duiliu,z,i (n) ± c · (δt z (n) - δt s (n) + X z,i (n) ± sagnac zz (n) (z1); wherein i=1, 2, …, m, and i is a positive integer; the re-transmitted range measurement value numbered j is represented by a re-transmitted range measurement expression shown in the following formula (z2): L z,j (n) = R true,zu,j (n) + R true,zd,j (n) + I zu,j (n) + I zd,j (n) + T duiliu,zu,j (n) + T duiliu,zd,j (n) + Y z,j (n) (z2); wherein j=1, 2, …, h, and j is a positive integer; wherein: p z,i (n) represents the pseudo-range measurement value of the i-th at the n-th moment, unit: meter; R true,z,i (n) represents the real space distance of the i-th pseudo-range measurement signal at the n-th moment, unit: meter; I z,i (n) represents the ionospheric delay of the i-th pseudo-range measurement signal at the n-th moment, unit: meter; T duiliu,z,i (n) represents the tropospheric delay of the i-th pseudo-range measurement signal at the n-th moment, unit: meter; X z,i (n) represents the hardware device delay of the i-th pseudo-range measurement signal at the n-th moment, unit: meter, which includes the transmission delay of the i-th pseudo-range measurement signal, the receiving delay of the i-th pseudo-range measurement signal; c represents the speed of light, unit: meter / second; δt s (n) represents the clock difference of the first device relative to the system time at the n-th moment, unit: second; δt z (n) represents the clock difference of the second device relative to the system time at the n-th moment, unit: second; sagnac zz (n) represents the Sagnac effect delay of the pseudo-range measurement signal at the n-th moment, unit: meter; L z,j (n) represents the real space distance of the uplink signal of the jth relay ranging signal at the nth moment, unit: meter; R true,zu,j (n) represents the real space distance of the uplink signal of the jth relay ranging signal at the nth moment, unit: meter; R true,zd,j (n) represents the real space distance of the downlink signal of the jth relay ranging signal at the nth moment, unit: meter; I zu,j (n) represents the ionospheric delay of the uplink signal of the jth relay ranging signal at the nth moment, unit: meter; I zd,j (n) represents the ionospheric delay of the downlink signal of the jth relay ranging signal at the nth moment, unit: meter; T duiliu,zu,j (n) represents the tropospheric delay of the uplink signal of the jth relay ranging signal at the nth moment, unit: meter; T duiliu,zd,j (n) represents the tropospheric delay of the downlink signal of the jth relay ranging signal at the nth moment, unit: meter; Y z,j (n) represents the hardware device delay of the jth relay ranging signal at the nth moment, unit: meter, the hardware device delay of the jth relay ranging signal includes the transmission delay of the uplink signal of the jth relay ranging signal, the relay delay of the downlink signal of the jth relay ranging signal, and the reception delay of the downlink signal of the jth relay ranging signal.

17. The method of claim 15 or 16, wherein, the determination of the ionospheric total electron content on the ranging signal path between the first device and the second device and the clock difference between the first device and the second device based on the m pseudo-range measurement values and the h re-transmitted range measurement values comprises: the m pseudo-range measurement values and the h re-transmitted range measurement values are respectively corrected to obtain m corrected pseudo-range measurement values and h corrected re-transmitted range measurement values; at least two of the corrected pseudo-range measurement values or at least two of the corrected re-transmitted range measurement values are used to determine the ionospheric total electron content on the ranging signal path, and the clock difference between the first device and the second device is determined by using the ionospheric total electron content, any of the corrected re-transmitted range measurement values, and any of the corrected pseudo-range measurement values. Or, determining the ionospheric total electron content on the ranging signal path between the first device and the second device and the clock difference between the first device and the second device by using at least two of the corrected forward ranging values and at least one of the corrected pseudo ranging values, or by using at least one of the corrected forward ranging values and at least two of the corrected pseudo ranging values; Wherein, the sum of the number of the corrected pseudo ranging values and the corrected forward ranging values is greater than or equal to 3.

18. The method of claim 17, wherein, The correction of the m pseudo ranging values and the h forward ranging values respectively to obtain m corrected pseudo ranging values and h corrected forward ranging values comprises: The pseudo ranging value numbered i represented by the pseudo ranging expression shown in the following formula (z1) is corrected to obtain the corrected pseudo ranging value numbered i shown in the following formula (z1'): p z,i (n) = R true,z,i (n) + I z,i (n) + T duiliu,z,i (n) ± c · (δt z (n) - δt s (n) + X z,i (n) ± sagnac zz (n) (z1); p z,i,a (n) = p z,i (n) - (X z,i (n) ± sagnac zz (n)) = R true,z.i (n) + I z,i (n) + T duiliu,z,i (n) ± c · (δt z (n) - δt s (n)) (z1') Wherein, i = 1, 2, …, m, i is a positive integer; The forward ranging value numbered j represented by the forward ranging expression shown in the following formula (z2) is corrected to obtain the corrected forward ranging value numbered j shown in the following formula (z2'): L z,j (n) = R true,zu,j (n) + R true,zd,j (n) + I zu,j (n) + I zd,j (n) + T duiliu,zu,j (n) + T duiliu,zd,j (n) + Y z,j (n) (z2); Wherein, j = 1, 2, …, h, j is a positive integer; wherein: p z,i,a (n) represents the modified pseudo-range measurement value of the i-th at the n-th moment, unit: meter; p z,i (n) represents the pseudo-range measurement value of the i-th at the n-th moment, unit: meter; R true,z,i (n) represents the real space distance of the pseudo-range measurement signal of the i-th at the n-th moment, unit: meter; I z,i (n) represents the ionospheric delay of the pseudo-range measurement signal of the i-th at the n-th moment, unit: meter; T duiliu,z,i (n) represents the tropospheric delay of the pseudo-range measurement signal of the i-th at the n-th moment, unit: meter; X z,i (n) represents the hardware device delay of the pseudo-range measurement signal of the i-th at the n-th moment, unit: meter, which includes the transmission delay of the pseudo-range measurement signal of the i-th, the receiving delay of the pseudo-range measurement signal of the i-th; c represents the light speed, unit: meter / second; δt s (n) represents the clock difference of the first device relative to the system time at the n-th moment, unit: second; δt z (n) represents the clock difference of the second device relative to the system time at the n-th moment, unit: second; sagnac zz (n) represents the Sagnac effect delay of the pseudo-range measurement signal at the n-th moment, unit: meter; L z,j,a (n) represents the modified round-trip ranging value of the jth at the nth moment, unit: meter; L z,j (n) represents the round-trip ranging value of the jth at the nth moment, unit: meter; R true,zu,j (n) represents the real space distance of the uplink signal of the jth round-trip ranging signal at the nth moment, unit: meter; R true,zd,j (n) represents the real space distance of the downlink signal of the jth round-trip ranging signal at the nth moment, unit: meter; I zu,j (n) represents the ionospheric delay of the uplink signal of the jth round-trip ranging signal at the nth moment, unit: meter; I zd,j (n) represents the ionospheric delay of the downlink signal of the jth round-trip ranging signal at the nth moment, unit: meter; T duiliu,zu,j (n) represents the tropospheric delay of the uplink signal of the jth round-trip ranging signal at the nth moment, unit: meter; T duiliu,zd,j (n) represents the tropospheric delay of the downlink signal of the jth round-trip ranging signal at the nth moment, unit: meter; Y z,j (n) represents the hardware device delay of the jth round-trip ranging signal at the nth moment, unit: meter, the hardware device delay of the jth round-trip ranging signal includes the transmission delay of the uplink signal of the jth round-trip ranging signal, the forwarding delay of the downlink signal of the jth round-trip ranging signal, and the receiving delay of the downlink signal of the jth round-trip ranging signal.

19. The method of claim 17 or 18, wherein, The determination of the clock difference between the first device and the second device by using the ionospheric total electron content, any corrected forward ranging value and any corrected pseudo ranging value comprises: The clock difference between the first device and the second device is obtained based on the ionospheric total electron content, any one of the corrected pseudo-range measurement values, and any one of the corrected retransmission range measurement values, according to a formula (z3) shown in the following: wherein: p z,i,a (n) represents the modified pseudo-range measurement value of the i-th at the n-th moment, unit: meter; L z,j,a (n) represents the modified pseudo-range measurement value of the i-th at the n-th moment, unit: meter; L s (n) represents the clock difference of the first device relative to the system time at the n-th moment, unit: second; δt z (n) represents the clock difference of the second device relative to the system time at the n-th moment, unit: second; Q ion represents the ionospheric delay coefficient, TEC(n) represents the total electron number of the ionosphere on the ranging signal path between the first device and the second device at the n-th moment, unit: electron / meter2; f z,i (n) represents the carrier frequency of the i-th pseudo-range ranging signal at the n-th moment, unit: hertz; f zu,j (n), f zd,j (n) respectively represent the carrier frequencies of the uplink signal and the downlink signal of the j-th ranging signal at the n-th moment, unit: hertz; Or, determining a plurality of clock differences between the first device and the second device based on the ionospheric total electron content, a plurality of corrected pseudo ranging values and a plurality of corrected forward ranging values; and averaging the clock differences between the first device and the second device to obtain the averaged clock difference between the first device and the second device.

20. The method of claim 17 or 18, wherein, The determination of the ionospheric total electron content on the ranging signal path between the first device and the second device and the clock difference between the first device and the second device by using at least two of the corrected forward ranging values and at least one of the corrected pseudo ranging values, or by using at least one of the corrected forward ranging values and at least two of the corrected pseudo ranging values comprises: In the case that the corrected pseudo ranging values are at least two and the corrected forward ranging values are at least one, selecting a from the m corrected pseudo ranging values and selecting β from the h corrected forward ranging values, wherein 2 ≤ a ≤ m and 1 ≤ β ≤ h; The difference between the a corrected pseudo ranging values shown in the formula (z1') and the β corrected forward ranging values shown in the formula (z2') is obtained to obtain the difference formula shown in the following formula (z10): p z,i,a (n) = p z,i (n) - (X z,i (n) ± sagnac zz (n) = R true,z.i (n) + I z,i (n) + T duiliu,z,i (n) ± c · (δt z (n) - δt s (n) = (z1'); Wherein, i = 1, 2, …, a, i and a are positive integers; j = 1, 2, …, β, j and β are positive integers; According to the formula (z10) and the zero baseline setting relationship between the repeater ranging device and the second pseudo-range ranging device, or using the zero baseline setting relationship between the repeater and the first pseudo-range ranging device, the matrix equation as shown in the formula (z18) is obtained: Solving the matrix equation (z18) yields the total electron content on the ranging signal path between the first device and the second device and the clock difference between the first device and the second device as shown in equation (z19): where: G z is a matrix of (a·b) x 2, with all 1s in the first column; b z is a matrix of (a·b) x 1; In the case that the corrected pseudo ranging values are at least one and the corrected forward ranging values are at least two, selecting λ from the m corrected pseudo ranging values and selecting θ from the h corrected forward ranging values, wherein 1 ≤ λ ≤ m and 2 ≤ θ ≤ h; The λ modified pseudo-range measurement values and the θ modified round-trip measurement values are subtracted from each other to obtain a difference value as shown in the following equation (u10): Wherein, i = 1, 2, …, λ, j = 1, 2, …, θ, i, λ, j and θ are positive integers; Wherein, i = 1, 2, …, λ, j = 1, 2, …, θ, i, λ, j and θ are positive integers; According to the formula (u10) and the zero baseline setting relationship between the repeater and the second pseudorange ranging device, or using the zero baseline setting relationship between the repeater and the first pseudorange ranging device, a matrix equation as shown in the formula (u18) is obtained: Solving the matrix equation (u18) gives the total electron content on the ranging signal path between the first device and the second device and the clock difference between the first device and the second device as shown in equation (u19): where: G u is a (λ·θ) x 2 matrix with all 1s in the first column; b u is a (λ·θ) x 1 matrix; wherein: L z,j,a (n) represents the modified round-trip ranging value of the jth at the nth moment, unit: meter; L z,j (n) represents the round-trip ranging value of the jth at the nth moment, unit: meter; R true,zu,j (n) represents the real space distance of the uplink signal of the jth ranging signal at the nth moment, unit: meter; R true,zd,j (n) represents the real space distance of the downlink signal of the jth ranging signal at the nth moment, unit: meter; I zu,j (n) represents the ionospheric delay of the uplink signal of the jth ranging signal at the nth moment, unit: meter; I zd,j (n) represents the ionospheric delay of the downlink signal of the jth ranging signal at the nth moment, unit: meter; T duiliu,zu,j (n) represents the tropospheric delay of the uplink signal of the jth ranging signal at the nth moment, unit: meter; T duiliu,zd,j (n) represents the tropospheric delay of the downlink signal of the jth ranging signal at the nth moment, unit: meter; Y z,j (n) represents the hardware device delay of the jth ranging signal at the nth moment, unit: meter, the hardware device delay of the jth ranging signal includes the transmission delay of the uplink signal of the jth ranging signal, the forwarding delay of the downlink signal of the jth ranging signal, and the receiving delay of the downlink signal of the jth ranging signal. ρ z,i,a (n) represents the corrected pseudo-range measurement value of the i-th at the n-th moment, unit: meter; ρ z,i (n) represents the pseudo-range measurement value of the i-th at the n-th moment, unit: meter; R true,z,i (n) represents the real space distance of the pseudo-range measurement signal of the i-th at the n-th moment, unit: meter; I z,i (n) represents the ionospheric delay of the pseudo-range measurement signal of the i-th at the n-th moment, unit: meter; T duiliu,z,i (n) represents the tropospheric delay of the pseudo-range measurement signal of the i-th at the n-th moment, unit: meter; X z,i (n) represents the hardware device delay of the pseudo-range measurement signal of the i-th at the n-th moment, unit: meter, which includes the transmission delay of the pseudo-range measurement signal of the i-th, the receiving delay of the pseudo-range measurement signal of the i-th; c represents the speed of light, unit: meter / second; δt s (n) represents the clock difference of the first device relative to the system time at the n-th moment, unit: second; δt z (n) represents the clock difference of the second device relative to the system time at the n-th moment, unit: second; sagnac zz (n) represents the Sagnac effect delay of the pseudo-range measurement signal at the n-th moment, unit: meter; Q ion denotes ionospheric delay coefficient, TEC(n) denotes total electron content of ionosphere on ranging signal path between first device and second device at n moment, unit: electron / m2; f z,1 (n), f z,2 (n), f z,α (n), f z,λ (n) respectively denote carrier frequency of pseudo-range ranging signal numbered 1, 2, ɑ, λ at n moment, unit: hertz; f zu,1 (n), f zu,2 (n), f zu,β (n), f zu,θ (n) respectively denote carrier frequency of uplink signal of transponding ranging signal numbered 1, 2, β, θ at n moment, unit: hertz; f zd,1 (n), f zd,2 ( n ), f zd,β (n), f zd,θ (n) respectively denote carrier frequency of downlink signal of transponding ranging signal numbered 1, 2, β, θ at n moment, unit: hertz.

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