A time synchronization method, device and medium for low-orbit satellite

Abstract

The present invention discloses a time synchronization method, device and medium for low-orbit satellites, which are applicable to the field of satellite communications. A first synchronization calibration is performed on the current satellite node according to the node time quality, and a second synchronization calibration is performed on the calibrated current satellite node through an improved RTT synchronization method to eliminate the delay difference; when each satellite node of the constellation network completes the time synchronization, the corresponding time synchronization maintenance strategy is executed according to the relationship between the node time quality corresponding to each satellite node and the preset conditions to achieve time synchronization of the low-orbit satellite. At the same time, the time synchronization maintenance strategy is added, so that in the case of communication interruption caused by a sudden loss of synchronization of a certain satellite or inability to locate and provide timing during a special period, time synchronization can be maintained autonomously, thereby improving the reliability of the low-orbit satellite communication system.

Description

Technical Field

[0001] The present invention relates to the field of satellite communications, and in particular to a time synchronization method, device and medium for a low-orbit satellite. Background Art

[0002] The whole network time synchronization technology is one of the core technologies of low-orbit communication satellite constellations. Especially for satellite networks that adopt the time division multiple access (TDMA) networking system or time division duplex communication mode, accurate timing of the whole network is a necessary condition for establishing communication.

[0003] Conventional satellite network time synchronization mostly uses the Global Positioning System (GPS) or BeiDou for time synchronization, which is heavily dependent on external navigation systems. However, in special periods, GPS or BeiDou may not be available. Commercial GPS receivers are used for time synchronization during project implementation. However, commercial GPS receivers may not be able to locate for a short period of time in the orbit environment. In the above two situations, when positioning and timing cannot be achieved, the satellite communication is interrupted and time synchronization cannot be achieved, resulting in reduced reliability of the low-orbit satellite communication system.

[0004] Therefore, it is urgent for technicians in this field to find a time synchronization method for low-orbit satellites. Summary of the invention

[0005] The purpose of the present invention is to provide a time synchronization method, device and medium for a low-orbit satellite, which can autonomously maintain time synchronization and improve the reliability of a low-orbit satellite communication system.

[0006] In order to solve the above technical problems, the present invention provides a time synchronization method for a low-orbit satellite, comprising:

[0007] Obtain the time reference point of the constellation network and the current satellite node that is not time synchronized, and initialize the current satellite node to output the corresponding node time quality, where the time reference point is the domestic earth station;

[0008] Performing a first synchronization calibration on the current satellite node according to the node time quality, and performing a second synchronization calibration on the calibrated current satellite node by using an improved RTT synchronization method, wherein the level of the first synchronization calibration is lower than the level of the second synchronization calibration;

[0009] The current satellite node after the second synchronization calibration is used as a new time reference point to calibrate the next current satellite node, and return to the step of performing the first synchronization calibration on the current satellite node according to the node time quality until the satellite nodes of the constellation network complete the time synchronization;

[0010] According to the relationship between the node time quality corresponding to each satellite node and the preset conditions, the corresponding time synchronization maintenance strategy is executed to achieve time synchronization of the low-orbit satellite.

[0011] Preferably, initializing the current satellite node to output the corresponding node time quality includes:

[0012] Get the time synchronization parameters of the current satellite node;

[0013] Establish a time monitoring model based on the time synchronization parameters and output the local system time corresponding to the current satellite node;

[0014] The node time quality of the current satellite node is determined based on the local system time and the time reference point.

[0015] Preferably, performing a first synchronization calibration on the current satellite node according to the node time quality includes:

[0016] When the current satellite node enters, the current satellite node is controlled to send a time broadcast request message to the time reference point so that the time reference point sends a response broadcast message to the current satellite node;

[0017] The local system time of the current satellite node is corrected according to the response broadcast information to complete the first synchronization calibration.

[0018] Preferably, performing a second synchronization calibration on the calibrated current satellite node by improving the RTT synchronization method, including:

[0019] Get the RTT query message information of the current satellite node;

[0020] The current satellite node is used as the interrogator and the time reference point is used as the responder;

[0021] The time when the inquiring party sends the RTT inquiry message information to the responding party is controlled as the first timestamp;

[0022] Control the responder to record the time of receiving the RTT inquiry message information as the second timestamp, generate corresponding RTT reply message information according to the RTT inquiry message information, record the sending time of the RTT reply message information as the third timestamp, and send the RTT reply message information to the inquiring party at the third timestamp, wherein the RTT reply message information includes the second timestamp, the third timestamp and the ephemeris information of the responder;

[0023] The control inquiring party records the time of receiving the RTT response message information as a fourth timestamp;

[0024] Obtain the inquiring party's ephemeris information;

[0025] Determine the actual delay difference between the inquiring party and the responding party according to the ephemeris information of the inquiring party and the ephemeris information of the responding party;

[0026] Subtracting the second timestamp from the first timestamp to obtain a first delay difference;

[0027] Subtracting the third timestamp from the fourth timestamp to obtain a second delay difference;

[0028] Subtracting the first delay difference from the second delay difference to obtain a third delay difference;

[0029] The two-way delay time between the inquiring party and the responding party is obtained by performing a difference processing based on the third delay difference and the actual delay difference;

[0030] The two-way delay time is averaged to obtain the one-way delay time, and the one-way delay time is used as the offset of the inquiry party to determine the completion of the second synchronization calibration.

[0031] Preferably, the preset conditions include a first preset condition, a second preset condition and a third preset condition, and the corresponding time synchronization maintenance strategy is executed according to the relationship between the node time quality corresponding to each satellite node and the preset conditions, including:

[0032] Acquire a current node time quality value and a time deviation reference value, a second synchronization threshold value and a first synchronization threshold value of a current satellite node, wherein the second synchronization threshold value is higher than the first synchronization threshold value;

[0033] Establish a time quality value report based on the node time quality corresponding to each satellite node;

[0034] Obtaining the time quality value of the adjacent satellite node of the current satellite node in the time quality value report, wherein the adjacent satellite node is located at the satellite node of the co-orbit link and the off-orbit link of the current satellite node;

[0035] When the time quality value of the adjacent satellite node meets the first preset condition, the adjacent satellite node is used as the time reference point to initiate fine synchronization of the current satellite node, and enter the step of performing a second synchronization calibration on the calibrated current satellite node by using the improved RTT synchronization method, wherein the first preset condition is that the time quality value of the adjacent satellite node changes;

[0036] When the time quality value of the current node meets the second preset condition, the highest time quality value in the adjacent satellite node is selected in the time quality value report, and fine synchronization is initiated to the adjacent satellite node corresponding to the highest time quality value, and the step of performing a second synchronization calibration on the calibrated current satellite node by using the improved RTT synchronization method is entered, wherein the second preset condition is that the time quality value of the current node is less than the second synchronization threshold value;

[0037] When the time quality value of the current node and the time deviation reference value meet the third preset condition, the highest time quality value among the adjacent satellite nodes is selected in the time quality value report, and a time broadcast request message is initiated to the adjacent satellite node corresponding to the highest time quality value, and the step of correcting the local system time of the current satellite node according to the response broadcast message is performed to complete the first synchronization calibration, wherein the third preset condition is that the time quality value of the current node is less than the first synchronization threshold value and the time deviation reference value is greater than the threshold value.

[0038] Preferably, the process of establishing a constellation network includes the following steps:

[0039] Configure multiple satellite nodes on the current orbital plane to be in co-orbital inter-satellite links;

[0040] The current satellite nodes at the plurality of satellite nodes are configured as satellite nodes on adjacent orbital planes so as to be in inter-satellite links on different orbits;

[0041] The current satellite node is fixedly connected to the adjacent satellite node according to the same-orbit inter-satellite link and the different-orbit inter-satellite link;

[0042] Connect the domestic earth station to any satellite node in the current orbital plane so that multiple satellite nodes and the domestic earth station are in the constellation network to complete the establishment process.

[0043] Preferably, it also includes:

[0044] Obtain error factor parameters of time synchronization of the constellation network;

[0045] Determine the error category and error magnitude based on the error factor parameters;

[0046] Error analysis is performed based on the error category, error factor parameters and error magnitude to determine the timing period of the corresponding domestic earth station.

[0047] In order to solve the above technical problems, the present invention also provides a time synchronization device for a low-orbit satellite, comprising:

[0048] An initialization module is used to obtain the time reference point of the constellation network and the current satellite node that is not time synchronized, and initialize the current satellite node to output the corresponding node time quality, where the time reference point is the domestic earth station;

[0049] A first calibration module is used to perform a first synchronization calibration on the current satellite node according to the node time quality, and perform a second synchronization calibration on the calibrated current satellite node by using an improved RTT synchronization method, wherein the level of the first synchronization calibration is lower than the level of the second synchronization calibration;

[0050] A second calibration module is used to use the current satellite node after the second synchronization calibration as a new time reference point, calibrate the next current satellite node, and return to the step of performing the first synchronization calibration on the current satellite node according to the node time quality until the satellite nodes of the constellation network complete the time synchronization;

[0051] The time synchronization maintenance module is used to execute the corresponding time synchronization maintenance strategy according to the relationship between the node time quality corresponding to each satellite node and the preset conditions to achieve time synchronization of the low-orbit satellite.

[0052] In order to solve the above technical problems, the present invention also provides a time synchronization device for a low-orbit satellite, comprising:

[0053] Memory for storing computer programs;

[0054] A processor is used to implement the steps of the above-mentioned low-orbit satellite time synchronization method when executing a computer program.

[0055] In order to solve the above technical problems, the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the time synchronization method for low-orbit satellites as mentioned above are implemented.

[0056] The present invention provides a time synchronization method for a low-orbit satellite, comprising: obtaining a time reference point of a constellation network and a current satellite node that is not time synchronized, and initializing the current satellite node to output a corresponding node time quality, wherein the time reference point is a domestic earth station; performing a first synchronization calibration on the current satellite node according to the node time quality, and performing a second synchronization calibration on the calibrated current satellite node through an improved RTT synchronization method; using the current satellite node after the second synchronization calibration as a new time reference point, calibrating the next current satellite node, and returning to the step of performing a first synchronization calibration on the current satellite node according to the node time quality, until each satellite node of the constellation network completes time synchronization; executing a corresponding time synchronization maintenance strategy according to the relationship between the node time quality corresponding to each satellite node and a preset condition to achieve time synchronization of the low-orbit satellite. The method performs a second synchronization calibration on the satellite node through an improved RTT synchronization method, eliminates the delay difference, achieves time synchronization of the constellation network, and simultaneously adds a time synchronization maintenance strategy, which can achieve autonomous time synchronization in the case of communication interruption caused by a sudden loss of synchronization of a certain satellite or inability to locate and provide timing in a special period, thereby improving the reliability of the low-orbit satellite communication system.

[0057] In addition, the present invention also provides a time synchronization device and medium for a low-orbit satellite, which have the same beneficial effects as the above-mentioned time synchronization method for a low-orbit satellite. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0059] Figure 1 A flowchart of a time synchronization method for a low-orbit satellite provided by an embodiment of the present invention;

[0060] Figure 2 A working principle diagram of the improved RTT synchronization method provided by an embodiment of the present invention;

[0061] Figure 3 An architecture diagram of a constellation network provided by an embodiment of the present invention;

[0062] Figure 4 A structural diagram of a time synchronization device for a low-orbit satellite provided by an embodiment of the present invention;

[0063] Figure 5 A structural diagram of another time synchronization device for a low-orbit satellite provided by an embodiment of the present invention;

[0064] Figure 6 A flowchart of another time synchronization method for a low-orbit satellite provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0065] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0066] The core of the present invention is to provide a time synchronization method, device and medium for low-orbit satellites, which can autonomously maintain time synchronization and improve the reliability of low-orbit satellite communication systems.

[0067] In order to enable those skilled in the art to better understand the solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0068] It should be noted that the time synchronization method for low-orbit satellites provided by the present invention can be applied to situations where GPS or Beidou cannot be used, or when there is a short-term non-positioning situation in the on-orbit environment of commercial GPS receivers. Because the time synchronization of well-known foreign communication satellite constellation systems basically relies on the ground station system deployed globally to complete. For example, the Iridium system with intersatellite links has 11 globally distributed ground stations; the Globalstar system without intersatellite links requires more than 300 ground stations. However, due to the international situation, most ground stations are located in the country, and the domestic revisit time of a single low-orbit satellite can reach up to more than ten hours. Obviously, this time synchronization method based on access control of ground stations is not suitable, so this method can also be applied to the above situation.

[0069] Figure 1 A flowchart of a time synchronization method for a low-orbit satellite provided by an embodiment of the present invention is shown in FIG. Figure 1 As shown, the method includes:

[0070] S11: Obtain the time reference point of the constellation network and the current satellite node that is not time synchronized, and initialize the current satellite node to output the corresponding node time quality, wherein the time reference point is the domestic earth station;

[0071] Specifically, the domestic earth station, as the time reference station of the entire constellation network, is turned on and waits for the satellite to enter. The satellite entry mentioned in this embodiment is mainly for the satellite nodes that have completed the launch but have not yet performed time synchronization. After each satellite node is turned on, time synchronization is started, so the time reference point of the constellation network and the current satellite node that is not time synchronized are obtained.

[0072] At the same time, the satellite node needs to be initialized to obtain the node time quality after processing. The initialization process can be a simple preprocessing process, in which the original node time quality of the satellite node is updated with the original node time quality of the satellite node based on the time reference station. Alternatively, by establishing a mathematical model, the time reference point and the original node time quality of the satellite node are input into the data model to perform initialization processing and output the corresponding node time quality. The present invention is not specifically limited and can be set according to actual conditions.

[0073] As an embodiment, the operation of each satellite node in the constellation network is a dynamically changing process, and needs to be adjusted in real time according to its own node time quality. Therefore, a data model is established to continuously improve and adjust its own node time quality.

[0074] It should be noted that time quality is a quantity that represents the degree to which the user's local system time deviates from the reference time. It is placed in the link layer frame header as a frequently updated information. The higher the time quality value, the higher the synchronization accuracy. The time reference point has the highest time quality value. The node in the out-of-sync state has the worst time quality value.

[0075] S12: performing a first synchronization calibration on the current satellite node according to the node time quality, and performing a second synchronization calibration on the calibrated current satellite node by using an improved RTT synchronization method, wherein the level of the first synchronization calibration is lower than the level of the second synchronization calibration;

[0076] After obtaining the node time quality of the current satellite node, the first synchronization calibration is performed on the current satellite node according to the node time quality. When the current satellite node enters, the entry here is based on the earth station, for example, the current satellite node enters the sky above China. The earth station distributes the time quality through the satellite-to-ground communication link, and the time quality of the incoming satellite monitoring communication peer is the time reference level, and the local system time of the current satellite node is corrected with the system time of the time reference station. The correction in this embodiment is only to update the local system time of the current satellite node through the system time of the time reference station. At this time, the first synchronization calibration is completed, and the updated local system time still includes errors caused by transmission processing delay, electromagnetic wave propagation delay, reception processing delay, etc., so a second synchronization calibration is required.

[0077] It can be understood that the level of the first synchronization calibration is lower than that of the second synchronization calibration. The first synchronization calibration is coarse synchronization, and the second synchronization calibration is fine synchronization. During the second synchronization calibration, it is based on the improved round trip time (RTT) synchronization method, and the current satellite node actively initiates improved RTT synchronization to the earth station.

[0078] For the RTT synchronization method, it is a two-way comparison method based on the measurement of the time of arrival (TOA). Its working principle is to use the two-way transmission of the TOA of the two parties involved in the time synchronization to offset the error of the wireless signal in the path transmission, and calculate the accurate time difference between the two parties. The effectiveness of this algorithm is based on the premise of symmetry of the transmission link. In fact, due to the long transmission distance and fast satellite movement speed, the transmission links of the satellite-to-ground and inter-satellite links of the low-orbit constellation are asymmetric and unstable. If the traditional RTT algorithm is used, the maximum measurement error of the same-orbit inter-satellite link can reach the microsecond level. The error of the inter-satellite link in the different orbit can reach the millisecond level when the satellite distance is closest near the poles and the radial velocity reaches the maximum. However, unlike the synchronization between the nodes of the ground network and the satellite network, due to the characteristics of the highly dynamically changing satellite, the link transmission delay error needs to know the specific location of the satellite node through the ephemeris information, so it is necessary to improve the RTT synchronization method to correct and calibrate the offset of the local system time of the current satellite node.

[0079] In the improved RTT synchronization, it is necessary to obtain the actual RTT inquiry delay, the actual RTT response delay, and the accurate delay difference to obtain the specific delay time to complete the second synchronization calibration. In addition, in the engineering implementation, the information content transmitted in the corresponding RTT inquiry and response process is not all the information transmission content of the inquiry party and the responder, which can be optimized according to the inter-satellite transmission system design, that is, not all information needs to be obtained through link transmission.

[0080] S13: Determine whether each satellite node of the constellation network has completed time synchronization. If not, proceed to step S14. If completed, proceed to step S15. S14: Use the current satellite node after the second synchronization calibration as a new time reference point, calibrate the next current satellite node, and return to step S12.

[0081] The time calibration between the earth station and the current satellite node in step S12 completes the initial synchronization of the satellite-to-ground transmission link time, and the initial synchronization of the inter-satellite transmission link time is required later. For example, five satellites (A, B, C, D, E) and the earth station are located in the constellation network. After the earth station and the C satellite are time-calibrated and synchronized, the C satellite has a new time reference point, that is, the time quality of the C satellite is updated, and the inter-satellite time synchronization is performed on the other satellites (A, B, D, E) based on C.

[0082] The time synchronization strategy is the same as the satellite-to-ground transmission link calibration in step S12, so the process returns to step S12 to complete the calibration of other satellites in the current constellation network.

[0083] Specifically, after the inbound satellite completes the synchronization of satellite and ground time with the earth station, it has the time quality of the time benchmark level, and distributes the time quality through the co-orbit and off-orbit intersatellite links. When its neighboring node satellite detects that the time quality of the other end is the time benchmark level, it sends a time broadcast request, the inbound satellite responds to the time broadcast message, the neighboring satellite node receives the broadcast message, uses the system time in it to correct the local system time to achieve the first synchronization calibration, and then actively initiates the improved RTT synchronization method to achieve the second synchronization calibration. By analogy, the satellite that has completed the second synchronization calibration of time will distribute the time quality to other unsynchronized neighboring nodes until the whole network time synchronization is completed.

[0084] It should be noted that due to the simultaneous entry of multiple satellites, overseas satellites may receive time quality updates from multiple neighboring nodes at the same time. Neighboring nodes with high time quality levels and fewer synchronization transmission hops should be selected to initiate round-trip timing improvement RTT synchronization. Inter-satellite links in different orbits may experience communication interruptions near the equator and the poles. When communication is interrupted, inter-satellite timing synchronization needs to wait. S15: Execute the corresponding time synchronization maintenance strategy based on the relationship between the node time quality corresponding to each satellite node and the preset conditions to achieve time synchronization of low-orbit satellites.

[0085] After completing the time synchronization of the constellation network, each satellite node monitors the time quality of neighboring nodes in the inter-satellite and satellite-to-ground networks in real time. Since the node time quality values ​​corresponding to each satellite node are different, the preset conditions they meet are different from the corresponding time synchronization maintenance strategies. Therefore, according to the relationship between the node time quality and the preset conditions, the corresponding time synchronization maintenance strategy is executed to avoid a slight deviation from causing the satellite-to-ground and inter-satellite time synchronization calibration of the above embodiment to be repeated, thereby improving the calibration time. Different time synchronization maintenance strategies are executed for different deviations. For example, when the node time quality value is less than the threshold value of the first synchronization calibration, it is necessary to restart the initialization phase. When the node time quality value is less than the threshold value of the second synchronization calibration, it is necessary to return to the first synchronization calibration step and repeat the second synchronization calibration, etc.

[0086] The present invention provides a time synchronization method for a low-orbit satellite, comprising: obtaining a time reference point of a constellation network and a current satellite node that is not time synchronized, and initializing the current satellite node to output a corresponding node time quality, wherein the time reference point is a domestic earth station; performing a first synchronization calibration on the current satellite node according to the node time quality, and performing a second synchronization calibration on the calibrated current satellite node through an improved RTT synchronization method; using the current satellite node after the second synchronization calibration as a new time reference point, calibrating the next current satellite node, and returning to the step of performing a first synchronization calibration on the current satellite node according to the node time quality, until each satellite node of the constellation network completes time synchronization; executing a corresponding time synchronization maintenance strategy according to the relationship between the node time quality corresponding to each satellite node and a preset condition to achieve time synchronization of the low-orbit satellite. The method performs a second synchronization calibration on the satellite node through an improved RTT synchronization method, eliminates the delay difference, achieves time synchronization of the constellation network, and simultaneously adds a time synchronization maintenance strategy, which can achieve autonomous time synchronization in the case of communication interruption caused by a sudden loss of synchronization of a certain satellite or inability to locate and provide timing in a special period, thereby improving the reliability of the low-orbit satellite communication system.

[0087] Based on the above embodiment, the step S11 of initializing the current satellite node and outputting the corresponding node time quality includes:

[0088] Get the time synchronization parameters of the current satellite node;

[0089] Establish a time monitoring model based on the time synchronization parameters and output the local system time corresponding to the current satellite node;

[0090] The node time quality of the current satellite node is determined based on the local system time and the time reference point.

[0091] Specifically, the time synchronization parameters of the current satellite node are obtained, wherein the time synchronization parameters at least include the clock index, the number of synchronization hops, the synchronization retention time, the time anomaly detection and other factor parameters, and a time monitoring model is established according to the time synchronization parameters. It should be noted that the time monitoring model is a model established by the local system of the current satellite node, and is a time monitoring model obtained by continuous training based on the time synchronization parameters. Its purpose is to monitor the offset deviation between the local system time and the time reference point, input the time synchronization parameters into the time monitoring model, and output the local system time of the current satellite node in real time.

[0092] Furthermore, the node time quality of the current satellite node is determined based on the local system time and the time reference point, and broadcast to the network. At the same time, it acts as a monitor in orbit to listen to the time quality of other satellite nodes and earth station nodes.

[0093] In addition, the synchronization hop count of the time synchronization parameter is the number of hops for the system time to be transmitted. For each level of transmission in the satellite network of the system time station, the synchronization hop count in the time broadcast message is accumulated by 1.

[0094] The embodiment of the present invention provides a method for initializing and outputting a corresponding node time quality of a current satellite node, thereby updating the node time quality of the current satellite node according to a time reference point and ensuring subsequent time synchronization.

[0095] Based on the above embodiment, the first synchronization calibration of the current satellite node is performed according to the node time quality in step S12, including:

[0096] When the current satellite node enters, the current satellite node is controlled to send a time broadcast request message to the time reference point so that the time reference point sends a response broadcast message to the current satellite node;

[0097] The local system time of the current satellite node is corrected according to the response broadcast information to complete the first synchronization calibration.

[0098] Specifically, when the current satellite node enters, the earth station distributes the time quality through the satellite-to-ground communication link. The incoming satellite detects the time quality of the communication counterpart as the time reference level, that is, the earth station is used as the time reference point. The current satellite node sends time broadcast information to the time reference point. At this time, the time reference point generates a corresponding response time broadcast message based on the sent time broadcast information, and sends it to the current satellite node.

[0099] The current satellite node receives the response broadcast information and uses the system time of its time reference point to correct the local system time of the current satellite node. Specifically, the local system time can be updated according to the system time of the time reference point to complete the first synchronization calibration.

[0100] The embodiment of the present invention provides a method for performing a first synchronization calibration on a current satellite node according to the node time quality, realizing a coarse synchronization calibration on the current satellite node, reducing errors, and facilitating subsequent time synchronization.

[0101] Based on the above embodiment, the second synchronization calibration of the calibrated current satellite node by improving the RTT synchronization method in step S12 includes:

[0102] Get the RTT query message information of the current satellite node;

[0103] The current satellite node is used as the interrogator and the time reference point is used as the responder;

[0104] The time when the inquiring party sends the RTT inquiry message information to the responding party is controlled as the first timestamp;

[0105] Control the responder to record the time of receiving the RTT inquiry message information as the second timestamp, generate corresponding RTT reply message information according to the RTT inquiry message information, record the sending time of the RTT reply message information as the third timestamp, and send the RTT reply message information to the inquiring party at the third timestamp, wherein the RTT reply message information includes the second timestamp, the third timestamp and the ephemeris information of the responder;

[0106] The control inquiring party records the time of receiving the RTT response message information as a fourth timestamp;

[0107] Obtain the inquiring party's ephemeris information;

[0108] Determine the actual delay difference between the inquiring party and the responding party according to the ephemeris information of the inquiring party and the ephemeris information of the responding party;

[0109] Subtracting the second timestamp from the first timestamp to obtain a first delay difference;

[0110] Subtracting the third timestamp from the fourth timestamp to obtain a second delay difference;

[0111] Subtracting the first delay difference from the second delay difference to obtain a third delay difference;

[0112] The two-way delay time between the inquiring party and the responding party is obtained by performing a difference processing based on the third delay difference and the actual delay difference;

[0113] The two-way delay time is averaged to obtain the one-way delay time, and the one-way delay time is used as the offset of the inquiry party to determine the completion of the second synchronization calibration.

[0114] Specifically, after the first synchronization calibration is completed, if the system time of the current satellite node still includes errors caused by transmission processing delay, electromagnetic wave propagation delay, reception processing delay, etc., the second synchronization calibration is continued. During the second synchronization calibration process, the current satellite node is synchronized with the time reference point in round-trip timing RTT. At the same time, since the motion state between satellite network nodes is highly dynamic, the link transmission delay error needs to be eliminated through specific ephemeris information, so the RTT synchronization is improved.

[0115] Figure 2 The working principle diagram of the improved RTT synchronization method provided by the embodiment of the present invention is as follows: Figure 2As shown, first obtain the RTT inquiry message information of the current satellite node, take the satellite to be synchronized, that is, the current satellite node as the inquirer, the current time reference point is the earth station, if for inter-satellite synchronization, its synchronized satellite node can also be used as the time reference point, and its responder is the earth station or the synchronized satellite node of the time reference point. The inquirer sends the RTT inquiry message information to the responder at the first timestamp T'1, and the responder receives the RTT inquiry message information sent by the inquirer at the second timestamp T2, generates corresponding RTT reply message information according to the RTT inquiry message information, and sends the RTT reply message information to the inquirer at the third timestamp. At this time, the RTT reply message information includes the second timestamp, the third timestamp and the ephemeris information (or the position of the earth station) of the responder. At this time, the inquirer receives the RTT reply message information at the fourth timestamp T'4.

[0116] It is worth noting that T'1 and T'4 are recorded based on the time base of the interrogator, and T2 and T3 are recorded based on the time base of the responder. The actual delay difference between the interrogator and the responder is determined based on their respective ephemeris information. The first delay difference obtained by subtracting the second timestamp from the first timestamp and the second delay difference obtained by subtracting the third timestamp from the fourth timestamp are not the actual transmission delay differences, so there are errors, and the inquiring party needs to correct them by subtracting the first delay difference from the second delay difference to obtain the third delay difference; subtract the third delay difference from the actual delay difference to obtain the two-way delay time between the inquiring party and the responding party, and average the two-way delay time to obtain the one-way delay time. The specific formula is as follows:

[0117]

[0118] Among them, T'1 and T'4 are the times recorded based on the time base of the inquiring party, and T2 and T3 are the times recorded based on the time base of the responding party. The actual delay difference between the two parties is determined based on the ephemeris information of the inquiring party and the responding party.

[0119] The second synchronization calibration provided by the embodiment of the present invention is performed by improving the RTT synchronization method, which takes into account the high dynamic changes of satellite nodes in the constellation network, and can eliminate the transmission delay error through the ephemeris information, so that the RTT algorithm can be applied to the inter-satellite communication link, and improve the accuracy of the time synchronization of the constellation network. The autonomous time synchronization of the constellation is achieved by combining the link layer frame interaction with the physical layer frame arrival time (TOA) detection, the engineering implementation is simple, the network overhead is small, the synchronization accuracy meets the conventional communication constellation accuracy requirements, and there are no special requirements for the satellite network transmission system and networking system, and it can be widely used in various types of low-orbit communication satellite networks.

[0120] On the basis of the above embodiment, after all initial time synchronization is performed, each satellite node is required to monitor the time quality of neighboring nodes in the inter-satellite and satellite-to-ground networks in real time. The preset conditions in step S14 include a first preset condition, a second preset condition, and a third preset condition. The corresponding time synchronization maintenance strategy is executed according to the relationship between the node time quality corresponding to each satellite node and the preset conditions, including:

[0121] Acquire a current node time quality value and a time deviation reference value, a second synchronization threshold value and a first synchronization threshold value of a current satellite node, wherein the second synchronization threshold value is higher than the first synchronization threshold value;

[0122] Establish a time quality value report based on the node time quality corresponding to each satellite node;

[0123] Obtaining the time quality value of the adjacent satellite node of the current satellite node in the time quality value report, wherein the adjacent satellite node is located at the satellite node of the co-orbit link and the off-orbit link of the current satellite node;

[0124] When the time quality value of the adjacent satellite node meets the first preset condition, the adjacent satellite node is used as the time reference point to initiate a second synchronization calibration for the current satellite node, and enter the step of performing a second synchronization calibration on the calibrated current satellite node by using the improved RTT synchronization method, wherein the first preset condition is that the time quality value of the adjacent satellite node changes;

[0125] When the time quality value of the current node meets the second preset condition, the highest time quality value in the adjacent satellite node is selected in the time quality value report, and a second synchronization calibration is initiated to the adjacent satellite node corresponding to the highest time quality value, and the step of performing a second synchronization calibration on the calibrated current satellite node by using the improved RTT synchronization method is entered, wherein the second preset condition is that the time quality value of the current node is less than the second synchronization threshold value;

[0126] When the time quality value of the current node and the time deviation reference value meet the third preset condition, the highest time quality value among the adjacent satellite nodes is selected in the time quality value report, and a time broadcast request message is initiated to the adjacent satellite node corresponding to the highest time quality value, and the step of correcting the local system time of the current satellite node according to the response broadcast message is performed to complete the first synchronization calibration, wherein the third preset condition is that the time quality value of the current node is less than the first synchronization threshold value and the time deviation reference value is greater than the threshold value.

[0127] Specifically, obtaining the current node time quality value of the current satellite node, the time deviation reference value, and introducing a threshold value in the time synchronization process can narrow the synchronization estimation search interval, improve the accuracy of the synchronization algorithm, and effectively reduce the probability of sending timing error estimation. Therefore, the second synchronization threshold value and the first synchronization threshold value are also obtained, wherein the second synchronization threshold value is higher than the first synchronization threshold value.

[0128] A time quality value report is established according to the node time quality corresponding to each satellite node, and the time quality value of the adjacent satellite node of the current satellite node is obtained in the time quality value report. It can be understood that there are at least two adjacent satellite nodes, such as a satellite located in a corner of a constellation network, and two adjacent satellite nodes. If the satellite node is located in the first row, last row, first column or last column of the constellation network, there are three adjacent satellite nodes. If the satellite is located in other positions, there are four adjacent satellite nodes. They are respectively located in the same track link and the different track link.

[0129] When it is monitored that the time quality value of the adjacent satellite node meets the first preset condition, the first preset condition is that the time quality value of the adjacent satellite node has changed. Then, taking the adjacent satellite node as the time reference point, a second synchronization calibration is initiated for the current satellite node, and the step of performing a second synchronization calibration on the calibrated current satellite node through the improved RTT synchronization method is entered. It should be noted that there may be multiple adjacent satellite nodes. If there are multiple adjacent satellite nodes that have changed, the second synchronization update can be performed one by one starting from the one with the largest changed time quality value, or the satellite node with the largest changed time quality value can be used as the reference point and only performed once. It can be set according to the actual situation and is not specifically limited here.

[0130] If the time quality value of the current node meets the second preset condition, the highest time quality value among the adjacent satellite nodes is selected in the time quality value report, and the second synchronization calibration is initiated with the adjacent satellite node corresponding to the highest time quality value, and the step of performing the second synchronization calibration on the calibrated current satellite node by the improved RTT synchronization method is entered, wherein the second preset condition is that the time quality value of the current node is less than the second synchronization threshold value. For example, when the local time quality is lower than the second synchronization threshold value, the node returns to the first synchronization calibration state, and the second synchronization calibration is initiated to the neighboring node with the highest time quality and available through the time quality internal report.

[0131] When the time quality value of the current node and the time deviation reference value meet the third preset condition, the highest time quality value in the adjacent satellite node is selected in the time quality value report, and a time broadcast request message is initiated to the adjacent satellite node corresponding to the highest time quality value, and the step of correcting the local system time of the current satellite node according to the response broadcast message to complete the first synchronization calibration is entered, wherein the third preset condition is that the time quality value of the current node is less than the first synchronization threshold value and the time deviation reference value is greater than the threshold value. Specifically, if the time drifts too far from the reference, that is, when the time deviation reference value is greater than the threshold value and the node time quality value is lower than the first synchronization threshold value, it returns to the initialization state, selects the neighbor node with the highest time quality and is available to send a time broadcast message request, obtains the system time to complete the first synchronization calibration, and then performs the second synchronization calibration.

[0132] The embodiment of the present invention provides a method for executing a corresponding time synchronization maintenance strategy according to the relationship between the node time quality corresponding to each satellite node and the preset conditions. When a sudden error occurs in the local time or the time offset is too far, the time of the neighboring node can be synchronized autonomously. When the constellation uses GPS or Beidou synchronization, a satellite can be resynchronized autonomously without the intervention of the earth station after a sudden loss of synchronization.

[0133] Based on the above embodiment, the process of establishing the constellation network in step S11 includes the following steps:

[0134] Configure multiple satellite nodes on the current orbital plane to be in co-orbital inter-satellite links;

[0135] The current satellite nodes at the plurality of satellite nodes are configured as satellite nodes on adjacent orbital planes so as to be in inter-satellite links on different orbits;

[0136] The current satellite node is fixedly connected to the adjacent satellite node according to the same-orbit inter-satellite link and the different-orbit inter-satellite link;

[0137] Connect the domestic earth station to any satellite node in the current orbital plane so that multiple satellite nodes and the domestic earth station are in the constellation network to complete the establishment process.

[0138] Figure 3 An architecture diagram of a constellation network provided by an embodiment of the present invention, such as Figure 3As shown, the constellation network system consists of N satellites distributed on M orbital planes, earth stations, business data centers, and user terminals and Internet users distributed all over the world. The present invention mainly solves time synchronization, which is only satellite-to-ground time synchronization performed with the earth station through a feeder link, and the satellite terminal of the user link is not used for timing. Each satellite is configured with two co-orbital inter-satellite links, which respectively communicate bidirectionally with the front and rear satellites on the same track. Two satellites are selected on each orbital plane, each of which is configured with two different-orbital inter-satellite links, which respectively communicate bidirectionally with two adjacent orbital neighbor satellites. Both the co-orbital inter-satellite links and the different-orbital inter-satellite links maintain a fixed connection with the neighboring satellites, and the different-orbital inter-satellite links may be periodically interrupted and reconnected near the equator and the poles.

[0139] The constellation network provided by the embodiment of the present invention can realize autonomous time synchronization of the entire network. In the event of communication interruption caused by a sudden loss of synchronization of a certain satellite or inability to locate and provide timing during a special period, the network can autonomously maintain time synchronization, thereby improving the reliability of the low-orbit satellite communication system.

[0140] Based on the above embodiment, the method further includes:

[0141] Obtain error factor parameters of time synchronization of the constellation network;

[0142] Determine the error category and error magnitude based on the error factor parameters;

[0143] Error analysis is performed based on the error category, error factor parameters and error magnitude to determine the timing period of the corresponding domestic earth station.

[0144] Specifically, the error factor parameters of the time synchronization of the constellation network are obtained, and the error category and error magnitude are determined according to the error factor parameters, and then the error is analyzed to determine the timing cycle of the corresponding domestic earth station. When designing the system according to different actual error analysis, a reasonable earth station timing cycle can be designed according to the accuracy requirements of time synchronization to ensure that the error of time synchronization is small.

[0145] Table 1 is an error analysis table of the constellation time synchronization method. As shown in Table 1, it includes three error categories: RTT fine synchronization error, that is, the error generated based on the second synchronization calibration, multi-level time synchronization error transmission and time synchronization maintenance error. The corresponding error factors, error magnitudes and impact analysis are as follows:

[0146] 1. RTT fine synchronization error mainly comes from the transmission delay error caused by the asymmetry of the communication link, the error caused by frequency accuracy, the receiver measurement error, the delay jitter of the receiving and sending processing, the influence of the atmosphere on the satellite-to-ground transmission, etc. The transmission delay error can be eliminated through estimation, and RTT fine synchronization can eventually achieve a synchronization accuracy of tens of nanoseconds.

[0147] Second, multi-level time synchronization transmission error. Domestic earth stations are selected as time reference stations. Due to visibility reasons, each satellite in the low-orbit constellation only establishes communication connections with two satellites in the same orbit in front and behind it, and two satellites in different orbits on the left and right. Therefore, only incoming satellites can directly complete accurate time synchronization with the reference station. Overseas satellites need to transmit synchronization step by step through inter-satellite links in the same orbit and different orbits. The more time synchronization jumps, the greater the transmission error. Low-orbit constellations generally have multiple satellites entering at the same time, and the maximum multi-level time synchronization transmission error can be controlled within 1 microsecond.

[0148] 3. Time synchronization error. The main error comes from the cumulative error of frequency source drift. Different from the ground environment, the satellite environment temperature changes dramatically, and the frequency source drift is more obvious. Assuming that the synchronization holding time is T and the frequency source accuracy index is Nppm, the maximum cumulative error of clock offset is TNppm. When designing the system, a reasonable earth station timing cycle can be designed according to the time synchronization accuracy requirements to ensure that time drift does not cause time unavailability.

[0149] Table 1 Error analysis of constellation time synchronization method

[0150]

[0151] The embodiment of the present invention provides error factor parameters for obtaining time synchronization of a constellation network; determining error categories and error magnitudes according to the error factor parameters; and performing error analysis processing in combination with the error categories, error factor parameters, and error magnitudes to determine the timing cycle of the corresponding domestic earth station. The reliability of the low-orbit satellite communication system is improved.

[0152] The above describes in detail various embodiments corresponding to the time synchronization method for low-orbit satellites. On this basis, the present invention also discloses a time synchronization device for low-orbit satellites corresponding to the above method. Figure 4 The structure diagram of a time synchronization device for a low-orbit satellite provided by an embodiment of the present invention. Figure 4 As shown, the time synchronization device of the low-orbit satellite includes:

[0153] Initialization module 11, used to obtain the time reference point of the constellation network and the current satellite node that is not time synchronized, and initialize the current satellite node to output the corresponding node time quality, wherein the time reference point is the domestic earth station;

[0154] A first calibration module 12 is used to perform a first synchronization calibration on the current satellite node according to the node time quality, and perform a second synchronization calibration on the calibrated current satellite node by using an improved RTT synchronization method, wherein the level of the first synchronization calibration is lower than the level of the second synchronization calibration;

[0155] The second calibration module 13 is used to use the current satellite node after the second synchronization calibration as a new time reference point to calibrate the next current satellite node, and return to the step of performing the first synchronization calibration on the current satellite node according to the node time quality;

[0156] The time synchronization maintaining module 14 is used to execute the corresponding time synchronization maintaining strategy according to the relationship between the node time quality corresponding to each satellite node and the preset conditions to achieve the time synchronization of the low-orbit satellite after the satellite nodes of the constellation network complete the time synchronization.

[0157] Since the embodiments of the device part correspond to the above embodiments, please refer to the description of the embodiments of the method part for the embodiments of the device part, and will not be repeated here.

[0158] For an introduction to a time synchronization device for a low-orbit satellite provided by the present invention, please refer to the above-mentioned method embodiment, and the present invention will not be repeated here. It has the same beneficial effects as the time synchronization method for a low-orbit satellite.

[0159] Figure 5 A structural diagram of another time synchronization device for a low-orbit satellite provided by an embodiment of the present invention, such as Figure 5 As shown, the device comprises:

[0160] A memory 21, used for storing computer programs;

[0161] The processor 22 is used to implement the steps of the time synchronization method for low-orbit satellites when executing a computer program.

[0162] The time synchronization device for the low-orbit satellite provided in this embodiment may include but is not limited to a tablet computer, a laptop computer, or a desktop computer.

[0163] Among them, the processor 22 may include one or more processing cores, such as a 4-core processor, an 8-core processor, etc. The processor 22 can be implemented in at least one hardware form of a digital signal processor (DSP), a field-programmable gate array (FPGA), and a programmable logic array (PLA). The processor 22 may also include a main processor and a coprocessor. The main processor is a processor for processing data in the awake state, also known as a central processing unit (CPU); the coprocessor is a low-power processor for processing data in the standby state. In some embodiments, the processor 22 may be integrated with a graphics processing unit (GPU), which is responsible for rendering and drawing the content to be displayed on the display screen. In some embodiments, the processor 22 may also include an artificial intelligence (AI) processor, which is used to process computing operations related to machine learning.

[0164] The memory 21 may include one or more computer-readable storage media, which may be non-transitory. The memory 21 may also include a high-speed random access memory, and a non-volatile memory, such as one or more disk storage devices, flash memory storage devices. In this embodiment, the memory 21 is at least used to store the following computer program 211, wherein, after the computer program is loaded and executed by the processor 22, it can implement the relevant steps of the time synchronization method for the low-orbit satellite disclosed in any of the aforementioned embodiments. In addition, the resources stored in the memory 21 may also include an operating system 212 and data 213, etc., and the storage method may be temporary storage or permanent storage. Among them, the operating system 212 may include Windows, Unix, Linux, etc. The data 213 may include, but is not limited to, data involved in the time synchronization method for the low-orbit satellite, etc.

[0165] In some embodiments, the time synchronization device of the low-orbit satellite may also include a display screen 23 , an input / output interface 24 , a communication interface 25 , a power supply 26 , and a communication bus 27 .

[0166] Those skilled in the art can understand that Figure 5 The structure shown in the figure does not constitute a limitation on the time synchronization device for low-orbit satellites, and may include more or fewer components than those shown in the figure.

[0167] The processor 22 implements the time synchronization method for the low-orbit satellite provided by any of the above embodiments by calling the instructions stored in the memory 21.

[0168] For an introduction to a time synchronization device for a low-orbit satellite provided by the present invention, please refer to the above-mentioned method embodiment, and the present invention will not be repeated here. It has the same beneficial effects as the time synchronization method for a low-orbit satellite.

[0169] Furthermore, the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by the processor 22, the steps of the time synchronization method for the low-orbit satellite as described above are implemented.

[0170] It is understandable that if the method in the above embodiment is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk and other media that can store program code.

[0171] For an introduction to a computer-readable storage medium provided by the present invention, please refer to the above method embodiment, and the present invention will not be repeated here. It has the same beneficial effects as the time synchronization method for a low-orbit satellite.

[0172] As a preferred embodiment, Figure 6 A flowchart of another method for synchronizing a low-orbit satellite time provided by an embodiment of the present invention is shown in FIG. Figure 6 As shown, including:

[0173] S21: Satellite power on;

[0174] S22: monitor inter-satellite and satellite-to-ground link messages;

[0175] S23: Determine whether the time quality of the time reference point is monitored, if so, proceed to step S24, if not, return to step S22;

[0176] S24: Send time broadcast request;

[0177] S25: receiving a time broadcast message, calibrating the local system time, and entering a first synchronization calibration state;

[0178] S26: Actively initiate RTT time synchronization and enter the second synchronization calibration state;

[0179] S27: Monitor the time quality of local and neighboring nodes, and execute corresponding time synchronization maintenance strategies according to the relationship between the node time quality corresponding to each satellite node and the preset conditions to achieve time synchronization of low-orbit satellites.

[0180] For an introduction to another time synchronization device for a low-orbit satellite provided by the present invention, please refer to the above method embodiment, and the present invention will not be repeated here. It has the same beneficial effects as the time synchronization method for a low-orbit satellite.

[0181] The above is a detailed introduction to a time synchronization method for a low-orbit satellite, a time synchronization device for a low-orbit satellite, and a medium provided by the present invention. The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the embodiments can be referenced to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0182] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

Claims

1. A time synchronization method for a low-orbit satellite, characterized in that: include: Acquire a time reference point of a constellation network and a current satellite node that is not time synchronized, and initialize the current satellite node to output a corresponding node time quality, wherein the time reference point is a domestic earth station; Performing a first synchronization calibration on the current satellite node according to the node time quality, and performing a second synchronization calibration on the calibrated current satellite node by using an improved RTT synchronization method, wherein the level of the first synchronization calibration is lower than the level of the second synchronization calibration; Using the current satellite node after the second synchronization calibration as a new time reference point, calibrating the next current satellite node, and returning to the step of performing the first synchronization calibration on the current satellite node according to the node time quality, until the satellite nodes of the constellation network complete time synchronization; Execute a corresponding time synchronization maintenance strategy according to the relationship between the node time quality corresponding to each of the satellite nodes and the preset conditions to achieve time synchronization of the low-orbit satellite; Correspondingly, performing a second synchronization calibration on the calibrated current satellite node by improving the RTT synchronization method includes: Obtaining RTT query message information of the current satellite node; Taking the current satellite node as the inquiring party and the time reference point as the responding party; Control the time at which the inquiring party sends the RTT inquiry message information to the responding party as a first timestamp; Control the responder to record the time of receiving the RTT inquiry message information as a second timestamp, generate corresponding RTT reply message information according to the RTT inquiry message information, record the sending time of the RTT reply message information as a third timestamp, and send the RTT reply message information to the inquiring party at the third timestamp, wherein the RTT reply message information includes the second timestamp, the third timestamp and the ephemeris information of the responder; Control the inquiring party to record the time of receiving the RTT response message information as a fourth timestamp; Obtaining ephemeris information of the inquiring party; Determine an actual delay difference between the inquiring party and the responding party according to the ephemeris information of the inquiring party and the ephemeris information of the responding party; Subtracting the second timestamp from the first timestamp to obtain a first delay difference; Subtracting the third timestamp from the fourth timestamp to obtain a second delay difference; Subtracting the first delay difference from the second delay difference to obtain a third delay difference; The two-way delay time between the inquiring party and the responding party is obtained by performing a difference processing on the third delay difference and the actual delay difference; The two-way delay time is averaged to obtain a one-way delay time, and the one-way delay time is used as the offset of the inquiring party to determine that the second synchronization calibration is completed.

2. The time synchronization method for a low-orbit satellite according to claim 1, characterized in that: The initializing and outputting the corresponding node time quality of the current satellite node includes: Acquire the time synchronization parameters of the current satellite node; Establishing a time monitoring model according to the time synchronization parameters, and outputting the local system time corresponding to the current satellite node; The node time quality of the current satellite node is determined according to the local system time and the time reference point.

3. The time synchronization method for a low-orbit satellite according to claim 2, characterized in that: The performing a first synchronization calibration on the current satellite node according to the node time quality includes: When the current satellite node enters, controlling the current satellite node to send time broadcast request information to the time reference point so that the time reference point sends response broadcast information to the current satellite node; The local system time of the current satellite node is corrected according to the response broadcast information to complete the first synchronization calibration.

4. The time synchronization method for a low-orbit satellite according to claim 3, characterized in that: The preset conditions include a first preset condition, a second preset condition and a third preset condition, and the executing a corresponding time synchronization maintenance strategy according to a relationship between a node time quality corresponding to each of the satellite nodes and the preset conditions includes: Acquire a current node time quality value and a time deviation reference value, a second synchronization threshold value and a first synchronization threshold value of the current satellite node, wherein the second synchronization threshold value is higher than the first synchronization threshold value; Establishing a time quality value report according to the node time quality corresponding to each of the satellite nodes; Acquire the time quality value of the adjacent satellite node of the current satellite node in the time quality value report, wherein the adjacent satellite node is located at the satellite node of the same-orbit inter-satellite link and the satellite node of the different-orbit inter-satellite link of the current satellite node; When the time quality value of the adjacent satellite node meets the first preset condition, the adjacent satellite node is used as the time reference point to initiate fine synchronization of the current satellite node, and enter the step of performing a second synchronization calibration on the calibrated current satellite node by using the improved RTT synchronization method, wherein the first preset condition is that the time quality value of the adjacent satellite node changes; When the time quality value of the current node meets the second preset condition, the highest time quality value among the adjacent satellite nodes is selected in the time quality value report, and the fine synchronization is initiated to the adjacent satellite node corresponding to the highest time quality value, and the step of performing a second synchronization calibration on the calibrated current satellite node by using the improved RTT synchronization method is entered, wherein the second preset condition is that the time quality value of the current node is less than the second synchronization threshold value; When the current node time quality value and the time deviation reference value meet the third preset condition, the highest time quality value among the adjacent satellite nodes is selected in the time quality value report, and the time broadcast request information is initiated to the adjacent satellite node corresponding to the highest time quality value, and the step of correcting the local system time of the current satellite node according to the response broadcast information to complete the first synchronization calibration is entered, wherein the third preset condition is that the current node time quality value is less than the first synchronization threshold value and the time deviation reference value is greater than the threshold value.

5. The time synchronization method for a low-orbit satellite according to claim 4, characterized in that: The process of establishing the constellation network includes the following steps: Configuring multiple satellite nodes on the current orbital plane to be located in the co-orbital inter-satellite link; Configuring the current satellite node at the plurality of satellite nodes as a satellite node on an adjacent orbital plane to be in the inter-satellite link of the different orbit; The current satellite node is fixedly connected to the adjacent satellite node according to the same-orbit inter-satellite link and the different-orbit inter-satellite link; The domestic earth station is connected to any satellite node of the current orbital plane so that a plurality of satellite nodes and the domestic earth station are within the constellation network to complete the establishment process.

6. The time synchronization method for a low-orbit satellite according to any one of claims 1 to 5, characterized in that: Also includes: Acquiring error factor parameters of time synchronization of the constellation network; Determine the error category and error magnitude according to the error factor parameters; An error analysis process is performed in combination with the error category, the error factor parameters and the error magnitude to determine the timing cycle of the corresponding domestic earth station.

7. A time synchronization device for a low-orbit satellite, characterized in that: include: An initialization module is used to obtain a time reference point of a constellation network and a current satellite node that is not time synchronized, and initialize the current satellite node to output a corresponding node time quality, wherein the time reference point is a domestic earth station; A first calibration module, configured to perform a first synchronization calibration on the current satellite node according to the node time quality, and perform a second synchronization calibration on the calibrated current satellite node by using an improved RTT synchronization method, wherein the level of the first synchronization calibration is lower than the level of the second synchronization calibration; a second calibration module, configured to use the current satellite node after the second synchronization calibration as a new time reference point, calibrate the next current satellite node, and return to the step of performing the first synchronization calibration on the current satellite node according to the node time quality, until the satellite nodes of the constellation network complete time synchronization; A time synchronization maintenance module, used to execute a corresponding time synchronization maintenance strategy according to the relationship between the node time quality corresponding to each satellite node and a preset condition to achieve time synchronization of the low-orbit satellite; Correspondingly, performing a second synchronization calibration on the calibrated current satellite node by improving the RTT synchronization method includes: Obtaining RTT query message information of the current satellite node; Taking the current satellite node as the inquiring party and the time reference point as the responding party; Control the time at which the inquiring party sends the RTT inquiry message information to the responding party as a first timestamp; Control the responder to record the time of receiving the RTT inquiry message information as a second timestamp, generate corresponding RTT reply message information according to the RTT inquiry message information, record the sending time of the RTT reply message information as a third timestamp, and send the RTT reply message information to the inquiring party at the third timestamp, wherein the RTT reply message information includes the second timestamp, the third timestamp and the ephemeris information of the responder; Control the inquiring party to record the time of receiving the RTT response message information as a fourth timestamp; Obtaining ephemeris information of the inquiring party; Determine an actual delay difference between the inquiring party and the responding party according to the ephemeris information of the inquiring party and the ephemeris information of the responding party; Subtracting the second timestamp from the first timestamp to obtain a first delay difference; Subtracting the third timestamp from the fourth timestamp to obtain a second delay difference; Subtracting the first delay difference from the second delay difference to obtain a third delay difference; The two-way delay time between the inquiring party and the responding party is obtained by performing a difference processing on the third delay difference and the actual delay difference; The two-way delay time is averaged to obtain a one-way delay time, and the one-way delay time is used as the offset of the inquiring party to determine that the second synchronization calibration is completed.

8. A time synchronization device for a low-orbit satellite, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the steps of the time synchronization method for a low-orbit satellite as described in any one of claims 1 to 6 when executing the computer program.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the time synchronization method for a low-orbit satellite as described in any one of claims 1 to 6 are implemented.

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