Multi-means high-reliability time-frequency system management method for high-orbit constellation

Abstract

The invention provides a multi-means high-reliability time-frequency system management method for a high-orbit constellation. The method comprises the following steps: step 1, time-frequency synchronization: step 101, local time reference generation; step 102, presetting initial time; and step 103, time-frequency synchronization: satellite synchronization modes of time-frequency synchronization comprise a satellite-ground synchronization mode, an inter-satellite synchronization mode and a Beidou receiver synchronization mode. Step 2, time frequency adjustment: step 201, ground instruction adjustment; step 202, performing autonomous time adjustment; and step 3, time autonomous recovery. And 4, performing autonomous time difference prediction based on the on-orbit real-time calculation clock error parameter. And 5, keeping autonomous time. According to the method, on-orbit time difference calculation can be realized without external information assistance, the time difference is optimally estimated by using a Kalman filtering algorithm, a dynamic clock difference parameter is predicted, autonomous time difference calculation and estimation are realized, constellation autonomous time frequency synchronization and time recovery are realized, and stable operation of a whole satellite time frequency system is ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of satellite communication, and relates to time-frequency management and time-frequency synchronization, in particular to a multi-means high-reliability time-frequency system management method of a high-orbit constellation. BACKGROUND

[0002] The time-frequency system mainly realizes functions such as time generation, time-frequency synchronization and time keeping of the constellation system, and is a key system for establishing a constellation time reference and constellation time-frequency synchronization.

[0003] Generally, the time-frequency system can complete time-frequency synchronization functions such as satellite-ground and inter-satellite synchronization after injecting time instruction and synchronization instruction from the ground, and further performs time correction or synchronization through a mode of remote measurement and artificial detection diagnosis. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the application is to provide a multi-means high-reliability time-frequency system management method of a high-orbit constellation, which solves the technical problem that the reliability of time-frequency synchronization and adjustment of the constellation system in the prior art needs to be further improved without external device support.

[0005] In order to solve the above technical problems, the application adopts the following technical solutions.

[0006] A multi-means high-reliability time-frequency system management method of a high-orbit constellation, the method comprising the following steps.

[0007] Step one, time-frequency synchronization: Step 101, local time reference generation; Step 102, initial time presetting; Step 103, time-frequency synchronization.

[0008] Step two, time-frequency adjustment: Step 201, ground instruction adjustment; Step 202, autonomous time adjustment.

[0009] Step three, autonomous time recovery.

[0010] Step four, autonomous time difference prediction based on on-orbit real-time calculation of clock difference parameters.

[0011] Step five, autonomous time keeping.

[0012] Compared with the prior art, the application has the following technical effects.

[0013] (I) The application can realize in-orbit time difference calculation without external information assistance, optimally estimate the time difference by using Kalman filtering algorithm, predict dynamic clock difference parameters, realize autonomous time difference calculation and prediction, adopt autonomous time adjustment and time recovery method, realize constellation autonomous time and frequency synchronization and time recovery, and ensure stable operation of the whole satellite time and frequency system.

[0014] (II) The method of the application proposes a constellation distributed working mode, obtains time difference data between each node of inter-satellite link in the constellation, and forms paper time through autonomous time integration, adjusts the satellite time according to the deviation of the self time from the paper time, realizes autonomous time keeping of the constellation, that is, the time and frequency system of the whole constellation does not depend on a satellite, a ground station or a link, and the time and frequency synchronization and autonomous time keeping of the constellation can be realized even when partial system failure occurs in the constellation.

[0015] (III) The autonomous time keeping system of the application has high reliability and strong error resistance. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Fig. 1 is a structural schematic diagram of a time and frequency system.

[0017] Figure 2 Fig. 2 is a flow schematic diagram of a time and frequency synchronization method.

[0018] Figure 3 Fig. 3 is a flow schematic diagram of autonomous time adjustment.

[0019] Figure 4 Fig. 4 is a flow schematic diagram of autonomous time difference prediction based on real-time calculation of clock difference parameters in orbit.

[0020] The specific content of the application is further explained and described in detail in combination with the embodiments. DETAILED DESCRIPTION

[0021] It should be noted that all the devices, models and algorithms in the application adopt known devices, models and algorithms in the prior art unless otherwise specified.

[0022] As a long-term running high-orbit communication satellite, the constellation system can adopt autonomous time and frequency system management and time keeping method under the condition that the ground injection and interference ability is limited, and can timely, efficiently and accurately complete time monitoring, time and frequency synchronization, time recovery, autonomous time and frequency adjustment and time keeping, so as to ensure real-time and reliable communication of the constellation under specific task conditions. The multi-means high-reliability time and frequency system management and time and frequency synchronization technology of the constellation is an important technical approach to improve satellite safety and reliability and effectively reduce cost.

[0023] As a high-orbit communication system networking star, a multi-means high-security high-reliability time-frequency synchronization and time keeping system is adopted to ensure the completion of satellite communication tasks and the dominant position in the execution of specific tasks.

[0024] The application adopts multi-means time-frequency system management and time-frequency synchronization technology, which is an important technical approach to improve the security and reliability of satellites and effectively reduce costs. In the initial stage of equipment operation, time-frequency system management and time-frequency synchronization can be performed in the mode of manual detection and diagnosis by ground telemetry, to ensure stable and reliable operation of the whole satellite communication system. During long-term stable operation in orbit, no continuous monitoring by ground personnel and resources is required, and autonomous monitoring of time-frequency synchronization state is performed in orbit. When the threshold is exceeded, small step time difference and frequency difference adjustment is performed autonomously to realize no-sense time adjustment. In the absence of ground system and Beidou satellite support, the constellation time-frequency system can be autonomously maintained through inter-satellite link.

[0025] The following gives specific embodiments of the application, and it should be noted that the application is not limited to the following specific embodiments, and any equivalent transformation made on the basis of the technical solutions of the application falls within the protection scope of the application.

[0026] Embodiment 1: This embodiment gives a time-frequency system, as shown in Figure 1 The time-frequency system includes a satellite constellation system, which includes a plurality of satellites forming inter-satellite links between the plurality of satellites, and the satellites can receive Beidou time service. It also includes a ground system, which includes a plurality of ground stations capable of ground communication between the plurality of ground stations, and the ground stations can receive both Beidou time service and Beidou ground time service. The satellite and the ground station form a satellite-ground link.

[0027] The standard time of the time-frequency system is Beidou time. In this embodiment, Coordinated Universal Time (UTC) is the world standard time formed by the integration of multiple clock groups around the world. Beidou Time (BDT) is generated and broadcast globally by the Beidou satellite navigation system and is China's space-based time reference. There is a fixed deviation between BDT and UTC time, which is traced back to UTC by the Beidou ground control system. In June 2020, the Beidou-3 global satellite system was completed and formed a service capability, therefore, the standard time of the time-frequency system is selected as Beidou time.

[0028] Embodiment 2: This embodiment gives a multi-means high-reliability time-frequency system management method for high-orbit constellation, and the time-frequency system adopts the time-frequency system given in embodiment 1, which includes the following steps.

[0029] Step one, time-frequency synchronization: In the embodiment, after the satellite is launched into orbit, the time-frequency system device as a basic load device is started by the ground through the integrated electronics. After the time-frequency system obtains the initial time information sent by the integrated electronics, the local time is calibrated by using the time deviation information from the ground, inter-satellite link and Beidou receiver, and is synchronized to the ground time and Beidou time respectively, so as to complete the initial time preset in orbit. In the normal case of satellite-ground time-frequency synchronization, the time-frequency system can perform Beidou time time tracing through the ground station; in the normal working case of the satellite-borne Beidou receiver, the time-frequency system can perform Beidou time time tracing to the Beidou and other global satellite navigation system time through the receiver.

[0030] In the embodiment, when the satellite-ground and inter-satellite time deviates, the threshold can be set, and when the threshold is exceeded, the time adjustment instruction or the autonomous time-frequency adjustment function is started to adjust the in-orbit autonomous time difference and frequency difference. In the in-orbit autonomous operation mode of the whole satellite, the time-frequency system receives the time difference information of the inter-satellite laser processor, calculates the time deviation through the constellation system scale algorithm, and performs in-orbit autonomous time adjustment.

[0031] In the embodiment, the satellite synchronization mode of the time-frequency synchronization includes a satellite-ground synchronization mode, an inter-satellite synchronization mode and a Beidou receiver synchronization mode.

[0032] As shown in Figure 2 The method for time-frequency synchronization includes the following steps.

[0033] Step 101, local time reference generation: A 1PPS (1 Pulse Per Second, 1PPS is a time pulse signal output by the Beidou receiver once per second, the pulse width is 1 millisecond, and the accuracy can reach nanosecond level) time reference is generated by using the 100MHz frequency reference in the time-frequency system; and then the local time reference is generated by using the 1PPS time reference, and the local time reference includes week count and intra-week second count.

[0034] Step 102, initial time preset: The local time reference is synchronized by receiving the integrated electronics time information, and is preset to the initial time.

[0035] Step 103, time-frequency synchronization: After the initial time preset is completed, the time-frequency system autonomously judges the satellite synchronization mode. If the satellite synchronization mode is the satellite-ground synchronization mode, the time-frequency synchronization is performed according to the satellite-ground measurement result; if the satellite synchronization mode is the inter-satellite synchronization mode, the time-frequency synchronization is performed through the laser link; and if the satellite synchronization mode is the Beidou receiver synchronization mode, the local time is time-granted by receiving the Beidou receiver time information.

[0036] In this embodiment, after the satellite enters steady-state operation, it obtains time difference data between the satellite and ground stations, between satellites, and with the BeiDou satellites. Then, it selects one of the time synchronization modes in descending order of priority for the satellite, between satellite and ground stations, between satellites, and with the BeiDou receivers to complete time-frequency synchronization. Autonomous judgment refers to the time-frequency system determining the satellite synchronization mode based on pre-set time difference and frequency difference thresholds, and according to pre-set synchronization priorities, thereby achieving time-frequency system synchronization. The time difference, frequency difference thresholds, and synchronization priorities can be adjusted in real time according to the satellite's on-orbit operating conditions.

[0037] Step 2, Time and Frequency Adjustment: Time and frequency adjustment includes ground command adjustment and autonomous time adjustment. In this embodiment, time and frequency adjustment is achieved through multiple means, such as ground command adjustment and on-board autonomous adjustment, when there are deviations in the time and frequency difference between the satellite and the ground or between satellites.

[0038] The time-frequency adjustment method includes the following steps.

[0039] Step 201, Ground Command Adjustment: Ground personnel adjust the satellite's on-board time by adding or subtracting a time value based on the on-board time correction implementation conditions and the deviation between the on-board time and the ground time, in order to correct the satellite-to-ground time error. After receiving the centralized time synchronization command, the satellite corrects the on-board time according to the correction time difference value given in the command. After receiving the second pulse adjustment command, the satellite takes the modulo of the count value in the second counter (the current second pulse deviation) by 10 ns, uses the modulo value to adjust the count value in the ten nanosecond counter, thereby adjusting the phase of the second pulse, retaining the remainder, and continuing to accumulate.

[0040] Step 202, Autonomous Time Adjustment: like Figure 3 As shown, during the long-term operation of the time and frequency system, autonomous time difference and frequency difference adjustment are initiated to maintain the time and frequency system autonomously; real-time monitoring is conducted to determine whether the filtered time difference and frequency difference exceed the adjustment threshold; when the frequency difference exceeds the adjustment threshold, the autonomous frequency difference adjustment program is initiated; when the time difference exceeds the adjustment threshold, the autonomous time difference adjustment program is initiated; when both exceed the adjustment threshold simultaneously, the autonomous frequency difference adjustment program is initiated first, followed by the autonomous time difference adjustment program.

[0041] In this embodiment, time and frequency synchronization between the satellite and other satellites (ground stations) is achieved through two autonomous adjustments. Autonomous time difference monitoring and prediction ensure the stable operation of the entire satellite system without human intervention, while reducing the computational and control burden on the ground telemetry and control system.

[0042] In this embodiment, both the autonomous frequency difference adjustment program and the autonomous time difference adjustment program adopt autonomous frequency difference adjustment programs and autonomous time difference adjustment programs known in the art.

[0043] Step 3, Time Recovers Autonomously: In this embodiment, when the time manager or reference frequency synthesizer of the time and frequency system malfunctions or is shut down, it can automatically restore the time to ensure the continuous and stable operation of the satellite time and frequency system under fault conditions.

[0044] The method for autonomous time recovery includes the following steps.

[0045] Step 301: The time manager and the reference frequency synthesizer of the time and frequency system send second pulse signals, time calibration commands, and time data to each other via an RS422 interface to update the time information in real time and realize the time information backup function. In this embodiment, the time manager and the reference frequency synthesizer are time managers and reference frequency synthesizers known in the art.

[0046] Step 302: After a failure or restart of the time manager and reference frequency synthesizer, on-board autonomous time recovery is achieved through autonomous synchronization of second pulses and extraction of backup time information. This reduces the burden on ground system monitoring and time frequency system recovery processing, ensuring the long-term autonomous and stable operation of the constellation.

[0047] Example 3: This embodiment presents a multi-means, highly reliable time-frequency system management method for high-orbit constellations based on Embodiment 2 above. The method further includes step four. Step four is used to predict time difference data when the constellation lacks measured time difference data.

[0048] Step four addresses the issue of providing time support for onboard payloads even when the constellation lacks time difference data. When time difference deviations occur in the time-frequency system, adjustments can be made through minor frequency tuning, ensuring long-term time-frequency synchronization of the constellation system. This also resolves link lockout issues caused during time adjustment, maintaining the stability of inter-satellite and satellite-to-ground links and ensuring uninterrupted satellite service operation.

[0049] Step four, as Figure 4 As shown, autonomous time difference prediction is based on real-time on-orbit calculation of clock difference parameters.

[0050] Step 401: The satellite calculates the clock difference parameters in real time on orbit using a two-way pseudorange comparison algorithm based on the atomic clock clock difference model; the clock difference parameters include time difference and frequency difference.

[0051] In this embodiment, the atomic clock error model is Δ = Δ0 + k1t + ½k2t 2 +ε(t); In the formula: Δ represents the second pulse deviation; t represents time; Δ0 represents the initial phase (time) deviation; k1 is the initial frequency deviation; k2 is the linear drift rate; ε(t) represents the random error.

[0052] In this embodiment, k2 and ε(t) are relatively small for time-frequency systems and can be ignored in actual calculations.

[0053] Step 402: Determine the validity of the clock error parameters. If the number of clock error parameters calculated in real-time on-orbit in step 401 is greater than or equal to 200, the validity of the clock error parameters is deemed valid, and the clock error parameters are retained. Step 403: Calculate the time difference data based on the clock difference parameters obtained in step 402. In this step, the specific method for calculating the time difference data based on the clock difference parameters can be any calculation method known in this field for time differences.

[0054] Step 404: Perform Kalman filtering on the 200 sets of latest calculated time difference data retained in step 403 to obtain filtered time difference data. Step 405: When time difference data is not available, the filtered time difference data obtained in step 404 is used as the predicted time difference data.

[0055] Example 4: This embodiment provides a multi-means, highly reliable time and frequency system management method based on a high-orbit constellation according to Embodiment 3 above. This method further includes step five. Step five is used to maintain time synchronization by relying on the satellite constellation system itself when the ground system is destroyed. The duration of this maintenance depends on the number of satellites and their time synchronization requirements.

[0056] After the constellation is formed, all satellites within the constellation acquire time difference data between various nodes of the inter-satellite links and autonomously synthesize this data to form a paper time. Each satellite then adjusts its own time according to the deviation between its own time and the paper time, ultimately achieving synchronization of all satellite times with this paper time. This distributed operating mode is a decentralized time-frequency network. The time synchronization of the entire constellation does not depend on the interruption of any single satellite, ground station, or link, and constellation time synchronization can still be achieved. It features high autonomous operation reliability and strong fault tolerance.

[0057] In this embodiment, the autonomous timekeeping capability is analyzed as follows: According to the atomic clock error model, before autonomous timekeeping, it is necessary to determine the accuracy of the initial phase (time) deviation Δ0 and the initial frequency deviation k1 through satellite-to-ground tracing. The drift rate k2 will change over time, that is, the time deviation caused by the rate of change of the drift rate needs to be considered.

[0058] The satellite constellation system is a distributed, decentralized system. Each satellite in the constellation system obtains time information with other satellites through inter-satellite time difference measurement; each satellite independently integrates space-based time to maintain time; the failure of some satellites does not affect the time maintenance of other satellites.

[0059] Step 5: Maintain autonomous time.

[0060] Step 501, in the i The calculation on the satellite i The difference between the time on a satellite and the time of the time-frequency system In satellite constellation systems, the same type of rubidium clock is used, and their frequency stability characteristics are basically the same. Therefore, they can be simplified by taking equal weights, i.e., the simplified expression is... ; In the formula: TA(i) Indicates the first i The time difference between the satellite and the time-frequency system; Δt ij Indicates the first i satellite and the first j Time difference between satellites; P j Indicates the first j Weighted parameters of the satellites; N This indicates the number of satellites in a satellite constellation system.

[0061] Step 502, knowing the number i The difference between the time on a satellite and the time of the time-frequency system TA(i) Then, the approach was to adjust the frequency gradually and evenly; based on Calculate the frequency that needs to be adjusted per second. Δf Frequency is adjusted in small steps, and autonomous time maintenance is achieved through this imperceptible time adjustment method.

Claims

1. A multi-method, highly reliable time-frequency system management method for high-orbit constellations, characterized in that, The method includes the following steps: Step 1, Time and Frequency Synchronization: Step 101, Local time base generation: A 1PPS time base is generated using a 100MHz frequency base within the time-frequency system; then a local time base is generated using the 100MHz frequency base, the local time base including week count and week-in-second count; Step 102, Initial time preset: By receiving integrated electronic time information, the local time base is synchronized and preset to the initial time; Step 103, Time and Frequency Synchronization: After the initial time is preset, the time and frequency system automatically determines the satellite synchronization mode. If the satellite synchronization mode is satellite-to-ground synchronization mode, it performs time and frequency synchronization based on satellite-to-ground measurement results. If the satellite synchronization mode is inter-satellite synchronization mode, it selects to perform time and frequency synchronization through the laser link. If the satellite synchronization mode is BeiDou receiver synchronization mode, it receives time information from the BeiDou receiver to synchronize the local time. Step 2, Time and Frequency Adjustment: Step 201, Ground Command Adjustment: Ground personnel adjust the satellite's on-board time by adding or subtracting a time value based on the on-board time correction conditions and the deviation between the on-board time and ground time, in order to correct the time error between the satellite and the ground. After receiving the centralized time synchronization command, the satellite corrects the on-board time according to the correction time difference value given in the command. After receiving the second pulse adjustment command, the satellite takes the count value in the second counter modulo 10ns, uses the modulo value to adjust the count value in the ten-nanosecond counter, thereby adjusting the phase of the second pulse. The remainder is retained and continues to accumulate. Step 202, Autonomous Time Adjustment: During long-term operation of the time and frequency system, autonomous time difference and frequency difference adjustment are initiated to maintain the time and frequency system autonomously; real-time monitoring is conducted to ensure that the filtered time difference and frequency difference do not exceed the adjustment threshold; when the frequency difference exceeds the adjustment threshold, the autonomous frequency difference adjustment program is initiated; when the time difference exceeds the adjustment threshold, the autonomous time difference adjustment program is initiated; when both exceed the adjustment threshold simultaneously, the autonomous frequency difference adjustment program is initiated first, followed by the autonomous time difference adjustment program. Step 3, Time Recovers Autonomously: Step 301: The time manager and the reference frequency synthesizer of the time and frequency system send second pulse signals, time calibration commands and time data to each other through the RS422 interface, update the time information in real time, and realize the time information backup function. Step 302: After the time manager and reference frequency synthesizer malfunction or are restarted, on-board autonomous time recovery is achieved through second pulse autonomous synchronization and extraction of backup time information.

2. The multi-means high-reliability time-frequency system management method for high-orbit constellations as described in claim 1, characterized in that, The time and frequency system includes a satellite constellation system, which comprises multiple satellites that form inter-satellite links and are capable of receiving BeiDou time signals; it also includes a ground system, which comprises multiple ground stations that are capable of ground communication and can receive both BeiDou time signals and BeiDou ground time signals; a satellite-to-ground link is formed between the satellites and the ground stations; and the standard time of the time and frequency system is selected from BeiDou time.

3. The multi-means high-reliability time-frequency system management method for high-orbit constellations as described in claim 1, characterized in that, The method also includes step four; Step 4: Autonomous time difference prediction based on real-time on-orbit calculation of clock bias parameters: Step 401: The satellite calculates the clock difference parameters in real time on orbit using a two-way pseudorange comparison algorithm based on the atomic clock clock difference model. Step 402: Determine the validity of the clock error parameters. If the number of clock error parameters calculated in real time on orbit in step 401 is greater than or equal to 200, the validity of the clock error parameters is determined to be valid, and the clock error parameters are retained. Step 403: Calculate the time difference data based on the clock difference parameters obtained in step 402; Step 404: Perform Kalman filtering on the 200 sets of latest calculated time difference data retained in step 403 to obtain filtered time difference data; Step 405: When time difference data is not available, the filtered time difference data obtained in step 404 is used as the predicted time difference data.

4. The multi-means high-reliability time-frequency system management method for high-orbit constellations as described in claim 3, characterized in that, The method also includes step five; Step 5, Maintaining Autonomous Time: Step 501, in the i The calculation on the satellite i The difference between the time on the satellite and the time of the time-frequency system ; In the formula: TA(i) Indicates the first i The time difference between the satellite and the time-frequency system; Δt ij Indicates the first i satellite and the first j Time difference between satellites; N Indicates the number of satellites in a satellite constellation system; Step 502, according to Calculate the frequency that needs to be adjusted per second. Δf Frequency is adjusted in small steps to achieve autonomous time maintenance.

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