CN111880204B - Hierarchical time frequency system for navigation satellite - Google Patents
Hierarchical time frequency system for navigation satellite Download PDFInfo
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Abstract
A hierarchical time frequency system facing a navigation satellite belongs to the technical field of time frequency systems of navigation satellites, a ground operation and control system sets the week count and the second count of a navigation processor, the injection of the week count and the second count is completed by utilizing a satellite-ground link, and the navigation processor adjusts the week count and the second count according to injection information; the ground operation control system corrects the PPS of the navigation processor 1; the navigation processor is connected with the central computer through a 1PPS signal interface, the central computer obtains time from the navigation processor through a bus, and then secondary precision time synchronization is completed by utilizing the 1PPS signal interface; the navigation processor is connected with the terminal single machine through a 1PPS signal interface and a 10.23M signal interface, and the central computer distributes secondary precision time to the terminal single machine through the bus. The hierarchical time frequency system has good robustness, and improves the reliability of the whole satellite of the navigation satellite.
Description
Technical Field
The invention relates to a hierarchical time frequency system facing a navigation satellite, and belongs to the technical field of navigation satellite time frequency systems.
Background
The Beidou satellite navigation system is a space-based satellite navigation and time service system independently developed and built in China, provides corresponding services by establishing a time reference and a space reference, and the time reference is a key factor influencing the navigation performance of a constellation system and a satellite system. The satellite-borne time frequency system is an important component of a navigation satellite, and the unified time frequency system can ensure that various functions, information processing and distribution of a navigation satellite platform and a load are carried out in order.
In the past, the time of a navigation satellite is managed by a ground measurement and control system and a ground operation and control system which are relatively independent and respectively manage the time of a satellite platform and the time of a satellite load, the time management mode is not beneficial to coordination of the whole satellite platform and the load work, and the time management mode and the time management system need to ensure normal time sequence of all functions of the whole satellite through various interfaces and control. When the ground operation and control system is used for management, the satellite time needs to be managed uniformly by a satellite-borne time frequency system due to the fact that the navigation satellite system, the subsystem and the single machines have various time frequency signals and are distributed, and the single machines have different requirements on time accuracy. After the navigation satellite obtains accurate system time from the ground, how to distribute the time to each subsystem and single machine reliably, accurately and efficiently is an important technical problem.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the ground operation and control system sets the week count and the second count of the navigation processor, the injection of the week count and the second count is completed by utilizing a satellite-ground link, and the navigation processor adjusts the week count and the second count according to the injection information; the ground operation control system corrects the PPS of the navigation processor 1; the navigation processor is connected with the central computer through a 1PPS signal interface, the central computer obtains time from the navigation processor through a bus, and then secondary precision time synchronization is completed by utilizing the 1PPS signal interface; the navigation processor is connected with the terminal single machine through a 1PPS signal interface and a 10.23M signal interface, and the central computer distributes secondary precision time to the terminal single machine through the bus.
The purpose of the invention is realized by the following technical scheme:
a hierarchical time frequency system facing a navigation satellite comprises a ground operation control system, a satellite-borne first-stage time system, a satellite-borne second-stage time system and a satellite-borne third-stage time system;
the satellite-borne first-stage time system comprises a navigation processor, the satellite-borne second-stage time system comprises a central computer, and the satellite-borne third-stage time system comprises a terminal single machine; the navigation processor, the central computer and the terminal single machine are all connected with the bus;
the ground operation and control system sets the week count and the second count of the navigation processor, the injection of the week count and the second count is completed by utilizing the satellite-ground link, and the navigation processor adjusts the week count and the second count according to the injection information; the ground operation and control system determines the direction and the size of phase adjustment of the 1PPS on the navigation processor by calculating the difference between the satellite-ground pseudo range measured by the satellite-ground channel and the estimated value of the satellite-ground pseudo range in a satellite-ground time synchronization state, and then corrects the 1PPS of the navigation processor to keep the time synchronization of the navigation processor and the ground operation and control system and establish first-level precision time;
the navigation processor is connected with the central computer through a 1PPS signal interface, the central computer obtains time from the navigation processor through a bus, and then secondary precision time synchronization is completed by utilizing the 1PPS signal interface; when the 1PPS signal of the 1PPS signal interface is available, the central computer completes zero clearing work of milliseconds by using the 1PPS signal, and when the 1PPS signal of the 1PPS signal interface is unavailable, the central computer performs time keeping by using an internal crystal oscillator;
the navigation processor is connected with the terminal single machine through a 1PPS signal interface and a 10.23M signal interface, and the central computer distributes secondary precision time to the terminal single machine through a bus; when the time precision requirement of the single terminal is low, only secondary precision time is received from the bus, and when the time precision requirement of the single terminal is high, the single terminal receives the secondary precision time from the bus and simultaneously introduces a 1PPS signal and a 10.23M signal;
the precision of the first-level precision time is superior to that of the second-level precision time.
In the hierarchical time-frequency system for a navigation satellite, preferably, the error of the primary precision time is not more than 1ms.
In the hierarchical time-frequency system for the navigation satellite, preferably, when the 1PPS signal is available, the central computer performs second accumulation on the rising edge of each 1PPS signal, and clears the millisecond count; in the 1PPS signal, the central computer utilizes the frequency signal provided by the internal crystal oscillator to carry out millisecond accumulation; when the 1PPS signal is not available, the central computer sets the 1PPS signal as not allowed to be used and automatically switches to an internal crystal oscillator.
In the hierarchical time-frequency system for a navigation satellite, preferably, the central computer determines that the 1PPS signal is abnormal when the deviation of the 1PPS signal is greater than a preset deviation value.
Preferably, before the first-level precision time is established, the satellite-borne first-level time system is calibrated through the ground operation control system.
Preferably, the ground operation control system performs time correction including absolute time correction, incremental time correction and uniform time correction;
the absolute timing is as follows: after the central computer receives a satellite time setting instruction sent by the ground operation and control system, setting the absolute time of the housekeeping unit of the central computer as a received time value;
the increment timing is as follows: after the central computer receives a remote control instruction sent by the ground operation and control system, the remote control instruction comprises an increment value, and the received increment value is added to the absolute time of the housekeeping unit of the central computer;
the uniform timing is as follows: and each time the satellite affair management unit of the central computer passes a time correction interval, adding a time correction increment set by the ground operation and control system to the absolute time of the satellite affair management unit.
In the hierarchical time-frequency system for a navigation satellite, preferably, the time precision of the secondary precision time distributed to the terminal single machine by the central computer through the bus is 5ms.
Preferably, in the hierarchical time-frequency system for a navigation satellite, the terminal single machine includes a terminal type I, a terminal type II, and a terminal type III;
the terminal type I receives secondary precision time from a bus only; on the basis that the terminal type II receives secondary precision time from a bus, 1PPS signals are introduced to determine time; the terminal type III determines the time using the 1PPS signal and the 10.23M signal.
In the hierarchical time-frequency system for a navigation satellite, preferably, after the terminal type II receives the second-level precision time from the bus, the terminal type II calibrates its own time with the second-level precision time, and waits for a 1PPS signal; when the 1PPS signal arrives, the terminal type II accepts or rejects the millisecond time after the time second of the terminal type II, and in the 1PPS signal, the terminal type II equipment utilizes the frequency signal provided by the internal crystal oscillator to perform millisecond accumulation.
In the hierarchical time-frequency system for a navigation satellite, preferably, after the terminal type III receives the secondary precision time from the bus, the terminal type III calibrates its own time with the secondary precision time while waiting for a 1PPS signal; when a 1PPS signal arrives, the terminal type III accepts or rejects millisecond time after the time second of the terminal type III, and counts and clears the 10.23M; within the 1PPS signal, the terminating type III device performs millisecond accumulation using a 10.23MHz frequency signal.
Compared with the prior art, the invention has the following beneficial effects:
(1) The invention divides the satellite-borne time frequency system into 3 levels according to the design characteristics and ground operation management characteristics of the navigation satellite in China, designs uniformly, and adopts different time establishing and maintaining strategies for each level to form a hierarchical and hierarchical system structure. The establishment and maintenance strategies at all levels fully utilize the correlation between various time-frequency signals of the satellite and a single machine, so that time-frequency systems can be mutually unified, and clear task interfaces can be kept.
(2) The hierarchical time frequency system architecture has universality, adopts standard interfaces and common time synchronization means, is easy to expand, and can meet the requirements of different single machines and subsystems on time precision.
(3) The hierarchical time frequency system has good robustness, redundant backup means are provided for establishing and maintaining all levels of time frequencies, and the reliability of the whole satellite of the navigation satellite is improved.
Drawings
FIG. 1 is a schematic diagram of a hierarchical time-frequency system according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
A hierarchical time frequency system facing a navigation satellite comprises a ground operation control system, a satellite-borne first-stage time system, a satellite-borne second-stage time system and a satellite-borne third-stage time system;
the satellite-borne first-stage time system comprises a navigation processor, the satellite-borne second-stage time system comprises a central computer, and the satellite-borne third-stage time system comprises a terminal single machine; the navigation processor, the central computer and the terminal single machine are all connected with the bus;
the ground operation and control system sets the week count and the second count of the navigation processor, the injection of the week count and the second count is completed by utilizing the satellite-ground link, and the navigation processor adjusts the week count and the second count according to the injection information; the ground operation and control system determines the direction and the size of phase adjustment of the 1PPS on the navigation processor by calculating the difference between the satellite-ground pseudo range measured by the satellite-ground channel and the satellite-ground pseudo range estimated value in the satellite-ground time synchronization state, and then corrects the 1PPS of the navigation processor to keep the time synchronization of the navigation processor and the ground operation and control system and establish first-level precision time;
the navigation processor is connected with the central computer through a 1PPS signal interface, the central computer obtains time from the navigation processor through a bus, and then secondary precision time synchronization is completed by utilizing the 1PPS signal interface; when the 1PPS signal of the 1PPS signal interface is available, at the rising edge of each 1PPS signal, the central computer performs second accumulation by using the 1PPS signal and clears the millisecond count, and in the 1PPS signal, the central computer performs millisecond accumulation by using a frequency signal provided by an internal crystal oscillator; when the 1PPS signal of the 1PPS signal interface is unavailable, the central computer sets the 1PPS signal as not allowed to be used and utilizes an internal crystal oscillator to keep time; when the deviation of the 1PPS signal is larger than the preset deviation value, the central computer judges that the 1PPS signal is abnormal.
The navigation processor is connected with the terminal single machine through a 1PPS signal interface and a 10.23M signal interface, and the central computer distributes secondary precision time to the terminal single machine through a bus; when the time precision requirement of the single terminal is low, only secondary precision time is received from the bus, and when the time precision requirement of the single terminal is high, the single terminal receives the secondary precision time from the bus and simultaneously introduces a 1PPS signal and a 10.23M signal;
the precision of the first-level precision time is superior to that of the second-level precision time; the error of the primary precision time is not more than 1ms; the time precision of the secondary precision time distributed to the terminal single machine by the central computer through the bus is 5ms.
Before the first-level precision time is established, the satellite-borne first-level time system carries out time correction through a ground operation control system; the ground operation control system performs timing including absolute timing, incremental timing and uniform timing;
the absolute timing is as follows: after the central computer receives a satellite time setting instruction sent by the ground operation and control system, setting the absolute time of the housekeeping unit of the central computer as a received time value;
the increment timing is as follows: after the central computer receives a remote control instruction sent by the ground operation and control system, the remote control instruction comprises an increment value, and the received increment value is added to the absolute time of the satellite affair management unit of the central computer;
the uniform timing is as follows: and each time the satellite affair management unit of the central computer passes a time correction interval, adding a time correction increment set by the ground operation and control system to the absolute time of the satellite affair management unit.
The terminal single machine comprises a terminal type I, a terminal type II and a terminal type III; the terminal type I receives secondary precision time from a bus only; on the basis that the terminal type II receives secondary precision time from a bus, 1PPS signals are introduced to determine time; the terminal type III determines the time using the 1PPS signal and the 10.23M signal.
After the terminal type II receives the secondary precision time from the bus, the terminal type II calibrates the self time by using the secondary precision time and waits for a 1PPS signal at the same time; when the 1PPS signal arrives, the terminal type II accepts or rejects the millisecond time after the time second of the terminal type II, and in the 1PPS signal, the terminal type II equipment utilizes the frequency signal provided by the internal crystal oscillator to perform millisecond accumulation.
After receiving the secondary precision time from the bus, the terminal type III calibrates the self time by using the secondary precision time and waits for a 1PPS signal; when a 1PPS signal arrives, the terminal type III accepts or rejects millisecond time after the time second of the terminal type III, and counts and clears the 10.23M; within the 1PPS signal, the terminating type III device performs millisecond accumulation using a 10.23MHz frequency signal.
Example (b):
a hierarchical time-frequency system facing to a navigation satellite, i.e. a hierarchical time-frequency system architecture facing to a navigation satellite, as shown in fig. 1.
1. Time-frequency system classification
According to the design characteristics of the navigation satellite, the satellite-borne time system is divided into three levels and uniformly designed, and different means strategies are adopted for time correction and time maintenance of each level of satellite-borne time system, so that a hierarchical and uniform time-frequency system architecture is formed. The on-board time system classification method is as follows.
Satellite-borne first-stage time system: a navigation processor;
satellite-borne second-stage time system: a central computer;
satellite-borne third-level time system: and the single machine of each terminal type comprises a terminal type I, a terminal type II and a terminal type III.
The ground operation and control system is responsible for the operation and control of the navigation satellite and transmits the accurate navigation system time to the satellite-borne time system through a satellite-ground link. The navigation processor generates satellite time, a 10.23MHz signal and a 1PPS signal which are accurately synchronous with the time of a ground operation and control system navigation system according to the satellite reference frequency; the central computer is used as a main control end of the satellite information bus, and the control bus distributes time to various terminals; and various terminals receive time information or time-frequency signals to ensure the precision of the service time.
2. Time frequency system architecture and workflow
The invention designs a hierarchical time frequency system architecture facing a navigation satellite, which is used for realizing the uniform satellite-borne time of the navigation satellite and ensuring the order of all functions. Fig. 1 shows the system components of the present invention, including a ground operation control system, a navigation processor, a central computer and other various terminal types.
The hierarchical time-frequency system architecture can establish and maintain uniform on-board time, reduce the load brought by time non-uniformity to satellite-borne processing, and is favorable for adapting to complex and variable whole satellite and load design.
According to the time frequency system classification, the satellite-borne time system at each level is completed by different components:
the transmission from the ground control to the satellite-borne first-level time system is realized through the ground to the navigation processor. The navigation processor is used as an important component of an on-satellite time frequency system, and can establish high-precision time with a ground operation and control system through a high-precision satellite-ground measurement link. And the ground operation control monitors the time established by the navigation processor and calculates time correction parameters, so that the satellite-borne first-stage time system and the ground operation control time are kept synchronous.
The transmission from the satellite-borne first-stage time system to the satellite-borne second-stage time system is realized through the navigation processor to the central computer. In the whole satellite information system, a central computer establishes information connection with each subsystem and a single machine through a bus. The time can be acquired from the navigation processor by using a dual-redundancy bus, and the accurate second synchronization is carried out by using a 1PPS signal interface, so that the time accuracy meeting the functional requirements of a central computer and the requirements of a second-stage time system is realized. In the initial stage of the satellite orbit, the navigation processor is not started, and the central computer time can be established and calibrated through the satellite-ground link.
The transmission from the satellite-borne second-stage time system to the satellite-borne third-stage time system is realized by a central computer, 1PPS and 10.23M signals to various terminals. The central computer distributes satellite-borne second-stage time to the terminal through the bus, and if the terminal has the time requirement of higher precision, 1PPS and 10.23M signals can be introduced.
The workflow of each stage of the time system and the related functions of the related modules are respectively described below.
1. Working process of satellite-borne first-stage time system
And the satellite-borne first-stage time system and the ground operation and control system carry out time synchronization to complete the establishment of the time system. The satellite-ground time synchronization process mainly comprises two steps of time correction and phase modulation.
(1) The first step is as follows: and the ground operation and control system sets the week count and the second count of the satellite-borne first-stage time system. The ground operation and control system sets the week count and the second count of the navigation processor, the injection of the week count and the second count is completed by utilizing the satellite-ground link, and the navigation processor adjusts the week count and the second count according to the injection information.
(2) The second step is that: and the ground operation and control system adjusts the phase of the satellite-borne first-stage time system. According to satellite-to-ground pseudo range estimation, phase modulation processing is carried out on the satellite 1PPS according to the one-way time service principle. And determining the direction and the size of the phase adjustment of the 1PPS on the satellite by calculating the difference between the satellite-to-ground pseudo range measured by the uplink injection receiver and the estimated value of the satellite-to-ground pseudo range in the satellite-to-ground time synchronization state. After the satellite-ground synchronization, the satellite-ground clock difference of the satellite is generally within 1ms. The magnitude of the 1PPS phase adjustment can be calculated by the following equation.
Δ1PPS＝T Measured in fact -(T RX +T TX +T Sagnac +T Star and earth )
Wherein is T RX Signal reception delay, T, of a satellite TX Time delay, T, for signal transmission from ground station Star and earth Estimated satellite-to-ground range, T Sagnac Sagnac effect correction for satellite uplink, T Measured in fact And satellite-to-satellite pseudo ranges measured for the on-satellite transmission and reception radio frequency channels.
The operation control system can further carry out fine synchronization through a phase modulation instruction, and is responsible for controlling the time difference between the clock face of the satellite and the system, so that the time difference is not more than 1ms (the time difference is broadcast in a navigation message through a clock difference parameter within 1 ms).
The satellite-borne first-stage time system navigation processor outputs 1PPS signals, 10.23MHZ signals and time.
2. Satellite-borne second-level time system work flow
(1) After the satellite-borne first-stage time system establishes stable time, the central computer acquires high-precision time from the navigation processor through a 1553B bus, and receives a 1PPS signal as a time reference of the satellite-borne second-stage time system.
When the 1PPS signal is available, the central computer performs a zero clearing operation for milliseconds with the 1 PPS. At the rising edge of each 1PPS signal, performing second accumulation, and simultaneously resetting the millisecond count; within the 1PPS signal, the central computer performs millisecond integration by using a frequency signal provided by an internal crystal oscillator.
When the 1PPS signal is unavailable, the central computer is timed according to the internal crystal oscillator. The central computer detects the rising edge time interval of the 1PPS signal in real time, when the 1PPS signal has phase adjustment or abnormal conditions, namely the deviation of the 1PPS signal is more than +/-Nms, the 1PPS signal is considered to be abnormal, the 1PPS signal is immediately set not to be allowed to be used, and the internal crystal oscillator is automatically switched. The time accuracy of the central computer is 5ms, and when the 1PPS signal is generally deviated from the threshold accuracy by 1 to 6 times and phase adjustment or abnormality of the 1PPS signal is considered, a typical value of N may be 5 (ms) × 3=15 (ms). Typical values for N may be chosen to be 5 to 30.
(2) And when the satellite-borne first-stage time system does not establish stable time, timing is carried out through the ground operation control system.
The ground operation and control system has three timing methods:
absolute timing: after receiving a satellite time setting instruction sent by the ground, the central computer sets the absolute time of the housekeeping unit as a received time value;
incremental timing: and after receiving a remote control command sent by the ground, the central computer adds the received incremental value to the housekeeping unit.
And (3) uniform timing: every time the housekeeping unit passes a timing interval, the on-board software increases the absolute time of the housekeeping unit by a timing increment (a time increment or positive or negative) which can be set by the ground remote control.
The time precision of the central computer after the time correction of the ground operation control system depends on the error of the crystal oscillator, and the current central computer uses the crystal oscillator as a temperature compensation crystal oscillator: the frequency stability of the product is 1 x 10 -6 . For a navigation satellite, the requirement that the absolute satellite-time precision of a central computer at any time is better than 600ms is met, and the longest ground timing cycle is obtained by considering the error margin of 5 ms: (600-5) (ms)/(1 x 10) -6 ) About 165 (hours)
That is, the ground needs to perform incremental time correction to the satellite every 165 hours, and the time of ground incremental time correction can be increased if uniform time correction is adopted.
3. Working process of satellite-borne third-level time system
(1) Terminal type I
The terminal type I is a terminal with low time precision requirement, and the terminal maintains the satellite borne time by adopting a central computer bus time service.
The central computer sends the self time to the terminal equipment needing time information through a 1553B bus every 448ms, and the time precision is 5ms. After receiving the time, the terminal device can use the time to correct the time according to the self time management strategy.
(2) Terminal type II
The type II of the terminal is a terminal with medium time precision requirement, and the type II of the terminal maintains the satellite borne time in a mode of combining a central computer bus time service and a navigation processor 1PPS signal.
The central computer sends its own time to all type II devices via the 1553B bus every 448ms, while the navigation processor provides the 1PPS signal to the type II devices. And the bus time service precision of the central computer is 5ms, the terminal type II equipment calibrates the self time by using the time after receiving 1553B bus time information, and waits for a 1PPS signal at the same time. Since the 1PPS signal is received at the time of the whole second, the terminal type II device rounds the millisecond time after the second bit of its own time at the arrival time of the 1PPS signal (the millisecond information is discarded when the millisecond bit is 0 to 499ms, the millisecond information is discarded when the millisecond bit is 500 to 999ms, and the second bit +1 s). Within the 1PPS signal, the terminating type II device performs millisecond integration using a frequency signal provided by an internal crystal oscillator.
(3) Terminal type III
After the terminal type III equipment receives the secondary precision time from the bus at the starting-up time, the secondary precision time is used for calibrating the self time, and meanwhile, 1PPS signals are waited; when a 1PPS signal arrives, the terminal type III accepts or rejects millisecond time after the time second of the terminal type III, and generates a 1PPS signal and clears a 10.23M count by using navigation 1PPS and a 10.23MHz signal; followed by a time keeping with a 10.23MHz signal.
When the 1PPS signal deviates or jumps, the terminal type III equipment automatically checks the 1PPS signal, and when the 1PPS signal is not stable in the adjustment process, the terminal type III equipment works according to the self time-keeping 1PPS signal; and after the 1PPS signal is adjusted and stabilized, the terminal type III equipment automatically locks to the new 1PPS signal after 3 seconds of judgment. The terminal type III equipment has to have 1PPS signals for time synchronization at the starting time, and the equipment cannot normally work if no 1PPS signals exist at the moment; when the terminal type III equipment receives the 1PPS signal and carries out time synchronization, the 1PPS signal has no influence on the equipment when drifting; when the 1PPS adjustment is finished, the terminal type III equipment automatically synchronizes to the new 1PPS time. The function of the signal transmitter is not influenced when the signal of the 1PPS is lost or is disordered.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (10)
1. A hierarchical time frequency system facing a navigation satellite is characterized by comprising a ground operation control system, a satellite-borne first-stage time system, a satellite-borne second-stage time system and a satellite-borne third-stage time system;
the satellite-borne first-stage time system comprises a navigation processor, the satellite-borne second-stage time system comprises a central computer, and the satellite-borne third-stage time system comprises a terminal single machine; the navigation processor, the central computer and the terminal single machine are all connected with the bus;
the ground operation and control system sets the week count and the second count of the navigation processor, the injection of the week count and the second count is completed by utilizing the satellite-ground link, and the navigation processor adjusts the week count and the second count according to the injection information; the ground operation and control system determines the direction and the size of phase adjustment of the 1PPS on the navigation processor by calculating the difference between the satellite-ground pseudo range measured by the satellite-ground channel and the satellite-ground pseudo range estimated value in the satellite-ground time synchronization state, and then corrects the 1PPS of the navigation processor to keep the time synchronization of the navigation processor and the ground operation and control system and establish first-level precision time;
the navigation processor is connected with the central computer through a 1PPS signal interface, the central computer obtains time from the navigation processor through a bus, and then secondary precision time synchronization is completed by utilizing the 1PPS signal interface; when the 1PPS signal of the 1PPS signal interface is available, the central computer completes the zero clearing work of millisecond by using the 1PPS signal, and when the 1PPS signal of the 1PPS signal interface is unavailable, the central computer uses an internal crystal oscillator to keep time;
the navigation processor is connected with the terminal single machine through a 1PPS signal interface and a 10.23M signal interface, and the central computer distributes secondary precision time to the terminal single machine through a bus; when the time precision requirement of the single terminal is low, only secondary precision time is received from the bus, and when the time precision requirement of the single terminal is high, the single terminal receives the secondary precision time from the bus and simultaneously introduces a 1PPS signal and a 10.23M signal;
the precision of the first-level precision time is superior to that of the second-level precision time.
2. The hierarchical time-frequency system for navigation satellites according to claim 1, wherein the error of the primary precision time is not more than 1ms.
3. The hierarchical time-frequency system for a navigation satellite according to claim 1, wherein the central computer performs a second accumulation at each rising edge of the 1PPS signal while clearing the millisecond count when the 1PPS signal is available; in the 1PPS signal, the central computer utilizes the frequency signal provided by the internal crystal oscillator to carry out millisecond accumulation; when the 1PPS signal is not available, the central computer sets the 1PPS signal as not allowed to be used and automatically switches to an internal crystal oscillator.
4. The system of claim 3, wherein the central computer determines that the 1PPS signal is abnormal when the 1PPS signal deviation is greater than a predetermined deviation value.
5. The hierarchical time-frequency system for navigation satellites according to claim 1, wherein the satellite-based first-level time system is time-calibrated by a ground operation control system before first-level precision time is established.
6. The hierarchical time-frequency system for navigation satellites according to claim 5, wherein the ground operation control system performs time correction including absolute time correction, incremental time correction and uniform time correction;
the absolute timing is as follows: after the central computer receives a satellite time setting instruction sent by the ground operation and control system, setting the absolute time of the housekeeping unit of the central computer as a received time value;
the increment timing is as follows: after the central computer receives a remote control instruction sent by the ground operation and control system, the remote control instruction comprises an increment value, and the received increment value is added to the absolute time of the satellite affair management unit of the central computer;
the uniform timing is as follows: and each time the satellite affair management unit of the central computer passes a time correction interval, adding a time correction increment set by the ground operation and control system to the absolute time of the satellite affair management unit.
7. A hierarchical time-frequency system for navigation satellites according to one of claims 1 to 6 wherein the time precision of the secondary precision time distributed by the central computer to the terminal units via the bus is 5ms.
8. The hierarchical time-frequency system for navigation satellites according to one of claims 1 to 6, wherein the terminal unit comprises a terminal type I, a terminal type II, a terminal type III;
the terminal type I receives secondary precision time from a bus only; on the basis that the terminal type II receives secondary precision time from a bus, 1PPS signals are introduced to determine time; the terminal type III determines the time using the 1PPS signal and the 10.23M signal.
9. The hierarchical time-frequency system for navigation satellites according to claim 8, wherein the terminal type II receives the time of second precision from the bus, and then uses the time of second precision to calibrate its time while waiting for 1PPS signal; when the 1PPS signal arrives, the terminal type II accepts or rejects the millisecond time after the time second of the terminal type II, and in the 1PPS signal, the terminal type II equipment utilizes the frequency signal provided by the internal crystal oscillator to perform millisecond accumulation.
10. The hierarchical time-frequency system for navigation satellites according to claim 8, wherein the terminal type III receives the time of second precision from the bus, and then uses the time of second precision to calibrate the time of the terminal type III while waiting for the 1PPS signal; when a 1PPS signal arrives, the terminal type III accepts or rejects millisecond time after the time second of the terminal type III, and counts and clears the 10.23M; within the 1PPS signal, the terminating type III device performs millisecond accumulation using a 10.23MHz frequency signal.
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