CN109991839B - Satellite timing method based on satellite clock drift iterative estimation - Google Patents
Satellite timing method based on satellite clock drift iterative estimation Download PDFInfo
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- G—PHYSICS
- G04—HOROLOGY
- G04R—RADIO-CONTROLLED TIME-PIECES
- G04R20/00—Setting the time according to the time information carried or implied by the radio signal
- G04R20/02—Setting the time according to the time information carried or implied by the radio signal the radio signal being sent by a satellite, e.g. GPS
- G04R20/04—Tuning or receiving; Circuits therefor
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- G—PHYSICS
- G04—HOROLOGY
- G04R—RADIO-CONTROLLED TIME-PIECES
- G04R40/00—Correcting the clock frequency
- G04R40/06—Correcting the clock frequency by computing the time value implied by the radio signal
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
- G06F17/10—Complex mathematical operations
- G06F17/18—Complex mathematical operations for evaluating statistical data, e.g. average values, frequency distributions, probability functions, regression analysis
Abstract
A satellite timing method based on iterative estimation of satellite clock drift comprises the following steps: 1) determining an increment timing parameter by using a ground station, and sending an increment timing instruction with the increment timing parameter to a satellite computer by the ground station according to a threshold value; 2) the satellite computer performs incremental timing according to the incremental timing parameters and iteratively updates the satellite clock drift amount; 3) uniformly correcting the on-satellite time after the incremental timing according to the iteratively updated satellite clock drift amount; 4) and repeating the step 3) by taking the uniform time correction interval as a period until the satellite computer receives a new increment time correction instruction, returning to the step 2), and continuing the satellite time correction. The invention also carries out iterative estimation of the satellite clock drift while carrying out absolute time correction, thereby realizing gradual approximation of the satellite clock drift and reducing the frequency of the ground station command.
Description
Technical Field
The invention relates to a satellite timing method based on satellite clock drift iterative estimation, and belongs to the technical field of satellite engineering.
Background
The satellite computer generally uses a timer to update the on-satellite time, and due to clock drift of the timer, the difference value between the on-satellite time and the real time, i.e., the satellite-ground time difference, will be increased continuously, thereby bringing about adverse effects such as increased orbit determination error.
In order to limit the satellite-ground time difference, the current on-board software widely uses an incremental time correction method and a uniform time correction method, and the incremental time correction, namely the ground station provides the satellite-ground time difference for the on-board software to compensate for once, which is also called as centralized time correction. The uniform timing method is that the ground station provides uniform timing parameters for the on-board software to periodically compensate the clock drift.
However, the existing method does not involve iterative estimation of the satellite clock drift, and when the residual error between the uniform timing parameter and the actual satellite clock drift is large, timing commands need to be frequently sent, so that a large burden is brought to the ground station.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method can reduce the timing and command frequency of the ground station when the satellite-ground time difference error calculated by the ground station is large or the satellite clock drift fluctuation is large.
The technical scheme of the invention is as follows:
a satellite timing method based on iterative estimation of satellite clock drift comprises the following steps:
1) determining an increment timing parameter by using a ground station, and when the increment timing parameter is larger than a threshold value, sending an increment timing instruction with the increment timing parameter to a satellite computer by the ground station;
2) the satellite computer performs incremental timing according to the incremental timing parameters sent by the ground station to obtain the on-satellite time after the incremental timing; iteratively updating the star clock drift amount according to the increment timing parameters to obtain the iteratively updated star clock drift amount;
3) uniformly correcting the on-satellite time after the incremental timing according to the iteratively updated satellite clock drift amount;
4) and repeating the step 3) by taking the uniform time correction interval as a period until the satellite computer receives a new increment time correction instruction, returning to the step 2), and continuing the satellite time correction.
Said step 1) determining an incremental timing parameter dtmThe method specifically comprises the following steps:
dtm＝(dt1+…+dtn)/n，
therein, dt1，dt2，…，dtnthe time difference between the satellite on-board time and the real time is obtained for each time Δ T.
The value range of delta T is 0.5 h-12 h, and the value range of n is 1-48.
The method for performing incremental time correction according to the incremental time correction parameters sent by the ground station in the step 2) to obtain the satellite time after the incremental time correction specifically comprises the following steps:
tm＝tS+dtm，
wherein, tSFor satellite time, t, corresponding to the time of receiving the incremental timing commandmAnd m is a positive integer, and the satellite time after the increment time correction is obtained after the satellite computer receives the increment time correction instruction for the mth time.
The step 2) is a method for iteratively updating the star clock drift amount according to the incremental timing parameters to obtain the star clock drift amount updated in the mth iteration, and specifically comprises the following steps:
driftm＝driftm-1+dtm/(tm-tm-1)，
wherein, tm-1The satellite time t is the satellite time after the increment time correction correspondingly obtained by the increment time correction instruction m-1 received by the satellite computermThe satellite time after the increment time correction correspondingly obtained by the mth increment time correction instruction is received by the satellite computer, namely, the driftm-1Obtaining the corresponding star clock drift amount, drift, of the m-1 th increment timing instruction received by the satellite computer1＝0。
The value range of the threshold value P in the step 1) is 10 ms-2000 ms.
The step 3) is a method for uniformly correcting the on-satellite time after the incremental time correction according to the iteratively updated satellite clock drift amount, and specifically comprises the following steps:
tJ＝tW+driftm*TB，
wherein, tWFor uniformly correcting the on-satellite time, t, corresponding to the time of occurrenceJTo make the satellite time T after time correction uniformBFor uniform timing intervals, TB≤△T。
Compared with the prior art, the invention has the beneficial effects that:
the satellite computer can autonomously carry out iterative estimation on the satellite clock drift through the incremental timing parameters and carry out uniform timing by using the obtained satellite clock drift, so that the timing and command sending frequency of the ground station is reduced; meanwhile, the ground station does not need to calculate uniform timing parameters, and engineering is simple to implement.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a variation curve of the estimated value of the clock drift according to an embodiment of the present invention;
FIG. 3 is a graph of the time interval between two incremental timing corrections according to an embodiment of the present invention.
Detailed Description
The method carries out iterative estimation on the star clock drift according to the incremental timing information, so that the star clock drift tends to a true value, and the accuracy of the star clock drift compensation is improved. As the drift of the star clock tends to the true value, the trend of the increase of the satellite-ground time difference is restrained, thereby reducing the ground command frequency and saving the workload of the ground station.
The invention is described in further detail below with reference to the figures and the detailed description.
The invention relates to a satellite timing method based on satellite clock drift iterative estimation, which comprises the following steps as shown in figure 1:
1) determining an increment timing parameter by using a ground station, and when the increment timing parameter is larger than a threshold value, sending an increment timing instruction with the increment timing parameter to a satellite computer by the ground station; the value range of the threshold value P is 10 ms-2000 ms.
Determining an incremental timing parameter dtmThe method specifically comprises the following steps:
dtm＝(dt1+…+dtn)/n，
therein, dt1，dt2，…，dtnthe time difference between the satellite on-satellite time and the real time is obtained every time △ T, the value range of △ T is 0.5 h-12 h, n is a positive integer, and the value range of n is 1-48.
2) The satellite computer performs incremental timing according to the incremental timing parameters sent by the ground station to obtain the on-satellite time after the incremental timing; and iteratively updating the star clock drift amount according to the increment timing parameter to obtain the iteratively updated star clock drift amount.
The method for obtaining the satellite time after the incremental time correction specifically comprises the following steps:
tm＝tS+dtm，
wherein, tSFor satellite time, t, corresponding to the time of receiving the incremental timing commandmAnd the satellite time after the increment time correction is obtained after the satellite computer receives the increment time correction instruction for the mth time. Generally, a computer system updates time according to a timer chip, so that the on-satellite time is periodically increased, and the error between the on-satellite time and the real time is reduced by incremental timing.
The method for obtaining the star clock drift amount updated by the mth iteration specifically comprises the following steps:
when the satellite computer receives the increment timing command for the first time, it sets t1For the satellite time, drift, after incremental timing1Equal to 0. And when the satellite receives the increment timing instruction for the mth time, performing the following iterative calculation of the clock drift:
driftm＝driftm-1+dtm/(tm-tm-1)，
wherein, tm-1The satellite time t is the satellite time after the increment time correction correspondingly obtained by the increment time correction instruction m-1 received by the satellite computermThe satellite time after the increment time correction correspondingly obtained by the mth increment time correction instruction is received by the satellite computer, namely, the driftm-1And correspondingly obtaining the satellite clock drift amount for the m-1 th increment timing instruction received by the satellite computer.
3) And according to the iteratively updated star clock drift amount, uniformly correcting the on-satellite time after the incremental time correction, specifically:
tJ＝tW+driftm*TB，
wherein, tWFor uniformly correcting the on-satellite time, t, corresponding to the time of occurrenceJThe satellite time after uniform time correction is obtained.
4) At uniform timing intervals TBIs periodic, i.e. every TBPerforming one-time satellite clock drift compensation on the satellite time, determining compensation frequency by uniform time correction intervals, repeating the step 3) until the satellite computer receives a new increment time correction instruction, returning to the step 2), continuing satellite time correction, and performing TB≤△T。
Examples
In order to simplify the expression, the real time of the initial moment and the on-satellite time are both recorded as 0, so the satellite-ground time difference is 0, and at the moment, the ground sends an incremental timing instruction with the parameter of 0 ms. After the satellite computer receives the increment timing instruction, the operation after the increment timing instruction is received for the first time in the step 3 is set to t1Is 0, drift1Equal to 0.
Assuming that the satellite's clock drift is 100ms per hour, the analysis is performed according to this example below.
according to the specific conditions of a ground station and a certain type of satellite, the threshold value P is 500ms, △ T is 1 hour, n is 3, and T isBIt was 0.5 hour. The ground station calculates the satellite-ground time difference (real time minus on-satellite time) every 1 hour, and the satellite-ground time difference becomes larger continuously due to the existence of 100ms/h satellite clock drift; the measured data are shown in table 1, taking into account the presence of measurement errors:
TABLE 1
| Real time | True star-ground time difference | Measuring satellite-to-ground time difference |
| 1h | 100ms | 80ms |
| 2h | 200ms | 230ms |
| 3h | 300ms | 350ms |
| 4h | 400ms | 360ms |
| 5h | 500ms | 450ms |
| 6h | 600ms | 540ms |
| 7h | 700ms | 690ms |
Step 1): the ground station calculates the satellite-ground time difference and injects an increment timing instruction. Dt was found at 7h2＝(450+540+690)/3＝560ms>The threshold P is 500ms, and an incremental timing command with a parameter of 560ms is injected into the satellite computer.
Step 2): and the satellite computer performs time correction after receiving the increment time correction instruction.
At this time the on-board time becomes t2＝tS+dt2＝7h-700ms+560ms＝7h-140ms
Step 3): the clock drift is updated.
drift2＝drift1+dt2/(t2–t1)＝0+560ms/(7h-140ms-0)≈80ms/h
To simplify the representation, 140ms is omitted from the above equation. The numerical error caused by the simplification is small, and the logical relation of the method cannot be influenced.
Step 4): and carrying out periodic uniform timing according to the latest star clock drift estimated value.
Every other TBOnce corrected for 0.5 hours:
tJ＝tW+driftm*TB＝tW+80ms/h*0.5h＝tW+40ms
the timing effect in this example is shown in table 2:
TABLE 2
In the table, the "on-satellite time before uniform timing" — after uniform timing "-100 ms/h 0.5h before half an hour; the "on-satellite time after uniform timing" +40ms is equal to the "on-satellite time before uniform timing" + in the same column; the real time difference between the stars is equal to the real time, and the even time correction time on the stars is equal to the real time.
It can be seen that the difference between the on-satellite time and the real time is increased continuously because the compensation amount of 80ms/h is different from the real clock drift of 100ms/h by 20 ms/h.
A second iteration was performed as follows, and the measured data are shown in table 3:
TABLE 3
| Real time | True star-ground time difference | Measuring satellite-to-ground time difference |
| 7h | 140ms | 80ms |
| 8h | 160ms | 230ms |
| … | … | … |
| 25h | 500ms | 460ms |
| 26h | 520ms | 550ms |
| 27h | 540ms | 550ms |
The real drift of 100ms/h is compensated by the clock drift of 80ms/h, so that the trend of increasing the satellite-ground time difference is restrained, at the 27 th hour, the satellite-ground time difference measured by the ground exceeds the threshold value of 500ms, the time interval of two instructions is 20 hours, and is greatly reduced compared with the last 7 hours.
The following steps are resumed:
step 1): the ground station calculates the satellite-ground time difference and injects an increment timing instruction. Dt was found at 27h3＝(460+550+550)/3＝520ms>The threshold P is 500ms, and an incremental timing command with a parameter of 520ms is injected into the satellite computer。
Step 2): and the satellite computer performs time correction after receiving the increment time correction instruction.
At this time the on-board time becomes t3＝tS+dt3＝27h-540ms+520ms＝27h-20ms
Drift3＝drift2+dt3/(t3–t2)＝80ms/h+520ms/[(27h-20ms)-(7h-140ms)]≈106ms/h
Step 4): and carrying out periodic uniform timing according to the latest star clock drift estimated value.
tJ＝tW+driftm*TB＝tW+106ms/h*0.5h＝tW+53ms
The timing effect in this example is shown in table 4:
TABLE 4
The subsequent satellite-to-ground time difference data is shown in table 5:
TABLE 5
| Real time | True star-ground time difference |
| 27h | 20ms |
| 28h | 14ms |
| … | … |
| 114h | -502ms |
It can be seen that after the second injection of the instructions, the error of the star clock drift becomes-6 ms/h, and the trend of the increase of the satellite-to-ground time difference is further restrained. After 114-27 hours, 87 hours, the absolute value of the real satellite-ground time difference is larger than 500ms, the time interval of the corresponding ground injection command becomes further larger, and the burden of the ground station becomes further smaller.
As shown in FIG. 2, curve 2 shows the true clock drift of 100ms/h, and curve 1 shows the estimated value of the clock drift of driftm. It can be seen that the star clock drift estimate converges gradually to the true value.
Fig. 3 shows the time interval between two incremental corrections, which can be seen as the ground station signaling time interval grows exponentially.
The above example illustrates that if the star clock drift is an invariant, i.e. 100ms/h does not change with time, even if there is a large measurement error of the satellite-to-ground time difference, the method described herein can make the star clock drift gradually converge to the true value, so that the time interval of the ground injection incremental timing command tends to infinity.
In fact, the star clock drift is not a constant value and comprises errors such as calculation errors of a satellite-to-ground time difference, day period fluctuation of the temperature of a star clock chip, year period fluctuation of the temperature of the star clock chip and the like, but the method can still reduce the frequency of the ground station command.
For a certain type of satellite, the ground station uses the traditional incremental time correction and uniform time correction methods, the time correction period is about two days, a special time period even needs one-day correction, and frequent time correction causes great burden to the ground station. After the satellite timing method based on the iterative estimation of the clock drift is used, the frequency of timing is reduced to one week, and the burden of a ground station is greatly reduced.
Those skilled in the art will appreciate that the details of the invention not described in detail in the specification are within the skill of those skilled in the art.
Claims (5)
1. A satellite timing method based on iterative estimation of satellite clock drift is characterized by comprising the following steps:
1) determining an increment timing parameter by using a ground station, and when the increment timing parameter is larger than a threshold value, sending an increment timing instruction with the increment timing parameter to a satellite computer by the ground station;
2) the satellite computer performs incremental timing according to the incremental timing parameters sent by the ground station to obtain the on-satellite time after the incremental timing; iteratively updating the star clock drift amount according to the increment timing parameters to obtain the iteratively updated star clock drift amount;
3) uniformly correcting the on-satellite time after the incremental timing according to the iteratively updated satellite clock drift amount;
4) repeating the step 3) by taking the uniform time correction interval as a period until the satellite computer receives a new increment time correction instruction, returning to the step 2), and continuing to perform satellite time correction work;
said step 1) determining an incremental timing parameter dtmThe method specifically comprises the following steps:
dtm＝(dt1+…+dtn)/n，
therein, dt1，dt2，…，dtnthe time difference between the satellite on-satellite time and the real time is obtained at intervals of time delta T;
the value range of the delta T is 0.5 h-12 h, and the value range of n is 1-48;
the step 2) is a method for iteratively updating the star clock drift amount according to the incremental timing parameters to obtain the star clock drift amount updated in the mth iteration, and specifically comprises the following steps:
driftm＝driftm-1+dtm/(tm-tm-1)，
wherein, tm-1The satellite time t is the satellite time after the increment time correction correspondingly obtained by the increment time correction instruction m-1 received by the satellite computermThe satellite time after the increment time correction correspondingly obtained by the mth increment time correction instruction is received by the satellite computer, namely, the driftm-1Obtaining the corresponding star clock drift amount, drift, of the m-1 th increment timing instruction received by the satellite computer1＝0。
2. The satellite timing method based on the iterative estimation of the star clock drift according to claim 1, wherein the step 2) performs incremental timing according to the incremental timing parameters sent by the ground station, and obtains the on-satellite time after the incremental timing, specifically:
tm＝tS+dtm，
wherein, tSFor satellite time, t, corresponding to the time of receiving the incremental timing commandmAnd m is a positive integer, and the satellite time after the increment time correction is obtained after the satellite computer receives the increment time correction instruction for the mth time.
3. The satellite timing method based on the iterative estimation of the star clock drift as claimed in claim 1 or 2, wherein the threshold value P in the step 1) ranges from 10ms to 2000 ms.
4. The satellite timing method based on the iterative estimation of the star clock drift as claimed in claim 3, wherein the step 3) is a method for performing uniform timing on the time on the satellite after the incremental timing according to the iteratively updated star clock drift amount, and specifically comprises:
tJ＝tW+driftm*TB，
wherein, tWFor uniformly correcting the on-satellite time, t, corresponding to the time of occurrenceJTo make the satellite time T after time correction uniformBAre at even timing intervals.
5. The method according to claim 4, wherein T is the time correction method for the satellite based on the iterative estimation of the clock driftB≤△T。
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