Hu Jinlun (Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030), Chinese Academy of Sciences Shanghai Astronomical Observatory Annual Comparison Comparison of Time Synchronization Accuracy A comparison was made. Both methods have their own characteristics and have practical value. Strict common-view GPS time synchronization accuracy is 5 ～ 10ns, less strict common-view GPS time synchronization accuracy is 10 ～ 20ns, and comprehensive GPS time synchronization accuracy is 6 ～ 12ns.
Key words: Global Positioning System (GPS)-time comparison-time synchronization 1 Introduction Strict common-view GPS time comparison, the reception conditions and data output format fully meet the requirements, and can eliminate the SA (Selec tive Avalability) effect on the coordination between the two places The effect of time synchronization in universal time. Single satellite data is difficult to maintain a good result of synchronization accuracy for a long time (sometimes in an unhealthy state).
GPS time comparison without strict common view, the reception conditions and the data output format sometimes do not fully meet the requirements, which can basically eliminate the SA effect on the time synchronization of the coordinated universal time of the two places. Multiple satellites on average can maintain good results for long-term synchronization accuracy.
The comprehensive GPS time comparison uses a suitable data processing method to normalize the data received by multiple satellites per day to obtain a comprehensive GPS time of UTC 0h per day. It does not require strict common viewing, and can basically eliminate the effect of SA effect on the time synchronization of the coordinated universal time of the two places, and can maintain a good result of synchronization accuracy for a long time.
2 Brief comparison of methods 1. Common view method (1) Strict common view GPS time comparison reception conditions and data output format must fully meet the requirements of international GPS common view time comparison: â‘ According to the International Bureau of Metrology (BIPM) Time Department The published international GPS tracking schedule (divided into 10 zones, adjusted and published every six months) receives satellite signals with the same classification number â‘¡ has accurate local measured ionospheric delay calibration and precise ephemeris correction â‘¢ the initial time of a set of received data Same as the termination time, the tracking length is enough for 13 minutes (780 seconds). â‘£ The received data is linearly fitted to give the time difference between the local coordinated universal time and the satellite GPS time at the midpoint of the tracking length (exactly 390 seconds). No abnormal data during long-term calculation.
(2) The reception conditions and data output format of GPS time comparison for non-strict common view basically meet the requirements of international GPS common view time comparison: â‘ Receive satellite signals with the same classification number according to the international GPS tracking plan table â‘¡ Have rough local measurement Ionospheric time delay calibration and ephemeris correction â‘¢The initial time and end time of a group of received data are close, and the tracking length is close to 13 minutes. â‘£The linear fitting of this group of received data gives the locality near the midpoint of the tracking length (around 390 seconds). The time difference between Coordinated Universal Time and the GPS time of the satellite. There are some abnormal data in the long-term calculation, which can allow about 3 to 5 days of data per month, and up to 10 days of data individually.
There are internal and external reasons for the GPS time comparison of non-strict common view: â‘ There is a jump in the time of the receiver's reception schedule, especially when the two adjacent days pass UTC 0h (the satellite operating cycle is calculated in stellar time, the same The reception schedule of the satellites is 4 minutes in advance every day. When the two adjacent days pass 0h, some reception time is 23h54min, and some reception time is 23h58min) â‘¡ The two places share a common view. The environmental conditions and weather conditions at the time of reception are different, In particular, some outdoor antennas are affected by thunderstorms, which reduces the signal-to-noise ratio of the signal, resulting in insufficient data. â‘¢ Other interference.
In the reduction process, a method of removing the singular point data (outliers) by setting criteria can be used. During the reduction (for example, once a month, the data sampling time is one day), the standard deviation of the linear fitting time is 3 times the standard deviation (3σ) is used as the criterion for eliminating singular point data. The actual calculations show that the incompletely strict common-view time synchronization accuracy is 10-20 ns, and 50 ns can be used as a criterion. When the time fluctuation data of linear fitting exceeds 50 ns, the singular point data is eliminated and recalculated. In order to calculate the frequency stability of the time synchronization data at the same time, the singular point data to be eliminated is interpolated and then reduced.
2. The comprehensive method of comprehensive GPS time comparison is to adopt an appropriate data processing method and normalize the data received by multiple satellites per day to obtain the integrated GPS time of UTC 0h per day. It determines the time synchronization accuracy of the coordinated universal time between the two places, and does not require strict common viewing.
The coordinated universal time of any two places in the world can easily use the integrated GPS time data for time synchronization comparison, and the result is related to the number of satellites received around the day (the number of satellites received per day is 20 to 25, which can improve the accuracy by about 5 times) , Long-term reliability is more guaranteed.
(1) BIPM method: smooth interpolation transformation, single satellite GPS time ratio received daily by the Paris Observatory (OP) in France (2) USNO method: two-day smooth filtering, single satellite GPS time received daily by the US Naval Observatory (USNO) Ratio (3) SO method: Cubic spline function interpolation smoothing, single satellite GPS received daily by Shanghai Astronomical Observatory (SO) in China. In the following results comparison review, Japan Communications Research Institute (CRL) and China Shaanxi Observatory (CSAO) The integrated GPS time is obtained by CRL and CSAO receiving the single-star GPS time comparison data daily and normalized by the SO method to obtain UTC 0h. The integrated GPS time obtained by other time centers and time laboratories is called local restoring GPS time (Local Restitu 3. Comparison of results The comparison of UTC time synchronization accuracy determined by the two places. According to the calculation and analysis of the exchanged data, it is shown that the reception data of some satellites between these three laboratories is not completely strictly common view or not. The combination of methods is practical and effective.
Time laboratory year and month satellite reception status common view data processing method reduced star number time synchronization accuracy frequency stability noise partial function monthly calculation results are 1. After single star reduction, the average number of multi-stars is 3. Most of the average post-reduction is 4. The multi-star comprehensive post-reduction monthly calculation result is 1. The single-star reversion after the multi-star average is yes or no. The multi-star post-reduction is mostly 4. The result of multi-star integration after month calculation is 1. The average of multi-star after single-star reduction is 3. The majority of multi-star after reduction is 4. The multi-star after reduction Note: Reduction In the number of stars, 22/19 and so on indicate that CRL and CSAO use 22 and 18 satellites to calculate the integrated GPS time, and the others are similar.
The difference between UTC time difference determined by TAI time bulletin and UTC time difference determined by integrated GPS time is the statistical category. Two UTC comparison system difference average precision system difference average precision precision system difference average precision Shanghai Institute of Observatory Annual Report 2000 Year-to-year comparison [1,2,3,4,5,6,7], that is, the impact of long-term UTC frequency system changes in various places is deducted. For example: TAI Time Bulletin uses the GPS common-view time comparison data for each month when calculating [UTCUTC (K)]. However, the number of stars used in each month may be different, and the results may vary. The results in Table 2 are also a comparison between the common view method and the comprehensive method.
The TAI time bulletin has 5 data points per day for 5 days. There were 73 data points for each of 1997 to 1998. In 1999, only 6 months of data were used, and only 37 data points. The statistical error was larger than the statistical error for the whole year.
4 Conclusions When determining the time synchronization level of the coordinated universal time of the two places, the GPS time of the common view method and the integrated method is used in combination, and the effect is better.
4 Shaanxi Observatory. Time Frequency Bulletin, 1999 (1 to 6) 5 Shanghai Observatory. Atomic Time Bulletin, 1997 ～ 1999 .6
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