| The on-board atomic clock is the core component of the satellite navigation system,and its performance directly determines the quality of navigation positioning and timing.At the same time,with the rapid development of satellite navigation and positioning,the accuracy requirements are getting higher and higher,so the clock difference prediction is particularly important in practical work.Based on this,this paper deeply studies the main performance indexes and clock error prediction models of the on-board atomic clocks of BDS and Galileo satellite navigation systems through the processing and analysis of post-accurate clock products and ultra-fast clock products.The performance level of the clock is compared with the performance analysis of the BDS spaceborne atomic clock using different precision clock products.The performance difference between the atomic clock of the Beidou-2 satellite atomic clock and the Beidou-3 satellite is compared and analyzed.The common forecasting model and the improved forecasting model are compared.The main research contents and research results are as follows:?1?The performance of the BDS and Galileo spaceborne atomic clocks was systematically evaluated using precision clock products of nearly six years and nearly five years respectively.The results show that the 10,000-second stability,daily drift rate,residual sequence,accuracy and stability of the Beidou satellite clock are maintained at 4×10-144×10-13 and-3×10-13,respectively.3×10-13,-2×10-92×10-9,1×10-114×10-11,3×10-144×10-13;comprehensive performance indicators,the best performing performance is the MEO satellite clock,followed by the IGSO satellite clock,and the worst is the GEO satellite clock.For the Galileo satellite clock,the tens of seconds stability,daily drift rate,residual sequence,accuracy,and day stability are maintained at 1×10-145×10-14,-5×10-145×10-14,respectively.-1×10-91×10-9,5×10-135×10-10,1×10-141×10-13;overall,Galileo satellite clock performance indicators are Better than the Beidou satellite clock.?2?Based on the precision clock products of different analysis centers at home and abroad,the performance of BDS satellite-borne atomic clocks is compared and analyzed in recent years.The two kinds of precision clock products,wum and gbm,with a sampling interval of 300seconds from 2014 to 2017 were used.The BDS spaceborne atomic clocks were evaluated from four aspects:data loss rate,accuracy,drift rate and stability.The results show that the performance of the GEO satellite clock is analyzed by two different precision clock products,wum and gbm,on the drift rate and the tens of seconds stability index.The results are quite different,and the performance analysis of the IGSO and MEO satellite clocks is analyzed.The results are less different.The difference between kilowatt-hour stability and accuracy of each satellite calculated by wum and gbm clock products is very small and has good consistency.?3?The BDS-3 precision clock products of Wuhan University Analysis Center used in the past three months,the performance of the atomic clock of Beidou 2 and Beidou 3 satellites from six aspects:phase,frequency,residual,drift rate,stability and accuracy.The comparative analysis is carried out.The results show that the number of frequency modulation and phase modulation of the Beidou-3 satellite atomic clock is significantly reduced,and the residual error is significantly reduced.The accuracy,daily drift rate and stability are better than the Beidou-2satellite atomic clock;compared with Beidou-2 The satellite atomic clock and the Beidou-3satellite atomic clock are the most obvious in terms of accuracy and thousand-second stability index,which are increased by 70%and 72%respectively.The daily drift rate,10,000-second stability and stable stability are all around 50%.?4?The real-time prediction performance of BDS/Galileo atomic clocks is evaluated and compared by quadratic polynomial model,grey model,spectral analysis model and time series model respectively.The systematic research compares the prediction effects of four common clock difference prediction models.The Beidou ultra-fast clock error data was used to carry out the forecasting experiment.According to the forecast results of each method,the clock difference prediction effects of each model were analyzed and compared,and their advantages and disadvantages were summarized.?5?In order to improve the real-time prediction accuracy of satellite clock difference,a real-time prediction method of satellite clock error combining singular spectrum analysis,grey model and robust estimation is proposed.Firstly,the spectrum analysis and signal fitting of the clock difference are carried out by singular spectrum analysis method.Based on the fitting residual,the robust gray model is used for modeling and residual prediction.The prediction values obtained by the above two models can be combined to obtain the final real-time.Clock difference forecast value.The experiment is carried out with iGMAS ultra-fast clock difference products.The results show that the prediction effect of this method is better than the commonly used quadratic polynomial model,and it can effectively control the influence of abnormal error and improve the accuracy and reliability of real clock difference prediction. |
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