The Analysis Of Time-frequency Characteristics And Short-term Prediction Performance Of BDS-3 And Galileo Spaceborne Clock

The performance of spaceborne atomic clocks directly affects the accuracy and reliability of the navigation,positioning and timing(PNT).Bei Dou Global Navigation Satellite System(BDS-3),which is equipped with spaceborne hydrogen clocks and a new generation of high-precision rubidium clocks,will be fully completed by 2020.And the BDS-3 will provide globle navigation,positioning and timing services.Meantime,all the official working satellites of the European Union's Galileo satellite navigation system(Galileo)are equipped with high-performance hydrogen clocks and are in the fast networking stage.Through in-depth analysis and evaluation of the timefrequency characteristics and short-term predition of BDS-3 and Galileo spaceborne clock,important reference can be provided for the national standard time precise timing service based on the BDS/GNSS multi-systems.The main works and contributions are summarized as follows.(1)The characteristic evaluation index,Satellite clock models and parameter estimation methods commonly used in analysis of spaceborne atomic clocks are summarized.And the method of clock offsets data preprocessing is also introduced.(2)Time-frequency characteristics analysis of BDS and Galileo satellite clock.The physical characteristics of BDS and Galileo spaceborne atomic clocks are analyzed using clock offsets data for up to one year by analyzing the phase,frequency,frequency drift rate and fitting noise.The results show that BDS-3 and Galileo have low drift rate and phase noise.At the same time,according to the types of clocks,Allan variance and Hadamard variance are used to analyze the three frequency stability indexes at 1000 s,10000s,86400 s of BDS and Galileo spaceborne clock.The results show that the frequency stability at averaging times of 86400 s of BDS and Galileo is better than 5E-14.The analysis results provide theoretical basis and practical reference for the establishment of BDS-3 and Galileo clock offsets model.(3)Periodic characteristic analysis of BDS-3 and Galileo satellite clock offsets.The fast fourier transform was used to analyze the spectral properties of BDS-3 and Galileo satellite clocks offsets,which provides a numerical reference for whether to consider the influence of period term when modeling BDS-3 and Galileo satellite clock offsets.The results show that the periodic characteristics of BDS-3 and Galileo satellite clock offsets are mainly affected by the orbital period of satellites.The BDS-3 satellite clock offsets are affected by the first main period term between 0.05 and 0.1 ns,and by the second main period term between 0.02 and 0.08 ns.And the Galileo satellite clock offsets are affected by the main period term less than 0.06 ns.(4)Short-term prediction performance analysis of BDS-3 and Galileo spaceborne clock.The short-term prediction performance of BDS-3 and Galileo spaceborne clock is analyzed by using the self-adaptive clock offsets prediction model,which provides important reference for the selection of the forecast duration and the fitting arc length in the BDS-3 and Galileo clock offsets forecasting strategies.The results show that BDS-3 and Galileo have excellent short-term prediction ability.The prediction accuracy of BDS-3 spaceborne rubidium clocks,BDS-3 spaceborne hydrogen clocks and Galileo spaceborne clocks is 0.46 ns?0.15 ns and 0.20 ns respectively for 6 h when the arc segment is fitted with 12 h.Meanwhile,the influence of fitting arc length on the accuracy of clock offsets prediction is also analyzed.For the clock offsets prediction of 2 h,6 h can be considered as the fitting arc length of BDS-3 rubidium clock.The BDS-3 hydrogen clock and Galileo spaceboren clocks can be considered to choose 22 h as the fitting arc length of clock offsets prediction.(5)Research on GNSS real clock difference algorithm based on short-term prediction.A real-time clock offsets algorithm of GNSS four systems based on prediction form is introduced with the explanation of the principle and strategy in detail.Based on this algorithm,BDS/GPS/GLONASS/Galileo real-time clock offsets calculation is implemented online routine operation.A satellite maneuver detection and processing scheme based on broadcast ephemeris health marker is proposed to eliminate the influence of Bei Dou satellite maneuver on the real-time clock offsets calculation timeliness and accuracy.Based on the GBM final clock offsets product provided by German Research Center For Geosciences,the accuracy of the current realtime clock offsets products is evaluated,which provides an important reference for the subsequent application of the real-time clock offsets products in the national standard time precise timing service based on multi-systems.The results show that the accuracy of real-time clock offsets of GPS,GLONASS,Galileo and BDS-2(including GEO satellites)is 0.24 ns,0.32 ns,0.12 ns and 0.49 ns respectively,and the accuracy of GNSS real-time clock offsets is better than 0.5 ns.To sum up,by studying the time-frequency characteristics and short-term prediction performance of BDS/Galileo spaceborne clocks,it can provide reference for improving the real clock offsets strategy based on the short-term prediction form,and further improve the national standard time high-precision timing performance based on the BDS/GNSS.