Research On BeiDou/GNSS Real-time Satellite Clock Offset Estimation

Centimeter-level real-time precise point positioning(RT-PPP)technology that does not rely on specific reference station has a widespread application prospect,the realization of RTPPP is inseparable from the two core products of real-time precise satellite orbit and clock offset to provide strong support for it.At the present stage,the timeliness and reliability of ultra-fast real-time forecasted orbits can already well meet the requirements of RT-PPP,but accurate prediction of clock offset is extremely susceptible to the constraints of the complex space environment and its own time-frequency characteristics,the accuracy of real-time clock offset prediction is difficult to meet the requirements.Therefore,the highly reliable centimeter-level GNSS real-time clock offsets need to be obtained by real-time parameter estimation using the observation data of the ground tracking stations.Considering that,the GNSS real-time orbit and clock offset correction information of different agencies are systematically evaluated,the combined calculation of BDS-2/BDS-3real-time clock offsets are realized,the real-time clock offset products of GNSS single system was self-estimated,and contrastive analyzed with the real-time clock offsets broadcasted by CNES.Finally,the real-time clock offset estimation algorithm of Bei Dou/GNSS multi-system fusion was implemented based on the BDS-3 new signal.The following main research results were obtained:(1)Comparative analysis of the accuracy and positioning performance of recent GNSS real-time service products of different institutions.The statistical results suggest that the average real-time orbit 1D RMS accuracy of GPS,GLONASS,Galileo,and BDS-3 is 2.77 cm,6.85 cm,4.50 cm,and 11.03 cm,respectively,and the average STD accuracy of the real-time clock offset is 0.18 ns,0.17 ns,0.50 ns and 0.32 ns.Meanwhile,the average positioning error of real-time products of various organizations in the horizontal and vertical component is better than 5 cm and 10 cm,respectively.(2)The algorithm of BDS-2 and BDS-2/BDS-3 real-time clock offset estimation was realized.The calculation example results indicate that the STD of the real-time estimated BDS-2 and BDS-2/BDS-3 clock offsets could be both better than 0.3 ns.Relative to BDS-2,the STD of the joint real-time estimated BDS-2/BDS-3 clock offsets would be averagely improved by26%.Meanwhile,the positioning performance of BDS-2/BDS-3 real-time kinematic PPP could achieve shorter convergence time and better positioning accuracy.(3)The real-time BDS/GPS/GLONASS/Galileo clock offsets between self-estimated and CNES are compared.The results of comparative analysis reveal that the accuracy and positioning performance of the clock offsets obtained by the calculation examples are better than the CNES products obtained in the real-time data stream mode,which further demonstrates that the correctness of GNSS single system real-time clock offset estimation algorithm.(4)Multi-GNSS real-time clock offsets were estimated based on the observation data of BDS-3 new signal B1C/B2 a.The results of the calculation example shows that the average STD precision of the real-time estimated GPS,BDS-3,GLONASS and Galileo clock offsets are0.049 ns,0.140 ns,0.101 ns and 0.048 ns,respectively.At the same time,the positioning results of the real-time kinematic PPP represent that the real-time estimated clock offset is equivalent to the precision of the post-precision clock product.