Research On Methodology Of GNSS Satellite Clock Offset Estimation And Precise Point Positioning Time Transfer

Precise positioning along with time and frequency transfer are important parts of GNSS comprehensive PNT service system.While for precise positioning,it is especially depend on the accuracy of navigation augmented information,such as the key factor satellite clock offset.Time and frequency is an important technology in establishing and maintaining the national standard time.With the development of GNSS,the BDS has finished global networking and become the third navigation system provided global sercices after GPS and GLONASS;meanwhile the GALILEO has also gone to the rapid development stage.The amount of the satellite and the frequency bands is also increasing radpidly,which provides more opportunities and challenges for the satellite clock offset estimation and time transfer.Therefore,it is needed to further research.Our work foucs on the three parts:GNSS satellite clock performance evaluation,the satellite clock offset estimation,and time transfer.The main research contents are as follows:1.The performance evaluation and stability change of satellite clock,and proposed the novel lag 1 autocorrelation function method based on overlapping samples for noise analysis.With the development of GNSS,GPS and GLONASS have the operation of changing clock.Part of GPS BLOCK ⅡR Rb clocks have been switched to new Ⅲ-A Rb clocks from January 2020.The R04 and R24 also respectively switched clock in January 2020 and April 2020.Besides,BDS3 and GALILEO have loaded passive hydrogen masers(PHMs).The frequency normal,frequency drift,and frequency stability have been analyzed to evaluate the performance of GNSS satellite clock,and the medium long-term(10000 s)stability has been assessed to reflect the performance change of satellite clock.As for the satellite clock noise analysis,the consistency and advantages of lag 1 autocorrelation method and Allan variance method are compared.At the same time,considering the shortcoming of lag 1 autocorrelation method,overlapping sampling lag 1 method is proposed to analyze the noise of satellite clock.The new lag1 noise analysis method can accurately identify the GPS and GLONASS satellite clock noise than the customary method.2.Proposed the post-precessing clock offset esatimation method considering the code bias,and the real-time clock offset esatimation method with mixed algorithm.Different chip shape distortions among the GNSS satellites,moreover,for different receivers with dissimilar correlator space,which provide different the tracking biases may vary for each satellite will cause code bias for the pseudorange observations.Because of the frequency division multiple access(FDMA)technique,the GLONASS pseudo-range ICBs is treated in four different ways,and the code bias is also introduced to GPS,BDS and GALILEO observation equation for post-precessing clock offset esatimation.Then,the accuracy of the estimated clock offset is evaluated by the reference product and PPP.As for real-time satellite clock offset estimation,a mixed difference algorithm is proposed to solve the huge load of ambiguity parameter and meet the demand of timeliness.The method is easily to implement,greatly reduces the amount of parameters,improves the timeliness of satellite clock offset estimation,and the accuracy is reliable verified based on reference products.3.Deduced and verified the dual frequency,triple frequency and quad frequency time transfer model.A prior constraint information model has proposed for time-transfer.The mathematical and stochastic model of dual frequency,triple frequency and quad frequency time transfer model are introduced.Then,the feasibility of the three models is assessed based on the time transfer test.The test found that the performance of the triple and quad frequency is basically consistent with dual frequency.The commonly time transfer method estimated the receiver clock offset as white noise.It neglects the correlation of the receiver clock offset between adjacent epoch and high stability of hydrogen clock.Therefore,we proposed the approach of prior information constraint information model based on clock offset prediction and process noise.Then,the performance of the proposed model has been verified according to experiment.The results show that the prior information constraint model can effectively improve the stability of time transfer,especially for short-term result.