The Research Of Key Technology And Approach For Time And Frequency Transfer Based On GNSS Carrier Phase Observation

Precise time and frequency transfer is one of crucial issues(the techinuqe of atomic clock,the technique of time and frequency transfer,and the algorithm for determining time scale)for establishing and keeping national standard time and frequency scale,which is employed to obtain the value of UTC(k)controlling,maintain the local atomic time(TA),trace to the international UTC.Thoes closely related to the performance of national standard time frequency reference.As one of time transfer techniques,GNSS carrier-phase time transfer has many advantages,such as low cost,high measurement precision,widely coverage and no distance limitation,and thereby gradually become hot topic in the domain of precise time and frequency transfer.However,there are still many theoretical and key technical problems need to be further refined and solved in current GNSS carrier-phase(CP)time transfer technique,particularly for the continuous construction and improvement of major global satellite navigation systems,more and more available satellites have great potential to be used in current time and frequency transfer.How to use the current multi-GNSS to achieve high performance have become hot topics in the domain of time and frequency transfer.Therefore,in this study,the key technique issues,the approach of data processing in GNSS carrier-phase time and frequency transfer have been focused.The main works and corresponding conclusions are summarized as follows.(1)The continuity of GPS CP time and frequency transferThe basic goal of precise time and frequency transfer is that the time and frequency information has been transmitted accurately with certain technique.However,the day-boundary discontinuity makes it a challenge to exploit the full potential of GPS CP time transfer,particularly for a long-term(e.g.> 1 day).In this study,we investigate the day-boundary discontinuity using geodetic data solution strategies from satellite products and user terminal,analyze the continuity of precise satellite products and carrier phase ambiguity in data processing,and propose the approach with two geodetic data solution strategies(i.e.,edge effect of satellite orbit and clock product interpolation and continuity of phase ambiguity).The approach has also been assessed based on the experiment of time and frequency transfer.The result shows that the approach is able to reduce the effect of day-boundary jump of traditional CP technique,and further improve time and frequency performance.(2)Impact of BDS satellite-induced code bias variations on precise time and frequency transferThe Chinese BeiDou navigation satellite system(BDS)is an new emerging satellite system operated by ourselves,and its time and frequency transfer performance has been gradually focused.As one of the important error sources of BDS,satellite-induced code bias variation has a great impact on the performance of time transfer by affecting the quality of pseudorange meaurement.In this study,the impact of BDS satellite-induced code bias variations on precise time and frequency transfer has been investigated,a code bias variation correction model has also been developed,and the approach of BDS CP time and frequency transfer with code bias variation correction has been proposed.The results shows that code bias variation on frequency B1 is worse than B2,and correction model is able to obviously improve the code bias variation no matter on B1 or B2 signal frequency.Meanwhile,the result shows that satellite-induced code bias variation is a crucial error term in practical time transfer work,which may induce nanosecond level error,whereas the performance of frequency transfer has little been affected.With respect to satellite-induced code bias variations in BDS-3e,it is not obvious.Combining the current BDS-2 and BDS-3e can increase the available satellites,and improve the performance of time and frequency transfer,particularly for noise level and frequency stability of time links.(3)The CP time and frequency transfer with prior constraint informationConsidering that the traditional CP technique has low utilize prior constraint information,which has not exploit the full potential of CP technique for precise time and frequency transfer.Therefore,we proposed the approach of CP time and frequency transfer with prior constraint information from receiver clock offset parameter and other related parameters in traditional CP mathematical model.Meanwhile,the corresponding mathematical model is established,and the performance has been assessed with time and frequency transfer experiment.The results show that the approach of prior constraint information with other related parameters(i.e.,station coordinate,troposphere delay)in Galileo time and frequency transfer has significant improved comparing the tradition CP technique in real-time mode.Additionally,the approach of atomic clock modeling CP time transfer outperformed the traditional CP technique by using atomic clock correlation between nearby epochs in terms of the time link noise level,day boundary discontinuity,and frequency stability indicators.(4)Multi-GNSS CP time and frequency transferWith the continuous construction and improvement of multi-GNSS,time laboratories are gradually equipped with multi-GNSS receivers.In order to fully exploit the potential of multi-GNSS for time and frequency transfer,the approach of combining multi-GNSS CP time and frequency transfer has been proposed.Meantime,the weight of different GNSS and quality control have also been focused,the approach of multi-GNSS time and frequency using robust Helmert variance component estimation also has been focused.The results show that combining multi-GNSS can increase the number of available satellite,and improve the performance of time and frequency transfer with respect to the traditional single GNSS in terms of noise level and frequency stability by reducing errors such as multipath and periodic errors,and improve the effect of satellite distribution on receiver clock error parameters.Meanwhile,the approach of multi-GNSS time and frequency using robust Helmert variance component estimation is able to determine the appropriate weights of different GNSS observations,and to control for the influence of outliers in these observations.