Performance Analysis Of Bei Dou Real-time Kinematic Timing

Time is an important physical quantity,and precise time is one of the basic guarantees for the normal operation of modern society.The Global Navigation Satellite System(GNSS)represented by Bei Dou Navigation Satellite System(BDS)and Global Positioning System(GPS)can provide standard timing services on the order of 10-50 ns,which has played an important role in the construction of national economy and national defense construction.With the rapid development of social economy and science and technology,industries such as the new generation of mobile communications have put forward ns-level or even higher precision requirements for timing accuracy.Using Bei Dou /GNSS carrier phase observations,RTK timing based on real-time Kinematic(RTK)differential positioning technology is expected to meet the demands of kinematic and static precision time users in the metropolitan area,which is an important improvement of the precision time service system based on International GNSS Monitoring and Assessment System(i GMAS)of National Time Service Center,Chinese Academy Of Sciences(NTSC).The main research contents of this paper are as follows:(1)This paper briefly introduces the basis and research background of GNSS precise time service and principle of Precise Time Service(PTS)based on i GMAS.This paper describes the relevant organization protocols used in this experiment,and summarizes the two GNSS time service / time transfer technologies used in this paper—Precise Point Positioning(PPP)time transfer technology and RTK time service technology.(2)Design and implementation of RTK timing software.This paper introduces the main functions of the open source software package RTKLIB and its commonly used programs.By debugging the core source of the relative positioning module in RTKLIB,analyzing its implementation principle,and performing secondary development on the source code,constructing the single difference observation equation between stations,so as to eliminate or weaken the common error between stations.At the same time,the receiver clock difference is retained and used as an unknown parameter for parameter estimation.In addition,the coefficient matrix and the initialization of the receiver difference is re-designed to meet the needs of the solution.Finally,with the launch of the RTKLIB b34 test version,it was adapted to realize the RTK timing function,and added functions such as observation value selection and different frequency selection.(3)Using the adapted and designed RTKLIB RTK time service software,the BDS-2satellite was tested and analyzed,and the BDS-2 satellite RTK time service performance was analyzed with the aid of PPP time transfer technology and optical fiber two-way time transfer technology.The test results show that the BDS-2 satellite RTK timing results are more consistent with the PPP time transfer results.The overall difference between RTK timing and PPP time transfer results can be kept within 1 ns,and even partial differences can reach 0.5 ns.The result of the optical fiber two-way time transfer is used as an external coincidence verification.The overall trend of the BDS-2 RTK timing results can also be basically consistent with it.The overall fluctuation range can be within ±1.5ns,and the STD of the comparison results can reach 0.48 ns.(4)B1I/B3I signal RTK timing performance analysis of BDS-3 satellite.Five stations,namely SE22,SEPT,XIA1,ZHHJ and XIA6,were selected to form different baselines to carry out RTK timing test performance analysis on B1I/B3 I signals of BDS-3 satellite.For different user terminals,although the baseline length is different,the test results show that the difference STD between the overall RTK timing result and the PPP time transfer result can be better than 0.2ns.In addition,the results of part of the optical fiber two-way time transfer are used to verify the RTK timing performance of BDS-3 satellite B1I/B3 I signals in different modes.The test shows that the difference between the RTK timing result of the BDS-3 satellite B1I/B3 I signal and the fiber two-way time transfer result can be better than0.3ns.As for the i GMAS tracking station XIA1,the long arc test results show that the overall RTK timing results of the BDS-3 satellite B1I/B3 I signal can be maintained within2.0ns,and the results of a single day can be maintained within the range of 0.5ns.