The Study of GNSS System Time Differences Monitoring Jihai ZHANG, Haibo YUAN, Wei GUANG National Time Service Center of CAS, PR China JULY 2017.Paris
The Content of Report Background Principle of GNSS time difference Monitoring Results and Analysis Summary 2
1. Background USER (1) Necessary for GNSS compatibility and interoperability. (2) Will improve the consistency of time service by GNSS. (3) Improve the responsibility of GNSS provider. 3
1. Background User Navigation Satellite GGTO GPST UTC(USNO) tutc UTC ( USNO ) User Navigation Satellite GST UTC(PTF) t UTC UTC ( PTF ) UTC UTC(SU) GLONASST Navigation Satellite User tutc UTC ( SU ) tutc UTC ( UTSC ) UTC(NTSC) BDT Navigation Satellite User Relationship of GNSS time and UTC Galileo has been broadcasting the GGTO. GLONASS and BDS are planning to broadcast time difference. 4
The Content of Report Background Principle of time difference Monitoring Results and Analysis Summary 5
2.Methods for GNSS time difference monitoring a) Time-link method Time links(tw,ppp,etc.) between GNSS time center b) Single Station method High performance GNSS receiver c) Multi-Station method Many stations with GNSS high performance receiver 6
2.1 The Principle of Time-link GNSS Time Difference Monitoring Time links between GNSS time center 7
2.2 The Principle of Single Station GNSS Time Difference Monitoring GNSS1 SV GNSS1/GNSS2 Combined Receiver GNSS2 SV 1PPS 5MHZ Reference Master Clock High performance GNSS receiver Real time data of RefT-GPST, RefT-GLONASST, RefT-BDT, RerT-GST 8
2.3 The Principle of Multi Stations GNSS Time Difference Monitoring GNSS Satellite GNSS Receiver GNSS Receiver GNSS Receiver GNSS Receiver GNSS Receiver 1pps 5/10MHz 1pps 5/10MHz 1pps 5/10MHz 1pps 5/10MHz 1pps 5/10MHz High performance Reference signal High performance Reference signal High performance Reference signal High performance Reference signal High performance Reference signal Data of Time links between two station Data of observations Multi stations time difference data processing Ref1T-GNSS1T Ref1T-GNSS2T Ref2T-GNSS1T Ref2T-GNSS2T Ref1T-Ref2T(time links), average the results, GNSS1T-GNSS2T 9
2.4 The Principle of Monitoring 1General relativity 2Sagnac 3The method of Satellite clock time difference. Navigation 导航卫星 satellite Antenna 天线 GNSST 1Dual-frequency ionosphere delay correction 2Troposphere model delay correction 1 REF DLY 2 INT DLY 3 CAB DLY 1PPS Local reference 本地参考时间 time Receiver 接收机 The random error is used for time difference monitoring and the error is eliminated by smoothing. As the system parameter used for time difference monitoring RefT-GNSST 10
2.5 GLONT and BDT monitoring Example: BGTO (Time offset of the BDT and GLONT) The RefGLONASS RefBDS are the time difference between local time and the navigation satellite system, then the time difference between two navigation satellite system can be calculated by: GLONT-BDT=RefT-BDT-(RefT-GLONT)=GLONT-BDT 11
2.6 GLONT and BDT monitoring (Time-link method) Time difference monitoring and checking system between GLONASS and BDS Example: GLONT and BDT, UTC(SU)-UTC (International links), UTC(SU)-GLONT (Domestic links), UTC(NTSC)-BDT(Domestic links), GLONT-BDT (Lagged) for checking /confirm 12
The Content of Report Background Principle of time difference Monitoring Results and Analysis Summary 13
UTC(NTSC)-GPST/ns 3. Results and analysis (Date:2017.04.09 2017.04.23) 5 4 Multi Station Single Station 3 2 1 0-1 -2 57,852 57,854 57,856 57,858 57,860 57,862 57,864 57,866 57,868 MJD The result of UTC(NTSC)-GPST by different ways (Multi Station& Single Station). Single Station Multi Stations STDEV (ns) 1.1055 0.8822 14
GPST-GLONT/ns 3. Results and analysis (Date:2017.04.09 2017.04.23) 28 26 24 NTSC SU BIPM 22 20 18 16 14 12 10 8 57,852 57,854 57,856 57,858 57,860 57,862 57,864 57,866 57,868 MJD The result of GPST-GLONT by different monitoring station. 15
GPST-BDT/ns 3. Results and analysis (Date:2017.04.09 2017.04.23) 105 GPST-BDT 100 95 15ns 90 85 80 57,852 57,854 57,856 57,858 57,860 57,862 57,864 57,866 57,868 MJD The data fluctuates within 15 nanoseconds. 16
GPST-GST/ns GPST-GLONT/ns GLONT-BDT/ns 3. Results and analysis (Date:2017.04.09 2017.04.23) 36 34 32 GLONT-BDT 42 40 30 28 26 24 22 20 18 16 14 57,852 57,854 57,856 57,858 57,860 57,862 57,864 57,866 57,868 MJD 72 GPST-GST 70 GPST-GLONT 38 36 68 66 64 34 62 32 57,852 57,854 57,856 57,858 57,860 57,862 57,864 57,866 57,868 MJD 60 57,852 57,854 57,856 57,858 57,860 57,862 57,864 57,866 57,868 MJD 17
UTC(NTSC)-GPST/ns 3. Results and analysis 6 5 Time Link Single Station 4 3 2 1 0-1 -2-3 57,852 57,854 57,856 57,858 57,860 57,862 57,864 57,866 57,868 MJD The result of UTC(NTSC)-GPST by different monitoring methods. 18
The Content of Report Background Principle of time difference Monitoring Results and Analysis Summary 19
4. Summary BDS has provided the time difference of BDT and GPST, BDT and GLONT in the test satellite, and will provide the formal time difference parameters in the BDS global navigation satellite system. The difference methods all can be adopted in the time difference monitoring, but the usage is different.» Single Station GNSS Time Difference Monitoring: real time GNSS time difference monitoring.» Time-link GNSS Time Difference Monitoring: time difference results verifying.» Multi-Station GNSS Time Difference Monitoring: study. 20
4. Summary The GNSS time difference prediction model should be studied. (quadratic model, linear model, the other) How many original data should be used in the construction of the prediction model? How long can the model parameter be used (the prediction window)? We just did a simple test for the GNSS time difference monitoring, many test will be done to check and verify the validity of the principle. We can use the time links between GNSS ground time center, and indirectly calculate the time offset between two GNSS, verify the results from the different methods. Time link calibration is also very important, all the time links used in the time difference monitoring must be calibrated accurately. 21