A method of GNSS system time offset monitoring

With the progress of Global Navigation Satellite Systems(GNSSs), which mainly includes GPS, GLONASS, GALILEO as well as BeiDou, multi-system joint working mode has become research focus and application trend. But, Each satellite navigation system has its own independent system time, such as GPST, GLONASST, GST and BDT. The System time offset between the two satellite navigation systems is one of the most important aspects of their interoperability. It will cause combined navigation position solution bias and time solution. Therefore, it is necessary and significant to monitor and research system time offset. A method of GNSS System Time Offset monitoring which is called Signal-in-Space Reception method is put forward and its principle is described. In this method, UTC(NTSC) time scale is regarded as reference time scale on account of its status of standard time and frequency resources. Then, The time offset between each satellite navigation system time and UTC(NTSC) which include UTC(NTSC)-GPST, UTC(NTSC)-GLONASST, UTC(NTSC)-BDT, UTC(NTSC)-GST can be acquired. Thus, system time offset among satellite navigation systems, such as GPST-GLONASST, can be acquired with about 5ns (1 σ) precision. On the basis of above described method, GNSS System time offset monitoring system has been set up since 2011 and it is gradually improved and perfected. A great deal of monitoring data has been collected. Addition to common error sources, some special error sources related to GNSS timing receiver such as receiver delay, inter-system hard delay bias, inter-frequency biases and so on are analyzed, as they can effectively affect monitoring results and precision. The monitoring data and IGS precision orbit as well as corresponding data published by BIPM Circular T Bulletin are combined together to determine above error values. The results of the error items and GNSS system time offset monitoring results are to be showed.