Performance Analysis of GNSS System Time Offset during GNSS Modernization

The rapid development of Global Satellite Navigation System (GNSS) not only provides more available satellites to the global GNSS users, but also accelerates the GNSS compatibility and interoperability. Currently, GNSS system time offset monitoring system at the National Time Service Centre has been upgraded. The system time of four GNSS can be monitored, which are BDS, GPS, GLONASS, and Galileo. First, the background and status of the four major GNSS are discussed. Then, monitoring principle of GNSS system time offset by receiving signal-in-space (SIS) and the handling methods of key parameters are introduced. Finally, monitoring results are analysed, which lasted 201 days. The results show that: during test period, 1) BDS time (BDT) and Galileo time (GST) have changed more than 10ns; 2) At the same epoch, there is certain deviation among the monitoring results of different BDS signals; 3) There is time offset about 10.01ns between monitoring results of BDS-2 and BDS-3 by dual-frequency signal (B1I/B3I); 4) The monitoring results’ stability of BDS dual-frequency signal is better than single-frequency signal.