Multi-GNSS System Time Offset Determination and Its Effect on Positioning Performance

In multi-GNSS applications, the difference among different time reference systems, called system time offset, has a significant impact on positioning, timing, velocity measurement, and frequency calibration. Therefore it must be taken into consideration. The paper first extends the two time offset determination methods for dual GNSS systems to the triple-system case, with one at system level and the other at user level. The geometry matrix and DOP parameters with triple-system time offsets are modeled accordingly. Then the satellite signals with different time offsets, different mask angles, and different combinations of GPS/Compass/Galileo systems are simulated respectively using a multi-GNSS constellation simulator, and sent to a multi-GNSS software receiver to obtain the position solutions using the two time offset determination methods. The simulation results show that the two methods yield very little difference on positioning precision with the system-level method slightly outperforming the user-level method.