Chapter 28 Performance Improvements of Combined Satellites Navigation System with System Time Offset

摘要

The time offset between different navigation systems are called the system time offset. It can be calculated either at user receiver, monitored by the public institutes or broadcast via the navigation message by navigation system. Currently, the research topic about system time offset is focused on how to accurately obtain its value. However, this paper will pay attention to the application of system time offset in combined navigation systems. The performance improvements of positioning accuracy and availability especially in the case of limited satellite visibility will be analyzed in this paper. According to the distribution of azimuth of visible satellites, ten different circumstances are simulated to implement the following researches. The first aspect is to analyze the improvements on PDOP and positioning accuracy with the application of system time offset. And the second aspect is to study the advancement in the ability of fault detection and exclusion with system time offset. The results indicate that the effects in improving availability and integrity become more obvious with the aggravating of obscured satellite visibility. Besides, the length of time that PDOP is smaller than 6 increases at most 3 h, equivalently 22 % improvements of availability. And the positioning accuracy in East direction enhances 41 %, North direction 61 % and Up direction 46 %. Meanwhile, the MDB of GPS satellites meanly decrease 17 m and coefficient decreases 0.24 in the worst condition with the system time offset.