Research On The Accuracy Improvement And Assessment Of GNSS System Time Offset Monitoring

With the popularization and development of satellite navigation application, thecurrent global navigation satellite system GNSS mainly includes GPS, GLONASS,Galileo and BDS. Multi-mode satellite navigation is a trend of the future satellitenavigation, its advantages are more and more recognized. Focuses on multi-modenavigation, one of which should be solved contains time compatibility andinteroperability.For the problem mentioned above, this paper has carried out a study based onspace-based signal receiving to implement the method of GNSS time offsetmonitoring, while has improved the method based on the principle of time offsetmonitoring and the error distribution in the study. The main researches of the thesisare as follows.1. Analysis of the principle to monitor the system time offset, the errordistribution which impacts the monitoring accuracy and the characterristic of theseerrors are given, and the precision of the system time monitoring is quantitativelyassessed.2. On the basis of the platform built for the GNSS system time offsetmonitoring, the method to measure the GLONASS inter-frequency biases and GPS/GLONASS internal system channel delay biases of receiver are studied andimplemented. The results show that GLONASS inter-frequency biases at the level ofns follows frequency numbers presenting a linear trend, between the GPS andGLONASS existed the internal system channel delay bias of Septentrio PolaRx4receiver for7.04ns. Taking GLONASS inter-frequency biases and GPS/GLONASSinternal system channel delay biases of receiver into account can effectively improvethe results of positioning and the accuracy of the system time offset monitoring.3. Post-correction via precise ephemeris of GPS and GLONASS provided byIGS for the results of system time offset monitoring, the precision of GNSS systemtime offset monitoring is improved, the monitoring accuracy of the revised UTC(NTSC)-GPST is promoted about2ns. Two different processing methods, using IGSTEC MAP to calculate the time delay in ionosphere and dual-frequency measured thetime delay in ionosphere, how they affect the results of GNSS system time offset monitoring is studied. The test shows that the later has improved about30%in theaccuracy of UTC(NTSC)/GPST system time offset monitoring compared with theformer.4. The correctness of system time offset monitoring results are evaluated inthese ways, compared with bulletin of system time offset from authorities, withuser-level resolutions in open environments, and multi-mode navigation application. Itturns out that system time offset monitoring has a higher accuracy.5. The use of system time offset is studied. Analysis of the limitation ofuser-level processing in multi-mode navigation application in more shelteredenvironments. Establishing the platform based on GNSS system time offsetmonitoring and forecast, multi-mode navigation aided by GNSS system time offset isstudied and validated. The results show that multi-mode navigation aided by thesystem time offset can improve the availability, the positioning accuracy and thenavigation performance.