Research On The Performance Analysis Of GNSS On-board Clock

As the core component of satellites, atomic clock is essential to the navigation and positioning, GPS satellites embark Rubidium clocks and Cesium clocks, BDS satellites embark Rubidium clocks, Galileo satellites are equipped with Rubidium clocks and Passive Hydrogen clocks, in addition, Cesium clocks are used in GLONASS. The main performance indexes include frequency accuracy and day drift rate, stability and predicting ability. Due to the complexity of the environment in space, it is more difficult to estimate the on-board clock than that on the ground. Therefore, monitoring and estimation to on-board clock are necessary. Based on the methods of time-domain analysis, the data preprocessing of the post precise clock products is studied in detail. The accuracy of the post precise clock products and the system noise of clock products are studied in detail. The performance of each satellite clock of GNSS is analyzed with precise clock product, and the researches on short-term and long-term clock prediction are done. In view of this, the main work and contributions are summarized as follows:1.Spectral analysis method is applied to analyze the precision of MGEX precise clock products. The conclusions show that different satellite clocks have different precisions. The precision of GPS Cesium clocks is around decimeter, which is lower than the others’, and the precision of the most GPS Rubidium clocks is better, which is at the level of centimeter. The precision of MEO Rubidium clocks of BDS is at the same level with the precision of GPS Rubidium clocks, which is at the centimeter level. While the precision of GEO and IGSO clocks of BDS is lower, and it’s around decimeter, which is similar as the Cesium clocks of GLONASS. In addition, the precision of Hydrogen clocks of Galileo is similar as the BLOCK IIF Rubidium clocks of GPS, which are the most precise clocks of GNSS. The conclusions also show that the precisions of the same type clocks are basically at the similar level and changed little.2. The performance of each satellite clock of GNSS is analyzed with the precise clock product produced by GBM. The conclusions suggest that the same type of satellite clock is at similar performance level and the performance of the GPS BLOCK IIF Rubidium clocks and Galileo IOV Hydrogen clocks are the best. The analysis of BDS clock performance shows that the frequency accuracy is about 2.26×10-11,the day drift rate is about 6.69×10-14 which is lower than that the clock of other systems, and the stability is about 5.20×10-14 per day which is at the similar level of GPS BLOCK IIF Rubidium clocks. The day drift rate of MEO clocks is similar as the GPS Rubidium clocks while the IGSO and GEO clocks are not, and the general performance of MEO clocks is better than that of the IGSO and GEO clocks. In addition, the general performance of Rubidium and Hydrogen clocks are better than the Cesium clocks.3. Three conventional clocks models are used to do the clock prediction of short-term(1 day) and long term(7 days,15 days and 30 days) in this thesis. The prediction results suggest that all the models are not suitable for every satellite clock, and the prediction of on-board clock should depend on the type of the clock. The short-term prediction results show that the predicting precision of polynomial model, gray model and time serial model are generally the same, which means these models could perform the prediction effectively, but the time serial model could provide more stable and precise prediction. As to the long-term prediction, the results suggest that the gray model is suitable but not the polynomial model and time serial model. 4. The clock offset contains system noise, the system noises of several clock offset access methods have been analysis by analytic method and measured method. The results show that system noise of IGS clock products is acceptable in the midterm and long term, and the IGS clock products could be used to estimate the mid-term and long-term performance of GPS on-board clock. The system noise of GBM clock products is only acceptable in long term as to 86400 s, and the GBM clock products could be used to estimate the long-term performance of BDS on-board clock.These conclusions proposed in this paper are obtained though comparison and analysis, these are very good supplement to the performance estimation method and theory of on-board clock.