Precise Point Positioning(PPP) Based On GPS/BeiDou Observations

Global Navigation Satellite System(GNSS)technology has achieved remarkable progress during the recent three decades.The majority of PNT(Positioning,Navigation,and Timing)applications are now based on GNSS.This growing dependence on GNSS technology is recognized by several nations.Some of these nations are even developing their own regional or global systems.Multi-GNSS combination can improve the performance of PNT services,such as the accuracy,reliability,and availability.Precise Point Positioning(PPP)is a popular technique which can obtain high accuracy positioning using observations collected by a single receiver.PPP can determine the position of a single station,as well as other parameters,like the receiver clock error and zenith tropospheric delay(ZTD).The PPP approach can achieve mm-level positioning in static mode and cm-level positioning in kinematic mode,through modeling of all error sources influencing the signal.The research in this thesis was undertaken at a very timely moment in the development of global navigation satellite systems(GNSS).During the course of this work,the signal structure of an entirely new generation of GNSS signals has been defined.The satellites producing a new range of different coding and modulation schemes have been launched,initiating the modernization of the American GPS,Russian GLONASS and the development of the European Galileo system,the Chinese BeiDou.BeiDou is currently undergoing upgrading in order to achieve more sustainable and comprehensive worldwide coverage.The main objective of this thesis is the implementation and analysis of PPP technique with combined GPS/BeiDou observations.The thesis presents a comprehensive background of Precise Point Positioning(PPP)using observations collected from two systems(GPS and BeiDou).Usually,PPP technique is implemented using GPS measurements only,which have poor performance in some situations due to insufficient satellite.In this thesis,PPP is improved in positioning accuracy and convergence time through combination of GPS and BeiDou.PANDA software package developed at GNSS research center,Wuhan University is used in this research.PANDA consists mostly of highly modular functions that form an excellent platform for the continued research on PPP.The combination of the two systems(GPS and BeiDou)has been implemented in a version of the PANDA software package.In this thesis,the performance improvement of combined GPS/BeiDou PPP model are investigated in static and kinematic modes using observations from CMONOC and IGS tracking network stations.After adding BeiDou observations,the positioning accuracy and convergence time have a significant improvement,demonstrated by numerical results.It is found that the BeiDou ionosphere-free code observation residuals are larger than that of GPS.The combination of two systems(GPS and BeiDou)proves to attain better performance under different elevation cutoff angles.The estimation of ZTD is also investigated using both single and combined systems.Numerical results demonstrate that the ZTD derived from combined GPS/BeiDou was closer to the ZTD values provided by the IGS.Inter System Bias(ISB)between GPS and BeiDou is discussed,which is caused by the difference between GPS and BeiDou signals.The investigation shows that the ISB remains very stable and its estimates are dependent on receiver types.A greater improvement can be expected when the Beidou constellation is completed in the near future.Recommendations for future work are also addressed.