Precise point positioning with wide area differential GPS corrections

Abstract

Wide area differential GPS (WADGPS) satellite-based augmentation system (SBAS) services, such as the Wide Area Augmentation System (WAAS) in U.S.A., provide satellite orbit and clock corrections and ionospheric delay corrections. Although their corrections are optimized for use with GPS single-frequency pseudorange measurements, the satellite orbit and clock corrections can be used to improve GPS positioning accuracy for dual-frequency users. The main objective of the research described in this dissertation is the design of a GPS dual-frequency data processing technique capable of producing high-accuracy point positioning results with WADGPS corrections. In this research, three major issues were identified as the satellite clock referencing issue, the resolution of the fast clock correction issue and the residual orbit and clock issue. By considering that the ways to handle the identified issues in a precise point positioning (PPP) process are different for different position estimator and different basis observables, a SBAS PPP with a weighted least-squares approach using a carefully designed sequential forward carrier-phase smoother and a SBAS PPP with sequential least-squares approach using un-differenced dual-frequency code and carrier-phase measurements have been developed. To account for the satellite clock referencing issue, the effects of the satellite instrumental biases have been precisely investigated and the observation equations for the different observables assuming the source of corrections is WADGPS have been developed. To account for the low resolutions of WAAS (or/and any SBAS corrections which follows the RTCA standard [2001]) fast clock corrections, a weighted moving average filter was adopted and a proper smoothing factor has been carefully determined. Finally, to take into account the residual orbit and clock errors, a varying carrier-phase ambiguity concept has been applied rather than assuming the ambiguity is constant over time. This method is only applicable for the SBAS PPP with a sequential least-squares method which has an ambiguity parameter for each satellite in the observation model. Results determined via developed software indicate a few decimeter-level of positioning accuracy for both developed PPP algorithms with (real-time) WADGPS orbit and clock corrections in kinematic mode could be attainable. Although a few decimeter-level of positioning accuracy are slightly less accurate than that of using precise orbit and clock products, it will give more flexibility and chances to choose a proper positioning technique, which can meet the majority of user expectations and their application needs. Furthermore, the algorithms developed in this research can be used for seamless PPP solutions with future SBAS corrections when all the planned SBASs are in operation.