Mathematic Model and Performance Comparison Between Ionosphere free Combined and Uncombined Precise Point Positioning

In order to overcome the shortcomings( e.g. to amplify measurement noise, loss of half observations) of traditional ionosphere free PPP model, recently some researchers have proposed a new PPP model by using uncombined original non differenced carrier phase and pseudorange observations to implement PPP, which named uncombined PPP. In this paper, the advantages and disadvantages of both PPP models are analyzed in detail. Observations from 10 IGS tracking stations on October 10th in 2011 are used to demonstrate the static and simulated kinematic PPP positioning performance with respect to positioning accuracy, convergence time and ZPD estimation accuracy between two PPP models. The results show that for both combined and uncombined PPP model, daily static positioning accuracy of mm~cm in horizontal, 1~3 cm in vertical and a kinematic positioning accuracy of 1~3 cm in horizontal, about 4 cm in vertical can be achieved. Observation residuals in uncombined PPP model are smaller than that of combined PPP model. For static case, the average convergence time of uncombined PPP is 38 min which is longer than that of combined PPP, For kinematic case, the average convergence time of uncombined PPP is 33min longer than that of combined PPP. For ZPD estimation, an accuracy level of about 6mm can be achieved from both PPP models.