Abstract

One of the dominant error sources for single frequency GPS users is the ionosphere. The magnitude of this error can vary from a few meters to hundreds of meters, especially during severe ionospheric disturbance periods. For undifferenced processing using a single frequency single receiver unit, the ionospheric error cannot be cancelled out using a differential process. Therefore, one needs to rely on using appropriate models or algorithms to correct this delay to achieve high accuracy point positioning. This paper reports on a study undertaken to evaluate two different ionospheric error mitigation methods for single frequency Precise Point Positioning (PPP) processing. The two methods studied were ionospheric modeling and ionosphere-free combination. The feasibility of using either of these methods was assessed using four processing options: code-only processing; code and carrier phase combination; single frequency ionosphere-free linear combination employing an additive combination of code and carrier phase measurements, which was abbreviated as the quasi-phase measurements; and the code and quasi-phase combination

For this study, GPS static data were collected from different latitudinal regions and during both ionospheric disturbance and benign periods. The results from this investigation have revealed that the ionosphere-free combination, in particular the code and quasi-phase combination, provided the best point positioning results and could provide decimeter-level point positioning accuracy and precision. In addition, the solutions from the ionosphere-free linear combination were more stable when compared to the code and carrier phase ionospheric modeling method. This makes the linear combination the preferred method for single frequency PPP processing.