Reducing PPP convergence time and improving precision through Spherical Harmonics-Based Global Iono corrections

Electrically charged particles present in this layer of Earth’s atmosphere can alter radio waves, such as those from GPS, Galileo, or BeiDou, resulting in non-estimated errors with respect to the available navigation models for the end user. For most positioning algorithms based in sequential filters, this effect is translated into a slow convergence towards a solution around decimeter error level. If we consider that ionosphere’s effect varies based on the user's location and solar activity due to the atmosphere particle composition, it becomes clear that a global accurate model, valid across wide areas accounting for different seasons and timespans is at the very least, quite challenging.

The focus of this paper is the demonstration of a global ionosphere model designed to improve the positioning accuracy of the end user through the estimation of ionospheric corrections to the broadcasted navigation message. Mathematically, this method is based on a spherical harmonic expansion model. This approach has the advantage of reducing the dependency from a highly densified station network where the ionosphere delay must be constantly estimated in dozens of locations; in favor of a simplified model, that barely needs to be adjusted with a limited set of real time data (around 40 stations). In this case, GMV’s global station network has been used, which comprises geodetic-grade receivers tracking the signal in open-sky locations around the globe. The global ionospheric model is configured to process signals from GPS and Galileo constellations.

To evaluate the performances of this model on the final user position estimation, several Precise Point Positioning (PPP) solutions are computed at different locations. The results have been compared with PPP solutions calculated without ionospheric corrections at the same stations. The goal of this paper is to show the significant performance improvement observed with the implementation of the global model.