Precise Point Positioning (PPP) techniques have been extensively investigated and developed in the last years by a number of teams in the world. PPP methods are defined as being the processing by a single receiver of its own pseudorange and carrier-phase asurements, aided by the satellite constellation precise orbits, their clock offsets and sometimes additional parameters, computed by other means and provided to the receiver by some communication channel. These methods are now rather mature and provide a very good mean to achieve in real time a few centimetres of accuracy and precision in remote areas, where other solutions like Real Time Kinematic are impracticable or too expensive. Although PPP algorithms are the cornerstone of these methods, another important issue for their practical use is the way the PPP corrections can be provided to the user receiver. Nowadays, typical solutions encompass Internet, mobile phone networks and dedicated channels on geostationary (GEO) satellites. Broadcast on other types of satellites constellations is also considered or planned like by example in European GALILEO. One important characteristic of PPP methods is that they generate a correction data flow of a noticeable size to achieve a good performance, especially when providing corrections for more than one satellite constellation. The transmission to the users of such a data flow is no more an issue when Internet of 3G/4G mobile phones networks are considered but is much more a determining factor for efficient satellite transmission as data bandwidth remains costly. After an introduction recalling PPP techniques this paper will describe a study performed by Thales Alenia Space on the optimization of PPP data flow for efficient satellite transmission. A first part will describe the PPP parameters retained and our initial choices to code them. The justification of these choices with regard to the expected impact on PPP performances and usability as well as other constraints will be shown. Then the testbed developed to experiment and validate these choices will be described. The first results obtained will be presented. Finally further planned work will be introduced together with remaining open issues.

Keywords: precise point positioning, PPP, GNSS, SBAS, GEO, satellite