Publications in Scientific Journals:
K. Huber, R. Lesjak, F. Hinterberger:
"Precise Point Positioning und Möglichkeiten für präzise Echtzeit-Anwendungen";
Österreichische Zeitschrift für Vermessung und Geoinformation (VGI),
Precise Point Positioning (PPP) is a modern Global Navigational Satellite Systems (GNSS) processing technique that enables the estimation of precise three-dimensional coordinates by means of code and phase measurements from a single GNSS receiver. To enhance the position accuracy so-called precise ephemerides are used, that are freely offered by analysis centers. Further, during PPP processing a lot of additional model corrections have to be considered (phase wind-up, tidal effects, instrumental biases, etc.). These would have cancelled in a relative positioning method (e.g. RTK) as a result of building differences between observations of multiple receivers. Usually, the ephemerides from external sources are globally valid and their transmission in real-time needs lower rates compared to RTK-services. Therefore, PPP offers the possibility of highly precise positioning in areas, where neither a dense reference station network, nor a good mobile data link is available. The resulting positions as well as troposphere or clock parameters are solely referred to the geodetic datum of the ephemerides. Nevertheless, real-time PPP is only in its starting phase, since the necessary correction data are available only for a short time with an adequate accuracy. It was not until 2011, when the transmission of PPP specific corrections for satellite orbits and clocks was standardized in the RTCM document (version 3.1) for the first time. Applying these so-called SSR (State Space Representation) corrections it is finally possible to process coordinates with an accuracy of only few centimeters in real-time. Nevertheless, for sub-decimeter accuracies an initialization phase of up to 30 minutes is necessary. This convergence time arises from the fact that ambiguities within PPP usually cannot be fixed to integer values, as their estimates contain not only the real ambiguities, but also instrumental biases that would have cancelled in RTK as a result of differencing observations. The real-valued parts of these phase biases can only be eliminated by phase corrections calculated in a network solution.
This contribution presents the current developments concerning PPP for real-time applications, as well as research projects at the Working Group Navigation of the Institute of Geodesy at the TU Graz, that among others investigate also the fixing of integer ambiguities within PPP processing. The integer ambiguity fixing would shorten the initialization phase of PPP solutions significantly, and make the technique more attractive for many real-time applications.
GNSS, PPP, ambiguity resolution, real-time
Electronic version of the publication:
Created from the Publication Database of the Vienna University of Technology.