Real-time PPP with ambiguity resolution – Determination and Application of Uncalibrated Phase Delays

Currently, the precise point positioning (PPP) technique is a well-established GNSS processing method for postprocessing applications, while real-time PPP is still a field of ongoing research. Meanwhile a new RTCM (Radio Technical Commission for Maritime Services) standard for exchanging PPP corrections has been released. This so-called state space representation (SSR) contains orbit and clock corrections for real-time PPP as well as differential code bias corrections (DCBs). Nevertheless the issue of ambiguity fixing within PPP is still not generally solved, which is why real-time PPP still suffers from long initialization phases until the solution converges to the desired accuracy. Several research institutions are working on services and solutions to enable PPP with ambiguity resolution (PPP-AR), which would ideally shorten the convergence time to a few seconds and therefore make PPP more attractive to a broader range of applications. Motivated by the aforementioned challenge, an Austrian consortium has spent the last two years on the research project PPPserve, which aimed at the development of appropriate algorithms for real-time PPP with special emphasis on the ambiguity resolution of zero-difference observations. A fully functional system was developed that consists of a network-side module, calculating satellite-based widelane (WL) and narrow-lane (NL) phase delays from a GPS station network, and a user-software that applies the calculated corrections in a modified PPP algorithm to enable integer ambiguity resolution on the basis of wideand narrow-lane observables. This paper gives an overview on the work performed in the research project PPPserve and especially deals with the design and algorithms implemented in the user client. The Uncalibrated Phase Delays (UPDs) are evaluated and problems and deficiencies of PPP with ambiguity resolution will be shown on the basis of the most recent results produced by the user client.