The CNES Real-time PPP with Undifferenced Integer Ambiguity Resolution Demonstrator

D. Laurichesse

Abstract:	Integer ambiguity resolution on undifferenced GPS phase data has made a lot of progress in recent years. By combining pseudo-range and phase information, it is possible to fix integer ambiguities on zero-difference phase measurements, for dual-frequency problems, without any atmospheric models. Phase measurements then become pseudo-range-like measurements with millimeter noise level. Using these measurements, and precise satellite ephemerides, it is possible to perform the synchronization of a regional network, to compute satellite clocks. These clocks have an interesting property: they allow the positioning of independent receivers using a PPP-like method, with integer ambiguity fixing. The achieved positioning accuracy is at the centimeter level. This method can also be applied to real-time positioning [ION NTM 2008, ION ITM 2009 and ION GNSS 2010 meetings]. The core of the real-time implementation is a Kalman Filter working with both real- and integer-valued phase ambiguities. The filter produces satellite orbits and clocks compatible with integer ambiguity fixing. These products are then ingested by algorithms developed for user receivers to perform real-time positioning with accuracy comparable to standard RTK. To demonstrate that this processing strategy is compatible with the latency constraints imposed by real-time applications, and with the level of performance typical of common personal computers, CNES has developed a complete real-time ‘integer PPP’ demonstrator. The paper presents the architecture of the demonstrator. It also presents results obtained within the framework of the Real-Time IGS Pilot project, as well as results from a stand-alone experiment. In order for users to assess the potential offered by this new approach to real-time positioning, CNES provides a free user test package containing all the tools needed to perform PPP with ambiguity resolution. This test package includes an access to the CNES caster, documentation to understand the nature of the ambiguity resolution parameters, and a modified version of the BNC software which handles ambiguity fixing. This material is available on a dedicated web site (www.ppp-wizard.net).
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	654 - 662
Cite this article:	Laurichesse, D., "The CNES Real-time PPP with Undifferenced Integer Ambiguity Resolution Demonstrator," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 654-662.
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