An Open-source PPP Client Implementation for the CNES PPP-WIZARD Demonstrator

D. Laurichesse, A. Privat

Peer Reviewed

Abstract:	In the framework of the IGS real-time service (RTS), CNES is now proposing for research purposes a new open source implementation of its PPP client. This PPP client corresponds to the user part of the PPP-WIZARD (With Integer And Zero-Difference Ambiguity Resolution) demonstrator. The paper presents this new product in details. Its architecture is designed to be as flexible as possible. Core algorithms are implemented in a library, compatible with other open sources implementations like BNC and RTKLIB. The architecture allows easy replay mode processing as well as parallel processing of a network of receivers. The C++ language was chosen for the implementation to allow high-level programming while maintaining a good level of portability, even on embedded devices with low CPU power. Special attention has been paid to ensure rapid execution on all platforms. The paper also details the functional model. This model exploits the concept of undifferenced and uncombined measurements. It is compatible with the most the latest state of the art techniques, such as ambiguity resolution, fast reconvergence, gap bridging, seamless regional augmentation, GNSS centric. It fully exploits the possibilities of the State Space Representation promoted by the RTCM standard. The estimation process is based on an extended Kalman filter. The parameters of the filter, i.e. the state vector, which reflect the functional model, are described. The filter process is split in two phases, propagation and estimation, that are also described, with an emphasis on the state estimation process based on an accurate measurement model. A typical tuning of the filter is proposed. Ambiguity resolution is an important aspect of PPP. Our model is by construction compatible with zero-difference ambiguity resolution. Since the formulation is uncombined, it is not only compatible with dual-frequency systems, but also paves the way for triple-frequency ambiguity resolution and the faster convergence time it allows reaching. Another important aspect of a PPP client is its robustness: to do so, several advanced algorithms, such as standard RAIM, advanced RAIM and gap bridging are implemented. These algorithms are detailed and typical improvement results are shown. Doppler smoothing is also implemented in the tool. This feature is particularly useful for single frequency applications, where the positioning solution is highly dependent on the quality of pseudo-range measurements. It is shown that adding Doppler data improves the quality of the solution in such a configuration. This PPP implementation is compatible with regional augmentation, thanks to the use of a specific atmospheric interface. This interface includes zenithal tropospheric delay and slant ionosphere delay . It is shown that this information, obtained for example from a dense network, allows reaching centimeter accuracy in a few minutes The constellations currently supported are those broadcast by the IGS RTS service i.e. GPS and Glonass; there is an on-going work to add Galileo and Beidou. Finally, results obtained with real data using various configurations are presented. These configurations include comparisons between single and dual frequency processing, standard or precise point positioning, and using global, regional or local atmospheric augmentation. The results show the typical performance that can be obtained using PPP technology in terms of convergence time and accuracy after convergence.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	2780 - 2789
Cite this article:	Laurichesse, D., Privat, A., "An Open-source PPP Client Implementation for the CNES PPP-WIZARD Demonstrator," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 2780-2789.
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