StarFire: A Global SBAS for Sub-Decimeter Precise Point Positioning

K. Dixon

Abstract:	The StarFire™ Global Satellite Based Augmentation System was developed by Deere and Company to provide a global Precise Point Positioning (PPP) capability for Precision Agriculture. With two USA based processing and distribution centers, StarFire has been commercially operational since 1999 and has expanded into the additional market segments of Land Survey, Construction, Military, Aerial Mapping and Hydrographic Positioning. Recent system modifications as presented in this paper have improved absolute positioning accuracies from the decimeter level to sub-decimeter. The paper provides an evolutionary synopsis and detailed overview of the current system architecture, including the reference network, communication infrastructure, data handling, network hub processing, operational redundancy, distribution mechanism, receiver hardware and real-time monitoring. A global common satellite visibility tool has been used to determine the level of observational redundancy within the reference network and the benefit provided by recent reference station additions. The communication network infrastructure improvements establish a new benchmark for reliability and robustness with real-time monitoring now at the system component level. The central processing hubs are based upon a version of the Real Time GIPSY (RTG) suite, originally developed by the Jet Propulsion Laboratory for precise real time orbit and clock determination of GNSS. This has been refined to optimize positioning accuracy of NavCom developed GNSS hardware. Distribution of the StarFire orbit and clock parameters is via a highly optimized data stream to minimize bandwidth requirements, reduce the L-Band satellite transmission cost and ensure sufficient signal strength across the L-Band satellite footprint. Static precise point positioning performance is compared long term against International Terrestrial Reference Frame (ITRF) absolute coordinates for the global StarFire monitoring network. A kinematic dataset for an aerial platform illustrates dynamic StarFire performance with respect to ITRF based Post Processed Kinematic. Using NavCom GNSS hardware, additional comparisons in the position domain are made between StarFire, the Wide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay System (EGNOS). StarFire real-time orbit and clock parameters compared to International GNSS Service Final post-processed orbit and clock parameters show agreement at the decimeter level. Combined GNSS and L-Band receiver hardware plus algorithm developments are presented with emphasis on tropospheric modeling, tidal models, integration of inertial sensors and reducing the convergence time for the precise point positioning algorithm to reach optimal accuracy. The paper also discusses RTK Extend™, the simultaneous use of Real Time Kinematic (RTK) and StarFire orbits and clocks to extend RTK positioning accuracies when the RTK base station data link is lost. The paper concludes with a summary of the current StarFire Global SBAS PPP performance with suggestions for further research and enhancement.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	2286 - 2296
Cite this article:	Dixon, K., "StarFire: A Global SBAS for Sub-Decimeter Precise Point Positioning," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 2286-2296.
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