A Fairy Tale Approach to Cooperative Vehicle Positioning

S. Stephenson, X. Meng, T. Moore, A. Baxendale, T. Edwards

Abstract:	This paper outlines an innovative approach to the cooperative positioning of road vehicles by sharing GNSS information. Much like the children’s fairy tale Hansel and Gretel by the Brothers Grimm, GNSS receivers on road vehicles generate detailed Pseudo-VRS “breadcrumbs” as they accurately position themselves. These breadcrumbs can then be shared with other vehicles in the locality to help position themselves, much like traditional RTK GNSS positioning. Similar to the breadcrumbs in the fairy tale that are eaten by birds shortly after being dropped, the Pseudo-VRS correction information is only valid for a short period of time. By using this technique, off-the-shelf GNSS receivers can be used without any major hardware or software adjustments, including those of different receiver brands or legacy receivers. The techniques employed in this paper aim to deliver absolute positions, to enable high-accuracy ITS applications that involve road agents and infrastructure alike. The Pseudo-VRS technique incorporates high-precision GNSS positioning methods, recent developments in vehicle-to-vehicle communication, and open source GNSS positioning software (RTKLIB). Pseudo-VRS is shown to significantly increase the availability of ambiguity fixed solutions, for both dual and single frequency receivers; and improves the performance of DGNSS receivers. However there needs to be caution, as the use of a single epoch of raw observations from a moving base station is less reliable than traditional static base station Network RTK GNSS positioning. Fixing the integer ambiguity is more likely to be successful (passing the ratio test), but also more likely to be incorrect, and relies heavily on the initial position of the moving base station. The processing parameters are adjusted to assess the optimum configuration for successful cooperative positioning (delivering accuracy and reliability), and the limitations of the technique are addressed. It is shown that the cooperative position of a second vehicle can match the positioning accuracy of the initial moving base station vehicle (<5 centimetre). However, if the delay or latency of the Pseudo-VRS message reaches 8 seconds, the successfulness of the dual frequency RTK ambiguity fixing begins to fall and the 3D positioning accuracy drops below 10 centimetres (based on epoch-by-epoch processing). Once the latency reaches 30 seconds to accuracy has dropped to 30 centimetres.
Published in:	Proceedings of the 2014 International Technical Meeting of The Institute of Navigation January 27 - 29, 2014 Catamaran Resort Hotel San Diego, California
Pages:	431 - 440
Cite this article:	Stephenson, S., Meng, X., Moore, T., Baxendale, A., Edwards, T., "A Fairy Tale Approach to Cooperative Vehicle Positioning," Proceedings of the 2014 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2014, pp. 431-440.
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