Adding Vehicle Dead-Reckoning Data for Improved Automotive GPS Performance in anUrban Environment. or

Dr Geraint Ffoulkes-Jones, Mr Gerald Whitworth

Abstract:	GPS based automotive navigation systems are currently being offered as an optional extra on many high end vehicles, and are being planned as a standard fixture for many models to be brought out in the next few years. These systems seem to fall into two categories, those which use stand-alone GPS and those which are combined with an external dead-reckoning (DR) sensors. The stand-alone units suffer severe masking in urban environments resulting in long periods of navigation outages, often at the time when it is really required. The units with added DR sensors typically use accelerometers or gyros, and although providing a good navigation solution, the systems rapidly become very expensive. Symmetricom Ltd (formerly Navstar Systems Ltd) has developed a GPS OEM module ideal for the emerging automotive mass market based around its new XR7 digital and RF technology. The XR7 OEM module only uses the DR data already available on the vehicle. For example, speed or distance moved from wheel click counts or the ABS (Anti-Breaking System). Additionally, direction and rate of change of direction from steering information or relative wheel counts may also be used. The philosophy is to use whatever data is available and provide the user with the best possible position information along with an accurate and reliable measure of its status and most importantly its estimated accuracy. An added benefit is that almost instantaneous re-acquisition is possible by maintaining receiver clock information from as little as one satellite plus DR “navigation” together with the reliable accuracy estimates. Very fast re-acquisition is particularly important in automotive applications, when satellites may only be visible for very short periods at road intersections. This paper presents the methodology used to combine the DR measurements and calibrate the error sources. This is followed by a description and results from a GPS Simulator test environment adapted to model the various vehicle DR sensor data in automotive urban environment scenarios.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	479 - 488
Cite this article:	Ffoulkes-Jones, Dr Geraint, Whitworth, Mr Gerald, "Adding Vehicle Dead-Reckoning Data for Improved Automotive GPS Performance in anUrban Environment. or," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 479-488.
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