The Physical Attributes of Autonomous GPS Mobile Navigation

M.E. Elder

Abstract:	The use of GPS for autonomous mobile navigation is a well established and proven technology. Advancements in receiver technology and corrections from various differential systems continue to enhance this technology with increased availability and accuracy. These advancements have helped to expand the growing market demands for precision GPS navigation. One of these growing markets has been recently witnessed in the DARPA Grand Challenge competition. The DARPA Grand Challenge was conceived in response to a Congressional mandate that the Department of Defense develop autonomous vehicles to minimize or eliminate the need for human drivers, thus saving lives on the battlefield. Convinced that an effective way to achieve this goal was to reach beyond the traditional government procurement process, DARPA focused on encouraging the involvement of a new 'community' of innovators, trailblazers and entrepreneurs (DARPA, 2004). The DARPA Grand Challenge 2005 is a competition of robotic ground vehicles with the intent of advancing autonomous vehicle technology. The course covered approximately 130 miles of rugged desert terrain. The vehicles could use only onboard sensors and navigation equipment to find and follow a predetermined route while at the same time avoiding obstacles. DARPA did award $2 million to the Stanford team whose autonomous vehicle successfully completed the 2005 route the fastest within a 10-hour period. All of the vehicles could only be equipped to receive and process electronic positiondetermination signals that were openly or commercially available to all teams. Positiondetermination signals that are neither openly available nor commercially available to all teams were prohibited. Navigation must also be autonomous except for signals received from the GPS satellites and the various systems which broadcast differential GPS corrections. The routes associated with the race were defined by a Route Data Definition File (RDDF). The RDDF is a DARPA generated formatted file that contained waypoints and other track information to specify the route for operation of an autonomous vehicle. RDDF's were provided to each team for a multiplicity of purposes. At the National Qualification Event, RDDFs were issued to specify multiple routes in the practice areas, to define the short routes used to validate operation of the vehicle E-stop system, and to specify the test course. At the Grand Challenge Event, RDDFs were used to specify the route for practice starts as well as the Grand Challenge route. The many challenges associated with navigating the DARPA Grand challenge begin with the accuracy and precision of the navigating and positioning system in the autonomous vehicles and their ability to navigate the RDDF waypoints. This paper will focus on the specific navigation requirements that are dependent on the physical attributes associated with optimizing the vehicles navigational ability. Some sources of position errors can be reduced by optimizing the mobile platform GPS physical installation and operations. These optimization practices can minimize the errors associated with mobile autonomous operations as well as quantify the amount of navigating error that can not be corrected. The physical sources of errors addressed by this paper will focus on the mobile platform field of view of the GPS constellation in uneven terrain, the enhancement of position accuracy by additional sensor inputs, GPS system platform installation, reducing the errors associated with multipath, and the efficient use of correction data from GPS differential systems.
Published in:	Proceedings of the 2006 National Technical Meeting of The Institute of Navigation January 18 - 20, 2006 Hyatt Regency Hotel Monterey, CA
Pages:	793 - 797
Cite this article:	Elder, M.E., "The Physical Attributes of Autonomous GPS Mobile Navigation," Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, January 2006, pp. 793-797.
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