Dead Reckoning Navigation (DRN) Assistance for GPS Based AVL Systems

Michael SK. Sushko

Abstract:	The primary disadvantage of GPS based Automatic Vehicle Location (AVL,) systems is in urban areas where tall building structures and overhead freeways can block the GPS signal from one or more GPS satellites. Since the accuracy of GPS depends on the geometry and the number of GPS satellites in view, blockage of a satellite that the GPS receiver is currently using will directly result in a navigation position error. This type of signal blockage in a typical mid-sized city can cause the loss of position accuracy for extended periods of time. The loss of the position of the vehicle in AVL makes the whole concept of tracking ineffective. Dead Reckoning Navigation (DRN) units are navigation computers that compute changes in direction by measuring speed and direction. DRN’s are initialized with a given position and continue to monitor the speed and direction of the vehicle through various communication sensors. A DRN typically uses a speed sensor and a heading sensor to compute a position. When a Dead Reckoning navigation unit is used to supplement GPS, it is then possible to continuously track vehicles in urban areas. The GPS unit is used to update the DRN when the GPS navigation solution is valid and the DRN is used for navigation when the GPS signals are blocked. The accuracy of the tracking in AVL will depend on if GPS is being used in a autonomous or differential mode. When the DRN is used for positioning, it will become less accurate over time without a position update from the GPS receiver. This paper examines in detail the use of dead reckoning navigation units used to supplement GPS in a AVL system. It discusses the general dead reckoning concepts used and the navigation errors due to inputs from the vehicle and heading sensors. An accurate Automatic Vehicle Location (AVL.) system based on GPS is not feasible without having DRN’s used to help supplement GPS. The Magnavox GPS Enhanced Dead Reckoning Module will be profiled in this paper as a typical dead reckoning device. It is not meant to serve as an endorsement but merely as an illustration.
Published in:	Proceedings of the 1993 National Technical Meeting of The Institute of Navigation January 20 - 22, 1993 Parc 55 Hotel San Francisco, CA
Pages:	161 - 169
Cite this article:	Sushko, Michael SK., "Dead Reckoning Navigation (DRN) Assistance for GPS Based AVL Systems," Proceedings of the 1993 National Technical Meeting of The Institute of Navigation, San Francisco, CA, January 1993, pp. 161-169.
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