GPS to the Rescue - Mayday for Motorists

John P. Kiljan, Alison Brown and Marc Morin

Abstract:	Although expected to be seldom used by any individual motorist, the presence of a Mayday system in a vehicle adds to the peace of mind of a motorist traveling in unfamiliar locations. Development of an effective motorist Mayday system for travelers in the United States and Canada has been hampered by the lack of a highway infrastructure to receive and process emergency requests, and by the inability of most motorists to precisely locate their vehicle. Current progress in creating intelligent vehicle/highway systems and an expanded network of computer- switched radio systems will greatly improve the ability of highway agencies, both public and private, to respond to emergency requests. The last missing element is an inexpensive and reliable means of determining the location of vehicles in distress. GPS has been proposed as a method of providing location in support of a Mayday service. However, the expense of a conventional GPS receiver prohibits widespread installation on vehicles. Another problem is the slow time-to-first-fix of a GPS receiver, which makes it unacceptable for use in an emergency situation. Also, the inability of a receiver to compute a navigation fix except when four satellites are in view hampers operation in mountainous regions or in metropolitan areas where there is poor satellite visibility. NAVSYS has developed a low cost GPS sensor, the TIDGET” (patent pending), which solves these problems for a GPS Mayday service. Instead of tracking the GPS signals, the TIDGET sensor captures a brief “snapshot” of raw GPS sampled data and transmits this snapshot to the emergency dispatch center which computes the location of the motorist. The central processing is aided by data from a map database when fewer than four satellites are in view of the sensor. The TIDGET requires no initialization or warm-up time since there is no processing of the data performed at the vehicle. In large quantities, the TIDGET cost is less than $100 a unit (not including the communications link). This paper includes a description of the TIDGET Mayday system and presents preliminary test results demonstrating the ability to locate a stranded motorist using this low cost GPS sensor. The paper also outlines the opportunities for the public and private sector to participate in the development of a Mayday service that has a potential market base of millions of vehicles.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	1195 - 1203
Cite this article:	Kiljan, John P., Brown, Alison, Morin, Marc, "GPS to the Rescue - Mayday for Motorists," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 1195-1203.
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