A sensor based tracking system using witnesses

Search and rescue of people in emergency situations, e.g. lost hikers, stranded climbers, or injured skiers has been difficult due to lack of information about their location at various times. Current location and tracking systems require a connected network via satellites, GSM base stations, or mobile devices. This requirement severely limits their applicability, particularly in remote wilderness areas where maintaining a connected network is very difficult. This paper proposes a new tracking system called Cenwits that is based on sensors that use RF for communication and emit beacons from time to time. When two sensors are in the range of one another, they record the presence of each other and exchange the information they recorded earlier. A sensor dumps all its information to an access point, whenever it is in the range of one. Important advantages of Cenwits include a loosely-coupled system that does not require network connectivity, power efficiency, and low cost. A preliminary prototype of Cenwits is being built using Berkley Mica2 Motes. The paper reports results from this preliminary prototype.