Sentries and Sleepers in Sensor Networks

A sensor is a battery-operated small computer with an antenna and a sensing board that can sense magnetism, sound, heat, etc. Sensors in a network can use their antennas to communicate in a wireless fashion by broadcasting messages over radio frequency to neighboring sensors in the same network. In order to lengthen the relatively short lifetime of sensor batteries, each sensor in a network can be replaced by a group of n sensors, for some n ≥ 2. The group of n sensors act as one sensor, whose lifetime is about n times that of a regular sensor as follows. For a time period, only one sensor in the group, called sentry, stays awake and performs all the tasks assigned to the group, while the remaining sensors, called sleepers, go to sleep to save their batteries. At the beginning of the next time period, the sleepers wake up, then all the sensors in the group elect a new sentry for the next time period, and the cycle repeats. In this paper, we describe a practical protocol that can be used by a group of sensors to elect a new sentry at the beginning of each time period. Our protocol, unlike earlier protocols, is based on the assumption that the sensors in a group are perfectly identical (e.g. they do not have unique identifiers; rather each of them has the same group identifier). This feature makes our protocol resilient against any attack by an adversary sensor in the group that may lie about its own identity to be elected a sentry over and over, and keep the legitimate sensors in the group asleep for a long time.