Energy Efficient Fault Tolerant Coverage in Wireless Sensor Networks

Abstract

WSN is a random or deterministic deployment of massive number of sensor nodes in a monitored area. WSNs have extensive applications, including military surveillance [1], target tracking, wild life monitoring, fire prevention, rescue operations, and air quality monitoring [2–4]. The primary goal of sensor nodes is to sense and collect raw data by monitoring particular environment, target, and barrier, and report that event to some sink node after some local processing or aggregation [5, 6]. Target coverage and network life time are two of the recent research trends in WSNs. Deployment of a set of sensors to cover a particular area, targets, or barrier is called coverage problem [7]. The main purpose of target coverage [8] is to continuously monitor a set of targets by using a subset of sensors. These sensor nodes are subject to failures due to various reasons. One of the common reasons is battery failure. Other reasons may include radio interference, software or hardware faults, and environmental changes. Sensor node failures may affect the coverage and connectivity adversely which in turn degrades the sensor network performance with higher network delays and higher energy consumption [9]. Sensor nodes are equippedwith limited capacity batteries. Recently, it has been investigated whether it is possible to conserve energy by using duty cycle protocols, where nodes switch their radio on and off periodically prolonging the life time of a WSN. Due to one time battery life and difficulty of replacing it, sensor nodes are densely deployed to increase connectivity and target coverage. However, if all the nodes are constantly on, it may quickly deplete their battery and may affect the network life time. Therefore it is important to tune these sensors to duty-cycled mode where they alternate between the active and sleep periods. Further, sensor hardware or software may fail due to weather or other physical conditions in a WSN affecting coverage of target nodes. If coverage of the target nodes is achieved by a single set of covering nodes, they may soon deplete their energy affecting the network life time. Therefore, it is important for WSNs to use redundant or disjoint covering sensors to cover particular area, targets, or barriers to construct a fault tolerant network which may still cover the targets, area, or barrier despite the failure of some covering sensors.