Wireless Sensor and Actuator Networks: Algorithms and Protocols for Scalable Coordination and Data Communication

10.1 INTRODUCTION

Sensor networks aim at monitoring their surroundings for event detection and/or object tracking (Akyildiz et al., 2002; Martincic et al., 2005). Because of this surveillance goal, coverage is a functional basis of any sensor network. In order to best fulfill its designated surveillance tasks, a sensor network must maximally or fully cover the right region, where interesting events occur, without internal sensing holes. Sometimes, additional requirements such as node degree (Poduri et al., 2009), node density (Garetto et al., 2007), or coverage focus (Garetto et al., 2007; Li et al., 2008a) may apply.

However, it cannot be expected that sensors are placed in a desired way at initiation as they are often randomly dropped due to operational factors. Further-more, sensors could fail at runtime for various reasons such as power depletion, hardware defects, and damaging events, degrading already poor coverage. In WSAN, the impact on coverage from stochastic node dropping and unpredictable node failure, coupling with controlled node mobility, brings about the problem of movement-assisted sensor placement for coverage formation and improvement.

There are different ways to place sensors by exploiting node mobility in WSAN. Sensors can be placed by mobile actuators. If sensors have locomotion, then they can place themselves by intelligently changing their geographic location without others' help. Because physical movement (including starting motors) consumes a large amount ...