Energy Restoration of Sensor Networks by Mobile Robots

Abstract

In this thesis, a variety of different approaches are proposed to study the energy restoration problem in wireless sensor networks by one or more robots. First, we introduce an on-demand decentralized strategy performed by a robot that visits the sensors in a predefined circular order. We study it both analytically and experimentally analyzing the impact of various network parameters on network coverage, disconnection time, and time sensors have to wait to be served. We then introduce an optimal centralized approach as a benchmark to assess how close to optimal our on-demand strategy is, and we discover that, for sufficiently large networks, the on-demand strategy is indeed optimal. We then propose an even simpler mechanism where the robot simply moves blindly along the circular order, which is experimentally shown to be as efficient as the other two. The results above apply to arbitrary sensor network; we then consider a common special topology: a linear arrangement of sensors, were we propose three restoring mechanisms. We compare them experimentally discovering, once again, that the simplest approach is also the best, in most cases. We finally consider the case of multiple robots. We propose two strategies where the network is portioned among the robots and each robot takes care of a portion, and we compare those with a collaborative strategy where all robots work on the global network. The main general result of this study is that simple solutions are often as good as more sophisticated ones. In fact, a totally blind strategy where a robot simply moves around restoring energy on its way turns out to be as efficient as the best possible centralized solution for most networks.