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

7.1 INTRODUCTION

Unless indicated otherwise, all the solutions presented in this chapter assume that every node is able to know its own position and the positions of its neighbors using exchanges of hello messages. These solutions also assume that no obstacles are present and that the network can thus be represented by a unit disk graph (UDG), that is, a graph where two vertices are joined by an edge (and called neighbors) if and only if the distance between the two corresponding nodes is under a given threshold R. The chosen value for R corresponds to the transmission radius, which is generally assumed to be the same for all nodes. Some variations of this model can however be considered to represent obstacles or different transmission radii among nodes, in which case the edges are considered either as directed (arcs), or used only if both communication directions are available. The min-power graph is an example of such a nonsymmetrical UDG that represents the cases where each node has the smallest possible transmission radius with respect to the network connectivity. Depending on the scenarios considered, the transmission power can be decided once at the starting time, or adjusted for each message.

The chapter starts with a discussion on the main general approaches used to control the connectivity in static sensor networks. The emphasis is put in particular on the problem of finding minimum transmission radii so that the network is connected (i.e., there exists a path between ...