Range-Free Localization

Advances in micro-electro-mechanical systems have triggered an enormous interest in wireless sensor networks (WSN). WSN are formed by large numbers of densely deployed nodes enabled with sensing and actuating capabilities. These nodes have very limited processing and memory capabilities, limited energy resources and it is envisioned that they will be mass produced, to reduce costs. Several challenging problems exist in wireless sensor networks. Among these is how to obtain location information for sensor nodes and events present in the network. From this perspective, we categorize the localization problem as: node localization, target localization and location service. Node localization is the process of determining the coordinates of the sensor nodes in the WSN. Target localization is the process of obtaining the coordinates of an event or a target present in the sensor network. The location of a target can be obtained either passively (the nodes sense the target) or actively, when the target cooperates and communicates with the sensor network. A location service acts as a repository that can be used to answer questions like “where is entity X?”. In the remaining part of this chapter we focus on the node localization problem in WSN. Node localization is a complicated and important problem for wireless sensor networks (WSN). The aspects of this problem that have challenged the research community can be summarized as follows: