I. Introduction
In recent years wireless sensor networks have received lots of attention due to their increasing capabilities, nevertheless, WSN deployments are still characterized by few bottlenecks, mostly related to energy resource management because they are mainly powered by batteries. Extending the lifetime of WSN deployment means using the available energy resources more efficiently. Most practical application scenarios will require a long-term monitoring capability, for example, a continuous monitoring of the evolution of temperature changes in a building could provide enough information for modelling the thermal behaviour of the building envelope and thus help the architects and civil engineers to decide when to carry out the necessary maintenance. Similarly, enough information on the background and statistical properties of a system are required to understand its behaviour, hence WSN plays a very important role in this process.