I. Introduction
The applications of Wireless Sensor Networks (WSNs) are increasing day by day and are expected to be widespread according to the paradigm of the Internet-of-Things [1] or smart cities [2]. In the environmental and industrial monitoring, these networks are composed of several hundreds of nodes which measure some magnitudes and transmit them to the Base Station (BS) for further processing [3]. The BS is a particular element in the network. Firstly, it is equipped with higher computational resources than other nodes do. Secondly, its functionality is global as it recollects the data from the whole network to take the corresponding decisions (e.g. activation of actuators) [4].