I. Introduction
WSNs consist of a large number of small wireless nodes equipped with a variety of sensors including infrared, ultrasonic, pressure, cameras, sonar, and radar to support different types of sensing functionalities. Sensor nodes are fitted with at least one microcontroller, which provides the processing capability. They are also equipped with RF transceiver with usually an omnidirectional antenna to allow the communication with each other or a central unit. As for the power source, sensor nodes usually rely on small batteries with a limited lifetime. [1]. Sensors are generally deployed in an ad hoc manner in physical environment for observation of an event of interest. The sensors in the vicinity of an event must be able to monitor it and send data back to one or several sink. A sink sensor node has capability to communicate with outside world such as laptop and base station. WSNs are used in numerous applications such as environmental monitoring, habitat monitoring, prediction and detection of natural calamities, medical monitoring, and structural health monitoring [2].