I. Introduction
A wireless sensor network is usually a collection of hundreds or thousands of resource-constrained devices with small memories, low bandwidth and limited power resources. They are deployed in fields where persistent human monitoring and surveillance are either impossible or infeasible. These small detectors can be used to sense events ranging from simple readings (e.g. sensing room temperature) to more important and sensitive measures (e.g. intruder detection in military applications, detecting wildfire or signs of any catastrophic phenomena). Raw data collected using these limited sensors are usually queried by a more powerful device called base station (BS) -which may be far away from sensing fields- for further analysis and event-based reactions [16].