Many applications of wireless sensor networks (WSNs) require events be detected around moving targets and delivered to a user, whose location may also change over time. Consequently, it is not desirable to have a single sensor node serving as the sink node for centralized event processing. Furthermore, an event usually occurs across different locations and lasts for a period of time that are unknown in advance. Hence it cannot be detected by a static set of sensor nodes. In this paper, we propose a general framework for such dynamic in-network event detection in WSNs. This framework enables a flexible number of sensor nodes to dynamically collaborate in detecting and delivering any specified event. So far there has been no such work reported in the literature. We have designed a protocol for the sensor nodes to autonomously determine whether they should participate in and which tasks they should perform to collaboratively process an event. We have implemented a prototype of the proposed framework using MicaZ motes and evaluated it through both simulations and experiments. The results demonstrate that our framework is effective and efficient in terms of energy cost and event processing delay.
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