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Wireless sensor networks are conceived to monitor a certain application or physical phenomena and are supposed to function for several years without any human intervention for maintenance. Thus, the main issue in sensor networks is often to extend the lifetime of the network by reducing energy consumption. When the network topology does not change very often, a clustering technique can be used to manage the network activity. Some applications have high priority traffic that needs to be transfered with bounded end-to-end delay. The IEEE 802.15.4 standard defines a MAC protocol that saves energy by putting nodes periodically in sleep mode. The ZigBee protocol defines a hierarchical addressing mechanism by creating cluster-tree based on regrouping the star topology of the IEEE 802.15.4 standard. In this paper, we show how these two standards fail to guarantee quality of service and energy saving at the same time. We propose a time segmentation approach that saves energy, enables quality of service in terms of guaranteed access to the medium and improves the overall performance of the network. This time segmentation is achieved by synchronizing nodes activity using a tree-based beacon diffusion. The tree-based topology is inspired from the cluster-tree proposed by ZigBee. Our solution guarantees end-to-end delay for high priority traffic. The efficiency of our solution is proven by simulation and implementation.
Date of Conference: 10-12 April 2010