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The adoption of wireless sensor networks (WSNs) in several key applications has recently became affordable thanks to technological advancements, leading to the definition of IEEE 802.15.4 standard. However to realize reliable end-to-end application by means of unreliable elements (since nodes usually cope with several limitations in terms of power supply, maintenance, hardware and software resources), a great deal of work needs to be done to design and optimize proper communications protocols. In particular, the medium access control (MAC) layer issues seems to be the most challenging in realizing such a system. In this paper, a novel class of MAC layer protocols, optimizing IEEE 802.15.4 basic scheme, is proposed. In particular, to enhance the overall performance, we resort to an adaptive approach able to dynamically vary the duty cycle at each node basing on the traffic load estimation. To this purpose, we first analyze an ideal algorithm, according to which, the traffic load is exactly known at the coordinator side. Moreover, we propose a real version of the MAC protocol in which the traffic amount is estimated by means of the channel occupation. Simulations performed on a realistic scenario point out remarkable gain both in term of communications efficiency, link throughput, node lifetime and adaptability in comparison with the static scheme.
Date of Conference: Nov. 27 2006-Dec. 1 2006