Distributed Contention-Free Access for Multi-hop IEEE 802.15.4 Wireless Sensor Networks
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The IEEE 802.15.4 standard is a low-power, low-rate MAC/PHY standard that meets most of the stringent requirements of single-hop wireless sensor networks. Sensor networks with nodal populations comprised of thousands of devices have been envisioned in conjunction with environmental, vehicular, and military applications, to mention a few. However, such large sensor network deployments necessitate multi-hop support as well as low power consumption. In light of the standard's extremely limited joint support of the two aforementioned attributes, this thesis presents two essential contributions. First, a framework is proposed to implement a new IEEE 802.15.4 operating mode, namely the synchronized peer-to-peer mode. This mode is designed to enable the standard's low-power features in peer-to-peer multi-hop-ready topologies. The second contribution is a distributed Guaranteed Time Slot (dGTS ) management scheme designed to function in the newly devised network mode. This protocol provides reliable contention-free access in peer-to-peer topologies in a completely distributed manner. Assuming optimal routing, our simulation experiments reveal perfect delivery ratios as long as the traffic load does not reach or surpass its saturation threshold. dGTS sustains at least twice the delivery ratio of contention access under sub-optimal dynamic routing. Moreover, the dGTS scheme exhibits minimum power consumption by eliminating the retransmissions attributed to contention, which in turn reduces the number of transmissions to a minimum.