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UBC Theses and Dissertations

The construction of a lifetime-preserving tree for data aggregation in wireless sensor networks Lee, Wi Nan Marc

Abstract

To meet the demands of wireless sensor networks (WSNs) where data are usually aggregated along its way to be collected at a single source prior to transmitting to any distant user, there is a need to establish a tree structure inside any given event region. Such a tree provides event sources with a mechanism to combine their readings, so that only a minimum amount of energy is required to deliver the same amount of information to the user when data aggregation is not used. In this thesis, we propose a novel technique to create one such tree, which preserves the lifetime of event sources while they are constantly transmitting, for data aggregation in future WSNs. We use the term Lifetime-Preserving Tree (LPT) to denote this tree. LPT features in nodes with higher energy tend to be chosen as data aggregating parents so that the time to detect the first broken tree link can be extended. In addition, by constructing the tree in such a way, the protocol is also able to reduce the frequency of tree reconstruction, which incurs an additional energy cost to all the sources. Furthermore, the protocol minimizes the amount of data lost after the network is impaired by the broken tree link. By choosing Directed Diffusion as our underlying routing platform, our simulation results have shown that the functional lifetime of event sources can be prolonged by a maximum of 139% when data are aggregated via a modified spanning tree prior to transmission to distant sinks. Our proposed LPT scheme can further extend this lifetime by a maximum of additional 13% without impairing the average latency and packet delivery ratio. When tree depth is also considered in the tree construction, our results have indicated that LPT is more likely to be centered at the event region, thereby reducing its delay when comparing to the modified spanning tree model. We expect all these differences to grow with an increasing number of event sources.

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