Date of Award

1-2011

Degree Name

Doctor of Philosophy

Department

Computer Science

First Advisor

Dr. Leszek T. Lilien

Abstract

Operational lifetime of a wireless sensor network (WSN) depends on its energy resources. Significant improvement of WSN lifetime can be achieved by adding spare sensor nodes to WSN. Spares are ready to be switched on when any primary (a node that is not a spare) exhausts its energy. A spare replacing a primary becomes a primary itself.

The LEACH-SM protocol (Low-Energy Adaptive Clustering Hierarchy with Spare Management) proposed by us is a modification of the prominent LEACH protocol. LEACH extends WSN lifetime via rotation of cluster heads but allows for inefficiencies due to redundant sensing target coverage. There are two energy-consumption inefficiencies in LEACH. The first one, the hotspot problem, is due to extra duties of cluster heads (as compared to regular nodes) that increase their energy usage. The second inefficiency is redundant data transmissions to cluster heads (made by regular nodes covering targets redundantly). Both inefficiencies are reduced by using spares in LEACH-SM.

LEACH-SM has three main features. First, from the subset of WSN nodes that provide redundant area coverage, we select the optimal collection of spares (to maximize extension of WSN lifetime). We overcome race conditions and deadlocks that can occur during the spare selection process. The second main feature is deciding how long spares should remain asleep, and which spares should be used as replacements for primaries that exhausted their energy. The third main feature is estimating WSN lifetime as determined by energy consumption of all its sensor nodes.

We provided analytical estimates and comparisons of LEACH and LEACH-SM for simplified cases. We also run simulation experiments (using MATLAB) to compare both protocols for general and complex cases. We studied the impact of the spare ratio and duration of the nap interval of cluster heads on the WSN lifetime for LEACH and LEACH-SM.

Even when no spares are used, LEACH-SM achieves 23% to 48% extension of the average WSN lifetime when compared to LEACH (this is due to switching off redundant nodes in LEACH-SM). When LEACH-SM uses spares, LEACH-SM achieves 183% extension of the average WSN lifetime when compared to LEACH (which is unable to use spares).

Access Setting

Dissertation-Open Access

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