Degree of: Doctor of Philosophy

Department: Computer Science

Title: LEACH-SM: A Protocol for Extending Wireless Sensor Network Lifetime by Management of Spare Nodes

Committee:
Dr. Leszek T. Lilien, Chair
Dr. Elise de Doncker
Dr. Ikhlas Abdel-Qader

Date: Thursday, March 17, 2011 1:00 p.m. to 3:00 p.m.
College of Engineering and Applied sciences, Room D210

Abstract:
Operational lifetime of a wireless sensor network (WSN) depends on its energy resources. Significant improvement of WSN lifetime can be achieved by adding to WSN spare sensor nodes. 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 randomized rotation of cluster heads but allows for inefficiencies due to redundant sensing area coverage.
LEACH-SM adds the spare selection phase to LEACH, which follows the setup phase (including cluster and cluster head identification). In turn, the spare selection phase is followed by the regular WSN operation, divided into frames.
Development of LEACH-SM has three main goals. First, from the subset of WSN nodes that provide redundant area coverage, we select the optimal collection of spares (to maximize WSN lifetime). Initially, the spares are asleep while maintaining the original monitored area coverage by the primary WSN nodes. We overcome race conditions and deadlocks that can occur during the spare selection process.
The second research goal is to decide how long spares should remain asleep and which spares should be used as replacements for primary nodes that exhausted their energy. All spares awake at time t (estimated during spare selection). From now on they follow a cycle with very short awake periods and very long nap periods. The larger time t is the more energy is saved by the spares. However, if t is too large, exhausted primaries have no spares ready for replacing them.
The third research goal is to estimate WSN lifetime as determined by energy consumption by all its sensor nodes. This goal requires calculating lifetime for cluster heads, primaries and spares, and also determining duty cycles (defined as the ratio of the awake interval to frame duration) for all node types.

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