Energy Efficiency and Reliability in Wireless Sensor Networks

The Hong Kong University of Science and Technology
Department of Computer Science and Engineering


PhD Thesis Defence


Title: "Energy Efficiency and Reliability in Wireless Sensor Networks"

By

Mr. Junhua Zhu


Abstract

Motivated by their tremendous potential in civil and military 
applications, wireless sensor networks have raised tremendous research 
interests in recent years. The fundamental function of wireless sensor 
networks is the gathering of information from a covered area. Information 
thus gathered by the sensor nodes are processed by sink nodes according to 
the applications deployed in the network. Therefore, delivering 
information from sensor nodes to sink nodes effectively is one of the 
fundamental challenges in wireless sensor networks. To achieve flexibility 
in deployment, sensor nodes are generally battery-driven. Furthermore, 
battery replacement is very difficult due to the random deployment nature 
of wireless sensor networks. Thus, sensor nodes have limited operational 
time and the operational time of the sensor networks is also limited. 
Hence, energy efficiency is another fundamental challenge in wireless 
sensor networks. To improve the performance of wireless sensor networks, 
data delivery in wireless sensor networks should be both energy efficient 
and effective, which is the focus of this thesis.

First, we observe the conflict of the two objectives --viz., the 
application performance and the network lifetime -- when optimizing the 
performance of wireless sensor networks. We find that the tradeoff between 
them can be studied by investigating the interaction between the network 
lifetime maximization problem and the rate allocation problem. Then, we 
formulate the tradeoff problem as a constrained convex optimization 
problem by introducing a tradeoff factor. We first tackle this problem at 
the transport layer, and then from a cross layer perspective. Using 
Lagrange dual decomposition, algorithms are obtained to achieve the best 
tradeoff. Then, we note that the notion of reliability in certain wireless 
sensor networks is probabilistic. Based on this, the problem of providing 
minimum energy probabilistic reliable data delivery is studied. First we 
tackle the problem at the MAC layer, using p-persistent CSMA protocols. We 
derive adaptive algorithms to tune the persistence probability of these 
p-persistent CSMA protocols. Then, we obtain the optimal allocation of 
per-hop reliability requirements for each sensor node, which further 
reduces the energy consumption with adaptive p-persistent CSMA protocols 
at the MAC layer.


Date:			Wednesday, 21 January 2009

Time:			10:30a.m.-12:30p.m.

Venue:			Room 3501
 			Lifts 25-26

Chairman:		Prof. Amine Bermak (ECE)

Committee Members:	Prof. Brahim Bensaou (Supervisor)
 			Prof. Mounir Hamdi
 			Prof. Jogesh Muppala
 			Prof. Danny Tsang (ECE)
 			Prof. Azzedine Boukerche (Comp. Sci., Univ. of Ottawa)


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