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


PhD Thesis Defence


"The Impact of Radio Signal Strength on the Design of Wireless Sensor
Networks"

By

Mr. Jian Ma


Abstract

Radio signal strength (RSS) is an attractive property since it can be
obtained without additional hardware. Based on various signal propagation
models that describe the relationship between RSS and distance, RSS can be
employed in network connectivity, localization, and link quality issues in
wireless sensor networks (WSNs). However, the deterministic propagation
models, in which RSS is only determined by distance, are far from reality.
We carefully design a series of experiments using MICA2 nodes in real
environments to investigate the parameters besides distance--frequency,
variation of transceivers, antenna orientation, battery voltage,
temporal-spatial properties of environment, and environmental dynamics.
All the parameters contribute to RSS irregularity, which can highly affect
the design of localization and topology control algorithms in wireless
sensor networks.

We derive the log-normal error model for RSS-based distance estimation
from the underlying propagation models and find out that the popular noisy
disk error model always underestimates distance error in localization. A
quality-based localization algorithm is proposed to handle the large error
in RSS-based distance estimation.

In WSNs, topology control achieves energy-efficiency by turning off
redundant nodes, while still satisfying the given network requirement. We
first propose several connectivity-based topology control algorithms,
which assume that links are either connected or disconnected. As our
experiments show that, besides the connected and disconnected region, a
large number of links reside in the transitional region with fluctuating
link quality. We then propose a link-quality-based topology control
algorithm, which employ opportunistic transmission to catch the best
transmission opportunities on transitional links. Our simulations
demonstrate that opportunistic transmission can significantly improve
energy-efficiency in topology control with low communication overhead. To
the best of our knowledge, we are the first to consider link quality and
apply opportunistic communication in topology control for WSNs.


Date:			Wednesday, 4 July 2007

Time:			3:00p.m.-5:00p.m.

Venue:			Room 3501
			Lifts 25-26

Chairman:		Prof. Bradley Foreman (PHYS)

Committee Members:	Prof. Lionel Ni (Supervisor)
			Prof. Shing-Chi Cheung
			Prof. Qian Zhang
			Prof. Lilong Cai (MECH)
			Prof. Jiannong Cao (Computing, PolyU)


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