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


PhD Thesis Defence


"A Delay Model Approach to Analysing the Performance of Wireless
Communications"

By

Mr. Kai-Wing Lee


Abstract

A novel Markov model, called the delay model, is proposed to find the
packet loss probability of wireless real-time communication systems.
Conventional queueing models, which track the number of packets in the
queue buffer, have been used successfully for decades but are not suitable
for the analysis since they usually lack the delay information of each
packet to model the dropping process. The delay model tackles the problem
by tracking the head-of-queue packet delay, which includes queueing and
retransmission delays, instead of the number of queueing packets.

Four problems in wireless real-time communications with progressive
difficulties have been solved. The solutions are useful in designing
wireless real-time communication systems to satisfy the quality of service
(QoS) requirements, including delay constraints and packet loss
probabilities for different users.

The first delay model solves a problem which was described as difficult in
a recent IEEE transactions paper. It is modeled by a two-dimensional
Markov chain and a simple closed-form expression of packet loss
probability has been obtained. In addition to correlated errors in the
first problem, the second problem further allows correlated arrivals,
which have significant impact on performance. Surprisingly, the Markov
chain and the solution are nearly the same in structure as those of the
first problem.

Wireless effective bandwidth, which is the bandwidth required to satisfy
the quality of service requirements, has been estimated in the third
problem. It uses hybrid ARQ for error correction and allows batch
arrivals. The last problem is the most general. The arrival and error
processes are discrete batch Markovian arrival and discrete Markovian
arrival processes respectively. The steady state probability of packet
loss probability is obtained by matrix-analytic techniques.


Date:			Tuesday, 31 May 2005

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

Venue:			Room 2304
			Lifts 17-18

Chairman:		Prof. Albert Lo (ISMT)

Committee Members:	Prof. Samuel Chanson (Supervisor)
                  	Prof. Brahim Bensaou
                        Prof. Jogesh Muppala
                        Prof. Chin-Tau Lea (ELEC)
                        Prof. Victor Leung (Elec. & Comp. Engg.,
					    Univ. of British Columbia)


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