MPhil Thesis Defence


"Link Adaptation and Scheduling in Wireless Local Area Network"

By

Mr. Lau Yung Hung


Abstract

Wireless Local area networks (WLANs) have become more and more popular
today. Through WLAN, people can access the Internet anytime, anywhere, as
WLANs are deployed in different areas such as malls, cafes, airports and
so on. Wireless Lans suffer dramatically from Path loss and interferences
and as a result channel errors rates are very high and are known to be
location dependent and bursty in nature. As a consequence, due to the
fairness of the medium access control protocol in sharing access
opportunities in WLANs, when one of the station observes a bad channel
state and continues to attempt transmission the throughput of the whole
network is greatly degraded.

In order to address this problem, link adaptation schemes and wireless
scheduling algorithms are proposed. The idea of link adaptation is to
improve the network throughput by adjusting some network parameters, such
as the frame size, the transmission rate, or the rate of error correcting
codes, to adapt to different channel conditions. Wireless scheduling is
based on swapping transmission opportunities among stations in order to
enable the stations with good channel to transmit first and postpone the
transmissions of the bad channel stations to a later time when their
channels become good. This reduces the number of frame errors and thus
improves the network throughput.

In this thesis, we study different link adaptation schemes and wireless
scheduling algorithms to improve the network throughput while providing
QoS guarantees. We propose a per-fragment link adaptation system with a
credit based scheduler that allows every fragment of a frame to be
transmitted at the best transmission rate and fragment size, and good
channel flows are allowed to transmit more than the bad channel flows.
This can greatly improve the network throughput. We also propose a delay
aware wireless scheduling algorithm which targets the support multimedia
traffic in WLAN. The scheduler improves the network throughput when the
traffic has a deadline constraint. The scheduler uses both the information
of the packet deadlines and the underlying link adaptation scheme to swap
the transmission opportunities based on different channel conditions
without violating the delay requirements of the packets.


Date:				Monday, 27 June 2005

Time:				9:00a.m.-11:00a.m.

Venue:				Room 2304
				Lifts 17-18

Committee Members:		Dr. Brahim Bensaou (Supervisor)
                        	Dr. Jogesh Muppala (Chairperson)
                        	Prof. Mounir Hamdi


**** ALL are Welcome ****