Providing guarantees in the Quality of Service (QoS) has become essential to the
transmission of multimedia traffic over wireless links with fading channels. However this
poses significant challenges due to the variable nature of such channels and the diverse QoS
requirements of different applications including voice, video and data. The benefits of
dynamic adaptation to system and channel conditions have been accepted, but the true
potential of optimized adaptation is lost if the layers operate independently, ignoring possible
interdependencies between them. Cross-layer design mechanisms exploit such
interdependencies to provide QoS guarantees for the transmission of multimedia traffic over
fading channels.
Channel adaptive M-QAM schemes are examples of some of the earliest works in the area of
cross-layer design. However, many of the original schemes use the assumption that
thresholds designed for AWGN channels can be directly applied to slow-fading channels.
The thresholds are calculated with a commonly used approximation bit error rate (BER)
expression and the first objective of the thesis was to study the accuracy of this commonly
used expression in fading channels. It is shown that that the inaccuracy of the expression
makes it unsuitable for use in the calculation of the threshold points for an adaptive M-QAM
system over fading channels. An alternative BER expression is then derived which is shown
to be far more accurate than the previous one. The improved accuracy is verified through
simulations of the system over Nakagami-m fading channels.
Many of the cross-layer adaptation mechanisms that address the QoS provisioning problem
only use the lower layers (physical and data link) and few explore the possibility of using
higher layers. As a result, restrictions are placed on the system which introduces functional
limitations such as the inability to insert more than one class of traffic in a physical layer
frame. The second objective in this thesis was to design a physical and application layer
cross-layer adaptation mechanism which overcomes this limitation. The performance results
of the scheme in both AWGN and fading channels show that the cross-layer mechanism can
be efficiently utilized for the purposes of providing error rate QoS guarantees for multimedia
traffic transmissions over wireless links. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/6894 |
| Date | January 2009 |
| Creators | Quazi, Tahmid Al-Mumit. |
| Contributors | Xu, Hong-Jun. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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