Ad hoc networks are commonly known to implement IEEE 802.11 standard as their medium
access control (MAC) protocol. It is well known that token passing MAC schemes
outperform carrier-sense-multiple-access (CSMA) schemes, therefore, token passing MAC
protocols have gained popularity in recent years. In recent years, the research extends the
concept of token passing ' scheme to wireless settings since they have the potential of
achieving higher channel utilization than CSMA type schemes.
In this thesis, a hybrid Token-CDMA MAC protocol that is based on a token passing scheme
with the incorporation of code division multiple access (CDMA) is introduced. Using a
dynamic code distribution algorithm and a modified leaky-bucket policing system, the
hybrid protocol is able to provide both Quality of Service (QoS) and high network resource
utilization, while ensuring the stability of a network. This thesis begins with the introduction
of a new MAC protocol based on a token-passing strategy. The input traffic model used in
the simulation is a two-state Markov Modulated Poisson Process (MMPP). The data rate
QoS is enforced by implementing a modified leaky bucket mechanism in the proposed MAC
scheme. The simulation also takes into account channel link errors caused by the wireless
link by implementing a multi-layered Gilbert-Elliot model. The performance of the proposed
MAC scheme is examined by simulation, and compared to the performance of other MAC
protocols published in the literature. Simulation results demonstrate that the proposed hybrid
MAC scheme is effective in decreasing packet delay and significantly shortens the length of
the queue.
The thesis continues with the discussion of the analytical model for the hybrid Token CDMA
protocol. The proposed MAC scheme is analytically modelled as a multiserver
multiqueue (MSMQ) system with a gated service discipline. The analytical model is
categorized into three sections viz. the vacation model, the input model and the buffer model.
The throughput and delay performance are then computed and shown to closely match the
simulation results. Lastly, cross-layer optimization between the physical (PHY) and MAC
layers for the hybrid token-CDMA scheme is discussed. The proposed joint PHY -MAC
approach is based on the interaction between the two layers in order to enable the stations to
dynamically adjust the transmission parameters resulting in reduced mutual interference and
optimum system performance. / 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:10413/6902 |
| Date | January 2009 |
| Creators | Liu, Yi-Sheng. |
| Contributors | Takawira, Fambirai., Xu, Hong-Jun. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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