Research Student Profile

Dr Mohamed Arabi

Research Student

Brief biographical information

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Improving Fairness and Utilisation in Ad Hoc Networks

Ad hoc networks represent the current de-facto alternative for infrastructure-less
environments, due to their self-configuring and resilience characteristics. Ad hoc networks
flexibility benefits, such as unrestrained computing, lack of centralisation, and ease of
deployment at low costs, are tightly bound with relevant deficiencies such as limited
resources and management difficulty.

Ad hoc networks witnessed high attention from the research community due to the numerous
challenges faced when deploying such a technology in real scenarios. Starting with the nature
of the wireless environment, which raises significant transmission issues when compared
with the wired counterpart, ad hoc networks require a different approach when addressing the
data link problems. Further, the high packet loss due to wireless contention, independent of
network congestion, requires a different approach when considering quality of service
degradation and unfair channel resources distribution among competing flows. Although
these issues have already been considered to some extent by researchers, there is still room to
improve quality of service by reducing the effect of packet loss and fairly distributing the
medium access among competing nodes.

The aim of this thesis is to propose a set of mechanisms to alleviate the effect of packet loss
and to improve fairness in ad hoc networks. A transport layer algorithm has been proposed to
overcome the effects of hidden node collisions and to reduce the impact of wireless link
contention by estimating the four hop delay and pacing packet transmissions accordingly.
Furthermore, certain topologies have been identified, in which the standard IEEE 802.11
faces degradation in channel utilisation and unfair bandwidth allocation. Three link layer
mechanisms have been proposed to tackle the challenges the IEEE 802.11 faces in the
identified scenarios to impose fairness in ad hoc networks through fairly distributing channel
resources between competing nodes. These mechanisms are based on monitoring the
collision rate and penalising the greedy nodes where no competing nodes can be detected but
interference exists, monitoring traffic at source nodes to police access to the channel where
only source nodes are within transmission range of each other, and using MAC layer
acknowledgements to flag unfair bandwidth allocation in topologies where only the receivers
are within transmission range of each other. The proposed mechanisms have been integrated
into a framework designed to adapt and to dynamically select which mechanism to adopt,
depending on the network topology. It is important to note that the proposed mechanisms and
framework are not alternatives to the standard MAC protocol but are an enhancement and are
triggered by the failure of the IEEE 802.11 protocol to distribute the channel resources fairly.

All the proposed mechanisms have been validated through simulations and the results
obtained from the experiments show that the proposed schemes fairly distribute channel
resources fairly and outperform the performance of the IEEE 802.11 protocol in terms of
channel utilisation as well as fairness.

Dr Mohamed Arabi

Director of studies: Dr Bogdan V Ghita
Other supervisors: Dr Xingang Wang

Conference papers

Improving Fairness in Ad Hoc Networks Based on Neighbour's Transmission Rate
Arabi M, Ghita BV
Proceedings of the Fourth International Conference on Internet Technologies and Applications (ITA 11), 6-9 September 2011, Wrexham, UK, pp 292-299, ISBN: 978-0-946881-68-0, 2011
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Improving Fairness in Ad Hoc Networks through Collision Rate Control
Arabi M, Ghita BV, Wang XG
Proceedings of the Eighth International Network Conference (INC 2010), Heidelberg, Germany, 8-10 July, ISBN: 978-1-84102-259-8, pp51-59, 2010
Can be ordered on-line.
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2 Conference papers

2 publication(s) - all categories.