MAC FLOW FAIRNESS IN IEEE 802.11 BASED WIRELESS MESH NETWORKS

MPhil Thesis Defence


Title: "MAC FLOW FAIRNESS IN IEEE 802.11 BASED
WIRELESS MESH NETWORKS"

By

Mr. Kin Wah Edward Lin


Abstract

In the past decade, IEEE 802.11 protocol, which is originally designed for 
wireless local area networks (WLAN), has been invoked repeatedly in the 
context of wireless mesh networks (WMNs) to provide last-mile broadband 
service and large-scale metropolitan area networks thanks its high data 
rate, wide coverage and reduced infrastructure expenditure. Nevertheless, 
such deployment makes the well-known WLAN problems, such as hidden or 
exposed terminals, channel impairments such as multi-path fading, and so 
on, more severe, resulting in several types of service provisioning 
problem in WMNs. Among such problems that are yet to be addressed, we 
list, fairness among MAC flows, and flow starvation, the ultimate 
manifestation of the lack of fairness. In this thesis, we aim to design a 
framework, to address these problems and to enable additional services 
such as QoS Routing and admission control. We also aim our framework to be 
easily deployable in a real system.

To begin with, we first study the trade-off between aggregate MAC flow 
throughput and the fairness in WMNs that utilize scheduling on top of the 
CSMA/CA access scheme. We propose an analytical model to study the 
interaction between contending links with non-saturated nodes. Based on 
this model, we formulate the bandwidth-scheduling problem as an aggregate 
MAC flow throughput maximization problem subject to the fairness 
requirement dictated by the scheduler. The rational of such study is to 
provide a theoretical benchmark to gage the performance of the plethora of 
non work-conserving schedulers designed to run on top of the CSMA/CA 
protocol in a distributed environment that have proliferated in recent 
years.

After understanding how much sacrifice in the aggregate MAC flow 
throughput or the fairness are made - due to the mismatch between the 
objective of the fair scheduler on one hand and the operation of the 
CSMA/CA algorithm on the other, we propose a distributed fair MAC flow 
allocation and scheduling framework for provisioning MAC flow fairness. 
The framework consists of (1) a modified wireless ad hoc routing protocol 
to take into account bandwidth requirement, (2) a link information 
dissemination protocol to propagate local topology information, (3) a 
cooperative gradient-based iterative algorithm to allocate fairly MAC flow 
bandwidth and (4) a distributed fair MAC scheduler to coordinate access to 
the channel according to the allocated bandwidth. We finally discuss how 
we implement this framework in the Linux operating system.


Date:			Wednesday, 6 January 2010

Time:			2:00pm – 4:00pm

Venue:			Room 3501
 			Lifts 25/26

Committee Members:	Dr. Brahim Bensaou (Supervisor)
 			Dr. Jogesh Muppala (Chairperson)
 			Prof. Danny HK Tsang (ECE)


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