STATE-AWARE JOINT CHANNEL ASSIGNMENT AND ROUTING IN MULTI-RADIO MULTI-CHANNEL

WIRELESS MESH NETWORKS

BY

OMAR ZAKARIA

A thesis submitted in fulfilment of the requirement for the degree of Doctor of Philosophy in Engineering

Kulliyyah of Engineering International Islamic University Malaysia

OCTOBER 2015

ii

ABSTRACT

Wireless Mesh Network is one of the promising architecture for providing last-mile broadband Internet connectivity to network users. The network capacity in 802.11-based single channel wireless mesh network is highly affected by interference caused by backhaul wireless links’ transmissions. This makes it inadequate for the new deployment scenarios with high number of users and traffic demands. To increase the network capacity, mesh routers are equipped with multiple radio interfaces. As a consequence, various wireless links can simultaneously operate within a set of orthogonal channels instead of a single channel. Routing and channel assignment are fundamental challenges in such networks, where the two functions determine how the traffic distributes over different links and channels. Therefore, for a given traffic load distribution, both channel assignment and routing need to be efficiently determined. The interdependent nature of routing and channel assignment has attracted researcher’s attention to address these two issues jointly. In addition, re-configuration is required in dynamic traffic loads to ensure optimal network resources utilization. Frequent re-configuration degrades the network performance. This is because re-configuration of channels and routes disrupt the network traffic and increase the packet loss and delay. The main objective of this research is to develop an efficient joint state-aware algorithm, which is capable of adapting the traffic load variation with less traffic disruption. In developing the proposed solution, the re-configuration cost should be identified and considered. Firstly, the problem is formulated as a multi-objective optimization problem. The aim of this optimization problem is to minimize four objective functions, namely the maximum channel-link utilization, average network contention, channel re-assignment cost and re-routing cost. Then a heuristic algorithm called State-Aware Joint Routing and Channel Assignment (SA-JRCA) is proposed to address these challenges. The proposed algorithm is compared with the proposal of Avallone et al., 2013 and the proposal of Raniwala et al., 2004. The ns-2 simulator is used for evaluation. The proposed and compared works are evaluated and analyzed based on various metrics, such as maximum channel-link utilization, average network contention, channel re-assignment cost, re-routing cost, average throughput, and average end-to-end delay. The proposed algorithm shows better performance compared with the other two proposals. A new metric is proposed to evaluate the network performance. The proposed average network contention metric shows more correlations with network performance than maximum channel-link utilization. The results show that the proposed algorithm achieved the highest packet delivery ratio with more consistency with the traffic variation. In contrast, the other two algorithms show degradation in the performance with higher traffic variation and their achieved packet delivery ratio, reduced by 13%, 21% respectively when the traffic load varied from 10% to 50%.

iii

خلاصة البحثAbst

تعتبر الشبكات اللاسلكية المتشابكة واحدة من أهم الشبكات الواعدة لتأمين الاتصال بالإنترنت ذو النطاق الأخير. وتتأثر الطاقة الاستيعابية للشبكات اللاسلكية المتشابكة التقليدية العريض لمستخدمي الشبكة في الميل

ذي القناة الواحدة بشكل كبير بالتداخل الناشئ بين الوصلات الاسلكية لنواة الشبكة، وهذا يجعلها غير مناسبة دة سعة للسيناريوهات الجديدة، وخصوصاً مع تزايد عدد مستخدمي الشبكة واحتياجاتهم. ومن أجل ز�

استيعاب مثل هذه الشبكات تم تزويد كل من الموجهات المتشابكة بأكثر من راديو، و بذلك يمكن لعدة وصلات لاسلكية أن تعمل على أكثر من قناة في نفس الوقت عوضاً عن القناة الواحدة. وتعتبر عملية التوجيه وعملية

في هذه الشبكات، لأ�ا تؤثر على توزعّ حركة البيا�ت توزيع القنواة على الراديوهات واحدة من أكبر التحد�تعلى الروابط اللاسلكية وعلى القنوات المختلفة. وللحصول على الإعداد الأكفأ للشبكة لا بد من تحديد طرق التوزيع لكل حمولة حركية بالتوازي مع تحديد القنوات المخصصة للراديوهات، وبسبب هذا الترابط بين كل من

لتوجيه وعملية التوزيع للقنوات يعمل الباحثون على حل كلا المسألتين مع بعضهما البعض. بالإضافة إلى عملية اأنه ولضمان الاستثمار الأمثل لموارد الشبكة فإنه من الضروري إعادة توجيه وإعادة توزيع القنوات على

اء الشبكة بإعادة الضبط المتكررة للشبكة نتيجة الراديوهات بعد كل تغيرّ في الأحمال المرورية.مع العلم أنه يتأثر أدللتغير المستمر بالأحمال المرورية وذلك لأن عملية إعادة الضبط تؤدي إلى تعطيل مؤقت في حركة البيا�ت في الشبكة و تزيد من فقدان الحزم وتأخيرها. إن الهدف الرئيسي من هذا البحث هو تطوير خوارزمية فعالة واحدة

التوجيه وإعادة تحديد القنوات بحيث تكون قادرة على التكيف مع أي تغير في توزيع الحمولة لكل من إعادةوبأقل تعطيل ممكن في حركة البيا�ت. وللبدء بالحل تمّ تصميم المشكلة كمشكلة تحسينٍ متعددة الأهداف، وتم

ؤشرات (الأهداف) الأربعة تحديد تكلفة إعادة الضبط، وحلّ هذه المشكلة يتضمن العمل على إنقاص قيمة المالتالية: مؤشر أكبر استخدام للقنوات ومؤشر متوسط التنافسية في الشبكة ومؤشر تكلفة إعادة التعيين للقنوات

تعمل على حل المشكلة السابقة. ولقياس أداء وفعالية وجيه. ومن ثم تم اقتراح خوارزميةومؤشر تكلفة إعادة الت النموذج المقترح من قبل رانيوالا ومع ٢٠١٣ آخرون،عامأفالون و مقترحتها مع كل من الخوارزمية المقترحة تم مقارن

كبر�مج للمحاكاة، بر�مج محاكات الشبكات النسخة الثانية وفي سبيل ذلك تم استخدام .٢٠٠٤ وآخرون عامالأقصى للقنوات ومؤشر وتمّ التقييم اعتماداً على مقاييس كثيرة للأداء، ومن هذه المقاييس: مؤشر الاستخدام

متوسط التنافس في الشبكة ومؤشر تكلفة إعادة تعيين القنوات ومؤشر تكلفة إعادة التوجيه ومؤشر متوسط أداءً أفضل بالمقارنة مع النموذج المقترح الإنتاجية ومؤشر متوسط التأخير من النهاية إلى النهاية. وقد أظهر

كما بينت التجارب أن مؤشر متوسط التنافس في الشبكة أكثر ترابطا مع . النماذج الأخرى التي تم المقارنة بها أداء الشبكة من مؤشر الاستخدام الأقصى. كما أظهرت الطريقة المقترحة أن نسبة تسليم الحزم فيها هي الأعلى

ليم الحزم عند . في حين انخفضت نسبة تسارنة مع كل من المقترحين الآخرينمقوالأقل تأثراً عند تباين حركة المرور % ١٠ على التوالي عند تغيير نسبة التباين في الحمل المروري من% ٢١، %١٣ إلى المقترحين الآخرينكل من

.%٥٠ إلى

iv

APPROVAL PAGE

The thesis of Omar Zakaria has been approved by the following:

_____________________________ Aisha Hassan Abdalla Hashim

Supervisor

_____________________________ Othman O. Khalifa

Co-Supervisor

_____________________________ Mohammad Azram

Co-Supervisor

_____________________________ Mohammad Umar Siddiqi

Internal Examiner

_____________________________ Azween Abdullah External Examiner

_____________________________

Kamaruzzaman Bin Seman External Examiner

_____________________________ Saadeldin Mansour Gasmelsid

Chairman

v

DECLARATION

I hereby declare that this thesis is the result of my own investigations, except where

otherwise stated. I also declare that it has not been previously or concurrently

submitted as a whole for any other degrees at IIUM or other institutions.

Omar Zakaria

Signature ........................................................... Date .........................................

vi

COPYRIGHT PAGE

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH

Copyright © 2015 by International Islamic University Malaysia. All rights reserved.

STATE-AWARE JOINT CHANNEL ASSIGNMENT AND ROUTING IN MULTI-RADIO MULTI-CHANNEL WIRELESS

MESH NETWORKS

I hereby affirm that the International Islamic University Malaysia (IIUM) holds all

rights in the copyright of this Work and henceforth any reproduction or use in any

form or by means whatsoever is prohibited without the written consent of IIUM. No

part of this unpublished research may be reproduced, stored in a retrieval system, or

transmitted, in any form or by any means, electronic, mechanical, photocopying,

recording or otherwise without prior written permission of the copyright holder.

Affirmed by Omar Zakaria.

……………………………. ……………….. Signature Date

vii

I dedicated this thesis to my beloved family:

To my beloved Father

To my beloved Mother

To my beloved brother and sisters

To my lovely Wife

To my lovely sons

viii

ACKNOWLEDGEMENTS

All praise be to ALLAH s.w.t, the Most Beneficial and the Most Merciful. Best prayers and greetings to our holy prophet Muhammad p.b.u.h and his family.

First and foremost, Alhamdulillah, all praise be to Allah, for having mercy on me and giving me the health, patience, courage and determination to carry out this research.

I would like to express my sincere gratitude to my main supervisors, Prof. Dr. Aisha Hassan Abdalla Hashim for her supervision. I greatly appreciate all her dedication, guidance, advice and inspiration to improve the quality of this research and thesis. This thesis would not have been possible without her help and motivation.

I also would like to forward my gratitude to my co-supervisors, Prof. Dr. Othman O. Khalifa and Prof. Dr. Mohammad Azram. I greatly appreciate their guidance and advice throughout my research. With their continuous support and guidance, I am able to complete my PhD.

My appreciation is also extended to Assoc. Prof. Dr. Wan Haslina Hassan, Dr.Rashid Saeed and Dr. Khalid Hindawi. I am very thankful for their support and help extended to me during my PhD.

Many thanks also to the Malaysia Ministry of Higher education for the scholarship assistance in financing my study.

Special thanks to IIUM for providing a comfortable environment and sufficient resources and services to me.

I am also extremely grateful to my parents whose continuous blessing and sacrifices for everything in my life. I would especially like to thank my wife, for all her patience and her understanding to all the difficulties that I have encountered. Without the patience of my family, to whom I owe everything, it would have been impossible to accomplish my study.

Lastly, I like to thank my fellow friends for their assistance during my study. Thank you very much to Faiz, Lalitha, Mojtaba, Yunus, Waleed, Mahmoud, Mohammad, Ali, Yahia, Loay, Mistura, and Khalid.

ix

TABLE OF CONTENTS

Abstract .................................................................................................................... ii Abstract in Arabic .................................................................................................... iii Approval Page .......................................................................................................... iv Declaration ............................................................................................................... v Copyright Page ......................................................................................................... vi Table of contents ...................................................................................................... ix List of Tables ........................................................................................................... xii List of Figures .......................................................................................................... xiii List of Abbreviations ............................................................................................... xvi CHAPTER ONE: INTRODUCTION .................................................................. 1

1.1 Introduction............................................................................................... 1 1.2 Background of Research ........................................................................... 1 1.3 Problem Statement .................................................................................... 4 1.4 Research Hypothesis and Philosophy ....................................................... 5 1.5 Research Objectives.................................................................................. 6 1.6 Research Methodology ............................................................................. 6 1.7 Scope of Research..................................................................................... 8 1.8 Thesis Organization .................................................................................. 9

CHAPTER TWO: CHANNEL ASSIGNMENT AND ROUTING IN MULTI-RADIO MULTI-CHANNEL WIRELESS MESH NETWORKS ..................... 12

2.1 Introduction............................................................................................... 12 2.2 Multi-Radio Multi-Channel Wireless Mesh Network Architecture ......... 12 2.3 Centralized Channel Assignment and Routing: Design Considerations

and Approaches ........................................................................................ 16 2.3.1 Channel Assignment Strategies ...................................................... 16 2.3.2 Routing Issues ................................................................................. 17 2.3.3 Traffic Load Information ................................................................ 19 2.3.4 Topology Formulation .................................................................... 20 2.3.5 Interference Modeling ..................................................................... 22 2.3.6 Mathematical Formulation .............................................................. 28

2.3.6.1 Network Model ................................................................... 29 2.3.6.2 Optimization Function and Fairness ................................... 30 2.3.6.3 Constraints .......................................................................... 32

2.3.7 Joint Channel Assignment and Routing Classification ................... 40 2.4 Related Works .......................................................................................... 44

2.4.1 Centralized Joint Channel Assignment and Routing ...................... 44 2.4.1.1 Static Channel Assignment and Routing ............................ 45 2.4.1.2 Static Channel Assignment with Link Scheduling and Routing ........................................................................................... 52 2.4.1.3 Dynamic Channel Assignment and Routing ...................... 54

2.4.2 State-aware Channel Assignment and Routing ............................... 63 2.4.2.1 Channel re-assignment Proposals ....................................... 64 2.4.2.2 Flow Re-routing .................................................................. 68

x

2.4.2.3 Reconfiguration Trigger ..................................................... 69 2.4.2.4 Dissemination of New Configuration ................................. 73

2.5 Summary ................................................................................................ 73 CHAPTER THREE: STATE-AWARE JOINT ROUTING AND CHANNEL ASSIGNMENT ALGORITHM ............................................................................ 74

3.1 Introduction............................................................................................ 74 3.2 System Model ........................................................................................ 74

3.2.1 Design Considerations and Assumptions ........................................ 75 3.2.2 Network Model ............................................................................... 76 3.2.3 Interference Model .......................................................................... 77

3.3 Mathematical Problem Formulation ...................................................... 78 3.3.1 Constraints ...................................................................................... 78

3.3.1.1 Radio Interface Constraints ................................................ 79 3.3.1.2 Topology Constraints ......................................................... 79 3.3.1.3 Flow Constraints ................................................................. 80 3.3.1.4 Interference Constraints ...................................................... 81

3.3.2 Objective Functions ........................................................................ 82 3.3.2.1 Channel-Link Utilization .................................................... 82 3.3.2.2 Average Network Contention ............................................. 82 3.3.2.3 Channel Re-assignment cost ............................................... 83 3.3.2.4 Flow re-routing cost............................................................ 85

3.3.3 Multi-Objective Optimization Problem (MOP) Formulation ......... 86 3.4 The Proposed State-Aware Joint Routing And Channel Assignment (SA-

JRCA) .................................................................................................... 90 3.4.1 Architecture Overview .................................................................... 90 3.4.2 Algorithms Description of SA-JRCA ............................................. 95

3.5 Summary ................................................................................................ 107 CHAPTER FOUR: PERFORMANCE EVALUATION AND RESULT ANALYSIS ............................................................................................................. 108

4.1 Introduction............................................................................................ 108 4.2 Performance Evaluation Metrics ........................................................... 108 4.3 Simulation .............................................................................................. 110

4.3.1 Simulation Environment ............................................................... 110 4.3.2 Traffic Load Generation ................................................................ 111 4.3.3 Simulation Scenarios..................................................................... 112 4.3.4 Simulation Parameters .................................................................. 114

4.4 Simulation Results and Performance Analysis. ..................................... 115 4.4.1 The Impact of Route-variation Weighting Parameter 𝝎𝝎 ............... 122 4.4.2 The Impact of Number of Radios ................................................. 125 4.4.3 The Impact of Number of Channels .............................................. 129 4.4.4 The Impact of Traffic Variation .................................................... 134 4.4.5 The Impact of Network Traffic Load ............................................ 135

4.5 Summary ................................................................................................ 137 CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS ................ 138

5.1 Conclusion ............................................................................................. 138 5.2 Dissertation Contribution ...................................................................... 138

xi

5.3 Recommendations.................................................................................. 139 REFERENCES ...................................................................................................... 141 APPENDIX I: Proposed Algorithms Pseudo Code ............................................ 148 APPENDIX II: Multiple Interfaces support in NS-2 ......................................... 154 APPENDIX III: Simulation Result Format ....................................................... 156

xii

LIST OF TABLES

Table No. Page No.

2.1 Notations for Mathematical Formulation 34

2.2 Mathematical Formulation (Interference and Radio Constraints) 38

2.3 Channel Assignment and Routing Proposals Summary 59

2.4 State-Aware Channel Assignment/Routing Proposals Summary 71

3.1 Notations Parameters and Variables 88

4.1 The Average Shorted Paths Number in Grid Topology 113

4.2 Simulation Parameters 115

xiii

LIST OF FIGURES

Figure No. Page No.

1.1 Wireless mesh networks architecture (Akyildiz & Wang, 2009) 3

1.2 Research methodology flow chart 8

1.3 Structure of the thesis (chapters one, two & three) 10

1.4 Structure of the thesis (chapters four & five) 11

2.1 Multi-radio multi-channel wireless mesh networks 14

2.2 Channel assignment types on a wireless link 17

2.3 Physical-to-logical links mapping 22

2.4 The transmission range using omni-directional antennas 24

2.5 Interference based on interference-range model 24

2.6 Interference based on protocol model 26

2.7 Interference based on physical model 26

2.8 Interference based on interference-range model for 802.11 27

2.9 Router-to-router vs. radio-to-radio models 30

2.10 Example of links scheduling (sufficient condition is not satisfied) 36

2.11: Centralized channel assignment and routing 42

2.12: Centralized channel assignment and routing 43

2.13: Joint channel assignment and routing proposals 44

3.1 The re-routing and channel re-assignment of a flow 85

3.2 The MOP formulation for the channel and routing reassignment problem 89

3.3 Routing update 92

3.4 Channel assignments update 92

3.5 Neighbor table 93

3.6 The proposed architecture for multi-interface wireless mesh router 94

xiv

3.7 Routing table entry 95

3.8 Routing table 95

3.9 Channel assignments to logical links 96

3.10 Top level flow chart of the proposed solution 98

3.11 Finding contention cost 100

3.12 Finding path cost 100

3.13 The proposed algorithm (initial routing phase) 102

3.14 Channel assignment algorithm 103

3.15 The proposed algorithm (routing adjustment phase) 104

3.16 Channel mapping weighted bi-partite graph 106

3.17 Weight calculation in weighted bi-partite graph 106

4.1 Simulation network topology 114

4.2 Comparison of maximum channel-link utilization over different time intervals 116

4.3 Comparison of average network contention over different time intervals 117

4.4 Comparison of the packet delivery ratio over different time period 118

4.5 Packet delivery ratio related to maximum channel-link utilization 119

4.6 Packet delivery ratio related to average network contention 119

4.7 Cumulative distribution function of channel-link utilization over all time intervals 120

4.8 Normalized channel re-assignment cost versus re-assignment steps 121

4.9 Impact of the weighting parameter on the normalized re-routing cost 123

4.10 Average normalized rerouting cost with different weight parameter 124

4.11 Packet drop due to re-routing with different weight parameter 125

4.12 Average maximum channel-link utilization with different weight parameter 126

4.13 Comparison of average network contention over different number of interfaces 127

xv

4.14 Comparison of the average packet delivery ratio (PDR) over different number of interfaces 128

4.15 Comparison of the average normalized channel re-assignment cost over different numbers of interfaces 129

4.16 Average network contention versus number of channels 130

4.17 The total aggregated throughput over different number of channels 131

4.18 The average end-to-end delay over different number of channels 132

4.19 Average normalized channel re-assignment cost versus number of channels 133

4.20 Jain’s fairness index for packet delivery ratio versus number of channels 134

4.21 Comparison of the average packet delivery ratio over different traffic variation 135

4.22 Comparison of average aggregated throughput versus total traffic load 136

xvi

LIST OF ABBREVIATIONS

ARP

Address Resolution Protocol

CA

Channel Assignment

CSMA/CA Carrier Sense Multiple Access/Collision Avoidance CTS

Clear to send

FCRA

Flow-based Channel and Rate assignment

HWMP

Hybrid Wireless Mesh Protocol

ILP

Integer Linear Programming

ILS

Iterated Local Search

IP

Integer Programming

JCAR

Joint Channel Assignment and Routing

LP

Linear Programming

LS

Link Scheduling

MAC

Multiple Access Control

MILP

Mixed Integer Linear Programming

MINLP

Mixed Integer Nonlinear Programming

MIS

Maximum Independent Set

MOP

Multi-Objective Optimization Problem

MVCRA Minimum Variation Channel Reassignment Algorithm

MVCRA-R Minimum Variation Channel and Rate Reassignment Algorithm

ns-2

Network Simulator Version 2

NIC

Network Interface Card

OLSR Optimized Link State Routing

xvii

PaMela Partitioned Mesh Network Traffic and Interference-Aware

Channel Assignment

PDR

Packet Delivery Ratio

RCART

Robust Joint Channel Assignment and Routing with Time Partitioning

RTS

Request To Send

SA-JRCA

State-Aware Joint Routing and Channel Assignment

SI

Scheduling Index

SINR Signal to Interference and Noise Ratio

1

CHAPTER ONE

INTRODUCTION

1.1 INTRODUCTION

Wireless mesh networks have been widely implemented to provide the last mile

wireless broadband access because of its multi-hop nature and stability. The work of

this thesis focuses on channel assignment and routing in multi-radio multi-channel

wireless mesh network. The first section within this chapter provides a background of

the research area. This is followed by the research problem and the research

hypothesis and philosophy. The research objectives are also presented in this section.

Then, it is followed by the research methodology and the research scope. Finally, the

thesis organization is presented.

1.2 BACKGROUND OF RESEARCH

Wireless Mesh Networks are one of the key technologies, which will dominate

wireless networking in this decade (Akyildiz & Wang, 2009). It helps to realize the

network connectivity anywhere, anytime with simplicity and low cost. Accordingly,

they will play a major role within the next generation Internet. Wireless mesh

networks consist of two kinds of network elements, namely, mesh routers and mesh

clients. While the mesh routers form the backbone, the mesh clients are the users that

generate traffic in the network. Figure 1.1 shows the wireless mesh network

architecture. When more mesh clients are connected to wireless mesh network, there

is a requirement to improve the transport capacity of the backbone. Wireless mesh

2

network configuration and management is still associated with many challenging

issues. For an instance, the configuration of the mesh routers with multiple radios

contributes to the channel assignment issue. In such a case, mesh routers may exploit

the availability of multiple radios to simultaneously transmit and/or receive on

different frequency channels. This will increase the throughput if the assignment of

channels to radios is carefully planned.

Channel assignment can follow the static assignment as in (Mohsenian-Rad &

Wong, 2007; Pries, Staehle, Staehle, & Tran-Gia, 2010; Raniwala, Gopalan, &

Chiueh, 2004), where each interface of every mesh router is assigned a channel

permanently or for long interval, or the dynamic assignment, such as in (Kodialam &

Nandagopal, 2005; H. Li, Cheng, Zhou, & Wan, 2010; X.-Y. Li, Nusairat, Wu, Qi,

Zhao, Chu, & Liu, 2009), each interface is allowed to switch from one channel to

another channel frequently. Static strategies do not require interfaces to switch

channels frequently, and thus have no switching overhead while dynamic strategies

assume that the underlying hardware support fast channel switching with negligible

overhead which is still difficult to achieve with recent available hardware.

The schemes which have been proposed in literature to deal with channel

assignment problem and routing problem can be divided into two classes; the first

considers the joint problem of channel assignment and routing, as in (Alicherry,

Bhatia, & Li, 2006; Bononi, Felice, Molinaro, & Pizzi, 2009; X.-Y. Li et al., 2009). In

contrast, the second treats the two problems separately and deal with channel

assignment as a separated problem, as in (Ko, Misra, Padhye, & Rubenstein, 2007; M.

Li & Feng, 2010; Trung, Geun, & Su, 2010). Channel assignment and routing

problems are closely dependent on each other and both influence the network

performance. With this, the channel assignment and routing is the process which sets

3

the network configuration. Throughout this thesis the term network configuration

refers to a set of channels and routes assigned to the network.

Furthermore, channel assignment algorithms can also be classified into

centralized and distributed algorithms. In centralized algorithms, as (Juan, 2008; Du,

2007), a centralized entity collects information on the network to assign channels to

each interface. While in distributed algorithms, as proposed in (Raju, Athota, & Negi,

2009; Wanli, Kun, & Lei, 2008), the channel assignments at each node are based only

on the local information. As stated in Hong, Gu, Hoque, and Tang (2010), centralized

algorithms outperform distributed algorithms due to the availability of network

knowledge. This knowledge includes the traffic load, routes, bandwidth of links, and

the mapping of links’ interferences. On the other hand, distributed algorithms require

only a small amount of network knowledge to improve the performance.

Figure 1.1: Wireless mesh networks architecture (Akyildiz & Wang, 2009).

To adapt the varying load distribution, most channel assignment and routing

algorithms in the literature do not account the overhead incurred during setting the

4

new network configurations. Throughout this thesis, the process of setting new

network configuration by considering the existing/current network configuration uses

the term state-aware. However, few works in literature are found to be state-aware.

1.3 PROBLEM STATEMENT

Due to the rapid growth of multimedia traffic demands, it is necessary to improve the

performance of wireless mesh networks so that it meets the requirements of

multimedia application. In multi-channel multi-radio wireless mesh networks, the

channel assignment and routing are interdependent, thus jointly finding channel

assignment and routing, further optimizes the network performance. For efficient

resource utilization, network re-configuration is performed for each traffic variation.

As in the case of dynamic traffic load, the re-configuration process will be frequently

triggered resulting higher overheads.

Channel re-assignment results channel switching in several wireless links and

radios. According to (P. Li, Scalabrino, Fang, Gregori, & Chlamtac, 2009), the

average traffic disruption time due to channel re-assignment is in the order of seconds,

even though the channel switching time of the interface cards is in the order of tenths

micro seconds. According to (Yun, Zhou, Arora, & Choi, 2009), the switching delay

in 802.11a is in the range of 328 microseconds. This time is equal to the time of

transmitting 1024 bytes in the rate of 25 Mbps using the same technology. As in (P. Li

et al., 2009), the upper layer protocols, such as MAC and routing layer protocols, have

a significant impact on the switching delay. Extensive experiments in (P. Li et al.,

2009) indicate that the cost of channel switching in terms of packet loss ratio increases

as the number of hops increases. On the other hand, unaware flow re-routing for a set

5

of new traffic load demands, causes higher flow disruption for on-the-fly packets

which results in higher packet loss.

Hence, if the re-configuration does not consider the existing/current network

configuration, this will result in reduced throughput, increased delay, increased packet

loss, channel underutilization and increased overhead associated with re-assignment

and re-routing. Currently, the channel assignment and routing algorithms are lacking

of an efficient re-configuration solution. Therefore, an efficient channel assignment

and routing strategy are needed to address the above-mentioned issues.

1.4 RESEARCH HYPOTHESIS AND PHILOSOPHY

In order to develop the state-aware channel assignment and routing, the proposed

solution is based on the following assumptions:

1. Joint approach is more efficient to address channel assignment and routing

problems in multi-channel multi-radio wireless mesh networks.

2. Centralized approach is more adequate to the channel assignment and routing

scheme, where information on the network status has higher availability.

There is interdependency between channel assignment and routing. The

routing determines the load on each wireless link, which affects the channel

assignment decision. On the other hand, different channel assignment leads to a

different routing decision. Therefore, both channel assignment and routing influences

the network performance and required to be solved simultaneously to improve the

network throughput.

Centralized and distributed approaches have been reviewed in literature.

Centralized algorithms outperform distributed algorithms due to the coordination and

6

consistency nature. The higher availability of the network knowledge makes it more

efficient and stable to be implemented for issues related to wireless mesh networks,

where its backhaul links are responsible in aggregating traffics for a high number of

mesh users. Furthermore, it is feasible to implement a centralized approach due to the

traffic and load information which can be easily obtained at a single point, gateway

node.

1.5 RESEARCH OBJECTIVES

The main aim of this research is to enhance the channel assignment and routing in

multi-radio multi-channel wireless mesh networks in order to increase the network

throughput. The specific objectives are as bellow:

1. To propose new metrics those reflect the merit network configuration and the

re-configuration overhead. These metrics are to be applied in designing the

centralized solutions.

2. To design a joint state-aware algorithm, that is adaptable to a dynamic traffic

load variation with a higher network throughput and less re-configuration

overhead.

3. To implement, evaluate and compare the proposed algorithm with the current

channel assignment and routing algorithms.

1.6 RESEARCH METHODOLOGY

In order to achieve the above-mentioned objectives the approach followed in this

research is as follows:

7

1. Investigate the current techniques in centralized and joint approaches for

multi-radio multi-channel wireless mesh networks. This is to highlight the

strengths and limitations of each approach. Furthermore, state awareness

approaches in literature also needed to be investigated.

2. Formulate the joint state-aware problem as an optimization problem with

identifying the cost (overhead) associated with the re-configuration process, in

addition to develop a metric to be used in finding the optimal configuration.

3. Design a channel assignment and routing algorithm that increases the network

throughput and reduces the reconfiguration overhead.

4. Implement the proposed algorithm using ns-2 simulator.

5. Evaluate and compare it with one static configuration (Raniwala et al., 2004)

and one with channel re-assignment algorithm (Avallone, Stasi, & Kassler,

2013). Performance metrics to be used are throughput, latency, packet loss and

re-configuration cost of the proposed algorithm cost. Figure 1.2 shows the

research methodology flow chart.