a study on the spectrum efficient multi-hop wireless network

A STUDY ON THE SPECTRUM EFFICIENT
MULTI-HOP WIRELESS NETWORK
By
WADHAH HAFIDH ALI AL MANDHARI
A dissertation submitted in Partial Fulfillment of the
Requirements for the Degree of
DOCTOR OF ENGINEERING
at
THE UNIVERSITY OF ELECTRO-COMMUNICATIONS
DECEMBER 2009

A STUDY ON THE SPECTRUM EFFICIENT
MULTI-HOP WIRELESS NETWORK
APPROVED BY SUPERVISORY COMMITTEE
Chairperson Professor
Professor
Professor
Associate Professor
Associate Professor
Associate Professor
NOBUO NAKAJIMA
HARUHISA ICHIKAWA
YOSHIO KARASAWA
KEIKI TAKADAMA
HIROKI TAKAHASHI
TAKEO FUJII

Copyright @ 2009 by WADHAH HAFIDH
ALI AL MANDHARI
All Rights Reserved

在 、マルチホップ 無 線 ネットワークが 急 速 に 発 展 している。このネットワークの 主 な 利 点 として、 無 線 の 適 用 範 囲 をより 広 くとることができ、 導 入 が 容 易 である 事 が 挙 げられる。 このため、データ 共 有 や 無 線 のバックボーンネットワークなどのアプリケーションや 無 線 現
接 続 性 の 向 上 のために 利 用 されている。 近 年 「Green Communication」という 言 葉 がしばしば 使 用 されるようになった。 地 球 資 源 の
環 境 保 護 のために、 低 消 費 電 力 で 効 率 的 な 通 信 ネットワークを 実 現 すること、な
通 信 技 術 を 環 境 保 護 に 役 立 てようという 考 えである。マルチホップ 無 線 ネットワー ならびに
目 的 に 有 効 である。 最 近 の 開 発 において、コストダウンや 回 路 の 低 消 費 電 力 化 が 進 み、それらの 技 術 が 高 度 クはこれらの
無 線 ネットワークに 適 用 されている。しかし、 各 ノード 間 の 通 信 が 周 波 数 リ ソースを 共 有 する 性 質 上 、 多 くの 課 題 を 克 服 せねばならない。 必 要 な 通 信 容 量 を 得 ること は、 最 も 重 要 でかつ 最 も 困 難 な 課 題 である。 マルチホップ
研 究 では、 無 線 マルチホップネットワークの 性 能 を 改 良 することを 目 的 とし、 動 的 ア 本
無 線 メッシュネットワーク(WMN)の2タイプにおいてその 研 究 を 行 った。 前 者 では、 動 的 ネットワークにおいてルートディスカバリー 動 作 とスループ ットの 関 係 を 求 め、スループット 向 上 の 条 件 を 明 らかにする。 後 者 では 複 数 の 無 線 チャネ ドホックネットワークおよび
利 用 したマルチホップネットワークにおいて、チャネル 間 干 渉 を 低 減 してスループッ
向 上 を 図 る。 ルを
周 波 数 効 率 に 優 れたマルチホップ
無 線 ネットワークの 研 究
ワダ ハフィッドゥ アリ アルマンダリ
論 文 概 要
Abstract in Japanese
動 的 アドホックネットワークの 検 討 では、IEEE802.11g 規 格 (11 Mbps)、 並 びにOPNET 仕 様 のAODVプロトコルを 用 いた。シミュレーションでは、500m 四 方 の 屋 内 モデルを 用 い、40 から70 個 の 独 立 に 移 動 するノードを 設 定 し、 移 動 速 度 、Active Route Timeout (ART)パラ
i
伝 送 効 率 (Packet Delivery Rate : PDR)の 関 係 を 求 めた。その 結 メータおよびパケット

、 上 記 条 件 下 で、4 m/sおよび10 m/sと 異 なるノードの 速 度 において、いずれもART=0.25 secでパケット 伝 送 効 率 90 %の 値 を 得 た。さらに、5ホップの 固 定 のアドホックネットワー クにおいて、 同 じパラメータ(ART=0.25 sec)を 用 いてEnd-End 遅 延 を50 % 短 くすることが 果
値 3 secよりも 短 い 値 となっている。 無 線 LANを 用 いたWMNのスループットを 実 験 により 測 定 したところ、 単 一 周 波 数 使 用 で できた。OPNETにおけるAODVのARTデフォルト
約 50 % 低 下 し、nホップでは1/n %となった。そこで、 複 数 の 周 波 数 を 用 いる マルチラジオ 型 のマルチホップネットワークにおいて、スループットを 向 上 させる 検 討 を は1ホップで
った。 単 一 周 波 数 の 場 合 よりもスループットは 向 上 したが、 複 数 周 波 数 でもスループッ トの 劣 化 は 生 じた。それは 中 継 ノードの 送 信 機 から 受 信 機 への 隣 接 チャネル 干 渉 が 影 響 し ていると 考 えられた。そこで、アンテナ 間 の 干 渉 キャンセル 回 路 を 試 作 して、スループッ 行
向 上 の 検 討 を 行 った。 各 種 条 件 下 の 実 験 においてスループットの 向 上 が 確 認 された。 具 体 的 には、 干 渉 キャンセル 回 路 の 適 用 で 中 継 ノードの 両 アンテナ 結 合 は15 dB 改 善 され、 屋 内 の1ホップの 実 験 でスループットは7.9 Mbpsから 11.9 Mbpsへと4 Mbps(50 %) 改 ト
された。 更 にパケットの 不 達 率 も25 %から0.1%へ 改 善 された。これらの 検 討 から、 干 渉 キャン 善
性 能 改 善 に 大 きな 効 果 があることが 確 かめられた。 これらの 結 果 動 的 マルチホップネットワークならびに 静 的 マルチホップネットワー クそれぞれにおいて、 周 波 数 利 用 効 率 の 向 上 に 寄 与 するものである。 セルは、マルチホップネットワークの
ii

A Study on the Spectrum Efficient Multi-hop Wireless
Network
Wadhah Hafidh Ali Al Mandhari
Abstract
The field of multi-hop wireless networks has evolved rapidly in the past few years.
These networks provide an extended coverage through multi-hop while maintaining the
ease of setup and deployment. With such features, it quickly emerge as an attractive and
appealing solution for wireless connectivity in many communication fields.
Applications ranges from simple data sharing to a wireless backbone network links,
multi-hop wireless networks rises as a strong contender for any kind of environment.
The term “Green Communications” became a popular field of research due to the
desire to save energy consumption in the field of Communications. Furthermore,
communication systems are expected to save energy of various industrial systems. The
multi-hop wireless network is useful for such requirements.
Recent development and decrease in manufacturing costs, more advanced equipment
(requires less power to operate) are used to route data using intelligent wireless
multi-hop network. However, due to the shared resources architecture, the wireless
networks face a lot of challenges. Achieving the desired capacity is one of the most
important and most difficult targets.
This research focuses on performance enhancement of two wireless multi-hop
network categories, Ad-hoc networks and Wireless Mesh Networks (WMN). In the
simulated Ad-hoc networks, an improvement of nearly 90% in the Packet Delivery Rate
(PDR) was achieved as a result of reducing the route state hold time parameter in the
AODV routing protocol at different station movement speeds. Moreover, the same
parameter resulted in a nearly 50% reduction in the end-to-end delay for a stationary
Ad-hoc network.
iii

The WMN experiments showed that there is a nearly 50% degradation in throughput
with each increment in number of hops. However, I managed to achieve a throughput
enhancement in multi-hop/ multi-radio wireless mesh network by reducing interference
using a proposed interference canceller circuit. The proposed multi-radio WMN
interference cancellation circuit showed an improvement in throughput during various
experiment scenarios. The canceller managed to reduce interference about 15dB and
also improve throughput (nearly 4 Mbps, 50%) in indoor wireless LAN mesh network.
In addition, the packet dropped also was reduced form 25% to 0.1% after implementing
the proposed canceller. The experiments results showed remarkable impact of
interference on the WMN throughput.
iv

Acknowledgments
First of all, I would like to express my sincere gratitude to Prof. Nobuo
Nakajima for his tremendous guidance, supervision and motivation along
my PhD course. I would like further to thank Prof. Koichi Gyoda for his
encouragement and constructive comments throughout My PhD <strong>study</strong>.
My deep appreciation also for the Ministry of Education, Culture, Sport,
Science and Technology (MEXT) of Japan represented by the Japanese
Embassy in Sultanate of Oman for the priceless opportunity of <strong>study</strong>ing in
Japan.
I also would like to thank the Disaster Management and Mitigation
Group in the National Institute of Information and Communications
Technology (NICT) and Trinity Security systems for allocating necessary
equipments and resources for realizing this research.
Finally, best wishes to my Family for their remarkable support, and
understanding through hard times; and to my friends in Japan for their help
and encouragement.
v

Table of Contents
Abstract in Japanese ................................................................................................................ i
Abstract ................................................................................................................................. iii
Acknowledgments ....................................................................................................................v
Table of Contents.................................................................................................................... vi
List of Figures ...................................................................................................................... viii
List of Tables ............................................................................................................................x
List of Abbreviations .............................................................................................................. xi
1 Introduction..................................................................................................................... 1
1.1 IEEE 802.11 Wireless LAN overview .......................................................................... 1
1.2 Multi-hop Topology.................................................................................................... 3
1.3 Spectral efficiency...................................................................................................... 4
1.4 Interference problem.................................................................................................. 5
1.5 Future Trends............................................................................................................ 5
1.6 Purpose of the Research............................................................................................. 6
1.7 Thesis overview.......................................................................................................... 8
2 Mobile Ad-hoc Network ................................................................................................... 9
2.1 Introduction .............................................................................................................. 9
2.2 Ad-hoc On Demand Distance Vector (AODV) ........................................................... 10
2.3 Route Discovery in AODV routing protocol............................................................... 12
2.4 Multi-hop wireless network ...................................................................................... 13
2.5 Active Route Timeout and Mobility........................................................................... 14
2.6 User density and capacity ......................................................................................... 15
2.7 Chapter Summary.................................................................................................... 16
3 Packet Delivery Rate (PDR) Improvement for Mobile Ad-hoc Network (MANET) ........ 17
3.1 Introduction ............................................................................................................ 17
3.2 Previous Simulation model....................................................................................... 17
3.3 Comparison with other Related Researches............................................................... 20
3.4 Proposed Mobility models......................................................................................... 23
3.5 Packet Delivery Rate (PDR) ..................................................................................... 26
3.6 Simulation setting and parameters............................................................................ 26
3.7 Convergence time .................................................................................................... 28
3.8 Simulation scenarios and results .............................................................................. 29
3.8.1 First Scenario ...................................................................................................... 30
3.8.2 Second Scenario................................................................................................... 32
3.8.3 Third scenario...................................................................................................... 34
vi

3.8.4 Forth scenario ..................................................................................................... 36
3.9 Chapter summary .................................................................................................... 37
4 Interference Cancellation for Wireless Mesh Network (WMN) Nodes............................ 38
4.1 Introduction ............................................................................................................ 38
4.2 Exposed Terminal phenomenon................................................................................ 39
4.3 Multi-radio Wireless Mesh Network (WMN) ............................................................. 40
4.4 IEEE 802.11 non-overlapping channels.................................................................... 41
4.5 Interference suppression .......................................................................................... 42
4.5.1 Interference in multi-radio equipment................................................................... 42
4.6 Related interference suppression researches.............................................................. 43
4.7 Proposed interference cancellation circuit................................................................. 44
4.7.1 Phase cancellation ............................................................................................... 44
4.7.2 Scattering Parameters .......................................................................................... 46
5 Improvement of the Throughput of Indoor Multi-hop Network ..................................... 48
5.1 Introduction ............................................................................................................ 48
5.2 Experiment procedure and equipment....................................................................... 49
5.3 Field experiment scenarios....................................................................................... 52
5.3.1 Scenario 1: Throughput vs Signal to Interference (SIR) Ratio characteristics......... 52
5.3.2 Scenario 2: Throughput vs. number of hops.......................................................... 55
5.3.3 Scenario 3: Channel selection vs. throughput........................................................ 58
5.3.4 Scenario 4: Throughput measurement for distance varying and hop count in Indoor
closed corridor environment. ............................................................................................... 60
5.3.5 Scenario 5: Interference cancellation experiment for 2 hops WMN........................ 62
5.3.6 Chapter summary................................................................................................. 67
6 Conclusion ..................................................................................................................... 68
Appendix A ............................................................................................................................ 70
Simulation of route stat hold time parameter in AODV and OLSR ........................................ 70
Scenario A.1....................................................................................................................... 71
Scenario A.2....................................................................................................................... 72
Destination address Table.................................................................................................... 73
Appendix B ............................................................................................................................ 74
Interference cancellation .................................................................................................... 74
References: ............................................................................................................................ 76
Publications ........................................................................................................................... 80
vii

List of Figures
Figure 1.1: Infrastructure network ....................................................................................... 2
Figure 1.2: Ad-hoc network ................................................................................................ 2
Figure 1.3: Relay multi-hop wireless network ...................................................................... 3
Figure 1.4: Mesh multi-hop wireless network....................................................................... 3
Figure 1.5: Proposed indoor multi-hop network.................................................................... 6
Figure 1.6: Thesis organization ........................................................................................... 7
Figure 2.1: Data forwarding to unknown destination............................................................. 9
Figure 2.2: AODV vs. OLSR .............................................................................................11
Figure 2.3: Route discovery process .................................................................................. 13
Figure 2.4: Higher mobility can improve connectivity ........................................................ 15
Figure 2.5: Increased number of stations improves route discovery time .............................. 16
Figure 3.1: Simulated Area Map........................................................................................ 18
Figure 3.2: AODV vs. OLSR ............................................................................................ 20
Figure 3.3: Random Waypoint Mobility Model .................................................................. 21
Figure 3.4: Random Waypoint Mobility Model .................................................................. 22
Figure 3.5: Proposed Mobility Model ................................................................................ 22
Figure 3.6: Throughput vs. Speed for random waypoint and the new mobility model ............ 23
Figure 3.7:Coverage area and movement direction ............................................................. 25
Figure 3.8: Simulated Ad-hoc mobile network ................................................................... 27
Figure 3.9: Example of Convergence time in the simulation ................................................ 29
Figure 3.10: Simulation scenarios ..................................................................................... 30
Figure 3.11: Active Route timeout vs. PDR........................................................................ 30
Figure 3.12: Number of RERR/second as a function of the ART, for each RERR[23]............ 31
Figure 3.13: Speed vs PDR for 50, 60 and 70 stations at default value of ART (3sec) ............ 32
Figure 3.14: Number of users vs. Message Delivery Rate (Adopted from reference [21]) ...... 33
Figure 3.15: Speed vs PDR for 50, 60 and 70 at 0.25 sec ART............................................. 34
Figure 3.16: Simulated Ad-hoc mobile network.................................................................. 35
Figure 3.17: Number of hops vs. Delay.............................................................................. 35
Figure 3.18: Number of hops vs. PDR ............................................................................... 36
Figure 4.1: The exposed node problem .............................................................................. 39
Figure 4.2: Multi-radio Wireless Mesh Network................................................................. 40
Figure 4.3: IEEE 802.11 Non-overlapping channels (adopted from [34]).............................. 41
Figure 4.4: Interference in Multi-radio AP ......................................................................... 43
Figure 4.5: Interference cancellation Circuit....................................................................... 44
Figure 4.6: Phase Shift and cancel..................................................................................... 45
viii

Figure 4.7: S 21 Parameter comparison................................................................................. 46
Figure 5.1:IPN-W100AP Trinity Security Systems access points ......................................... 49
Figure 5.2: AirMagnet Surveyor interface .......................................................................... 51
Figure 5.3: SIR measurement using Signal generator .......................................................... 52
Figure 5.4: Directional Coupler......................................................................................... 52
Figure 5.5: SIR vs Throughput (Continuous Interference) ................................................... 53
Figure 5.6: SIR measurement using two interfering networks.............................................. 54
Figure 5.7: Throughput vs. SIR (Interference with co-channel WLAN)................................ 55
Figure 5.8: Three hop WMN with Single radio AP ............................................................. 55
Figure 5.9: Number of hops vs. throughput for one radio AP ............................................... 56
Figure 5.10: Three hop WMN with two radios AP .............................................................. 57
Figure 5.11: Number of hops vs. throughput for two radio AP (2.4GHz and 5GHz)............... 57
Figure 5.12: Single radio vs. Multi-radio ........................................................................... 58
Figure 5.13: Single access point field intensity................................................................... 60
Figure 5.14: Received signal power versus range in a corridor............................................. 61
Figure 5.15: Received signal power measurement points in the corridor............................... 61
Figure 5.16: Interference cancellation Circuit connected on two radios AP........................... 62
Figure 5.17: Actual Interference cancellation Circuit .......................................................... 63
Figure 5.18: Two-hops WMN with cancellation circuit ....................................................... 63
Figure 5.19: S 21 Parameter ................................................................................................ 64
Figure 5.20: Attenuation value vs. throughput .................................................................... 65
Figure 5.21: Two hop WMN in closed corridor with cancellation circuit .............................. 66
Figure 5.22: S 21 Parameter................................................................................................ 66
Figure A.1: The Simulated Area map................................................................................. 70
Figure A.2: Throughput vs. ART ....................................................................................... 71
Figure A.3: Throughput vs. NHT/HI.................................................................................. 72
Figure B.1: Attenuation value vs. throughput ..................................................................... 74
Figure B.2: Attenuation value vs. throughput ..................................................................... 75
ix

List of Tables
Table 2.1: Comparison between AODV and OLSR............................................................. 12
Table 3.1: Simulation Parameters ...................................................................................... 19
Table 3.2: Simulation Parameters ...................................................................................... 28
Table 3.3: Second model Simulation parameters................................................................. 34
Table 5.1: IPN-W120AP Wireless (2.4GHz - 802.11b/g)..................................................... 50
Table 5.2:Throughput of Mutli-hop WMN ......................................................................... 59
Table 5.3: Throughput measured at different hop distance ................................................... 62
Table A.1: Destination address for the map area simulation ................................................. 73
x

List of Abbreviations
WLAN Wireless Local Area Network
QoS Quality of Service
BBS Basic Service Set
EBSS Extended Basic Service Set
WMN Wireless Mesh Networks
MANET Mobile Ad-hoc Networks
ITU International Telecommunication Union
AODV Ad hoc on-demand Distance Vector
PDR Packet Delivery Rate
ART Active Route Timeout
OLSR Optimized Link State Routing Protocol
RREQ Route Request
RREP Route Reply
ACI Adjacent Channel Interference
SIR Signal to Interference
AP Access Point
MIMO Multiple-Input, Multiple-Output
DSR Dynamic Source Routing
SNR Signal to Noise Ratio
CSMA/CA Carrier Sense Multiple Access with Collision Avoidance
RTS/CTS Request To Send/ Clear To Send
xi

CHAPTER
1
Introduction
1.1 IEEE 802.11 Wireless LAN overview
IEEE standard for Local Area network 802.11 proved to be very successful. The group
started with 802.11b at 11Mbps in the 2.4GHz band. The current popular 802.11g
54Mbps also utilizes the 2.4GHz band. The IEEE 802.11 work group presented many
sub-standards each to focus on different aspects in the standard such as 802.11e for
Quality of service and 802.11n for MIMO [1].
This short range wireless network eliminates the need for running cables and
simplifies the process of establishing fast Ad-hoc connection. Many new types of
networks established as an evolution of this short range wireless networks such as
sensor networks. With a coverage that can reach up to 100m in the free space, and its
ability to penetrate walls, it became popular for many indoor environments such as
hotels, airports, offices and so on [1].
In general, Wireless LANs are primarily a single hop network; the network size is
virtually unlimited due to the use of IP stack. Wireless LAN is a multiple-access
network, which means that all nodes within the range of a single hop can hear each
other. This makes the topology not very important. Problem arises in wireless LAN
when more hops are needed to cover more area which results in more networks co-exist.
IEEE 802.11 Wireless Local networks in general are categorized into two main types,
wireless infrastructure and multi-hop Ad-hoc wireless networks. Infrastructure networks
consist of fixed and wired gateways. All stations communicate within the access point
coverage range. The so called Wireless Local Area Networks (WLAN) is an example of
such networks and it is illustrated in Fig 1.1 [2].All stations cannot communicate
directly with each others; instead packets go through a central access point before they
arrive to destination. The stations can roam within the coverage area of a single access
point (Basic Service Set (BBS)) or multiple access points (Extended Basic Service Set
(EBSS)).
1

Figure 1.1: Infrastructure network
The second type is the Multi-hop Ad-hoc wireless networks. (Infrastructure less) [3].
Wireless Mesh Networks (WMN) and Ad-hoc networks are two examples of the
multi-hop wireless networks. These types of networks have no fixed router or access
points. Stations have the ability to move around with freedom of connecting
dynamically to other stations. Moreover, the mobile stations can emulate a router by
discovering and maintaining routes to others in the network [2] [4]. Figure 1.2 presents
an example of Ad-hoc networks. The red lines indicate the best possible route to a
destination while the green dotted lines indicate the secondary possible route to an
arbitrary destination. Mobility is a very important issue in Ad-hoc networks. It is
important to keep the connections between users alive while moving. Since the users are
allowed to join in or leave the network freely, the network is expected to change rapidly.
This requires management between users to keep track of the connections between them
[1].
Figure 1.2: Ad-hoc network
2

The performance of a random media access such as CSMA/CA is characterized by
throughput. Throughput has no unit and it is defined as the ratio of the average rate of
packets successfully transmitted divided by the channel packet rate [5].
1.2 Multi-hop Topology
WMN is a wireless network adopting a multi-hop wireless technology without
deployment of wired backhaul links. WMN is similar to Mobile Ad-hoc Networks
(MANET); however, the nodes are relatively fixed. Another difference is that WMN can
introduce hierarchy network architecture. Multi-hop networks are divided into two
categories, relay and mesh. Relay (Flat Topology) is a tree based topology where one
end of the path is the base station as shown in Fig 1.3.
Figure 1.3: Relay multi-hop wireless network
Mesh on the other hand has multiple connections between users as illustrated in Fig 1.4.
Figure 1.4: Mesh multi-hop wireless network
Multi-hop wireless networks have an advantage of rapid deployment, ease to provide
coverage in hard to reach places, extend coverage due to multi-hop forwarding. The
3

more hops introduced, the less power required to transmit. In some cases, this could
result in an increased battery life for users on mobile devices. Multi-hop is also known
to introduce some challenges such as routing complexity and extra delay due to
multi-hop.
1.3 Spectral efficiency
Radio resources are scarce and expensive. In order to have an economically feasible
system, the available resources must be used in an efficient way. In cellular systems,
maximizing the number of users in each cell while maintaining an adequate level of
Quality of Service (QoS); is the key to achieve efficient spectral optimization. In
general, the spectrum efficiency is defined as the useful information (excluding
overhead and control packets) that can be transmitted per second per bandwidth. It is the
optimized use of spectrum or bandwidth so that the maximum amount of data can be
transmitted with the least amount of transmission errors. It is also can be considered as a
measure of how well the spectrum is utilized by the physical layer protocol or even the
media access control.
The spectral efficiency of a digital communication system is expressed in (bit/s)/Hz.
It is the maximum throughput divided by the bandwidth in hertz of a communication
channel or a data link. Consequently, the better maximum throughput and packet
delivery achieved, the higher the spectrum efficiency is.
The overall spectral efficiency of the system in (bit/s)/Hz is calculated using (1) [6]
Overall . spectral . efficiency = Max. Throughput
Bandwidth
= KR
W
(Bits/s/Hz) (1)
Where K is the number of users in the network of in the case of cellular networks, the
number of users in the cell. R is the maximum throughput and W is the bandwidth of the
system.
From the equation we can conclude that’s more users served in the cell of the network,
the better the overall spectral efficiency of the system. Moreover, improving the
maximum throughput also will improve the overall spectral efficiency [6].
4

1.4 Interference problem
Interference occurs between users communicating over air in wireless communications.
It can be between: [6]
Transmitter communicating with common receiver.
Transmitter with multiple receivers.
Different transmitter-receiver pairs.
Future mobile devices (Laptops, Phones, etc) are expected to have multiple radios
interface on them. These radios are subject to interfere since they are located very
closely to each other, and in some case utilizing the same frequency bands. In this
research I tackle different kind of interference, which mainly occur between a
transmitting and receiving antenna of a system equipped with multi-radios that is called
interradio interference [7].
The main goal for spectrum management is to maximize the use of spectrum by
limiting interference to acceptable level. Normally, achievable systems have frequency
response that is not perfectly band limited [8]. As a result, transmitters will have
out-of-band unavoidable emission, and receivers will be vulnerable to these emission.
The International Telecommunication Union (ITU) defined destructive Interference by:
“interference which seriously degrades obstructs or repeatedly interrupts a radio
communication service operating in accordance with the ITU radio regulations” [8].
Recently, with the evolution of wireless technology, the spectrum utilization became
much higher than before; which made the spectrum utilization upper limit also higher.
Interference became a much serious issue that needs to be considered in any wireless
mobile network. There is a big need in the development of spectrum efficient wireless
devices.
1.5 Future Trends
With the beginning of research and development of the beyond 3G mobile
communications (4G), many corporations such as NTT DoCoMo, Motorola, Siemens,
etc. began developing 4G systems. The spectrum allocation for the 4G system is
specified in 2007. According to ITU, 4G standardization will finish in 2011. it is
expected that the Local Wireless access sub-system of the 4G system to achieve data
rate up to 1Gbps with bandwidth requirement of single user around 100MHz.
It is estimated that spectrum efficiency of mobile communications and wireless
networks will increase about 10 times in 10 years, from the current 0.5-2.5 bit/Hz to
5

5-20 bit/Hz in 2015. With this trend, it seams that the spectrum efficiency will not be
enough with the increasing requirements of mobile communications service [9]
1.6 Purpose of the Research
The aim of this research is to propose a high performance indoor wireless multi-hop
network by solving some of the problems that affect such networks in an indoor
environment. High performance is usually achieved by improving throughput and
packet delivery rate, reducing packet dropped, improve connectivity in different
mobility conditions, reducing end-to-end delay and minimizing interference in a
multi-hop multi-radio wireless networks.
Up
Figure 1.5: Proposed indoor multi-hop network
Figure 1.5 illustrates the goal to be achieved by proposing solutions to the multi-hop
challenges. Generally, indoor environments are divided into the (end-user) access
network and the backbone network. End-user station mobility has a great effect on the
Packet Delivery Rate and throughput. However, to accurately measure the impact of
mobility on performance, a unique mobility model is proposed to duplicate a human
mobility behavior. An example of this model is presented in Fig 1.5 with the red arrows.
My aim is to propose a packet delivery enhancement through route life time parameter
tuning.
6

On the other hand, the backbone network is represented by the dotted purple arrows in
Fig 1.5. My research focuses on wireless backbone instead of the conventional wired
network. The aim is to investigate on how to achieve a low delay/high throughput
wireless multi-hop. Using a multi-radio wireless access points, investigated the
interference effect on throughput in a short rage wireless network and a long corridor
environment as shown in Fig 1.5. Moreover, I proposed an interference canceller for
such kind of interference and tested it in different actual indoor environments.
To summarize this research, it deals with some of the issues which hinder the ability of
multi-hop wireless network to achieve the desired performance. The aim is to maximize
the spectral efficiency of the multi-hop wireless network by proposing solution on some
of the common problems that faces the multi-hop wireless network such as, mobility
and interference.
The research is organized into two main divisions as shown in Fig 1.6. User mobility
has a huge impact on the throughput. The mobility model used also has impact on the
simulated results. I proposed a different mobility model than the conventional random
way point model. The choice of routing protocol also has an impact on the performance
(throughput). My focus is on the route state hold time parameter in AODV routing
protocol to achieve packet delivery rate improvement.
Multi-hop
wireless
networks
Mobility
Interference
Figure 1.6: Thesis organization
Due to the fact that more devices recently are equipped with multiple radio interfaces,
the interference problem became much more severe than before. The focus is on the
inter-channel interference between multiple antennas on the same device in WMN.
All the simulated results and the conducted experiments are indoor environment. For
7

the mobility case, the Mobile Ad-hoc network (MANET) was the clear choice because it
is a mobility centric multi-hop wireless network. Different mobility models can be
implemented in MANET due to the availability of wide range of routing protocols
suitable for mobility cases.
In case of the interference, I focused on the interference between radios in multi-radio
devices. These devices became very popular recently in Wireless Mesh Networks
(WMNs) due to its advantages in offering enhanced performance.
1.7 Thesis overview
This thesis is organized in 6 chapters as follows:
Chapter 2: This chapter gives an overview of the route discovery process in Ad-hoc on
Demand Routing Protocol and importance of ART parameter in MANET. The chapter
also presents the background of the Ad-hoc routing protocols and a comparison between
two Ad-hoc routing protocols.
Chapter 3: This chapter presents the Simulated MANET model for the proposed Mobile
in OPNET with a description of the simulation parameters and scenarios. In addition, an
explanation about the mobility model utilized in the simulation is discussed in the
chapter along with the analysis of results collected from the simulation.
Chapter 4: This chapter gives an introduction about multi-hop/ multi-radio Wireless
Mesh Networks (WMN). Furthermore, the chapter focuses about the interference
problem in general and WMN interference challenges. Effect of interference was
investigated. A novel interference canceller is proposed and tested experimentally.
Chapter 5: This chapter focuses on the various experimental scenarios conducted about
throughput improvement of wireless mesh networks. The proposed interference
cancellation circuit is implemented in this chapter along with the discussion of the
results collected.
Chapter 6: This chapter concludes the research that’s has been done in this thesis.
Suggestions for future work are also given in this chapter.
8

CHAPTER
2
Mobile Ad-hoc Network
2.1 Introduction
With significant increase in the popularity of wireless networks, more and more
communication engineers showed their interest in implementing mobility in the wireless
networks [2]. Mobile Ad-hoc networks consist of wireless stations which communicate
with each other without a centralized access point or any kind of established
infrastructure. Stations that are within each other’s coverage range can communicate
directly, while others (which are not within each other’s coverage range) depend on
their neighboring stations to route information towards destination. Since the stations
can act as routers or clients, they can easily join or leave the network freely. The self
configuring advantage of Mobile Ad-hoc networks resulted in a highly dynamic
network environments [10]. Such networks can be utilized in various fields such as,
emergency cases like natural disaster (earthquakes, typhoons, tsunami, etc.), battlefields
and emergency medical situations [11]. Other application includes the Wireless
Community Networks to provide broadband Internet access to communities that
previously didn’t have such access due to terrain or cost restrictions [12].
Figure 2.1: Data forwarding to unknown destination
9

Routing protocols were developed to overcome limitations of the Ad-hoc mobile
networks (MANET) such as high error rates, low throughputs and high power
consumption [2], [2]. It’s a difficult task to maintain a route path for a long time in
MANET due to limited resources (bandwidth, battery, etc), limited security and
multi-hop nature. These limitations create a lot of constraints on the routing protocols
[11], [4]. Moreover, Ad-hoc networks have lower capacity compared to WLANs
although they utilize the same radio technology, channel reservation and data link
protocols. Fig 2.1 illustrates the information exchange between neighboring stations in
order to discover the best route between the source and destination. The yellow area
represents the field in which the station can communicate with others. The black lines
represent the request from the source stations to send data, and the blues lines indicate
the reply for request from the destination.
2.2 Ad-hoc On Demand Distance Vector (AODV)
The control information sent by stations in ad-hoc networks limits the capacity of the
network. These control information are required to maintain the routing information
while allowing mobility to the stations in the network. Each node in the network is
required to locate a route to the destination and announce this routing information to the
neighboring stations. One of the challenges in large networks is the congestion due to
the large amount of control massages which consume a major part of the available
bandwidth [14]. Routing protocols are categorized as reactive or proactive protocols.
Proactive routing protocol such as Optimized Link State Routing Protocol (OLSR)
maintains reliable routing information in the network by updating the topological
information of the network continually. This is done through announcing (broadcasting)
any changes in the route information to other nodes. This information is stored in the
routing tables within the mobile nodes. On the other hand, the reactive routing protocol
such as Ad-hoc On Demand Distance Vector (AODV) differs in that it defines the most
suitable route from source to destination only when required. In this case, the route
discovery is initiated when need by the source node. Once the route is established, it
will be maintained by the route maintenance procedure until the route is no longer
desired or the destination is no longer accessible from all routes[2][14].
10

Route Request
AODV
Intermediate
node 2
Intermediate
node 1
Route Reply
Destination
Source
Data
OLSR
Intermediate
node 2
Intermediate
node 1
Destination
Source
Data
Figure 2.2: AODV vs. OLSR
Figure 2.2 illustrates the difference between AODV and OLSR`s route discovery
methods. AODV, the source has no information about the destination and will start by
sending the Route request to every neighbor to ask about the destination. If located, the
destination will answer with a route reply, and finally the data (represented by the blue
lines) will be sent to the destination. Because OLSR stations have information about all
station on the network prior to sending data (represented by the red dotted lines), the
OLSR stations can send data directly once they are available. This might seam as an
advantage for OLSR, however, since stations are moving in MANET, it is a difficult
task to collect the routing information for all stations in the network.
Table 2.1 compares between the two routing protocols AODV and OLSR. The two
routing protocols are characterized with many parameters which define how the
protocol will perform in different situation.
11

Table 2.1: Comparison between AODV and OLSR
Features AODV OLSR
Protocol type Reactive Proactive
Route discovery
Link-state
Distance –victor
routing
routing
algorithm
Reliability low high
Complexity low high
Scalability High low
Latency High low
Network size limit Up to 1000 station
Can handle more
then 1000
Band width required Low High
Mobility High low
My focus is on the parameters which have an impact on the route discovery and route
states hold times. For example in AODV, we consider the ART which was a static
parameter that defines how long a route is kept in the routing table after the last
transmission of packet on this route. As a comparison, in OLSR, the route state hold
time is characterized by Hello-Interval and Neighbor Hold-Time [15]. The Hallo
packets are necessary to maintain the relation between nodes. They can carry 1-hop
neighbor and 2-hop neighbor information. Neighbor Hold Time parameter specifies the
expiry time for the link between the nodes. This is similar to ART in AODV. A longer
hello-interval is generally preferable in congested networks. That is because stations in
congested networks tend to be less mobile will small changes in topology. If the
hello-interval changed, the hold-time must also be modified. A rule of thumb is to keep
the hold-time at three times the hello-interval. There is no need for the hello-interval
and the hold-time to be the same for all routers in the network. Each router will
advertise it own hold-time and it will be stored into the neighbor’s routing table [16].
2.3 Route Discovery in AODV routing protocol
All active stations in AODV routing protocol broadcast Hello messages to detect links
to any neighboring nodes. These Hello messages also used to detect link break, that’s
when the node fails to receives any hello messages from a specific neighbor. Prior to
sending data to any unknown destination, stations have to go through the process of
route discovery indicated in Fig2.3. Initially, the source station broadcasts a Route
12

Request (RREQ) [4] in order to identify the best route to the destination. When an
intermediate node receives the RREQ, it will create the route to the source. If this
intermediate node is the destination or has a route to the destination, it will generate a
Route Reply (RREP). The source station will record the route after it receives the RREP.
If multiple RREP are received by the source station, the path with the least amount of
hops will be chosen [17]. As the data flow from the source to the destination, the
intermediate nodes will update their timer which is associated with maintaining the
route. For the case of AODV, the routing table holds information about the destination
address, next hop address, number of hops for the route, destination sequence number,
and active neighbors for this route and the expiration time for this route table entry.
Expiration time is reset after successful utilization of the route. The new time is found
using the relation:
New Expiration time = Current time + Active route Timeout (2)
2.4 Multi-hop wireless network
Figure 2.3: Route discovery process
Multi-hop networks suffer from long transmission delays and frequent link breakages if
conventional routing protocols such as AODV are used [18]. Generally, throughput
degrades quickly as the number of hops increase. One of the reason for that is because
the Ad-hoc networks utilizes only a small portion of the spectrum because only single
13

adio is used for transmitting and receiving. And since the 802.11 MAC is naturally
unpredictable because of the collision avoidance, radio cannot be used for two
operations at the same time. This may stall the flow of the packets over multi-hop
wireless networks [12].
As the data flow from the source to the destination, the intermediate nodes will
update their timers associated with maintaining the route. For the case of AODV, the
routing table holds the current information:
- Destination.
- Next hop.
- Number of hops.
- Destination sequence number.
- Active neighbors for this route.
- Expiration time for this route table entry.
Expiration time is reset each time the route has been utilized using Eq. (2).
2.5 Active Route Timeout and Mobility
The Ad hoc On-Demand Distance Vector Routing Protocol (AODV) is a routing
protocol which is intended to be used in high mobile Ad-hoc networks. AODV is a
reactive protocol where the route discovery process is initiated only when it is needed.
MANET routing protocol plays an important role in the performance of the network. A
wide range of parameters controls the behavior of the routing protocol. One particular
parameter in AODV is the Route states hold time.
When the route is not used for some time, the nodes remove the route from its routing
table. The time until the nodes remove the route states is called the Active Route
Timeout (ART). In other words, ART is the time after the route is considered invalid.
In an Ad-hoc mobile network, the station movement speed is very crucial. The speed
has an effect on the throughput. Fig 2.4 is an example on how the mobility has an effect
on the connectivity between the stations. In a normal case, node C will have to
communicate with node A through node B. however, since node C is moving closer to A,
it can communicate directly to node A. This example illustrates only one case in which
the station movement could be an advantage in MANET [19].
14

DATA
Motion
Figure 2.4: Higher mobility can improve connectivity
At high speed situations, the mobility could be a disadvantage. At high speed
situations, there is a high probability for sudden change in topology especially if not all
the stations move at the same speed. Depending on which routing protocol is used for
the network, some routing protocol may perform better then others. For example, in
theory AODV (reactive routing protocol) should perform better the OLSR (Proactive
routing protocol) in a high mobility network. In such networks it is advised to have a
routing protocol which adapt to this kind of mobility each time there is a request to send
data.
Important parameter in the AODV is the ART. As the speed of the stations increases,
the throughput will decrease with higher values of ART. Low values of ART are needed
to keep the throughput high. Basically, the routing table in AODV routing protocol is
the memory which stores the location of the neighboring stations. And since the stations
are moving and their locations are changing, this memory has to be refreshed with the
new locations every some time. This time is called the ART in the AODV routing
protocol.
2.6 User density and capacity
The number of stations within the network is an important factor which affects the
throughput. The more the stations exist within the same area in a mobile Ad-hoc
network, the higher the probability of interconnections between stations in the network.
15

The example in Fig 2.5 shows that for route 2 from node A to node C, there is no need
to establish a connection between nodes F and C which is already established from
route 1[19]. That’s resulted because many stations exist in same area which make the
probability of established connections between stations is very high.
Figure 2.5: Increased number of stations improves route discovery time
The increased number of stations could also result in a negative effect as a result of
Route request (RREQ) flood from the nodes which congest the network.
2.7 Chapter Summary
This chapter denotes the importance of route state hold time information in the routing
protocol which is called ART in AODV routing protocol. In MANET networks,
Mobility and user density are important factor which have an effect on PDR. Our focus
is to demonstrate the effect of ART parameter on improving the PDR on different
mobility and user density values. This is investigated in the next chapter through
different simulation scenarios.
16

CHAPTER
3
Packet Delivery Rate (PDR) Improvement for
Mobile Ad-hoc Network (MANET)
3.1 Introduction
The importance of Route State Hold-time parameter such as ART in AODV is often not
realized due to sheer amount of factors involved in the route discovery process. This
chapter presents a series of simulations scenarios to emphasize the importance of such
parameters not only in mobile Ad-hoc, but also in non-mobile networks.
3.2 Previous Simulation model
This simulation is based on the previous work done by the Disaster Management and
Mitigation Group in the National Institute of Information and Communications
Technology (NICT) and JOHOKOBO,Inc. in OPNET modeler 11.0 is used for
simulating the Ad-hoc mobile network [20]. The previous work simulated a disaster
stricken area of 500x500 meters as shown in Fig 3.1. The work focused on the
multimedia information gathering at disaster and movement behavior in an emergency
case. The map in Fig 3.1 represents the simulated map area of a floor in a campus or
huge building like a shopping mall (which consists of rooms and corridors). The black,
blue and red lines in the map represent different kind of corridors which the stations can
move through. The yellow sections represent rooms, offices and storage areas. Two
routing protocols were utilized in the simulated map area, AODV and OLSR. These
routing protocols are built-in functions in OPNET modeler 11.0. The behavior of these
routing protocols can be control through different specific parameter for each routing
protocol.
17

Figure 3.1: Simulated Area Map
The previous work focused on these scenarios:
- Simulating up to 50 station movements in the map.
- Comparison of the new mobility model with the random way point model.
- Comparison between the AODV and OLSR routing protocol throughput.
- The effect of changing the station speed movement.
- Comparison between variable bit rate encoding and constant bit rate encoding.
Table 3.1 shows different parameters in the simulation for the routing protocols,
encoding types and protocols used
18

Table 3.1: Simulation Parameters
Parameter
Value
Simulated time
900 seconds
WLAN protocol 802.11g
Bit rate
11 Mbps
Station transmission power
0.05 mW
Encoding type 1
Constant Bit Rate (CBR)
Packet Inter-Arrival time
0.25 seconds
Packet size
64 byte (512 bits)
Encoding type 2
Variable Bit Rate (VBR)
Packet Inter-Arrival time
Packet size
1 second
17280byte
Routing Protocol Parameters
Active Route Timeout
Hello Interval
Neighbor Hold Time
Topology Hold Time
3sec (Default)
2 seconds
6 seconds
15 seconds
In order to describe the movement behavior of mobile users especially in indoor
environment, mobility models are used for simulation and evaluation purposes. The
mobility model indicates the change in location, velocity and acceleration over time for
the mobile users.
Both AODV and OLSR showed similar behavior for the mobility model. In my work,
I didn’t consider the random way model nor did I simulate the new proposed model,
instead I assigned the movement path for each station with the desired speed in the
network prior to simulation. My main focus was the station speed movement while
moving through the corridor of the building. In addition, I only focused on AODV in
this work due to its better overall performance in mobility and from the results from the
pervious work as shown in Fig 3.2.
19

Figure 3.2: AODV vs. OLSR
Another difference between my work and the pervious one is the metric used for
evolution. Instead of using throughput for performance assessment, PDR was used as a
metric for ART evaluation against mobility speed, number of stations and number of
hops. OPNET defines throughput as the “total number of bits (in Mbits/sec) forwarded
from wireless LAN layers to higher layers in all WLAN nodes of the network”.
However, this doesn’t count the dropped packets in case of collision. For that reason we
measured PDR for every scenario in the performed simulations.
3.3 Comparison with other Related Researches
A performance comparison between two On-Demand routing protocols Ad hoc
on-demand Distance Vector (AODV) and Dynamic Source Routing (DSR) was
simulated in Ref [2] for 15 stations. In comparison, my research simulates the Packet
Delivery Rate (PDR) improvement for AODV routing protocol (AODV achieve better
results in [2] compared to DSR) using Active Route Timeout (ART) for 50, 60 and 70
stations.
Reference [14] studies the impact of mobility and user density on the performance of
routing protocol for the purpose of designing a new routing protocol. I draw similarity
in the simulation of mobility and user density effect on the performance of routing
protocol. However, this research proposed a solution to the mobility problem in terms of
20

oute stat hold time parameter in the routing protocol.
Random waypoint model is one of the popular models used in many mobile
communication simulations due to its simplicity. In random waypoint model as shown
in Fig 3.3, speed and direction are all chosen randomly from a fixed set. This could lead
to rapid change in direction and speed which does not represent accurately the actual
human movement within a building. Therefore, indoor environments (such as buildings)
contain corridors and pre defined pathways. The movement usually consists of straight
line paths with equally probability of turning into all directions at any turning point.
Figure 3.3: Random Waypoint Mobility Model
The Authors in Ref [10] showed a comparison between three different mobility
models, Random Waypoint, Random Walk with reflection and Random Walk with
wrapping. While the Random Waypoint model produced the highest throughput, my
research aimed to propose a variation to mobility model that is a variation to the
Random Waypoint model suitable for indoor environment simulation. In the new
proposed model, the MANET stations moves along a corridors of a building. Both the
random waypoint model and the newly proposed model are illustrated in Fig 3.4 and Fig
3.5 respectively.
21

Figure 3.4: Random Waypoint Mobility Model
Figure 3.5: Proposed Mobility Model
One of the highlights of my previous work was a comparison between a new
proposed indoor mobility model (which represents a realistic human movement inside a
building) and the conventional Random Way Point model at different speed values as
shown in Fig 3.6. The Random Way Point model achieved a better result for different
22

speed values due to the ability of the stations and nodes to move in all direction and not
respecting the walls and corridors represented in the simulated map area. Although this
result was expected since the nodes will not be limited to the corridors presented in the
map, my aim was to simulate a mobility model closer to the human movement pattern.
Figure 3.6: Throughput vs. Speed for random waypoint and the new mobility
model
3.4 Proposed Mobility models
Simulating mobile communication systems requires a mobility model which is intended
to illustrate the movement pattern of mobile stations. The mobility model should have
the ability to determine the change in location, velocity and acceleration over time. The
mobility model is an important part in performance evaluation on Mobile ad-hoc
wireless networks because it represents the moving behavior of each mobile in the
wireless network [10].
One of the most popular mobility models is the Random Waypoint Model. This
model is used for mobility management schemes for mobile communication systems. In
this model, the users move randomly and freely without restrictions. The direction and
speed of movement are chosen randomly and independently from other users and the
environment. This model is considered to be benchmark mobility model and used to
evaluate the Mobile ad hoc network (MANET) routing protocols, because of its
23

simplicity and wide availability. Although this model is very popular in many
simulation studies, its randomness and independence from other users and the
environment, makes it inadequate in representing a real human movement pattern in
indoor environment. Reference [22] also agrees with this fact. Moreover, the authors of
[22] encouraged <strong>study</strong>ing mobility models that characterize human’s real movement
pattern.
The reason I present this model is for comparison purposes to the model proposed in
this research. The aim is to simulate a mobility pattern closer to the movement of a real
human than the conventional random mobility model that is utilized in most
simulations.
Because I focused in my simulation on measuring the speed effect on the PDR, the
movement speed and path is assigned to the station prior to simulation. That’s to
eliminate the need for the station to make decisions about the movement path and focus
of evaluating the effect of speed on PDR. I used three speed values 0m/s, 4m/s and
10m/s for all stations in the network. The fixed case is represented by the 0m/s value.
These speeds represent human movement speed relative to the simulated area map
environment. The 10m/s speed represents the state of emergency case where stations
will move at a much faster velocity.
The reason why I didn’t assign different speed values for each station is because it is
not common for a group people within the same area to move with speed values that
differs greatly. However, for simulation purposes, the case where each station in the
network is moving at different speed value can cause some challenges that will be
difficult to evaluate the overall change in packet delivery rate.
24

Figure 3.7:Coverage area and movement direction
Figure 3.7 illustrates and example of the movement model simulated in my work.
Each mobile station will start moving from randomly defined point and move through
the corridors indicated in the map until it reaches a random destination. The station will
move within the corridors of the map while turning in different randomly predefined
directions without crossing the wall of the building. Each station will communicate with
a specific station the map area while moving. The destination address for each station is
illustrated in Table A.1 in the appendix.
To achieve a coverage radius of 100 m for each station for a free space propagation
model, equation (3) was utilized.
4 2
πD
⎤ − 12.5
⎡
P =
⎢
⎣0.12476⎥
⎦
× 10
(3)
Where P is the transmission power in Watt and D is the coverage distance in meter.
25

3.5 Packet Delivery Rate (PDR)
The PDR is the usual metric used to indicate the performance of Ad-hoc mobile
networks protocol [23]. The PDR is the ratio between the total number of messages
send out and the number of messages that were successfully delivered to their
destination [14]. The relation between the total messages sent to the messages delivered
is indicated in Eq. (4).
Total ⋅ messages ⋅ sent
PDR = (4)
Total ⋅ messages⋅
delivered
The highest possible value of PDR is 1; which indicates the best performance since all
the sent messages are successfully delivered.
3.6 Simulation setting and parameters
Figure 3.8 illustrates the simulated map with the mobile stations. Each station will move
through a predefined path. 50, 60 or 70 mobile stations are moving in the simulated area.
The main focus in this research is the communication between two stations which
represents the disaster stricken point and the headquarters (which are represented by the
two blue nodes in Fig 3.8).
26

Figure 3.8: Simulated Ad-hoc mobile network
The default OPNET values of the route state hold time parameters ART is 3 seconds.
Table 3.2 summarizes the parameters used in the simulation for the stations in the
network.
27

Table 3.2: Simulation Parameters
Parameter
Value
Active Route Timeout
3 sec (Default)
Simulated time
900 seconds
WLAN protocol 802.11g
Bit rate
11 Mbps
Station coverage distance
100 meter
Station transmission power
0.05 mW
Station movement speed 0m/s, 4m/s, 10m/s
Encoding type
Constant Bit Rate (CBR)
Packet Inter-Arrival time
0.25 seconds
Packet size
64 byte (512 bits)
Traffic generation start time
[0,10] with uniform distribution
The Active Route Timeout is set to 3 seconds in the default case. The station
transmission power was set to 0.05mW to achieve a 100m coverage distance for each
station. The simple Constant Bit Rate (CBR) encoding type was utilized with packet
size of 64 byte and Packet Inter-Arrival time of 0.25 seconds.
3.7 Convergence time
Convergence time is the minimum simulation time of the model so that the reference
values achieved with fixed set of parameters such as throughput, delay and packet
delivery rate, do not oscillate significantly in sequential runs. In other words, it’s the
minimum simulation time to achieve the expected value of the distribution. To achieve a
reliable result, it’s important to define a convergence time for the simulation. Some
parameter’s effect cannot be observed with a simulation time less then the convergence
time [14]. Figure 3.9 indicates an example for the convergence time for the simulated
model under the condition described in the section 3.6 Figure 3.9 shows the traffic sent
by a station do not oscillate significantly around 2,000 bits/sec after 4 simulated minutes
which is the convergence time for our simulations.
28

Figure 3.9: Example of Convergence time in the simulation
3.8 Simulation scenarios and results
Figure 3.10 illustrates a diagram of the scope of this chapter. Two ad-hoc network
arrangements are simulated in my research. The first setup was implemented to evaluate
the effect of ART value, station’s speed and number of stations in a mobile ad-hoc
network. The second arrangement evaluates the effect of number of hops on PDR and
on the end-to-end delay in a wireless multi-hop Ad-hoc network. The main difference
from the first arrangement is that the stations fixed. The results from these simulations
are important for proposing solution to the throughput degradation problem in Ad-hoc
mobile networks.
29

Simulation
Mobile Ad-hoc
Network, Using the
500x500 Map
Fixed 5 hops Adhoc
Network
First Scenario
ART vs. PDR
Second Scenario
Speed vs. PDR
Third Scenario
Number of hops
vs. delay
Forth Scenario
Number of hops
vs. PDR
Figure 3.10: Simulation scenarios
3.8.1 First Scenario
In this scenario, the ART parameter was changed from 0 to 5 seconds for different
movement speeds in a 50 nodes network.
Figure 3.11: Active Route timeout vs. PDR
Figure 3.11 shows that for low values of ART, the PDR will have higher values when
moving. At ART 0 sec, the nodes will not keep the route states after it has been used,
which will cause the node to repeat the route discovery process after each use of the
30

oute. This caused the 10m/s speed to have a slightly higher PDR. Fig 3.11 also shows
that at 0m/s speed, the throughput was higher than other speeds and nearly unchanged
for ART value greater than 0.2 seconds. This result was expected since the stations are
stationary and changing the ART value will not affect the PDR. At higher speeds of
4m/s and 10m/s, the values of PDR decreased with the increase of ART. This results
from the continuous change in the position of the nodes which makes it difficult to
establish connection between the stations.
In general, the figure shows that we could achieve a higher PDR values for lower
values of ART than the default OPNET value 3 sec. It is also noticeable that ART value
of 0.25 sec gave the highest PDR value at the simulated conditions of 11Mbps, 802.11g,
Constant Bit Rate encoding and the proposed mobility model. Due to these results, ART
value of 0.25 sec was chosen to be the optimum value under these conditions.
From the ART simulation in [14], it was proven that the ART value has a negligible
effect on the throughput of the Ad-hoc network in case of 0m/s (stationary) which is
consistent with our results in Fig 3.11.
Reference [23] focused on the effect of the ART values on route error (RERR). It was
found that the network had less total RERRs at the low values of ART (0.2s- 1.6s) as
shown in Fig. 3.12. This result agrees with our simulation which achieves the best PDR
values in the same region. Although, the mobility model in [23] is the Random
Waypoint Model with high mobility values (up to 20m/s).
Figure 3.12: Number of RERR/second as a function of the ART, for each
RERR[23]
31

Generally, finding an optimal ART value is very challenging due to the fact that the
ART value for a network is a function of node mobility and depends on many of the
network characteristics such as, mobility model and traffic generation patterns. However,
the pattern at which the ART value changes with mobility and speed do not change in
the same conditions of a selected routing protocol and the encoding type.
3.8.2 Second Scenario
In this scenario, the PDR is compared against the station speed for different number of
stations at the default value of ART (3sec). The number of station was increased to 60
stations then to 70 stations for the same network size. Figure 3.13 shows the result
obtained from this scenario’s simulation.
Figure 3.13: Speed vs PDR for 50, 60 and 70 stations at default value of ART (3sec)
For the default value of ART, the PDR value dropped sharply with the increase in
movement speed. This was expected since the stations will react slowly to the rapid
change in the topology which is represented by the 4m/s and 10m/s speeds. Moreover,
there was no obvious difference in the performance between the different numbers of
user. From reference [14], it was proven that the number of users has a significant
impact on the performance of AODV especially on the PDR. However, the PDR
increases very rapidly with the increase of number of users until 45 stations as shown in
Fig 3.14.
32

Figure 3.14: Number of users vs. Message Delivery Rate (Adopted from reference
[14])
With further increment in number of users, no change was observed which explains
why there was no difference in PDR with the increase in number of users in our
simulation results in Fig 3.13.
The same conditions were simulated with the ART value of 0.25 sec instead of the
default values as shown in Fig 3.15. The PDR values exhibit a significant improvement
at 4m/s and 10m/s speeds. In general, the PDR values were between 1 and 0.8 for all
number of stations which is considered to be high. The result was as expected because
with smaller ART values, the network will be capable of adapting to the topology
change as a result of station movement. Again, the increased number of station did not
impact the PDR values as explained in the pervious case.
33

Figure 3.15: Speed vs PDR for 50, 60 and 70 at 0.25 sec ART
3.8.3 Third scenario
This simulation focuses on the relation between the number of hops against PDR and
the end-to-end delay in a stationary wireless multi-hop Ad-hoc network. The network is
composed of 6 stations arranged in a way to achieve maximum of 5 hops as shown in
Fig 3.16. The number of hops will be changed after each simulation (5,4,3,2,1) while
measuring the delay and packet delivery rate. The parameters used in this simulation are
summarized in Table 3.3. The station transmission power was changed to 0.00128mW
due to the change in the simulated area. The distance between stations was fixed at 20m.
In this simulation, the area map was not utilized because the stations are not mobile in
this scenario.
Table 3.3: Second model Simulation parameters
Parameter
Value
Active Route Timeout 3 sec (Defualt), 0.25 sec
Simulated time
900 seconds
WLAN protocol 802.11g
Bit rate
11 Mbps
Station coverage distance
20 meter
Station transmission power
0.00128 mW
Station movement speed
0m/s(stationary)
Encoding type
Constant Bit Rate (CBR)
Packet Inter-Arrival time
0.25 seconds
Packet size
64 byte (512 bits)
Traffic generation start time [0,10] with uniform distribution
34

Figure 3.16: Simulated Ad-hoc mobile network
The aim is to measure the effect of number of hops on the end-to-end delay in the
wireless ad-hoc network. Two values of ART (0.25 sec and 3 sec) were used in the
simulation.
Figure 3.17: Number of hops vs. Delay
35

From Fig 3.17, it is shown that as the number of hops increase, the delay will also
increase. The end-to-end delay was expected to increase with the decrease in ART value.
However, the end-to-end delay experienced a decrease at the 0.25sec. This could be due
to the specific parameters utilized in this scenario. End-to-end delay is very important in
time sensitive applications such as voice communications. It is also noted that ART
values affects PDR values in a mobile station and also affects the end-to-end delay in
non mobile station. The importance of ART parameters is evident from the previous
simulation results.
3.8.4 Forth scenario
For the second scenario, the PDR is measured against the number of hops. The
arrangement is basically the same as the previous scenario with the same parameters
from Table 3.3.
Figure 3.18: Number of hops vs. PDR
Figure 3.18 indicates that with the increase in number of hopes, the PDR is slightly
decreased. We can also conclude that for stationary stations, it is advised to use high
values of ART to achieve a better performance then the lower values of ART. With low
values of ART, the stations have to rediscover the route frequently in a given time which
causes a delay that has a small but obvious effect on PDR.
36

3.9 Chapter summary
Four simulation scenarios are presented in this chapter. The first two scenarios, utilize
the area map developed from the pervious research at the NICT and focusing on
mobility. My proposal for PDR enhancement with ART value of 0.25sec (at the
simulated conditions of 11Mbps, 802.11g, Constant Bit Rate encoding and the proposed
mobility model) has indeed achieved the highest PDR (0.9) compared to other values (1,
3 and 5sec) from Fig 3.11. Figure 3.17 illustrated also the effect of ART in network with
stationary stations. Naturally, the end-to-end delay increases with the increase in the
number of hops in multi-hop network. However, using low ART (at 0.25sec) values
resulted in a decrease in the end-to-end delay (eg. At forth hop, 0.75sec to 0.4sec). This
is resulted from the fact that when a link break occurs, it do not take a long time to
rediscover and reestablish connections to neighbor stations as a result of low value of
ART (at 0.25sec) compared to the default value of 3sec. Consequently, it helped
reducing the end-to-end delay significantly.
37

CHAPTER
4
Interference Cancellation for Wireless Mesh
Network (WMN) Nodes
4.1 Introduction
Wireless multi-hop networks such as MANET and WMN are in high demand to support
the increasing need for multimedia communications [24]. WMN is an attractive
alternate solution for providing internet access to places with difficult terrain while
maintaining low cost and scalability. The term “Wireless Community Networks” is used
to describe this kind of wireless mesh networks that aims to deliver wireless
communications over large and complex areas where running cables is not cost effective
due to terrain limitations [25]. Other advantages of WMNs are the ability to
self-organize, auto-configure and self-healing [26], [27].
Current 802.11 system operates in the 2.4GHz band which is very much populated
with a wide range of devices (cordless phones, microwaves oven, Bluetooth, ZigBee,
etc). These devises could interfere with one another. In general, fading and
interference are two fundamentals aspects of wireless communications that are present
in wired communications. These two aspects what makes wireless communication both
challenging and interesting. Dealing with fading and interference is vital in designing
wireless communication. As for IEEE 802.11 WMN, since the 2.4GHz ISM band is
unlicensed, throughput of wireless network is greatly affected by the interference from
nearby devices which utilize this free band. For example, many Bluetooth Pico nets in
one area can significantly decrease IEEE 802.11 network throughput [25].
Moreover, wireless networks performance is affected by the number of users and the
distance from access point due to the shared bandwidth. The probability of channel
interference increases with the number of users and the number of access points which
access the available bandwidth at the same time. Any slight interference at the receiver
antenna could result in a noticeable effect on throughput. Some types of tolerable
interference can be removed by simple procedure. Others are more challenging and
require additional procedures to eliminate or reduce interference effect [28]. Thus,
38

suppressing channel interference is expected to play an important role in improving the
throughput of network. Managing network resources such as, energy, bandwidth,
transceiver and storage is vital to any network wireless design. One of the energy saving
method is to equip the node with an additional low-power transceiver. This low power,
low-data rate transceiver is used to send management and control packets. Moreover,
load balancing between multiple transceivers in multi-radio system could help
preventing a channel getting heavily congested and therefore becoming a bottleneck.
Bandwidth aggregation of multiple radios to achieve a higher effective data rate is also
an effective and efficient resource management model. [7]
4.2 Exposed Terminal phenomenon
Single radio (transceiver) WMN is a half-duplex system where no node can transmit
and receive simultaneously. The single radio system causes high throughput unfairness
in WMN. The exposed node also is one of the main contributions to throughput
degradation in single radio transceiver WMN system [29].
The exposed node phenomenon takes place when a node is not permitted to send
packets due to an ongoing communication between other nodes. The example in Figure
4.1 illustrates the exposed terminal problem where transmitter 1 is communicating with
receiver 1 while transmitter 2 wants to send packets to receiver 2. Since receiver 1 and
receiver 2 are out of range of each other, transmission 1 and transmission 2 can occur at
the same time without interference. On the other hand, transmitter 2 maybe rejected by
transmission 1 and halt communication 2 to receiver 2. That is because transmitter 2
concludes after carrier sense that it will interfere with the transmission 1.
Figure 4.1: The exposed node problem
39

This situation could be resolved with IEEE 802.11 Request To Send/ Clear To Send
(RTS/CTS) if the nodes are synchronized with similar packet size and data rates for all
nodes. Recently, the advancement of WMN using multiple radio interfaces have
improved significantly due to the fact of availability of inexpensive off-the-shelf IEEE
802.11 based wireless interfaces [7].
4.3 Multi-radio Wireless Mesh Network (WMN)
IEEE 802.11 MAC layer protocol utilizes CSMA/CA mechanism for medium access.
This mechanism is based on medium sharing and designed mainly for single hop
transmission [27].WMN suffers from limitations in the available bandwidth and
unpredicted delays. The reason for that is partly due to the number of radios utilized
when forwarding packets. Generally, WMN stations receives and forwards packets
using the same physical radio, a (per hop delay) is introduced as a result of utilizing the
same channel for successive hops. However, with the rapid decrease in the radio
manufacturing cost, it became more feasible to equip multiple radios on the same WMN
station. The performance is expected to double with each added radio. That is because
the introduction of a second radio enabled the node to transmit and receive
simultaneously [12]. Access points equipped with multiple radios operating in the same
frequency band (e.g. 2.4GHz) can scan multiple channels simultaneously. As a result,
utilizing two radios on a WMN station is expected to improve the performance with
factor of 2. This improvement is facilitated by efficient spectrum utilization, improved
connectivity and increased coverage area [30]. Fig 4.2 shows an example of Multi-radio
WMN. The multi-radio WMN can consist of stations which are stationary or mobile
[31].
Figure 4.2: Multi-radio Wireless Mesh Network
40

The two radios provide the ability for interchanging between multiple non interfering
channels and in some case even between different frequency bands (2.4GHz with
802.11b/g and 5GHz with 802.11a). This allows simultaneous communications with
multiple neighboring stations while reducing the channel interference. The throughput
also is expected to be higher in the multi-radio network.
In general, the single radio interface system has a lot of waste resources due to the
exposed terminal problem. Nevertheless, multi-radio interface also have its share of
disadvantages such as the adjacent radio interference, dynamic management of
spectrum resources and efficient management of multiple radios [7].
4.4 IEEE 802.11 non-overlapping channels
The IEEE 802.11 MAC protocol was adopted as the medium access control of choice
for the wireless mesh networks. IEEE 802.11 standard for the 2.4GHz frequency band
define three non-overlapping (non-interfering) [32] channels as shown in Fig 4.3. These
non-overlapping channels can operate simultaneously with minimal interfering. What it
means is that these three channels can co-exist within the same coverage area without
interfering with each other. Fig 4.3 shows that channel 1, 6, and 11 logically do not
interfere with each other. Nevertheless, the Inter-channel interference (Adjacent
Channel Interference (ACI)) cannot be completely eliminated even if the nodes use
chipsets that satisfy the transmission mask requirements set by IEEE802.11 standard
[30]. This channel interference was confirmed in field experiments of reference [33].
Thus, even for multi-radio devices, where the node’s own transmission and reception
radios utilize different channels, ACI still exists.
Figure 4.3: IEEE 802.11 Non-overlapping channels (adopted from [34])
41

This unavoidable interference is indicated in the upcoming experimental results. The
throughput or system capacity is affected by this channel interference.
4.5 Interference suppression
It is a challenging task to achieve a robust performance when dealing with transmitter
(high-power) in close proximity to receivers. The strong field from transmitters does not
allow the receiver to operate efficiently. A specialized filter could help the transmitter to
perform better when placed close to the receiver. However, such a case is applicable
only to widely separated frequency channels. A proper cancellation technique is
required to eliminate or reduce interference at the receiver which is useful for effective
frequency reuse [35].
4.5.1 Interference in multi-radio equipment
Devices equipped with multiple radios are subject to interference between these radios.
The access point in Fig 4.4 illustrates an example of multi-hop/ multi-radio WMN
where the access point will receive data with one radio and forward it through the
second radio. Since both radios can transmit and receive, both will have similar effect
on another. The out-of-band unavoidable emission from the transmitter (purple line) will
interfere with the vulnerable receiver (blue line). The interference is presented with the
back dotted line. Interradio interference is due to the design of the hardware components
and the interface itself. Usually, the use of number of low-cost filters and associated RF
components also magnify the interradio interference [12].
42

Figure 4.4: Interference in Multi-radio AP
4.6 Related interference suppression researches
In Wireless Mesh Network (WMN) field, many interference cancellation methods have
been proposed such as in [22], which proposed a redesign for the MAC layer. Other
point is that most researches focus on the interference from an outside source rather than
the interference within the network it self on a single device level which is the main
focus in my research. Moreover, my work focuses on actual implementation of the
interference technique with consideration to real world effects.
One of the most common methods to reduce interference in multi-radio interface
devices is to increase the separation between interface radios. A solution proposed in
reference [7] to mitigate the problem is to modify the mechanical design of the node to
provide enough separation between antennas or the network interface cards. A challenge
is present when the separation is increased in small devices such as access points.
Moreover, when utilizing low-cost components, the between radios separation do not
affect or improve the interradio interference. In this research, I maintained the original
separation distance between the antennas throughout the experiments.
43

4.7 Proposed interference cancellation circuit
To reduce interference between the two antennas of an access point, we proposed an
interference cancellation circuit shown in Fig 4.5. This circuit is located between the
access point’s transmission and reception radios. The circuit consists of two 3dB
couplers, variable attenuator and Coaxial Line Stretchers for phase shifting.
Figure 4.5: Interference cancellation Circuit
4.7.1 Phase cancellation
The idea behind the cancellation technique is to obtain a sample of interference and
subtract it from the receiver signal with proper tuning in amplitude and phase shift. The
interference sample is captured from the transmitter by a coupler (Fig 4.5).
A phase shifter is used to change the phase of the interference sample. Most of the
phase shifters allow signal passing in either direction which makes them reciprocal
devices. Phase shifters permit total phase variation up to 360 degrees. Line stretcher is
one of the phase shifting devices [37]. Figure 4.6 illustrates the concept of phase
shifting and utilizing two separate antennas to achieve the removal of unwanted singles.
44

Figure 4.6: Phase Shift and cancel
The signals (A) and (B) from Fig 4.6 represents the signals from the transmit
antenna and the coupled respectively. Since each signal travel in space from transmitter
in cycles of 360 degrees, shifting one of the singles (signal B in this case) 180 degrees
and superimpose it on top of the other signal will cancel each other [37]. Changing the
relative levels with a variable attenuator and combining them with couplers results in a
reduction of strength of the unwanted signal.
The optimum attenuation depends on the distance between the two antennas and its
calculated using (5):
⎛ 4πL
⎞
Attenuation value=
20 log⎜
⎟ - 4.3dB
⎝ λ ⎠
(5)
Where L is the distance (mm) between the two antennas and λ is the wavelength
(mm).
Each antenna gain is 2.15 dBi (Half-wavelength dipole antenna). The phase shift
including those of phase shifter, attenuator and couplers is calculated using (6) and (7)
[38]:
L
T = (6)
300
θ = 360 T F±(2N-1)180º (7)
Where L is the distance (mm) between the two antennas, T is the Delay Time (ns), F
is the Frequency (GHz) and θ is the phase shift (degree)
45

4.7.2 Scattering Parameters
Scattering parameters or S-parameters mostly used in communications systems to
describe the behavior of the currents and voltages in a transmission line when they meet
discontinuity. The parameters are measured in terms of complex amplitude. Moreover,
many electrical properties of networks or components may be expressed using
S-parameters, such as gain, attenuation and return loss.
To evaluate the effect of the proposed circuit, the scattering parameter S 21 measured
using a network analyzer with two antenna ports as shown in Fig 4.5. Figure 4.7 shows
a comparison in the S 21 parameter before and after applying the interference cancellation
circuit. A drop in the S 21 parameter after applying the cancellation circuit indicates more
than 10dB reduction in channel interference between the two antennas at 100MHz in the
2.4GHz band. Since the two antennas utilize two different channels, the aim is to have
the lowest S 21 value possible at any of the two channels.
Figure 4.7: S 21 Parameter comparison
46

As mentioned before, it was shown in the field experiment in [33] along with our own
experiments that the Adjacent Channel Interference (ACI) exists even if the nodes use
chipsets that satisfy the transmission mask requirements set by IEEE802.11 standard.
This interference caused from the node’s own transmission and reception radios although
they utilize separate channels [33]. The proposed cancellation circuit is applied to
enhance the total throughput in the multi-hop network by reducing interference in the
next chapter.
47

CHAPTER
5
Improvement of the Throughput of Indoor
Multi-hop Network
5.1 Introduction
A series of experiments on WMN are carried out to identify and improve the throughput
degradation in Indoor environments. Indoor Wireless networks experiments can be
relatively challenging due to many factors such as high probability of attenuation,
multipath, fading and noise. Any small changes in the environment can result in big
changes in results collected form the experiments.
The topology type used in this research is the Flat WMN topology. In this topology,
nodes have the same level and can act as both hosts and routers. This topology was
selected due to its simplicity and similarity to the structure of ad-hoc network presented
earlier in the first part of the research. However, this topology is not without limitations
such as, lack of scalability and high resource constraint.
The decision for the type of technology utilized in WMN depends on the available
resources and the purpose (experiment and analysis) of the established WMN. Due to
the wide availability of the off-the-shelf equipment and moderate cost, a homogenous
(same technology for all nodes) type network with IEEE 802.11 technology was
selected.
Due to the fact that the network was experimenting purposes, there was no need to
create an infrastructure at this stage. As a result, a host-based network was selected for
the node type that is similar to Ad-hoc network architecture [7].
Since WMN is relatively static and we used the flat WMN topology, we built a
routing backbone using Wireless Distribution System (WDS). Wireless Distribution
System (WDS) is a method that allows wireless interconnection of access points in an
IEEE 802.11 network. It allows a wireless network to be expanded using multiple
access points without the need for a wired backbone to link them. Connections between
clients are made using MAC addresses rather than by specifying IP assignments [7].
48

Basically, the experiments are categorized into four scenarios:
- Throughput vs Signal to Interference Ratio (SIR) plot for one hop WMN.
- Throughput measurement for different number of hop count in multi-radio
WMN.
- Channel selection vs. throughput
- Throughput measurement for distance varying and hop count in Indoor closed
corridor environment.
- Interference cancellation experiment with the proposed interference canceller
circuit.
5.2 Experiment procedure and equipment
For UDP throughput measurement, Netperf [39] and Qcheck [40] are utilized to capture
the throughput while transferring data from any desired source to destination through the
assigned network and with any number of hops. The equipment utilized through out the
experiment are, IPN-W100AP Trinity Security Systems, Inc access points with dual
radio module 2.4GHz (Fig 5.1) [41]. The specifications for the AP are given in Table
5.1.
Figure 5.1:IPN-W100AP Trinity Security Systems access points
49

Standard
Transmission mode
Radio frequency
Speed
Standard
Transmission mode
Radio frequency
Speed
Security
Antenna
Standard
Networking
Table 5.1: IPN-W120AP Wireless (2.4GHz - 802.11b/g)
Interface RJ-45 ×1
Protocol
Power supply
Power consumption
Current consumption
Dimensions
Weight
Operating environment
Supporting Web browser
Certification
IEEE802.11g/IEEE802.11b, ARIB STD-T66
DS-SS, OFDM, half-duplex communication
IEEE802.11g : 2,412~2,472MHz(13ch)
IEEE802.11b : 2,412~2,484MHz(14ch)
IEEE802.11g: 54Mbps (maximum rate derived from IEEE
specification)
IEEE802.11b: 11Mbps (maximum rate derived from IEEE)
Wireless (5GHz - 802.11a)
IEEE802.11a (W52/W53), ARIB STD-T71
OFDM, half-duplex communication
5,180~5,310MHz (8ch)
54Mbps (maximum rate derived from IEEE specification)
Wireless (common)
IPN-WLAN,WEP (64/128/152bi)
IEEE802.11i,WPA2,WPA,IEEE802.1X/EAP
Inhibit SSID broadcast, MAC address filtering, Surrounding AP
detection
2 (external)
Ethernet
IEEE802.3(10BASE-T/100BASE-TX auto sense) IEEE802.3af
Power over Ethernet (PoE)
IEEE802.1p (MAC layer QoS)
IEEE802.1q (Dynamic VLAN), Spanning Tree Protocol
TCP/IP
General specification
DC12V (external AC adapter or PoE)
10W (maximum. With AC adapter) / 9W (maximum. With PoE)
1.2A (maximum. With AC adapter or PoE)
W280 x H45 x D180 mm (excluding antennas)
1,400g (excluding AC adapter and antennas)
0~55 o C,0~90% (humidity. Without condensation)
Windows : Internet Explorer 5.5 and later
Wireless(TELEC,Wi-Fi),Safety(PSE,VCCI), Environment(RoHS)
50

Figure 5.2: AirMagnet Surveyor interface
AirMagnet Surveyor [42] was utilized to measure the field distribution. Figure 5.2
illustrates the interface of AirMagnet along with an example of filed distribution for one
access point.
Channel utilization in the environment which we experiment has a huge influence on
the experiment results. Because of that, the environment is carefully checked for any
possible interference form outside source prior to performing the experiment. Moreover,
distances between access points and antennas are carefully maintained throughout all
experiments.
.
51

5.3 Field experiment scenarios
5.3.1 Scenario 1: Throughput vs Signal to Interference (SIR) Ratio
characteristics
In the first part of this scenario, the aim is to plot the relation between the throughput
and Signal to Interference ratio (SIR) for one hop network using a signal generator as
the interference source.
Figure 5.3: SIR measurement using Signal generator
Figure 5.3 shows the experiment setup. It consists of two networks interconnects at
the Coupler.
Figure 5.4: Directional Coupler
52

The directional coupler is a passive device that has four-port circuits where one port
is isolated from the input port. Figure 5.4 illustrates a diagram of the coupler structure
along with the coupler used in the experiment. The transmitted port 2 is where most of
the incident signal (from the input port 1) exits. The coupled port 3 is where a fixed
fraction of the input signal appears. The last port (isolated port 4) is terminated. The
coupler is a reversible device; meaning that if 2 became the input port, then 1 will be the
transmitted port and 4 will be the coupled port. Finally 3 will change into the terminated
port. The coupled port is a function of which port is the incident or input port. Real
couplers will have some leak power to port 4, but ideally, the power port 1 will only
appear at ports 2 and 4[43].
In Figure 5.3, the upper section consists of one hop WMN by IEEE 802.11. Cables
are used in this experiment instead of wireless to avoid any unwanted interference from
outside source. 30dB attenuators are used at the access points to limit signals from
damaging the AP. The signal generator from the lower section produces an RF signal at
same frequency channel as the upper network; which then is fed into the upper network
to act as interference to the original communication between the two APs. The
generated signal is increased to a level which the measured throughput becomes very
low to indicate a break in the communication between the two APs. The results are
shown in Fig 5.5.
Figure 5.5: SIR vs Throughput (Continuous Interference)
The results indicate that at SNR 15dB, the communication is nearly stops between the
two access points. There was a steep change in the line between SNR 25 and 23dB
which resulted in a significant change in the throughput. These results may be due to the
carries sense level at the APs. The interference generated by the secondary network is a
53

continuous signal which is not the case in a realistic interference from other sources.
Figure 5.6 illustrates the second part of this scenario. It consists of two networks
interconnect with an isolator. The upper section consists of one hop network. 30dB
attenuators are utilized at the access points to guard the AP.
The lower section of the experiment (indicated by the blue devices), acts as
interference to the upper network. While operating at the same frequency channel, the
signals from the lower section are fed into the upper network while changing the
transmission power of the interference network. The isolator allows a single direction
signal pass to prevent affecting the interference circuit with the signal from the upper
network.
Figure 5.6: SIR measurement using two interfering networks
The results obtained are shown in Fig5.7. It is concluded that severe throughput
degradation occurs at low Signal to Interference Ratio (SIR) values. In order to avoid
the interference effect, the SIR values at the reception radio must be more than 25dB
[34].
54

Figure 5.7: Throughput vs. SIR (Interference with co-channel WLAN)
It is also noticed that the network didn’t arrive to a state where the throughput is zero
even with SNR=0dB which indicates that the interference is equal to the signal. That is
because the signals are timely sharing the channel medium between them. So the
communication not be completely halted regardless the intensity of the interference,
5.3.2 Scenario 2: Throughput vs. number of hops
The aim of this scenario is to determine the effect of number of hops on the
throughput .Up to three hops was experimented with as shown in Fig5.8. For the first
part of this scenario, only single radio AP was utilized.
Figure 5.8: Three hop WMN with Single radio AP
55

Figure 5.9 shows the resultant throughput from the experiment. The line represents
the throughput for 1, 2 and 3 hops with a single radio interface. Channel 1 was utilized
for the three hops. From the experimental results of [44] it was found that using Carrier
Sense Multiple Access with Collision Avoidance (CSMA/CA)-based MAC protocol like
IEEE 802.11 that in flat (string) topology such the one used in our experiment, the
throughput degrades approximately 1/n of the raw channel bandwidth (20MBps in our
case). This results are similar of which obtain in our experiments shown in Fig 5.9.
Figure 5.9: Number of hops vs. throughput for one radio AP
In the second part of the scenario, the two radios of the access point were utilized.
The experiments were conducted with different frequency bands for successive hops to
reduce the effect of interference between hops. IEEE 802.11a (5GHz) was utilized for
the first and last hop (CH 44 and 36 respectively). For the middle hop, CH 11 was used
with IEEE 802.11g (2.4GHz) as shown in Fig 5.10.
56

Figure 5.10: Three hop WMN with two radios AP
From Fig 5.11 the result is shows that this setup achieved the high throughput
compared to the previous case. The throughput for three hops was above 10Mbps which
is significantly higher then using only 2.4GHz for all hops. Although, the performance
was the same in single hop for any channel, the inter-channel interference effect on the
throughput is small with the increase in number of hops.
Figure 5.11: Number of hops vs. throughput for two radio AP (2.4GHz and 5GHz)
57

5.3.3 Scenario 3: Channel selection vs. throughput
Although, the previous results indicated the presence of interference as a result of
utilizing the same channel for all the hops, our aim in this scenario is to examine the
channel selection effect on the throughput for single and two radio AP for two hops
WMN. In this scenario, we utilized the 2.4GHz frequency band only. The introduction
of the second radio in access point is expected to improve capacity, connectivity and
better utilization for the frequency band. Figure 5.12 indicates the two WMN that were
tested in this scenario.
Figure 5.12: Single radio vs. Multi-radio
The upper network in Fig 5.12 utilizes two radios at the middle access point to route the
data between the source and destination. The red network on the other hand utilizes only
a single radio to do the routing. For this simple two hop WMN, it was expected to
achieve better throughput with the two radio setup since they utilized different channel
for the two hops. However, the results summarized in Table 5.2 show that the single
radio setup achieved slightly higher throughput than the two radio setup.
58

Table 5.2:Throughput of Mutli-hop WMN
Multi-Radio Throughput
(Mbps)
Channel 1
8.408
Channel 3
Channel 1
9.094
Channel 6
Channel 1
9.00
Channel 11
Single radio Throughput
(Mbps)
Channel 1 10.25
The first column indicates the channel combination used for the fist and the second
hops. For the multi -radio setup, we notice that as the channel separation increase, the
throughput is slightly improved. The small improvement in throughput is due to
utilizing non overlapping channels. In case of a single radio, the only channel 1 is
utilized, and the throughput achieved was the highest among the other combination. In
the two radios case, the first hop and the second hop do not tightly interfere with each
other since they utilize different frequency channels. The degradation in throughput is
due to the dropped packets as a result if interference between the transmitting and
receiving radios on the access point. On the other hand, the single radio case do not face
such a problem since the two hops utilizes the same frequency channel. As a result,
when hop 1 is using the channel, hop 2 cannot transmit until hop 1 finishes transmitting.
For this reason, the dropped packet may be decreased and slightly higher throughput is
achieved.
In the experiment, the single channel, single radio scenario, the second hop cannot
occur with the first hop simultaneously because they utilize the same channel for
communication. Although this might seam as a disadvantage, however, it eliminates the
possibility of interference between the first and second hops because they cannot
happen at the same time. In this scenario, the delay will be higher than the next scenario
for the multi-radio case, which affects time sensitive applications (such as VOIP, and
streaming) and not the throughput. This work, my focus was the throughput and not end
to end delay in this stage of the research.
In the multi-radio case, since I utilized two different sets of radios for the first hop
and the second hop, they both can occur at the same time and utilize two different
channels. Even thought these channels are non-interfering channels according to the
59

IEEE 802.11 standard, I still found that the performance (throughput) is affected when
utilized within the same area. However, the delay in this case is lower than the single
radio case, but my focus was just the throughput.
In this scenario, and looking at the throughput alone, the single radio achieved a
better throughput because of the nonexistence (absence) of interference between the
first and the second hop.
5.3.4 Scenario 4: Throughput measurement for distance varying and
hop count in Indoor closed corridor environment.
In this experiment we performed a site survey using Air Magnet Surveyor. The aim is to
measure the field distribution in a long corridor of the venture building at the Yokosuka
research park (YRP). The total length is 88m with a slight bent at the middle as shown
in Fig 5.13. Figure 5.13 also demonstrates the results obtained from our site survey. A
single access point was placed at one end of the corridor. It is a typical indoor office
corridor with glass doors and office partitions.
Figure 5.13: Single access point field intensity
The stronger received power is indicated by the blue region. The yellow region
represents a weak received power.
In general, the relation between path loss and the distance between the transmitter and
receiver at 2.4 GHz is approximated in [31] as shown in Eq. (8):
60

PathLoss ( dB)
= 40 + [35log10 D(
meters)]
(8)
Were D is the distance between the transmitter and the receiver.
Figure 5.14 indicates the relation between the received power and distance from
access point. The figure shows that the coverage range is relatively high through
corridors. This is explained by the waveguide property for the corridor, which state that
the signals travel longer distances through corridors and narrow paths.
Figure 5.14: Received signal power versus range in a corridor
After the site survey, we intended to plot a graph of distance against throughput in a
closed corridor environment. We placed one AP at one end point of the corridor and
measure the single hope throughput while changing the position of the second access
point as shown in Fig 5.15.
Figure 5.15: Received signal power measurement points in the corridor
61

Table 5.3 indicates the throughput achieved at different separation distance with the
corresponding receiving power level. IEEE 802.11g was utilized with channel 7 at
2.4GHz. The degradation in throughput was not severe in the corridor which agrees
with the wave guide property for corridors.
Table 5.3: Throughput measured at different hop distance
Distance 25m 41m 61m 88m
Received
power (dB)
Throughp
ut (Mbps)
-41 -53 -69 -72
15.5 14.26 13.68 13.22
5.3.5 Scenario 5: Interference cancellation experiment for 2 hops WMN
The proposed interference cancellation circuit is utilized in this scenario to test its
impact on the throughput. The circuit is expected to cancel interference between the two
antennas of a WMN access point equipped at the center of the corridor. Figure 5.16
shows the structure of the circuit and antennas.
Figure 5.16: Interference cancellation Circuit connected on two radios AP
Figure 5.17 demonstrates the actual experiment setup and components of the
interference circuit.
62

Figure 5.17: Actual Interference cancellation Circuit
A two hop WMN with three IPN-W100AP Trinity Security Systems, Inc. access
points operating by 2.4GHz IEEE802.11g with dual radio were utilized for this
experiment as shown in Fig 5.18.
Figure 5.18: Two-hops WMN with cancellation circuit
The APs connected to the source and destination use only one antenna. The second
AP will utilize both antennas to route the data from the source to destination. Figure
5.18 indicates how the cancellation circuit is installed between the two antennas of the
middle access point. Netperf software was utilized to evaluate the UDP throughput
while transferring data from the source to the destination.
63

The distance between the access points is maintained throughout the experiment at
1.5m. The distance between the two antennas in the cancellation circuit was fixed to
21cm which is similar to the original spacing between the two antennas before utilizing
the circuit.
Figure 5.19: S 21 Parameter
In this experiment we utilized channel 2 for the first hop and channel 7 for the second
hop. Fig 5.19 shows a plot of the S 21 Parameter to achieve the highest possible
cancellation. The aim was to have the lowest possible value of S 21 at channel 2 or
channel 7 to achieve the desired cancellation. The centre frequency was 2.442GHz
which represents Channel 7. Using the combination of the phase shifters and the
attenuator, we managed to suppress interference around 15dB.
The selection of the channels is governed by channel utilization in the field. That is to
minimize interference from outside sources. Channel 2 and 7 are almost
non-overlapping channels according IEEE 802.11 standard for 2.4GHz band. We
measured the change in throughput as a result of using the interference cancellation
circuit. The green line (at 7.984Mbps) in Fig 5.20 represents the throughput achieved in
a normal case (with the presence of interference).
64

Figure 5.20: Attenuation value vs. throughput
In order to achieve the no interference ideal case for two hops WMN, we utilized
coaxial cables between the access points to avoid any possible interference between the
radios. The throughput was 12.712Mbps (red line). The blue line indicates the results
obtained after tuning the variable attenuator values (1dB-7dB) while fixing the Phase at
180°. The highest throughput achieved was 11.7 Mbps at 2dB attenuator value. To
compare that result with the normal case (the green line at 7.984Mbps), we managed to
achieve an improvement of nearly 4Mbps.
Qcheck [40] software was utilized for UDP data streaming estimation of the
interference cancellation circuit. Streaming 1Mbps for 30sec resulted in a 25% dropped
data from the total data streamed without using a cancellation circuit. The dropped data
reduced to 0.1% in case of cancellation circuit.
The cancellation circuit was tested in the closed corridor environment to measure the
improvement in throughput. The experiment of interference cancellation for 2 hops in
long corridor is shown in Fig 5.21.
65

Figure 5.21: Two hop WMN in closed corridor with cancellation circuit
Figure 5.21 shows the setup of a two hop WMN along with their coverage field
intensity. The cancellation circuit was installed at the middle access point (at 41m).
Figure 5.22: S 21 Parameter
66

Figure 5.22 illustrates the S 21 parameter for the cancellation circuit which gave the
highest improvement in throughput for the circuit in Fig 5.21. The proposed circuit in a
closed corridor environment resulted in nearly 3Mbps improvement in throughput (from
5.3Mbps to 8.3Mbps).
5.3.6 Chapter summary
The experiments results showed serious impact of interference on the WMN throughput.
The proposed multi-radio WMN interference cancellation circuit showed an
improvement in throughput during various experiment scenarios. The proposed
cancellation circuit managed to improve the throughput from 7.9Mbps to 11.9Mbps in
typical indoor environment (1.5m between the access points) and from 5.3Mbps to
8.26Mbps in a long corridor (88m) environment in a 2 hop WMN with channel 2 for the
first home and channel 7 for the second hop.
Interestingly, the single hop WMN managed to achieve higher throughput
(13.22Mbps) than the two hop WMN (8.26Mbps) at the same distance of 88m in the
corridor. However, the single hop mesh network would not maintain reliability at low
values of received power compared to the multi-hop network. For such a case, the
multi-hop WMN would be preferred over the single hop.
67

CHAPTER
6
Conclusion
Challenges occur in wireless LAN when more hops are needed to cover more area
which results in more networks co-exist. Multi-hop is key issue to form WMN and
MANET. In this work we studied different challenges that face both MANET and
WMN.
The previous work done by the NICT focused on the comparison between two
routing protocols, AODV and OLSR and a comparison between the random way point
mobility model with the their own map mobility model at different station speed values.
My aim was to emphasize on the importance of ART values in AODV routing protocol
to improve PDR utilizing my own predefined movement path and speed values.
Simulations were carried out under the condition that a disaster stricken indoor area of
500 m x 500 m with 50 mobile terminals moving through several corridors. Simulating
MANET station’s speed at different values is particularly important in disaster and
emergency situations. In this research I focused on three station values (0, 4 and 10m/s).
My proposal simulation showed that for high speeds (4m/s and 10m/s, ART value of
0.25sec) resulted in higher PDR values. However, at slow speeds, higher ART (1, 3 and
5sec) values resulted in a better PDR (at the simulated conditions of 11Mbps, 802.11g,
Constant Bit Rate encoding and the proposed mobility model).
My second proposal of improving the end-to-end delay using ART values in a fixed
Ad-hoc network was simulated in the third scenario and showed that using low ART (at
0.25sec) values resulted in a decrease in the end-to-end delay (e.g. At forth hop, 0.75sec
to 0.4sec which represents 88% improvement) .
For MANET, mobility is the main concern especially when we need to keep the
connection alive between the stations using route state hold time parameter (ART in
AODV).The ART parameter importance was evident through the simulated scenarios in
both mobile and stationary Ad-hoc networks. For future work, a robust Ad-hoc network
with improved performance (PDR and end-to-end delay) will be proposed on the bases
of the results simulated in this research.
For the case of WMN, a series of experiments was conducted to measure throughput
in indoor environment. Initially, I measured the effect of number of hops on the
throughput for the wireless LAN which achieves 20 Mbps throughput in the case of one
68

link. The experimental results showed that there is a nearly 50% degradation in
throughput with each increment in number of hops. On the other hand, if multi-radio
structure is introduced in WMN, noticeable improvement is expected by utilizing
non-interfering channels (for example, ch.1-6 and ch.1-11). However, the throughput
was 7.9 Mbps which wasn’t as high as expected due to the interference between the two
radios. The same experiment was repeated for an ideal case (using coaxial cables to
avoid any kind of interference) and the highest possible throughput for two hops WMN
was 12.712Mbps. I set this result as my goal for to achieve after utilizing proposed
interference cancellation circuit made of directional couplers, valuable attenuator and
phase shifter. More than 15dB interference was reduced and the throughput was
improved by nearly 4 Mbps (from 7.9Mbps to 11.9Mbps which represents a 50%
improvement). In addition, I tested the packet dropped rate using Qcheck software to
stream 1Mbps for 30sec and resulted in an obvious improvement (from 25% to 0.1%)
after implementing the proposed interference cancellation circuit.
The proposed interference cancellation circuit was tested in the long (88m) corridor
environment and the throughput was improved from 5.3Mbps to 8.26Mbps (60%
improvement). Interestingly, the single hop WMN managed to achieve higher
throughput (13.22Mbps) than the two hop WMN (8.26Mbps) at the same distance of
88m in the corridor. However, the single hop mesh network would not maintain
reliability at low values of received power compared to the multi-hop network. For such
a case, the multi-hop WMN is preferred over a single hop.
Analysis indicates that the requirements of wireless communications in general can
increase 100 times in data rate every 6-7 years. It is also expected that by 2015, the
requirement for data rate will be 100-1000 times higher comparing the current
requirements [9]. These analyses signify the importance of spectrum management.
Since, spectrum efficiency will not be enough with the increasing requirements of
wireless communications in the future; researches like this will help get the most out of
the spectrum by limiting interference to acceptable level.
As for Future work, the interference cancellation circuit will be further improved to
achieve better performance using a wide band canceller. This could lead to interesting
and useful applications to the multi-radio WMN. Finally, the interference cancellation
circuit will be utilized for a robust mutli-radio mutli-hop WMN backbone internet
access with high throughput. Moreover, implement, test, evaluate and experiment with
the findings of this research to construct or build a high performance indoor multi-hop
wireless system that is less susceptible to interference, and achieve high level of
throughput and packet delivery rate.
69

Appendix A
Simulation of route stat hold time parameter in AODV and
OLSR
This simulation compares the route state hold time parameters in AODV and OLSR
routing protocols for 50 stations as shown in Fig A.1
Figure A.1: The Simulated Area map
The simulation map used is similar to the simulation done section 3.5. However, in
this simulation, the speed values are 2, 4, 8, 10m/s. The ART values on the other hand
range from 0 to 5 seconds.
70

Scenario A.1
This scenario simulates a network of 50 stations; the AODV routing protocol was used
with value of the parameter ART was change from 0 to 5 seconds. The default value set
by OPNET is 3 seconds. Figure A.2 shows the throughput variation with different
values of ART for different station speed.
Figure A.2: Throughput vs. ART
The figure shows that for law values of ART (especially lower then 2 sec), the
throughput will have higher values. At 0 sec, the stations will not keep the states for the
route after it has bean used, which will cause the station to repeat the route discovery
process after each use of the route. This will be useful in case of a highly mobile
network which should give higher values for throughput. The figure shows that at
higher speeds of 8m/s and 10m/s, the values of throughput were lower then the low
speeds. These results where as expected since at higher speeds, the throughput is
affected because of the constant change in the position of the nodes which makes it
difficult to have interconnections.
In general, the figure shows that we could achieve a higher throughput values for
lower values of ART then the default value 3sec. its is also noted that after 2sec, the
change in throughput is not very noticeable.
71

Scenario A.2
For the second scenario, the route state hold time parameters used in OLSR routing
protocol are Neighbor Hold Time and Hello Interval. Since the two values are related,
both values have to be changed together with respect of the relation between them.
These two values are related to each other. (Neighbor Hold Time/3 = Hello Interval).
The smallest value simulated in OPNET was 1.5sec for Neighbor Hold Time and 0.5 sec
for Hello Interval. Since the station has to send the Hallo packets, we could not set the
value to zero. Figure A.3 shows the relation between different values of the parameters
and the throughput for different station speeds.
Figure A.3: Throughput vs. NHT/HI
From the Fig A.3, for low values of the parameters, the throughput had higher values.
After the values 3/1.0, the change in throughput values is not very noticeable. The
results were as expected speed variation of the stations. In case of the OLSR, because
it’s a link state routing protocol which maintains a partial or full state of the topology, it
was expected that’s it will perform better at law values of speed.
The effect changing parameters for both OLSR and AODV was very apparent for the
simulated results. For the default value of the parameters, the throughput value didn’t
have a big increment because of the slow adaptation to the new positions of the stations
as a result of the rapid movement on high speeds. In general, AODV achieved higher
throughput compared to OLSR which is similar to the results form previous work
presented in section 3.2.
72

Destination address Table
Table A.1: Destination address for the map area simulation
Source Address Destination Address Source Address Destination Address
192.0.0.1 192.0.0.33 192.0.0.26 192.0.0.9
192.0.0.2 192.0.0.5 192.0.0.27 192.0.0.1
192.0.0.3 192.0.0.40 192.0.0.28 192.0.0.12
192.0.0.4 192.0.0.18 192.0.0.29 192.0.0.34
192.0.0.5 192.0.0.47 192.0.0.30 192.0.0.21
192.0.0.6 192.0.0.41 192.0.0.31 192.0.0.16
192.0.0.7 192.0.0.21 192.0.0.32 192.0.0.12
192.0.0.8 192.0.0.26 192.0.0.33 192.0.0.32
192.0.0.9 192.0.0.47 192.0.0.34 192.0.0.15
192.0.0.10 192.0.0.27 192.0.0.35 192.0.0.14
192.0.0.11 192.0.0.9 192.0.0.36 192.0.0.24
192.0.0.12 192.0.0.13 192.0.0.37 192.0.0.35
192.0.0.13 192.0.0.3 192.0.0.38 192.0.0.20
192.0.0.14 192.0.0.20 192.0.0.39 192.0.0.3
192.0.0.15 192.0.0.25 192.0.0.40 192.0.0.31
192.0.0.16 192.0.0.4 192.0.0.41 192.0.0.30
192.0.0.17 192.0.0.24 192.0.0.42 192.0.0.8
192.0.0.18 192.0.0.27 192.0.0.43 192.0.0.28
192.0.0.19 192.0.0.31 192.0.0.44 192.0.0.43
192.0.0.20 192.0.0.9 192.0.0.45 192.0.0.23
192.0.0.21 192.0.0.4 192.0.0.46 192.0.0.41
192.0.0.22 192.0.0.28 192.0.0.47 192.0.0.50
192.0.0.23 192.0.0.35 192.0.0.48 192.0.0.26
192.0.0.24 192.0.0.33 192.0.0.49 192.0.0.44
192.0.0.25 192.0.0.45 192.0.0.50 192.0.0.35
73

Appendix B
Interference cancellation
The scenario implemented in section 5.3.5 with similar setup in Figure 5.16, the two
hops WMN was implemented with channel 2 for the first hop and channel 7 for the
second hop. We measured the change in throughput as a result of using the interference
cancellation circuit with a 3dB coupler instead of the 10dB coupler in section 5.3.5.
Figure B.1 illustrates the results obtained after varying with the variable attenuator
values (10dB-70dB) while fixing the Phase at 180°. However, the throughput achieved
without the cancellation circuit was 7.3Mb/s.
Figure B.1: Attenuation value vs. throughput
There was an improvement in throughput values which jumped from 7.3Mb/s to
nearly 10Mb/s at 30dB attentions value.
74

Figure B.2: Attenuation value vs. throughput
Figure B.2 represents finer tuning values for the attenuation with a range that
extends from 25dB to 35dB. The highest throughput achieved was in the vicinity of
30dB attenuation value.
75

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Publications
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parameter”, WSEAS TRANSACTIONS on COMMUNICATIONS, Issue 9,
Volume 7, September 2008, pp.912- 921.
2. Wadhah H.Al-Mandhari, Nobuo Nakajima, “Inter-Channel Interference
Cancellation in Wireless Mesh Network”, WSEAS TRANSACTIONS on
COMMUNICATIONS, Issue 8, Volume 8, August 2009, pp.765- 774.
Conference paper:
1. Wadhah H.Al-Mandhari, Koichi Gyoda, Nobuo Nakajima, “Performance
Evaluation of Active Route Time-Out parameter in Ad-hoc On Demand Distance
Vector (AODV) ”, 6th WSEAS International Conference on APPLIED
ELECTROMAGNETICS, WIRELESS and OPTICAL COMMUNICATIONS
(ELECTROSCIENCE '08), Trondheim, Norway, July 2-4, 2008, pp.47-50.
2. Wadhah H.Al-Mandhari, Nobuo Nakajima and Pham Huy Hoang, “The Effect of
Channel selection and interference on throughput in multi-radio wireless mesh
networks”, Proceedings of Triangle Symposium on Advanced ICT 2008 (TriSAI),
October 2008, pp. 74-77.
3. Wadhah H.Al-Mandhari, Nobuo Nakajima, “Throughput Enhancement with
Channel Interference Cancellation in Multi-Hop/Multi-Radio Wireless Mesh
Network”, Proceedings of the 1st international conference on Wireless
Communication, Vehicular Technology, Information Theory and Aerospace &
Electronic Systems Technology (Wireless VITAE), Aalborg Congress and Culture
Cenetre, Aalborg, Denmark, May 17-20, 2009, pp.248-251.
4. Wadhah H.Al-Mandhari, Nobuo Nakajima, “Channel interference effect on
throughput in Wireless mesh network”, Proceedings of the 13th WSEAS
International Conference on Communication (part of 13th WSEAS Multiconference
on CIRCUITS, SYSTEMS, COMMUNICATIONS and COMPUTERS), Rodos,
Greece, July 23-25,2009, pp.95-98.
5. Wadhah H.Al-Mandhari, Nobuo Nakajima, “Interference Suppression in indoor
multi-radio multi-hope wireless mesh network”, Proceedings of the 12th
International Symposium on Wireless Personal Multimedia Communications, Hotel
Metropolitan Sendai, Sendai, Japan, September 7 – 10, 2009.
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