ABSTRACT
WLAN performance in Nigeria is adversely affected by incessant traffic overloads that
constantly lead to congestion, since bandwidth is very limited. This work, therefore,
addressed the issue of defining optimum performance parameters in WLAN under
traffic saturation. A WLAN model was developed and simulated using MATLAB block
oriented simulation package. The model was validated through extensive simulation
results related to the simulation result of Nurul I. Sarkar. The relationships between the
networks Quality of Service (QoS) parameters under excessive traffic loading were
TABLE OF CONTENTS
Title Page – – – – – – – – – –
i
Approval Page – – – – – – – – –
ii
Certification – – – – – – – – – –
iii
Dedication – – – – – – – – – –
iv
Acknowledgement – – – – – – – – –
v
Table of contents – – – – – – – – –
vi
List of Figures – – – – – – – – – vii
List of Tables – – – – – – – – – x
Abstract – – – – – – – – – –
xi
CHAPTER ONE: INTRODUCTION
1.0 Background – – – – – – – – –
1
1.1 Objective of Study – – – – – – – –
2
1.3 Scope of the Study – – – – – – – –
2
1.4 Methodology – – – – – – – – –
3
7
1.5 Thesis Outline – – – – – – – –
3
CHAPTER TWO: LITERATURE REVIEW
2.0 Introduction – – – – – – – – –
4
2.1 Wireless Networks – – – – – – – –
4
2.2 Multi hop Wireless Networks – – – – – – –
5
2.2.1. Mobile ad-hoc network – – – – – –
5
2.2.2. Wireless sensor network – – – – – –
6
2.2.3. Hybrid wireless network – – – – – –
7
2.2.4. Wireless mesh network – – – – – –
7
2.3 Evolution of IEEE WLAN Standard – – – – – –
8
2.4 IEEE 802.11 architecture – – – – – – –
18
2.4.1 Basic service set – – – – – – –
19
2.4.2 Extended service set – – – – – – –
19
2.4.3 Distribution system – – – – – – –
19
2.4.4 Physical Layer- – – – – – – –
21
8
2.5 Medium Access Control Layer – – – – – –
22
2.5.1 IEEE 802.11 MAC Architecture – – – – –
23
2.5.2. Distributed Coordination Function – – – – –
25
2.5.2.1. The Basic Access Mechanism – – –
26
2.5.2.2. The RTS/CTS Mechanism – – – –
28
2.5.3. Point Coordination Function – – – – – –
30
2.6 Frame Structure and Addressing – – – – – –
30
2.6.1 The General Frame Format – – – – – –
34
2.6.2 Format of individual frame types – – – – –
34
2.6.2.1. Control frames – – – – –
34
2.6.2.2. Data Frames – – – – – –
38
2.6.2.3. Management Frames – – – – –
38
2.7 Spread Spectrum Allocation for WLAN – – – – –
39
2.8 Network Performance Management – – – – – –
42
2.9 Related Works – – – – – – – –
43
9
CHAPTER THREE: WIRELESS LAN MODEL
3.0 Introduction – – – – – – – – –
54
3.1 Adopted WLAN Architecture- – – – – – –
54
3.2 WLAN Model – – – – – – – –
56
3.2.1 WLAN traffic model – – – – – – –
57
3.2.2 CSMA/CA As Realized In the Model – – – –
59
3.2.3 Queuing model- – – – – – – –
60
3.3 Timing Sequence – – – – – – – –
61
CHAPTER FOUR: SIMULATION AND SIMULATION RESULT ANALYSIS
4.0 Introduction – – – – – – – – –
62
4.1 Computer Simulation – – – – – – – –
62
4.2 Parameters Considered for Simulation – – – – –
63
4.3. Modeling Assumptions and Configuration- – – – – –
65
4.4 Model Validation – – – – – – – –
67
4.5 Simulation Results – – – – – – – –
67
4.6 Throughput Result Analysis – – – – – – –
69
10
4.6.1 Effect of Workstations on Net. Throughput Performance – –
69
4.6.2 Throughput Performance of Selected Stations – – –
73
4.7 Delay Result Analysis- – – – – – – –
73
4.7.1 Effect of Workstations on Net. Mean Delay Performance – –
73
4.8 Packet Loss Rate Result Analysis – – – – – –
77
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION
5.0 Conclusion – – – – – – – – –
82
5.1 Recommendation – – – – – – – –
82
5.2 Reference – – – – – – – – –
84
CHAPTER ONE
INTRODUCTION
1.0 Background
In recent years, the family of IEEE 802.11 protocols has become the most
popular access method for Wireless LANs (WLANs) [1]. With wireless access, a user
can connect its wireless network-equipped laptop or portable devices to the network
anywhere and anytime without cumbersome cable or wire connections [1].
The IEEE 802.11 Wireless LAN [2] is the predominant technology for wireless
access in local areas. The IEEE 802.11b Wi-Fi networks with data rates up to 11 Mbps
in the 2.4 GHz frequency band have been widely deployed as hotspots. Furthermore,
The IEEE 802.11a in the 5 GHz band and IEEE 802.11g in dual bands (2.4 GHz and 5
GHz) are being deployed to provide data rates up to 54 Mbps. To further increase data
rates and throughput, the IEEE 802.11 work group created a new task group, namely
IEEE 802.11n, which focuses on the standardization issues of next-generation WLANs
to achieve 100 Mbps net throughput [3]. In other words, the last decade has witnessed
rapid growth in the deployment of wireless LANs (WLANs) based on the IEEE 802.11
standard. This growth has been propelled by the high capacity links offered by these
networks. Unlike 3G cellular networks, which offer a data rate of 2Mbps, Wi-Fi
networks offer 11Mbps (IEEE 802.11b) and 54Mbps (IEEE 802.11a/g) [1]. It is
envisioned that this growth would continue till the goals of 4G to offer ubiquitous
WLAN services integrated with other wireless technologies like IEEE 802.15, 3G etc
are met [1]. Due to the universality in the application of WLANs access protocol in
connecting mobile users, an in-depth analysis of WLAN access protocol is necessary.
When nodes or stations are connected to a common link, there is need to
coordinate the access to the link. A number of access protocols have been devised to
handle access to a shared link. The protocols for WLAN are basically random access
protocols which may include ALOHA and Carrier Sense Media Access with Collision
Avoidance (CSMA/CA) [4].
Distributed Coordinated function (DCF), Point Coordinated function (PCF) and
the combination of DCF and PCF are for IEEE 802.11 WLAN [5].
18
WLAN performance in Nigeria is adversely affected by incessant traffic
overloads that constantly lead to congestion, since bandwidth is very limited. This work,
therefore, addressed the issue of defining optimum performance parameters in WLAN
under traffic saturation.
1.1 Objective of the Study
The objective of this thesis was to determine the optimum WLAN performance
parameters under saturated traffic loading. This is intended to provide a congestion
control measure for WLAN in a high traffic loading situation for network service
providers.
The said objective is to be realized by pursuing the following sub-objectives:
1. The development of WLAN network model.
2. The conversion of the WLAN network model into a computer simulation
model using MATLAB block oriented simulated package.
3. The simulation of the computer model and collection of simulation results.
4. The analysis of the simulation results to establish the set of optimum
performance parameters.
1.2 Scope of the Study
The scope of this work covers both the Physical layer architecture and MAC
layer architecture. The distributed coordination function (DCF) of WLAN popularly
known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), the
RTS/CTS mechanism, MAC sub-layer service specifications, physical layer description
and specifications, frame structure and addressing, WLAN spectrum allocation and
network performance management are also addressed. Logical link control (LLC) layer,
Centralized and hybrid coordination function, power management, security etc., are not
considered.
19
1.3 Methodology.
The approach used in the actualization of optimum performance in this project
work, is based on the principles of CSMA/CA using the MATLAB Simulink Simevent
Block oriented simulation package.
Subsequently, the physical architecture used for the modeling was converted into
computer simulation model using MATLAB Block oriented simulation package. The
computer simulation model is probed and simulated, for Quality of service parameter
collation.
1.4 Thesis Outline.
The rest of this thesis is organized as follows. Chapter 2 presents the literature
review of the thesis. Chapter 3 presents the Network model for IEEE 802.11 MAC DCF
saturated Traffic Loading for achieving optimum performance. Chapter 4 presents the
simulation results and results analysis. Finally, the observations and conclusion were
presented in Chapter 5.
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