ABSTRACT
Achieving seamless homogeneous handover in mobile WiMAX due to its low cost and state of the
art technology will enable ubiquitous broadband access to high volume applications especially
with the high global increase in mobile subscribers. Extending this seamless handover across
network technologies-heterogeneous handover- like WiFi will further lower cost, improve battery
life and enable high productivity for end users. In this project, ways of optimizing handover in
mobile WiMAX network, and the design and evaluation of system-level performance of different
select handover scenarios were analyzed. Modeled voice application on a mobile node at
pedestrian and vehicular speeds was used for the analysis with the media independent handover
(MIH) network simulator 2 (NS-2) as simulation tool. MATLAB-based Trace Graph and
Microsoft excel were used as the MAC layer packet-level analysis tools. The average handover
delay from the simulation result is found to be 46 msec in all the simulation which fell below
the WiMAX forum’s recommended handover delay of 150 msec for VoIP. The average handover
jitter of 47msec also fell under the standard value of 50 msec. It was determined that the
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heterogeneous handover to WiFi network has acceptable throughput, delay, latency with no
packet lost for voice packets. However, there were significant drop in throughput observed
during WiMAX handover periods with highest drop of 5 packets/sec from 50 packets/sec at
normal operation. This is due to packet loss caused by Doppler spread at vehicular speed and low
SINR (signal-to-interference noise) at non overlapping cells and large base station distances.
These throughput drops can be mitigated by appropriate channel modelling, adaptive sampling of
Orthogonal Frequency Division Multiplexing (OFDM) symbols at high speed, antenna diversity,
and also bymaking sure that all cells overlap during base station deployments.
TABLE OF CONTENTS
DECLARATION I
DEDICATION II
ACKNOWLEDGEMENT III
ABSTRACT IV
TABLE OF CONTENTS V
LIST OF FIGURES X
1 INTRODUCTION 1
1.1 Introduction To The Problem 1
1.2 Motivation 2
1.3 Research Objectives 2
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1.4 Organization of Thesis 2
2 WIMAX TECHNOLOGY AND IMPLEMENTATION 4
2.1 Introduction to Mobile Broadband Wireless Access 4
2.2 Brief Review of WiMax Concept 6
2.2.1 Introduction 6
2.2.2 Technical Overview 6
2.2.3 Uses of WiMax 8
2.3 Overview of IEEE 802.11 standard 9
2.3.1 Network Topology 9
2.4 Comparison Between WiMax and WiFi 12
2.5 Physical (PHY) Layer 13
2.6 Media Access Control (MAC) Layer 15
2.7 Mobility Management 16
2.7.1 Frequency Reuse 16
2.7.2 Network Entry 16
2.7.3 Location Management 17
2.7.4 Radio Resource Management 17
2.7.5 Power Management 18
2.7.6 Handover Management 18
3 HANDOVER IN MOBILE WIMAX 19
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3.1 Introduction 19
3.2 Homogenous Handover 19
3.2.1 Hard Handover 23
3.2.2 Soft Handover 23
3.3 Heterogeneous Handover 30
3.4 Handover Optimization Mechanisms 38
3.4.1 GPS-based Handover 38
3.4.2 Smoothening Prediction and Trend Analysis of Signal 39
3.4.3 Adaptive Channel Scanning 40
.4.4 Integration of layer 2 and layer 3 Handover 41
3.4.5 Handover Decision based on Fussy Logic 43
3.5 Handover Performance Metrics 43
3.5.1 Handover Throughput 44
3.5.2 Handover Delay or Latency 45
3.5.3 Handover Jitter 46
3.5.4 Packet loss 47
4 DESIGNS AND SIMULATION WITH NS-2 48
4.1 Introduction 48
4.2 The NS-2 Simulator 48
4.3 Debugging of the NIST Mobile WiMAX Module 49
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4.4 Handover Scenario Designs 50
4.4.1 Scenario 1: Full Cell Overlap 50
4.4.2 Scenario 2: Half Cell Overlap 51
4.4.3 Scenario 3: No Cell Overlap with Zero Distance 51
4.4.4 Scenario 4: 10 metre Distance No Cell Overlap 52
4.4.5 Scenario 5: Vertical WiFi-WiMAX-WiFi handover 53
4.5 Speed and Application Traffic Modelling 54
4.6 Simulation 55
4.6.1 The Handover API Flow chart 56
4.6.2 Configuration and Simulation Parameters 58
4.6.3 MIP address modeling 60
4.6.4 Network Animations (NAM) of the Simulation Scenarios 62
5 ANALYSIS OF SIMULATION RESULTS 65
5.1 Introduction and Observations 65
5.2 Scenario 1: Full Cell Overlap 66
5.2.1 Pedestrian Speed 66
5.2.2 Low Vehicular Speed 67
5.2.3 High Vehicular Speed 68
5.3 Scenario 2: Half Cell Overlap 70
5.3.1 Pedestrian Speed 70
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CHAPTER ONE
1 INTRODUCTION
1.1 Introduction to the Problem
WiMAX (Worldwide Interoperability for Microwave Access) is a certification that denotes
interoperability of equipment built to the IEEE 802.16 or compatibility standard. It is based on
the wireless Metropolitan Area Network technology, optimized for the delivery of IP centric
services over a wide area.
This thesis introduces the IEEE 802.16e-2005 standard, also known as Mobile WiMAX, which
defines the physical (PHY) and Medium Access Control (MAC) layers of it. The 802.16e-2005
[1] is the new, mobile version of the older WiMAX specification known as 802.16-2004 [2],
which is a wireless but fixed, data transmission scheme for providing broadband connection to
metropolitan areas. The traditional WiMAX has lacked the ability for the user to move during
transmission. The importance of mobile WiMax becomes imperative, due to the need for a mobile
user to change from one serving base station to another. The handover should be fast enough, so
that the on-going video or voice call is not interrupted long enough for the user to notice. The
support for seamless mobility in mobile broadband radio access network, will give opportunity
for anytime, anywhere, any network and any device communication, especially for high
bandwidth-hungry internet applications like online gaming, video and audio streaming, voice
over IP, video conferencing and location based services.
Mobile WiMAX enjoys wide support from telecom industry leaders such that by creating a
common platform, which addresses a wide range of market and business segments, it will be well
placed to assume the global standard for mobile broadband wireless. Achieving seamless
mobility across different wireless technologies like WiFi (wireless fidelity) or other 3G (third
generation) broadband networks like UMTS (universal mobile telecommunication services)
will further have a user advantage of keeping cost very low and productivity very high while
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saving battery life. In December 2005, the 802.16-2004 WiMAX standards was amended to the
802.16e-2005 and ratified by the IEEE (Institute of Electrical and Electronics Engineers). This
amendment added the features and characteristics that makes it necessary to support
mobility in the air interface [2, 3] [3]. The WiMAX Forum, which is pioneering this technology,
defined system performance and certification profiles based on the IEEE 802.16e-2005
amendment to go beyond the air interface and identify network architecture necessary for
implementing end-to-end mobile architecture [4]. This forum is making sure that WiMAX
standard have benefits that cuts across equipment vendors, consumers, service providers and
component makers.
1.2. Motivation
The motivation for this thesis is to determine how seamless mobility in WiMAX network can be
achieved, keeping in mind the need to maintain tolerable system throughput, delay, jitter and
packet lose during homogenous (horizontal), and heterogeneous (vertical) handover, between
mobile broadband networks at pedestrian and vehicular speeds
1.3. Research Objectives
The aim of this project is to analyze the various mechanisms for optimizing handover in mobile
WiMAX so as to achieve seamless handover session of broadband applications. Also different
handover scenarios will be designed in an attempt to demonstrate possible real life deployment of
WiMAX base stations, based on site logistics and existing infrastructure constraints. Performance
metrics of throughput, delay, jitter and packet loss will be used to evaluate the performance of a
mobile subscriber (MS) on a voice session with a user in a correspondent node (CN) during
normal (interleaving) and homogenous handover intervals at different speeds using NS-2. Finally,
the same performance metrics will also be used to analyze heterogeneous handover of voice
session between a multimode MS and same user in the CN while traversing a WiFi and a
WiMAX coverage area at various speeds and trajectory. This is an attempt to demonstrate the
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possibility of saving cost, battery life and achieving high productivity by a very busy business
executive or telecoms professional that starts a voice session from home and finishes up in the
office while communicating with his client or technical manager respectively
1.4. Organization of Thesis
The thesis starts with an overview and background of WiMAX Technology. Chapter two takes a
look at the underlying technology and foundation of mobile WiMAX. Chapter three discusses
handover types in detail, with current and ongoing research for optimizing handover techniques.
Chapter four discusses different handover scenarios carried out and the methods used and results
achieved, at the same time testing the performance of mobile WiMAX handovers. Chapter five
analyses the trace file output from the simulation. Finally, chapter six concludes the report with
standard comparisons and possible ways of improving handover issues with recommendation for
further work.
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