Analysis and Simulation of MC-CDMA System for WiMAX ...libback.uqu.edu.sa/hipres/ABS/ind10609.pdf · 2.9.3 WiMAX vs. UMTS ... 5.2.6 Nominal Channel Bandwidth ……………………

Analysis and Simulation of MC-CDMA System

for WiMAX Technology / IEEE 802.16

Ali Hasan Ali Al-Qahtani

A thesis submitted for the requirements of the degree of Master of Science

[Electrical and Computer Engineering / Communications and Electronics]

Faculty of Engineering

King AbdulAziz University, Jeddah

Rajab, 1430 H – June, 2009 G

تحليل و محاكاة نظام اتصاالت رقمي متعدد النواقل في

IEEE 802.16معيار ( /WiMAXتقنية الـ )

القحطانيعلي حسن علي

بحث مقدم لنيل درجة الماجستير في العلوم

)الهندسة الكهربائية وهندسة الحاسبات / هندسة االتصاالت(

كلية الهندسة

جدة -جامعة الملك عبد العزيز

م 9112 يونيو -هـ 0341 رجب

تحليل و محاكاة نظام اتصاالت رقمي متعدد النواقل في تقنية الـ

(WiMAX معيار / )IEEE 802.16

علي حسن علي القحطاني

المستخلص

االتصاالت الالسلكية )الجيل الرابع( هي التقارب بين الميزة المشتركة للجيل القادم من تقنية

خدمات الوسائط المتعددة مثل االتصاالت الصوتية والصورة والفيديو والمعلومات بسرعة عالية

وتنقل عال.هناك عدة تقنيات تحقق هذا المطلب ومن أهمها نظام تعدد تقسيم التردد المتعامد

(OFDM. )

ير من اهتمام الباحثين وهو مرشح بقوة للجيل الرابع في نظم اكتسب حديثاً هذا النظام الكث

االتصاالت الالسلكية وذلك بسبب خاصيته في نقل البيانات بسرعة عالية من المتوقع أن تصل

ميقابت لكل ثانية في حالة 100قيقا بت لكل ثانية أو أقل في حالة عدم التنقل و حوالي 1إلى

يرات قنوات الخفوت متعددة المسارات .التنقل و له ممانعة عالية لتأث

الدخول المتعدد بتقسيم الشفرة( هي في األصل نظام -)تعدد النواقل MC-CDMAتقنية

(OFDM ولكن يتم نشر رموز المعلومات بواسطة شفرة نشر في نطاق التردد. شفرة النشر )

خل .تقدم تقنية دخول متعدد وكذلك إزالة للتدا MC-CDMAالمستخدمة في الـ

( OFDM( تعتمد على الـ )WiMAXتقنية التعامل العالمي المتبادل بموجات الميكروويف )

لتفي بمتطلبات االتصال الالسلكي واسع النطاق للجيل القادم. التطبيق األهم لهذه التقنية هو في

المحطات الرئيسية ومحطات الربط للشبكات الالسلكية واسعة النطاق والشبكات الالسلكية

75كم وبسرعة انتقال للبيانات تصل إلى 50حضرية. و تقدم هذه الخدمة لمسافة أقصاها ال

( على غرار المعيار IEEE 802.16على المعيار ) WiMAXالـ ميقابت لكل ثانية. وتعتمد

IEEE 802.11 المصمم للعمل داخل المباني في تقنية الـWi-Fi).)

ليستخدم في تقنية الـ MC-CDMAتهدف هذا األطروحة إلى تحليل و محاكاة نظام

(WiMAX بدالً من نظام الـ )OFDMبرنامج تم استخدام . وMATLAB لمحاكاة هذا

وحالة التنقل ( IEEE 802.16 d- Fixed WiMAXالنظام في كال الحالتين :الحالة الثابتة )

(Mobile WiMAX - IEEE 802.16 e )ارنة بين خصائص األداء لكل ويشمل التحليل المق

. OFDMيحسن أداء النظام أكثر من الـ MC-CDMA, وقد وجد أن الـ منهما

Analysis and Simulation of MC-CDMA System for WiMAX

Technology / IEEE 802.16

By :

Ali Hasan Ali Al-Qahtani

Abstract

The common feature of the next generation of wireless communications technologies

(or 4G ) will be the convergence of different wireless networks with multimedia

services such as speech, audio, video, image, Internet services, and data at high data

rates and with high mobility, high capacity and high QoS. There are many techniques

that fulfill these requirements. One of the most important technique is Orthogonal

Frequency Division Multiplexing (OFDM) .

OFDM has recently gained a lot of attention and is a potential candidate for 4G

wireless systems because it promises data rates up to one Gbps or less under

stationary conditions and up to about 100 Mbps under vehicular conditions and it has

robustness against multipath fading channels effects. A variation of OFDM is Multi-

Carrier Code Division Multiple Access (MC-CDMA) which is an OFDM technique

where the individual data symbols are spread using a spreading code in the frequency

domain. The spreading code associated with MC-CDMA provides multiple access

technique as well as interference suppression.

WiMAX (Worldwide Interoperability for Microwave Access) is OFDM-based

technology that supports point to multi-point (PMP) Broadband Wireless Access

(BWA) for the next generation radio access. Main application (fixed and mobile) of

WiMAX today is for MAN/WAN base stations and link stations. It delivers the

maximum range (50 km) and higher data rates (up to 75 Mbps) than Wi-Fi. WiMAX

has been implemented depending on IEEE 802.16 standard which was designed by

Institute of Electrical and Electronic Engineers (IEEE).

This thesis aims to analyze and simulate a MC-CDMA system to be used in WiMAX

instead of OFDM system. A MATLAB code had been written to simulate both Fixed

WiMAX (IEEE 802.16d) and Mobile WiMAX (IEEE 802.16e). The analysis part

includes a comparison between them in performance evaluation.

The simulation results include the performance analysis based on bit error rate (BER)

versus bit energy to noise rate (Eb/No) plots and spectral efficiency of different

modulation and channel coding schemes according to the standard IEEE 802.16. The

results show that MC-CDMA outperforms OFDM in WiMAX system and enhances

the performance more when spreading factor increases.

TABLE OF CONTENTS

Examination Committee Approval

Dedication

Acknowledgements ................................................................................................................................... i

Abstract ........................................................................................................................................................... ii

Table of Contents ..................................................................................................................................... iii

List of Figures .............................................................................................................................................viii

List of Tables .............................................................................................................................................. xv

List of Symbols and Terminology...................................................................................................xvi

Chapter 1: Introduction .......................................................................................................................... 1

1.1 Wireless Broadband Beyond 3G ...........................................................................................1

1.2 Motivation of The Thesis .......................................................................................... ..............10

1.3 Objectives and Thesis Plan ….................................................................................................11

1.4 Structure of Thesis ..................................................................................................................... 12

Chapter 2 : Overview of WiMAX....................................................................................................13

2.1 What is WiMAX ? .....................................................................................................................13

2.2 History of WiMAX .................................................................................................................. 14

2.3 WiMAX – How does it work ? .............................................. .......................................... 15

2.4 WiMAX Standards .................................................................................................................. 16

2.4.1 IEEE 802.16d ................................................................................................................ 17

2.4.2 IEEE 802.16e .............................................................................................................. 18

2.4.3 IEEE 802.16m .............................................................................................................. 19

2.5 WiMAX Physical Layer .................................................................................................... 19

2.5.1 Features of IEEE 802.16d OFDM PHY Layer ........................................... 21

2.5.2 Features of IEEE 802.16e OFDM PHY Layer ............................................ 23

2.6 WiMAX MAC Layer ............................................................................................................. 24

2.7 Differences Between Fixed and Mobile WiMAX .................................................. 26

2.8 Spectrum Influence in WiMAX Network ................................................................... 26

2.8.1 WiMAX License Spectrum ..................................................................................... 26

2.8.2 WiMAX Unlicensed Spectrum ............................................................................ 27

2.9 Comparison of WiMAX with Other Wireless Technologies ............................. 28

2.9.1 A Comparison of WiMAX and 3G .................................................................... 29

2.9.2 WiMAX vs. Wi-Fi ..................................................................................................... 32

2.9.3 WiMAX vs. UMTS ................................................................................................... 33

2.9.4 WiMAX vs. LTE ........................................................................................................ 34

2.9.5 WiMAX vs. Ultra-Wide Band (UWB) Technology.................................. 35

2.10 Elements in WiMAX Network ..................................................................................... 36

2.10.1 WiMAX Radios....................................................................................................... 38

2.10.1.1 Macro and Micro Base Station ................................................... 38

2.10.1.2 WiMAX CPE ..................................................................................... 39

2.10.2 WiMAX Antennas................................................................................................ 40

2.11 Applications of WiMAX .................................................................................................. 42

2.12 WiMAX Advantages and Drawbacks ........................................................................ 43

2.13 Challenges of Deploying WiMAX............................................................................... 45

Chapter 3 : OFDM and MC-CDMA ........................................................................................ 46

3.1 Advantages of Multicarrier Modulation (MCM) ................................................... 46

3.2 Orthogonal Division Multiplexing (OFDM ) ........................................................... 49

3.2.1 OFDM Basic ................................................................................................................. 49

3.2.2 Orthogonality of Signals ........................................................................................ 52

3.2.3 Frequency Domain Orthogonality .................................................................... 55

3.3 OFDM System Implementation ..................................................................................... 57

3.4 Cyclic Prefix Addition ........................................................................................................ 59

3.4.1 Analysis of Cyclic Prefix in OFDM ................................................................ 60

3.4.2 ICI Analysis for OFDM systems ....................................................................... 64

3.5 OFDM System Design Consideration .......................................................................... 66

3.5.1 OFDM System Design Requirements ............................................................. 67

3.5.2 OFDM System Design Parameters.................................................................... 67

3.6 Throughput and Data rate of OFDM ............................................................................. 70

3.7 Benefits and Drawbacks of OFDM ................................................................................ 70

3.8 Application ………………………………………….................................................................. 72

3.8.1 OFDM Implementation in WiMAX…………………………………………. 73

3.8.2 OFDMA Technique ………….……………………………………...……………. 73

3.9 The MC-CDMA Principle …………………………………………...……….…………. 75

3.9.1 CDMA Basics ………………………………………………………………………. 76

3.9.2 Advantages of MC-CDMA …………..………………………...………………. 76

3.9.3 Applications …………………………………...………………..……………….……. 77

3.9.4 MC-CDMA System Model …………………..……………….….……..….…..…77

3.10 Spread Spectrum Techniques ……………………….………………..…….…….….…. 79

3.10.1 Multi-Carrier Spread Spectrum ………………..…………..………….……. 82

3.10.2 MC-CDMA and MC-DS-CDMA ………………………..…………...……. 82

3.10.3 Comparisons ………………………………………………..………..……………. 84

3.11 MC-CDMA System Implementation ……………………………..……….………. 85

Chapter 4 : Multipath Fading Channels ……………………...........................………….. 91

4.1 Propagation Characteristics of Mobile Radio Channels ………….…..……….. 92

4.1.1 Path loss and Shadowing ……………………………….………….…………… 93

4.1.2 Multipath Delay Spread ……………...………………….……………….……... 95

4.1.3 Multipath Fading Characteristics ……………………….……….…………... 99

4.1.3.1 Channel Fade Statistics …………………………..…….………….... 103

4.1.4 Doppler Spread ……………………………………………….....…….………….... 104

4.1.5 Spatial Characteristics, Coherence Distance ……...…….……...……….... 109

4.1.6 Co-Channel Interference ...…….………………………..……………....……… 110

4.2 Wireless Channel Modeling ...………...…………………………..…………....……… 112

4.2.1 Theoretical Channel Model …………………………………......……………… 112

4.2.2 Tapped Delay Line Model …………………………………..…...………...…… 113

4.2.3 Physical Channel Models ………………………………………...….………..… 114

4.2.4 Empirical Channel Models ………………………………...………….……….. 115

4.2.4.1 Stanford University Interim (SUI) Channel Models …….. 116

4.2.4.2 SUI channel models Implementation ……………………...…….. 119

4.2.4.3 COST-231 Hata Model ………………………………..………..……121

4.3 Multipath Fading Channels Simulation in MATLAB …………...………….….122

4.3.1 Specifying Fading Channels ……………………………………...……………. 125

4.3.2 Specifying the Doppler Spectrum of a Fading Channel …………….… 126

4.3.3 Creating Doppler Objects ………………………………………...……….…….. 126

Chapter 5 : Simulation Model ……………………………………………………….………….. 127

5.1 OFDM Symbol Description ………………………………………………….…….……. 128

5.2 OFDM Symbol Parameters for WiMAX ……………………………….……….….. 129

5.2.1 Number of data subcarriers …………………………………………...…………. 130

5.2.2 Number of pilots subcarriers ………………………………………….………… 130

5.2.3 Number of guard subcarriers ……………………………………………….…..130

5.2.4 Number of used subcarriers ………………………………………………….…..130

5.2.5 FFT size …………………………………………………………………………….…..130

5.2.6 Nominal Channel Bandwidth ……………………….……………………….…..130

5.2.7 Used Channel bandwidth ………………………….………………………….…..131

5.2.8 Sampling frequency …………………………………………………………….…..131

5.2.9 Sampling factor ……………………………….………………………………….…..132

5.2.10 Sampling time …………………………………….…………………………….…..132

5.2.11 Subcarrier spacing …………………………………… ……………………….…..132

5.2.12 Useful symbol time ………………………………..………………………….…..132

5.2.13 Guard period ratio ……………………………….…………………………….…..132

5.2.14 Cyclic Prefix Time ……………………………………..…………………….…..132

5.2.15 Frame duration ………………………………………………………………….…..133

5.2.16 Number of transmitted OFDM symbols per frame

………….……….…133

5.2.17 Total number of transmitted data symbols per frame …………………134

5.2.18 Total number of coded bits per frame ….……………………………….…..134

5.2.19 Total number of data bits per frame ………………………….…….…….…..134

5.2.20 Bit rate ………………………………………………………………….………….…..134

5.3 Simulation of WiMAX with OFDM System …………………….…….……..….…..137

5.3.1 Random Data Generation ……………………………………….……………..…..139

5.3.2 Channel Coding ………….………………………………………….………………..139

5.3.2.1 Randomization …………………………………………….……..…….…..139

5.3.2.2 Forward Error Correction ……………………………….………….….140

5.3.2.2.1 Reed Solomon Encoder …………………….…….….…..140

5.3.2.2.2 Convolutional Encoder ……………………….….…….…..143

5.3.2.3 Interleaver …………………………………………………….………....…..145

5.3.3 Data Symbols Modulation Mapper …………………………….………....…..146

5.3.4 Subcarriers Allocation …….……………………………………….…..…..……..148

5.3.5 IFFT …….……………………………………………………………..…….…....…..... 150

5.3.6 Cyclic Prefix Insertion ……………………………………………….………....…..152

5.3.7 The Transmitter and Receiver Filters ……………………………….…....……152

5.3.8 RF Up-Converter ……………………………………………………….………....….157

5.3.9 The Channel …………………………………………..………………….………....….159

5.3.10 Receiver …………………………………………………...……………….……....…..164

5.3.10.1 Channel Estimation and Equalization .………….….……....…..165

5.3.10.2 BER Calculations .……………………….………………………....…166

5.3.10.3 Spectral Efficiency Plot .………….…………………………....…..167

5.4 Simulation of WiMAX with MC-CDMA System .……………..….….…….....…..168

Chapter 6 : Simulation Results and Analysis ……………………...……………..…….... 170

6.1 Simulation Results of Fixed WiMAX with OFDM system …………..…….... 172

6.2 Simulation Results of Mobile WiMAX with OFDM system………..….…...… 187

6.3 Simulation Results of Fixed WiMAX with MC-CDMA system ….....…....… 197

6.4 Simulation Results of Mobile WiMAX with MC-CDMA system ..…....…… 226

6.5 The Effect of Equalization ..………………………………………………….…………... 242

6.6 Comparing Fading Channel and AWGN channel Performance …....…......… 243

6.7 Results from other simulation ..…………………………………………….………….... 247

Chapter 7 : Conclusion and Future Work ..……..………………………….….…………... 248

7.1 Conclusion .................................................................................................................................. 248

7.2 Future Work .............................................................................................................................. 253

Reference ....................................................................................................................................................256

Appendices .................................................................................................................................................261

A. Main Code ......................................................................................................................................262

B. Randomizer function .................................................................................................................274

C. RS encoder function ..................................................................................................................275

D. RS decoder function ..................................................................................................................276

E. subchannelization function ....................................................................................................277

F. spreading process .......................................................................................................................278

G. Some used built-in MATLAB Functions in the simulation …………………......279

Introduction

1.1 Wireless Broadband Beyond 3G

Wireless communication is facing one of the fastest developments of the last years in

the fields of technology and computer science in the world. According to the

Ericsson’s official forecasts, the addressable global market of wireless internet

broadband connectivity will reach to 320 million users by the end of 2010 [1]. Third

Generation (3G) mobile communication systems are already in deployment in several

countries and this has enabled whole new ways to communicate, access information,

conduct business and be entertained, liberating users from slow, cumbersome

equipment and immovable points of access. In a way, 3G has been the right bridge for

mobile telephony and the internet. 3G services enable users to make video calls to the

office and access to the internet simultaneously, or play interactive games wherever

they may be second and third generation systems like EDGE, IS-95 and WCDMA can

provide nominal data rates of about 50 – 384 Kbps [2]. While 3G is just transforming

itself into a reality from an engineer’s dream, research efforts are already on to look

into systems that can provide even higher data rates and seamless connectivity [3].

The current and future mobile systems are shown in Figure 1.1 where noted that the

increasing in data rates and mobility is a major goal in wireless communication

systems advance.

Figure 1.1 Current and future mobile systems [3].

Before describing the requirements of the next generation ,we can look at Figure

1.2 that shows the evolution of radio access. The first generation systems were

analog and could not provide data access. The second generation systems, which

were launched around 1995, had digital technologies and could work with data

access. However, the data transmission rate of these systems was not sufficient to

provide multimedia services. The third generation systems were launched around

2000 to provide multimedia services [4].

Figure 1.2 Mobile Multimedia services [4].

The rapid growth of internet and increasing interest in portable computing devices are

likely to push demand for high-speed wireless data services with aggregated higher

information bit rates. High throughput is needed especially in the downlink because

the number of downloads of large data files from web sites and servers are expected

to increase. 3G and Wireless broadband technologies are converging to accommodate

these requirements by Beyond 3rd

Generation (B3G) systems [5].

Such systems are categorized under Fourth Generation (4G) and are predicted to

provide packet data transmission rates of 100 Mbps in outdoor macro-cellular

environments and up to 1 Gbps in indoor and microcellular environments. While

wide-band systems could be a natural choice to provide high data rates, service

providers have to pay dearly for the spectrum necessary. Hence, spectrum efficiency

is always a factor on the choice of any wireless technology. Very wide-band systems

usually require complex receivers as the channel is frequency selective due to the

presence of large number of resolvable multipaths . Table 1.1 shows a comparison

between 2G , 2.5G , 3G and 4G.

Research has just recently begun on the development of 4th generation (4G) mobile

communication systems. Currently, there are several ongoing research projects

regarding the design and development of a high flexible and scalable next generation

(4G) mobile radio access concept with respect to high data rates and spectral

efficiency. For these 4G systems, several attractive candidates of transmission

TABLE 1.1 Comparison 2G, 2.5G, 3G and 4G.

GSM (2G) GPRS (2.5G) 3G 4G

Radio

Transmission

Tech.

Circuit-switched

Circuit-

switched,

packet-

switched

Packet-switched

Architecture MS, BSS , NS Base on GSM Base on GSM Hybrid

Frequency 1850~1990

MHz

1800~2400

MHz 2~8 GHz

Data Rate 9.6~19.2 kbps 64~115 kbps 115~384 kbps /

384~2000 kbps

2~20/100

Mbps

Access

Method TDMA / FDMA TDMA W-CDMA

OFDM,

MC-CDMA

systems exist [6,7,8]. Figures 1.3 and 1.4 show 4G objectives and 4G networks

respectively. 4G aims to optimal connectively anywhere, anytime, with any person /

object, through any network and on any device.

Figure 1.3 4G objectives.

Figure 1.4 4G Networks.

The commercial rollout of these systems is likely to begin around 2008 - 2012, and

will replace 3rd

generation technology. Few of the aims of 4G networks have yet been

published, however it is likely that they will be to extend the capabilities of 3G

networks, allowing a greater range of applications, and improved universal access.

Ultimately, 4G networks should encompass broadband wireless services, such as

High Definition Television (HDTV) (4-20 Mbps) and computer network applications

(1 - 100 Mbps). This will allow 4G networks to replace many of the functions of

WLAN systems. However, to cover this application, cost of service must be reduced

significantly from 3G networks. The spectral efficiency of 3G networks is too low to

support high data rate services at low cost.

As a consequence one of the main focuses of 4G systems will be to significantly

improve the spectral efficiency. In addition to high data rates, future systems must

support a higher Quality of Service (QoS) than current cellular systems, which are

designed to achieve 90 – 95 % coverage [9], i.e. network connection can be obtained

over 90 – 95 % of the area of the cell. This will become inadequate as more systems

become dependent on wireless networking. As a result , 4G systems are likely to

require a QoS closer to 98 - 99.5 %.

In order to achieve this level of QoS it will require the communication system to be

more flexible and adaptive. In many applications , it is more important to maintain

network connectivity than the actual data rate achieved. If the transmission path is

very poor, e.g. in a building basement, then the data rate has to drop to maintain the

link. Thus the data rate might vary from as low as 1 kbps in extreme conditions, to as

high as 20 Mbps for a good transmission path. Alternatively, for applications

requiring a fixed data rate, the QoS can be improved by allocating additional

resources to users with a poor transmission path.

As 3G and wireless broadband technologies are converging to form 4G , a significant

improvement in spectral efficiency will be required in order for 4G systems to provide

true broadband access. This will only be achieved by significant advances in multiple

aspects of cellular network systems, such as network structure, network management,

smart antennas, RF modulation, user allocation, and general resource allocation.

From the previous discussion , the 4G main demand is to investigate and develop a

new broadband air interface which can deal with high data rates, high mobility, high

capacity, and high QoS. We can summarize the requirements for next-generation

radio access below and describe some techniques for satisfying these requirements [4]:

1) High peak data rate operation :

• Wide frequency band operation

- Orthogonal frequency division multiplexing (OFDM)

• Improvement of spectral efficiency (more than 5 bit/s/Hz)

- Multiple input multiple output (MIMO) multiplexing

- Higher-order modulation

• Improvement of data rate at the cell edge

- Low-rate channel coding

- Interference coordination/cancellation

- Transmitter beamforming/adaptive array antenna reception

2) Multimedia operations

• Realize low-delay and highly reliable radio transmission using error control

techniques.

- Hybrid automatic repeat request (HARQ)

• Enable flexible allocation of radio resources according to the required transmission

rate and QoS.

- Orthogonal frequency division multiple access (OFDMA)

- Frequency and time domain scheduling

3) Operation conditions

• Support a maximum terminal speed of 100 km/h (preferably, a maximum of

approximately 300 km/h)

- Advanced channel estimation.

In general , we can say that the orthogonal frequency division multiplexing (OFDM)

in combination with Code division multiple access (CDMA) is considered to be the

method most likely to satisfy those requirements.

The goal of 4G is to have on the order of 100 Mbps link data in outdoor environments

and 1 Gbps in indoor channels. In fact, broadband system could be a choice to provide

high data rates. In the other word, service providers must pay for additional increase

in radio spectrum. Therefore, one of the biggest challenge in wireless system is a

design air-interface schemes to achieve higher bandwidth efficiencies with limited

radio spectrum.

Using the large bandwidth, the channel is frequency selective due to the presence of

large number of resolvable multipaths. It results in a large delay spread causing very

severe intersymbol interference (ISI). The MC-CDMA (multi-carrier code division

multiple access) is lately considered as a promising modulation technique for 4G. Its

benefits are based on the combination of OFDM and CDMA .

OFDM is to split the signal bandwidth into a large number of narrow subcarriers.

Then, it can support high data rate transmission over frequency selective channel

while symbol interval is so long that ISI can be reduced.

CDMA provides multiple access capability. However, the MC-CDMA performance

degrades resulted from multiple access interference (MAI) due to the loss of

orthogonality introduced by multipath channels [2].

The multi-carrier transmission have been considered as attractive technique offers the

desired high data rates for the 4G mobile environments and also has advantages for

spectral efficiency and low-cost implementation. The principle of multi-carrier

transmission is to convert a serial high rate data stream onto multiple parallel low rate

sub-streams. Each sub-stream is modulated on another sub-carrier. Since the symbol

rate on each sub-carrier is much less, than the initial serial data symbol rate, the

effects of delay spread, ISI significantly decrease.

Multi-carrier modulation, in particular OFDM, has been successfully applied to a

wide variety of digital communications applications over the past several years.

Although OFDM has been chosen as the physical layer standard for a diversity of

important systems, the theory, algorithms, and implementation techniques remain

subjects of current interest. This is clear from the high volume of papers appearing in

technical journals and conferences.

OFDM is a special case of multi-carrier transmission where the sub-carriers are

orthogonal. Prior to its use in wireless systems, OFDM was more common known as

DMT (Discrete Multi-Tone Transmission) and found use in ADSL (Asymmetric

Digital Subscriber Line).

A variation of OFDM is CDMA (MC-CDMA) which is an OFDM technique where

the individual data symbols are spread using a spreading code in the frequency

domain. The spreading code associated with MC-CDMA provides multiple access

technique as well as interference suppression.

MC-CDMA is the most promising candidate for this next generation of mobile radio

communication for achieving high data rate transmission.

OFDM is now a bandwidth efficient digital modulation technique that forms the basis

of many wireless standards currently under development. OFDM techniques are

extremely popular for wireless communications and are the base algorithm technology

for standards as IEEE 802.11, 802.16 and 802.20.

A lot of applications that use OFDM technology have initiated over the last few years.

For example, ADSL, Digital Audio Broadcasting (DAB) , Digital Video Broadcasting

(DVB) , Optical OFDM (IEEE 802.17) ,Wireless Local Area Networks (LANs)(

HIPERLAN/2, IEEE 802.11a , IEEE 802.11g) and Broadband Wireless Access

(BWA) Systems (IEEE 802.16).

The term WiMAX (Worldwide Interoperability for Microwave Access) has become

synonymous with the IEEE 802.16 Wireless Metropolitan Area Network (WMAN)

air interface standard. WiMAX was designed for the transmission of multimedia

services (voice, Internet, email, games and others) at high data rates. It is OFDM

based and can deliver speeds of 75 Mbps and can cover a distance of 50 km under

LOS conditions and typical cell radii of up to 5 miles (8 km) under NLOS conditions.

This technology is meant for the backhaul and wireless infrastructure needs on

WMANs and WWANs. It is based on IEEE802.16 standards designed for Broadband

Wireless Access (BWA) networks.

Fixed WiMAX based on IEEE 802.16d while Mobile WiMAX based on IEEE

802.16e. Mobile WiMAX technology had been incorporated in notebook computers

and PDA's in 2006 , allowing for urban areas and cities to become "Metro Zones" for

portable and mobile outdoor broadband access.

1.2 Motivations of The Thesis

What has been seen and observed in recent years is a remarkable increase in the

Broadband Wireless Access (BWA) networks as the need for broadband and mobile

services are getting into demand. BWA is increasingly acquiring a great deal of

popularity as an alternative "last-mile” technology to DSL and cable modems.

In today’s world, a large number of wireless transmission technologies exist. These

technologies are distributed over different network families depending upon the

network scale such as PAN, WLAN, WMAN and WAN. As the demand for data

transmission with higher rates changed so is the focus on the deployment of wireless

networks. Technologies that promise to deliver higher data rates are attracting more

and more vendors and operators towards them. One of the most promising candidates

of such arising technologies is WiMAX.

Many researchers do believe that WiMAX can move the wireless data transmission

concept into a new dimension. There are basically three limiting factors for

transmitting high data rate over the wireless medium that mainly include multipath

fading, delay spread and co-channel interference . The published WiMAX standard

(IEEE 802.16d) describes a MAC layer and five physical layers, each suitable for

particular application and frequency range [10]. Wireless MAN-OFDM is one of them

[11]. The Wireless MAN-OFDM interface can be extremely limited by the presence

of fading caused by multipath propagation and as result, the reflected signals arriving

at the receiver are multiplied with different delays, which cause Inter-symbol

interference (ISI). OFDM basically is designed to overcome this issue and for

situations where high data rate is to be transmitted over a channel with a relatively

large maximum delay. If the delay of the received signals is larger than the guard

interval, ISI may cause severe degradations in system performance.

Recent studies have combined CDMA with Orthogonal Frequency Division Multiplex

(OFDM) to allow efficient use of available spectrum while retaining many advantages

available in the CDMA system. This combination of OFDM-CDMA (MC-CDMA) is

a useful technique for 4G systems where you need variable data rates as well as

reliable communication systems. By making a hybrid combination of OFDM and

CDMA, MC-CDMA enjoys the advantages of both systems.

WiMAX is one of the hottest broadband wireless technologies around today. And this

gave me motivation to make this research for study and comparison the performance

of the OFDM and MC-CDMA systems used for fixed and mobile WiMAX.

1.3 Objectives and Thesis Plan

The main objective of this thesis is to implement and simulate the fixed and mobile

WiMAX using OFDM and MC-CDMA by MATLAB and study the system

performance for the two systems to see the enhancement of MC-CDMA over OFDM.

This involves studying, through simulation, the various PHY modulation, coding

schemes and interleaving in the form of bit error rate (BER) performance under

reference channel models. Thesis plan is as following :

1) Understanding the WiMAX

2) Understanding the theory and principle of OFDM and MC- CDMA.

3) Understanding multi-path fading channels.

4) Choosing the system models parameters that makes the simulation possible.

5) The complete system will be simulated and tested by MATLAB.

6) Results are analysed and Conclusion is given

1.4 Structure of The thesis

The first Chapter is an introduction of the thesis work. The rest of the chapters are

organized as follows :

Chapter 2 gives a background of WiMAX technology including its various standards,

equipments , advantages and disadvantages .

Chapter 3 discusses in detail the OFDM and MC-CDMA techniques. The principles

of OFDM and MC-CDMA are given in general view.

Chapter 4 discusses the multipath fading channels and presents the method to model

the channel in wireless communication. SUI channel models ,which are widely used

in Fixed WiMAX simulation , and COST 231, used for Mobile WiMAX , are given in

this chapter.

Chapter 5 explains in details the simulation models. The block diagram of every part

of the system is given and how it works.

In Chapter 6 we present the simulation results of Fixed and Mobile WiMAX using

OFDM and MC-CDMA. The results are discussed and compared for different

modulation schemes and channel coding.

Chapter 7 concludes the thesis work and also includes the future work that can be

conducted by using the useful information presented in this thesis.

The MATLAB codes are given in Appendices A ot G to help students and researchers

to produce the results presented in this thesis and compare them with their work.