THE PERFORMANCE OF OFDM IN MOBILE RADIO CHANNEL

TEDDY PURNAMIRZA

A thesis submitted in fulfilment of the requirements for the award of the Degree of

Master of Engineering (Electrical-Electronic & Telecommunication)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

APRIL 2005

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Dedicated to my beloved Papa and Mama

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ACKNOWLEGMENT

First of all, I would like to thank God “Allah SubhanaWaTaala” for

his mercy and charity. In preparing this thesis, I have been helped by many people.

In particular, I would like to express my deepest appreciation to my supervisor,

Encik Amerrudin Baharom for his invaluable guidance in the completion of this

thesis. Special thanks to Accociate Prof. Dr. Norsheila Fisal, Accociate Prof. Dr.

Mazlina and Dr. Kamal for their suggestions and correction to my thesis.

My appreciation, thanks and love to Papa and Mama and all my

family members who always give me support and love. To someone that always give

me inspiration

Many thanks to all my course mates especially to Hafiz, Samsul,

Kseven, Lester for their friendship and kindliness. You all are the best.

Last but not at least, I would like to address my thanks to my hostel

mates, “Tun Safar” for his delicious mie ayam, to Aan and bang Herman for their

asam padeh dagiang, to Doni for his salty sala lauak, to Mr Liem, don’t know when

we will play badminton again, to Jasril and bang Nesdi who helped me when I first

arrived in Johor. Also to all people that I can not mention their names one by one that

have directly or indirectly help me in completing my study and thesis.

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ABSTRACT

OFDM as a transmission technique has been known having a lot of

strengths compared to any other transmission technique, such as its high spectral

efficiency, its robustness to the channel fading, its immunity to impulse interference

and its ability in handling very strong echoes.

It is mentioned in several papers and by the OFDM theory itself that

because of its strength, OFDM can overcome the effect of several radio impairment

factors such as the effect of AWGN, impulse noise, multipath fading, etc. In

addition, several papers proposed OFDM as a transmission technique either in fixed

or mobile radio channel. The efficacy of OFDM implementation in many areas such

as DAB (Digital audio Broadcasting), DVB (Digital Video Broadcasting) and

Wireless LAN has gained its popularity.

This project is to study and investigate the effect of some radio

channel impairment factors to the performance of OFDM as well as to study and

investigate the performance of OFDM in mobile radio channel including rural

channel, urban channel, terrain channel and rician channel.

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ABSTRAK

OFDM merupakan suatu teknik perhubungan yang terkenal

mempunyai kelebihan tersendiri berbanding dengann teknik perhubungan lainnya,

contohnya ia mempunyai efesiensi spekra yang tinggi, keteguhan terhadap

pemudaran saluran komunikasi, kekebelannya terhadap gangguan impuls dan

kemampuannya menangani echo.

Beberapa kertas penyelidikan dan teori OFDM menyatakan bahawa

disebabkan oleh kelebihannya, OFDM mampu mengatasi kesan kesan yang

disebabkan oleh faktor faktor penjejasan perhubungan radio, seperti AWGN,

gangguan hingar impuls, kesan berbilan laluan dan lain lain. Tambahan pula,

beberapa kertas penyelidikan mengusulkan OFDM sebagai teknik perhubungan sama

ada untuk saluran radio tetap mahupun saluran radio bergerak. Kejayaan penerapan

OFDM diberbagai aplikasi seperti DAB, DVB dan wireless LAN menyebabkan ia

semakin populer.

Projek ini bertujuan untuk menyelidiki dan memahami kesan faktor faktor penjejasan

terhadap prestasi OFDM dan menyelidiki prestasi OFDM didalam saluran radio

bergerak, meliputi saluran kawasan terpencil, saluran kawasan bandar, saluran

kawasan terbuka dan saluran rician.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xiii

LIST OF APPENDICES xiv

LIST OF ABBREVIATIONS xv

CHAPTER 1 INTRODUCTION

1.1 Project Background 1

1.2 Objective 2

1.3 Scope of Project 2

1.4 Organization of Thesis 3

CHAPTER 2 BASIC THEORY AND LITERATURE REVIEW

2.1 The principles of OFDM 4

2.2 OFDM History 6

2.3 OFDM Operation 8

2.3.1 Definition of the Orthogonality 8

2.3.2 Preliminary Concepts 9

2.3.3 Definition of Carriers 10

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2.3.4 Modulation 11

2.3.5 Transmission 16

2.3.6 Reception and Demodulation 18

2.3.7 Guard Period 21

2.4 The Strength and Weakness of OFDM 23

2.4.1 OFDM uses much more efficient bandwidth 23

2.4.2 OFDM Overcomes the Effect of ISI 24

2.4.3 OFDM Combats the Effect of Frequency Selective Fading 25

2.4.4 The weakness of OFDM 26

2.5 Mobile Radio Channel 27

2.5.1 Attenuation 28

2.5.2 Multipath Effects 29

2.5.2.1 Rayleigh Fading 29

2.5.2.2 Frequency Selective Fading 30

2.5.2.3 Delay Spread 31

2.5.3 Doppler Shift 32

CHAPTER 3 THE SIMULATION MODEL OF OFDM SYSTEM

3.1 The Simulation Model of OFDM System 35

3.1.1 Random Data Generator 35

3.1.2 Serial to Parallel Conversion 36

3.1.3 Modulation of Data 36

3.1.4 Inverse Fourier Transform 36

3.1.5 Guard Period 36

3.1.6 Parallel to Serial Conversion 37

3.1.7 Channel 37

3.1.8 Receiver 38

3.2 Flowchart for OFDM Transceiver 38

3.3 OFDM Simulation Parameters 43

CHAPTER 4 SIMULATION RESULT AND ANALYSIS

4.1 The Effect of AWGN 46

4.2 The Effect of Power Clipping 47

4.3 The Effect of Delay Spread 49

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4.4 The Effect of Impulse Noise 50

4.5 The Performance of OFDM in Urban Channel 52

4.6 The Performance of OFDM in Rural Channel 53

4.7 The Performance of OFDM in Terrain Obstructed Channel 54

4.8 The Performance of OFDM in Rician Channel 55

4.9 The Effect of Mobile Velocity 56

4.10 Conclusion Table 60

CHAPTER 5 CONCLUSION AND FUTURE WORKS

REFERENCE 62

APPENDIX A MATLAB PROGRAM CODE 67

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LIST OF TABLES

TABLE NO TITLE PAGE

2.1 Typical shadowing in a radio channel

2.2 Cummulatif Distribution for Rayleigh distribution

2.3 Typical delay spread

3.1 Simulation parameters for OFDM transceiver

3.2 Power delay profile for mobile radio channel

4.1 Conclusion of Analysis

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Parameter Mapping from Time to Frequency for the DFT

2.2 OFDM Carrier Magnitude Prior to IFFT

2.3 OFDM Carrier Phase Prior to IFFT

2.4 OFDM Signal, 1 Symbol Period

2.5 Separated Components of the OFDM Time Waveform

2.6 OFDM Time Waveform

2.7 OFDM Spectrum

2.8 OFDM Carrier Magnitude following FFT

2.9 OFDM Carrier Phase following FFT

2.10 Guard Period via Cyclic Extension

2.11 Spectrum of Orthogonal Carriers

2.12 Traditional versus OFDM Transmission

2.13 An OFDM Signal Time Waveform

2.14 Radio Propagation Effects

2.15 Multipath Signal

2.16 Multipath Delay Spread

3.1 The Model for OFDM System

3.2 The Flowchart for transmit Function

3.3 The Flowchart for genrand Function

3.4 The Flowchart for receive Function

3.5 The Flowchart for Main Program

4.1 BER verses SNR for OFDM in AWGN channel using

BPSK, QPSK and 16 PSK Modulation

4.2 BER verses Power Clipping for OFDM System Using

BPSK, QPSK and 16PSK Modulation

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4.3 BER verses SNR for OFDM in Noisy Channel using BPSK,

QPSK and 16PSK

4.4 BER verses Normalized Length of Impulse Noise

4.5 BER verses SNR in Urban Channel

4.6 BER verses SNR in Rural Channel

4.7 BER verses SNR in Terrain Obstructed Channel

4.8 BER verses SNR in Rician Channel

4.9 BER verses SNR for OFDM System using QPSK

Modulation in Urban Channel for Varying Mobile Velocities

4.10 BER verses SNR for OFDM System using 16PSK

Modulation in Urban Channel for Varying Mobile Velocities

4.11 BER verses SNR for OFDM System using BPSK

Modulation in Urban Channel for Varying Mobile Velocities

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A OFDM Matlab Program Code

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LIST OF ABBREVIATIONS

OFDM - Orthogonal Frequency Division Multiplexing

DVB - Digital Video Broadcasting

DAB - Digital Audio Broadcasting

LAN - Local Area Network

PAPR - Peak to Average Power Ration

BPSK - Binary Phase Shift Keying

QPSK - Quadrature Phase Shift Keying

16PSK - 16 Phase Shift Keying

COFDM - Coded Orthogonal Frequency Division Multiplexing

FDMA - Frequency Division Multiple Access

TDMA - Time Division Multiple Access

ICI - Inter Carrier Interference

DMT - Discrete Multi Tone

MCM - Multi Carrier Modulation

DFT - Discrete Fourier Transform

QAM - Quadrature Amplitude Modulation

CNR - Carrier to Noise Ratio

HDSL - High bit rate Digital Subscribers Line

VHDSL - Very High speed Digital Subscriber Line

HDTV - High Speed Digital Television

FFT - Fast Fourier Transform

IFFT - Inverse Fast Fourier Transform

AWGN - Additive White Gaussian Noise

SNR - Signal to Noise Ratio

ISI - Inter Symbol Interference

BER - Bit Error Rate

FEC - Forward Error Correction

RF - Radio Frequency

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FM - Frequency Modulation

UHF - Ultra High Frequency

CDMA - Code Division Multiple Access

DBPSK - Differential Binary Phase Shift Keying

DQPSK - Differential Quadrature Phase Shift Keying

D16PSK - Differential 16 Phase Shift Keying

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CHAPTER 1

INTRODUCTION

1.1 Project Background

Nowadays, the mobile telecommunications industry faces the

problem of providing the technology that be able to support a wide variety of

services ranging from voice communication with a bit rate of a few kbps to wireless

multimedia in which bit rate up to 2 Mbps. In order to support that kind of

technology, third generation (3rd) for mobile communication is now being developed,

and still not be mature yet.

Several systems have been proposed as candidate for the 3rd

generation mobile telecommunication system, OFDM is one of proposed system that

have a lot of attentions for some reasons.

The first reason is that the successful implementation of OFDM in

several applications. OFDM has successfully been implemented in the wireless

broadcasting applications such as DVB (Digital Video Broadcasting) and DAB

(Digital Audio Broadcasting). Recently, OFDM has been successfully used in

wireless LAN application. Standard such as IEEE 802.11a and HIPERLAN/2 are the

results of the growing interest in OFDM. [1]

The second reason is that OFDM has a lot of advantages compared to

the conventional systems. OFDM uses spectrum efficiently by spacing its carriers as

close as possible, this is enabled by making the carriers orthogonal to each other.

2

Since OFDM can overcome the effect of multipath fading by using a guard period,

OFDM need only a simple equalization method in combating selective fading

channels [2]. The weakness of an OFDM system is its sensitivity to frequency offset

and its high Peak to Average signal Power Ratio (PAPR) [1].

Since OFDM has a lot of advantages compared to conventional

systems and the successfulness of its implementation, therefore it is interesting and

challenging to investigate the characteristic and performance of this systems in

mobile radio channel.

1.2 Objective

The main objective of this project is to study and investigate the effect

of several radio channel impairment factors to the performance of OFDM system as

well as to study and investigate the performance of OFDM in mobile radio channel.

1.3 Scope of Project

The scope of this project is limited to OFDM system with IFFT size

512 and number of carrier 200. The guard period type used is a cyclic extension of

symbol where has the length of 20 percents of length of symbol. The useful part of

OFDM symbol is 40 us and the length of guard period is 8 us. The carrier spacing is

1/40 us = 25 KHz so that the 5 MHz bandwidth is occupied with 200 carrier. The

total symbol rate of this system is 40/48x 5 MHz = 4.166 Msps.

In this project, The OFDM transceiver used three modulation

techniques those are BPSK, QPSK and 16 PSK to show the trade off between system

capacity and system robustness. The mobile radio channel is modeled based on

model that explained in subchapter 3.3 and its delay profile parameter is taken from

reference 28.

3

The OFDM system is simulated using Matlab 6.5 and all the

simulation results are represented in term of Bit Error Rate (BER) in 2-D graph.

1.4 Organization of Thesis

The first chapter briefly introduces this project by explaining the

project background, objectives and scope of project.

Second chapter were written based on study literature reading,

covering the explanation of basic theory of OFDM transceiver and radio mobile

channel.

Third chapter explains about the model of OFDM system including

OFDM transmitter, OFDM receiver, and mobile radio channel. The simulation

parameters that were used in this simulation and the OFDM model program

flowcharts are also explained

The simulation results and its analysis are presented in chapter four

along with its conclusions.

Chapter 5 concludes the analysis results and propose some future

works that can be done in order to dig this project deeper and wider.

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CHAPTER 5

CONCLUSION AND FUTURE WORK

As the conclusion, the objectives of this project have been achieve. The study

and investigation on the performance of OFDM signal in mobile radio channel including

rural channel, urban channel, terrain obstructed channel and rician channel have been

done as well as the study and investigation several effect of radio channel impairment

factors such as AWGN, impulse noise, delay spread.

Below are the conclusion of about the study results:

• Since OFDM is not intended to combat the noise effect, it is observed and

concluded that the performance of OFDM is similar to a standard single

carrier digital transmission

• OFDM signal is resistant enough to clipping distortion caused by nonlinearity

in power amplifier

• The effect of multipath can be eliminated by using guard period, as long as

guard period is longer than delay spread.

• OFDM signal can tolerate impulse noise

• OFDM for this particular simulation shows good enough performance in

rural, urban and rician channel

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• For this particular simulation, OFDM signal can not be used in rural channel.

To make it acceptable in rural channel, it is needed to add guard period time

longer than delay spread (16 us)

• Mobile velocity does not effect significantly to the performance of OFDM.

Although the objective of this project has been achieved successfully,

it is still need further study in order to dig this project deeper and wider. Several

suggested future works that can be done are listed below

• In this project, several factors including the effect of AWGN, clipping, delay

spread and impulse noise have been simulated, more work can be done on

investigating the effect of frequency stability error, the effect of phase offset

and the effect of phase noise

• In this project, OFDM was simulated in its basic system without applying any

error correction method, equalization and interleaving. Future work can be

done on investigating the effect of these factors in order to increase the

performance of OFDM.

• Future work can be also done on comparing the performance of OFDM using

different modulation techniques

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