THE PERFORMANCE OF OFDM IN MOBILE RADIO CHANNEL...
Transcript of THE PERFORMANCE OF OFDM IN MOBILE RADIO CHANNEL...
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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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 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.
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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.
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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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