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SIMULATION AND PERFORMANCE ANALYSIS OF THE SUB CARRIER
MULTIPLEXED RADIO OVER FIBER SYSTEM
MAHYUDDIN BIN ARSAT
UNIVERSITI TEKNOLOGI MALAYSIA
To my beloved mother and father
ii
ACKNOWLEDGEMENT
In preparing this thesis, I was in contact with many peoples, researchers,
academicians and practitioners. With a deep sense of gratitude, I wish to express my
sincere thanks to my supervisor, Dr. Sevia Mahdaliza Idrus, for her immense help in
carrying out the project. Profound knowledge and timely with came as a boon under
the guidance of Dr. Sevia M. Idrus. Her valuable suggestions as final words during
the course of work are greatly acknowledge.
The acknowledgement would not be complete without the mention of my
project master colleagues at Universiti Teknologi Malaysia, Hamim bin Nasoha and
Hilman bin Harun for their timely help on simulation session during my research.
I also want to thank my parent, who taught me the value of hard work by
their own example. I would like to share this moment of happiness with my father,
mother, sisters and brothers. They rendered me enormous support during he whole
tenure of my project.
Finally, I would like to thank all whose direct and indirect support helped me
completed my thesis.
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ABTRACT
Radio over Fiber (RoF) technology or micro cellular over fiber is proposed
solution for the reducing cost and providing highly reliable communication services.
The system is a technique that modulates RF in microwave signals on an optical
carrier to take advantage of the low loss of optical fiber characteristic. The RoF
system is very cost-effective because the localization of signal processing in central
station and also use a simple base station. In this system, the subcarrier multiplexed
system for data transmission has been developed and the performance of the system
was analyze in term of signal power, Bit Error Rate (BER), Carrier-to-Noise ratio
(CNR) and Eye diagram. This system was focus on a link between two stations; a
transmitter and receiver. The designed of SCM-RoF system employing PSK as the
RF modulation scheme. In this work, the transmitter presenting four input signal and
each of the signal will be modulate using PSK individually. At the optical domain,
the CW Laser diode was used as the optical source, while Mach Zender as the
optical modulator. Whereby, the transmission link was modelled using standard
single mode fiber up to 150 km communication distance with EDFA 0m – 5m
length. At the receiver end, the light carrying the radio subcarrier multiplexed signal
is photo-detected by a PIN photodiode.
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ABSTRAK
Teknologi penghantaran Radio melalui Fiber (RoF) telah memperkenalkan
pengurangan kos dan penyediaan servis komunikasi yang boleh dipercayai. Sistem
ini merupakan teknik memodulatkan isyarat frekuensi radio dengan isyarat pembawa
optik dengan memanupulasi kelebihan kadar kehilangan yang rendah yang ada pada
karakter fiber optik. Sistem RoF ini juga sangat kos-effektif kerana system ini
manjalankan pemprosesan isyrat secara berpusat dan hanya memerlukan stesen
utama yang ringkas. Sistem subcarrier multiplexed untuk sistem penghantaran data
telah dibangunkan dan prestasi sistem ini telah dianalisi menerusi Kadar Ralat Bit
(BER), Nisbah Pembawa dan Hingar (CNR) dan rajah mata. Sistem ini
memfokuskan pengahantaran melalui satu penghantar dan satu pernerima. Sistem ini
juga menggunakan PSK sebagai teknik memodulat isyarat. Pada kajian ini, empat
saluran isyarat RF telah diperkenalkan yang mana setiap isyarat dimodulatkan
dengan teknik PSK. CW laser telah digunakan sebagai sumber optik dan modulator
Mach Zender digunakan sebagai modulator optik. Selain itu, Fiber satu mod (SMF)
telah digunakan pada talian penghantaran dengan kadar jarak maksimum 150 km
serta EDFA pada kadar 0 m – 5m. Pada bahagian penerima pula, pengesan optik
PIN telah digunakan untuk mengesan isyarat termodulat tersebut.
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
TITLE PAGE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF SYMBOLS xv
LIST OF ABBREVIATIONS xvi
LIST OF APPENDICES xvii
1 INTRODUCTION 1
1.1 Historical Perspective 1
1.2 Project Background 2
1.3 Objectives 4
1.4 Scope of work 4
1.5 Methodologies 5
1.6 Thesis Outline 7
2 LITERATURE REVIEW 9
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2.1 Radio over Fiber 9
2.2 Sub Carrier Multiplexing 10
2.7.1 Analog SCM System 13
2.7.2 Digital SCM System 13
2.3 Optical Modulator 14
2.3.1 Mach-Zender Modulator 14
2.3.2 Electrooptic Phase Modulator 15
2.4 Light Source 20
2.5 Fiber Link 22
2.7.1 Step-Index Fiber 22
2.7.2 Graded-Index Fiber 25
2.6 Optical Amplifier 26
2.7.1 Noise 29
2.7.2 Gain Saturation 30
2.7.3 Inhomogeneous Broadening Effects 30
2.7.4 Polarization Effects 31
2.7 Receiver Part 32
2.7.1 Receiver Sensitivity 33
2.7.2 Dynamic Range 34
2.7.3 PIN Photodetector 36
2.7.4 Avalanche Photodetector 39
2.7.5 Photodetector Noise 42
3 SCM – ROF MODELLING 43
3.1 The Transmitter Model 45
3.2 The Transmission Link Model 49
3.3 The Receiver Model 51
4 SIMULATION RESULT 54
4.1 The Transmitter Simulation Results 55
4.2 The Transmission Link Simulation Results 58
4.3 The Receiver Simulation Results 59
4.4 The Eye Diagram 62
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5 PERFORMANCES ANALYSIS 65
5.1 Analysis on Fiber Length without EDFA Introduced 65
5.1.1 The Bit Error Rate Performances 66
5.1.2 The Carrier to Noise Ratio Performances 68
5.1.3 The Eye Diagram 69
5.2 Analysis on EDFA Length 70
5.2.1 The Carrier to Noise Ration Performances 71
5.2.2 The Bit Error Rate Performances 72
5.2.3 Quality Factor 73
5.2.4 The Eye Diagram 74
5.3 Analysis on Fiber Length with EDFA 74
5.3.1 The Carrier to Noise Ratio Performances 75
5.3.2 The Bit Error Rate Performances 76
5.3.3 Quality Factor 77
5.3.4 The Eye Diagram 78
5.4 Analysis on nonlinearity due to optical power level 79
5.4.1 The Bit Error Rate Performances 80
5.4.2 The Carrier to Noise Ratio 81
5.4.3 Quality Factor 82
5.4.4 The Eye Diagram 83
5.5 Analysis on number of channels in the system. 83
5.5.1 The Bit Error Rate Performances 84
5.5.2 The Carrier to Noise Ratio 85
5.5.3 The Eye Diagram 86
6 CONCLUSION AND RECOMMENDATION 87
6.1 Conclusion 87
6.2 Recommendation 89
6.3 Future Work 90
6.4 Publication 91
x
REFERENCES 89
APPENDIX A 94
APPENDIX B 96
xi
LIST OF TABLES
TABLE NO TITLE PAGE
2.1 Typical Step-Index Fiber characteristic 22
3.1 Global simulation setup 44
3.2 Subcarrier frequency allocation 45
3.3 Spectrum frequency 45
3.4 Simulation setup for EDFA 48
3.5 Simulation setup for Single Mode Fiber 48
3.6 Simulation setup for APD Photo detector 51
5.1 Basic Simulation Specification for Analysis on
Fiber Length 64
5.2 Basic simulation setup for Analysis on EDFA length 68
5.3 Basic simulation setup for SCM_ROF with EDFA 73
5.4 Basic simulation setup for nonlinearity of power levels 77
5.5 Frequency allocation for 8 channels 81
6.1 Length of fiber with reasonable BER 86
xii
LIST OF FIGURE
NO TITLE PAGE
1.1 Basic architecture of a single end-to-end SCM system 3
1.2 The project flow chart 6
2.1 A basic configuration of SCM system. 8
2.2 Basic configuration of RF modulation 10
2.3 Basic configuration of Optical modulator 12
2.4 The spectrum of Optical Double Side Band (ODSB) 12
2.5 The spectrum of Optical Single Side Band (OSSB) 13
2.6 Basic configuration of Optical Modulator for OSSB 14
2.7 The optical signals modulated by a single wavelength. 17
2.8 Basic architecture of using Phase Modulator. 17
2.9: Step-Index Fiber. (a) Refractive index profile.
(b) End view.(c) Cross-sectional side view. 21
2.10 Graded-Index Fiber. (a) Refractive index profile.
(b) End view.(c) Cross-sectional side view. 24
2.11 Schematic diagram of a simple Doped Fiber Amplifier 25
2.12 A basic structure of PIN diode 26
2.13 Cross-sectional view of PIN diode 35
2.14 Energy-band diagram under reserve bias 35
2.15 Structure of an APD 38
2.16 Gain versus reverse bias characteristic of APD 39
3.1 Model of four channels SCM-ROF system. 42
3.2 Transmitter for electrical domain 43
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3.3 Transmitter for optical domain. 46
3.4 Transmission link 50
3.5 The receiver for optical domain. 51
4.1 Signal wave modulated by PSK 53
4.2 (a) RF spectrum for data signal on first channel
(3.6 GHz). 54
(b) RF spectrum for data signal on second
channel (7.2 GHz). 54
(c) RF spectrum for data signal on third
channel (10.8 GHz). 54
(d) RF spectrum for data signal on fourth
channel (18.0 GHz). 54
4.3 RF spectrum for adding four channels. 55
4.4 Amplified composite signal 55
4.5 Spectrum of the signal after Mach Zender modulator. 56
4.6 Optical spectrum after EDFA. 57
4.7 Optical spectrum after propagated 65km in fiber. 57
4.8 RF spectrum detected by photo detector 58
4.9 Amplified received RF spectrum 58
4.10 RF spectrum for channel 1 59
4.11 Received electrical signal wave 59
4.12 Eye Diagram for the channel 1. 60
4.13 Eye Diagram for the channel 2. 61
4.14 Eye Diagram for the channel 3. 61
4.15 Eye Diagram for the channel 4. 61
5.1 BER Performance for channel 1. 65
5.2 BER Performance for channel 4. 65
5.3 CNR for the all channels. 66
5.4 Eye diagram for channel 1 67
5.5 CNR for 4 channels 69
5.6 Log of BER for 4 channels 70
5.7 Q factor versus EDFA length. 71
5.8 Eye Diagram for channel 1 72
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5.9 CNR performance for 4 channels 74
5.10 BER performance for 4 channels 75
5.11 Quality factor for 4 channels. 75
5.12 Eye diagram for fiber length 1 km to 150 km 76
5.13 BER for channel 1 versus optical power. 78
5.14 BER for channel 2 79
5.15 CNR for versus optical power 79
5.16 Q factor for channel 1 and 2. 80
5.17 The eye diagram for channel 1 80
5.18 BER performance for 8 channels 82
5.19 CNR performance for 8 channels 83
5.20 The eye diagram for channel 5 84
5.21 Eye diagram for channel 6 84
xv
LIST OF SYMBOLS
f : Frequency
λ : Lambda
P0 : Input optical power
Lis : Insertion loss
φBias : Bias phase shift
Vл : Half wave voltage
c : Critical angle,
∆ : Refractive index change
n1 : Refractive index
Er+3 : Erbium ion
J : Quantum number
dB : Decibel
N : Average number of electrons
T : Bit interval of time
m : Number of electrons generated
η : Quantum efficiency
ρ : Resistivity
Ω : Ohm
GHz : Giga Hertz
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LIST OF ABBREAVIATIONS
TDM : Time Division Multiplexed
FDM : Frequency Division Multiplexed
SCM : Sub Carrier Multiplexed
WDM : Wavelength Division Multiplexed
SCM-ROF : Sub Carrier Multiplexed Radio over Fiber
CNR : Carrier to Noise Ratio
BER : Bit Error Rate
EDFA : Erbium Doped Fiber Amplifier
MZM : Mach Zehnder modulator
FM : Frequency modulation
AM-VSB : Amplitude modulation with vestigial sideband
IMD : Intermodulation distortion
ODSB : Optical Double Side Band
OSSB : Optical Single Side Band
SCM/WDM : Sub Carrier Multiplexed and wavelength-division
multiplexing
LO : Local Oscillator
DFB LD : Distributed-feedback laser diode
ASE : Amplified Spontaneous Emission
PSC : Plastic-cladded silica fiber
PDG : Polarization Dependent Gain
LNA : Low noise amplifier
RMS : Root-mean-square
xvii
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Graph for Extended Performances Analysis 94
B Published Conference Papers 96
CHAPTER 1
INTRODUCTION
1.1 Historical perspective
The technology of communication in huge bandwidth was the global demand
either for industrial field or consumer interest. Basically, drastic demand of high
bandwidth on communication was cause of a new communication application which
required higher bandwidth such as internet video and audio and others new
application. In recent years, optical communications networks are finally feeling the
bandwidth constraints already in other type of communication networks such as
wireless and satellite communication systems. In fact, service providers are searching
a ways to increase their fiber optic network capacity.
Optical communication was one of the best ways in term of high bandwidth data
communication. Even there a lot of parameters that will affect the performance of
optical communication especially in term of dispersion and attenuation, server
providers were have full of excitation to use optical fiber as medium. Technology like
TDM, FDM, SCM and WDM and their combination are used and improved the
performance of the optical communication.
2
The use of subcarrier multiplexing (SCM) transmission using an optical carrier
instead of the traditionally used super carrier over optical fibers is very attractive. This
technology has found wide spread application because of its simplicity and cost-
effectiveness.
Error correction coding techniques, such a block convolution, and trellis, have
advanced, further enhancing the noise immunity of multi state modulation scheme.
Hus, the type of modulation mentioned plus coding techniques can be very good
candidates for SCM application.
1.2 Project Background.
This project was focus on a link between two station; one transmitter and
receiver. The link was applying SCM and Radio Over Fiber (ROF) system the
schemes that has been applied to perform the communication system were PSK as a
RF modulation techniques.
For this project, the transmitter has been focus only four input signal and each
of the signal will be modulate using PSK individually. All the input signals so called
as data signals has been multiplexed and allocated closely to each other. At the optical
domain, the optical source was used CW Laser diode and Mach Zender modulator
which is an external optical modulator. The composite signal (multiplexed signals)
has been modulated with single optical wavelength by the MZM.
3
The transmission link has been replaced the typical transmission line (coaxial
cable) with optical fiber. The system used a standard single mode fiber for long haul
communication system which was able to exceed several kilometre. However, in this
study, several components has been introduced or applied in the system such as
optical amplifier which was post-amplifier and pump laser. Other than that, in the
electrical domain, numbers of Band Bass Filter (BPF) has been applied at the
transmitter and receiver part as well. In other to achieved better Carrier to Noise Ratio
(CNR) of the system, electrical amplifier has been introduced after multiplexer and
before demultiplexer.
At the receiver end, the light carrying the microwave subcarrier multiplexed
composite signal is photo-detected by a photodiode. For this project, the system
applies PIN as a photo detector at the receiver part.
Figure 1.1: Basic architecture of a single end-to-end SCM system
4
1.3 Objectives
The objectives on this project are:
1) To model and simulate optical Sub Carrier Multiplexed – Radio over Fiber
(SCM-ROF) System.
2) To analyze the performance of the SCM-ROF System in term of CNR, BER,
Quality Factor, losses and attenuation.
1.4 Scope of Work
The scopes of this project are:
1) Modeled and analyzed specific to Sub Carrier Multiplexed – Radio Over Fiber
System.
2) Completed a transmission system included single transmitter, optical link and
single receiver.
5
1.5 Methodologies
The methodology of this project has been followed the list below and flow chart
found in Figure 1.2
1) Full understand and literature review on current development of the optical
system especially Sub Carrier Multiplexed – Radio over Fiber (SCM-ROF)
System.
2) The system architecture has been identified and modeled.
3) The system has been modeled which was represented the connection from
transmitter to receiver.
4) Suitable simulation software has been identified and applied to the system
which was OptiSystem software.
5) The analysis of the system has been on to Fiber length without EDFA
introduced, EDFA length, Fiber length with EDFA, nonlinearity due to optical
power level, and number of channel in the system.
6) The system performances have been represented by the BER, CNR, Q Factor
and eye diagram.
6
START
Literature review on current development of the optical system especially Sub Carrier Multiplexed – Radio over Fiber (SCM-ROF)
System.
Identify and modeled system architecture.
Model the connection from transmitter to receiver.
Identify the simulation software.
Analysis of the system will be on to Fiber length without EDFA introduced, EDFA length, Fiber length with EDFA, nonlinearity due to
optical power level, and number of channel in the system.
The system performances have been represented by the BER, CNR, Q Factor and eye diagram.
END
Figure 1.2: The project flow chart
7
The project has been following the basic outline that shows by the flow chart.
However, there were several parameter need to be concern before shift one to another
analysis. It was vital process especially that contributed the changes of frequency at
the electrical domain and data rate of the incoming signals.
In addition, each of the components applied in the system has their own
contribution in the system performance. Therefore, knowing the function,
characteristic, response and also the parameters all the components was an obligation
to the researchers before get through the simulation stage.
Last but not least, the performance analysis has been represented with suitable
graphs, diagrams, and tables which were able to be referring for further study and the
results compatible for some practical and industrial needs.
1.6 Thesis Outline
This project report is organized into 6 chapters which are introduction,
literature review, SCM-ROF modeling, simulation results, performances analysis,
conclusion and recommendation.
The first chapter will be discussed on the project background, scope of work
and the methodologies applied in this project. In depth reviewed of the theoretical and
previous study will be presented in the chapter 2 with literature review as the title.
The reviewed will be cover from the basic knowledge of SCM system until to the
8
receiver part of the system. In chapter 3, the system of SCM-ROF will be discuss and
describe the model for this project. In this chapter also presented the basic simulation
setup from the modeled system. The simulation results will be presented and the
issues involved will be explained in details in the chapter 4. These issues include
general simulation method; simulation implementation of the modulations, optical
fiber, and PMD issues. This chapter also presented the RF spectrum, electrical wave,
eye diagram and optical spectrum for the system.
In chapter 5, the simulation results will be focused on five different of analysis
of SCM-ROF system which was analysis on fiber length without EDFA introduced,
analysis on EDFA length, analysis on fiber length with EDFA, analysis on
nonlinearity due to optical power level, and analysis on number of channels in the
system. These analyses will be presented the system performances by BER, CNR,
Quality Factor and Eye Diagram as well.
And finally, in chapter 6, the thesis is concluded and the problems that need
further studies are discussed and prospected. All publications paper also will be
mentioned in this particular chapter.