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

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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

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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

xvi

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

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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.

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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

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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

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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.