DEVELOPMENT OF A DYNAMIC FREQUENCY
HOPPING CODE SYSTEM FOR OPTICAL CODE
DIVISION MULTIPLE ACCESS
COMMUNICATIONS
MOHAMMAD MAHMOUD NAJI AHMAD
HAMARSHEH
DOCTOR OF PHILOSOPHY
UNIVERSITI PUTRA MALAYSIA
2006
DEVELOPMENT OF A DYNAMIC FREQUENCY HOPPING CODE
SYSTEM FOR OPTICAL CODE DIVISION MULTIPLE ACCESS
COMMUNICATIONS
BY
MOHAMMAD MAHMOUD NAJI AHMAD HAMARSHEH
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia,
in Fulfilment of Requirement for the Degree of Doctor of Philosophy
July 2006
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To the future of my nation
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Abstract of the thesis presented to the Senate of Universiti Putra Malaysia in
fulfilment of the requirement for the degree of Doctor of Philosophy
DEVELOPMENT OF A DYNAMIC FREQUENCY HOPPING CODE
SYSTEM FOR OPTICAL CODE DIVISION MULTIPLE ACCESS
COMMUNICATIONS
By
MOHAMMAD MAHMOUD NAJI AHMAD HAMARSHEH
July 2006
Chairman: Associate Professor Mohamad Khazani Abdullah, PhD
Faculty: Engineering
In this work, a novel method of optical code division multiple access (OCDMA)
communication system is proposed. This method is based on a code changes
dynamically as a function of time and frequency. Thus, the system is referred to as
dynamic frequency hopping OCDMA (DFH-OCDMA). The fundamental principles
are defined and described with implementation solutions for DFH-OCDMA system.
DFH-OCMDA system implementation based on tunable optical filter is found to be
an effective solution. Tunable optical filter is found to be able to provide a simple,
programmable, and effective solution for the encoding and decoding functions. Only
one filter at the encoder and one more at the receiver are required to implement the
proposed coding scheme. Special simple codes based on orthogonal sinusoidal
functions are also proposed for DFH-OCDMA system. These codes are generated
and used to control the tunable optical filters. The effectiveness of the new system
with the proposed special codes has been verified and demonstrated using theoretical
analysis and computer simulations. Theoretical analysis has been done using
4
MATLAB and MathCAD softwares, while Optisystem 3.0 is used for the computer
simulations. A clipping scheme at the receiver is also proposed to enhance the
performance of the system and reduce the multiple access interference.
The performance results of DFH-OCMDA system shows that the effect of all types
of noise, specifically, multiple access interference, phase induced intensity noise, and
shot noise have been reduced compared to other OCDMA systems. Thus, the signal
to noise ratio and bit error rate performance parameters are improved. For example,
at an error rate of 1110− , DFH-OCDMA can accommodate up to 80 users, whereas for
other systems, the maximum simultaneous users are 32 for spectral amplitude coding
system using Hadamard code, 52 for spectral amplitude coding system using
modified quadratic congruence code, 58 for spectral amplitude coding system using
modified frequency hopping code, and 24 for fast frequency hopping system. The
BER of the DFH-OCDMA system is increasing at a slower rate than that of the other
systems, which indicates that there is a significant improvement in performance at
large number of users. Indeed it is shown that the BER for DFH-OCDMA is better
than any other system at any number of users of more than 50. However, for less
than 50 active users, spectral amplitude coding systems gives BER better than that of
DFH-OCDMA system. It should be noted that for this range of users, the error rate is
too small (less than 1410− ).
5
Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai
memenuhi keperluan untuk ijazah Doktor Falsafah
PEMBANGUNAN SISTEM KOD LOMPATAN FREKUENSI DINAMIK
UNTUK KOMUNIKASI CAPAIAN PELBAGAI PEMBAHAGIAN KOD
OPTIK
Oleh
MOHAMMAD MAHMOUD NAJI AHMAD HAMARSHEH
Julai 2006
Pengerusi: Profesor Madya Mohamad Khazani Abdullah, PhD
Falkulti: Kejuruteraan
Di dalam kajian ini, suatu kaedah novel bagi sistem komunikasi optikal capaian
pelbagai pembahagian kod (OCDMA) telah di perkenalkan. Kaedah yang di gunakan
ini berasaskan perubahan kod secara dinamik sebagai fungsi antara masa dan
frekuensi. Sistem ini dikenali sebagai Frekuensi Dinamik Hoping OCDMA (DFH-
OCDMA). Prinsip asas telah di jelaskan secara terperinci beserta dengan
penyelesian penggunaan bagi sistem DFH-OCDMA ini.
Pelaksanaan sistem DFH-OCDMA berasaskan penapis bolehlaras optikal dan ini di
kenalpasti sebagai suatu penyelesian yang berkesan. Penapis bolehlaras optikal di
kenalpasti berkeupayan menyediakan suatu penyelesaian yang mudah, tersusun dan
berkesan bagi fungsi enkoder dan dekoder. Hanya satu penapis di perlukan pada
enkoder dan satu pada penerima di perlukan bagi pelaksaanan skim pengkodan yang
di cadangkan. Suatu kod mudah yang khas berasaskan fungsi sinusoidal yang
orthogonal juga di cadangkan bagi sistem DFH-OCDMA ini. Kod yang di hasilkan
ini di gunakan untuk mengawal penapis bolehlaras. Keberkesanan sistem baru ini
yang di lengkapi dengan kod baru yang telah di cadangkan telah di buktikan secara
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analisa teoritikal dan simulasi komputer. Analisa secara teortiikal di hasilkan
mengunakan perisan MATLAB dan MathCAD dan manakala simulasi komputer
menggunakan perisian Optisystem 3.0. Kami juga mencadangkan suatu skim yang
di kenali sebagai skim pengetipan pada bahagian penerima untuk meningkat prestasi
sistem serta mengurangkan gangguan capaian pelbagai (MAI).
Keputusan prestasi bagi sistem DFH-OCDMA dapat mengurangkan kesan yang di
sebabkan oleh semua jenis ganguan hingar terutamanya adalah ganguan capaian
pelbagai (MAI), hingar PIIN dan letusan berbanding dengan sistem OCDMA yang
lain. Dengan ini prestasi nisbah isyarat-hingar (SNR) dan kadar ralat bit (BER) dapat
di tingkatkan. Sebagai contoh, pada kadar ralat bit 1110− sistem ini dapat menampung
sehingga 80 pengguna, manakala sistem lain, sistem yang mengunakan keadah
pengkodan amplitud spektra dan kod Hadamard hanya dapat menampung maksima
32 penguna, 52 pengguna untuk sistem menggunakan kod MQC, 58 pengguna untuk
sistem menggunakan kod MFH dan 24 pengguna untuk sistem FFH. Kadar ralat bit
(BER) bagi sistem. DFH-OCDMA meningkat pada kadar yang perlahan berbanding
sistem lain dan ini merupakan suatu peningkatan prestasi pada kadar pengguna yang
tinggi. Kadar ralat bit (BER) bagi sistem DFH-OCDMA lebih baik berbanding
sistem lain pada yang melebihi 50 pengguna. Walau bagaimanapun, untuk sistem
yang kurang daripada 50 pengguna kaedah pengkodan amplitud spektra memberikan
kadar ralat bit yang lebih baik daripada sistem DFH-OCDMA. Pada julat pengguna
ini, kadar ralat bit adalah terlalu rendah (kurang daripada 1410− )
7
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I would like to deeply thank my supervisor, Associate Professor Dr. Mohammad
Khazani Abdullah for his valuable support and guidance for me through my research
studies at University Putra Malaysia. I will never forget his constant support and the
chance he gave me to do my PhD study.
I also want to thank Professor Dr. Hossam M. H. Shalaby for his valuable ideas,
comments and advices. Although we have not met but all our extensive discussions
through e-mails are very helpful to me during most phases of the work. His
experience in the field of OCDMA was very helpful for me. I hope we can meet one
day and I can do some extra research work with him.
My thanks are also extended to my supervisory committee members Associate
Professor Dr. Mohamad Adzir Mahdi and Dr. Sabira Khatun for their valuable
comments and discussions. I would like also to thank all photonics lab members who
make the study in the lab enjoyable.
I am grateful to my mother who always encourages me to get the PhD. May Allah
bless my father who was supporting me in my first degree and encouraging me to go
further. Thanks are also extended to all my brothers and sisters.
Finally, I would like to express my deepest gratitude to my wife Rasha Hamarsha for
her love, support, patience, and taking care of our baby Obada during the last few
years.
8
I certify that an Examination Committee has met on 24 July 2006 to conduct the final
examination of Mohammad Mahmoud Naji Ahmad Hamarsheh on his Doctor of
Philosophy thesis entitled "Development of a Dynamic Frequency Hopping Code
System for Optical Code Division Multiple Access Communications" in accordance
with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti
Pertanian Malaysia (Higher Degree) Regulations 1981. The Committee recommends
that the candidate be awarded the relevant degree. Members of the Examination
committee are as follows:
Adznan bin Jantan, PhD Associate Professor
Faculty of Engineering
Universiti Putra Malaysia
(Chairman)
Borhanuddin bin Mohd. Ali, PhD Professor
Faculty of Engineering
Universiti Putra Malaysia
(Internal Examiner)
Sudhanshu Shekhar Jamuar, PhD Professor
Faculty of Engineering
Universiti Putra Malaysia
(Internal Examiner)
Kazuro Kikuchi, PhD Professor
Research Center for Advanced Science and Technology
University of Tokyo
(External Examiner)
__________________________________
HASANAH MOHD GHAZALI, PHD Professor/Deputy Dean
School of Graduate Studies
Universiti Putra Malaysia
Date :
9
This thesis submitted to the Senate of Universiti Putra Malaysia and has been
accepted as fulfilment of the requirement for the degree of Doctor of Philosophy.
The members of the Supervisory Committee are as follows:
Mohammad Khazani Abdullah, PhD Associate Professor
Faculty of Engineering
Universiti Putra Malaysia
(Chairman)
Mohamad Adzir Mahdi, PhD Associate Professor
Faculty of Engineering
Universiti Putra Malaysia
(Member)
Sabira Khatun, PhD Associate Professor
Faculty of Engineering
Universiti Putra Malaysia
(Member)
__________________
AINI IDERIS, PhD Professor/Dean
School of Graduate Studies
Universiti Putra Malaysia
Date:
10
DECLARATION
I hereby declare that the thesis is based on my original work except for the quotations
and citations, which have been duly acknowledged. I also declare that it has not been
previously or concurrently submitted for any other degree at UPM or other
institutions.
_________________________________
MOHAMMAD MAHMOUD NAJI
AHMAD HAMARSHEH
Date:
11
TABLE OF CONTENTS
DEDICATION 2
ABSTRACT 3
ABSTRAK 5
ACKNOWLEDGMENTS 7
APPROVAL 8
DECLARATION 10
LIST OF TABLES 14
LIST OF FIGURES 15
LIST OF ABBREVIATIONS 19
CHAPTER
1 INTODUCTION 21 1.1 Fiber Optic Communication 21
1.2 Problem Statement and Motivation 22
1.3 Aim and Objectives 27
1.4 Brief Methodology 28
1.5 Contribution 30
1.6 Organization of the Thesis 31
2 REVIEW ON OPTICAL CODE DIVISION MULTIPLE
ACCESS SYSTEMS 33 2.1 Multiple Access Techniques 33
2.1.1 Time Division Multiple Access 33
2.1.2 Wavelength Division Multiple Access 35
2.1.3 Code Division Multiple Access 37
2.2 Optical Code Division Multiple Access 38
2.3 Optical Code Division Multiple Access Schemes 39
2.3.1 Coherent Optical Code Division Multiple Access
Systems 40
2.3.2 Incoherent Optical Code Division Multiple Access
Systems 45
2.4 Optical Code Division Multiple Access Codes 51
2.4.1 Maximal Length Codes 52
2.4.2 Gold Codes 52
2.4.3 Prime Codes 53
2.4.4 Optical Orthogonal Codes 54
2.4.5 Hadamard Code 55
2.4.6 Modified Quadratic Congruence Code 55
2.4.7 Modified Frequency Hopping Code 57
2.5 Mathematical Models of Optical Code Division Multiple
Access Systems 59
2.5.1 Optical Direct Sequence and Fast Frequency Hopping
Systems Model 59
12
2.5.2 Spectral Amplitude Coding System Model 62
2.6 Design Issues of Optical Code Division Multiple Access
Systems 64
3 DYNAMIC FREQUENCY HOPPING OCDMA
DESCRIPTION AND IMPLEMENTATION PRINCIPLES 66 3.1 Introduction 66
3.2 Dynamic Frequency Hoping OCDMA Principle of Operation 66
3.2.1 Transmitter Description 66
3.2.2 Mathematical Model of Encoded Signal 67
3.2.3 Mathematical Model of Decoded Signal 69
3.2.4 Transmitter Configuration 71
3.3 Encoding and Decoding 73
3.3.1 Coding Based on Tunable Optical Filter 74
3.3.2 Coding Based on Chirped Fiber Bragg Grating 76
3.4 Receiver Design 78
3.4.1 Receiver Structure Based on Tunable Optical Filter 78
3.4.2 Receiver Structure Based on Chirp Fiber Bragg
Grating 79
3.5 Conclusion 80
4 ANALYTICAL MODEL OF DYNAMIC FREQUENCY
HOPPING OCDMA SYSTEM 81 4.1 Introduction 81
4.2 System Configuration 81
4.2.1 Functional Codes Construction 83
4.2.2 Bit Rate Capacity 85
4.2.3 Modulation Format 87
4.3 System Mathematical Modeling 88
4.4 Mathematical Modeling of Performance Parameters 90
4.4.1 Correlation Properties of the Codes 90
4.4.2 Noise Effect and Signal to Noise Ratio 91
4.4.3 Bit Error Rate 96
4.5 Conclusion 97
5 ANALYTICAL RESULTS AND PERFORMANCE
ANALYSIS OF DYNAMIC FREQUENCY HOPPING
OCDMA SYSTEM 98 5.1 Introduction 98
5.2 Simulation Design Parameters 98
5.3 Signal Representation 102
5.4 Performance Simulation Results 104
5.4.1 Noise Analysis and Comparison 105
5.4.2 Cross Correlation 110
5.4.3 Signal to Noise Ratio 110
5.4.4 Bit Error Rate 112
5.4.5 Effect of Tunable Optical Filter (TOF) Bandwidth 113
5.4.6 Effect of the Functional Codes Parameters 115
5.4.7 System Performance Comparison 117
5.5 Conclusion 119
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6 PERFORMANCE ENHANCEMENT OF DYNAMIC
FREQUENCY HOPPING OCDMA BY SIGNAL CLIPPING 121 6.1 Signal Clipping 122
6.2 Mathematical Modeling 123
6.2.1 System Modeling 123
6.2.2 Performance Modeling 125
6.3 Performance Analytical Calculation Results 126
6.3.1 Multiple Access Interference 126
6.3.2 Signal to Noise Ratio 128
6.3.3 Bit Error Rate 129
6.4 Conclusion 130
7 SIMULATION RESULTS OF DYNAMIC FREQUENCY
HOPPING OCDMA SYSTEM 131 7.1 Introduction 131
7.2 System Configuration 131
7.3 Components Description 132
7.3.1 Code Generator 133
7.3.2 Encoder and Decoder 133
7.4 Simulation Results and System Comparison 134
7.4.1 Input Power Effect on the System 137
7.4.2 Effect of Bit Rate on the Performance of the System 141
7.5 Conclusion 145
8 CONCLUSION AND FUTURE WORK 146 8.1 Conclusion 146
8.2 Future Work 149
APPENDICES 150
REFERENCES 175
BIODATA OF THE AUTHOR 186
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LIST OF TABLES
Table Page
1.1 Design and performance parameters of the proposed DFH-
OCDMA system 29
5.1 Typical parameters used in the calculations 101
15
LIST OF FIGURES
Figure Page
2.1 Frame and slot structure with basic TDMA 34
2.2 WDMA long distance fiber transmission link. 36
2.3 Block diagram of OCDMA network 38
2.4 Block diagram of the coherent DS-OCDMA system 41
2.5 Block diagram of the pulsed based temporal phase CDMA
system 42
2.6 Block diagram of an ultra-short pulse OCDMA system 44
2.7 DS-OCDMA system encoders 47
2.8 Spectral amplitude coding CDMA system 48
2.9 Optical FFH-CDMA system configuration 50
3.1 (a) DFH-OCDMA transmitter configuration (b) Data signal
and the spectrum after each device in the transmitter 67
3.2 Encoder output signal for (a) DFH-OCDMA system using
shifted sine code (b) FFH-OCDMA system using random
code of weight 6. 68
3.3 Transmitter design using tunable laser source 72
3.4 Transmitter design using tunable optical filter 72
3.5 Transmitter design using chirp fiber Bragg grating 73
3.6 Spectrum of the encoded signal 74
3.7 Decoding procedure of interfering signal (a) The optical
frequency as function of time at a point of interference (b)
The intensity of the optical signal at five different time
shots near the interference point 76
3.8 Encoding and decoding principle using chirped FBG 77
3.9 Receiver block diagram of a DFH-OCDMA system using
TOF 79
16
3.10 Receiver block diagram of a DFH-OCDMA system using
chirp FBG 80
4.1 Block diagram of dynamic OCDMA system. 82
4.2 (a) The power spectral density of one signal at the output of
one decoder using the proposed sine shifted functions
family. (b) The photocurrent at the output of the photo
detector at the same receiver. 85
4.3 TOF (a) central wavelength and (b) speed along the data bit
interval 87
5.1 Power spectral density of encoded signal 102
5.2 Power spectral density of the signal at the input of the
decoder 103
5.3 Power spectral density of an optical signal at the output of
the decoder for “101” transmitted data bit stream 103
5.4 Photocurrent as function of time for “101” transmitted data
bit stream 104
5.5 Different noises as function of average received power 105
5.6 Comparison of noise effect on DFH-OCDMA and its
relation to the number of active users 106
5.7 Effect of the number of users on SNR considering only
MAI 107
5.8 PIIN comparison with SAC-OCDMA system at different
values of received power 107
5.9 PIIN comparison with SAC-OCDMA system at different
number of simultaneous users 108
5.10 Effect of received power on shot noise in DFH and SAC-
OCDMA systems 109
5.11 Shot noise as function of number of users 109
5.12 Cross correlation function between two different SSC
codes 110
5.13 SNR as function of the number of simultaneous active
users 111
5.14 SNR against received power at different numbers of active
users 111
5.15 Bit error rate as function of simultaneous active users 112
17
5.16 Probability of error versus effective power from each user
when K=110 113
5.17 The effect of TOF bandwidth on DFH-OCDMA system
performance 114
5.18 Signal and noise power at the receiver of DFH system as
function of TOF bandwidth 115
5.19 The effect of SSC phase shift on the BER of DFH-
OCDMA system 116
5.20 Effect of SSC code frequency on the BER of DFH-
OCDMA system 116
5.21 BER performance of DFH-OCDMA as function of SSC
code amplitude 117
5.22 DFH-OCDMA BER performance comparison 118
5.23 DFH-OCDMA BER comparison as function of received
power 119
6.1 Schematic diagram of DFH-OCDMA system with signal
clipper 122
6.2 Signal clipping at the output of the photocurrent (a) The
photocurrent signal before clipping (b) The photocurrent
signal after clipping 123
6.3 MAI of clipped system compared with MAI of unclipped
system 127
6.4 The effect of received power on the MAI for both clipped
and unclipped systems 127
6.5 SNR for both clipped and unclipped DFH-OCDMA system 128
6.6 SNR against received power for both clipped and unclipped
systems 128
6.7 BER as function of simultaneous users for both clipped and
unclipped systems 129
6.8 BER as function of average received power for both
clipped and unclipped systems 130
7.1 Configuration of DFH-OCDMA system simulated with
Optisystem 3.0 software. 132
7.2 Input of the code generator (solid line) and the functional
code output (dashed lines). 133
18
7.3 Eye pattern of the dynamic frequency hopping system at -
10 dBm input power and 155 Mbps bit 134
7.4 SAC-OCDMA system using Hadamard code simulated
with Optisystem 3.0 software. 135
7.5 Configuration of SAC-OCDMA system using MFH code
simulated with Optisystem 3.0 software. 135
7.6 Eye pattern of the spectral amplitude coding system using
Hadamard code at 155Mbps 136
7.7 Eye pattern of the spectral amplitude coding system using
MFH code at 155Mbps. 137
7.8 Effect of input power on the bit error rate of the DFH-
OCDMA system 138
7.9 Effect of input power on the eye opening of DFH eye
diagram 139
7.10 Effect of input power on the quality factor of DFH
compared with SAC systems 140
7.10 Effect of input power on the output optical power of the
DFH and SAC systems 141
7.11 Effect of bit rate on the bit error rate of the DFH and SAC
systems 142
7.12 Effect of bit rate on the eye opening of DFH and SAC
systems 143
7.13 Effect of bit rate on the quality factor of DFH and SAC
systems 143
7.14 Effect of bit rate on the output power of the DFH and SAC
systems 144
19
LIST OF ABBREVIATIONS
ASE Amplified Spontaneous Emission
ASK Amplitude Shift Keying
AWG Array Waveguide
BER Bit Error Rate
CDMA Code Division Multiple access
DCF Dispersion Compensating Fiber
DFH Dynamic Frequency Hoping
DS Direct Sequence
EDFA Erbium Doped Fiber Amplifier
ERFC Error Function Complementary
FBG Fiber Bragg Grating
FFH Fast Frequency Hoping
FH Frequency Hopping
FWHM Full Wave Half Maximum
Gbps Giga bit per second
GF Galois Field
IM/DD Intensity Modulation/Direct Detection
LAN Local Area Network
LED Light Emitting diode
MAI Multiple Access Interference
Mbps Mega bit per second
MFH Modified Frequency Hoping
MQC Modified Quadratic Congruence
20
NRZ Non Return to Zero
OCDMA Optical Code Division Multiple access
OOC Optical Orthogonal Code
OOK On-Off Keying
PIIN Phase Induced Intensity Noise
PIN Positive Intrinsic Negative
PRBS Pseudo Random Binary Sequence
PSD Power Spectral Density
RF Radio Frequency
SAC Spectral Amplitude Coding
SLM Spatial Light Modulator
SMF Single Mode Fiber
SNR Signal to Noise Ratio
SOA Semiconductor Optical Amplifier
SONET Synchronous Optical Network
SSC Sine Shifted Code
TDM Time Division Multiplexing
TDMA Time division Multiple Access
TLS Tunable Laser Source
TOF Tunable Optical Filter
WDMA Wavelength Division Multiple access
