Free Space Optical Communication (eBook)

Hemani Kaushal is currently working as Associate Professor at The NorthCap University (former name ITM University), Gurgaon, India. Dr. Kaushal received her Ph. D degree from the Electrical Engineering Department, Indian Institute of Technology Delhi (IITD), New Delhi, India. She completed her Master of Engineering in Electronics Product Design and Technology from the Punjab Engineering College University of Technology (PECUT), Chandigarh and Bachelor’s degree in Electronics and Communication Engineering from Punjab Technical University (PTU), Punjab, India. She has worked on various industry sponsored projects related to free space optical communication for Indian Space Research Organization (ISRO) and Aeronautical Development Agency (ADA), India. Her areas of research include wireless communication systems specifically in free-space, underwater, and indoor visible-light optical communications. She has over 30+ publications in international journals and conferences. She has received best presentation award in International Conference on Light: OPTICS’11 held at National Institute of Technology (NIT), Calicut, Kerala, India in May 2011. She also received second best award on National Science Day held at IIT Delhi in Feb 2011. She is a life member of Indian Society of Technical Education (ISTE) and member of Institute of Electrical and Electronics Engineers (IEEE), USA. Virander Kumar Jain is working as Professor of Electrical Engineering at IIT Delhi. He obtained his Master of Science (Electronics) degree in 1973 from the Meerut University, India. He did M.Sc. (Tech.) in Electronics from the Birla Institute of Technology and Science (BITS) Pilani in 1975. He completed his Ph. D in Communication Engineering from IIT Delhi. His research areas are photonics switching and networking, optical fiber and optical space communications, optoelectronic instrumentation, wireless communications, digital communications, noise study and modeling. He has published over 160 papers in various International and National journals and conferences. He has also co-authored 2 books entitled “Optical Communication Systems” and “Optical Communications: Components and Systems”. He is a life member of ISTE, Senior Member, IEEE and Fellow, Institution of Electronics and Telecommunication Engineers (IETE), India. Subrat Kar is a Professor of Electrical Engineering at IIT Delhi. His research interests are optics, embedded telecom systems, telecom transmission and switching, automotive networks, deep space communications and bio-medical instrumentation. Dr. Kar has over 80 journal publications to his credit. He has also co-authored a book titled “Optical Fiber Communication: Principles and Systems”.

Preface 7
Contents 9
List of Figures 13
List of Tables 19
List of Symbols 21
List of Abbreviations 26
1 Overview of Wireless Optical Communication Systems 29
1.1 Introduction 29
1.1.1 History 32
1.1.2 Indoor Wireless Optical Communication 33
1.1.2.1 Types of Link Configurations 34
1.1.3 Outdoor/Free-Space Optical Communication 38
1.2 Comparison of FSO and Radio-Frequency Communication Systems 40
1.3 Choice of Wavelength in FSO Communication System 42
1.4 Range Equation for FSO Link 43
1.5 Technologies Used in FSO 48
1.5.1 Direct Detection System 49
1.5.1.1 Baseband Modulation 50
1.5.1.2 Statistical Model for Direct Detection 51
1.5.1.3 Subcarrier Modulation 54
1.5.2 Coherent Detection 55
1.5.3 Optical Orthogonal Frequency-Division Multiplexing 57
1.6 Eye Safety and Regulations 60
1.7 Applications of FSO Communication Systems 62
1.8 Summary 65
Bibliography 65
2 Free-Space Optical Channel Models 68
2.1 Atmospheric Channel 68
2.1.1 Atmospheric Losses 71
2.1.1.1 Absorption and Scattering Losses 71
2.1.1.2 Free-Space Loss 74
2.1.1.3 Beam Divergence Loss 74
2.1.1.4 Loss due to Weather Conditions 76
2.1.1.5 Pointing Loss 79
2.1.2 Atmospheric Turbulence 80
2.1.2.1 The Effect of Beam Wander 83
2.1.2.2 The Scintillation Effect 86
2.1.3 Effect of Atmospheric Turbulence on Gaussian Beam 90
2.1.3.1 Conventional Rytov Approximation 93
2.1.3.2 Modified Rytov Approximation 96
2.2 Atmospheric Turbulent Channel Model 97
2.3 Techniques for Turbulence Mitigation 103
2.3.1 Aperture Averaging 104
2.3.2 Spatial Diversity 107
2.3.3 Adaptive Optics 109
2.3.4 Coding 110
2.3.5 Hybrid RF/FSO 111
2.4 Summary 112
Bibliography 113
3 FSO System Modules and Design Issues 117
3.1 Optical Transmitter 118
3.1.1 Choice of Laser 120
3.1.2 Modulators 122
3.1.2.1 Modulation Schemes 124
3.2 Optical Receiver 125
Background noise: 126
Dark current noise: 128
Signal shot noise: 128
Thermal noise: 129
3.2.1 Types of Detectors 129
3.2.2 Receiver Configuration 131
3.2.2.1 Coherent PSK Homodyne Receiver 132
3.2.2.2 Coherent FSK Heterodyne Receiver 134
3.2.2.3 Direct Detection (PIN+OA) Receiver for OOK 134
3.2.2.4 Direct Detection (APD) Receiver for OOK 136
3.2.2.5 Direct Detection (APD) for M-PPM 138
3.3 Optical Post and Preamplifiers 139
3.4 Link Design Trade-Off 141
3.4.1 Operating Wavelength 141
3.4.2 Aperture Diameter 142
3.4.3 Receiver Optical Bandwidth 142
3.5 Summary 143
Bibliography 144
4 Acquisition, Tracking, and Pointing 145
4.1 Acquisition Link Configuration 145
4.1.1 Acquisition Uncertainty Area 148
4.1.1.1 Probability Distribution Function of Satellite Position 149
4.1.2 Scanning Techniques 150
4.1.3 Acquisition Approach 153
4.1.4 Beam Divergence and Power Criteria for Acquisition 155
4.2 Tracking and Pointing Requirements 156
4.3 Integration of Complete ATP System 159
4.4 ATP Link Budget 160
4.5 Summary 162
Bibliography 162
5 BER Performance of FSO System 164
5.1 System Model 164
5.2 BER Evaluation 164
5.2.1 Coherent Subcarrier Modulation Schemes 166
5.2.2 Noncoherent Modulation Schemes 170
5.2.2.1 On Off Keying 170
5.2.2.2 M-ary Pulse-Position Modulation 173
5.2.2.3 Differential PPM 175
5.2.2.4 Differential Amplitude Pulse-Position Modulation 178
5.2.2.5 Digital Pulse Interval Modulation 179
5.2.2.6 Dual Header-Pulse Interval Modulation 181
5.3 Summary 184
Bibliography 184
6 Link Performance Improvement Techniques 186
6.1 Aperture Averaging 186
6.1.1 Aperture Averaging Factor 187
6.1.1.1 Plane Wave with Small lo 187
6.1.1.2 Plane Wave with Large lo 188
6.1.1.3 Spherical Wave with Small lo 189
6.1.1.4 Spherical Wave with Large lo 189
6.2 Aperture Averaging Experiment 191
6.3 Diversity 193
6.3.1 Types of Diversity Techniques 195
6.3.2 Diversity Combining Techniques 196
6.3.3 Alamouti's Transmit Diversity Scheme 200
6.3.4 Two Transmitter and One Receiver Scheme 201
6.3.5 BER Performance with and Without Spatial Diversity 203
6.4 Coding 206
6.5 Channel Capacity 207
6.5.1 Channel Coding in FSO System 208
6.5.1.1 Convolutional Codes 209
6.5.1.2 Low Density Parity Check Codes 212
6.6 Adaptive Optics 214
6.7 Relay-Assisted FSO Transmission 217
6.8 Summary 218
Bibliography 219
7 Link Feasibility Study 221
7.1 Link Requirements and Basic Parameters 221
7.1.1 Transmitter Parameters 222
7.1.2 Atmospheric Transmission Loss Parameter 224
7.1.3 Receiver Parameters 224
7.2 Link Power Budget 225
7.3 Summary 227
Bibliography 228
Index 229