System Design and Modeling of Optical Scattering Communications = 광 산란 통신 시스템 설계 및 모델링

다국어 초록 (Multilingual Abstract)

Demand for optical wireless communications (OWCs) is growing at a rapid pace. There is a growing interest from the commercial and the military in having secure, efficient, and high bandwidth OWC systems for tactical applications. An OWC system relies on optical wavelength, ranging from infrared to ultraviolet (UV) to convey a piece of information. With recent advances in the design and manufacturing of UV sources and detectors, optical scattering communication has attracted much interest for diverse applications. Atmospheric scattering in the deep UV band is much higher than other optical bands. This phenomenon enables establishing of a non-line-of-sight (NLOS) link. This thesis is devoted to the system design and modeling of various aspects of optical scattering communications employing ultraviolet wavelength. It provides the most comprehensive NLOS optical scattering communication systems design and modeling.

The focus of the studies discussed in the second chapter is to investigate the spatial diversity techniques for optical scattering communications. With the received signal characterized by a continuous waveform detector, the switch and stay combining (SSC) diversity technique is implemented at the receiver over correlated turbulence fading channel. Next, to avoid the requirement of an adaptive threshold in demodulating the on-off keying (OOK) symbol, the SSC diversity technique equipped with M-ary phase-shift keying (MPSK) is presented. The chapter also presents a maximal selection transmit diversity for optical scattering communications.

The third chapter presents techniques for optical spectrum sensing for distributed optical scattering communications. First, we develop an energy detection-based optical spectrum sensing for a UV network where each user is equipped with a continuous waveform detector. Second, we propose a new generic blind optical spectrum sensing technique. The proposed technique is based on finding the statistical ratio of the received continuous waveform signal. It does not require prior knowledge of the signal and noise power. Next, we propose two novel cooperative spectrum sensing techniques for optical scattering communication networks with randomly distributed collaborative users pointing in arbitrary directions. In particular, we present centralized- and decentralized-based cooperative spectrum sensing with hard decision fusion. We assume multiple scattering and characterize the received signal by the photon-counting receiver. To obtain the distribution of the received irradiance over the multi-scattering channel, a novel method based on the Mellin transform is proposed. In the centralized technique, all the raw data (in the form of statistically dependent random variables) available at the collaborative users are combined using AND rule for decision, whereas, in the decentralized-based spectrum sensing, instead of sending all the raw data, only one-bit information is required to be sent to the fusion center to make the decision.

In the fourth chapter, we present an artificial neural network (ANN) based algorithm to estimate the data.
In addition, analytical frameworks are presented to estimate the channel model parameters under different fading distributions.

In the fifth chapter, we present a novel state-of-the-art UV-based indoor optical communications. The channel model is developed and analyzed. To ensure that the UV radiations are under allowable safety exposure limits, strict peak and average power constraints are imposed. Based on the power budget, the necessary conditions for the input distribution of the intensity-modulated direct detection (IM/DD) OOK modulated signal are derived. The link gain analysis is presented to investigate the directed line-of-sight (LOS) component and diffused links with multiple reflections and NLOS scattered components. The time-delay statistics for various paths are analyzed. Next, we present a novel multiuser indoor communication over a power-constrained Poisson channel. To reject the interference from multiple users, we present a minimum mean square error (MMSE) receiver. Moreover, a downlink beamforming optimization problem is formulated using second-order cone programming to maximize the received signal-to-interference-plus-noise ratio (SINR). The proposed multiuser system is also realized in the experiment. The influence of the control parameter, that is, the average-to-peak power ratio, on the performance is investigated.

The next chapter is dedicated to implementing orbital angular momentum (OAM) with UV communications. As a method to improvise the reliability of the UV communication system, we develop an OAM-based UV communication. Our work presents a significant increase in the UV channel capacity.

The seventh chapter presents a novel decentralized and self-organizing non-line-of-sight (NLOS) UV-based V2V communication (IVC). Experiments for proof-of-principle purposes were conducted with two vehicles in both stationary and time-varying UV channels. It is demonstrated that the proposed UV-IVC is capable of providing low-cost, low-power, and NLOS capable V2V communications with acceptable performance.

The last chapter concludes and summarizes the optical scattering communication systems developed in the previous chapters. In conclusion, the results and analysis presented in this thesis show the feasibility of employing optical scattering communication technologies in next-generation free-space optical communications. The future scope of optical scattering communications is also elaborated in the conclusion.

목차 (Table of Contents)

• 1. Introduction 1
• 1.1. Optical Wireless Communications 1
• 1.2. Optical Scattering Communications 3
• 1.2.1. Atmospheric Scattering of UV Signal 4
• 1.2.2. Common Volume and UV Channel Bandwidth 8
• 1.2.3. UV Safety Exposure Limit 9
• 1.3. Motivation 11
• 1.4. Dissertation Organization 12
• 2. Diversity Techniques for Optical Scattering Communications 13
• 2.1. Spatial Diversity 13
• 2.2. Switch and Stay Combining 14
• 2.2.1. System Model 14
• 2.2.2. Performance Analysis 15
• 2.2.3. Results and Discussions 17
• 2.3. Switch and Stay Combining with M-PSK Subcarrier Intensity Modulation 22
• 2.3.1. System Model 22
• 2.3.2. Average Bit Error Rate 26
• 2.3.3. Outage Probability 27
• 2.3.4. Results and Discussions 28
• 2.4. Maximal Selection Transmit Diversity 33
• 2.4.1. System Model 34
• 2.4.2. Marginal Distribution of Received UV signal 37
• 2.4.3. CDF of Largest Order Statistics 38
• 2.4.4. Average BER 40
• 2.4.5. Outage Probability 41
• 2.4.6. Channel capacity 43
• 2.4.7. Results and Discussions 43
• 2.5. Amplify-and-Forward Multihop NLOS UV Communications 49
• 2.5.1. System Model 50
• 2.5.2. Derivation of the PDF of the Instantaneous End-to-end Received SNR 52
• 2.5.3. Algorithm to Obtain the Optimal Number of Relay Nodes 55
• 2.5.4. Results and Discussions 56
• 3. Spectrum Sensing Techniques for Optical Scattering Communication Networks 59
• 3.1. Optical Spectrum Sensing over FSO in Strong Turbulence Channel 60
• 3.1.1. System Model 60
• 3.1.2. Probability of False Alarm 62
• 3.1.3. Probability of Detection 63
• 3.1.4. Results and Discussions 64
• 3.2. Generic Blind Spectrum Sensing Technique for all Optical Wavelength Multiuser Communications 70
• 3.2.1. System Model 72
• 3.2.2. Blind SNR Estimation 73
• 3.2.3. Estimate of the Noise Power 76
• 3.2.4. Results and Discussions 77
• 3.3. Cooperative Spectrum Sensing for Optical Wireless Multi-Scattering Communications over Málaga Fading 78
• 3.3.1. System Model 79
• 3.3.2. Non-Coplanar NLOS UV Link Geometry 83
• 3.3.3. Multi-Scattered Photon Trajectory 86
• 3.3.4. Distribution of Received Irradiance 89
• 3.3.5. Distribution of Photons Arrival Rate 91
• 3.3.6. Cooperative Spectrum Sensing with Centralized Technique 92
• 3.3.7. Results and Discussions 95
• 3.4. Artificial Bee Colony Based Heuristic Algorithm for Optical Spectrum Sensing 102
• 3.4.1. System Model and Methodology 103
• 3.4.2. Flowchart: ABC-based Threshold Optimization 111
• 3.4.3. Results and Discussions 112
• 4. Artificial Neural Network Assisted Optical Scattering Communications 116
• 4.1. ANN Assisted Signal Classification Algorithm 117
• 4.1.1. Parameters Estimation for Log-normal Distributed Turbulence Channel 117
• 4.1.2. Parameters Estimation for Gamma-Gamma Distributed Turbulence Channel 118
• 4.1.3. System Model 122
• 4.1.4. Results and Analysis 123
• 5. Indoor Optical Communications 130
• 5.1. Introduction and Motivation 130
• 5.2. UV Safety Exposure Limit for Indoor Communications 133
• 5.3. Signal Model 134
• 5.3.1. Necessary Conditions for the IM/DD OOK Modulated Signal 139
• 5.3.2. Signal-to-Noise Ratio in Poisson Channel 140
• 5.3.3. Derivation of BER Satisfying the Constraints 140
• 5.3.4. BER Performance Enhancement 143
• 5.3.5. Link Gain Analysis 145
• 5.3.6. Results and Discussions 146
• 5.4. State-of-the-art Multiuser Indoor Communication over Power-Constrained Poisson Channel 152
• 5.4.1. System Model 153
• 5.4.2. Receiver Characterization 154
• 5.4.3. Low-power Transmission Regime 155
• 5.4.4. Second-Order Cone Programming for Convex Optimization for Downlink Beamforming 156
• 5.4.5. Detection Techniques: Decision Rule with Perfect CSI 158
• 5.4.6. Detection Techniques: MLSD 159
• 5.4.7. Experimental Setup 160
• 6. Orbital Angular Momentum Assisted Optical Communications 164
• 6.1. Signal Model 165
• 6.2. Transmitter and Receiver Design 170
• 6.2.1. Transmitter Section 170
• 6.2.2. Receiver Section 171
• 6.2.3. Detection of Total OAM 171
• 6.3. Results and Discussions 175
• 7. Optical Scattering Based Intervehicular Communications 179
• 7.1. System Overview and Experimental Setup 181
• 7.2. Experimental Conditions and Environment 185
• 7.3. Received Power Profile 187
• 7.4. Baseband Representation of the UV-based IVC Channel 193
• 7.5. Future Scope 200
• 8. Conclusion 202

참고문헌 (Reference)

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2 Z. Xu, "`` Approximate performance analysis of wireless ultraviolet links", 2007

3 R. A. Beth, "`` Mechanical detection and measurement of the angular momentum of light", vol . 50 , no . 2 , p. 115 ,, 1936

4 H. Ding, "Modeling and characterization of ultraviolet scattering communication channels", 2011

5 D. M. Junge, "Non-line-of-sight electro-optic laser communications in the middle ultraviolet", 1977

6 A. Garcia-Zambrana, "`` Error rate performance for STBC in free-space optical communications through strong atmospheric turbulence ,", vol . 11 , no . 5 , pp . 390-392, 2007

7 S. C. Y. H. Arya ,, "`` Generic blind spectrum sensing scheme for all opticalwavelength multi-user free space optical communications", vol . 450 , pp . 316-321, 2019