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This book focuses on optical wireless communications (OWC), an emerging technology with huge potential for the provision of pervasive and reliable next-generation communications networks. It shows how the development of novel and efficient wireless technologies can contribute to a range of transmission links essential for the heterogeneous networks of the future to support various communications services and traffic patterns with ever-increasing demands for higher data-transfer rates.

The book starts with a chapter reviewing the OWC field, which explains different sub-technologies (visible-light, ultraviolet (UV) and infrared (IR) communications) and introduces the spectrum of application areas (indoor, vehicular, terrestrial, underwater, intersatellite, deep space, etc.). This provides readers with the necessary background information to understand the specialist material in the main body of the book, which is in four parts.

The first of these deals with propagation modelling and channel characterization of OWC channels at different spectral bands and with different applications. The second starts by providing a unified information-theoretic treatment of OWC and then discusses advanced physical-layer methodologies (including, but not limited to: advanced coding, modulation diversity, cooperation and multi-carrier techniques) and the ultimate limitations imposed by practical constraints. On top of the physical layer come the upper-layer protocols and cross-layer designs that are the subject of the third part of the book. The last part of the book features a chapter-by-chapter assessment of selected OWC applications.

Optical Wireless Communications is a valuable reference guide for academic researchers and practitioners concerned with the future development of the world’s communication networks. It succinctly but comprehensively presents the latest advances in the field.

Inhaltsverzeichnis

Frontmatter

Chapter 1. An Overview of Optical Wireless Communications

Abstract
We are continuously witnessing the emergence of new data services and applications in wireless transmission systems, in particular mobile broadband services, which require enhancing user’s experience. The existing radio frequency based wireless communications are facing challenges in so far as being able to cope with these varied, sophisticated and bandwidth hungry services and applications. The ever evolving optical wireless communications (OWC) technology with its unique features such as a license-free frequency spectrum, an inherent security, and significantly higher transmission rates is seen as a potential alternative and complementary to the radio frequency based wireless communications, which can address some of these challenges. This technology can be used for short to long distance applications as in indoor visible light communications, ultra-violet, and free space optics. The chapter gives an overview of the OWC system focusing on the historical development and current status, as well as existing and envisioned applications areas.
Z. Ghassemlooy, M. Uysal, M. A. Khalighi, V. Ribeiro, F. Moll, S. Zvanovec, A. Belmonte

Chapter 2. Optical Propagation in Unguided Media

Abstract
This chapter provides fundamentals of light propagation in unguided media and particularly discusses turbulence of transmission environment. The degradation effects of turbulence in the received signal of an OWC system are presented. The turbulence power spectra used in the formulation of various entities are given in various links operating in different environments such as atmosphere, space and underwater. The Rytov method and the extended Huygens–Fresnel principle are employed in the evaluation of the average intensity and the scintillation index. Effects of different optical beam profiles in the average received intensity and the scintillation index are further examined. Finally, some mitigation methods, such as the transmitter and the receiver aperture averaging, to reduce the turbulence degradation are given.
Yahya Kemal Baykal

Chapter 3. Effects of Adverse Weather on Free Space Optics

Abstract
The transmission of optical waves through the atmosphere can be severely hampered by adverse weather. This chapter is a state-of-the-art assessment of the models quantifying laser beam attenuation by fog and hydrometeors. The approach used here is, first, to set up a microphysical model of the interaction between an optical wave and the atmospheric particles, which works as a benchmark. Then, a number of empirical formulas used in the engineering practice are validated against the model. The former are based on simple relations between attenuation and easily accessible quantities, such as the visibility or the precipitation rate.
Roberto Nebuloni, Carlo Capsoni

Chapter 4. Experimental Validation of FSO Channel Models

Abstract
This chapter deals with the FSO link attenuation measurements at very special (severe) climatic conditions of the mountain Milesovka observatory being appropriate for the research but being not typical one. Therefore, examples of measurements from Prague, Budapest, and Milano are added. Fog attenuation (in combination with cloud) is discussed and Kim formula predicting the fog attenuation from visibility was more or less acknowledged. More accurate results are provided for rain attenuation estimation using the Carbonneau formula. Examples discussing concurrent occurrence of rain, fog, and clouds are analyzed. In the last part, we analyze the attenuation due to atmospheric turbulences concluding that the Rytov formula overestimates the attenuation on one hand, but is in good correlation with the measured attenuation on the second hand.
Ondrej Fiser, Vladimir Brazda

Chapter 5. Channel Characterization and Modeling for LEO-Ground Links

Abstract
This chapter describes low Earth orbit to ground optical communications. The scenario is outlined and introduction to atmospheric turbulence in this slant geometry is given. The scintillation index of incident intensity and aperture averaged received power are given by means of evaluation of common analytical expressions. Furthermore, the most important statistical parameters of fading are introduced and given. The new part in this chapter is the presentation of an analysis of satellite-ground measurements with two apertures (40 and 5 cm diameter). The experiment campaign is outlined as well as the results of the individual measurements. The power scintillation index and fading statistics are calculated over satellite elevation angle and averages of the measurements are created and compared to common theory. The measurements match quite well weak fluctuation theory. The theory is also used to extrapolate the measurements of power scintillation index, which were taken at a wavelength of 847 nm, to the wavelength of interest 1550 nm.
Florian Moll

Chapter 6. Channel Modeling for Visible Light Communications

Abstract
In this chapter, we present a novel and realistic channel modeling approach for visible light communications that overcomes the limitations of previous works. In our work, we consider wavelength dependency, effect of realistic light sources as well as different types of reflections such as specular and mixed cases of diffuse and specular. We use nonsequential ray tracing algorithms to calculate the detected power and path lengths from source to detector for each ray. These are then processed to yield the channel impulse responses for various indoor environments. We further present a channel characterization study where channel parameters such as channel DC gain, root mean square delay spread, coherence bandwidth, mean excess delay are calculated for different environments.
Farshad Miramirkhani, Murat Uysal, Erdal Panayirci

Chapter 7. Diffraction Effects and Optical Beam Shaping in FSO Terminals

Abstract
The first part of the chapter is focused on the wave effects, which occur when the Gaussian beam is being restricted by a circular aperture, e.g., by a lens socket. An elliptically symmetrical Gaussian beam is considered in the analysis to improve the generality and to analyze beams produced by edge-emitting semiconductor lasers. From the Huygens-Fresnel principle, two models of the Fresnel diffraction were derived. These models provided means for defining contrast of the diffraction pattern that can be used to quantitatively assess the influence of the diffraction effects on the optical link performance. The second section is devoted to the study that shows the misalignment analysis for two cases—lateral displacement and angular misalignment of the transmitter and the receiver, respectively. The expression for the misalignment attenuation of the elliptical Gaussian beam in FSO links is derived. It will be also shown, how the elliptical Gaussian beam can be used to improve the system’s resistance to some deteriorating effects, e.g., building sway. The third part of the chapter is focused on the analysis of the optimal optical intensity distribution within a radiated laser beam at a transmitter plane which is propagated through free space. The aim of the chapter is to determine the optimal parameters for a Flattened Gaussian beam at the transmitter plane.
Juraj Poliak, Peter Barcik, Otakar Wilfert

Chapter 8. Ultraviolet Scattering Communication Channels

Abstract
Tropospheric molecular and particle scattering in ultraviolet (UV) scattering wavelengths enable non-line-of-sight (NLOS) communication which brings robustness to blockage or shadowing. NLOS communication is particularly desirable to relax or eliminate pointing, acquisition and tracking requirements. NLOS-UV links can be used as an alternative to outdoor infrared or visible light links or in combination with existing optical or radiofrequency wireless links. Analytical, experimental and numerical approaches have been used to determine the NLOS-UV channel impulse response and path loss. These studies demonstrate that UV channel is of multipath nature due to the volumetric scattering due to air molecules, aerosols and hydrometeors. Besides inter-symbol interference and bandwidth limitation resulting from frequency-dispersive nature of NLOS-UV channel, performances may be also degraded by high path losses and turbulence-induced fading as the link range increases. This chapter provides an overview of latest advances in NLOS-UV channel modeling and results.
Saverio Mori, Frank S. Marzano

Chapter 9. Information Theoretical Limits of Free-Space Optical Links

Abstract
Generalized fading has been an imminent part and parcel of wireless communications. It not only characterizes the wireless channel appropriately but also allows its utilization for further performance analysis of various types of wireless communication systems. Under the umbrella of generalized fading channels, a unified ergodic capacity analysis of a free-space optical (FSO) link under both types of detection techniques (i.e., intensity modulation/direct detection (IM/DD) as well as heterodyne detection) over generalized atmospheric turbulence channels that account for generalized pointing errors is presented. Specifically, unified exact closed-form expressions for the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system are presented. Subsequently, capitalizing on these unified statistics, unified exact closed-form expressions for ergodic capacity performance metric of FSO link transmission systems is offered. Additionally, for scenarios wherein the exact closed-form solution is not possible to obtain, some asymptotic results are derived in the high SNR regime. All the presented results are verified via computer-based Monte-Carlo simulations.
Imran Shafique Ansari, Hessa AlQuwaiee, Emna Zedini, Mohamed-Slim Alouini

Chapter 10. Performance Analysis of FSO Communications Under Correlated Fading Conditions

Abstract
This chapter considers performance evaluation of space-diversity free-space optical (FSO) communication systems over correlated Gamma-Gamma (\(\Gamma \Gamma\)) fading channels. To do this, we firstly describe in detail the \(\Gamma \Gamma\) model and explain how to model space-diversity FSO channels. Next, we investigate the fading correlation existing in real space-diversity FSO systems using wave-optics simulations. To integrate the fading correlation into the \(\Gamma \Gamma\) channel model, we decompose the correlation coefficient into large- and small-scale correlation coefficients. Then, the generation of correlated \(\Gamma \Gamma\) random variables (RVs) corresponding to the correlated FSO channel fading coefficients is presented for evaluating the system performance via Monte-Carlo simulations. Because Monte-Carlo simulations are in general highly time-consuming, analytical performance evaluation methods are also introduced.
Guowei Yang, Mohammad-Ali Khalighi, Zabih Ghassemlooy, Salah Bourennane

Chapter 11. MIMO Free-Space Optical Communication

Abstract
In this chapter, we study multiple-input multiple-output (MIMO) free-space optical (FSO) communication systems degraded by atmospheric turbulence, absorption, scattering, diffraction, and misalignment. The employment of multiple transmit/receive apertures are studied as a means to enhance the reliability of FSO links by combating atmospheric turbulence through the insertion of redundancy (i.e. spatial diversity). The fundamental differences between RF and optical wireless MIMO channels are discussed and the most recent results reported for different channel models are presented. We further extend our investigation to include some important results on distributed MIMO FSO systems.
Majid Safari

Chapter 12. OFDM-Based Visible Light Communications

Abstract
This chapter provides an overview of the latest enhancements of the orthogonal frequency division multiplexing (OFDM)-based visible light communications. The principals of OFDM techniques for intensity modulation and direct detection (IM/DD) systems are explained in detail in Dimitrov and Haas, Principles of LED Light Communications: Towards Networked Li-Fi, (2015) [1]. A number of inherently unipolar OFDM techniques were recently proposed as power efficient alternatives to the widely deployed direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM). The unipolar orthogonal frequency division multiplexing (U-OFDM) technique achieves higher power efficiency compared with DCO-OFDM. However, due to the spectral efficiency loss of the U-OFDM technique, the power efficiency advantage over DCO-OFDM starts to decrease as the spectral efficiency increases. Multiple U-OFDM streams are superimposed in enhanced unipolar orthogonal frequency division multiplexing (eU-OFDM) to double the spectral efficiency of U-OFDM technique. For the first time, the novel eU-OFDM allows unipolar OFDM techniques to have same spectral efficiency of DCO-OFDM. In this chapter, the concept of eU-OFDM is generalised to GeneRalizEd ENhancEd UnipolaR OFDM (GREENER-OFDM), and extended to other unipolar OFDM schemes (asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and pulse-amplitude-modulated discrete multitone modulation (PAM-DMT)).
Dobroslav Tsonev, Mohamed Sufyan Islim, Harald Haas

Chapter 13. Block Transmission with Frequency Domain Equalization for VLC

Abstract
OFDM and its real-valued version discrete multitone transmission (DMT) are popular schemes to compensate dispersion in direct detection optical systems. They employ an inverse fast Fourier transform (IFFT) at the transmitter and a fast Fourier transform (FFT) at the receiver, whereas the data symbols are processed block-wise. Pulse-amplitude modulation (PAM) or single subcarrier (SSC) modulation combined with block transmission and frequency domain equalization (FDE) has been recognized as a possible alternative to the DMT schemes. Here, the IFFT is moved from the transmitter to the receiver, since the modulation takes place directly in the time domain. In this chapter, we investigate the suitability of FDE for Li-Fi (light fidelity) systems based on visible light communications. Such systems require nonnegative and real-valued signals, which additionally offer a DC-balance. We discuss the theoretical background of FDE under the intensity modulation constraint and compare its performance with the performance of bit-loading enhanced DC-biased DMT in multipath indoor channels.
Mike Wolf, Sher Ali Cheema, Martin Haardt

Chapter 14. Satellite Downlink Coherent Laser Communications

Abstract
Free-space coherent laser downlinks can potentially provide high data rates in space-to-Earth communications, and are a key enabler for future optical information systems in space. There is growing interest in the high sensitivity and spectral efficiency of coherent optical receivers for downlink systems, despite a higher cost and complexity than direct-detection receivers. In practice, however, when the link passes through the atmosphere, clear-air turbulence induces serious phase distortions and fading that impair coherent receivers. The impact of turbulence can be mitigated conveniently by using channel matched array receivers, which comprise multiple subapertures. Alternatively, this impact can be mitigated using a single-aperture receiver with adaptive optics to correct wave front distortion. Here we provide a comprehensive, unified analysis of these two fundamental techniques in atmospheric downlink coherent systems. Our results demonstrate how array receivers and adaptive optics are expected to perform in tracking and correcting atmospherically distorted signals.
Aniceto Belmonte, Joseph M. Kahn

Chapter 15. Cooperative Visible Light Communications

Abstract
In this chapter, we explore the concept of cooperative transmissions in the context of visible light communications (VLC). An indoor office space is considered with two light sources; the one at the ceiling is connected to the backbone network and provides ambient light to the environment while the other one is mounted on the desk and used for task lighting. The system architecture builds upon DC-biased optical orthogonal frequency-division multiplexing (DCO-OFDM). The task light performs relaying operation in either amplify-and-forward (AF) or decode-and-forward (DF) mode. Illumination constraints for task lighting are further considered in order to design a cooperative VLC system that provides satisfactory lighting. The communication performance of the system is optimized through a subcarrier-based power allocation mechanism. Numerical results incorporating practical issues such as band-limited channel process and imperfect channel estimation reveal that cooperative VLC systems can significantly outperform the conventional point-to-point VLC systems.
Omer Narmanlioglu, Refik Caglar Kizilirmak, Farshad Miramirkhani, Murat Uysal

Chapter 16. Coded Orbital Angular Momentum Modulation and Multiplexing Enabling Ultra-High-Speed Free-Space Optical Transmission

Abstract
To simultaneously achieve high throughput and low energy consumption, in this chapter we advocate the use of energy-efficient N-dimensional coded orbital angular momentum (OAM)-based modulation and multiplexing for ultra-high-speed optical transmission over free-space optical (FSO) links. OAM is associated with the azimuthal phase dependence of the complex electric field. Because its eigenvectors are orthogonal, they can be used as basis functions for multidimensional signaling. Because the information capacity is linear in the number of dimensions, we can dramatically improve the overall optical channel capacity through multidimensional signal constellations. On the other hand, energy efficiency can be achieved by properly designing the N-dimensional signal constellation. To deal with time-varying FSO channel conditions, OAM modulation can be combined with rateless coding. Atmospheric turbulence effects can be handled, in addition to FSO-MIMO, through the use of the azimuthal phase correction method, similar to the Gerchberg-Saxton (GS) phase retrieval algorithm. Moreover, distortions introduced by turbulence will be compensated for via adaptive optics approaches. Additionally, LDPC-coded OAM-based free-space optical FSO transmission system is experimentally studied in both the absence and presence of emulator-induced atmospheric turbulence.
Ivan B. Djordjevic, Zhen Qu

Chapter 17. Mixed RF/FSO Relaying Systems

Abstract
In this chapter, we are focused on wireless optical communications utilizing in overcoming a connectivity gap between the backbone and last mile access networks. The outage performance of dual-hop amplify-and-forward (AF) relaying systems, composed of mixed radio frequency (RF)/free-space optical (FSO) links is presented, when the partial relay selection is considered based on outdated channel state information (CSI). We analyze an example when the RF link is subjected to Rayleigh fading, while the FSO link is affected by atmospheric turbulence, which results in the intensity fluctuations of the optical signal, following the Gamma–Gamma distribution with taking the pointing errors into account. Analytical expressions for the outage probability are presented. The effects of atmospheric turbulence strength, pointing errors standard deviation, number of relays and rank of selected relay, are observed, considering the effect of time correlation between current and outdated CSI of the source-relay channel.
Milica I. Petkovic, Aleksandra M. Cvetkovic, Goran T. Djordjevic

Chapter 18. Dimming and Modulation for VLC-Enabled Lighting

Abstract
Advances in high brightness light emitting diode (LED) technology are enabling myriad applications in lighting including visible light communications (VLC) technology that has the potential to complement RF technology to provide wireless data access for indoor coverage. This chapter reviews various dimming techniques suitable for VLC, and presents an LED driver circuit architecture incorporating digitally controlled analog circuit blocks to deliver concurrent dimming control and data transmission for VLC-enabled lighting. To achieve this target, a bi-level pulse-width modulation (PWM) driving scheme is applied to enable data transmission during the “off” period of the LED drive current while concurrently providing dimming control. The proposed architecture is compatible with digital baseband modulation schemes and implements a mechanism for ease of integration with commercial off-the-shelf (COTS) LED drivers for VLC system realization. This chapter also discusses a dimming compatible analog baseband modulation scheme. The reverse polarity optical orthogonal frequency-division multiplexing (RPO-OFDM) is a recent approach to realize compatibility between any format of an analog OFDM signal suitable for optical transmission and the concept of a digital pulse-width modulation (PWM) technique for dimming control. We also describe an implementation of the RPO-OFDM approach as part of a wireless access testbed. Experiments reveal that bit-error and bit-rate performances are maintained over a wide range of dimming.
Ali Mirvakili, Hany Elgala, Thomas D. C. Little, Valencia J. Koomson

Chapter 19. Diversity for Mitigating Channel Effects

Abstract
There is a need to compensate for the power fluctuations in free space optical (FSO) communication links due to the turbulence and other atmospheric phenomena. In order to overcome atmospheric turbulence induced fades, several techniques have been proposed. These include: spatial transmitter/receiver diversity, adaptive beam forming based on the wave front phase error measurement and the setting of the opposite phase aberration on the beam by a deformable mirror, wavelength diversity, multiple-beam communication and novel modulation techniques. In this chapter, the performance of FSO systems with spatial and time diversities is presented. To illustrate the diversity techniques, only the subcarrier intensity modulation scheme will be considered. The diversity techniques outlined can however, be extended to other modulation schemes without any loss of generality. The spatial diversity analysis is based on the linear combining techniques: equal gain combining, maximum ratio combining and selection combining. Inter-symbol interference is not being considered since terrestrial FSO links are basically a line-of-sight technology with the negligible delay spread. The chapter also outlines experimental results for verification of the diversity schemes for FSO links. To ensure link availability at all weather conditions the chapter also presents measurement campaign for an outdoor FSO/radio frequency link.
Zabih Ghassemlooy, Wasiu Popoola, Stanislav Zvanovec

Chapter 20. Multiple Access in Visible Light Communication Networks

Abstract
Visible light communication (VLC) is a high-speed wireless communication technology that has emerged in the recent years, as a strong alternative to existing communication technologies. The features such as high data rates, immunity to electromagnetic interference, and operation in unlicensed bands with high reuse factor make it a favorable option for broadband wireless communications. In 2011, the Institute of Electrical and Electronics Engineers (IEEE) published the 802.15.7 standard as a member of the personal communications family of standards which defines the physical and medium access control (MAC) layers of VLC. This chapter starts with an overview of multiple access techniques that can be considered for VLC networks with inherently directional light sources. The second part of the chapter focuses on the IEEE 802.15.7 VLC standard and thoroughly discusses MAC protocols therein, namely non-beacon mode without CSMA/CA; non-beacon mode with CSMA/CA; beacon-enabled mode without CSMA/CA and beacon-enabled mode with CSMA/CA. The performance of a standard-compliant VLC network is presented in terms of for throughput, drop probability, and power consumption.
Melike Erol-Kantarci, Murat Uysal

Chapter 21. Link Layer Protocols for Short-Range IR Communications

Abstract
The Infrared Data Association (IrDA) has standardized the widely used IrDA 1.x protocol stack for low-cost, indoor, short-range, point-to-point connectivity. The early adoption of IrDA and the widespread installation of millions of IrDA infrared ports in mobile devices for wireless communication applications necessitates for throughput performance optimization of the IR links at the link layer. The lessons learnt from the IrDA standard adoption issues should be a guide for future 5G device to device developments and other personal Infrared devices and applications, when it comes to the introduction of optical wireless and protocols into products. This chapter provides a review of a mathematical model, based on which we derive simple equations linking the link layer throughput with physical and link layer parameters. Simple equations for optimum values of window and frame size lengths for maximum link layer throughput as a function of BER are derived, and a study of the importance of parameters such as link minimum turnaround time and timeout timer is presented. Finally, a protocol improvement that utilizes special Supervisory frames (S-frames) to pass transmission control is proposed to deal with delays introduced by F-timer expiration. Results indicate that employing the special S-frame highly improves throughput performance when optimum window and frame size values are implemented.
A. C. Boucouvalas, K. P. Peppas

Chapter 22. On the Resilient Network Design of Free-Space Optical Wireless Network for Cellular Backhauling

Abstract
With the densification of nodes in cellular networks, free-space optics (FSO) connections are becoming an appealing low cost and high rate alternative to copper and fiber backhaul solutions for wireless communication systems. To ensure a reliable cellular backhaul, provisions for redundant, disjoint paths between the nodes must be made in the design phase. This chapter aims at finding a cost-effective solution to upgrade the cellular backhaul with pre-deployed optical fibers using FSO links and mirror components. A novel integer linear programming model to approach optimal FSO backhaul design, guaranteeing K-disjoint paths connecting each node pair is presented. Next, a column generation method to a path-oriented mathematical formulation is developed. Applying the method in a sequential manner enables high computational scalability. Realistic scenarios are used to demonstrate the proposed approaches which efficiently provide optimal or near-optimal solutions, and thereby allow accurate dealing with the trade-off between cost and reliability.
Yuan Li, Nikolaos Pappas, Vangelis Angelakis, Michał Pióro, Di Yuan

Chapter 23. FSO for High Capacity Optical Metro and Access Networks

Abstract
Free-space optic (FSO) with optical metro and access networks should couple very efficiently since they work in the same wavelengths with a transparent link. Moreover, coherent detection with advanced modulation formats can fully utilize the bandwidth and increase the transmission capacity of FSO links. This chapter considers several optical wireless systems used in metro and access networks. Advanced modulation formats and Nyquist pulse-shaping technology are discussed for future implementations of optical access networks. A fully ultra broadband optical wireless link in a building to building scenario is demonstrated. Moreover, an innovative bi-directional ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) based on advanced modulation formats and Nyquist pulse shaping in a hybrid fibre plus FSO is experimentally demonstrated.
Antonio Teixeira, Ali Shahpari, Vitor Ribeiro, Ricardo Ferreira, Artur Sousa, Somayeh Ziaie, Jacklyn Reis, Giorgia Parca, Silvia Dibartolo, Vincenzo Attanasio, Stefano Penna, Giorgio Maria Tosi Beleffi

Chapter 24. Multiuser Diversity Scheduling: A New Perspective on the Future Development of FSO Communications

Abstract
In this chapter, the multiuser diversity scheduling, as a well-known effective RF technique, is extended to the point-to-multipoint Free-Space Optics (FSO) networks where the data transmission experiences the atmospheric-induced turbulence fading. In particular, the limitations on adapting this method to FSO systems along with their solutions are discussed and addressed. Average throughput and latency performances of different scheduling protocols including Round-Robin, Opportunistic Round-Robin, Select-Max, and best user selection are investigated and compared.
Jamshid Abouei, Seyyed Saleh Hosseini, Konstantinos N. Plataniotis

Chapter 25. Optical Camera Communications

Abstract
Visible light communications (VLC) has been evolving at a much faster rate because of the development of high energy efficient white light emitting diodes (LED). For the first time, we see a unique device which offers triple functionalities of illumination, data communications and indoor localization, thus opening up the opportunities for applications at homes, offices, planes, trains, etc. In modern vehicles with LED-based head and tail lights, VLC can be used for car-to-car communications to convey regular traffic information to other vehicles as well as the road side infrastructure. Cameras are also being widely used in vehicles for monitoring speed, collision detection avoidance, traffic sign and object recognition. The VLC technology employing the camera as a receiver opens up new possibilities offering multiple functionalities including data communications. This chapter gives an overview of the optical camera communications and outlines the technological concept behind it.
Zabih Ghassemlooy, Pengfei Luo, Stanislav Zvanovec

Chapter 26. Optical Wireless Body Area Networks for Healthcare Applications

Abstract
Since Optical Wireless Communications (OWC) results in significant reduction of electromagnetic pollution in human environment, this technology is a good candidate for Wireless Body Area Networks (WBANs) in particular for medical applications such as health monitoring. This chapter investigates the use of on-body OWC for mobile medical WBANs. Based on transmission scheme exploiting diffuse optical reflections over the patient environment, a star BAN topology using spreading codes is proposed for multiple accesses and the performance is evaluated in presence of patient mobility. The achievable quality of service for a typical health monitoring application is reported and discussed regarding the performance required by medical applications.
Anne Julien-Vergonjanne, Stéphanie Sahuguède, Ludovic Chevalier

Chapter 27. Free-Space Quantum Key Distribution

Abstract
Based on the firm laws of physics rather than unproven foundations of mathematical complexity, quantum cryptography provides a radically different solution for encryption and promises unconditional security. Quantum cryptography systems are typically built between two nodes connected to each other through fiber optic. This chapter focuses on quantum cryptography systems operating over free-space optical channels as a cost-effective and license-free alternative to fiber optic counterparts. It provides an overview of the different parts of an experimental free-space quantum communication link developed in the Spanish National Research Council (Madrid, Spain).
Alberto Carrasco-Casado, Verónica Fernández, Natalia Denisenko

Chapter 28. VLC-Based Indoor Localization

Abstract
The omnipresence of LEDs for illumination provides unique opportunities for indoor localization. Signals transmitted by the LEDs can be used to determine the position of a person or object within a room with high precision. The requirements of such applications are different from high speed VLC systems. One of the commonly employed methods for VLC-based localization is optical tracking and imaging while the other is based on trilateration/triangulation. However, in both the methods it is critical that the user device is able to recover signals from each luminaire separately. In order to achieve this, a number of processing methods and devices can be chosen, which will be elaborated in this chapter. Practical implications including the required modifications/additions on the illumination infrastructure to enable positioning are also covered.
Gábor Fehér, Eszter Udvary

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