Wireless Optical Communications E-Book

Olivier Bouchet

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 351

Veröffentlichungsjahr: 2013

Beschreibung

Wireless optical communication refers to communication based on the unguided propagation of optical waves. The past 30 years have seen significant improvements in this technique - a wireless communication solution for the current millennium - that offers an alternative to radio systems; a technique that could gain attractiveness due to recent concerns regarding the potential effects of radiofrequency waves on human health. The aim of this book is to look at the free space optics that are already used for the exchange of current information; its many benefits, such as incorporating channel properties, propagation models, link budgets, data processing including coding, modulation, standards and concerns around health and safety (IEC 60825 or FCC - Class 1 for example), etc. will become indispensable over the next decade in addressing computer architectures for short-, medium- and long-range telecommunications as we move from gigabytes to terabytes per second. Wireless Optical Communications is an excellent tool for any engineer wanting to learn about wireless optical communications or involved in the implementation of real complete systems. Students will find a wide range of information and useful concepts such as those relating to propagation, optics and photometry, as well the necessary information on safety. Contents 1. Light. 2. History of Optical Telecommunications. 3. The Contemporary and the Everyday Life of Wireless Optical Communication. 4. Propagation Model. 5. Propagation in the Atmosphere. 6. Indoor Optic Link Budget. 7. Immunity, Safety, Energy and Legislation. 8. Optics and Optronics. 9. Data Processing. 10. Data Transmission. 11. Installation and System Engineering. 12. Conclusion.

Leseprobe

Table of Contents

Foreword

Acronyms

Introduction

Chapter 1: Light

Chapter 2: History of Optical Telecommunications

2.1. Some definitions

2.2. The prehistory of telecommunications

2.3. The optical aerial telegraph

2.4. The code

2.5. The optical telegraph

2.6. Alexander Graham Bell’s photophone

Chapter 3: The Contemporary and the Everyday Life of Wireless Optical Communication

3.1. Basic principles

3.2. Wireless optical communication

Chapter 4: Propagation Model

4.1. Introduction

4.2. Baseband equivalent model

4.3. Diffuse propagation link budget in a confined environment

Chapter 5: Propagation in the Atmosphere

5.1. Introduction

5.2. The atmosphere

5.3. The propagation of light in the atmosphere

5.4. Models

5.5. Experimental set-up

5.6. Experimental results

5.7. Fog, haze and mist

5.8. The runway visual range (RVR)

5.9. Calculating process of an FSO link availability

5.10. Conclusion

Chapter 6: Indoor Optic Link Budget

6.1. Emission and reception parameters

6.2. Link budget for line of sight communication

6.3. Link budget for communication with retroreflectors

6.4. Examples of optical budget and signal-to-noise ratio (SNR)

Chapter 7: Immunity, Safety, Energy and Legislation

7.1. Immunity

7.2. The confidentiality of communication

7.3. Energy

7.4. Legislation

Chapter 8: Optics and Optronics

8.1. Overview

8.2. Optronics: transmitters and receivers

8.3. Optics

Chapter 9: Data Processing

9.1. Introduction

9.2. Modulation

9.3. The coding

Chapter 10: Data Transmission

10.1. Introduction

10.2. Point-to-point link

10.3. Point-to-multipoint data link

10.4. Summary

Chapter 11: Installation and System Engineering

11.1. Free-space optic system engineering and installation

11.2. Wireless optical system installation engineering in limited space

Chapter 12: Conclusion

APPENDICES

Appendix 1: Geometrical Optics, Photometry and Energy Elements

A1.1. Geometrical optics elements A1.1.1. Refractive index

A1.2. Photometry elements

A1.3. Equivalence between visual and energetic photometry

Appendix 2: The Decibel Unit (dB)

Bibliography

List of Figures

List of Tables

List of Equations

Index

First published 2012 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

ISTE Ltd John27-37 St George’s RoadLondon SW19 4EUUKWiley & Sons, Inc.111 River StreetHoboken, NJ 07030USAwww.iste.co.ukwww.wiley.com

© ISTE Ltd 2012

The rights of Olivier Bouchet to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Cataloging-in-Publication Data

Bouchet, Olivier.

Wireless optical telecommunications / Olivier Bouchet.

p. cm.

Includes bibliographical references and index.

ISBN 978-1-84821-316-6

1. Wireless communication systems. 2. Optical communications. I. Title.

TK5103.2.B69 2012

621.382'7--dc23

2012005891

British Library Cataloguing-in-Publication Data

A CIP record for this book is available from the British Library

ISBN: 978-1-84821-316-6

Foreword

Modern telecommunication, at least in the vicinity of terminals (TV receivers, computers, recorders, smartphones, network games consoles, e-books, etc.), will be “wireless” and high speed: the physical link will not be a copper wire, or made from fiber, silica, or other, but an electromagnetic wave propagating in free space between one transmitter–receiver and another transmitter–receiver.

The most common physical wireless link is the use of radio, an electromagnetic wave in the range of radio spectrum. It is a well-developed technology, but we can see the limitations in terms of speed (bits per second), frequency, power, electromagnetic compatibility, and electromagnetic pollution among others. Regarding transmission of information, we know that the higher the frequency of the electromagnetic transmitted wave, the higher the speed. Hence, current laboratory studies are looking at communication systems operating at frequencies of gigahertz (GHz) to terahertz (THz) and above. For frequencies beyond terahertz, and particularly in the ranges corresponding to optical waves, infrared or visible light (100–1,000 THz), a communication speed in the range of terabits per second can be achieved.

Because of the laser (invented in 1960) and silica fiber (the potential of silica fiber for telecom applications was demonstrated in 1961), optical telecommunications together with the fantastic progress made in the manufacturing technology of lasers and optoelectronic systems, in parallel to those of silica fibers, have enabled the irreversible development of optical fiber telecommunication. These optical communications have generated intercontinental telecommunications and broadband internet. From basic-oriented research, they have an obvious important societal impact.

Wireless optical communications use the atmosphere as a transmission medium. The ambient atmosphere is much more complex than the fibrous silica in terms of composition, uniformity, and reproducibility. But taking advantage of advanced technologies useful for fiber telecommunications, it gives excellent results for broadband transmitted over short distances and even allows us a glimpse of wireless optical communication with terabits per second, even though today (in 2011) we are using gigabit to the terminal (GTTT) in a limited confined environment.

The atmospheric optical links are always subject to environmental variations (dust, fog, rain, etc.), which can cause temporary performance degradation of the telecommunications system. The propagation properties of optical beams in this environment must provide a good quality of service as in the model of Al Naboulsi et al. [NAB 04], based on visibility, the setting that characterizes the opacity of the atmosphere. Using components (LED, laser, photodetectors, etc.) at wavelengths that are non-ionizing photons whose technologies are now mature, in free-space communication over short distances, especially indoors (in rooms), has great potential. The book Wireless Optical Communications follows a previous book Free-Space Optics — Propagation and Communication [BOU 06] that presented the physics and foundations useful for communications in free space and in limited spaces. Since the last book, great progress has been made on all issues related to a real telecommunications system incorporating channel properties, propagation models, link budgets, and the data processing including coding, modulation, standards, and safety.

This book is designed as an excellent tool for any engineer wanting to learn about wireless optical communications or who is involved in the implementation of real complete systems. Students will find lots of information and useful concepts such as those relating to propagation, optics, and photometry, as well as the necessary information on safety.

This book is written with as an overview of a useful technology for telecommunications. The ideas developed allow us a glimpse of the applications in the field of communication devices by photons. Since the early work of Gfeller in 1979 on optical wireless limited space [GFE 79] or the work of Kintzig et al. [KIN 02] published in 2002, who suggested solutions for optical wireless communication devices, we can now glimpse totally secure wireless optical communication, from “n” objects to “m” objects and very high data rates (up to THz soon?) limiting itself to the walls of a room.

Optical wireless telecommunications also allow absolute security in communications, subject to having transmitters in a single reliable and reproducible photon. These free-space quanta in free space will certainly find useful applications for those who want absolute security in their information exchange.

Pierre-Noël FAVENNEC

URSI-FranceMarch 2012

Acronyms

AAmpereAACAutomatic attenuation controlAcArea coverACGAutomatic control gainAELAccessible emission limitAIRAdvanced infraredAPAccess pointAPDAvalanche photodiodeAPPMAmplitude pulse position modulationARIBAssociation of Radio Industries and BusinessesARPAddress resolution protocolASCIIAmerican standard code for information interchangeASKAmplitude shift keyingATMAsynchronous transfer modeATPCAutomatic transmit power controlAWGNAdditive white Gaussian noiseBCHBose–Chaudhury–Hocquenghem codeBCJRBahl–Cocke–Jelinek–Raviv codeBERBinary error rateBPMBeam propagation method in time domainBTBritish TelecomCAOConcentrateur amplificateur optique (Fireball)BCConduction bandCCConvolutional codeCCDCharge coupled deviceCCETTCentre Commun d’Etudes de Télévision et de TélécommunicationsCDCompact discCDMACode division multiple accessCEICommission Electrotechnique InternationaleCEPTConférence Européenne des Postes et TélécommunicationsCIRChannel impulse responseCNESCentre National d’Etudes SpatialesCNETCentre National d’Etudes des TélécommunicationsCOFDMCoded orthogonal frequency division multiplexCPGConference Preparatory GroupCQIColor quality indicationCRCCyclic redundancy checkCSIChannel state informationCSMACarrier sense multiple accessCSMA/CACarrier sense multiple access with collision avoidanceCSMA/CDCarrier sense multiple access with collision detectionDARPADefense Advanced Research Projects AgencyDCDirect currentDDDirect detectionDFBDistributed feedbackDIFDiffusionDIVDivergenceDLRDeutsch Land Radio: German Spatial agencyDMTDiscrete multitone modulationDPIMDigital pulse interval modulationDPPMDifferential pulse position modulationDRMDigital Radio MondialeDSLDigital subscriber lineDSSSDirect sequence spread spectrumDVDDigital versatile discECCError corrector codeECMAEuropean Computer Manufacturers AssociationEDFAErbium-doped fiber amplifiersEDRSEuropean Data Relay SatelliteEELEdge emitting laserEFIRExtremely fast infrared communicationEHFExtremely high frequencyENEuropean Norm (Euronorm)EROEuropean Radiocommunication OfficeESAEuropean Space AgencyEthernetLAN packet protocolFCSFrame check sequenceFDDFrequency division duplexFDDIFiber distributed data interfaceFDMAFrequency division multiple accessFDTDFinite difference time domainFETField effect transistorFFTFast Fourier transformFIRFast infraredFOVField of viewFSOFree-space opticFTTxFiber to the Home, Business....FTTHFiber to the homeGSMGlobal system for mobile communicationsGUIGraphical user interfaceHAPHigh-altitude platformHFHigh frequencyHHHHirt–Hassner–Heise codeHPOptical transmitted half-power angleHTTPHypertext transfer protocolIBMInternational Business MachinesICSAInfrared Communication Systems AssociationICTInformation and Communication TechnologiesIdDark currentIdPIndoor positioningIECInternational Electrotechnical CommissionIEEInstitution of Electrical EngineersIEEEInstitute of Electrical and Electronics EngineersIISInterference intersymbolIMIntensity modulationIM/DDIntensity modulation/direct detectionInGaAsIndium gallium arsenideIPInternet protocolIPv6Internet protocol version 6IRInfraredIRCInfrared communicationIrDAInfrared Data AssociationIrLAPInfrared link access protocolIrLMPInfrared link management protocolISCAInfrared communication Systems AssociationISIIntersymbol interferenceISOInternational Standards for OrganizationITSIntelligent transport systemITUInternational Telecommunication UnionITU-RInternational Telecommunication Union Radiocommunication sectorJVCJapan Victor CompanyKDDIJapanese telecommunication operatorLAPLink access protocolLASERLight amplification by stimulated emission of radiationLDLaser diodeLCDLiquid crystal displayLCRLine clock recoveryLDPCLow-density parity check codeLEDLight-emitting diodeLEOTLaser electro-optics technologyLLCLogical link controlLMPLink management protocolLOSLine of sightLRCLongitudinal redundancy checkMACMedium access controlMIMOMultiple-input multiple-outputMPDUMAC protocol data unitMPEMaximum permissible exposureMPEGMoving Picture Experts GroupMRRModulating retroreflectorMSMultispotMSDMultispot diffuseMSDUMSMAC service data unitMSMMetal-semiconductor-metal photodiodeMozillaCode name for the web Netscape NavigatorNASANational Aeronautical and Space AdministrationNECNippon Electric Company LimitedNFIRENear-field infrared experimentNLOSNon-line of sightNRZNon-return to zeroNTTNippon Telegraph and Telephone CorporationOBEXObject Exchange (IrDA exchange protocol)OFDMOrthogonal frequency division multiplexOMEGAHOME Gigabit AccessOOKOn–off keyingOPPMOverlap pulse position modulationOQAMOffset quadrature amplitude modulationOSIOpen systems interconnectionOWMACOptical wireless media access controlPCPersonal computerPERPacket error ratePDPhotodiodePDAPersonal digital assistantPDUProtocol data unitPHYOSI physical layerPINPositive intrinsic negative diodePLCPower line communicationPLCPPhysical layer convergence procedurePmPPoint-to-multipoint communicationPtPPoint-to-point communicationPPDUPLCP protocol data unitPPMPulse position modulationPSDUPhysical service data unitPSKPhase-shift keyingQAMQuadrature amplitude modulationQKDQuantum key distributionQOFIQualité Optique sans Fil IndoorQOSQuality of serviceRC5Philips IRDA remote control protocolRGBRed green blueRLLRun length limited encodingRRRadio regulationRSReed–Salomon codeRSARivest–Shamir–Adleman codeRSVAssociation of Reed–Salomon and Viterbi codeRS232Universal data interfaceRTSPReal-time streaming protocolRVRRunway visual rangeSAPService access pointSDMASpace division multiple accessSEISpace Exploration InitiativeSFDStart frame delimiterSFTFSpaceborne flight test systemSHFSuper high frequencySILEXSemiconductor intersatellite link experimentSIMOSingle-input multiple-outputSIRSerial infraredSIRSCSony IrDA data transmission protocolSISOSingle-input single-outputSMTPSimple mail transfer protocolSNRSignal-to-noise ratioSPIESociety of Photo-optical Instrumentation EngineersSWOSmart wireless opticTIATransimpedance amplifierTFTPTrivial file transfer protocolTCPTransmission control protocolTCP/IPTransmission control protocol/internet protocolTDDTime division duplexTDMATime division multiple accessTGTask groupUDPUser datagram protocolUFIRUltrafast infraredUHFUltrahigh frequencyUSBUniversal serial busUVUltravioletVBValence bandVCSELVertical external-cavity surface-emitting laserVFIRVery fast infraredVISPLANInfrared wireless LAN systems: WLAN system which combine IR technology (Ethernet 100 Mbps) and LAN mobilityVLCVisible light communicationVLCCVisible Light Communication ConsortiumVoIPVoice over IPVRCVertical redundancy checkWWattWDANWireless domestic area networksWDDWavelength division duplexWDMWavelength division multiplexingWDMAWavelength division multiple accessWIFIWireless communication protocols governed by IEEE 802.11 normsWLANWireless local area networksWPANWireless personal area networksWLOSWide line of sightWONWireless optical networkWSWeapons systemWWRFWireless World Research ForumWWWWorld wide web

Introduction

Telecom operators are finding themselves confronted by a growing demand for a higher volume of information to be transmitted (voice, data, pictures, etc.). The increasing frequency in the systems used is a solution because it is able to offer higher bandwidth and allow higher flow rates. In the field of wireless communications, the use of links in the range of optical wavelengths, visible, ultraviolet, and infrared constitutes a form of wireless transmission of a few kilobits per second to hundreds of gigabits per second. They can be implemented either over short distances, limited to one room (office, living room, car, airplane cabin, etc.), or over medium distances (a few tens of meters to several kilometers) outside (atmospheric optical links or free-space optics — FSO), or over large distances in space (high-altitude platform — HAP, planes, drones, intersatellite, etc.).

This technique is not new. Over thousands of years, well before the work of the Abbot Claude Chappe, communication processes, although very primitive, were implementing optical transmission. But the amount of information provided remained low. Optical communications over long distances did not really start until the late 18th Century with the optical telegraph. But the quality of service (QoS) was low; the transmitters and receivers, men and materials’ lack of reproducibility and reliability; and the transmission medium, the air, was changeable.

Soon, electricity (electrical charges) and copper replaced the optical (photons) and air. Transporting information through a copper line allows relatively high flow rates. At the beginning of the third millennium, these connections with copper as the medium are still widely used. For very large distances, for many decades, copper was the base material; it has covered the planet with a vast network of information transmission.

The invention of the laser in 1960 paved the way for an alternative solution — that of fiber optic telecommunication — offering a virtually unlimited transmission capacity. In 1970–1971, the almost simultaneous development of low-loss fiber optics and a semiconductor laser emitting in continuous operation at room temperature led to the explosion in wire optical communication. Glass is the medium for transmission of photons, and glass fibers may have lengths of several thousand kilometers. The optical wires were, therefore, unchallenged in underwater transmissions, transmissions over long distances, and interurban transmissions. It is the essential element of the information superhighway.

Since the liberalization of the telecommunications sector, motivation for the transmission of digital signals by the laser beam in free space is apparent. Several factors condition the renewal of this technology. First, regulatory reasons: there is no need for frequency authorizations or a special license to operate such links, in contrast to a large number of radio links. Second, economic reasons: the deployment of a wireless link is easier, faster, and less expensive for an operator than the engineering of optical cables. Finally, in the race for speed, the optical flow is the winner over the radio (even for millimeter wave) for desirable rates of several gigabits per second. In addition, the availability of components (lasers, receivers, modulators, etc.) widely used in optical fiber telecommunications technology potentially reduces equipment costs. The global market for digital wireless data transmission today is based primarily on radio wireless technologies. However, they have limitations and cannot be absorbed on their own, with a limited spectral width; development increases the need for higher speed.

The main applications of optical wireless focus on wireless telephony, information networks, and high-definition TV.

The objective of this book is to present the FSO that is currently used for the exchange of information, but, because of its many benefits (speed rates, low cost, mobility equipment, safety, etc.), it will explode as a telecommunications technique over the next decade and even become indispensable in computer architectures on short-, medium-, and long-range telecommunications.

From a didactic point of view, the book is organized into 12 chapters supplemented by two Appendices.

Chapter 1 discusses the basic concepts relating to light: the symbolism of the history, the different theories (wave, particle), the propagation and its various laws (reflection, transmission, refraction, diffusion, diffraction, etc.), interference, speed, spectral composition, emission, etc. That ends in 1960 with the laser invention, which opened up the way for many applications: CD, DVD, printers, computer disks, optical fibers, welding, surgery, etc.

Chapter 2, after some definitions related to telecommunications, reviews the various phases of the development of wireless optical communications over the centuries (smoke signals, light signals, movement of torches, etc.). And then in the 18th Century, after many tests, we review the appearance of Chappe’s optical telegraph, the solar telegraph or heliograph, and the photophone of Graham Bell. Their principles (mechanism, code, etc.) are detailed and applications are described.

Chapter 3 presents the contemporary and the everyday life of wireless optical communications: the basic principles, the elements of electromagnetism, the electromagnetic spectrum, the propagation modes (line of sight, wide line of sight, diffusion, etc.), the different layers of OSI model, and the standardization aspects (VLC, IEEE 802.15.7, ECMA, IrDA). Then, contemporary and daily applications of wireless optical communication are described: indoor (limited space), outdoor (free-space optic), or spatial (links to aircraft, drones, HAP, intersatellite communications, etc.).

Chapter 4 is dedicated to the modeling of the propagation channel. It outlines the optical channel baseband and different types of modulation (on-off key (OOK), intensity modulation (IM), pulse position modulation (PPM), etc.). A comparison of the radio model is presented. The noise disturbance (thermal noise, periodic noise (artificial light), shot noise, etc.) is described. The signal-to-noise ratio compares the performance of different systems based on different technologies of digital communication. The channel is multipath (direct, reflected, diffused, etc.); the different paths are combined together. Intersymbol interference may occur. The different models of reflection (specular and diffuse (Lambert, Phong)) are presented. Reflection occurs when the wave encounters a surface on which the dimensions are large compared to the wavelength (floor, wall, ceiling, furniture, etc.). The reflection characteristics depend on the material surface, the wavelength, and the angle of incidence. Emphasis is then placed on the different models of diffusion.

Chapter 5 deals with propagation in the atmosphere. Atmospheric effects on propagation such as absorption and diffusion (molecular and aerosol particles), the scintillations due to the change in the index of air under the influence of temperature variations, and attenuation by hydrometeors (rain, snow) and their different models (Kruse, Kim, Bataille, Al Nabulsi, Carbonneau, etc.) are presented along with experimental results. The experiment implemented to characterize the channel optical propagation in the presence of various weather conditions (rain, hail, snow, fog, mist, etc.) is presented. Fog, whose presence is most detrimental to optical and infrared wave propagation, is explained (definition, formation, characteristics, and development). Visibility, the parameter that characterizes the opacity of the atmosphere, is defined. Measuring instruments for this characterization are described (transmissometer, scatterometer). The features of the “FSO Prediction” software simulating an atmospheric optical link in terms of probability of availability or interruption are described. It is a tool designed to help support decisions for the development of atmospheric optical links at high speeds over point-to-point links on short and medium distances.

Chapter 6 discusses the optical link budget in limited space, which is an important step in establishing a link. Knowing the sensitivity of the receiver, the goal is to calculate the power to implement at the emitter, to enable taking into account the losses in the optical channel. These various losses are identified and evaluated: geometric loss, optical loss, pointing loss, molecular loss, etc. Different cases are considered: a line of sight system and an optical system with reflection. The knowledge of the signal-to-noise ratio is then used to determine the error rate. It is connected to the different attenuations or disruptions of the transmitted signal in the channel.

Chapter 7 deals with immunity and standards’ aspects as well as security and energy issues. For safety reasons, care must be taken to transmit power. Standards were developed by the International Electrotechnical Commission. They list the optical sources in seven different classes according to their level of dangerousness. Communication security is provided either in hardware or in software (encryption). The energy consumption of systems is an important parameter in choosing a technology. Finally, a presentation of the legislative aspect ends this chapter.

Chapter 8 entitled “Optics and Optronics” addresses the analog physical part of an optical device. Optical devices for transmission and reception and optical filtering are presented. The issue of optronics is then developed: the operating principle of the device and optronics emitters (white LEDs, infrared LEDs, laser, etc.) and receivers (photovoltaic cell, PIN photodiode, avalanche photodiode (APD), MSM photodiode, etc.).

Chapter 9 deals with data processing before the digital/analog conversion at the emission and after the analog/digital conversion at the reception. The data processing includes operations such as filtering, compression, analysis, prediction, modulation, and coding. Only modulation and coding parts in a specific configuration to optical wireless are described. Other items not directly related to the optical wireless are described elsewhere in the literature. Different modulations are explored: OOK, NRZ, ASK, QAM, PPM. OFDM and MIMO techniques are discussed. Coding aspects are detailed: principle, definition, performance, and many examples are mentioned: parity checks, cyclic redundancy check, block codes, BCH, RS, convolutional, etc.

Chapter 10 presents the “data link” layer, the second layer of the OSI system. The protocols of this layer handle service requests from the network layer and perform a solicitation of requests for services to the physical layer (downlink direction) and vice versa (upward direction). Access methods (TDMA, FDMA, CDMA, CSMA, WDMA, and SDMA) are described. The QoS parameters are mentioned. The various protocols used in wireless optical communications are presented for different types of data links: point-to-point (remote control, IrDA, VLC), point-to-multipoint (IEEE 802.11 IR, IEEE 802.3 Ethernet (ISCA-STB50), IEEE 802.15.3, IEEE 802.15.7, OWMAC).

Chapter 11 is dedicated to engineering of the installation of wireless optical communication in free space and limited space. In the area of free space (FSO), first there is a description of the principles of operation before turning to the characteristics of the equipment and recommendations for implementation. Optical budget calculations are detailed and examples of the availability of links for various French cities are presented. In the area of limited space, the habitat structure is first described: the distribution of areas of different rooms and the population percentage of a communication covered area. In the architecture of a wireless optical system, there is at least one optical wireless transmission/reception system per room, called base station (BS).

Each BS communicates with the terminals present in every room via a wireless optical communication. Finally, these terminals are connected or integrated to multimedia communication equipment (PC, monitor, PDA, etc.). Different simulations of optical system installations are carried out with a free software tool called “QOFI” and the link budget prepared: the base station is located in the middle of the ceiling (case A), above the door (case B), or on a socket (telephone, Ethernet, PLC (case C)); the terminal is installed in the lower opposite corner of the room (case 1), at a height equivalent to the top of a door (loud speaker, motion detector) (case 2), or on the ground in the middle of the room (case 3).

The aspects of the system are then discussed (the production of optoelectronics modules suitable for optical wireless, taking into account the safety aspect by using a diffuser at the emitter, obtaining an optical gain reception by setting in place an optical device called “fisheye”, or processes such as equalization and OFDM, etc.).

Chapter 12 discusses the future of wireless optical communications in free and limited space at a home or an office. In each case, the advantages of this medium are underlined. The home and office potential are evaluated and faced with the economic and commercial realities.

Appendices remind the reader of various concepts related to optical geometric (refractive index, Snell’s law, sources definition, image, focus, etc.), photometry (steradian, solid angle, etc.), and energy (light intensity, luminous flux, illuminance, luminance, energy flow, lighting, geometric extent, etc.), and various items relating to the use of logarithmic notation (dB, dBW, dBm, etc.).

Various elements described in this book contributed to the development of new recommendations at ITU-R, the Radiocommunication Sector of the International Telecommunication Union, dedicated to propagation data and prediction methods required for the design of terrestrial free-space optical links and the definition of associated systems.

Chapter 2

History of Optical Telecommunications

“I have heard a ray of the sun laugh and cough and sing”1884, Alexander Graham Bell,Inventor of the photophone and probably the phone,Patent 235.496 from 12/14/1880

2.1. Some definitions

2.1.1. Communicate

The verb “communicate” appeared in the French language around 1370. It was derived from the Latin communicare meaning “to share, import”. The idea became enriched as a result of the meaning of the Latin cum (with) and municus (burden).

With this idea of sharing, the word first got a sense of participation in something. It lost the right to be in mutual relationship, in communion with someone. From the 16th Century, the word experienced a new extension in its meaning “transmit” (communicate news, spread disease, share a sense). It is also used in physics, “communicate the heat”.

2.1.2. Telecommunication

The definition of the word “telecommunication” adopted during the 1947 International Radiotelegraphic Conference held at Atlantic City (USA) is:

any transmission, emission or reception of signs, signals, writings, images, sounds or information of any nature by wire, radioelectricity, optics or other electromagnetic systems.

The means of transmission must be of the electromagnetic type, which gives a very wide scope, since, as Maxwell showed, electromagnetic waves include electricity and optics.

2.1.3. Optical telecommunication

This involves any transmission, emission, or reception of visual signs and optical signals on guided and unguided support.

2.1.4. Radio frequency or Hertzian waves

These are electromagnetic waves of frequency lower than 3,000 GHz; they are propagated in space without artificial guidance (in optics, frequencies are significantly higher: hundreds of terahertz).

2.2. The prehistory of telecommunications

In the beginning, the need to remotely communicate was a natural reaction to life in a community. Communication would have been essential from the earliest times: even from the days of Adam and Eve. The first men were already “wireless operators”, since they communicated with each other without wire, using sound and luminous waves (optical signals).

In ancient times, signal fires were used extensively to communicate and transmit a message from one place to another. The smoke was used during the day and the fire was used during the night.

Homer mentions light signals in the Iliad (late 8th Century BC): the fall of Troy was announced by fires lit on the hilltops. The Anabasis indicates this same mode of correspondence between Perseus and the army of Xerxes in Greece. In Agamemnon, Clytemnestra says to Coryphee agreeing with Agamemnon that the announcement of the capture of Troy reached him quickly through relay fires. As soon as Ilion was taken, a fire shone on Ida, a fire that other places copied, to transmit the news. In total, nine bonfires were used probably covering about 550 km relay: Ida, the rock of Hermes in Lemnos, the Mount of Athos, Makistos in Euboea, Messapios, rock of Cithaeron, Epiglancte, the Arachne mount, and Mycenae.

In 426 BC, Thucydides (460–400/395 BC) reports that during the Peloponnesian attack on Corcyra, signs of fire were brandished during the night, announcing the arrival of 60 Athenian ships. Based on this warning signal, the Peloponnesian fleet left quickly during the night.

Later, the Greeks developed more complex processes operating between cities or from one island to another. Aeneas the Tactician (4th Century BC) conceived a code of communication based on fire and water (Figure 2.1). To send a message, two groups of two men on each side had an earthenware pot of exactly the same diameter and height. The base of these vases is a hole of exactly the same size. Initially, the hole is plugged and the two containers are filled with a meter of water. In each of the vases, a cork floats and serves as the cap, with a rod, along its entire length having a succession of military terms placed at a distance determined by each other. These are military terms relating to possible events in war, e.g. riders arrived in the country, heavy infantry, and ships.

Figure 2.1. Aeneas the Tactician device

When one of the events listed on the stick occurs, simple torch signals suffice for groups to come into contact. Once both groups have established contact, they hide the torches and open the holes of their containers.

The corks are lowered at the same time as the liquid drains away, and when the relevant military term of one of two groups reached the top of the container, the operator shakes the torch again to show the flow is ‘off ’. Recipients only have to read the words inscribed on their rod and so on for the next message. Polybius (210/202–126 BC) improved this system by replacing monoalphabetic symbol, by multiple representation, the Polybius square or square of 25. This square is based on a system for converting letters into movements of torches. The letters of the alphabet are divided into five groups of five letters arranged in columns and rows. And to convey a message, it was enough to raise torches on the left to indicate the column and torches on the right to indicate the row.

This transmission process evolved very quickly in a cryptographic technique. Indeed, with such a simple letter shift, even though an enemy could observe the signals exchanged, he/she could not know its meaning.

Later, the Carthaginians linked Africa to Sicily by very bright signals. Then the Romans appropriated the formula and communication throughout the Roman Empire was driven by fire signal lines located on watchtowers that Caesar made great use of in his campaigns in Western Europe.