Satellite Communication Systems Design - S. Tirró.pdf

SatelliteCommunicationSystemsDesign


Editedby

SebastianoTirro

TomysonEmanuele,loveofhismotherandfathermadeperson

ContributorsF.Ananasso

TelespazioS.p.A.,ViaTiburtina965,00156Roma,Italy

A.Bonetto


G.Chiassarini

SpaceEngineeringS.r.l.,ViadeiBerio91,00155Roma,Italy

R.Crescimbeni


E.DAndria


G.Gallinaro


R.LoForti

SpaceEngineeringS.r.L,ViadeiBerio91,00155Roma,Italy

A.Puccio


G.Quaglione


E.Saggese

SpaceEngineeringSr.!.,.ViadeiBerio91,00155Roma,Italy

V.Speziale


S.TirrO


A.Vernucci

SpaceEngineeringS.r.I.,ViadeiBerio91,00155Roma,Italy

V.Violi


G.Vulpetti

PrefaceWriting a comprehensive book on satellite communications requires the command ofmanytechnicaldisciplinesandtheavailabilityofup-to-dateinformationon internationalrecommendations,systemarchitectures,andequipmentstandards.Itisthereforenecessaryto involve many authors, each possessing a good level of knowledge in a particulardiscipline.

Theproblemofusingacoherentandunambiguoussetofdefinitionsandbasic termshas been solved by including in the book all the background information needed forunderstanding satellite communication systems, without any major reference to othertextbooksspecializinginparticulardisciplines.Theobviousconsequenceofthisapproachhasbeenthelargesizeofthebook,withtheadvantages,however,ofpracticallycompleteindependence from other books, more systematic discussion of the subject matter, andbetterreadability.

After the required background information, emphasis has been placed on thediscussion of techniques and system design criteria rather than on specific equipmentimplementationordescriptionofparticularsystems.

Thebookmaybedividedinfivepartsasfollows:

Thefirstfivechaptersprovidemostoftherequiredbackgroundinformation.

Chapter6isanintroductoryoutlineofsatellitecommunicationsystems.

Chapters7to13dealwiththevariousaspectsoftechnicalsystemdesign.

Chapter14discussessystemeconomics.

Chapter 15 provides a brief insight into some foreseeable future developments ofsatellitecommunications.

More specifically, Chapter 1 defines the basic characteristics of the various signaltypes;fourdifferenttypesofsignalsareconsideredinthebook:speech,sound-program,television,anddata.

Chapter2discussesallthecausesofsignalimpairment,suchasthermalnoise,radio-frequency (RF) intermodulation noise generated in nonlinearmulticarrier amplification,linear distortions, propagation delay, and echo. The importance of each cause ofimpairment is strictly related to the type of signal, so that it is not possible to defineperformancespecificationsindependentlyofthesignal.

Chapter 3 concentrates on the source signal processing, including source coding,deterministic or statisticalmultiplexing of various signals (of equal or different nature),and cryptography. This chapter comprises the discussion of the various speechinterpolationtechniques,whichhavefoundwideapplicationinsatellitesystems,butnotyetinterrestrialones.

ThevarioustelecommunicationservicesareclassifiedinChapter4withreference to

theirmajorcharacteristics,suchasunidirectionalityandbidirectionality,point-to-pointorpoint-to-multipoint connectivity, transmission capacity assigned in real time or on areservationbasis,etc.

Chapter5isacomprehensiveandup-to-datereviewofthevariousCCIRandCCITTrecommendationsconcerningthequalityofserviceforthevarioustypesofsignalsdefinedinChapter1and the limits tobe imposedon thesinglesourcesofsignal impairmentasdefinedinChapter2.TherelevantINTELSATspecificationsarealsosummarized.

Chapter 6 gives an introductory outline of satellite communication systems and isthereforeaveryarticulatedchapter,comprisinghistoricalnotes(moredetailedthanthoseprovided in the introduction), a preliminary assessment of the link budget problem, thediscussionofsatellitesandearthstations(ESs)majorcharacteristics,etc.

Particularemphasishasbeenplacedinthischapterontheconceptofmargin,i.e.,ofdifference(indecibels)betweenthecarrier-to-noiseratios(CNRs)experiencedatthetimepercentages defined in CCITT-CCIR recommendations (see Chapter 5) or between theCNRsnecessary toobtainfromtheconsidered transmissionsystemthesignalqualityasspecified by CCITT-CCIR in some recommendations previouslymentioned. These twomarginsmaybecalledatmosphericmarginandtransmissionmargin,respectively.Amajorpeculiarityofthebookistheimportancegiventoabalanceddesignofthesystem,suchthatneitherbandwidthnorpowerresourcesarewasted.Balancedconditionsareobtainedwhenthetransmissionmarginequalstheatmosphericmargin.Attentionmustbepaidtoaprecise definition of the margins, since various types of atmospheric and transmissionmargins exist. An additional consideration is that, whereas frequencymodulation (FM)generallyallowsabalancedconditiontobeattainedwhenevertheatmosphericmarginisnottoolarge,othermodulationtechniquesgenerallyproduceunbalancedsystems.

When the communication service is bidirectional, an additional problem of designoptimization arises, since it is useless to have available for service just one of the twochannels composing the transmission circuit. When atmospheric events produceattenuationof thecarrier atoneof the twocommunicatingESs,onechannelwillsufferfadingintheuplinkandtheotheroneinthedownlink,Thetwochannelsmaythereforebecalled up-faded (UF) and down-faded (DF), respectively, and an optimally designedsystemwillbeUF-DFbalanced,inadditiontobeingpower-bandwidthbalanced.

Apportionmentof thetotalspecifiedserviceunavailabilitytoequipmentfailuresandtopropagationeventsexperiencedinthetwocommunicatingESsallowsdeterminationoftheCNRdeteriorationduetoatmosphericpropagation.

Thesubjectofoptimaloperationalorbitsforcommunicationsatellitesandofthebeststrategy tobe followed for injecting thesatellite in theoperationalorbit isdealtwith inChapter7.Particularemphasis isplacedon thecharacteristicsof thegeostationaryearthorbit (GEO), by far the most interesting for present satellite communications. TheproblemsofvisibilityfromGEO,Dopplereffect,andeclipseareaddressed.Thesatelliteorbitissubjecttoperturbations,sothatmaneuversareperiodicallyrequiredtomaintainitthroughout satellite life. The discussion in Chapter 7 is limited to the causes of theperturbations.Afterashortdiscussionofsomeadvancedpropulsionandorbitalconcepts,

the chapter concludes with a presentation of the available launch vehicles and of thedevelopmentsforeseeableinthefieldofspacetransport.

Chapter8dealswithsomemajorRFdesignissues,suchasantennasandatmosphericpropagation.

Chapter 9 discusses analog transmission, emphasis being on FM and the relatedthreshold phenomenon.Much attention is also paid to the use of syllabic compandors,whichhasbeenratherfrequentwithFM(compandedFM)fordomesticcommunicationsindevelopingcountries,andwithsinglesideband(amplitudecompandedsinglesideband,ACSB)fortrunkingcommunicationsindomesticU.S.systems.

Frequencymodulation isalso thepreferred technique for television transmissions ingeneral and for television broadcasting satellites (TVBS) systems in particular. TheWARC77 plan for TVBS and the perspectives for high-definition television arediscussed.

Digital transmission,which isbecomingmoreandmorepopularwith the advent ofthe integrated services digital network (ISDN) is the subject of Chapter 10, whichdiscussesbothmodulationandchannelcoding,plusthejointoptimizationofmodulationandcoding,whichisalsocalledcodulation.Abasictheoremofsystemstheorystatesthatanoptimalsystemisingeneralcomposedofnonoptimalsubsystems.Itmustthereforebeexpected that an optimalmodulation scheme combinedwith an optimal channel-codingschemecannot reach theperformance offered by an optimal codulation scheme. Phase-shiftkeying(PSK)isbyfarthemostutilizedmodulationschemeforbidirectionalfixed-pointcommunications.ThisjustifiestheemphasisputonPSK,forwhichmanyresultsofcomputersimulationsandfieldtrialsarereported.Manyotherdigitalmodulationschemesarealsodiscussed,suchasfrequency-shiftkeying(FSK),whichfindsapplicationindatacollection systems, and pulse position modulation (PPM), which is used in someintersatellite link(ISL)configurations to increase thediode laser life.Channelcoding isextensively discussed, the emphasis being on convolutional coding with soft Viterbidecoding, a scheme often used, since superior performancemay be coupledwithVLSIimplementationofcodingdecodingcircuits.

Chapter11dealsindetailwiththeoptimaldesignofabidirectionalcircuit,wheretheUF-DFbalanceconditionmustbeimplemented.Thisisdoneforseveraltypesofanalogand digital transmission systems. An interesting conclusion is that coded 8-PSK onlylooks attractive in C-band, whereas uncoded 4-PSK seems generally preferable in K-band, and4-PSKplus convolutional coding/Viterbi decodingmay be convenient inKs-band,whereexcessbandwidthisgenerallyavailable.

Channel access schemes are discussed inChapter 12.Themost complex scheme istime-divisionmultipleaccess(TDMA),whichisgiventhemostattention,butfrequency-division multiple access (FDMA) and code-division multiple access (CDMA) are alsodiscussed, and their performances are compared with that of TDMA. The satellite-switchedversionsofTDMAandFDMA, respectivelycalledSS-TDMAandSS-FDMA,arealsoconsidered.

Thesubjectofnetworking,whichisoftenoverlooked,receivesextensiveattentioninChapter13.

Terrestrial networks and satellite systems are typically rather different from atopological viewpoint. In particular, the location of several ESs in the same satelliteantennabeammakespossiblethefeaturesofmultipleaccessandmultipledestination.Thetransmissioncapacityisthereforeassignedinprimitive(globalcoverage)satellitesystemsaccording tomodalitieswhich justify thenameof demand assignment, as opposed toswitching,which is used to designatemodalities adopted in terrestrial networks. Theunificationofthetwodisciplinesinasinglewidercontextrequiresthedefinitionofanewtechnicalterm:commutationisthetermsuggestedinthisbook.Chapter13discussesthevariouscommutationfunctionspossibleinasatellitesystem,andtheachievablenetworkefficiencies, computed as the ratio between the handled traffic and the transmissioncapacity.

The analysis of the system performance for telephony is performed by using theclassicalErlangandEngsetformulas.Also,packetservicesusingrandomaccessschemes(e.g., ALOHA) and point-to-multipoint videoconferences are examined. The possiblesignalingstandardsusablefortelephony,packetservices,andvideoconferencingarealsooutlined.Finally,thesubjectofintegratingasatellitesystemwithaterrestrialnetworkisdiscussed.

Chapter14dealswith systemeconomics, firstby suggestingamethodology for thedesign of a viable satellite system, then by analyzing several important examples. Theviabilityofthesystemmustbeassessedcomparingitscostbothwiththepriceofferedbycompetitors in themarket andwith the amount the customer is prepared to pay for theservice.The analysis confirms that the satellite is generally attractive for unidirectionalsystems and formobile systems,whereas the comparison ismuchmore articulated forbidirectionalfixed-pointcommunications.

The implementation of systems heavily using the space-segment capacity (e.g., filetransfer,videoconferencing,etc)atacostwhichtheuser iswillingtopay,willprobablyimplytheuseofsophisticatedonboardprocessingtechniques.

ThepossiblefuturedevelopmentsofsatellitecommunicationsarebrieflyaddressedinChapter15,whichconcentratesonISLs,satelliteantennas,andprocessingrepeaters, forreasonsalreadymentioned.

The book concludes with four appendixes, which deal respectively with radioregulations provisions, coordination between a satellite system and terrestrial systems,coordinationbetweensatellitesystems,andoptimaluseoftheGEOfrequencyresource.

Thisbookcame intoexistence thanks tomanycontributions,which Iampleased toacknowledge. First of all, I would like to thank my parents, Francesco Tirro andGiuseppina Lombardo, to whom I will be eternally indebted for their sacrifices thatenabledme to get a degree in electronics. I would also like to thank Professor BrunoPeroni, my most important teacher at the University of Rome, who guided me to adoctoralthesisonthresholdextensiondemodulatorsandgavehelpfulsuggestionsforthe

productionofthebook,andMr.LivioBruno,DirectorGeneralofTelespaziofrom1984to1989,whohasbeenmyprofessional teacherand towhomIammostly indebtedformypersonalcompetenceinsatellitecommunications.

When Iwas contacted byPlenum towrite a book on satellite communications,myfirst consideration was that, because of the wide and multidisciplinary nature of thedomaintobecovered,competenceinmanyareaswasrequired.Therefore,Idecidedtobethe editor of the book and to ask other expo is to contribute as authors. A luckycircumstancewastheavailabilityinmycompanyofpracticallyalltherequiredexpertise.Therefore, I asked and obtained from Telespazio the necessary support to produce thebook. Grateful acknowledgment is therefore made to Telespazio S.p.A., the companywhere I spent about 22 years of my professional life, and to all the authors for theircompetentandenthusiasticcooperation.

MyspecialgratitudetoMr.CesareBenigni(DirectorGeneralofTelespaziofrom1971to1984)forauthorizingtheworkandprovidingmanyhelpfulcomments.Aheartynodofappreciation to Mr. Ken Derham, my Plenum Publishing interface, and to Prof. BarryEvansoftheUniversityofSurrey,forimportantsuggestionsconcerningeditorialaspectsandbookstructure.

Finally,tomysecretary,Mrs.MarinaMinorenti,forherpatientandpreciouswork,toMr.BrunoCacciamani,whoproducedmostof thedrawings,andtomywifeRosangela,whomadethefinalrevisionofthemanuscript,mydeepestthanks.Toallofthem,maythisbookbeanevidenceofthehighprofessionalleveloftheirassistance.

S.Tirro

ContentsIntroduction.I

S.Tirro

TheHistory....1

ThePerspectives..6

TheRegulatoryBodies..7

1.Signals..11

E.SaggeseandS.Tirro

1.Introduction.11

II.SpeechSignals11

A.Bandwidth12

B.VoiceActivityFactorandSpeechInterpolation.12

C.TheConstant-VolumeTalkerandtheMeasuredSpeechVolumes13

D.LaplacianRepresentationofaSpeechSignal...14

E.MultichannelSpeech.16

F.PeakFactor..16

G.TestToneLevel...16

H.MultichannelTelephonyLoad...18

111.Sound-ProgramSignals..19

A.Bandwidth19

B.SourceActivity....19

C.PowerLevelStatistics.20

D.TestToneLevel...21

E.CompatibilitywiththeFDMTelephonyPrimaryGroup....21

IV.VideoSignals21

A.ColorimetryFundamentals..21

B.MonochromeTelevision25

C.ColorTelevision...28

D.MACSystems....33

E.High-DefinitionTelevision..36

References..38

2.CausesofSignalImpairment.41

S.Tirr6

1.Introduction.41

II.InternalNoise42

A.ShotNoise42

B.ThermalNoiseandNoiseTemperature..42

C.NoiseofanAttenuator43

D.NoiseFigure..44

III.ExternalNoise..44

IV.ModelingofInternalandExternalNoise46

V.QuantizingNoiseandDigitalCompanding..48

VI.EquipmentLinearDistortions..54

VII.NonlinearDistortions..57

A.General.57

B.UnmodulatedCarriersandIntermodulationLines59

C.ModulatedCarriersandIntermodulationNoise.62

VIII.SpectrumTruncation...67

IX.IntelligibleCrosstalk....68

X.EchoduetoEquipmentMismatching.68

XI.Interferences70

XII.PropagationDelayandEcho..70

A.General.70

B.TheEffectsofPropagationDelay.71

C.TheEchoPhenomenon71

References..72

3.BasebandSignalProcessing..75

E.Saggese

1.Introduction.75

II.SpeechSourceCoding..76

A.General.76

B.WaveformCoding..78

C.Vocoders83

D.HybridSolutions....85

E.SomeMajorCommercialStandards.85

F.Conclusions..87

III.VideoSourceCoding...87

A.General.87

B.RedundancyReduction88

C.ControlledImageDegradation...91

D.CodingColorSignals.95

E.EffectsofChannelErrors..96

F.AchievementsandTrendsinImageCoders...96

IV.Cryptography97

A.Private-KeyCryptography..97

B.Public-KeyCryptography..99

C.BlockCipheringandStreamCiphering..99

D.CryptographyinCommunicationNetworks...101

E.CryptographyinSatelliteCommunicationSystems102

F.Pay-per-viewTelevision104

V.Multiplexing.105

A.DeterministicMultiplexing..105

B.StatisticalMultiplexing109

References..118

4.Services....121

A.Puccio

1.Introduction.121

II.DefinitionofService...122

III.TechnicalAttributesofBearerServices.123

A.InformationTransferAttributes..123

B.AccessAttributes...126

C.GeneralAttributes..126

IV.CategoriesofService...127

V.TheServicesHorizon...128

A.General.128

B.TelephonyEvolution.128

C.TelexEvolution...130

D.DataEvolution....130

E.TelevisionEvolution.131

References..131

5.QualityofService133

A.Puccio,V.Speziale,andS.Tirro

1.Introduction.133

II.ReferenceCircuits....134

III.SNR.BEPandConventionalLinkQuality..135

IV.AvailabilityObjectivesofSatelliteSystems..136

V.PropagationPerformanceofSatelliteSystems....137

A.PerformanceCriterionforAnalogTelephony..137

B.PerformanceObjectivesforDigitalTelephony..139

C.PerformanceObjectivesforInternationalISDNLinks....141

D.PerformanceEvaluationforaDigitalSatelliteSystem..145

E.PerformanceObjectivesforSound-ProgramCircuits..146

F.PerformanceObjectivesforTelevisionSignalsTransmission151

G.SubjectiveAssessmentofSoundand/orVideoSignalQuality154

VI.TransmissionPerformanceofSatelliteSystems...156

A.PropagationDelayandEcho....156

B.LinearandNonlinearDistortionsinFDM-FMTelephony...157

C.LinearandNonlinearDistortionsinFMTelevision157

D.LinearDistortionsinDigitalSystems163

VII.TrafficabilityPerformance.164

References..167

6.SystemOutline.171

A.Bonetto,S.Tirro,andV.Violi

1.Introduction.171

II.BasicConfigurationofaSatelliteCommunicationSystem..172

III.EvolutionofSatelliteCommunicationSystems...174

IV.ArchitecturesofSatelliteSystemsforNetworkServices175

V.SummaryofImpairmentSources...176

VI.AntennaCharacterization.179

A.General.179

B.Gain..180

C.EffectiveAreaandApertureEfficiency..181

D.NoiseTemperature..182

E.Polarization..183

VII.EarthStationCharacterization..188

A.General.188

B.TheFrequencyCoordinationProblem..189

C.GeneralLayoutofaSatelliteEarthStation...189

D.EarthStationBlockDiagram...189

E.Low-NoiseAmplifiers.191

F.High-PowerAmplifiers192

G.Front-EndSpecifications..194

VIII.SatelliteCharacterization.195

A.General.195

B.SatelliteConfigurations195

C.TheEnvironment...199

D.SatelliteImplementationProgram.201

E.PayloadEfficiency..204

F.ReliabilityConsiderations..205

G.Front-EndSpecifications..209

IX.LinkBudgets210

X.GEOSatellitesversusTerrestrialRadioLinks....215

XI.GEOSatellitesversusnon-GEOSatellites..217

XII.PowerversusBandwidthTrade-offs..219

XIII.TheVariousMargins...222

A.General.222

B.RainMargin..223

C.BreakingMargin...224

D.DemodulatorMargin.224

E.TransmissionMargin.225

F.AvailableMargin...225

XIV.TheBalancedSystem.PowerandBandwidthLimitation..225

XV.ServiceRequirementsandPropagationStatistics...227

XVI.Propagation-andTransmission-limitedSystems...229

XVII.Clear-WeatherandBad-WeatherDefinitions....233

XVIII.ApportionmentofImpairments....233

References..241

7.OrbitsandControlledTrajectories....243

V.VioliandG.Vulpetti

1.Introduction.243

II.OrbitalElements....244

III.FundamentalOrbitalLaws247

IV.OrbitPerturbationsforaTelecommunicationSatellite252

V.TargetOrbits256

A.Sun-SynchronousOrbits257

B.Low-PerigeeHigh-EccentricityOrbits258

C.GeostationaryandQuasi-GeostationaryOrbits..258

VI.AchievementoftheGeostationaryOrbit258

A.RocketPropulsion..258

B.ThrustandSpecificImpulse....259

C.PropellantCharacteristics..260

D.PoweredFlightEquation..261

E.TheHohmannProfile.265

F.Staging.267

G.Multiple-BurnMissionProfiles...270

VII.TheGeostationaryOrbit.273

A.Introduction..273

B.SatelliteEphemeridesandDistance.274

C.CentralProjectionoftheEarth..275

D.Eclipse.277

E.SunInterference...279

F.ApparentMotionofaQuasi-GeostationarySatellite..280

G.VelocityIncrementsNeededforStation-KeepingintheGeostationaryOrbit.281

H.DopplerEffect....282

I.PolarizationRotation.282

VIII.AdvancedConcepts...285

IX.LaunchVehicles..287

References..296

8.Radio-FrequencyDesignIssues299

A.BonettoandE.Saggese

1.Introduction.299

II.BasicAntennaConfigurations..300

A.General.300

B.FactorsLimitingAntennaEfficiency300

C.RadiationPatterns..302

D.TheParabolicAntenna305

E.TheCassegrainAntenna..307

F.OffsetAntennas...308

III.PropagationPhenomena.310

A.FaradayRotation...310

B.Attenuation..311

C.Depolarization....323

D.RefractionEffects..326

E.AdaptiveFadeCountermeasures..327

References..331

9.AnalogTransmission....333

S.Tirro

1.Introduction.333

II.SyllabicCompandors...334

A.General.334

B.CompandorTransferCharacteristics334

C.EffectsofCompanding335

III.AmplitudeModulation..338

A.PowerSpectrum...338

B.Carrier-to-NoiseandSignal-to-NoiseRatios...339

C.TransmissionQualityforMultichannelTelephoneSignalsinSSBSystems....341

D.Amplitude-CompandedSingleSidebandwithMultichannelLoading.341

IV.FrequencyModulation..342

A.PowerSpectrumofaCarrierModulatedbyaSinusoid....342

B.BandwidthOccupiedbyaMultichannelTelephoneSignal...343

C.PowerSpectrumduetoMultichannelTelephoneSignalModulation..343

D.PostdetectionNoiseSpectrumandEmphasisLaws344

E.MeasurementofMultichannelTelephoneSignalQuality...345

F.FrequencyModulationAdvantagewithSinusoidalModulation.346

G.FrequencyModulationAdvantagewithMultichannelTelephoneSignals..347

H.Single-Channel-Per-CarrierSystemsinFM...347

1.SignalSuppressionandDemodulationThresholdinFM....349

J.ExplanationoftheThresholdPhenomenonduetoRice....351

V.DesignofFMMultichannelTelephoneSystems...353

A.General.353

B.ParametricCalculationofLinkParameters...355

C.CalculationofLinkParametersforaGivenDemodulatorMargin.357

D.ThresholdExtensionandRelatedAdvantagesonLinkParameters..

357

E.TheFMBalancedSystem..358

F.CompandedFMwithMultichannelLoading...362

G.ExperimentalResultsforMultichannelTelephonyPLDemodulators..367

H.Success,Decline,andPossibleFutureofthePLDemodulator376

1.IntermodulationNoise378

J.EffectofInterferences389

K.TruncationEffectsduetoFiltering.393

L.CarrierEnergyDispersal..395

M.Time-AssignedSpeechInterpolationanditsEffects396

VI.TheDesignofFM-SCPCTelephoneSystems....398

A.General.398

B.UncompandedFM-SCPCSystems.398

C.CompandedFM-SCPCSystems..399

D.VoiceActivation...401

VII.DesignofFMTelevisionSystems...401

A.ExperimentalResultsforTelevisionPLDemodulators....401

B.TruncationEffectsduetoFiltering.402

C.NonlinearDistortionsofFMTVSignals....404

D.EffectofInterferenceonFMTVSignals....406

E.CarrierEnergyDispersal..406

F.Point-to-PointLinks:VideoOnly..407

G.Point-to-PointLinks:Video+Audio409

H.BroadcastingSystems.412

References..414

10.DigitalTransmission..417

F.Ananasso,R.Crescimbeni,G.GallinaroandS.Tirro

I.Introduction.417

II.EvaluationofTransmissionErrorProbability....419

A.General.419

B.StructureoftheOptimalReceiver.422

C.ErrorProbabilityinBinaryCommunicationSystems..425

D.L-aryCommunicationSystems...426

E.TransmissionBounds.TheShannonLimit....428

III.ISIandModelingofDigitalCommunicationSystems.429

A.General.429

B.IntersymbolInterferenceandNyquistPulses...430

C.DesignofLinearChannels....433

D.ApportionmentofFilteringwithPracticalPulses.433

IV.DigitalAmplitudeModulationSystems.436

A.General.436

B.On-OffKeying....436

C.Amplitude-ShiftKeying442

D.PulsePositionModulation..443

V.Frequency-ShiftKeying..445

VI.Phase-ShiftKeying....448

A.General.448

B.PSKasaLinearModulationScheme449

C.ErrorProbability...451

D.CarrierRecovery...454

E.ClockRecovery...457

F.UnbalancedQPSKModulation...460

G.CarrierEnergyDispersal..460

VII.SimulationofaQPSKChannel....461

A.General.461

B.RegenerativeChannelSimulation.466

C.TransparentChannelSimulation..474

VIII.OffsetBinaryModulations478

A.Spectrum-SpreadingEffect..478

B.Offset-QPSKandMinimum-ShiftKeying....480

C.TheQuadratureOverlappedRaised-CosingModulation....483

IX.Channel-CcdingBackground..485

A.General.485

B.CodeRate486

C.CodingGain..487

D.Hard-SoftDecisors..488

E.Weight,HammingDistance,andCorrectableErrors..490

F.TypesofCodes...491

G.SystematicCodes...491

H.Encoding-DecodingOperations..492

1.DecodingThreshold.497

J.DecoderSynchronization..498

K.Variable-RateCoding.498

X.AutomaticRepeatRequest499

A.Stop-and-WaitARQ.5(X)

B.ContinuousARO5(X)

XI.BlockCodes500

A.General.500

B.CyclicCodes..501

C.WordErrorandBitErrorProbabilities..504

D.GolayCodes..505

E.BCHCodes..506

F.Reed-SolomonCodes507

XII.ConvolutionalCodes...511

A.CodedSignalGeneration..511

B.DistanceProperties..513

C.Performance..516

D.TheViterbiAlgorithm519

XIII.AdditionalTopicsonForwardErrorCorrection...521

A.Interleaving..521

B.ConcatenatedCodes.521

C.ConcatenatedBlockCodes....522

D.ConcatenatedBlockPlusConvolutionalCodes..523

E.PerformanceComparisonforVariousCodingSchemes....526

XIV.CombinedCodingandModulation...528

A.General.528

B.DistancePropertiesofSignalSets.530

C.Continuous-PhaseModulations...533

D.Trellis-CodedModulations..540

E.Block-CodedModulations..546

XI.Conclusions.548

References..549

11.BidirectionalCircuitDesign.553

S.Tirro

1.Introduction.553

II.PowerControlPoliciesandOptimumSystemDesign.555

III.CNRVariationsduetoAtmosphericPropagation..563

IV.IntrasystemInterferencesandAtmosphericPropagation..565

V.TransparentSingle-Carrier-Per-TransponderSystems.568

A.General.568

B.SCPTSystemswithFullUPPC...569

C.SCPTSystemsNotUsingUPPC..570

D.SCPTSystemswithPartialUPPC.570

VI.TransparentFDMASystems..573

A.General.573

B.FDMASystemswithFullUPPC..574

C.FDMASystemsNotUsingUPPC.578

D.FDMASystemsUsingPartialUPPC579

VII.RegenerativeSystems..579

VIII.DeterminationofTransmissionParameters..582

A.General.582

B.FDM-FMCarriers..582

C.PSKCarriers..584

IX.DeterminationofFront-EndCharacteristics..584

X.DiscussionofTypicalExamples....584

References..587

12.Channel-AccessSchemes...589

A.Vernucci

1.Introduction.589

II.Frequency-DivisionMultipleAccess..590

A.General590

B.FDMASolutions...591

C.EnhancedFDMAArchitectures..596

D.FrequencyPlan...598

III.Time-DivisionMultipleAccess....601

A.General.601

B.TrafficBursts....603

C.Packetizing-Depacketizing....605

D.TheTDMAFrame..607

E.TheReferenceBurst.608

F.TheUniqueWord..610

G.TDMASystemArchitectures...613

H.TheBurstTimePlan.617

1.AcquisitionandSynchronization..619

IV.Code-DivisionMultipleAccess....622

A.General.622

B.Spread-SpectrumConcept..623

C.Spread-SpectrumTechniques...626

D.SynchronizationAspects627

V.AccessTechniquesComparison....629

A.General.629

B.FundamentalBehavior629

C.PracticalComparison.631

D.Conclusions..634

References..634

13.Networking...637

S.Tirro

1.Introduction.637

H.DefinitionsandBasicAssumptions...638

A.NodesandEdges.638

B.Circuits,Channels,Half-Circuits,andTerminations(Trunks)639

C.BundlesofCircuitsandBundlesofHalf-Circuits.640

D.One-WayandTwo-WayCircuitOperation...640

E.TrafficRearrangement,Commutation,andDynamicManagementofResources..640

F.DemandAssignmentandSwitching:WhyTwoDifferentNames?.641

G.CallBlockingandNetworkEfficiency642

H.DelayandThroughput643

III.TerrestrialNetworkStructure..643

A.TypicalStructureofaTelephoneNetwork....643

B.ISDNandNx64Services....646

C.PacketServices....646

D.High-SpeedServices.647

IV.TypicalStructuresofSatelliteSystems.649

A.GlobalCoveragewithSingleTransparentRepeater650

B.GlobalCoveragewithMultipleTransparentRepeaters....651

C.Multiple-BeamSystemswithTransparentRepeaters..652

D.Scanning-BeamSystemswithSingleTransparentRepeater..654

E.MixedSystems....656

F.RegenerativeSystemswithT-StagesOnboard..657

V.ConnectionTechniquesandNetworkStructuresforTelephony..657

A.HierarchyofTrafficSources....657

B.HierarchyofBundles.658

C.SymmetricandAsymmetricBundles658

D.NumberofBundlesandNetworkEfficiency...659

E.CommutationFunctions662

F.SystemswithT-StagesOnboard..667

G.OptimizationofSystemEfficiency.668

H.EvolutionfromLongtoShortFrames..670

1.CompatibilityProblemsbetweenT-StagesOnboardandDSI671

J.Double-RateSystems.672

K.AlgorithmsforDynamicManagementofResources..672

VI.ConnectionTechniquesandNetworkStructuresforOtherServices673

A.Nx64Services...673

B.PacketServices....675

C.High-SpeedServices.678

D.Point-to-MultipointConnectionTechniquesforVideoconferencing..679

VII.SummaryofAdvantagesandDisadvantagesofT-StagesLocationOnboardtheSatellite...683

VIII.SignalingProblems....684

A.TelephoneSignaling(FixedAssignmentoftheSatelliteChannel)684

B.TelephoneSignaling(DemandAssignmentoftheSatelliteChannel)686

C.Nx64Services...688

D.PacketTransmissions.688

E.Packet-SwitchingServices..688

F.High-SpeedServices.689

G.PossibleGatheringProtocolforVideoconferencing689

H.AsynchronousProtocolsforDynamicManagementofResources691

IX.IntegrationofSatelliteSystemswithTerrestrialNetworks..692

A.DevelopingCountries.692

B.DevelopedCountries.692

C.InternationalSystems.694

X.Conclusions.695

References..695

14.SystemEconomics697

S.Tirro

1.Introduction.697

II.Definitions.698

A.SystemTypes....698

B.SystemComponents..700

C.EconomicDefinitionsandBasicCostData...700

D.Trunking,Network-Oriented,andUser-OrientedSystems...707

III.AMethodologyforSystemOptimization709

A.Introduction..709

B.GroundSegmentTrade-Off....710

C.SpaceSystemTrade-Off711

IV.UnidirectionalSystemsExamples...712

A.PlatformDataCollection..713

B.DataDissemination..713

C.SoundBroadcasting..714

D.TelevisionBroadcasting714

V.TrunkingSystems....716

A.Introduction..716

B.TheINTELSATSystemCase...717

C.TheEUTELSATSystemCase...721

D.North-AmericanSystems..724

VI.SatelliteSystemsforPublicTelephoneNetworks..774

VII.InteractiveDataUser-OrientedSystems726

VIII.Voice-Video-FileTransferUser-OrientedSystem..728

A.Configuration1...728

B.Configuration2...728

C.Configuration3...728

D.Configuration4...730

IX.SatelliteSystemsforMobileCommunications....732

X.Conclusions.734

References..734

15.FutureDevelopments....737

G.Chiassarini,R.Crescimbeni,G.Gallinaro,R.LoForti,A.PuccioandS.Tirro

1.Introduction.737

11.IntersatelliteLinks....737

A.General.737

B.ISLViabilityforSeparatedGEOSatellites...739

C.OpticalIntersatelliteLinks....740

D.MicrowaveIntersatelliteLinks...743

III.SatelliteAntennas....744

A.General.744

B.SomeAntennaConfigurations...745

C.FocusedMultibeamAntennas...748

D.TheMultiportAmplifier750

E.DirectRadiatingArrays751

F.ImagingAntennaSystems..753

G.ActiveAntennasAssessment...754

IV.OnboardProcessing...756

A.General.756

B.SpaceRadiationsandRadiationHardening...756

C.MulticarrierDemodulators....761

D.FECDecodingOnboard..766

E.OnboardSwitching..767

F.FROBEProcessingforSS-FDMASystems...771

References..772

Appendix1.RadioRegulationsProvisions...775

E.DAndria

1.Introduction.775

II.FrequencyAllocations..776

III.InterferenceCoordination.777

A.ModesofInterferencebetweenSpaceandTerrestrialServices778

B.ModesofInterferencebetweenStationsofDifferentSpaceSystemsinFrequencyBandswithSeparatedEarth-to-SpaceandSpace-to-EarthAllocations..779

C.ModesofInterferencebetweenESsofDifferentSpaceSystemsinFrequencyBandsforBidirectionalUse779

IV.RadiationLimitations..779

References..781

Appendix2.FrequencySharingamongFixed-SatelliteServiceNetworks..783

E.DAndria

1.InterferenceEvaluationtoDetermineifCoordinationisRequired783

II.DetailedCoordinationCalculationsandInterferenceCriteria...785

III.PossibleMethodstoSolveIncompatibilities..787

A.IncreaseinAngularSeparation...787

B.AdjustmentofNetworkParameters788

C.FrequencySeparation(Staggering).788

D.DeparturefromCCIRRecommendations....788

References..789

Appendix3.FrequencySharingbetweentheFixed-SatelliteServiceandtheFixedService..791

E.DAndria

I.DeterminationoftheCoordinationArea791

II.DetailedCoordinationCalculationsandInterferenceCriteria...795

III.PossibleMethodstoSolveIncompatibilities..795

A.FrequencySeparation.796

B.AdjustmentofNetworkParameters797

C.OtherMethods....797

References..797

Appendix4.EfficientUseoftheGeostationaryOrbit-SpectrumResource799

G.Quaglione

1.OvercrowdingintheGeostationaryOrbit799

II.CommunicationCapacityoftheGeostationaryOrbit.800

A.MethodA(Pessimistic)800

B.MethodB(Optimistic)801

C.CCIRMethods....801

III.MajorFactorsAffectingtheEfficiencyofGeostationaryOrbit-SpectrumUtilization

801

A.FrequencyReusePotential..802

B.SpacecraftAntennaRadiationCharacteristics..803

C.EarthStationAntennaRadiationCharacteristics.804

D.Stationkeeping....805

E.InterferenceAllowance805

F.OptimizationofFrequencyAssignmentsandModulationCharacteristics....806

IV.OutlineoftheMainResultsofWARC-ORB85-88.806

References..809

Appendix5.AuthorsofIndividualSections..811

Appendix6.ListofAcronyms..813

Index.821

IntroductionS.Tirro

TheHistory

First communications using artificial satellites of the earth were implemented at thebeginningof thesixties,using lowearthorbit (LEO)satellites likeEcho (1960),Telstar(1962),andRelay(1962).

The satellite was used as a cable in the sky to connect two points on the earthssurface, generally very far from each other. The satellite potential was particularlydemonstrated by transmitting television signals over the Atlantic Ocean, since noterrestrialalternativeswereavailableatthattimeforthistypeofservice.

Amajor improvement of the system configurationwas obtained by using satellitespositioned at 35,786 km over the earths surface, in a circular equatorial orbit. At thisaltitude the orbital period is exactly one sidereal day, so the satellite is seen in a fixedposition of the sky.A single satellite positioned in this geostationary earth orbit (GEO)over the Atlantic Ocean therefore enables continuous communications between EuropeandNorth America, using earth stations (ESs) equipped with a single antenna system,withoutseveretrackingrequirements.

The first GEO satellites were Syncom 2 (1963) and Early Bird (1965), also calledINTELSAT-1, since it was the first satellite commercially used by INTELSAT (theINternationalTELecommunicationSATelliteConsortium,whichwas later tobecomeanorganizationandtoassumelegalcharacter).

Primitive space technology could only implement small and simple satellites,emphasisbeingplacedonreliabilityofdesign,inordertoachieveasatellitelifeofseveralyears.Conversely,theESshadtobelarge,complex,andexpensiveinordertoobtainanacceptablereceivedsignal.TheESsusedfor thefirst transatlanticcommunicationswereprovidedwithantennasof25-32mdiameter,verycomplexlow-noiseamplifiers(LNAs),andverypowerfulhigh-poweramplifiers(HPAs).Thistypeofradiofrequency(RF)frontendwasstandardizedbyINTELSATandnamedstandardA.ForseveralyearsonlyESsrespectingthisstandardwereusedintheINTELSATsystem.

S.TIRROSpaceEngineeringS.r.l.,ViadeiBerio91,00155Roma,Italy.

The frequencies selected for the first implementations were 6 GHz for the uplink(earth to satellite) and4GHz for thedownlink (satellite toearth).At these frequencies,atmospheric attenuation is small, and full advantage could be taken of the basictechnologyalreadydevelopedfortheterrestrialradiolinks.However,thismeantthatESshad to be located very far from traffic sources, in areas well protected from terrestrialinterferences.ESsizewasanotherfactorrequiringaremotelocationoftheES.

TheEScomplexityrequiredhighlyqualifiedtechnicalpersonnelforitsoperationand

maintenance.

Inaddition,severalsystemdesignproblemsandpossibilitieswereexperienced,suchas the multidestination feature, multicarrier operation of a nonlinear amplifier, andoptimizationofafrequencymodulation(FM)systemworkingveryclosetothethresholdpoint.

Peculiardesign,highpersonnelqualification, and remoteES locationcontributed toan initiate atmosphere around satellite communications but, although extremelymotivatingformanypeoplewhothusfeltpartofaspaceelite,thesefactorscontributed,inthelongrun,communicationdifficultiesbetweenterrestrialandsatellitecultures.

Only a few developed countries took part in the first satellite communicationexperiments; at the start of commercial operationswith theEarlyBirdonly sixstationswereoperational:AndoverintheUnitedStates,MillVillageinCanada,PlemeurBodouinFrance,GoonhillyDowns in theUnitedKingdom,Raisting inGermany, and Fucino inItaly.

Two companies, COMSAT (the COMmunication SATellites Corporation) in theUnited States and Telespazio in Italy, were created in those years specifically for thedesign,implementation,andoperationofsatellitecommunicationsystems.

Most communication engineers were skeptical about the future development ofsatellitecommunicationsforservicesotherthantelevision,sincesubmarinecablesseemedsatisfactoryfor theservicedemand.Muchofthisskepticism,however,canbeexplainedbythepoliticalwilltoperpetuatetheexistingstructureoftheinternationalcommunicationnetwork,whichwasstronglyhierarchicalandbasedonveryfewmajornodes,whereasthesatellite was offering, by its nature, a democratic structure of the network and theeliminationofmanytransits.

Thesuccessfuldeploymentofaninternationalsatellitecommunicationnetworkmusttherefore be considered as the result of several enlightenedpolitical decisions. In 1959,Resolution1472oftheUnitedNationsGeneralAssemblystatedthebasicprinciplesoftheopenskypolicyandofspacecooperation,andwasinstrumentalintheestablishmentoftheCommitteeonthePeacefulUsesofOuterSpace.In1962,theU.S.CongresspromulgatedtheSatelliteCommunicationsActwiththeaim,amongothers,ofpromotinginternationalnegotiationswhichled,in1964,totheAgreementEstablishingInterimArrangementsforaGlobalCommercialCommunicationsSatelliteSystem (i.e., to the Interim INTELSATAgreements).

The Federal Communications Commission (FCC) imposed, till 1986, on U.S.internationalcarriers therequirementofsatisfyingthetrafficdemandacrosstheAtlanticOcean with submarine cables and satellites on a 50-50 basis. This policy was alsofollowedbyEuropeancorrespondents.

The quick development of an INTELSAT ground segment in developing countrieswasmadepossiblebyaveryopenpolicyforthetransferofhigh-techproducts,andbyastrongconsultingsupportinthedesign,procurement,andinitialoperationsphases.

ThenumberofcountriesusingtheINTELSATsystemincreasedgraduallytoabout30at the endof the1960s, about 130 at the endof the1970s, and160 in1985,when thenumberofearthantennas(foreitherdomesticorinternationaluse)wasabout800,andthenumber of telephone half-circuits was about 80,000. In 1989 the number of countriesusingthesystemwas173,andthenumberofmembercountrieswas117.

The spectacular development of the INTELSAT system was not only beneficial tointernationalcommunicationsandaverygoodbusinessforinvestingcountries(therateofreturnoninvestmenthasneverbeenlessthan14%),butwasalsoanimportantvehiclefortheworldwidedisseminationof thesatellitecommunicationsculture.Itmaybesaid thatINTELSAT has been the school for other organizations and for thousands of satellitecommunicationsengineers.

The present institutional instruments of INTELSAT are an agreement amonggovernments(alsocalledparties)andanoperatingagreementamongoperationalentities(also called signatories),which are governments or entities designatedbygovernments;bothagreementsenteredintoforceonFebruary12,1973,supersedingthepreviousinterimagreementsofAugust20,1964.

Theagreements are integratedbyaheadquarters agreementwith thegovernment oftheUnitedStates,wheretheorganizationisbasedinWashington,D.C.

TheorgansofINTELSATare

TheAssembly ofParties, composedby all parties,wheremajor policy issues andmattersofgeneralinterestarediscussed.Decisionsaremadeatthislevelaccordingtotheone-country-one-voteprinciple.

The Meeting of Signatories, composed by all signatories, which supervises theactivityoftheBoardofGovernors.Theone-country-one-voteprincipleisalsousedfordecisionmaking.

The Board of Governors, consisting of approximately 20 representatives of thosesignatories or groups of signatories holding an investment share sufficient to giveright to a seat.Thenumberof seats on theBoard canbe integratedbyup to fiverepresentatives, each designated by the signatories of a different InternationalTelecommunicationUniongeographical area.TheBoard is the principal decision-making body, acting on consensus. Whenever a consensus cannot be reached,decisions are made by weighted vote according to the financial participation ofsignatories represented on the Board. Financial participations are periodicallyadjustedsoas tobein linewiththefractionofoverallsystemcapacityutilizedbyeachsignatory.

The Executive Organ, which reports to the Board of Governors about the actualmanagementandoperationofthesystem.Itisheadedbyadirectorgeneral,whoisthe legal representative of the organization.An international staff of about 600 ispermanentlyemployedintheexecutiveorgan.

The right of access to the INTELSAT space segment is granted under equal utilization

chargestousersofmember,aswellas,nonmembercountries.

Since INTELSAT was conceived as a unique global system, a provision wasincorporated in Article XIV of the agreement for protection against interference andpossible economic harm. Under that provision all systems other than INTELSAT,implemented or utilized by any member of the organization, must be coordinated. Inpractice,everycasesubmittedforcoordinationhasalwaysfoundasolution,thusallowingagradualproliferationofothersystems.

Withregardtothebasicissueofprocurement,theagreementprovidesthatitmustbebasedonopeninternationaltendersinordertostimulateworldwidecompetition,andthatcontractsmustbeawardedbasedon thebestcombinationofquality,price, anddeliverytime.

The INTELSAT structure has been assumed as amodel bymost other internationalorganizations, such as EUTELSAT (EUropean TELecommunication SATelliteOrganization), based in Paris, and INMARSAT (International MARitime SATelliteOrganization),basedinLondon.

A slightly different structure has been assumed by the INTERSPUTNIK system, inwhichthesignatoryalwayscoincideswiththeparty.Thisorganizationhasthesamebasicobjectives of INTELSAT, and includes 16 members (Russia, Poland, Germany,Czechoslovakia, Hungary, Rumania, Bulgaria, Mongolia, Vietnam, North Korea, Laos,Cuba, Nicaragua, Yemen, Syria, and Afghanistan). In the past, these countries weretypicallynotmembersoftheINTELSATsystem,butrecentpoliticaleventsdramaticallychanged the situation,and todaymany INTERSPUTNIKmembers are alsomembers ofINTELSAT.

Amajorstepforsatellitecommunicationtechnologywasthetransitionfromthird-tofourth-generationINTELSATsatellites.INTELSAT-!Vwasthefirstsatellitetousesmallantenna beamwidths (just a few degrees), thereby obtainingmuch higher EIRP values.Furthermore,IS-/VwasthefirstsatelliteallowingtheuseofreducedstandardESs,withanantennadiameterofabout10masopposedtothe30mofstandardA.AlgeriawasthefirstcountrytoleaseanIS-/Vtranspondertocreateadomestictelephonenetwork,basedonstandardBantennaspreviouslydefinedandoncompandedFMtransmission.LeasesofINTELSAT transponders grew: in 1989, 33 countries were using 61 INTELSATtranspondersfordomesticpurposes.Morerecently,INTELSATdecidedtooffersomeofits transponders for sale. This is an important new element in the INTELSAT picture.Whereas leasing simply increases the system share owned by the interested membercountry,asoldtransponderisnolongerthepropertyofINTELSAT,andthustheinterestedmembercountryandINTELSATfindthemselvesinacondominiumsituation.

Domestic satellite communication systems were also implemented out of theINTELSATframework.Canada,withitsANIK(Eskimowordforbrother)system,wasthefirstcountrytodevelopanindependentsystem(firstlaunchinNovember1972),andseveral U.S. domestic systems shortly followed. Several other countries, includingIndonesia, Brazil, and Mexico, started their domestic satellite systems by leasingINTELSATcapacity, and then turned to the use of independent satellite systems.Many

people still question the reasoning for these other systems, since INTELSAT-basedsolutionsfordomesticcommunicationsaregenerallycheaperandoperationallysimpler.Avery convincing explanation was given at the 1988 Satelconseil Operator and UserSymposiumbyMr.J.AguileraBlanco,SecretaryGeneralofASETA,anorganizationofseveral South American countries for implementing a regional satellite system calledCONDOR: countries leave INTELSAT, after INTELSAT has helped them start theirdomesticcommunications,justasyoungpeopleleavetheirparents.Stayingathomewithones parents is surely much cheaper and more comfortable than any independentarrangement,butyoungpeopleleaveforvariousreasons,suchasautonomy,possibilityofdirectcontrolandgrowthcapability,justascountriesleaveINTELSAT.Thepossibilityofdevelopingastrongnationalindustryforspacecommunicationsmaybeanimportantpartoftheseconsiderations.Anotherargumentinfavorofanindependentsolutionisthebettertailoring of a national system to national requirements, which can produce economicadvantages. In this respect it ispossible to compare INTELSAT topublic transportationandthenationalsystemtoprivate transportation,bothbeingusedaccordingtoneedandconvenience.

In recent years two new types of satellite communication systems have developedoperationally, namely television broadcasting satellites (TVBS) and data relay satellites(DRS).Thefirstsystemhasaverysimplearchitectureand,usingabrute-forceapproach,distributes television programs to very small user terminals (antenna diameter about 50cm).SatelliteHPApowerof200-25OWmaybeneededtoprovidetherequiredqualityina typical European country. Conversely, the second system is intended to providecommunicationsbetweenLEOsatellitesandalargeandcomplexESusingaGEOsatelliteasarepeater.ThearchitectureofaDRSsystemisgenerallycomplexandrequirestheuseofintersatellitelinks(ISLs)betweenGEOandusersatellitesorbitinginLEO.

To conclude, we stress that communication satellites have already proven to be apowerfultoolforimplementingnewservicesorforupgradingexistingservicesaccordingto new operational criteria. This originated a strong push for revision of existingregulations and laws. In particular, when it is practically impossible to monitor userbehavior,anintelligentpoliticalpowerusuallypreferstomodifylawsandregulationssothattheusersbehaviorisacceptablewithinthelaw.Someinterestingexamplesare

Thecompletederegulationofreceive-onlyantennas

The provision of maritime services by INMARSAT to ships located in nationalwaters(previouslyserviceableonlybynationalmeans)

Manyotherexamplesofthistypeareexpectedtooccurinthefuture.

ThePerspectives

Communicationsatelliteshavebeenverysuccessfulforimplementinganefficientandcost-effectiveinternationalnetwork.Formanyyearstheyearlyrateof traffic increase inthe INTELSAT system has been higher than 15%. The INMARSAT system hasimplemented communication services otherwise not achievable. The proliferation ofregional and domestic systems has helped to solve local communication problems.However, the technological and political equilibriumwhich set the basis for the initialdevelopment of satellite communications was perturbed in the last decade by severalimportantfactors:

1. The development of amature optical fibers technology. Thismakes the satelliteunattractive on high-capacity routes, even when the distance is very large. Theimplementation in 1988 of the first transatlantic telephone (TAT) cable in opticalfibers,namelytheTAT-8,wasamajorstep towardreducingcircuitcost.Althoughsatellites specially designed for high-capacity routes may still be preferable tosubmarinecables,thecomparisonisnolongerobvious.

2.Thedevelopmentofaprime-contractorcapabilityoutoftheUnitedStates.AfterthesuccessoftheArianelaunchvehicle,andthecontractsgainedthroughinternationalcompetition for the INMARSAT 2 and ARABSAT procurements, the Europeanspace industry has shown it can compete with the United States. The Japaneseindustry is expected to soon join this club, therefore creating a very competitiveenvironment.

3. The success of a new deregulation policy in the United States. The FCC hasabandoned theold50-50rule forsharing trafficbetweensatellitesandcablesoverthe Atlantic and has promoted the implementation of privately owned satellitesystems, incompetitionwithINTELSAT.After the launchover theAtlanticof thefirst PANAMSAT satellite (a U.S. initiative), another example of deregulationoccurred in Europe, with Luxembourg implementing the ASTRA system incompetitionwithEUTELSAT.ItisinterestingtorememberheretheFCCdecisiontofavorthedevelopmentofprivatelyownedsubmarinecables.

TheresultofthischangedenvironmentisthatINTELSATisnolongerdevelopingattheimpressiveyearlyrateof15%,andthattheroleofsatellitesvis-a-visterrestrialmeansis being questioned more and more.Whereas a general consensus exists that satellitesremain unbeatable for implementing aeronautical andmaritime communication servicesand unidirectional systems such as data collection or broadcasting, the development ofsatellitesystemsforfixed-pointcommunicationsisfacingincreasingdifficulties.Opticalfiberisatoughcompetitorforhigh-densityroutes,wherethefiberfillingcoefficientmayheveryhighandtheaveragecostpercircuitverylow.Asatellitecancomparemuchmorefavorablywhenthepurposeofthesystemistocreateanend-to-endconnectivity,pickingupthetrafficdirectlyattheuserpremisesandcompletelybypassingallterrestrialmeans.This type of system is called user oriented andmay prove attractive for implementing

businessservices.Ofcourse, the trafficcapturecapabilityofauser-orientedsystemwillvary inversely to theESdimensions, complexity, and cost. It is therefore of paramountimportance todecrease theESstandard, thuspaying thepriceofamuchmorecomplexsatellite.

Becauseoftheseconsiderations,itisnotdifficulttounderstandwhysatellitesystemscomplexity is quicklymigrating from the ground segment to the space segment.Majordevelopmentsareexpectedinthreeareas:

1. Implementation of ISLs, at microwave or optical frequencies, which will allowunification of the presentmultiplicity of global, regional, and national systems sothatausermayaccessasinglesatellitenetworkbyusingasingleearthantenna.

2.Developmentofincreasinglycomplexsatelliteantennas,toachievehighdirectivitywithoutlossofflexibilityorreliabilityofthesystem.

3.Developmentofprocessingrepeaters,usingonboardregeneration,coding-decoding,complexconnectionnetworkstoachievesatisfactoryconnectivityamongthevarioussatelliteantennabeams,andmulticarrierdemodulators to allow the coexistenceofsmall-capacitycarriersintheuplinkwithhigh-capacitycarriersinthedownlink.

Morespectaculardevelopmentsofthespacesegmentmaybeexpectedinthedistantfuture,whenspacetransportationwillbecomecheaperbyatleastoneorderofmagnitude.An inexpensiveway toput robotsandmen inspacewouldallowa failed satellite toberepaired, with accompanyingmajor impacts on reliability design, satellite developmentphilosophy,spacesegmentoperationalcriteria,spacesegmentcost.

A major decrease in space transportation cost could also make possible thedevelopmentofpersonalcommunicationsbysatellite,withaneliminationof thepresentsubdivisionbetweenfixed-pointandmobilecommunications.

In addition to technical developments already discussed, important changes couldoccur froman institutionalviewpoint.Thesatellite isan idealderegulation tool,since itallowsthecreation,atreasonablecost,ofafullyautonomousandfullyconnectednetworkin a relatively short time. The attention of political powers has therefore becomeincreasinglyfocusedonsatellitecommunications.After theformulationof thenewFCCpolicyinfavorofderegulation, theEuropeanEconomicCommunities(EEC)inanearlyversion of their Green Book pushed for a deregulation of communication services inEurope, with an important role to be possibly assigned to satellite communications.DespitethereactionoftheEuropeanPostandTelecommunications(PT)Administrations,whichrecentlycausedsomeinvolutionoftheEECpolicy,thepossibilitiesofferedbythemodern space technology will continue de facto to push in the direction of aderegulation.Inthelongtermthepresenceofprivateoperatorseveninsideinternationalorganizationscouldbecomearealpossibility.

TheRegulatoryBodies

The InternationalTelecommunicationUnion (ITU) is themost important regulatorybody for communication systems in general and satellite communication systems inparticular.All countries take part in thework of ITU,with the aim of definingwidelyaccepted standards, thus making it easy to implement an internationally compatiblecommunicationsystem.*

Inside ITU the InternationalConsultativeCommittee forTelegraphy andTelephony(CCITT) is responsible for thedefinitionof theend-to-endserviceperformancecriteria,generating recommendations for signal quality, quality measurement criteria, signalingsystems,etc.

CCITTrecommendationsaredesignatedbyacapitalletterfollowedbyanumber.Theletter indicates a series of recommendations, all pertaining to the same subject; forinstance, series 0 contains all recommendations for measuring instruments, series Qcontainsrecommendationsforsignalingsystems.

TheInternationalRadioConsultativeCommittee(CCIR)producesrecommendationsand reports and is responsible for the normalization of radio transmission systems. Atpresent, the CCIR classifies communications systems in three categories: fixed-point,broadcasting, and mobile. The classification applies to both terrestrial and satellitesystems. TheCCIR is organized into study groups; for example StudyGroup IV dealswith fixed-satellite service, Study Groups X and XI with broadcasting-satellite service(soundandtelevision),andStudyGroupVIIIwithmobile-satelliteservice.

Assignment of frequency bands to the various types of terrestrial and spacecommunications is decided in theWorld Administrative Radio Conferences (WARCs).Sometimesafrequencybandmaybeassignedtoterrestrialsystemsortosatellitesystemson an exclusive basis,whereas at other times itmaybe assigned to both terrestrial andsatellitesystems.Inthesecondcasetechnicalcoordinationbetweenterrestrialandsatellitesystemsisneeded.

AnotherimportantorganoftheITUistheInternationalFrequencyRegistrationBoard(IFRB),whichisresponsiblefor intersystemcoordinationat theinternational level.Thisapplies to the coordination of terrestrial systems with satellite systems, and to thecoordinationofanewsatellitesystemwithexistingonesorsystemssimplyregisteredattheIFRBatthetimethenewsystemissubmittedtotheIFRB.

The proliferation of satellite systems has led to the development of rigid plans forefficientuseofthegeostationaryorbitandfrequencyresource.ThefirstexamplewastheWARC77,whichproducedarigidplanforbroadcastingsatelliteservice,using800MHzforthedown-link.InalaterWARC,rigidplanningfortheuplinkwasalsoproduced.Ofcourse, this a priori planning approach eliminates the need for complex coordinationprocedures and guarantees to all countries equal access to the GEO and frequency

resources.However,supportersofthefirst-come,first-servedcriterionarguethat,whereasthetheoreticalefficiencyofuseoftheresourcesobtainedbyarigidplanningapproachisvery high, the efficiency actually obtained may be very small. Only 12 years afterWARC77 thefirstTVBSsystemswere implemented,andstrongdoubtsexistabout thefuturedevelopmentofthistypeofsystem,especiallyindevelopingcountries.Meanwhile,apreciousresourceof1600MHzofbandatfrequenciesbetween10and20GHz,whichsufferonlymoderateatmosphericattenuation,isleftpracticallyunused.

Important specifications about satellite communication systems originate frominternational organizations such as INTELSAT, INMARSAT, and EUTELSAT. UsuallythesespecificationsagreewiththestandardsdefinedbythevariousITUorgans.Importantexceptionsmay,however,exist,duetothepeculiarwayofoperatingasatellitesystem.Aninteresting example is the transmission rate of a satellite time-division multiple-access(TDMA) system,which generally does not coincidewith any of the hierarchical levelsdefinedbytheCCITTfortheterrestrialdigitalnetwork.ThisdeviationismadepossiblebythenecessityofbufferinganddebufferingtosupportaburstyTDMAtransmission.

A set of particularly important specifications are the INTELSAT earth stationstandards (LESS), which have become a practical reference also for other satellitecommunicationsystems.

Otherorganizations,consideredofminorimportanceinthecontextofthisbook,are

The International StandardOrganization (ISO), grouping themajormanufacturingcompanies,whosestandardshavesometimesanticipatedCCITTdecisions

The Commission Internationale de lEclairage (CIE), which defines the standardsrelevantforcolorimetryandvisionsignals

The EEC, promoting the definition of some new standards through cooperativeresearchprogramslikeCOST,RACE,ESPRIT,EUREKA,etc.

SignalsE.SaggeseandS.Tirro

I.Introduction

Thepurposeofeverytelecommunicationsystemisthetransmissionofusefulinformationto a remote location. This chapter discusses the main characteristics of the electricalsignals conveying the information as generated by each source. The combination ofseveralsourcesinamultiplexedbasebandsignalisdiscussedinChapter3,togetherwithindividualsourcecodingandcryptography.

Examplesofnaturalinformationsourcesarethehumanmouth,generatingspeech,andthephysicalbodies,generatingvideoinformation.

Special components called transducers are used to transform the original physicalquantity variations into variations of an electric quantity; for instance, a microphonetransformsairpressurevariations,whereasatelevisioncameratransformsluminosityandcolorvariations.

In addition to audio and video signals, this chapter discusses sound signals. Datasignalsareneglected,sincetheirstructureisverysimpleandtherelatedinformationcanbefoundelsewhere.Afacsimileservicediffersfromadata transmissionservicesince itpreserves,inadditiontothelogicalcontentofthemessage,therelatedvisualinformation(type of alphanumerical character, character spacing, complete pictures, etc.); in form,however,a facsimile signal is indistinguishable fromadata signal, so it isnot speciallytreatedhere.

II.SpeechSignals

Theaudiosignalgeneratedbythehumanmouthiscalledspeech,andistransformedintoelectricalsignalsbyamicrophone.Transmissionchannelssuitedto the transmissionofspeechsignalsmayproveinadequateforothertypesofaudiosignals;thenextsectiondiscusses the characteristics of another audio signal, the sound program, which isgeneratedbymusical instruments, talking,or singing.Whereas telephonenetworksmaytransmit only speech signals, radio and television broadcasting must allow thetransmissionofsound-programsignals.

E.SAGGESEANDS.TIRROSpaceEngineeringS.r.I.,ViadeiBerio91,00155Roma,Italy.

The following information about speech signal statistics is mostly devised fromextensivemeasurements and data analyses performed byBell Laboratories for theU.S.network.

A.Bandwidth

The human voice typically contains frequencies between 30 and 10,000Hz (this isalso thesensitivity rangeof thehumanear).Mostof theenergy isconcentratedbelowIkHz, so signal intelligibility ispreserved if this frequencyband is correctly transmitted.However, the voice, so limited in frequency, would become unnatural, and talkerrecognitionwouldbeimpossible.Forcommercialapplicationsit isgenerallyagreedthatallthefrequenciesbetween300and3400Hzmustbecorrectlytransmitted.

B.VoiceActivityFactorandSpeechInterpolation

Thevoiceactivityofatelephonechannelisdefinedasthepercentageoftimeduringwhich voice is present on the channel. Two channels compose a circuit, which in turnincludestwocircuitterminations,alsocalledtrunks(seeSectionIIBofChapter13).

Thevoiceactivityistheproductofthreecomponents:

1.The trunkefficiency?1,:not all trunksareoccupiedat the same time,due to thenecessityofdialingandofkeepingtherejectedcallpercentageloweveninthebusyhour;measuredvaluesofil,intheUnitedStatesare0.7fordomesticchannelsand0.9foroverseaschannels.

2.Thetalk-listenactivityfactorr1,_,,equalto0.5.

3.The continuous talker activity factor rf,.: in fact, pauses are generated evenby acontinuous talker due to intersyllabic gaps and the need to think and breathe; thevalueofrl,.isabout0.65-0.75intheUnitedStates.

ThetotalvoiceactivityforU.S.overseaschannelsistherefore

rl=t~,tl,_rrf,.=0.75x0.5x0.9=33.75%(1)

As a consequence of the limited talker activity, it is possible to use a number oftelephonechannelssmaller than thenumberof talkersforasufficiently largenumberoftalkers.Thespeechinterpolationadvantageisdefinedastheratiobetweenthenumberoftalkersandthenumberofchannelsandincreaseswhenthenumberofchannelsincreases,due toobviousstatisticaladvantages.Table Igives thevalue suggestedby INTELSAT2forthespeechinterpolationadvantage.

C.TheConstant-VolumeTalkerandtheMeasuredSpeechVolumes

The power generated by a continuous constant-volume talker already takes intoaccount the >), activity factor.When analyzed over a sufficiently large population, thecontinuoustalkervolumeisfoundtobenormallydistributed,withmeanvaluePdBmOandstandarddeviationadB.

ThedBmOmeasuringunitindicatesthatthelevelhasbeenmeasuredindecibelswithrespect toapowerof1mWatapointof thelinkchosenasareference;inthepast thispointwasaccessibletosignalgeneratorsormeasuringinstruments,buttodayitgenerallyis not. It is common practice to use for test purposes the outgoing side of the toll-transmittingswitch,which is typicallyatapower level2-3dB lower than the referencepoint.

Thevolumedistribution isnormalwhenpower ismeasured indB,but is lognormalwhenpower ismeasured linearly (seeFig.1).Average talkerpower is computed as themeanofthelognormaldistribution,andaccordingtoBennettitsvalueis

PO,=PO+0.115x2dBmO(2)

where P and a are, respectively, the mean and standard deviation of the normaldistribution.Several extensive surveyshavebeenperformed in theUnitedStatesby theBell Laboratories to determine experimentally the values of P and a. The results aregiveninTableIIandshowacleartendencytodecreasethecontinuoustalkervolumeastimepassesandnetworkqualityimproves.Table11alsoprovidestheaveragepowerperchannelinthebusyhour,whichis6dBlowerthanthecontinuoustalkerpower,duetothe0.25 activity factor for trunk efficiency and talk-listen activity. The firstmeasurementsperformedbyHolbrookandDixonprovidedanaveragepowerperchannelof-16dBmO,andthatwasthebasisforthe-15-dBmOvaluesubsequentlyadoptedbytheCCITT(seeSection II H). The table also shows, for comparison, the results obtained by severalEuropeanadministrations.

Fig.1.Anexampleofequivalentnormalandlognormalprobabilitydensityfunctions.(ReprintedfromRef.1,withpermissionofAT&T,(D1982AT&T.)

Avery important point is the dependency of the talker volumeon the distance, theimportance ofwhich changes significantly fromone survey to another.Bell surveys, inparticular, have shown that in 1960 the speech power on transatlantic submarine cablecircuitswas3.5dBhigher thanondomestic toll circuits,butdecreased toonly1dB in1975. The uniformization of national and international networks characteristics isthereforeeducatingsubscriberstoamoreuniformbehavior.

D.LaplacianRepresentationofaSpeechSignal

Themost-usedstatisticalrepresentationofaspeechsignalistheLaplaciandistributionlaw,i.e.,

P(X)=aV2-exp(-VQI)(3)

whereaisthermsspeechsignalvoltage.

Fig.2a.ComparisonofGauss,Laplace,andRayleighdistributionsofequalrmsvalue.

Fig.2b.ComparisonofGauss,Laplace,Rayleighintegraldistributions.Theordinategivestheprobabilitythatthevalueinabscissabeexceeded.or2isthepowerofthezero-meanstochasticprocessrepresentedbyGaussianorLaplaciandistributions;intheGaussian

case,ifthenoiseisnarrowband,itsenvelopehasaRayleighdistribution.

Figure2ashowsGauss,Laplace,andRayleighdistributionsofequalpowers,whereas

Fig.2bcomparesthecorrespondingintegraldistributions.

The 0.001%peak value given by theLaplacian law is 18.4 dB, in good agreementwiththe18.6-dBvalue(seeSectionIIF)measuredforthesingletalker.ThepeakvalueprovidedbytheGaussian lawis13dB, ingoodagreementwiththemultichannelsignalmeasuredvalue(againseeSectionIIF).

E.MultichannelSpeech

Whenntalkersaresimultaneouslyactive,thetotalgeneratedpoweris

P,=Pp+10Log,,,n(4)

PowerP,maybeexpressedasafunctionofthenumberofchannelsN,.asfollows;

P,=P,p+10Log,,,N,.+10Log,,,rl,_,xill+A,(5)

whererl,_,xrl,isthechannelactivityfactor(thecontinuoustalkeractivityisincludedinPop), and A, takes into account the difference between n and N,. x rl,_, x rl,. Thisdifference exists because the rl, and rl,_, values have been averaged over largepopulations.Thus,A,tendstozeroforsufficientlylargevaluesofN,.ThevalueofA,isgiveninTableIII.

F.PeakFactor

ThepeakfactorA2isdefinedastheratiobetweenthepowernotexceededformorethan0.001%ofthetimeandtheaveragepower.Forasinglecontinuoustalker,18.6dB.Whennsimultaneouslyactivetalkersaremultiplexedtoproduceamultichannelbasebandsignal,theprobabilityofcoincidentpeaksforalltalkersrapidlydecreasesasnincreases.For large values of n the peak factor rapidly approaches the value typical of Gaussiannoise(seeFig.3),i.e.,about13dB.ThesumA,+A2isgiveninFig.4,forrl,_,xrl,=0.25.

G.TestToneLevel

Whenlinkperformancemustbechecked instrumentally, it isconvenient to inject inthechannelasinusoidal10(X)-Hztesttonewithpeakpowerequaltothecontinuoustalkerpeakpower. Itwas seen inSection IIChowcontinuous talker power slowlydecreasesovertime;hence,thetesttonelevelshouldalsochange,butthisisnotpractical,sothetesttone levelhasbeen fixedat0dBmO.Thisvaluematchesverywellwith theBell 1960surveyresults;infactwithanaveragecontinuoustalkerpowerof-15dBmOandapeakfactorofabout18dB,apeakpowerofabout+3dBmOisobtained.Sincethepeakfactorofasinusoidis3dB,anrmspower levelof0dBmOisobtainedfor theequivalent testtone.Iftheimpedanceis600Q,thesinusoidaltesttonewillhaveanrmsvoltageof0.775Vandapeakvalueof1.1V.

Fig.3.Peakfactorfornactivespeechchannels.(ReprintedfromRef.I,withpermissionofAT&T,1982AT&T.)

Fig.4.A,+A,forrl,_~rt,=0.25.(ReprintedfromRef.I,withpermissionofAT&T,(D1982AT&T.)

H.MultichannelTelephonyLoad

TheCCITThaslongsinceadoptedtheformulasprovidedbyHolbrookandDixonforcalculatingtheaveragemultichanneltelephonyload;i.e.,

L=-15+10Log,,)N.dBmO,N?240(6)

L=-1+4Log,,,NdBmO,12

III.Sound-ProgramSignals

A.Bandwidth

Thenominalbandwidthforsound-programsignalstoberadiatedaloneorassociatedwith television signals is usually assumed to be 15 kHz, which is also suitable forstereophonictransmissions.re

Contrary to speech, sound-program signals are often emphasized at the source (i.e.,thestudio)forartisticreasons.Theeffectsofthisstudioemphasismustbeconsideredanintegralpartofthenaturalcharacteristicsofthesound-programsignalspectrum.CCIRReport 491-2.21 provides the typical spectral characteristics of various types of sound-program signal. Although power spectral density declines, for every type of music orspeech,beyondthe3-4kHzregion(seeFig.5),thehigh-qualitytransmissionofasound-programsignalrequiresabandwidthof15kHz.

Itisimportanttorememberthattheuseofacompressordoesnotgenerallyalterthespectralcharacteristicsofthesignal.z

B.SourceActivity

Incontrasttospeechsignals,thereare,ingeneral,nopausesinsoundprogramsignals.Thisdoesnotallowthesametypeofsignal-to-noiseratio(SNR)advantageobtainableonspeechsignalswhensyllabiccompandorsareused,asweshallsee inChapters5and9.Also, the use of interpolation techniques is, in general, excluded for sound-programsignals.

Fig.5.Meanspectralpowerofsoundsignals:curveA,classicalmusic;curveB,jazz;

curveC,speech.(ReprintedfromRef.20bycourtesyCCIR.)

C.PowerLevelStatistics

Similarly to telephony, the level of a sound-program signal ismeasured in dBmOs,where the s stands for sound and the zero indicates that the measurement must beperformedatapointofzerorelativelevel.Thezerorelativelevelpointistheoriginoftheinternationalsound-programconnection.21

Thedynamicrangeofasound-programsignalproducedbyasymphonyorchestra istypically60-70dB,whereastherangespecifiedforasound-programcircuitisonly40dB.Itisthereforenecessarytocompressthedynamicrangeofthesignalpriortopassingittothesound-programcircuit.AnotherreasonforsuchcompressionistomaketheSNRmoreuniformovertheentiredynamicrange(seeSectionVEinChapter5).

Themost important experimentalwork on power level statistics for sound-programsignalshasbeenperformedundertheauspicesoftheAdministrationofGermany.21Thecumulativedistributionoftheinstantaneouspowervalueswascomputedforthefollowingcases:

a.Unchangedsoundsignal

b. Sound signal emphasized using the preemphasis network defined inCCITTRec.J.1722withaninsertionlossof1.5dBat800Hz

c.Sound signal emphasized J.17,with1.5-dB loss at800Hz, andcompressedbyacompandorconformingtoCCITTRec.J.3123

The results of these exhaustive analyses are given in Fig. 6. The power level notexceededformorethan10-5ofthetimeisconventionallyassumedtohethepeakvalueofthesound-programsignal.TheuseofaJ.17preemphasisincreasessignificantlythepeaklevel,whilethesimultaneoususeofemphasisandcompressionleavesitalmostunchangedandequalto+12dBmO.Thisvalueofpeakpowerisgenerallyconfirmedbymanyothermeasurement campaigns 2 and broadcasters limit the sound signal overload peaksbeyondthisvaluebyappropriatelimitingdevices.21

Fig.6.Cumulativedistribution.CasesA,B,andC:distributionoftheprogramlevelin100%ofthetime:curveA,unchangedsignal;curveB,changedbypreemphasis1.5

dB/0.8kHz;curveC,changedbypreemphasis6.5dB/0.8kHzandcompressor.(ReprintedfromRef.20bycourtesyCCIR.)

D.TestToneLevel

Asalreadyseenforspeechsignals,asinusoidaltesttoneof1000Hzisusedtocheckinstrumentally the link performance,with a peak power equaling the sound signal peakpower.Sincethepeakfactorofasinusoidis3dB,thermspowerofthetesttonemustbe+9dBmO,asstatedinCCITTRec.J.14.21Iftheimpedanceis600Q,thepeakvalueofthesinusoidis3.1V,anditsrmsvalueis2.2V.

E.CompatibilitywiththeFDMTelephonyPrimaryGroup

AccordingtoCCITTRec.G.22324thepeakvaluewhichmaybeexceededfor10-5ofthetimeinafrequency-divisionmultiplex(FDM)primarygroup(12telephonechannels)is+19dBmO.Sinceitispossibletotransmitthreesoundprogramchannelswith15-kHzbandwidthinaprimarygroup, itfollowsthatanFDMtelephonecarriercomplyingwithCCITTrecommendationsisabletotransmithigh-qualitysound-programchannels.

IV.VideoSignals

A.ColorimetryFundamentals

Thesensitivityofthehumaneyetotheelectromagneticwavesinthevisibleband,i.e.,between400and700nm(10-9m)ofwavelength,isthebasicinputforthedefinitionofatelevisionsystem.

The transducer of the eye-the retina-has two groups of receptors: rods and cones.Rods, which are numerous, are responsible for monochrome vision at low illuminancelevels, whereas cones are responsible for color recognition. Three types of cones arepresent,withamaximumsensitivityrespectivelytored(580nm),green(540nm),orblue(440 nm). Each color will then excite each type of cone to a different extent, and theadditionofthethreestimuliwilldeterminetheeyeresponsetothatcolor.Theamountsofthethreebasiccolorsperceivedbythemeanhumaneyeinagivencolordefinetherelated tristimulusvalues. It is important to note thatwhen thedimensionsof anobjectdecrease,shape information prevails over color,which tends not to be observed by theeye.

Beforeenteringaquantitativecoloranalysis,somedefinitionsmustbeprovided.Anideal light having constant energy distribution throughout the visible spectrum will becalled equal-energywhite light. This ideal distribution is not present in nature, and theCommissionInternationaledelEclairage(CIE)hasstandardizedsomesources,asshowninFig.7forthefollowingtwo.25

Fig.7.LightsourcesstandardizedbytheCIE.(ReprintedwithpermissionfromRef.25.)

IlluminantA:EmissionequivalenttothatofaPlanckradiatoroperatingat2856K(colortemperature)

IlluminantDr,5:Emissionsimilartodaylight,withacolortemperatureof65(14K

Whena luminouspowerreaches thehumaneye, it isweightedbytheeyeresponse,i.e.,bythecapabilityoftheeyetoreacttosomewavelengthsmorethantoothers.TheCIEhas defined a standard observer through the curve V (A) of Fig. 8. Maximum eyesensitivity is experienced at a wavelength of 540 nm, where V(A) = 1; hence, theluminous intensitymeasuring unit, the candela (cd), is defined at thiswavelength.Onecandelais theluminousintensityofasourceradiating0.0184Wofpowerat540nm;ifthe radiation intensity is uniform in all directions (isotropic radiation), this valuecorrespondsto1/683W/sr.Theintegraloftheluminousintensityoveragivensolidangleis the luminous flux, and is measured in lumens (Im); one lumen is defined as theluminousfluxprovidedbyasourceof1cdwhenradiatinguniformlyallitspowerwithinasolidangleof1sr.Therefore,1lumen=1cd/sr.Theilluminanceisthemeasureoftheluminous flux per unit area and is measured in lux (lx), 1 lx being defined as theilluminanceprovidedbyaluminousfluxof1Imoveranareaof1mz.

Fig.8.CIEV(A)curve.(ReprintedwithpermissionfromRef.25.)

Thebasisofthequantitativecolorimetryisthedemonstratedpossibilityofmatchingeverycolorthroughappropriatetristimulusvalues.TheCIE-chosenprimarycolorsarethemonochromatic radiationsatwavelengthsof700nm(red),546.1nm(green), and435.8nm (blue). These wavelengths differ significantly from those of maximum conesensitivity, due to the necessity of limiting color overlapping. Actually, for technicalreasons, theprimarycolorsarenotperfectlymonochromaticbutspectracenteredon thedesiredidealcolors.Thesespectraoverlapnoticeably.

Equal-energywhitecanbeexpressedas

5.65lmW=1ImR+4.59ImG+0.061mB(8)

Newvalues(N.V.)arethenadoptedasmeasuringunitsforgreenandbluesoastoobtainaconventionallyuniformcompositionofthewhiteasfollows:

5.65ImW=1ImR+1N.V.G+1N.V.B(9)

Inordertomakethecolormatchingindependentoftheluminance,relativevaluescanbeintroducedasfollows:

Inthissystem,sincer+g+b=1,onlytwovariablesareindependent.

Due to the relative sensitivity of rods to primary colors (see Fig. 9), a blue-greencombination in defined quantities will, in some cases, equal a given color plus somequantityofred;thisintroducestheconceptofanegativeredcomponentinthetristimulusvalues for thatcolor.Toavoid thesenegativevaluesanewsetof tristimulusvalueshasbeenadoptedwiththefollowingtransformation:

X=0.49R+0.31G+0.20BY=0.18R+0.81G+0.01EZ=0.00R+0.01G+0.99B(11)

Usingtherelativevaluesx,y,z,onecandrawchromaticitydiagramsinthexyplane(Fig. 10), where all the colors of the visible spectrum can be shown over a curve(spectrumlocus).

ThepointsZ(0,0),X(1,0),andY(0,1)ofthexyplanedonotidentifyanyphysicalmonochromaticradiation,sincetheyareoutsidethespectrumlocus.TheequienergywhiteisgivenbythepointW(0.33,0.33).AllthepointsCinternaltotheenveloperepresentasaturatedcolor (interceptofWCwith thespectrumlocus:dominantwavelength)dilutedwithsomewhite.Hence,thechromaticitydiagramcangivethehueandsaturationofanyrepresentedcolor.Thismap,however, doesnot provide aproportional representationofcolor differences. A uv chromaticity diagram which reduces the distortions was thendefined(Fig.11)byCIE7626asfollows:

Fig.9.Rodssensitivitytoprimarycolors.(ReprintedwithpermissionfromRef.26.)

Fig.10.ChromaticitydiagramsintheXYplane.(ReprintedwithpermissionfromRef.26.)

4x9y-2x+12y+3U-2x+12y+3(12)

B.MonochromeTelevision

TelevisionstandardsforamonochromesignalaregiveninCCIRRec.470-227andinCCIRReport624-3.2xDifferentstandards(B,G,I,D,K,L)refertotheEuropeansystemat625lines,25frames/s,whereasstandardMreferstotheAmericansystemat525lines,30frames/s;standardMisusedintheUnitedStates,Canada,Japan,andsomeCentralandSouthAmerican countries. The basic characteristics of the televisionwaveformwill bediscussedherewithreferencetothe625linesstandard.

Fig.11.CIEchromaticitydiagramwithdistortionsreduction.

A two-dimensional image is decomposed in elementary picture elements (pixels)throughphotoelectrictransducers.Theelectricaloutputofthesetransducers,togetherwithinformationforimagereconstruction(synchronizationsignals)andtheaudiosignal,formthetelevisionwaveform.

Thecameraatthetransmittingendexplorestheimagebysequentiallyscanningitlinebyline,startingfromthetopleftend.Aftereachlinearapidflybackrestartsthescanatalower position until all the image has been covered to the bottom right end. A frameflybackwillthenrestarttheoperation.Thetelevisionreceivermustrepeatsynchronously

thesameoperation,deflectinghorizontallyandverticallytheelectronbeamofacathoderaytubebeforeitsimpactonthescreenphosphors.

A sufficiently small scan time will permit transmission of numerous images persecond,whichwill thenbe integratedby thepersistence timeof thehumaneye. In thisway rapid movements can be correctly reproduced. Conversely, if the scan time isincreased,therequiredsignalbandwidthisreduced,butbeyondcertainlimitsflickerwillappear.Inthe625-linetelevisionsystema50-scan/srateischosen,butacompleteimageis reconstructedwith two interleaved scans (fields); i.e., the odd lines are scanned in afieldandtheevenones in thesubsequentfield tocomplete theframe(seeFig.12).Theoddfieldendsathalfaline,andthefieldflybackrestartstheevenfieldhalfalinebeforeline 1. The even field ends at the end of a line, and the process is repeated. The oddnumber of lines (625) ensures interleaving. Each area of the screen is thus scannedapparently 50 times/s, but the bandwidth requirements are linked to the 25 completepictures/s.Obviously,horizontalalternateblack-and-whitebarswillproducelocalflickers.

Since the luminance signal has amean value (dc component) variable from line toline, the line synchronization signal is preceded and followed by two pedestals, calledfrontandbackporches(seeFig.13).

Fig.12.Framestructureforthe625/50televisionsignalstandard.

Fig.13.Horizontalsyncpulse(L=lineduration).

The line flyback pulses (and sometimes also the back-porch pedestals) are oftenutilizedforsoundanddatatransmission,asdiscussedinSectionVIIGinChapter9.

The field flyback lasts25 linesand is triggeredbya seriesof fieldpulsesprecededand followed by equalizing pulses to reset the proper circuitry in the receiver, thuspermittingcorrectfieldinterleavingbyappropriateverticaldeflection(Fig.14).

The televisionwaveformbandwidth isdeterminedby thenumberofpixelsper line.Thepictureaspectratio(width:height)is4:3;since575usefullinesarepresentineachframe, the horizontal resolution is 767 pixels/line transmitted in about 52s: this isequivalent toaminimumbandwidth(fundamentalfrequency)ofabout7.4MHz.Takingintoaccountthephysicaldimensionoftheelectronbeamandtheusualdistancefromtheviewertothescreen,theactualbandwidthisbetween4.2and6MHz.

The third component of a monochrome television signal, in addition to vision andsynchronizationsignals,isthesoundsignal,whichhasabandwidthofabout15kHz(seeSectionIII).

Television broadcasting on terrestrial means utilizes vestigial sideband (VSB)modulation(seeSectionXIIofChapter6)toguaranteecorrecttransmissionofthesignalcomponentsatlowfrequency(downtocontinuous),whichcontainthegreatestpartofthe

signal energy.The sound is transmitted on anFM subcarrier;TableVgives the relatedradiofrequencycharacteristics.Theluminanceinformationisusedtoamplitude-modulatethe carrier between two levels which depend on the particular standard. Negativemodulation (i.e., decrease in carrier modulation when luminance increases) is usuallyused.At theendofeach line the synchronization flyback is transmittedbyutilizing theremainingmodulationdepthuptocarriercancellation.

C.ColorTelevision

Thecolor television signal is specified tobecompatiblewith themonochromeone.ThismeansthatamonochromeTVsetmustbecapableofreceivingacolorTVsignalandofdetectingandshowingwithoutdegradationitsluminancecontent,whereasacolorTVset must be capable of receiving, detecting, and showing without degradation amonochromeTV signal.The characteristics of color television standards dependon themonochromestandardtheyhavetomatch,asspecifiedbytheCCIR.28

Fig.14.Structureofthefieldtransitionssignal.

1.TheNTSCSystem

The first color TV system, (National Television SystemCommittee), calledNTSC,wasdevelopedintheUnitedStateswithsuchcharacteristicsastobecompatiblewiththeMstandard. In specifying the system the firstpoint tobeconsidered is thedisplay tubewithitsprimarycolors.InNTSCthephosphorsgiven inTableVIwerechosen togetherwith thewhite (illuminantQ.Asaconsequence,only thecolorscontained in theNTSCtriangleofFig.15canbereproduced.InasystemutilizingNTSCprimariestheluminancesignal(quantityofilluminantC)canbeexpressedas

Y=0.299R+0.587G+0.1148(13)

Theluminancesignal

E=0.299ER+0.587E+0.114Eg(14)

Colordifferencesfalltozeroifamonochromecameraistransmitting,thusensuringacorrectreceptionbyacolorreceiver(reversecompatibility).Furthermore,differenceswithrespect to luminance of red and blue have been preferred to that of green, since greencontributesmosttoluminance;thatis,greenproducesaverylowcolordifferencelevel,soitismoresensitivetonoise.

Fig.15.ColorsreproduciblebytheNTSCsystemandbythePAL-SECAMsystems.(CourtesyIBA.)

Inan10Cartesianplaneeverycolormayberepresentedbyavector,theamplitudeofwhichisproportionaltothesaturation,whereasthehueisafunctionoftheangleformedwiththeaxes.ThecolorsalongtheIaxischangefromcyantowhitetored,whereascolorsalongtheQaxischangefrombluetowhitetoyellowgreen;theQcolorsareinaregionwherethehumaneyehasahighersensitivitytohuedifferences.TheIandQsignalsareused toamplitudemodulate twocarriers inquadraturewith twobandwidths (1.3and0.4MHz, respectively). The chrominance subcarrier is at 3.579545MHz, which is an oddinteger multiple of half the line frequency, to reduce the noise due to chrominanceresiduals in a monochrome receiver. This value guarantees that all lines of thechrominance spectrum are interleaved with the luminance lines. To permit thesynchronous detection of I andQ in the receiver, a burst of the subcarrier frequency istransmittedinthebackporchofthelinesynchronizationpulse.

2.ThePALSystem

The phase alternation line (PAL) system was developed in Germany by Bruch(Telefunken) to improve some NTSC characteristics. The primary colors and white

(illuminantD6)werechosenasdefinedinTableVI.ThePALtriangleinFig.15includesall the colors which may be reproduced by the PAL system. The luminance signal isthereforeexpressedas

Y=0.222R+0.707G+0.071B(16)

with a larger contribution of green than in the NTSC system. However, for historicalreasons the studio camera is lined up to transmit the same luminance signal as in theNTSCsystem;i.e.,aftertheycorrection(2.8inPAL),theluminanceis

E=0.229ER+0.587EG+0.114E6(17)

Thefrequencyof thechrominancesubcarrierhasbeenchosenas4.433161875MHzsoastoguaranteeperfectchrominanceandluminanceinterleaving.

Thepeakvaluesofchrominancearelimitedtoonethirdoftheluminancemaximumvalue. To obtain this result (Fig. 17) the color difference signals, always derived fromNTSCencoding,mustbe

E~=0.493(EB-EY)=-0.147ER-0.289E+0.437E6E;,=0.877(ER-E)=0.615ER-0.515EG-0.100EB(18)

3.TheSECAMSystem

The sequentiel couleur a memoire (SECAM) system was developed by Henry deFrance.TheprimarycolorsselectedforthedisplaytubephosphorsareidenticaltothoseforthePALsystem.

SECAM is based on the idea of reducing the chrominance vertical definition bytransmitting for each line just one piece of color information, whereas the second istransmitted in the following line. In thisway the quadraturemodulation, and hence the

mutual interference between the chrominance signals, can be avoided. The followingsignalsareproportionaltothecolordifferences:

Fig.16.Constructionofthecolorbarsignal.

DR=-1.9(ER-E)=-1.332ER+1.115E,;+0.217EgDB=1.5(EB-EY)=-0.449ER-0.881E,;+1.329E(19)

These signals frequency-modulate two different subcarriers at 4.40625 and 4.250 MHzrespectively.Themaximumfrequencydeviationis0.5MHz.

Inthereceiver,foreachlinethecorrectchrominanceisreconstructedonthebasisofthe color difference signal present at that moment and of the color difference signaltransmittedduringthepreviouslineandstoredinadelayline,similarlytowhatisdoneinthePALsystem.

D.MACSystems

Thefirstsystemofthemultiplexanalogcomponents(MAC)familywasconceivedintheUnitedKingdombytheIndependentBroadcastingAuthority(IBA).Themainfeatureof thesesystemsis the time-domainmultiplexinganalogtime-compressedvisionsignals(luminance and color differences) and of a digital signal containing sound, data, andsynchronization. These systems were designed to make the best possible use of theradiofrequency channels defined for direct satellite TV broadcasting by the WorldAdministrative Radio Conference WARC-BS-77 and by the Regional AdministrativeRadioConferenceRARCSAT-83.Specialequipment(outdoorandindoorunits)isneededin addition to the usual television receiver, regardless of the standard utilized on thesatellite;however,theindoorequipmentmaybeparticularlysimpleforsomestandards.

Fig.17.Compressedcolorbarsignalstructure.

The basic TDM frame format for all MAC standards is shown in Fig. 18. Byappropriateuseofthetimezones,calleddataandverticalintervalinthefigure,itispossible to change the picture aspect ratio from 4:3 to amore pleasant value.MAC istherefore a powerful tool for the transition to more advanced television standards andpossiblytohigh-definitiontelevision.Eachlineof64psissubdividedinto1296intervals,witha correspondingclock frequencyof1296/64=20.25MHz.The1296 intervals areused for data, chrominance, and luminance information, as shown in Fig. 18.29 Time

compressionofvisioninformationinordertoobtainatime-multiplexedanalogsignal isconveniently performed with digital techniques, by sampling the video signal at 20.25MHz.

IntheC-MACpacketsystemoriginallyproposedbyIBA,soundanddatasignalsareinsertedintotheline-blankingintervalofthemodulatedvideosignalatRFintheformofa digitally modulated carrier. At the transmission point, time-division multiplexing iscarriedoutat IF,switchingbetweenanalogFMvideoanddigital frequency-shift-keying(FSK)-modulated sound and data, while the phase continuity is maintained for thetransmitted radiofrequency.3o The C-MAC system has been adopted by th

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