CATV HFC Basic（英文版）(ppt 96页).ppt

CATVHFCBasic The StoneAge ofTV TelevisionSignals Originally Televisionsignalswereonlyavailableasbroadcastsfromantennaslocatedatoptowersnearlargecities Thetypicalbroadcastcouldonlybereceivedwithin15to50milesofthetransmitter andiftherewerehills valleysorotherobstructions thesignalwasdisrupted Veryfewchannelsexisted Thetypicalviewingareareceivedlessthanfivechannels Aslongasyougot PerryMason youwerehappy TowatchyourfavoriteSaturdayNightProgram itusuallyinvolvedmultipleadjustmentstoyourroofmountedantennasystem CATVHistory CATV CommunityAntennaTeleVisionInitiallyextendedthecoveragerangeofthefewexistingTVstationsusingabroadbandhard wireddistributionnetworkThereisdisagreementastothehistoryandevolution1948EdParsonofAstoria OregonbuiltthefirstCATVsystembystringingtwin leadtransmissionwirefromhousetoptohousetop Until1952wartimeandpostwarpoliciespreventedwidespreaddeploymentofover the airTVbroadcast ThisleadtoCATV CommunityAntennaTV CATV MiltonJerroldShapp 1948MiltonJerroldShapp formergovernorofPennsylvania returnedhomefromtheservice HevacationedathisfamilyhomeinthePoconomountainsofPennsylvaniaandwasunabletoreceivetelevisionsignalsfromeitherthePhiladelphiaorNewYorkregion ShapphadafriendwhoworkedasanRFengineeratthePhilcoRadioplantonFoxStreetinPhiladelphia ThetwodecidedtoerectalargeantennaontopofthehighestmountaininhisPoconovillage ShappFormsJerroldElectronics Theyrantwinleadantennawiredownthesideofthemountainwithsomenewlycreatedbroadbandamplifiersappropriatelyspacedalongtheroutetoprovidegoodsignalquality ShapplaterformedtheJerroldElectronicsCompanyandbecameapioneerinthecableindustry 1950BobTarltonbuiltasysteminLansford PAusingcoaxialcableonutilitypolesunderafranchisefromthecity ShappSellsJerrold 1967ShappsellshisinterestinJerroldElectronicstoGeneralInstrumentasheseekstheofficeofgovernorforthestateofPennsylvania 1972ChuckDollanandRobertLevystartupHomeBoxOffice 1984GeneralInstrumenthassoldover1millionaddressableset tops converters worldwide CATVEvolution 1986HBObecomesthenumberonepremiumcableservice 1991DigitalAudioisdeployedovercablebyseveraldifferentcableoperatorsprovidingservicebyDigitalCableRadio MusicChoice DigitalMusicExpress DMX andthenowdefunctCD 8 1992ReedHuntisappointedtoheadtheFCCbyPresidentClinton bringingawholeneweratothecableTVindustry ReedHuntstartsoutonhispathtoderegulatecableTV De regulationofCable 1994Billionsofdollarsaregeneratedbythefederalgovernmentasitsellstherighttoownspecificfrequencybands TheFCCmandateshowcableTVispackagedtosubscribers forcingallUScableoperatorstoperformchannelline upchanges 1995WithcableTVfullyderegulated BabyBellsenteredtheCATVmarketwithtremendousfinancialresourcesandstarttooverbuildexistingcableoperators CableConglomerates 1995 1997Cableoperatorsconsolidateholdingsandmanylongtimecableoperatorsdecidetogetoutofthebusiness Opportunityexistforlargercompaniestobuy outsmalleroperators PresentTherearenowmorethat500UScablecompanies systems However asmoremergersandacquisitionstakeplace itisnotimprobablethatinthefutureyouwillseelessthantenmajorcablecompaniesthatpossessallofthemarbles TheFutureofCATV Nobodycanpredictthefuture butmanyindustryleadersaretryingtodirecttheindustryintoafullyfunctionalnetworkproviderofserviceslike VideoserviceInternetaccessDigitaltelephoneserviceDigitalaudio videoStockquotes Largeset topmanufacturershavealreadystartedmassdeploymentofdigitalset topterminalstoavarietyofcableoperators TheFutureofCATV Digitalset topunitsreceive64QAMmodulatedsignalsdeliveringMPEG2digitalvideoandDolbyAC 3digitalaudio ThisprovidesthesubscriberwithpristinequalityvideoandaudioequaltothatlaserdiskorDVDvideoformats Additionally futureinteractiveTVservicesarebeingdevelopedbyprogrammers Therefore theprospectofhaving500videochannelsisnotasmuchofanimpossibledreamasitwasonceconsidered B Wbroadcaststandardestablished FCCderegulatestelecommunications 1948 Firstcommunityantennatelevision CATV systemsestablished 1970 s SatellitesSuperstationsSpecialtystationsMoviechannels 1994 FCCmandateshowcableTVispackagedtosubscribers 1996 1953 Colorbroadcaststandardestablished 1984 Stereobroadcaststandardestablished 1941 Timeline 1991 Digitalaudio MusicChoice etc TimelineHistoryofCableTelevision BroadcastTV Vendors Programmers Customers FranchisingAuthority LocalSystemOperator MSO Telco ModernCableInfrastructure TelevisionSignals Thetelevisionsignalcontains3typesofinformationthatmustbetransmittedandreceivedwithoutimpairmenttocreateacompleteprogram Thebasicpictureinformationisblackandwhiteinnature Italsocontainssynchronizationinformationtokeepthereceiverlockedtothetransmittedsignal Thecolorisseparatefrom butlinkedto theblackandwhite luminance information TheAudioisthefinaltypeofinformationincludedtocompletethetransmission TelevisionSignals VideoCarrier Color AudioCarrier 6MHzBandwidth SignalsusedtotransporttheVideo Colorandaudioareassignedspecificfrequenciestokeepthemseparatefromoneanother Eachtelevisionchanneloccupiesafrequencybandwidthof6MHz i e Channel2existsfrom54MHzto60MHzfrequencybandwidth Thespecificfrequenciesareassignedtothevideo colorandaudioinformationtokeepthemseparatefromoneanother ForChannel2 Video 55 25MHzColor 58 83MHzAudio 59 75MHz WhatisthisMegahertzthing 1cycle OnefullsignalcycleequalsoneHertz Measurementisincycles Hertz persecond OneMillioncyclesperSecondequalsaMegaHertz MHz Energytravelsinsinewavepatterns TVreceiversmusthave tuners toselectthevariouschannelssenteitherthroughtheairoronthecable EarlyTVshadverylimitedtuningrange TypicallytheycouldtuneVHFchannels2 13andUHFchannels14 83 Therewerefrequencygapsbetweenchannels6 7 Cablecompanieswantedtousethegapsintheover the airfrequencyplans PlacingchannelsonfrequenciesnotavailablewiththestandardTVtunercreatedtheneedfor converters Thefirst pay channelswerealsolocatedonthesefrequencieshiddenfrommostreceivers Howdoesatelevisionwork HeadendTrunkCable ThisisFiberOpticinaHFCPlant Distribution feeder cableintheneighborhoodDropcabletothehomeandin housewiringTerminalequipment set topterminalsandconsumerelectronichardware FiveMajorPartstoaCableSystem 5 4 3 2 1 Headend SignalConsolidationPoint HBOESPN TBSCNNShowtime WEDU WTOG Microwavewasoneofthefirstmethodsusedtoacquireotherthanlocalsignals StationssuchasWGN WORandWTBSbegansendingtheirsignalsviamicro waveacrossthecountry Microwavehasalsobeenusedextensivelybycablecompaniestoprovidesignalstoareasthatwouldbedifficulttoreachwithcables Signalstransportedviamicrowavearesusceptibletoweather othermicrowavesignalsandotherproblems Cablesystemsstillusemicrowavetoday butitislesspopularthanitusedtobe Forthosesystemsthathaveit technicianshavetobetrainedtoamuchhigherleveltomaintainit Satellitetransmissionoftelevisionsignalsforcommercialusebeganinthemid 1970 s Earlysatelliteswereverylowinpowerandonlylastedfrom5to10years Receiveantennaswereverylargebecausethereceivedsignalwasweak Earlyantennaswere10metersindiameter Eachsatellitewascapableofreceivingandre transmitting24televisionsignals Analog Today satelliteslastmuchlongerandhavegreatercapacity DigitalCompressedSignals Satellitesorbittheearthattheequator ThesesatellitesareinaGEOSYNCHRONOUSorbit Thatis theyremaininthesamepositionRELATIVETOAPOINTONTHEEARTH Thisallowsantennastoremainstationary Satellitescantransmittheirsignaloverawideareaorcanspotbeamtorelativelysmallgeographicpointsthatarejustafewmilesindiameter Head end SignalConsolidationPoint Theequipmentinthehead endincludesmodulators processors microwavereceiversandtransmitters satellitereceivers fibertransmittersandreceivers scramblers de scramblers andaddinsertionequipment Eachpieceofequipmenthasaspecificpurposeanditsownmaintenancerequirements Thepicturesatthehead endarethebestinthecablesystem Picturequalitywilldegradeasthesignalsgothroughcableandamplifiers Thereliabilityofthehead endiscriticalbecauseitservesallcustomers PowerSupply Hybrid FiberCoax HFC Architecture CABLE ASICS PowerSupply Hybrid FiberCoax HFC Architecture PowerSupply Hybrid FiberCoax HFC Architecture PowerSupply Hybrid FiberCoax HFC Architecture PowerSupply Hybrid FiberCoax HFC Architecture SignalSecurity SignalSecurityisaspecialissue Manysecurityapproachesarehandledinatypicalheadend Somesignalsarescrambledbeforebeingreceivedattheheadend Theheadendmustthendescramblethemforcarriageonthesystem Thecablesystemmayelecttosecuresomesignalsviascramblingorjammingcarriers Additionally thecontrollersthatauthorizedescramblersinthecustomershomeareusuallylocatedintheheadend CableTheory TheHeadend TelevisionsignalsarecollectedattheCATV sreceivesite Numerousoff the airantennasandsatellitedishesreceivemultiplesignals ThecollectedsignalsareprocessedattheCATVheadend Thisincludesallstereoprocessingandscrambling Themultitudeofdifferentchannels frequencies arenowcombinedintoasinglebroadbandfeed ThisfeedisinsertedintotheHFCdistributionpathandisnowcalledtheforwardpathordownstreampath 4GHz 1GHz Receiver Modulator video audio Carriers Channels Combiner MHz Headend SignalModulation CableTheory Distribution Inaconventionalcableplant thebroadbandsignalisthendistributedtosubscribersAsthesignaltravelsdowntheHFCplant Thesignalstrengthstartstodiminish Thiseffectiscalled AttenuationAmplifiersandlineextendersareusedtokeepthesignallevelconstant Unfortunately amplifierscausedistortionofthesignal sothereisatechnicallimittothenumberofamplifiersthatcanbecascaded CableTheory Distribution Differenttypesofamplifiersareusedforvariousapplications Trunkamplifiersareveryhighqualityamplifiersthatintroducesminimaldistortion Thetrunksystemisusedtotransportsignalsoverthegreatestdistancesominimaldistortioniscritical Lineextendersareallowedtocontributemoredistortionsbecausethedistancecoveredisshorter Powersuppliesmustbeusedtoprovidethevoltagetoruntheamplifiers Standbypoweringhasbeenaddedinrecentyearstohelpassurereliability HybridFiber coax HFC InanHFCcableplant signalsaresentoutasRFenergyandchangedtolightviaopticaltransmitters HFC Isacablearchitecturehavinganoptimizedcombinationoffiberinthetrunkandcoaxialcableinthedistributionplant Hasmadeitpossibletoincreasesignalquality bandwidth andreliabilityinacost effectivemanner Reducesmaintenancecostsbybeingeasytoworkwithor Craft friendly HybridFiber Coax HFC RF RadioFrequency Anelectromagneticsignalabovetheaudiofrequencyrange 20Hzto20 000Hz andbelowtheinfraredfrequencyrange TheElectromagneticRadiationSpectrum FiberNode HybridFiberCoax HFC TheHFCApproach Tominimizesignallossesreferredtoearlier thecablesystemisbrokenintomanysmallercablesystemswithamplifiercascadeslimitedtobetweenfourandsixamplifiers Eachofthesesmallcable systems isfedwithafiberlinktotheheadend FiberNode TrunkAmplifiers BridgerAmplifiers LineExtenders Dropcable Fibervs longamplifiercascadesGreaterchannelcapacityHigherreliabilityHigherqualitytosubscribers HybridFiberCoax HFC ReceiveAntennaFarm ScramblerandProcessors AdInsertionLocalOrg CATVHeadend FiberNode Amplifiers AddthePowerSupplies HFCPlant LaserHistory Theory TheimplementationofnewservicessuchasHigh Speeddataandtelephonyrequirestheuseof two way transmission Two waytransmissionhasbeenavailableformanyyears QubewasanearlyservicedeployedbyWarnerintheearly1980 stodemonstratethecapabilitiesoftwo waysystems Thesystemswork buttheircostlinesshaspreventedwidespreaddeployment Todaywefindthatcablesubscribersareexcitedabouthigh speedaccesstotheinternet Willthisbethebusinessthatwillprovidethemoneytoconvertmostcablesystemstotwo waycapability LaserHistory Theory LaserGun WideuseoffiberopticsincableTVbeganinthemid1980 s Fiberwasfirstusedtoreducelongamplifiercascadesorreplacemicrowavepaths CostwasveryhighearlyonbecauseoftheLASERshadtobespeciallybuiltforanalogTVsignals Fiberopticsisnowwidespread andcostshavesignificantlydecreasedwithnewmanufacturingtechniquesandvolumepurchases Lightisjustahigherfrequencyofradioenergy LaserHistory Theory VisiblelightexistsintheElectromagneticspectrumatveryhighfrequencies Lightisusuallyreferredtointermsofwavelengthratherthanfrequency Thewavelengthsofvisiblelightexistfromapproximately400to750nanometers Wavelengthsusedfortransmissionofcabletelevisionsignalsaretypicallyeither1310or1550nanometers Thesewavelengthsexhibitverylowloss LaserHistory Theory OpticalFibersareverystrong Scientistshavecalculatedthatasinglefibercouldholdtheweightof16rhinos Fibersareverytiny aboutthesizeofahumanhair butcancarryvirtuallyunlimitednumbersoftelevisionchannels Fibersareputincablestoprotectthemfromtheelementsandmakethemeasiertoplaceonpolesorintheground LaserHistory Theory ThetransmitterthatplacesthelightenergyontheopticalfiberisusuallyaLASER TherearemanytypesofLASERsthatareusedforspecificapplications LightEmittingDiodes LEDs arealsousedinsomeapplications Thereceiverrespondstothelightsignalsandconvertsthemtoelectricalsignalsforcontinueddistributionthroughthecablesystem Televisionsmuststillreceiveanelectricalsignaltodisplayapicture Willthischangeinthenearfuture Itwillwhenalow costinternalconverterisdeveloped LighttoRFConverter LightSignal Laser HFCnetworks HybridFiber Coax arethenormtoday Theyincorporatetheadvantagesofbothfiberopticandcoaxsystems Fiberisusedtotransportsignalstoagroupofhomes ANodeisthelocationwhereanopticalreceiverconvertsthelightsignalsbacktoelectricalsignalsfordistributionthroughthecoax Thenumberofhomesinanodeisdeterminedbytheeconomicsofthetypesofservicestobeprovidedandthetechnicaloperatingparametersthatneedtobemet HFCNetworks LaserHistory Theory HFCNetworksprovideafewkeyadvantagesovertraditionalcablesystemdesign Reliabilityishigher Reverse two way transmissioniseasier Targetedadvertisingandmarketingcanbeaccomplished Signalqualityisbetter Maintenanceiseasier Outagesaffectsmallernumbersofsubscribers CableTheory TheDrop Theinstallationofserviceincludesconnectingdropcablefromthe tap tothetelevisionset Installationofthedropmustmeetcompany localandnationalcodesforsafety Fences trees busystreets dogs spiders rattlesnakes childrenwithpelletguns crankycustomers crankyneighbors complexentertainmentsystems trafficproblemsandimproperworkordersallchallengetheinstaller Clearances grounding bonding signalleakage signallevelsandmanyotherrequirementsmustbemetintheinstallation CableTVGuy CableTheory TheDrop Installationsmustbecompletedtointerfacewithmanydifferenttypesofequipment CustomerequipmentincludeseverytypeofTV HomeTheatre VCR DVD XYZ ABC videogame surroundsoundsystem etc Theinstallermustbequalifiedtoknowhowtointerconnectnumeroustypesofequipmenttoassuretheyallworkwiththesignalsprovided Technicalknowledge abilitytoproperlyinstallF connectorsanduseofthebasictestequipmentareallNecessaryskillsfor THECABLEGUY Mostoften thingsworkreallywell Occasionally thereisaprobleminthesystemandservicetechniciansareaskedtofindandfixtheproblem Othersrespondtocustomerdemands sometimesinthemiddleofthenightorduringstorms InstallersandservicetechniciansarechallengeddailytoprovidetheBestservicethecompanycanoffer CableTheory TheNeedforMeters CableTheory TheNeedforPathTrak Withthedeploymentofcablemodemsandtelephonyservice thereisamuchgreaterneedforthereturntobeactiveandreliable Cableoperatorsarenowforcedtodealwithtransmissionofdigitalsignalsovertheirplantandmustnowmakeaconcertedefforttoquicklyactivateorcleanupthereturnpaths WorldwideBroadcastStandards MostcountriesuseTVStandardsthatareincompatiblewithothercountries AvideorecordingmadeintheUKcouldnotbeplayedonUSstandardVCR sorshownonaUSTV Effectively therearethreeworldstandards NTSC PAL SECAM NationalTelevisionSystemCommittee NTSC OrganizationthatformulatedstandardsfortheNTSCtelevisionsystem BeganBroadcastingin1954 NTSCwasdevelopedintheUSandwastheworld sfirstcolorTVsystem DescribesAmericansystemofcolortelecastingusedmainlyinNorthAmerica JapanandpartsofSouthAmerica NationalTelevisionSystemCommittee NTSCemploys525linesperframeand59 94fieldspersecond NTSCusessubcarrier 3 57945MHz whosephasevarieswiththeinstantaneoushuesofthetelevisedcolor Theamplitudevarieswiththeinstantaneoussaturationofthecolor ChannelBasics ATVchannelintheUSAtakesupa6MHzwideportionofbandspace Thebottom orlower edgeoftheover the airChannel2is54 0027MHz Thetop upperedge isapproximately60MHz Containedinthis6MHzspaceisa VideocarrierAural audio carrierColorcarrier 6MHz VideoCarrier ColorSub carrier AudioCarrier StandardChannelAllocation VideoCarriers NTSC Thefrequencyofthevideocarrieris1 25MHzabovetheloweredge Therefore thevideocarrierforchannel2wouldstartat55 25MHz ColorCarriers NTSC ForNTSC thecolorcarrierisapproximately3 58MHzabovethevideocarrier nottheloweredge Soforchannel2thecolorcarrierwouldcenterat58 83MHz AudioCarrier NTSC Theauralcarrieris4 5MHzabovethevideocarrierputtingita59 75MHzonChannel2 6MHz 4 5MHz 3 58MHz Video Audio Color 1 25MHz 25kHz StandardChannelAllocation 6MHz 54MHz 55 25MHz 59 75MHz Channel2 Level Level Frequency Frequency CableBasics PerformanceMonitoring CATVChannels Channels2to13arenotinacontinuousband Totalnumberofchannelsonagivencablesystemcanvary Oldercablesystemsmightonlygoupto300or350MHz Ithasbecomecommontoseecablesystemsemployinga550MHzbandwidth Therearesystemsusinguptoa1GHzbandwidth Trapping Thereare2typesoffiltering trapping schemesthathelppreventsignal theft PositiveTrapping addsahighlevelinterferingcarrierbetweenthepictureandsoundcarriers Afiltercanbeinstalledtoremovetheinterferingcarrier Negati