《电子信息专业英语》-Chapter 5 New Technology

Text1NewNanoCoatingBoostsSolarEfficiencyINTRODUCTION:太阳能电池是通过光电效应或者光化学效应直接把光能转化成电能的装置，现阶段以光电效应工作的薄膜式太阳能电池为主流。目前，许多国家正在制订中长期太阳能开发计划，准备在21世纪大规模开发太阳能。太阳能电池的应用已从军事领域、航天领域进入工业、商业、农业、通信、家用电器以及公用设施等部门。从长远来看，随着太阳能电池制造技术的改进以及新的光—电转换装置的发明，各国对环境的保护和对再生清洁能源的巨大需求，太阳能电池仍将是利用太阳辐射能比较切实可行的方法，可为人类未来大规模地利用太阳能开辟广阔的前景。下一页返回Text1NewNanoCoatingBoostsSolarEfficiencyResearchershavedevelopedanewanti-reflectivecoatingthatbooststheefficiencyofsolarpanelsandallowssunlighttobeabsorbedfromalmostanyangle(Fig.5-1).RensselaerPolytechnicInstituteresearcherssaythey'vemadeadvancesinabsorptionofsunlight.ScientistsfromtheFutureChipsConstellation(FCC)attheRensselaerPolytechnicInstitutenNewYorkhavecreatedthecoatingusingnanotechnology(engineeringdevicesonamolecularscale).Theyarehopefulthatitcantransformthesolarenergymarketinthecomingyears.下一页返回上一页Text1NewNanoCoatingBoostsSolarEfficiencyAtypicaluntreatedsiliconsolarcellabsorbsjustovertwothirdsofsunlight.ButwiththeFCC'snanoengineeredcoatingthatfigurerisesto96.21percent.Intheirpaper“Realizationofanearperfectanti-reflectioncoatingforsiliconsolarenergyutilization"publishedinthescientificjournalOpticsLetters,researchersreportthatgainsinabsorptionwereconsistentacrosstheentirespectrumofsunlight-ultraviolet,visiblelight,andinfrared.下一页返回上一页Text1NewNanoCoatingBoostsSolarEfficiencyProfessorofphysicsatRensselaer,andheadoftheFCCresearchteam,Shawn-YuLinsaid:“Togetmaximumefficiencywhenconvertingsolarpowerintoelectricity，youwantasolarpanelthatcanabsorbnearlyeverysinglephotonoflight，regardlessofthesun'spositioninthesky.Ournewanti-reflectivecoatingmakesthispossible.”Comprisedofseventinylayers-eachoneis50-100nanometersinheight-thecoatingismadeofsilicondioxideandtitaniumdioxidenanorodspositionedatanobliqueangle.下一页返回上一页Text1NewNanoCoatingBoostsSolarEfficiencyTheFCCteamfoundthatstackingthecoatingsoneontopofanotherenhancedtheanti-reflectivepropertiesofeachlayer.Havingaseriesoflayersalsohelpsto“bend”theflowofsunlightwhichassistsincapturinglightthatwouldotherwisebereflectedoff.ProfessorLin,anexpertinnanostructurephotonicsandapioneerinthefieldofphotoniccrystals,saysthatthenewcoatingcouldbeappliedtojustaboutanyphotovoltaicmaterial.Conventionalsolartechnologyhasthusfardictatedthatsolarpanelsbemountedonsouth-facingroofs,orinlocationswherethesunsourceisunrestrictedandstrong.Butthisnewcoatingcouldchangeallthis.下一页返回上一页Text1NewNanoCoatingBoostsSolarEfficiencyItwouldalsomeanthatlargescalesolarfarms,likethegiantarrayinAlentejo,Portugal,couldincreasetheiroutputwhilesavingonenergyusedtotrackthesun.ProfessorLintoldCNN:“Theanti-reflectivecoatingrequiresmulti-layercoatingswhichareslightlymorecomplexthanthetypicalsingle-layerones.However,thethicknessofeachindividuallayerdoesnotneedtobeprecise.Thismakesmanufacturingeasier.”Liniscurrentlyexploringpartnershipsandlicensingarrangements.Andasfarasbringingtheproducttomarket,Linestimatesthatitcouldbeassoonasthenexttwotothreeyears.下一页返回上一页Text1NewNanoCoatingBoostsSolarEfficiency“Theeconomicsofmoderndaysolarcellsdependslargelyonthethicknessofthesubstrate(500-1,000micrometer)andtheprocessingcostformakingthejunctions.Ourcoatinghasathicknessof0.7to1micrometer.Theadditionalcostforincorporatingouranti-reflectivecoatingshouldnotexceedtwotofourpercentofthatforexistingsolarcells,”Linsaid.TheonlydownsidethatLinandhisteamhavefoundsofaristhatthenanorodscanbefragile.Futureresearchwillfocusonprotectingthembetterandinvestigatingtheuseofathinporousfilmtomakethemmorerobust.下一页返回上一页Text1NewNanoCoatingBoostsSolarEfficiencyInresponsetothepaper'spublication,ProfessorDarrenBagnallfromtheNanoscaleSystemsIntegrationGroupattheUK'sUniversityofSouthamptontoldCNN:“It'sareallyimpressivesurface,andtogetdowntoreflectivityfromallanglesof3.5percentisprettyimpressive.Butit'sreallyonlygoingtodelivermaybefourorfivepercentmorepowerfromthesolarcell.”Bagnallishimselftryingtonanoengineersurfacesforsolarcellsbymimickingthesurfaceofmotheyes,whichposesexcellentanti-reflectivesurfaces.下一页返回上一页Text1NewNanoCoatingBoostsSolarEfficiencyHesaysthattheFCCpaperisonlytalkingabouttheamountoflightthat'stransmittedtothedevice,nottheefficiencyofthedeviceitself.“Reflectionisarelativelysmallpartoftheproblem,”hesaid.JeremyLeggett,founderoftheUK'sSolarCentury,alsogaveacautiouswelcometothenewresearch.“I'veseenthisbeforefromotheruniversityresearchgroupsandthereisaworldofdifferencebetweenniceresultsinthelabandcommerciallyviableproducts,”Leggettsaid.“Butatsomepointoneofthemisgoingtowork.”下一页返回上一页Text1NewNanoCoatingBoostsSolarEfficiencyLeggettbelievesthatthefutureisalreadyverybrightforthesolarindustry.Hesaysthat$150billionwasinvestedinrenewableenergylastyear,with$28billionofthatgoingonphotovoltaics.“Withthecurrentefficiencies,weareoneofthefastestgrowingmarketsintheworld.Solaristhefastestgrowingcleantechnologywithexistingtechnology.Anyotherincreasesinefficiencyaregoingtobetheicingonaverynicecake.”下一页返回上一页ReadingOptoelectronicsOptoelectronicsisthestudyandapplicationofelectronicdevicesthatsource,detectandcontrollight,usuallyconsideredasub-fieldofphotonics.Inthiscontext,lightoftenincludesinvisibleformsofradiationsuchasgammarays,X-rays,ultravioletandinfrared,inadditiontovisiblelight.Optoelectronicdevicesareelectrical-to-opticaloroptical-to-electricaltransducers,orinstrumentsthatusesuchdevicesintheiroperation.Electro-opticsisoftenerroneouslyusedasasynonym,butisinfactawiderbranchofphysicsthatdealswithallinteractionsbetweenlightandelectricfields,whetherornottheyformpartofanelectronicdevice.下一页返回上一页ReadingOptoelectronicsisbasedonthequantummechanicaleffectsoflightonsemiconductingmaterials,sometimesinthepresenceofelectricfields.Photoelectricorphotovoltaiceffect,usedin:photodiodes(includingsolarcells)phototransistorsphotomultipliersintegratedopticalcircuit(IOC)elements下一页返回上一页ReadingPhotoconductivity,usedin:photoresistorsphotoconductivecameratubescharge-coupledimagingdevicesStimulatedemission,usedin:injectionlaserdiodesquantumcascadelasers下一页返回上一页ReadingLosseveffect,orradiativerecombination,usedin:light-emittingdiodesorLEDPhotoemissivity,usedinphotoemissivecameratubeImportantapplicationsofoptoelectronicsinclude:ptocouplerpticalfibercommunications返回上一页Text2E-PaperINTRODUCTION:电子技术的发展已经将柔性显示器变成了现实，尽管离投入市场还有一定距离。再过几年，你就再也不用每天早上买报纸了，取而代之的便是采用柔性显示器的电子报纸，这种显示器的尺寸和重量都像一本薄薄的杂志，可以让你在上班的路上方便地阅读。索尼、松下、E-Ink公司都已经开发出了电子图书，而且即使放在阳光直射的地方也能很容易地阅读。下一页返回Text2E-PaperE-paperisathin,flexiblepolymersheetwiththelookofpaper(Fig.5-2).Bute-paperisabitthickerthanregularpaperandweighsmorebecauseitcontainsmicroscopicelectronicinkparticlessandwichedbetweentwopolymersheetsthatdisplayaseitherwhiteorblackinresponsetoanelectricalcharge.E-paperisreflective,likerealpaper,soitcanbereadinanylight.E-paperisalsobi-stable,whichmeansthatthedisplayusespoweronlytochangethecontent.下一页返回上一页Text2E-PaperThosetwomaincharacteristicsarewhatgiveapaperlikedisplayitsgoodqualities-it‘scomfortabletoreadbecauseit‘sreflective,andthebi-stableaspectallowsyoutohavelowpowerandlightweightbatteriessothewholedevicecouldbeextremelythinandlightweight.E-InkandGyriconbothoffere-paperproducts.Thebasictechnologythevendorsuseisthesame,buteachtakesaslightlydifferentapproach.下一页返回上一页Text2E-PaperE-Ink'se-inkconsistsofmillionsofmicrocapsulesaboutthediameterofahumanhair.Theseclearcapsulescontainaclearfluid,aswellastinyblackandwhiteparticles.Thetwocolorseachcarryoppositecharges.Whenanelectricalfieldisapplied,theparticlesmoveupanddownwithinthecapsules.Anegativeelectricfieldmakesthewhiteparticlesmovetothetopofthemicrocapsule,wheretheyarevisibletotheuser.Apositivechargepullstheblackparticlestothebottomofthemicrocapsules,hidingthem.Thetechnologyisusedfore-paperandcanbeembeddedinelectronicdisplays.下一页返回上一页Text2E-PaperSmartPaper,ane-papertechnologyfromGyriconLLC,awhollyownedsubsidiaryofXeroxCorp,consistsoftwosheetsofthinplasticwithmillionsoftinybeadsembeddedbetweenthem.Eachbead,smallerthanagrainofsand,hasadifferentcoloroneachside.Thehemispheresalsocarryoppositecharges.Eachbeadresidesinitsownoil-filledcavitywithintheflexiblesheet,andundertheinfluenceofavoltageappliedtothesurface,itrotatestopresentonesideortheothertotheviewer.Theimagestaysinplaceuntilanewvoltagepatternisapplied,whicherasesthepreviousimageandgeneratesanewone.下一页返回上一页Text2E-PaperSeveralcompaniesaredevelopingcommercialapplicationsofe-papertechnology.SmartPaperisusedinane-paperpricing一signsystemforretailstores.Thesigniscontrolledbysoftwarethatlinksitwirelesslytoin-storepricingdatabases.Sothepriceonthesigncanbeupdatedinstantly.Andit'salwaysthesameasthepriceinthepoint-of-saledatabase.GyriconalsooffersSmartPaperinalineofdynamicmessageboards,whichitsellstohotels,conferencecentersandlargecampuses.Themessageboardssellfor$1,295each.下一页返回上一页Text2E-PaperInApril,E-InkCorp.,RoyalPhilipsElectronicsandSonyCorp.togetherlaunchedtheirfirst-generatione-inkdisplayinSony'se-bookreader,theLibrie,inJapan.Thee-bookincorporatesthee-inktechnologyusedine-paperintoatraditionaldisplay.FujitsuLaboratoriesLtd.isdevelopingapaperlikedisplaythatitsayscouldbeusedwithaterminalforreadingbusinessdocumentsdownloadedfromaPC.Thepapershouldbeinproductionby2006,andFujitsuisbullishonitsprospects.Thisinventionmaypavethewaytoapaperlessofficeandreducepaperconsumption.下一页返回上一页Text2E-PaperAlthoughe-papertechnologyisprogressing,therearesomedownsides.Oneisthate一paperackscolor.Andwhilee-inkhasbeenincorporatedintodisplays,thebi-stablee-papertechnologycan'tsupportfull-motionvideobecauseupdatingorrewritingapagetakestoolong.Today,e-paperisstilllookingforakillerapplication.Whileafewretailersareexperimentingwithe一paperpricinglabels,thetechnologyhasyettocatchon.Butthatcouldchange.Inthreetofiveyears,we‘llseesecond-generationtechnologieswillprobablyhavebettercharacteristics,reducecostsandaddflexibilitytothemix.下一页返回上一页ReadingTelevisionSometelevisionsinusetodayrelyonadeviceknownasthecathoderaytube(CRT).SometelevisionsuseLCD.Theothersrelyonplasmadisplays.LiquidCrystalDisplay(LCD)ThereisfarmoretobuildanLCDthansimplytocreateasheetofliquidcrystals.ThecombinationofthefollowingfourfactsmakesLCDpossible.下一页返回上一页ReadingLightcanbepolarized;Liquidcrystalscantransmitandchangepolarizedlight;Thestructureofliquidcrystalscanbechangedbyelectricitycurrent;Therearetransparentsubstancesthatcanconductelectricity.TherearetwomaintypesofLCDsused:passivematrixandactivematrix.MostLCDdisplaysuseactivematrixtechnology.Athinfilmtransistorarrangestinytransistorsandcapacitorsinamatrixontheglassofthedisplay.Toaddressaparticularpixel,theproperrowisswitchedon，andthenachargeissentdownthecorrectcolumn.下一页返回上一页ReadingSincealloftheotherrowsthatthecolumnintersectsareturnedoff,onlythecapacitoratthedesignatedpixelreceivesacharge.Thecapacitorisabletoholdthechargeuntilthenextrefreshcycle.TheothertypeofLCDtechnologyispassivematrix.ThistypeofLCDdisplayusesagridofconductivemetaltochargeeachpixel.Theyarelessexpensive.PlasmaDisplayPlasmadisplayisonly4inchesthickandhangingonthewall.下一页返回上一页ReadingWhenweplayananaloguesourcelikeavideotapeorregularTV,theplasmadisplayupconvertsthesesignalstodigital,foravastlyimprovedpicture.Whenwewatchamovie,thedisplaydetectsthefilm-basedoriginalsourceandinstantlyrecreateseachindividualstillframe,foramorefilm-likepresentation.DigitalTelevisionDigitaltelevisionisanewwayoftransmittingtelevisionservices.Soundandpicturesareprocessedelectronicallyintodigitalsignals,whicharethentransmittedasabitstreamandreconvertedbydigitalTVsetsorappropriateset-topboxesintotelevisionprogrammes.下一页返回上一页ReadingDigitaltelevisionsetsreceiveelectricalsignals.Thesignalsrepresenteitherazerooraone.Adecoderthenturnsthisdigitalstreamintopatternsorpixelsonthescreen.Digitaltelevisionisgoingtoprovideuswithmorechannelsandhigherqualityimages,whetherthesearestandarddefinitionofhigherdefinition.Digitaltelevision,encompassinghigh-definition,isasetofstandardsforvideo-signalandaudio-signalquality.下一页返回上一页ReadingNewservicesmakinguseoftheadvancedfeaturesofdigitaltechnologywillpresentmany-to-one,many-to-manyandone-to-onecommunication.Incombinationwithaninteractivereturnchannel,digitalreceiverswillbeabletoofferusersavarietyofenhancedservices,fromsimpleinteractivequizshows,toInternetovertheair,andamixoftelevisionandweb-typecontent.下一页返回上一页ReadingEverythingwecandoonthecomputerwillbedoneonTV.ThebenefitsofDTVaremanifold:EfficientutilizationofbandwidthBetterpictureandsoundqualityInnovativeservicesGovernment'spolicyinitiatives返回上一页Text3WhatIsBluetooth?INTRODUCTION:蓝牙是一种支持设备短距离通信(一般是10m之内)的无线电技术。能在包括移动电话、PDA、无线耳机、笔记本电脑、相关外设等众多设备之间进行无线信息交换。蓝牙的标准是IEEE802.15，工作在2.4GHz频带，带宽为1Mb/s.Bluetoothisauniversalradiointerfaceinthe2.45GHzfrequencybandthatenablesportableelectronicdevicestoconnectandcommunicatewirelesslyviashort-range,adhocnetworks.Eachunitcansimultaneouslycommunicatewithuptoseveralotherunitsperpiconet.Moreover,eachunitcansimultaneouslybelongtoseveralpiconets.下一页返回Text3WhatIsBluetooth?WhatIsBluetoothTechnology'sBluetoothtechnologywhichapartfromEricsson,hasgainedthesupportofNokia,IBM,Toshiba,Intelandmanyothermanufacturers,eliminatestheneedforwires,cablesandconnectorsforandbetweencordlessormobilephones,modems,headsets,PDAs,computers,printers,projectors,localareanetworks,andsoon,andpavesthewayfornewandcompletelydifferentdevicesandapplications.Thecharacteristicsofbluetoothtechnologyareasfollows.1Ms/ssymbolrateexploitsmaximumavailablechannelbandwidth下一页返回上一页Text3WhatIsBluetooth?FastfrequencyhoppingavoidsinterferenceAdaptiveoutputpowerminimizesinterferenceShortdatapacketsmaximizecapacityduringinterferenceFastacknowledgeallowslowcodingoverheadforlinksCVSD(ContinuousVariableSlopeDeltaModulation)voicecodingenablesoperationathighbiterrorratesFlexiblepackettypessupportwideapplicationrangeAirinterfacetailoredtominimizecurrentconsumption下一页返回上一页Text3WhatIsBluetooth?BasicTechnicalInformationBaseduponasmall,highperformanceintegratedradiotransceiver，eachofwhichisallocatedaunique48-bitaddressderivedfromtheIEEE802standardOperateintheunrestricted2.45GHzISMfreeband,whichisavailablegloballyalthoughslightvariationoflocationandwidthofbandapplyRangesetat10mtooptimizefortargetmarketofmobileandbusinessuser下一页返回上一页Text3WhatIsBluetooth?Grossdatarate1Mbit/swithsecondgenerationplanstoincreaseto2Mbit/s.One-to-oneconnectionsallowmaximumdatatransferrateof721kbit/s(3voicechannels)Usespacketswitchingprotocolbasedonfrequencyhopschemewith1,600hops/stoenablehighperformanceinnoisyradioenvironments.Theentireavailablefrequencyspectrumisusedwith79hopsof1Mhzbandwidth,analogoustotheIEEE802.11standard.Lowpowerconsumptionlongevityforbatterypowereddevices.Duringdatatransferthemaximumcurrentdrainis30mA.Howeverduringpausesoratlowerdataratesitwillhelower.下一页返回上一页ReadingBluetooth'sQuietSuccessItwasbornamidablazeofhypeattheheightofthedotcomboom,butinitiallyfailedtothrive.Indeed,Bluetooth,ashort-rangewirelesstechnologyusedtointerconnectportabledevices,hasbeendeclareddeadonmanyoccasions.Earlyversionsofthetechnologysufferedfromcompatibilityproblems;anambitiousdemonstrationofthetechnologyatatradeshowin2001failedtowork.AndwhileBluetoothstruggleddespiteallthehypefromitsbackers,anotherwirelesstechnology,Wi-Fi,tookoffonitsown.下一页返回上一页ReadingObituariesofBluetoothhaveappearedmanytimesinthetechnologypress,usuallyattributingitsdemisetothesuccessofWi-Fi.“Bluetoothisinfullretreat,”declaredSeanMaloney,anIntelexecutive,in2001.Otheranalystsissuedsimilarverdicts.ButreportsofthedeathofBluetoothprovedtobepremature:Todayitisinrudehealth.SalesofBluetoothdevicesmorethandoubledin2005toreach320munits,andthefigureisexpectedtoexceed520mthisyear-equivalenttomorethan10munitsaweekandfaroutstrippingsalesofWi-Fichips.AroundoneinfourmobilephonessoldnowsupportBluetooth.下一页返回上一页ReadingAndafteryearsofinsistingthatBluetoothwasmorethanjustawaytolinkawirelessheadsettoamobilephone,itsbackersseemtohavebeenvindicated,asotherusesforBluetoothhaveatlastbeguntoemerge.Lastyear60%ofBluetoothchipswentintomobilehandsetsand15%intowirelessheadsets,saysScottSmyserofiSuppli,amarketresearchfirm,buttheother25%wentintootherdevices,fromlaptopcomputers,keyboardsandmicetoBluetooth-enabledclothing.Thissuccess,afteritsrockystart,isduetoacombinationoffactors,saysStuartCarlaw,ananalystatABIResearch.下一页返回上一页ReadingInmanycountriesBluetooth'sfortuneswereboostedbynewlegislationbanningtheuseofmobilephoneswithoutahands-freekitwhiledriving.ThispromptedmanypeopletobuyBluetoothheadsets.Severalcarmakers,ledbyAudi,alsobegantoincorporatemicrophonesandspeakers,capableofconnectingtoahandsetviaBluetooth,intotheirvehicles.AsconsumersbecamemoreawareofBluetoothandbegantoaskforit,handsetmakersstartedtoincludeitasameansofdifferentiatingtheirproductsandincreasingtheirmargins.下一页返回上一页ReadingAddingaBluetoothchiptoaphonenowcostsverylittle-around$2,saysMrCarlaw,downfrom$20in2001-butallowsthemanufacturertoincreasethepriceofthehandsetbyfarmore,andopensupanewmarketforhigh-marginaccessories.Finally,operatorsbeganofferingBluetoothheadsetsasincentivestonewcustomers.Again，theperceivedvalueoftheheadsetisfarhigherthanitscosttotheoperator,sothisincreasesmargins.下一页返回上一页ReadingGreateradoptionhas,inturn,clearedthewayfortheinclusionofBluetoothinallkindsofnewproducts.InadditiontoBluetooth-enabledjackets,motorcyclehelmetsandsunglasseswithbuilt-inwirelessheadsets,thecontrollersfortwonext-generationvideo-gamesconsolesduetobelaunchedlaterthisyear,Sony'sP1ayStation3andNintendo'sWii,willuseBluetooth.BecauseBluetoothisanindustrystandard,bothconsole-makerscanbuychipsandsoftwareofftheshelf,whichisquickerandcheaperthandevelopingtheirownproprietarytechnologies,saysMrCarlaw.返回上一页Text43GINTRODUCTION:3G是英文3rdGeneration的缩写，指第三代移动通信技术。相对第一代模拟制式手机(1G)和第二代GSM,TDMA等数字手机(2G)，第三代手机一般地讲，是指将无线通信与国际互联网等多媒体通信结合的新一代移动通信系统。它能够处理图像、音乐、视频流等多种媒体形式，提供包括网页浏览、电话会议、电子商务等多种信息服务。Themobilecommunicationsindustryhasevolvedinthreestages:Analogue→Digital→Multimedia.下一页返回Text43GThreegenerationsofmobilephoneshaveemergedsofar,eachsuccessivegenerationmorereliableandflexiblethanthelast.Youcouldonlyeasilyuseanaloguecellulartomakevoicecalls,andtypicallyonlyinanyonecountry.Digitalmobilephonesystemsaddedfax,dataandmessagingcapabilitiesaswellasvoicetelephoneserviceinmanycountries.Multimediaservicesaddhighspeeddatatransfertomobiledevices,allowingnewvideo,audioandotherapplicationsthroughmobilephones一allowingmusicandtelevisionandtheInternettobeaccessedthroughamobileterminal.下一页返回上一页Text43GWitheachnewgenerationoftechnology,theserviceswhichcanbedeployedonthembecomesmoreandmorewiderangingandtrulylimitedonlybyimagination.Wearereachingthatstagewith3G.Duringthefirstandsecondgenerations,differentregionsoftheworldpursueddifferentmobilephonestandards,butareconvergingtoacommonstandardformobilemultimediacalledThirdGeneration(3G)thatisbasedonCDMAtechnology.3Gwillbringtheseincompatiblestandardstogether.下一页返回上一页Text43GThethirdgenerationofmobilecommunicationssystemswillsoonbeimplemented.Followingonthehealsofanalogueanddigitaltechnology,thethirdgenerationwillbedigitalmobilemultimediaofferingbroadbandmobilecommunicationswithvoice,video,graphics,audioandotherinformation.Thistransitionisshownbelow:FirstAnalogue1980sVoicecentric,multiplestandards(NMT,TACS,etc.).SecondDigital1990sVoicecentric,multiplestandards(GSM,CDMA,TDMA).下一页返回上一页Text43G2.5HigherRateDataLate1990sIntroductionofnewhigherspeeddataservicestobridgethegapbetweenthesecondandthirdgenerations,includingservicessuchasGeneralPacketRadioService(GPRS)andEnhancedDataRatesforGlobalEvolution(EDGE).ThirdDigitalMultimedia2010sVoiceanddatacentric,singlestandardwithmultiplemodes.ThefollowingtableliststhecomparisonandevolutionofWirelessSystemsfrom1G,2Gto3G.下一页返回上一页Text43G下一页返回上一页Text43G3Ghasthefollowingfeatures.PacketEverywhereWithThirdGeneration(3G),theinformationissplitintoseparatebutrelatedpacketsbeforebeingtransmittedandreassembledatthereceivingend.Packetswitchingissimilartoajigsawpuzzle一theimagethatthepuzzlerepresentsisdividedintopiecesatthemanufacturingfactoryandputintoaplasticbag.Duringtransportationofthenowboxedjigsawfromthefactorytotheenduser,thepiecesgetjumbledup.Whentherecipientemptiesthebagwithallthepieces,theyarereassembledtoformtheoriginalimage.下一页返回上一页Text43GAllthepiecesareallrelatedandfittogether,butthewaytheyaretransportedandassembledvaries.Packetswitcheddataformatsaremuchmorecommonthantheircircuitswitchedcounterparts.Otherexamplesofpacket-baseddatastandardsincludeTCP/IP，X.25,FrameRelayandAsynchronousTransferMode(ATM).InthemobileworldCDPD(CellularDigitalPacketData),PDCP(PersonalDigitalCellular,Packet),GPRS(GeneralPacketRadioService)andwirelessX.25technologieshavebeeninoperationforseveralyears.X.25istheinternationalpublicaccesspacketradiodatanetworkstandard.下一页返回上一页Text43GInternetEverywhereTheWorldWideWebisbecomingtheprimarycommunicationsinterfacepeopleaccessInternetforentertainmentandinformationcollection,theintranetforaccessingcompanyinformationandconnectingwithcolleaguesandtheextranetforaccessingcustomersandsuppliers.TheseareallderivativesoftheWorldWideWebaimedatconnectingdifferentcommunitiesofinterest.下一页返回上一页Text43GThereisatrendawayfromstoringinformationlocallyinspecificsoftwarepackagesonPCstoremotelyontheInternet.Webbrowsingisaveryimportantapplicationforpacketdata.HighSpeedSpeedsofupto2Megabitspersecond(Mbps)areachievablewithThirdGeneration(3G).Thedatatransmissionrateswi