矿用隔爆型移动变电站低压保护系统的设计英文翻译Word文档下载推荐.docx
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矿用隔爆型移动变电站低压保护系统的设计英文翻译Word文档下载推荐.docx
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学院(部):
电气与信息工程学院
专业班级:
学生姓名:
2012年6月1日
xDSLAnalogCircuitsandSignalProcessing
xDSLreferstodifferentDSL,suchasADSL,HDSLandRADSL.DSLusesordinarytelephonelinestohigh-bandwidthinformationintothehomeandsmallbusinessenterprisetechnologies.Traditionaltelephonebusinessthroughthetwisted-pairfamiliesorcompaniesconnectedwiththetelephonecompany.Inputdevicessuchasaccesstotelephonevoicesignal(analogsignal),itwillbetransformedintoelectricalsignals.Becausethetelephonecompany'
ssignalhasbeensettouseanalogsignaltransmission,soeasilyonthephoneandexchangeofinformationbetweenthephonecompany.Thatiswhytheneedtouseacomputermodemreasons,sothatitwillbethevalueofanalogsignalandconvertedtodigitalsignals.
DSLwillnotassumethatdigitalsignalandthenbackintoanalogsignals.Digitalsignaldirectlyintheformofdigitaltransmissiontothecomputer,whichallowsphonecompaniestogreaterbandwidthtotransmitinformation.Atthesametime,partofthesignalisstillanalogsignaltransmissioninordertousethephoneatthesametime.
DSLincludingADSL,CDSL,DSLLite,HDSL,IDSL,RADSL,SDSL,UDSL,VDSL,x2/DSL.
1.Outline
xDSLisaDSL(DigitalSubscriberLine)ofcollectively,thatis,digitalsubscriberline,basedoncoppertelephonelinesfortransmissionofpoint-to-pointtransmissionmedium.DSLtechnologyinthetraditionaltelephonenetwork(POTS)usersloopssymmetricalsupportandasymmetrictransfermode,oftenresolvedinthenetworkserviceprovidersandend-usersamongthe"
lastmile"
oftransmissionbottlenecks.Becauseofthelargenumberofusershasbeenlayingloop,sotomakefulluseofexistingresourcesofcopper,twisted-paircopperthroughthehigh-speedaccesshasbecometheminimumcostofdoingbusinessdeliveredthemostrealisticsolutionforbroadbandaccessnetworks.DSLtechnologyhasbeenalargenumberofapplications,isaverymaturetechnologyaccess.
SystemismainlycomposedofxDSLcentralofficeequipment(DSLAM-DigitalSubscriberLineAccessMultiplexer)andcustomerpremiseequipment(CPE),fromthecentralofficeDSLAMaccessplatform,DSLcentralofficecard,voiceseparator,IPC(dataconvergencedevice)andsoonComposition.Asshown,voiceseparatorwillbeonthelineandhigh-frequencydigitalaudiosignalmodulationsignalseparation,andaudiosignalsintothetelephoneexchange,high-frequencysignalsintodigitalmodulationDSLaccesssystem;
DSLAMaccessplatformcanbeinsertedatthesametimedifferentDSLaccessNetworkcardsandcards;
centralofficelinecardswillbeonthesignalmodulationfordigitalsignalandprovidesdatatransferinterface;
IPCforDSLaccesssystemtoprovidedifferentWANinterfacessuchasATM,FrameRelay,T1/E1,andsoon.Thesefacilitiesarelocatedinthetelephoneswitchsystemsintheroom.DSLModembytheuserequipmentandvoicecomponentseparator,DSLModemusersonthepacketmodulationanddemodulationandprovidesdatatransferinterface.
2.DSLmodulationtechniques
DSLtechnologyistheuseofthephonesystemnotbeingusedforhigh-frequencysignalstotransmitdata.DSLuseofmoreadvancedmodulationtechniques.Atpresent,thewidelyusedADSLmodulationtechnology3:
QAM(quadatureamplitudemodulation),CAP(carrierlessamplitude-phasemodulation),DMT(discretemultitone),whichtheDMTmodulationtechnologyANSISubcommitteeT1E1.4standardizedthedevelopmentofthecountryStandardused.However,duetotheintroductionofthestandardswillnotbelong;
therearestillaconsiderablenumberofADSLproductsusingCAPorQAMmodulation.
QAMmodulationtechnologytoachievethefollowingmethods:
sendingdatabits/symbolencoderhasbeendividedintotwo(theratefortheoriginal1/2),withapairoforthogonalmodulationweightmultiplied,afterthesummationoutput.Comparedwithothermodulation,QAMcodinghastomakefulluseofbandwidth,andstronganti-noiseadvantages.QAMforADSLmainproblemishowtoadapttodifferenttelephonelinesbetweentheperformancesofalargerdifference.Toobtainamoredesirablecharacteristicsofthework,QAMreceiverandatransmitterwiththesamefrequencyandphasecharacteristicsoftheinputsignalfordecoding,QAMreceivertouseadaptiveequalizertocompensateforthetransmissionsignaldistortionproducedby,theuseofQAM'
sADSLsystemsfromthecomplexityofitsadaptiveequalizer.
CAPisbasedonQAMmodulationtechnologydeveloped,youcansayitisavariantofQAMtechnology.Enterdataintotheencoder,encoderwithin,m-bitinputhasbeenmappedfork=2mdifferentcomplexsymbolsAn=an+jbn,bytheKdifferentsymbolsconstitutepluralk-CAPlinecoding.Andanencodedbnrespectively,weresenttoin-phaseandquadraturedigitalshapingfilter,afterthesummationintotheD/Aconverter,asthefinallow-passfiltersignalsent.CAPtechnologyforADSListhemaintechnicaldifficultiestoovercomeonthelocalsignalcrosstalkinterference.Generalcrosstalkcanbeoffsetthroughtheuseoflocalorproximalcrosstalkequalizertoresolvethisproblem.
DMTmodulationtechnology,themainprincipleistoband(0-1.104MHZ)dividedinto256bytheinstructionsoforthogonalfrequencychannel(oneforeachchannelbandwidthoccupiedby4KHZ),afterabitoftheinputsignaldistributionandcaching,willenterdataintobitsBlock,theTCMcodefor512pointsafterthediscreteFouriertransform(IDFT)willtransformintotime-domainsignal,thenbitblockwillbeconvertedto256-QAMcharacters.Theneachbitblockaddcyclicprefix(fortheeliminationofISI),thedataconversionmodule(DA)andsendthesignalsenttofilterchannel.Onthecontraryatthereceivingendinordertocarryoutdecodingreceive.
3.DSLclassification
SymmetricDSLtechnologyasfollows:
(1)HDSL(highbit-rateDSL)
HDSLisxDSLtechnologyinthemostmatureone,hasbeenmorewidelyused.Thetechnologycanbeavailabletofull-duplextwisted-paircopperT1orE1transmissionway.Itfeatures:
twopairsoftwisted-pairtransmission;
N×
64kbpstosupportavarietyofspeedsuptoE1rates.HDSLisanalternativetoT1/E1technology,mainlyusedtoconnectdigitalswitches,high-bandwidthvideoconferencing,distancelearning,cellularphonebasestationtoconnect,suchastheestablishmentofprivatenetworks.AndtraditionalT1/E1technology,HDSLhasthefollowingadvantages:
lowerprices;
easytoinstall,T1/E1requestevery0.9to1.8kilometersontheinstallationofanamplifier,andHDSLinthe3.6kmdistancetransmissionwithoutamplifiers.
(2)SDSL-Single-lineDSL,whichisone-wayversionofHDSL,whichcanprovidetwo-wayhigh-speedvariablebitrateconnectionspeedsrangingfrom160Kbpsto2.084Mbps.Itfeatures:
aone-ontwistedpair;
ratetosupportmultipleT1/E1;
usersbasedonthedataflow,tochoosethemostappropriaterateoftheeconomy,therateofuptoE1,HDSLthansavingapairofcopperwire;
0.4mmtwistedpairofthelargesttransmissiondistanceof3km.
(3)MVL-MultipleVirtualLine,itscharacteristicsareasfollows:
useapairoftwisted-pair;
easytoinstall,inexpensive;
low-power,high-densitycanbeinstalled;
theuseofISDNtechnologywiththesamefrequency,thesamecablesignalinterferencewithotherVerysmall;
supportthetransmissionofvoice,novoiceintheclientseparator;
supportatthesametimeonthesamelinetoconnectupto8MVLuserequipment,dynamicbandwidthallocation;
up/down-sharingrateofupto768Kbps;
transmissiondistanceofupto7km.
(2)AsymmetricDSLTechnology
AsymmetricDSLtechnologyasfollows:
1)ADSL-AsymmetricDSL(asymmetricDSL),ADSLnetworkstospeeduptheflowfromthe1Mand8Mdownthetraffic,atthesametimewithanonlineoffervoicetelephoneservices.Characterizedby:
apairoftwisted-pairtransmission;
upfromtherateofupto1M,downasmuchas8M;
atthesametimesupportthetransmissionofdataandvoice.
2)RADSL-RateAdaptiveDSL(rateadaptiveDSL),thistechnologyallowsserviceproviderstoadjustbandwidthxDSLconnectionsinordertomeettheactualneedsandsolvequalityproblemsandlonglines.Itscharacteristicsareasfollows:
useapairoftwisted-pairtransmission;
supportsynchronousandasynchronoustransfermode;
adaptiverate,downfromarateof640Kbpsto12Mbps,upfromtherateof128Kbpsto1Mbps;
3)VDSL-VeryHighDataRateDSL,VDSLandADSLsystems,canmakeuseofordinarycoppertelephonewithoutaffectingthenarrow-bandvoiceservices(POTS,ISDN),high-speeddatatransmissionbusiness.VDSLsystemandstructureisverysimilartoADSL.VDSLusedinawidespectrum,upto12MHz.Thescopeofthespectrumcanbedividedintoanumberofdownstream(DS)andupstream(US)band,thebandcommonlyusedininternationaldivisionoftheway(BandPlan),therearemainlytwo:
Plan997,Plan998.Plan998undertheNorthAmericandivisionofbusinessneeds,mainlybusiness-orientedasymmetric;
Plan997andaccordingtobusinessneedsintoEurope,mainlybusiness-orientedsymmetric.ADSLasaresultoftheuseofspectrumtoonlythehighest1.1MHz,comparison,VDSLcanprovidehighertransmissionspeed,moreflexibilityfordifferentbusinessneedstoprovidedifferenttransmissioncapacity(ofcourse,transmissiondistancegenerallyshorterthanADSL).VDSLapplicationenvironmentcanbedividedintothreecategories:
(a)short-rangehigh-speedasymmetricoperations,forexample,lessthan300m,downlinktransmissionrate26Mb/sandabovecanbemainlyusedforvideotransmission;
(b)distanceinsymmetricalorasymmetricalclosetothebusine
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