通信工程 毕业设计外文文献翻译:超宽带系统的数据通信..docx
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通信工程 毕业设计外文文献翻译:超宽带系统的数据通信..docx
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英文资料
Ultra-WidebandSystemsforDataCommunications
G.Racherla,J.L.Ellis,D.S.Furuno,S.C.LinGeneralAtomics,AdvancedWirelessGroup
10240FlandersCt.SanDiegoCA92121
E-mail:
{gopal.racherla,jason.ellis,susan.lin,david.furuno}@Website:
luwb
ABSTRACT
Ultra-Widebandt(UWB)isaradiotransmissionschemethatusesextremelylowpowerpulsesofradioenergyspreadacrossawidespectrumoffrequencies.UWBhasseveraladvantagesoverconventionalcontinuouswaveradiocommunicationsincludingpotentialsupportforhighdatarates,robustnesstomultipathinterferenceandfading.WepresentanoverviewofUWBtechnologyanditsuseindatacommunicationsandnetworking.WelookatdesignconsiderationsforUWBbasednetworksatvariouslayersoftheprotocolstack.
1.INTRODUCTION
Ultra-Wideband[1-6]一alsoknownasbasebandorimpulseradio一isacarrier-freeradiotransmissionthatusesnarrow,extremelylowpowerpulsesofradioenergyspreadacrossawidespectrumoffrequencies.UWBhasrecentlygainedagreatdealofinterestduetotherecentFederalCommunicationsCommission(FCC)ReportandOrderwhichallocatestheUWBband一7.5GHzofunlicensedspectrumforindoorandoutdoorcommunicationapplications.UWBcommunicationsarerequiredtohavea-10dBfractionalbandwidthofmorethan20%ora-10dBbandwidthofmorethan
500MHz[7].ItisimportanttonotethattheFCChasnotdefinedaspecificmodulationschemetobeused.UWBsystemsofferthepromiseofhighdatarate,lowsusceptibility
tomultipathfading,hightransmissionsecuritylowprimepowerrequirements,lowcost,andsimpledesign[1,2,5,6].UWBhasbeenusedinmilitaryapplicationsforthepastseveralyearsforground-penetratingprecisionradarapplicationsandsecurecommunications[3,8].Forthepastfewyears,UWBhasbeendevelopedforcommercialapplications[1,2,5,6].WiththerecentFCC[7]reportandorderforthe
useofUWBtechnology,therehasbeenanaddedimpetustothisendeavor.OthernotableUWBapplicationsincludecollisionavoidanceradar,tagging/identification;geolocation[9]anddatacommunicationsinpersonalareanetworks(PAN)andlocalareanetwork(LAN)environments.
UWBpresentsagreatopportunityfordatacommunicationsfortoday'smedia-richconsumerelectronicsandhomeentertainmentsystemsthatrunonbatterypoweredhandhelddevices.Itcanformthebasisofalowcost,lowpowerandveryhighdataratesolutionasawireless"cablereplacement"technologyforcomputer-to-peripherals,peripherals-to-peripheralsanddigitalhomenetworkingapplications.AveryusefulattributeofUWBtechnologyisitsabilitytoperformprecisiongeo-locationwhichcanaidinad-hocormeshnetworkingwheretheoperationsofthemobilehostsbenefitbyknowingthelocationoftheotherhosts.UWBtechnologypromisestofillthevoidleftbyestablishedstandardslikeBluetoothand802.11a/b/g.
ThereareseveralfuturechallengestothewideadoptionofUWBforwirelessdatacommunicationsincludingtheinfancyofthetechnologyinthecommercialarena,lackofreliable
channelmodels,theearlystagesofstandardizationeffortandlackoflow-costsystemonchip(SoC)implementations.Inthispaper,welookatUWBtechnologyfordatacommunicationsandinsideaUWBphysical(PHY)layercharacteristics.Wealsobrieflyintroduceotherrelatedwirelessstandardssuchas802.11[10],802.15.3[11-13]Bluetooth[14],HomeRF[15]andHIPERLAN[16]andpresentabriefsynopsisoftheregulatoryeffortworldwidewithspecialemphasisontheFCC.WealsopresentthedesignconsiderationsforUWBbaseddatanetworking.
2.ULTRA-WIDEBANDTECHNOLOGY
ThebasicwaveformthatemployedinaUWBsystemisanapproximationtoanimpulse,suchasthatshowninFig.1.Theshortdurationofthepulseisassociatedwithlargeinherentbandwidth;hence,thenomenclature"Ultra-Wideband".TypicalattributesofUWBwaveformsaresummarizedinTable1.
Fig.1.UWBwaveformexample.
ThehighspectralcontentoftheUWBwaveformgivesrisetooneoftheprimaryadvantagesUWBoperationforcommunicationswhereaUWBsystemisrobustagainstmultipathfading[17]andnarrowbandinterference[18].Inmultipathfading,wherethetransmittedradiofrequency(rt)signalcanreflectoffobjectsinitstransmissionpathandcancausedestructiveinterferencesatthereceiver,alossofreceptioncanoccur.This
Table1:
CharacteristicsofTypicalUWBSystemsFractionalBandwidth>20%
PulseWidth0.1-2as
PulseRepetitionFrequency1kHz-2GHzAverageTransmittedPower<1mW
effectisparticularlyproblematicindoorswheretherearemanyreflectingsurfaces.Inthefrequencydomain,multipathisshownasfrequencyselectivefading.BecauseUWBcommunicationssystemsspreadsthetransmitteddataoverabroadfrequencybandifdestructiveinterferenceoccursataspecificfrequency,whetherduetomultipathornarrowbandinterference,theinformationcanstillberecoveredoverthegoodfrequencies.
UWBimplementationscanprovidelowcomplexity,lowcostsolutions[19],thusenablingvastdeploymentsofthetechnology.Acriticalcomponentthatreaffirmsa
3
lowcostsolutionisnotingthatUWBsignals,beingcarrier-less,havegreatersimplicityovernarrowbandtransceiversandrequiresmallersilicondiesizes[20].UWBcanbedesignedtoachieveveryhighbitrateswhilestillachievinglowpowerconsumption,afeaturesetwhichwillbeexploitedbytheconsumerelectronicsindustry[21].UWBschemescanfurtherbedesignedtobeveryscalableintermsofcomplexity,bitrate,powerconsumption,andrange.
UWBtechnologycansupportmanyapplications.DifferentUWBmodulationschemesofferdifferentadvantagesforcommunication,radar,andprecisiongeo-locationapplications.UWBtechnology,whichoperatesbetween3.1and10.6GHz,intrinsicallyoffersanefficientreuseofpreciousspectrumbyoperatingstealthilyatthenoisefloor[22].ThisUWBsystemoperatesatlowpower,tobecompliantwithoperatingunderFCCPart15emissions,acrossawiderangeoffrequencies.Asaspreadspectrumtechnology,UWBoffersalowprobabilityofinterceptandalowprobabilityofdetection[8].Thus,itisparticularlywellsuitedforcovertmilitaryorsensitiveusageseenarios[8].BecauseUWBsignalshaveextremelyshortburstsintime(e.g.,durationsof1nsorless)theyaresuitedforprecisiongeo-locationapplications.ThoughUWBintrinsicallyofferstheabove-mentionedfeatures,applicationoptimizationandimprovementsonthesecharacteristicsarelefttospecificdesignsandimplementations,mostnotablybycarefulconsiderationofmodulationschemes.
2.1.UWBSystemDesignConsiderations
SeveralconsiderationsareneededwhendesigningaPAN.First,lowpowerdesignisnecessarybecausetheportabledeviceswithinthenetworkarebatterypowered.Second,highdataratetransmissioniscrucialforbroadcastingmultipledigi\talaudioandvideostreams:
Lastly,lowcostisaprerequisitetobroadeningconsumeradoption.Inadditiontothesecriteria,theUWBsystemdesignermustaddresssynchronizationandcoexistence.Capturingandlockingontotheseshortpulsesmakesynchronizationanon-trivialtask.Coexistingpeacefullywithotherwirelesssystemswithoutinterferenceisimportant;Inparticular,oneneedstopayattentiontothe802.1lawirelessLANsthatoperateinthe5GHzISMbands.
Atthephysicallayer,additionalchallengeslieinthetransceiverandantennadesign.Atthetransmitter,pulseshapingisrequiredtoproduceflatandwidebandemissioninthedesiredfrequencybands.Althoughnewintegratedcircuitsprovidelessexpensiveformsofintegration,thepulsescanbeaffectedbytheparasiticsfrom
thecomponentandpackaging[23].Toaccommodatethehighdatarates,tradeoffsbetweenhighandlowpulserepetitionfrequency(PRF)andmodulationschemesmustbeconsidered.ThelowPRFsystemwithhighermodulation(morebitspersymbol)mayrequireamorecomplexreceiver,whilethehighPRFsystemwithlowermodulationmayleadtoperformancedegradationfordelayspreadinthechannel.Finally,traditionalantennadesignsgeartowardsnarrowbandsystems.Toavoiddispersionatthereceiver,thenewwidebandantennasneedphaselinearityandafixedphasecenter[23].
3.UWBSTANDARDIZATIONANDREGULATORYEFFORTS
Thereareseveralstandardsbodiespresentlyconsidering,atsomelevel,UWBtechnologies.ThestandardsbodymostadvancedintheconsiderationofUWBisstudygroup"a"ofIEEE802.15.3,whichwasformedinNovember2001[11-13].AseriouseffortiswellunderwaytodefineaUWBchannelmodel,andnumerousUWBtutorialshavebeengiven.Manyhallwayconversationstalktoaphysicallayerstandardbeingratifiedin2004(thoughthereisnoformalknowledgeorpositiononthis)andwillaccompanythesoontobeapproved802.15.3MediumAccessControl(MAC)whichsupportsqualityofservice(QoS)forreal-timemultimediaapplications[12].Thetechnicalrequirementspresentlycallforbitratesof110to200Mbpsatrangesupto10m,withtheoptiontoachieve480Mbpspossiblyatshorterdistances.
Thepower
consumptionrequirementispresentlysetat100to250mWwithlOe5biterrorrateatthetopofthephysicallayer.Complexity/costarepresentlyexpectedtobecomparabletoBluetoothandthephysicallayerisrequiredtosupportfourcollocatedpiconets.Coexistenceispresentlycrucial(e.g.,IEEE802.1la)andtheabilitytoscalethetechnologyiskeytoalonglastingandwidelyadoptedstandard.Thesetechnicalrequirementscomefromdocumentsthatarestillbeingrevised;additionally,itisnotpossibletopredictifproposalsmayfallshortofmeetingsome
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