通信工程 毕业设计外文文献翻译:超宽带系统的数据通信资料文档格式.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资料文档格式.docx
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G.Racherla,J.L.Ellis,D.S.Furuno,S.C.LinGeneralAtomics,AdvancedWirelessGroup
10240FlandersCt.SanDiegoCA92121
E-mail:
gopal.racherla,jason.ellis,susan.lin,david.furuno@gatWebsite:
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ABSTRACT
Ultra-WidebandtUWBisaradiotransmissionschemethatusesextremelylowpowerpulsesofradioenergyspreadacrossawidespectrumoffrequencies.UWBhasseveraladvantagesoverconventionalcontinuouswaveradiocommunicationsincludingpotentialsupportforhighdatarates,robustnesstomultipathinterferenceandfading.WepresentanoverviewofUWBtechnologyanditsuseindatacommunicationsandnetworking.WelookatdesignconsiderationsforUWBbasednetworksatvariouslayersoftheprotocolstack.
INTRODUCTION Ultra-Wideband[1-6]一alsoknownasbasebandor
impulseradio一isacarrier-freeradiotransmissionthatusesnarrow,extremelylowpowerpulsesofradioenergyspreadacrossawidespectrumoffrequencies.UWBhasrecentlygainedagreatdealof
interestduetotherecentFederalCommunicationsCommissionFCCReportandOrderwhichallocatestheUWBband一7.5GHzofunlicensed
spectrumforindoorandoutdoorcommunicationapplications.UWBcommunicationsarerequiredtohavea-10dBfractionalbandwidthofmorethan20%ora-10dBbandwidthofmorethan500MHz[7].ItisimportanttonotethattheFCChasnotdefinedaspecificmodulationschemetobeused.UWBsystemsofferthepromiseofhighdatarate,lowsusceptibility
tomultipathfading,hightransmissionsecuritylowprimepowerrequirements,lowcost,andsimpledesign[1,2,5,6].UWBhasbeenusedinmilitaryapplicationsforthepastseveralyearsforground-penetratingprecisionradarapplicationsandsecurecommunications[3,8].Forthepastfewyears,UWBhasbeendevelopedforcommercialapplications[1,2,5,6].WiththerecentFCC[7]reportandorderfortheuseofUWBtechnology,therehasbeenanaddedimpetustothisendeavor.OthernotableUWBapplicationsincludecollisionavoidanceradar,tagging/identification;
geolocation[9]anddatacommunicationsinpersonalareanetworksPANandlocalareanetworkLANenvironmentsUWBpresentsagreatopportunityfordata
communicationsfortoday'
smedia-richconsumerelectronicsandhomeentertainmentsystemsthatrunonbatterypoweredhandhelddevices.Itcanformthebasisofalowcost,lowpowerandveryhighdataratesolutionasawireless"
cablereplacement"
technologyforcomputer-to-peripherals,peripherals-to-peripheralsanddigitalhomenetworkingapplications.AveryusefulattributeofUWBtechnologyisitsabilitytoperformprecisiongeo-locationwhichcanaidinad-hocormeshnetworkingwheretheoperationsofthemobilehostsbenefitbyknowingthelocationoftheotherhosts.UWBtechnologypromisestofillthevoidleftbyestablishedstandardslikeBluetoothand802.11a/b/gThereareseveralfuturechallengestothewideadoptionofUWBforwirelessdatacommunicationsincludingtheinfancyofthetechnologyinthecommercialarena,lackofreliable
channelmodels,theearlystagesofstandardizationeffortandlackoflow-costsystemonchipSoCimplementations.Inthispaper,welookatUWBtechnologyfordatacommunicationsandinsideaUWBphysicalPHYlayercharacteristics.Wealsobrieflyintroduceotherrelatedwirelessstandardssuchas802.11[10],802.15.3[11-13]Bluetooth[14],HomeRF[15]andHIPERLAN[16]andpresentabriefsynopsisoftheregulatoryeffortworldwidewithspecialemphasisontheFCC.WealsopresentthedesignconsiderationsforUWBbaseddatanetworking.
ULTRA-WIDEBANDTECHNOLOGY
ThebasicwaveformthatemployedinaUWBsystemisanapproximationtoanimpulse,suchasthatshowninFig.1.Theshortdurationofthepulseisassociatedwithlargeinherentbandwidth;
hence,thenomenclature"
Ultra-Wideband"
.TypicalattributesofUWBwaveformsaresummarizedinTable1.
Fig.1.UWBwaveformexample.
ThehighspectralcontentoftheUWBwaveformgivesrisetooneoftheprimaryadvantagesUWBoperationforcommunicationswhereaUWBsystemisrobustagainstmultipathfading[17]andnarrowband
interference[18].Inmultipathfading,wherethetransmittedradiofrequencyrtsignalcanreflectoffobjectsinitstransmissionpathandcancausedestructiveinterferencesatthereceiver,alossofreceptioncanoccur.This
Table1:
CharacteristicsofTypicalUWBSystemsFractionalBandwidth 20%
PulseWidth0.1-2as
PulseRepetitionFrequency1kHz-2GHzAverageTransmittedPower1mW
effectisparticularlyproblematicindoorswheretherearemanyreflectingsurfaces.Inthefrequencydomain,multipathisshownasfrequencyselectivefading.BecauseUWBcommunicationssystemsspreadsthetransmitteddataoverabroadfrequencybandifdestructiveinterferenceoccursataspecificfrequency,whetherduetomultipathornarrowbandinterference,theinformationcanstillberecoveredoverthegoodfrequencies.
UWBimplementationscanprovidelowcomplexity,lowcostsolutions[19],thusenablingvastdeploymentsofthetechnology.AcriticalcomponentthatreaffirmsalowcostsolutionisnotingthatUWBsignals,beingcarrier-less,havegreatersimplicityovernarrowbandtransceiversandrequiresmallersilicondiesizes[20].
UWBcanbedesignedtoachieveveryhighbitrateswhilestillachievinglowpowerconsumption,afeaturesetwhichwillbeexploitedbytheconsumerelectronicsindustry[21].UWBschemescanfurtherbedesignedtobeveryscalableintermsofcomplexity,bitrate,powerconsumption,andrange.
UWBtechnologycansupportmanyapplications.DifferentUWBmodulation schemes offer different advantages for communication,radar,andprecisiongeo-locationapplications.UWBtechnology,whichoperatesbetween3.1and10.6GHz,intrinsicallyoffersanefficientreuseofpreciousspectrumbyoperatingstealthilyatthenoisefloor[22].ThisUWBsystemoperatesatlowpower,tobecompliantwithoperating under FCC Part 15 emissions, across a wide range offrequencies. As a spread spectrum technology, UWB offers a lowprobabilityofinterceptandalowprobabilityofdetection[8].Thus,itisparticularlywellsuitedforcovertmilitaryorsensitiveusageseenarios[8].BecauseUWBsignalshaveextremelyshortburstsintimee.g.,durationsof1nsorlesstheyaresuitedforprecisiongeo-locationapplications.ThoughUWBintrinsicallyofferstheabove-mentioned features, application optimization and improvements onthese characteristicsarelefttospecificdesignsandimplementations,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,thepulsescanbeaffectedbytheparasiticsfromthecomponentandpackaging[23].Toaccommodatethehighdatarates,tradeoffsbetweenhighandlowpulserepetitionfrequencyPRFandmodulationschemesmustbeconsidered.ThelowPRFsystemwithhighermodulationmorebitspersymbolmayrequireamorecomplexreceiver,whilethehighPRFsystemwithlowermodulationmay
leadtoperformancedegradationfordelayspreadinthechannel.Finally,traditionalantennadesignsgeartowardsnarrowbandsystems.Toavoiddispersionatthereceiver,thenewwidebandantennasneedphaselinearityandafixedphasecenter[23].
3.UWBSTANDARDIZATIONANDREGULATORYEFFORTSThereareseveralstandardsbodiespresentlyconsidering,atsomelevel,UWBtechnologies.ThestandardsbodymostadvancedintheconsiderationofUWBisstudygroup"
a"
ofIEEE802.15.3,whichwasformedinNovember2001[11-13].AseriouseffortiswellunderwaytodefineaUWBchannelmodel,andnumerousUWBtutorialshavebeengiven.Manyhallwayconversationstalktoaphysicallayerstandardbeingratifiedin2004thoughthereisnoformalknowledgeorpositiononthisandwillaccompanythesoontobeapproved802.15.3MediumAccessControlMACwhichsupportsqualityofserviceQoSforreal-timemultimediaapplications[12].Thetechnicalrequirementspresentlycallforbitratesof110to200Mbpsatrangesupto10m,withtheoptiontoachieve480Mbpspossiblyatshorterdistances.
Thepower
consumptionrequirementispresentlysetat100to250mWwithlOe5biterrorrateatthetopofthephysicallayer.Complexity/costarepresentlyexpectedtobecomparabletoBluetooth
andthephysicallayerisrequiredtosupportfourcollocatedpiconets.Coexistenceispresentlycruciale.g.,IEEE802.1laandtheabilitytoscalethetechnologyiskeytoalonglastingandwidelyadoptedstandard.Thesetechnicalrequirementscomefromdocumentsthatarestillbeingrevised;
additionally,itisnotpossibletopredictifproposalsmayfall
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