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1、计算机专业时文选读——超宽带无线技术（一）Ultrawideband(1)There'scertainlynolackofchoiceswhenitcomestowirelesscommunicationsandnetworkingtechnologies.Withallthecurrentlyavailableformsofwirelessaccesscellphones,3G,Wi-Fi,WiMax,Bluetooth,powerlines,and802.11a,b,gandnyouwouldn'tthinkthere'sroomforanythingmore.Buttechno
2、logymarchesforward,andinthenextcoupleofyears,we'regoingtobeseeinganewanddifferentwirelesstechnology.Thenewkidontheradioblockisultrawideband,alsoknownasUWBordigitalpulsewireless.Itwillhelpdelivertelevisionprograms,movies,gamesandmultimegabytedatafilesthroughoutourwirelesshomesandoffices.UWBisfas
3、terthancurrentwirelessLANtechnologiesandprovidesashort-range,high-bandwidthpipethateliminatesinterference.OriginsofUWBGeraldF.RossfirstdemonstratedthefeasibilityofUWBwaveformsforradarandcommunicationsapplicationsinthelate1960sandearly1970s.OriginallydevelopedbytheDefenseAdvancedResearchProjects
4、Agency,thetechnologywascalledbaseband,carrier-free,impulsecommunicationsortime-domainsignaling,untiltheU.S.DepartmentofDefensenameditultrawidebandin1989.Insomerespects,UWBtechnologygoesbacktothedawnofradioandGuglielmoMarconi,searlyspark-gaptransmissions.UWBisalsoasuccessortospread-spectrumradio
5、(alsocalledfrequency-hopping),aWorldWarIItechnologythatsplitsabroadcastacrossmanydifferentradiofrequencies,usingoneatatimetoavoidjamming.Incontrast,UWBuseseveryfrequencyavailabletoit,allatthesametime.UWBisn'tadirectsubstituteforanyotherformofwirelesscommunications,butitdoessomethingsthatnoother
6、technologycanmatch.AUWBtransmittersendsbillionsofshort-durationpulsesacrossawidespectrumofradiofrequencies.TheseRFburstscomesofastlastingonlyfromafewtrillionthsofasecondtoafewnanosecondsthateachactuallyusesonlyafewcyclesofanRFcarrierwave.ThisshortdurationgivesUWBwaveformssomeuniqueproperties.Th
7、eyarerelativelyimmunetomultipathcancellationeffects,suchaswhenastrongreflectedwavearrivesoutofphasewiththedirectpathsignal,reducingthesignalstrengthinthereceiver.UWBpulsesaresoshortthatthedirectsignalhascomeandgonebeforethereflect
