最新CISCO无线射频技术基础教学讲义PPT.ppt

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1、CISCO无线射频技术基础无线基本组件馈线发射器天线接收器所有的无线设备(客户端和接入端)分贝（dB）的定义功率度量PowerdBm—deciBelsreferencedto1mW0dBm=1mWPdBm=10Log10PdBm/1mW)dBW—deciBelsreferencedto1WPdBm=10log10(pW/1W)+30dBm=0dBW-30dBW=0dBmGaindBi—deciBelsreferencedtogainofanisotropicantennadBd—deciBel

2、sreferencedtogainofadipoleantennadB—deciBel,UsedtoExpresstheRatioofTwoValues,UsuallyGainorLossastheRatioBetweenTwoPowers:dB=10Log10P2/P1馈线－功率衰减DirectlyproportionaltothesquarerootofthelengthofthecableInverselyproportionaltothediameterofthecable,assumi

3、ngsimilarconstructionmaterialsProportionaltofrequency:foragivenlengthofcable,ahigherfrequencysignalwillalwaysexperiencemorelossthanalowerfrequencysignalNotdependuponwhichdirectionthesignaltravelsthroughthecable(transmittedsignalslosethesamepercentageo

4、fstrengthasreceivedsignals)Typicallyassume.25dBoflossperconnectorCableType2.4GHz5.8GHzLoss(dB/100ft.)Loss(dB/100ft.)LMR4006.710.8LMR6004.47.3接收灵敏度Examplefor2.4GHzDirectSequenceIndicationoftheabilityofthereceivertodecodethedesiredsignalTheminimumrecei

5、vedsignallevel,intheabsenceofinterference,atwhichthedesiredsignalcanbedecodedwithaparticularBitErrorRate(BER)TypicallyexpressedindBmThemorenegativethevalue,thebetterFunctionofthedatarate:thehigherthedatarate,thehigherthereceiversensitivityrequiredR

6、eceiverNoiseFloor(WillVaryforEachEnvironment)-92dBmReceiverSensitivity@2MbpsReceiverSensitivity@1Mbps-94dBm-98dBm-90dBmReceiverSensitivity@5.5Mbps-87dBmReceiverSensitivity@11Mbps接收灵敏度NotallreceiversarethedesignedthesameNoisecanaffectthequalityofthesi

7、gnalSignal/Noiseratio=Signal–NoiseLevelExample:CurrentS/N=CurrentSignalStrength–CurrentNoiseLevel天线UsedtoradiatetransmittedsignalsandtocapturereceivedsignalsTypes:DirectionalantennasRadiate/captureRFenergypredominantlyinonedirectionYagi,ParabolicDish,

8、Sector,PatchOmnidirectional(or“Omni”)antennasRadiate/captureRFenergyequallyinallhorizontaldirections,360degreesCharacteristics:BandwidthBeamwidthGainPolarizationCrosspolarizationdiscrimination天线的带宽AntennabandwidthBandoffrequenciesoverwhichthea