wifi basic study

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1、WifiBasicStudyDate:10/25/2017ContentBasicIntroductionWifi、Wlan&802.11xBlockDiagramKeyTechnologyOFDMDSSSMIMOTestSpecificationMaximumOutputPowerlevelTransmitspectrummaskEVMFrequencyerrorReceiveadjacentchannalrejectionSensitivityWifi、Wlan&802.11xIEEE802.11xisasetofstandardsdefi

2、ningawirelesscommunicationsystemintheGHzrange.WiFiisacommunicationtechnologyinaccordancewiththeIEEE802.11xprotocals,alogoofWlan.Wlanisakindofdatatransmissionsystem,itcontainslotsofwirelesstransmissionprotocals.StandardfrequencyallocationDevelopmentofWifiDataRateDataRateRc(bi

3、ts/symbol)rb(bits/s)Symboldimension：Timedimension：SymboltimeSymboltime=basicsymboltime+cycllcextensionFor800nsSymboltime=3.2us+0.8us=4usFor400nsSymboltime=3.2us+0.4us=3.6us802.11a/g协议采用48个副载波，802.11n在20Mhz采用52个，40Mhz采用108个MCS0~15MCS(ModulationCodingScheme)MCS0~7for1xstreamMC

4、S8~15for2xstreamHT20(20MHz)(MCS0-MCS7)6.5M、13M、19.5M、26M、39M、52M、58.5M、65M(MCS8-MCS15)13M、26M、39M、52M、78M、104M、117M、130MHT40(40MHz)(MCS0-MCS7)13.5M、27M、40.5M、54M、81M、108M、121.5M、135M(MCS8-MCS15)27M、54M、81M、108M、162M、216M、243M、270MWifiBlockDSSS:DirectSequenceSpreadSpectrum二进制

5、数据源高速率的扩频序列扩展频谱高功率&窄带低功率&宽带.....DSSSRb=1/TbRc=1/TcNormallyMb/sDSSSMorerobustagainstmultipathpropagationeffects.Highsecurity.Morerobustagainstinterference.C=B*Log2(1+S/N)Rationale:Shannon'sChannelCapacityTheoremC——ChannelCapacity，b/s；B——ChannelBandwidth，Hz；S——SignalPower，W；N—

6、—NoisePower，W。ForanygivenSignalNoiseRatio,therateoferror-freetransmissioninthechannelwillincreaseaslongasthetransmissionbandwidthwasexpanded.AstheSignalNoiseRatiofalls,increasingthetransmissionbandwidthcouldcompensatetheChannelCapacity.MIMOBasicConceptDefinitionAtonetime,inw

7、irelesstheterm"MIMO"referredtotheuseofmultipleantennasatthetransmitterandthereceiver.AdvantagesIncreasethechannelcapacityImprovethereliabilityofthechannelMIMOSDandSMThespatialdiversityisdividedintoRXandTXdiversity,andthesignalreplicasaresentfromanotherantennaorreceivedatmult

8、ipleantennas.Inspatialmultiplexing,thesystemcantransmitmorethanonespatialda