IEEE80211nTechnology

802.11n-1IEEE802.11nTechnology802.11n-2Outline•OverviewoftheIEEE802.11•Multiple-InputMultiple-Output(MIMO)CommunicationSystems•OrthogonalFrequencyDivisionMultiplexing(OFDM)•802.11nBasebandFeatures802.11n-3OverviewoftheIEEE802.11•IEEE802.11–AsetofWirelessLANstandardsdevelopedbyworkinggroup11oftheIEEELAN/MANStandardsCommittee–Thetermalsousedtorefertotheoriginal802.11,whichisnowcalled“802.11legacy”–Themostpopulartechniquesinthe802.11familyarethosedefinedbythea,b,andgamendmentstotheoriginalstandard–Otherstandardsinthefamily(c–f,h–j,n)areserviceenhancementandextensions,orcorrectionstopreviousspecifications802.11n-4¾IEEE802.11Standards•IEEE802.11-Theoriginal1Mbpsand2Mbps,2.4GHzRFandIRstandard•IEEE802.11a-54Mbps,5GHzstandard(1999)•IEEE802.11b-Enhancementsto802.11tosupport5.5and11Mbps(1999)•IEEE802.11d-International(country-to-country)roamingextensions•IEEE802.11e-Enhancements:QoS•IEEE802.11f-Inter-AccessPointProtocol(IAPP)•IEEE802.11g-54Mbps,2.4GHzstandard(backwardscompatiblewithb)(2003)•IEEE802.11h-5GHzspectrum,DynamicChannel/FrequencySelection(DCS/DFS)andTransmitPowerControl(TPC)forEuropeancompatibility802.11n-5•IEEE802.11i(ratified24June2004)-Enhancedsecurity•IEEE802.11j-ExtensionsforJapan•IEEE802.11k-Radioresourcemeasurements•IEEE802.11n-Higherthroughputimprovements•IEEE802.11p-WirelessAccessfortheVehicularEnvironment•IEEE802.11r-Fastroaming•IEEE802.11s-Wirelessmeshnetworking•IEEE802.11t-WirelessPerformancePrediction(WPP)-testmethodsandmetrics•IEEE802.11u–Inter-workingwithnon-802networks•IEEE802.11v-Wirelessnetworkmanagement802.11n-6•802.11legacy–TheoriginalversionofthestandardIEEE802.11releasedin1997•Specifiestworawdataratesof1and2Mbps•Transmittedviainfrared(IR)signalsorintheISMbandat2.4GHz–DefinestheCarrierSenseMultipleAccesswithCollisionAvoidance(CSMA/CA)asthemediaaccessmethod•Asignificantpercentageoftheavailablerawchannelcapacityissacrificed(viaCSMA/CA)toimprovethereliabilityofdatatransmissions802.11n-7•802.11b–UsesthesameCSMA/CAmediaaccessmethoddefinedintheoriginalstandard•DuetotheCSMA/CAprotocoloverhead,inpracticethemaximum802.11bthroughputisabout5.9MbpsoverTCPand7.1MbpsoverUDP–DirectextensionoftheDSSSmodulationtechniquedefinedintheoriginal802.11standard–Usuallyusedinapoint-to-multipointconfiguration(1APtomanySTAs)–Canoperateat11Mbps,butwillscalebackto5.5,2,and1Mbpsifsignalqualitybecomesanissue802.11n-8•802.11a–Usesthesamecoreprotocolastheoriginalstandard–Operatesin5GHzbandandusesa52-subcarrierOFDM(OrthogonalFrequencyDivisionMultiplexing)withamaximumrawdatarateof54Mbps•Thedatarateisreducedto48,36,34,18,12,9,and6Mbpsifrequired–Non-interoperablewith802.11b,exceptequipmentthatimplementsbothstandards–Usingthe5GHzbandgives802.11atheadvantageoflessinterference;howeveritalsobringsdisadvantages•Restrictstheuseof802.11atoalmostlineofsight,necessitatingtheuseofmoreAPs•Cannotpenetrateasfaras802.11bsinceitisabsorbedmoreeasily802.11n-9•802.11g–Worksinthe2.4GHzband(like802.11b)butoperatesatamaximumrawdatarateof54Mbps•Fullybackwardscompatiblewith802.11b–Whileholdingthepromiseofhigherthroughput,actualresultsweremitigatedbysomefactors:•Conflictwith802.11b-onlydevices•Exposuretothesameinterferencesourcesas802.11b•Limitedchannelization(only3fullynon-overlappingchannelslike802.11b)•Moresusceptibletointerferencethan802.11b–Causingthe802.11gdevicetoreducethedataratetothesameratesusedby802.11b802.11n-10•802.11n–Therealdatathroughputwillbeatleast100Mbps(upto200Mbps)•upto4to5timesfasterthan802.11aor802.11g•Itisprojectedthat802.11nwillalsoofferabetteroperatingdistancethancurrentnetworks–Buildsuponprevious802.11standardsbyaddingtheMIMO(multiple-inputmultiple-output)feature•Theadditionaltransmitterandreceiverantennasallowfor–increaseddatathroughputthroughspatialmultiplexing–increasedrangebyexploitingthespatialdiversity–Thestandardizationprocessisexpectedtobecompletedbytheendof2006802.11n-11–Twocompetingvariantsofthe802.11nstandard:•WWiSE–BackedbycompaniesincludingAirgoNetworks,Broadcom,ConexantSystems,Motorola,Nokia,TexasInstruments,andothers•TGnSync–BackedbyAtheros,Intel,Sony,Matsushita,Toshiba,andothers–Statusofthe802.11nstandard••AntypicalMIMOsystemisshownbelow:–Ntransmitantennae,Mreceiveantennae–Wideantennaspacing802.11n-13•Assumptions:–IndependentRayleighfadingchannels––––SNRateachreceiveantenna:powertotal:,PINPRNNxx×=21||,1,,;NijjhNiM===∑MMvvIR×=2σ221σσPNNP=×1111,1yHxv;H=MMNNMijiMjNh××××≤≤≤≤=+802.11n-14•Hcanbedecomposedas•Then,wehaveHNNNMMMNM××××=VDUHU:eigenvectorsofHHH,V:eigenvectorofHHHUHU=I,VHV=I,D:diagonalrivxyiiiiHHHHHHH,,1,'''=+=→+=→===+=→+=λv'Dx'y'vUv'xVx'yUy'vUxDVyUvxUDVyr:rankofH802.11n-15•Theequivalentchannelhasindependentsub-channels.Thus,•Itcanbeshownthat222211log1log1rriiiiPPCWWNλσσ===+=+∑∑++=MNNPIWMNNPIWCHH,detlog,detlog2222HHHHσσ802.11n-16•Examples:–N=M=1,H=1–M=N;HHH=NINxN•Aswecansee,thecapacitycanbegreatlyenhancedbytheMIMOsystem.+=221logσPWC+=