WHITEPAPER

NavigatingWi-Fi7

ADeepDiveintoNext-GenAdvancements

WHITEPAPER

NavigatingWi-Fi7

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Tableofcontents

Abstract 4

Wi-FiLegacy 4

IntroductionofWi-Fi7 5

4096QAM 6

NewPreambledesign 7

320MHzBandwidth 7

MultiRU 8

512MPDUcompressedblock-ack 9

EnhancedQoS 9

Wi-Fi6Latencyimprovements 9

Wi-Fi7RestrictedServicePeriodsforLatencyguarantees 10

RestrictedTWT 11

TriggeredPeer-to-Peer(P2P)Transmission 11

Multi-LinkOperation 12

Multi-LinkArchitecture 12

ReliabilityvsLatency 13

TypesofMLDs 13

Multi-LinkChannelaccess 14

Multi-linkperformance 15

Multi-linkdiscovery 16

Legacylinkdiscovery 16

Wi-Fi7Multi-linkdiscovery 17

Multi-linkAssociation 17

Multi-linksecuritysetup 18

NSEP 19

NewWi-Fi7testingchallenges 19

Testingsystems 20

OCTOBOXTestbeds 20

OCTOBOXsoftware 21

RESTAPI 22

ScriptManager 22

References 23

AppendixA 24

AppendixB 25

Figures

Figure1 Wi-Fi7developmenttimeline 5

Figure2 Wi-Figenerationalincreaseinconstellationsize 6

Figure3 Diversitygainsusingmultipleantennas 6

Figure4 EHTpreamble 7

Figure5 Worldwide6GHzadoption 7

Figure6 Illustrationofpuncturing 8

Figure7 ExamplesofMultiRUoperation 8

Figure8 OFDMAminimizeschannelcontentionformultipleusers.SourceWFA 9

Figure9 Wi-Fi6latencyimprovementcomparedtolegacy 9

Figure10EnhancedQoSusingrestrictedserviceperiods 10

Figure11ComparisonofOWDspreadsfordeviceswithandwithoutdeterministicQoS 10

Figure12RestrictedTWTSPoperation 11

Figure13TriggeredP2Poperation 11

Figure14MLDArchitecture 12

Figure15MLOreducedlatencyorincreasedthroughput 13

Figure16MLOforincreasedreliability 13

Figure17Multi-linkdevicehierarchy 13

Figure18SimultaneousasynchronousoperationSTR 14

Figure19NonsimultaneoussynchronousoperationNSTR 14

Figure20PerformancecomparisonofdifferentMLDs 15

Figure21ExampleofMLDdiscovery 17

Figure22Multi-Linkassociation 17

Figure23Four-wayhandshakeforsecuritysetup 18

Figure24GroupKeyHandshake 18

Figure25OCTOBOXSTACK-MAXtestbed 20

Figure26OCTOBOXsmallanechoicchamberwithturntable 20

Figure27AviewoftheSpirentOCTOBOXuserinterface 21

Figure28ScriptManagerprovidesorganizationandautomationoftestsuites 22

Figure29LegacyMACandU-MACillustration 25

Abstract

ThiswhitepaperexploresWi-Fi7’sadvancementsthroughatestingsystemoverviewandfeatureintroduction.ItdiscusseslegacyWi-Fi,OCTOBOXtestbeds,andOCTOBOXsoftwarewithRESTAPIandScriptManagerintegration.ChallengesintestingWi-Fi7’scapabilitiesarenoted.

Wi-Fi7’sfeaturesencompass4096QAM,newpreambledesign,320MHzbandwidth,multiresourceunitsforconcurrentusers,andenhancedqualityofservice(QoS).ThisincludesWi-Fi7’slatencyimprovements,restrictedserviceperiodsforlatencyassurance,restrictedtargetwaketime,andtriggeredpeer-to-peertransmission.

AcorefocusisMulti-LinkOperation,detailingarchitecture,reliabilityvs.latencytrade-offs,Multi-LinkDevicetypes,channel

access,andperformance.Multi-LinkDiscoverycontrastslegacymethods,coveringassociationandsecuritysetup.

ThewhitepaperservesasaconciseguideforWi-Fienthusiasts,spotlightingitsrevolutionaryfeaturesandtestinginsightsforfuturewirelesstechnology.

Wi-Filegacy

Traditionally,eachnewgenerationofWi-Fihasconsistentlydeliveredhigherdatarates,primarilyfocusingonindividualusers.However,Wi-Fi6introducedawiderangeofnewfeaturesandenhancementsaimedatimprovingtheoveralluserexperienceinscenarioswithmultiplesimultaneoususers.Notableadvancementsincludedorthogonalfrequency-divisionmultipleaccess(OFDMA),whichsignificantlyimprovedlatencyforuserswithlightdataloads.Targetwaketime(TWT)wasspecificallydesignedtoscheduletrafficinatime-divisionmultipleaccess(TDMA)manner,butitalsofoundutilityinpowersavingbyenablingdevicestosleepbetweenscheduleddatadeliveries.Additionally,multi-usermultiple-inputmultiple-output(MU-MIMO)wasenhancedtosupportsimultaneousuplinkanddownlinkconnections,therebyservingmultipleusersconcurrently.Theintroductionofbasic

serviceset(BSS)coloringhelpedfacilitatespatialre-useindenseenvironmentslikeairportsorsportsstadiums.WhileWi-Fi6didextendsupportforhigherdataratesthroughtheexpansionofbandwidthto160MHzandtheintroductionof1024quadratureamplitudemodulation(QAM),theprimaryfocusremainedondeliveringimprovedservicetomultiplesimultaneoususers.

Inthispaper,wewillexplorethenewfunctionalitiesthatWi-Fi7bringstotheforefrontanddelveintohowSpirentispreparingtoprovidetestingsolutionstailoredforWi-Fi7.Wi-Fi7isbaseduponIEEE802.11be,extremelyhighthroughput(EHT),whilethetermultrahighreliability(UHR)hasbeenearmarkedbyIEEEasthedesignationfortheupcomingWi-Fi8,whichisalreadyindevelopment.

IntroductionofWi-Fi7

TheWi-FigenerationalnamingconventionisaWi-FiAllianceinnovationthathelpscustomersdistinguishwhichflavorofWi-Fitheyhave.Previously,Wi-FiflavorsweredenotedbythelastlettersoftheIEEEtaskgroupdevelopingthestandard.InthecaseofWi-Fi7thisistheIEEE802.11betaskgroup.ThedistinctionbetweenthesetwonamesisimportantbecausetheIEEEtaskgroupmaydevelopfeaturesinthestandardthatarenotadoptedbytheWi-FiAlliance.

The11betaskgroupisstillworkingoncompletingthestandardwithanindicationofthetimelineinFigure1.Nevertheless,siliconvendorshavealreadydevelopedchipsetswhichareseeingearlyadoptionintothemarket.

July

May

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D2.0–D5.0

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D0.1

EHTSG

Figure1Wi-Fi7developmenttimeline

IEEEnamed11be,ultra-highthroughput(UHT)andasUHTimplies,throughputisthegame.Higherthroughputisachievedbytwomechanisms.Firstly,thePHYrateisincreasedbyusing4096QAMandwideningthebandwidthto320MHztoprovide30Gbps.

LatencyisakeypriorityforWi-Fi7andthereareseveralmechanismstoimprovelatencyincludingamechanismtoprovidedeterministiclatency.

Secondly,theconceptofaMulti-LinkDevice(MLD)isintroduced.Multi-LinkOperation(MLO)hasseveraldifferentmodesbut

essentiallyitusesaframeworktocoordinatethemultipleradiosinadevicetoactasone.

Thecombinationofthesemechanismsleadstothroughputsthat,inpractice,topat11to12Gbps.Andjustincasewewantedmore

antennas,802.11besupports16antennas,althoughthisisunlikelytofinditswayintomanyactualimplementationsofWi-Fi7.

4096QAM

Wi-Fi7introducesmodulationcodingscheme(MCS)12and13,whichuses4096QAMtoreach12bitspersymbol.4KQAM,asitissometimescalled,leadstoaverydenseconstellationascanbeseeninFigure2.

ThedensityofthisconstellationplacesseveralchallengesontheWi-Firadio,bothonthetransmission(TX)sideaswellasthereceive(RX)side.

4KQAMtheoreticallyrequiresanerrorvectormagnitude(EVM)ratioof-38dBorbettertoensurethattheconstellationpointsareasclosetopinpricksizeaspossible.ThisimposeswhatsomeviewasalmostmilitarygradelinearityrequirementsontheTXandRX.

Channelnoiseeffectivelyblursthepinprickssothattheyoverlapwithoneanothermakingdemodulationimpossibleso4KQAMoperationislimitedtooperationwherethesignaltonoiseratio(SNR)isbetterthan42dB.

Achieving42dBSNRmeansbeingveryclosetotheAPtolimitpathloss,butvendorsareachieving

successfuloperationatdistancesofupto18feet.ThisisbecausetheyexploitthediversitygainsprovidedbybeamforminginamultipathenvironmenttoincreasetheSNR.

Figure2Wi-Figenerationalincreaseinconstellationsize

Figure3Diversitygainsusingmultipleantennas

Thediversitygainsachievedbyusing4antennaswhencomparedwith1antennaisnearly13dB,whichishighlysignificantand

inlinewithcommunicationstheory.Increasingto8or16antennasgivesonlyincrementalgains.

4KQAMneedsverygoodSNRtoworkandsopathlossbetweenchamberswillbecriticalforproperoperation.Severalchipsetvendorsclaimthatbeamformingisabsolutelynecessary,butitisnotcleariftheyaretalkingaboutRayleighfadingchannels,oradditivewhiteGaussiannoise(AWGN)channels.Someexperimentationwillbenecessary.

Newpreambledesign

Everynewamendmentto802.11keptbackwardcompatibilitybutintroducednewadditionstothepreamble.Thisarrangementintroducesoverhead,probablyisn’tsustainable,andmakestheautodetectionmoreandmoredifficult.802.11bedefinesanewuniversalsignalfield(U-SIG)inthepreamble.TheU-SIGistwosymbolsinlength1andcontainsbothversion-dependentandversion-independentinformationthatfacilitateslegacyaswellasfuturePHYs.

Theextremelyhighthroughput(EHT)fieldcontainsinformationforthereceivertodemodulatethephysicallayerprotocoldataunit(PPDU)andisfollowedbytheEHT-STFandEHT-LTF.TheSTFandLTFareusedtodeterminetimingsyncandperformchannelestimationforcorrectdemodulationofthetransmission.

Figure4EHTpreamble

320MHzbandwidth

Withtherecentopeningupofthe6GHzband,moreandmorecountriesareadoptingitasseeninFigure5.Forthelatestview,visit

/countries-enabling-wi-fi-in-6-ghz-wi-fi-6e

.

The6GHzbandprovidesseveralGHzofcontiguousspectrumand

allows320MHzchannels,whichweredifficulttoachievein5GHz.

Theintroductionof6GHzhasledtowhatsomebelievetobeamoreconsistentchannelnumberingsystemsothat,forexample,20MHzchannelshavedifferentnumberingthan40MHzchannelsandtherearetwosetsofthree320MHzchannels,chosentofitwiththeregulatoryrequirementsofsomecountries.

Withsuchwidechannels,itispossiblethatinterferersmaybepresentintheband,orindeedtheremaybesectionsofthechannelthataredisallowedbecauseofincumbents.

Theprobabilityofencounteringinterferersisproportionaltothewidthofthechannel,makingnoise-freeverywidechannelsverydifficulttofind.Wi-Fi7brings“preamblepuncturing”whereby,inawidechannel,thoseproblematicsectionsofthechannelarenotused(i.e.,punctured).Thisgreatlyimprovesthechancesofusingwidechannels.

1Symbollengthis4ustokeepbackwardcompatibility.

Figure5Worldwide6GHzadoption.

Puncturingresolutionis20MHzandpuncturingisindicatedintheDisabledSubchannelBitmap,whereeachbitissetto1forthose20MHzsubchannelsthatarepunctured.Forexample,theDisabledSubchannelBitmapforchannel95wouldbe0000100000110000.

Theabilitytopunctureinthe6GHzbandisamandatoryrequirement.Puncturinginthe5GHzbandisoptional.

Figure6Illustrationofpuncturing

MultiRU

Wi-Fi6OFDMAallowsmultipleuserstoaccessthechannelsimultaneouslybyallocatingresourceunits(RUs),orportionsofthespectrumtoeachuser.Thisisdonedynamicallyonapacket-by-packetbasisandhastheadvantageofreducingchannelcontention,whichreduceslatency.

However,forwidechannels,whenthereisalargediscrepancyintheamountofdataeachdeviceneeds,theremaybeRUsthatarenotallocated.Thiswastesbandwidth.

Wi-Fi7allowstheunusedspectrumtobereclaimedbyallowinguptotwoRUstobeallocatedtoadevice.ItisworthnotingthatthecombinationsofRUsizesarelimitedtokeepthingspractical–sonotallcombinationsofallRUsizesarepossible.

Figure7ExamplesofMultiRUoperation

512MPDUcompressedblock-ack

Wi-Fi7introducesafeatureknownas“512compressedblock-ack,”enablingthetransmittertoconsolidateasmanyas512MACprotocoldataunits(MPDUs)intoasingleframe.Likewise,itallowsthereceivertoacknowledgeupto512MPDUswithinasingleblockacknowledgment(BA)frame.ThisisanotableenhancementcomparedtoWi-Fi6,whereaggregationwaslimitedto256MPDUsperframe.Theintroductionof512compressedblock-acksignificantlyreducesprotocoloverheadandenhancesthetransmitter’sperformance,particularlywhentransmittingdataathighthroughputPHYratesusinga320MHzchannelwidthandMCS13modulationinWi-Fi7.

EnhancedQoS

Wi-Fi6latencyimprovements

Moreandmorepeopleareusinginternetapplicationssuchasteleconferencingandgamingthatarelatencysensitive.TheWi-Fiindustryhassoughttocontrollatencybyvariousmeansformanyyears.Datarateshaveincreased,whichhelpsabit,butwithgrowingpopularitymultiplesimultaneoususerstendtoworsenthisperformance.

Themainreasonforthisdegradedperformanceisthefactthatmanyusersareseekingaccesstothechannel,albeitwithsmallpackets,butatahighrate.Theresultisconfusiononthechannelwithsomanydeviceshavingtobackoff,perhapsevenintoexponentialbackoff.

Wi-Fi6introducedOFDMAasawayofmakingchannelusagemoreefficientbyassigningRUstoeachuser,groupingthedata,andservingmultipleusersforasinglechannelaccess.

OFDMAmayormaynothavemarginalgainsintermsofthroughputdependinguponthetypeoftraffic.However,theprimarypurposeofOFDMAistoreducelatencyforsmallpackets,anditachievesthisobjectiveverywell,ascanbeseeninFigure8.

InFigure9,weseethecumulativeprobabilitydistributivefunctions(CDFs)of12non-APSTAssendingisochronousUDPtrafficwithameandatarateof30Mbps,astandarddeviationof2Mbps,andaframerateof60FPStosimulatesimultaneousaudio/videotransmissions.

Notehow,inthelegacycase,thedistributionisspreadoverawiderange.ThetailsofthePDFreachasmuchas150ms,andinthetruncatedviewseenhere,noneoftheSTAsachieveeven90%certaintyofreaching30msone-waydelay(OWD).ThisisaccompaniedbylargeOWDstandarddeviations,whichwouldbeextremelyuncomfortablefortheuser.

ThisisindirectcontrasttothecasewhereWi-Fi6employsOFDMA.Here,thePDFismuchmoreorderly;the97thpercentileisgenerallybelowabout20ms.Thestandarddeviationofthespreadisminimized,butthereisstillasignificantnumberofsamplesinexcessof30ms.

Figure8OFDMAminimizeschannelcontentionformultipleusers.SourceWFA

Figure9Wi-Fi6latencyimprovementcomparedtolegacy

Wi-Fi7restrictedserviceperiodsforlatencyguarantees

WhileOFDMAsignificantlyimprovestheOWDsituationformultipleusers,itdoesnotguaranteeperformance.Therearemanyapplicationssuchasgaming,industrialcontrol,andIoTwheredelaymustbedeterministicandguaranteedtobelessthansomethreshold.

Wi-Fi7introducestheconceptofrestrictedserviceperiods(RSP),whichareperiodsoftimewhereonlycertaindevicesmayaccessthemediumiftheybelongtoanappropriatemembershipgroup.

Inthisscheme,thenon-APSTAswithspecialQoSneedssendtheirrequirementstotheAP,whichinturnadvertisestheRSPthatonlymembersofeachdesignatedRSPgroupareallowedtouse.Thisguaranteeschannelaccessforshortperiodsatregularintervalswherethelatencysensitivedatacanbeexchanged.

Considerthepracticalexampleofagamerwhorequiresveryregularrepeatedaccessforsmallpackets–mouseclicks.Therequirementisforadeterministiclatencyof99.9%tobelessthan10ms.Thiscanbesetupasthediagramindicateswith1msRSPsrepeatingevery10ms.Additionally,anEHTAPcanadvertisequietperiodswherenon-APSTAsmaynotaccessthemedium.

Figure10EnhancedQoSusingrestrictedserviceperiods

Figure11isanexemplaryillustrationofthePDFsandCDFsofpacket-by-packetOWDofanAPsendingto12non-APSTAs,oneofwhichisamemberofthegroupdiscussedabove.

HereweseeitsOWDisconfinedtoanarrowintervalofdelayabout10mswide.Itsprobabilityoffallingwithinthisregionisbetterthan99%,ascanbeseenintheCDF,makingtheOWDofthisdevicehighlydeterministic.Whiletheothernon-APSTAssometimesachievebetterthan10msOWD,theprobabilityofthisismuchlower;indeed,thedistribution,whichistruncatedinthisexample,extendsbeyond100ms.Thesedelayspreadsarecommoninlargepopulationsofdevicesbecausethedistributionoflegacy

OWDishighlynon-deterministic. Figure11ComparisonofOWDspreadsfordevices

withandwithoutdeterministicQoS

Restrictedtargetwaketime

Wi-Fi6introducedtargetwaketime(TWT)asawayofschedulingtransmissionsinakindofTDMA-likeapproach.TWTismostoftenusedasapower-savingmechanism,allowingtheSTAtosleepuntilthetargetedtime.TheWi-Fi7restrictedTWTextendscapabilitiestoprovidereservationmechanismsformorepredictablelatencyandgenerallyhigherreliabilityforlatency-sensitivetraffic.

TheEHTAPannouncesserviceperiods(SPs)thatanon-APSTAcansignuptobecomeamember.Thismeansthatitcanattemptchannelaccessintheserestrictedslotsasalimitedmemberwithfewerotherdeviceswithwhichtocontend.Themembernon-APSTAand/ortheAPmustceasetransmissionbeforetheendoftherestrictedperiod.

Figure12RestrictedTWTSPoperation

Triggeredpeer-to-peer(P2P)transmission

Therearemanyapplicationswherecommunicationisbetweentwopeers.Printingfromaphone,virtualrealityapplications,andMiracastareexamples.SincethecontentisgeneratedononeSTAandconsumedbytheotherSTA,thereisnorealvalueinrelayingitthroughtheAP.Indeed,relayingthroughtheAPintroducesdelaysanddoublestheairtimeused,whichimpactsotherusersneedlessly.Although,itcouldbearguedthattheAPhasavaluableroleinsofarasit“controls”thenetworkandtherelayingfunctionhelpscoordinationbetweendevices,minimizingcollisionsandthehiddenSTAproblem.

Wi-Fi7recognizesthevalueofmanagingthenetworkofmanyusersandintroducestriggeredP2PoperationwheretheAPissuesamultiuserrequesttosend(MU-RTS).

WhereasthelegacyRTSwasafirst-personrequesttoallusers,“IwouldliketohavethechannelforaTX,”theMU-RTSisathird-personrequest,“STA1andSTA2wouldliketohavethechannelforaTX.”

So,theAPreservesaTXOPforSTA1andSTA2tocommunicate,asshowninFigure13.

ThismechanismefficientlymanagestheotherdevicesbecausetheywillholdofffortheTXOPwhileSTA1sendsdirectlytoSTA2,thusminimizingcollisionsandavoidingthedataoccupyingthemediumtwice.

Figure13TriggeredP2Poperation

Multi-linkoperation

Wi-Fiiscurrentlyabletosustainmultipleradiolinksondifferentradios,eitherinthesamebandoracrossdifferentbands,however,thereisnocoordinationbetweentheradios,andthereareinefficiencies.

Wi-Fi7takesacoordinatedapproachtousingmultiplelinks,resultinginanumberofbenefits.Themulti-linkdevice(MLD)views

theindividualradiosasoneradiowithoneMACaddressandschedulescommunicationaccordingtotherequirementsatthetime.

Forexample,multi-linkoperation(MLO)couldbeusedtoachieveadditivethroughputbyaggregatingthelinksanddistributingtheloadoverthedifferentlinks.MLOcanalsobeemployedtoenhancereliabilitybysendingredundantdataoneachlink,increasingtheprobabilitythatapacketwillgetthroughcorrectly.

Latencyimprovementandloadbalancingcanbeachievedbyallocatinglinksaccordingtotheuserpriorityordegreeoftimesensitivityofthedata.

Multi-linkarchitecture

Multi-linkAP

logicalentity

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MAC(UMAC)

UnifiedUpper

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PHY

PHY

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MLDTA

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UnifiedUpper

Control(LLC)

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Multi-linkAPlogicalentity

Themulti-linkdevice(MLD)consistsofseveralso-calledaffiliatedradios.EachradiohasitsownPHYandlowerMAC,buttheyarecoordinatedbyaunifiedupperMAC(UMAC).TheUMACapproachwaschosentopreservethelong-established

802.11MACPHYconcepts.Fromtheoutside,theMLDdevicepresentsitselfasasingleMACaddress;thus,thehigherlayerprotocolsviewitasasingledevice.

LMAC

TA-2

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TA-6

PHY

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PHY

AsinthelegacyMAC,theUMAChandlesfragmentation,packetreassembly,duplicationdetection,dynamiclinkswitching,andACKs.Thesequencenumbersforthepacketsaregenerateduniquelyfromthesamesequencenumberspace,whichsimplifiestheabovetasks.Italsohandlespacketre-transmission,whichcanoccuronanylink,regardlessoftheoriginallinkthepacketwastransmittedon.

MLDRA

UnifiedUpper MAC(UM

LMAC

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UnifiedUpper MAC(UMAACC))

LogicalLink Control(LLC)

logicalentity

Associationandauthenticationoneachlinkmayoccurindependentlyorjointly.Intheformercase,capabilitiesforeachlinkareexchangedoneachrespectivelink.Inthelattercase,thecapabilitiesofeachcanbecommunicatedinacombinedfashionononelink.

MLDswithmultipleradiosallowlinkstooperatesimultaneously;however,thisisnotarequirementofanMLD.AnMLDcouldhaveonlyoneradio,butthemultiplelinksthatitaccesseswouldbeoneatatime.SomeradioscapableofmultiplestreamscanconfigureeachRXchainasa1x1oneachchannel/band/linkandlistentoincomingpacketsoneachchannel.Datatransmissioncanonlybedoneononelinkatatime.Thisprovidesmostofthebenefitsofamulti-radioMLD,especiallywhenreceivingdata.

Figure14MLDArchitecture

Reliabilityvslatency

Packetscanbeallocatedtolinksinvariouswaysdependingontherequirementsoftheapplication.

Wherereducedlatencyorincreasedthroughputisrequired,uniquedatapacketsareassignedtoeachlink.

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Figure15MLOreducedlatencyorincreasedthroughput

Insituationswherehighreliabilityisrequired,packetscanberepeatedoneachlink.TheUMACperformsthetaskofremovingduplicategoodpackets,notespacketsthatdidnotgetthroughonanylink(lostpackets),andcomposesanappropriateBlockAckatUMAClevel.

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Figure16MLOforincreasedreliability

Thesetwomodescanbeuseddynamicallyaschannelconditionschange,reducinglatencyingoodconditionsandextending

rangeinpoorconditionsduetoeffectivechanneldiversity.

NotetheelegancyoftheUMACusingsequencenumbersforallpacketsfromthesamespace.ThismeansthattheUMACdoesnotneedtobesignaledaboutwhichmodeisbeingused;indeedthesemodescanbeintermixedatwill.TheUMACwilldetermineduplicatesbasedontheirsequencenumberanddiscardthem.

TypesofMLDs

Multi-linkdevicescanbecreatedinvariousconfigurationsdependingupondevicerequirements.AllMLDsoperateonmultiplelinks.Linksarelogical,soanMLDmaynothaveindividualradiosforeachlink.IfanMLDdoeshavemultipleradios,theymayormaynotbeabletoTXandRXsimultaneously.Figure17isahierarchicalrepresentationofMLDtypesassummarizedinTable1.

Figure17Multi-linkdevicehierarchy

TypeofMLD NumberofRadios Characteristics

Multi-linksingleradio(MLSR)

EnhancedMulti-linksingleradio(EMLSR)

Simultaneoustransmitandreceivemulti-linkradio(STRMLMR)

Non-simultaneoustransmitandreceivemulti-linkmulti-radio(NSTRMLMR)Enhancedmulti-linkmulti-radio(EMLMR)

1

1

>=2

>=2

>=2

Therecouldbemultiplelinks,

butonlyonelinkcanbeactiveatatime

Abilitytolistentomultiplelinkssimultaneously,butTXononlyonelinkatatime.

SimultaneousTX/TX,

RX/RXandTX/RXovermultiplelinksSimultaneousTX/TXor

RX/RXovermultiplelinks

MLMRwithadditionaltodynamically

reconfigurespatialmultiplexingoneachlink

Multi-linkchannelaccess

Table1Multi-linkdevicetype

Multi-linkoperationallowstheindividuallinkstooperateasynchronouslyofoneanother.Thishasadvantagesbecausethe

probabilityoffindingaTXOPforanindividuallinkishigherthanfindingaTXOPforalllinkssimultaneously.

Tobeabletooperateeffectively,eachlocaltransmittershouldnotinterferewiththelocalreceivers.Formanydevices,thisrequirementcanbeachievedgiventhatthefrequenciesofthelinksaregenerallywidelyspread–2.4GHz,5GHz,6GHz.TheseMLDsarecalledsimultaneoustransmitreceive(STR)devices.

SimultaneousUplinkandDownlink

(STR)

Uplinkdata

BA

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Downlinkdata

BA

BA

Link1

Link2

Figure18SimultaneousasynchronousoperationSTR

However,theremaybedeviceswhereRForphysicalconstraintsresultinlocalTX/RXinterference–thesearetermednon-STR(NSTR)devices,andinthiscase,dataonthelinksmustbesynchronous.

UplinkorDownlink(NSTR)

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BA

BA

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Figure19NonsimultaneoussynchronousoperationNSTR

Multi-linkperformance

Asexpected,thedifferenttypesofMLDsofferdifferentqualityofperformance.OBSSisacommonreal-lifetypeofinterferenceandshowsthethroughputofalegacysingleradiolinkincomparisontoatwo-linkmulti-linksingleradio(MLSR)andatwo-linksimultaneousTX/RXmulti-linkmultiradio(STRMLMR).Clearly,bothMLDsofferimprovement;theSTRMLMRdeviceperformsatroughlydoublethesinglelink.Interestingly,theMLSRoffersimprovedperformance,too.Thisisbecauseusingmultiplelinksimprovesfrequencydiversity.

Figure20PerformancecomparisonofdifferentMLDs

Multi-linkdiscovery

Legacylinkdiscovery

InlegacyWi-Fi,anon-APSTAdiscoversanAPbyeitherpassivelylisteningforbeaconsorbyactivelysendingproberequestsoneachofthedifferentchannels.Passivescanningisaslowprocess;activescanningissomewhatfasterbecauseiftheSTAdoesn’tgetaresponseveryquickly,itmovestothenextchannel.

Thesemechanismsworkreasonablywellin5GHz,butin6GHztherearepotentiallyfifty-nine20MHzchannelstoscan,whichwouldbeverytime-consumingandnotacceptable.Activescanningrepresentsasignificantwasteofbandwidthbecausealthoughtherequestsa