《物联网专业英语教程》课件第9章

Unit9Network[156]

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IEEE802.15.4[167]

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ZigBee[173]参考译文IEEE802.15.4

IEEE802.15.4isastandardwhichspecifiesthephysicallayerandmediaaccesscontrolforlow-ratewirelesspersonalareanetworks(LR-WPANs).ItismaintainedbytheIEEE802.15workinggroup.ItisthebasisfortheZigBee,IEEE802.15.4ISA100.11a,WirelessHART,andMiWispecifications,eachofwhichfurtherextendsthestandardbydevelopingtheupperlayerswhicharenotdefinedby802.15.4.Alternatively,itcanbeusedwith6LoWPANandstandardInternetprotocolstobuildaWirelessEmbeddedInternet.(SeeFigure9.1)Figure9.1IEEE802.15.4protocolstack

1.Overview

IEEEstandard802.15.4intendstoofferthefundamentallowernetworklayersofatypeofWirelessPersonalAreaNetwork(WPAN)whichfocusesonlow-cost,low-speedubiquitouscommunicationbetweendevices(incontrastwithother,moreend-userorientedapproaches,suchasWiFi).Theemphasisisonverylowcostcommunicationofnearbydeviceswithlittletonounderlyinginfrastructure,intendingtoexploitthistolowerpowerconsumptionevenmore.

Thebasicframeworkconceivesa10-metercommunicationsrangewithatransferrateof250kbit/s.Tradeoffsarepossibletofavormoreradicallyembeddeddeviceswithevenlowerpowerrequirements,throughthedefinitionofnotone,butseveralphysicallayers.Lowertransferratesof20and40kbit/swereinitiallydefined,withthe100kbit/sratebeingaddedinthecurrentrevision.

Evenlowerratescanbeconsideredwiththeresultingeffectonpowerconsumption.Asalreadymentioned,themainidentifyingfeatureof802.15.4amongWPAN'sistheimportanceofachievingextremelylowmanufacturingandoperationcostsandtechnologicalsimplicity,withoutsacrificingflexibilityorgenerality.

Importantfeaturesincludereal-timesuitabilitybyreservationofguaranteedtimeslots,collisionavoidancethroughCSMA/CAandintegratedsupportforsecurecommunications.Devicesalsoincludepowermanagementfunctionssuchaslinkqualityandenergydetection.

802.15.4-conformantdevicesmayuseoneofthreepossiblefrequencybandsforoperation.

2.Protocolarchitecture

Devicesareconceivedtointeractwitheachotheroveraconceptuallysimplewirelessnetwork.ThedefinitionofthenetworklayersisbasedontheOSImodel;althoughonlythelowerlayersaredefinedinthestandard,interactionwithupperlayersisintended,possiblyusingaIEEE802.2logicallinkcontrolsublayeraccessingtheMACthroughaconvergencesublayer.Implementationsmayrelyonexternaldevicesorbepurelyembedded,self-functioningdevices.

2.1ThePhysicalLayer

ThePhysical

Layer(PHY)ultimatelyprovidesthedatatransmissionservice,aswellastheinterfacetothephysicallayermanagemententity,whichoffersaccesstoeverylayermanagementfunctionandmaintainsadatabaseofinformationonrelatedpersonalareanetworks.Thus,thePHYmanagesthephysicalRFtransceiverandperformschannelselectionandenergyandsignalmanagementfunctions.Itoperatesononeofthreepossibleunlicensedfrequencybands:

·868.0-868.6MHz:Europe,allowsonecommunicationchannel(2003,2006);

·902-928MHz:NorthAmerica,uptotenchannels(2003),extendedtothirty(2006);

·2400-2483.5MHz:worldwideuse,uptosixteenchannels(2003,2006).

Theoriginal2003versionofthestandardspecifiestwophysicallayersbasedonDirectSequenceSpreadSpectrum(DSSS)techniques:oneworkinginthe868/915MHzbandswithtransferratesof20and40kbit/s,andoneinthe2450MHzbandwitharateof250kbit/s.

The2006revisionimprovesthemaximumdataratesofthe868/915MHzbands,bringingthemuptosupport100and250kbit/saswell.Moreover,itgoesontodefinefourphysicallayersdependingonthemodulationmethodused.ThreeofthempreservetheDSSSapproach:inthe868/915MHzbands,usingeitherbinaryoroffsetquadraturephaseshiftkeying(thesecondofwhichisoptional);inthe2450MHzband,usingthelatter.Analternative,optional868/915MHzlayerisdefinedusingacombinationofbinarykeyingandamplitudeshiftkeying(thusbasedonParallel,notSequentialSpreadSpectrum,PSSS).Dynamicswitchingbetweensupported868/915MHzPHYsispossible.

Beyondthesethreebands,theIEEE802.15.4cstudygroupisconsideringthenewlyopened314-316MHz,430-434MHz,and779-787MHzbandsinChina,whiletheIEEE802.15TaskGroup4disdefininganamendmenttotheexistingstandard802.15.4-2006tosupportthenew950MHz-956MHzbandinJapan.FirststandardamendmentsbythesegroupswerereleasedinApril2009.

InAugust2007,IEEE802.15.4awasreleasedexpandingthefourPHYsavailableintheearlier2006versiontosix,includingonePHYusingDirectSequenceUltra-WideBand(UWB)andanotherusingChirpSpreadSpectrum(CSS).TheUWBPHYisallocatedfrequenciesinthreeranges:below1GHz,between3and5GHz,andbetween6and10GHz.TheCSSPHYisallocatedspectruminthe2450MHzband.

InApril2009,IEEE802.15.4candIEEE802.15.4dwerereleasedexpandingtheavailablePHYswithseveraladditionalPHYs:onefor780MHzbandusingO-QPSKorMPSK,anotherfor950MHzusingGFSKorBPSK.

2.2TheMAClayer

TheMediumAccessControl(MAC)enablesthetransmissionofMACframesthroughtheuseofthephysicalchannel.Besidesthedataservice,itoffersamanagementinterfaceanditselfmanagesaccesstothephysicalchannelandnetworkbeaconing.Italsocontrolsframevalidation,guaranteestimeslotsandhandlesnodeassociations.Finally,itoffershookpointsforsecureservices.

2.3Higherlayers

Otherhigher-levellayersandinteroperabilitysublayersarenotdefinedinthestandard.Thereexistspecifications,suchasZigBee,whichbuildonthisstandardtoproposeintegralsolutions.

3.Networkmodel

3.1Nodetypes

Thestandarddefinestwotypesofnetworknode.

ThefirstoneistheFull-FunctionDevice(FFD).Itcanserveasthecoordinatorofapersonalareanetworkjustasitmayfunctionasacommonnode.Itimplementsageneralmodelofcommunicationwhichallowsittotalktoanyotherdevice:itmayalsorelaymessages,inwhichcaseitisdubbedacoordinator.

OntheotherhandthereareReduced-FunctionDevices(RFD).Thesearemeanttobeextremelysimpledeviceswithverymodestresourceandcommunicationrequirements;duetothis,theycanonlycommunicatewithFFD'sandcanneveractascoordinators.

3.2Topologies

NetworkscanbebuiltaseitherPeer-to-Peerorstarnetworks(SeeFigure9.2).However,everynetworkneedsatleastoneFFDtoworkasthecoordinatorofthenetwork.Networksarethusformedbygroupsofdevicesseparatedbysuitabledistances.Eachdevicehasaunique64-bitidentifier,andifsomeconditionsaremetshort16-bitidentifierscanbeusedwithinarestrictedenvironment.Namely,withineachPANdomain,communicationswillprobablyuseshortidentifiers.

Figure9.2IEEE802.15.4starandPeer-to-Peer

Peer-to-Peer(orPoint-to-Point)networkscanformarbitrarypatternsofconnections,andtheirextensionisonlylimitedbythedistancebetweeneachpairofnodes.Theyaremeanttoserveasthebasisforadhocnetworkscapableofperformingself-managementandorganization.Sincethestandarddoesnotdefineanetworklayer,routingisnotdirectlysupported,butsuchanadditionallayercanaddsupportformultihopcommunications.Furthertopologicalrestrictionsmaybeadded;thestandardmentionstheclustertree(SeeFigure9.3)asastructurewhichexploitsthefactthatanRFDmayonlybeassociatedwithoneFFDatatimetoformanetworkwhereRFD'sareexclusivelyleavesofatree,andmostofthenodesareFFD's.Thestructurecanbeextendedasagenericmeshnetworkwhosenodesareclustertreenetworkswithalocalcoordinatorforeachcluster,inadditiontotheglobalcoordinator.

Amorestructuredstarpatternisalsosupported,wherethecoordinatorofthenetworkwillnecessarilybethecentralnode.SuchanetworkcanoriginatewhenanFFDdecidestocreateitsownPANanddeclareitselfitscoordinator,afterchoosingauniquePANidentifier.Afterthat,otherdevicescanjointhenetwork,whichisfullyindependentfromallotherstarnetworks.

Figure9.3IEEE802.15.4clustertree

4.Datatransportarchitecture

Framesarethebasicunitofdatatransport,ofwhichtherearefourfundamentaltypes(data,acknowledgment,beaconandMACcommandframes),whichprovideareasonabletradeoffbetweensimplicityandrobustness.Additionally,asuperframestructure,definedbythecoordinator,maybeused,inwhichcasetwobeaconsactasitslimitsandprovidesynchronizationtootherdevicesaswellasconfigurationinformation.Asuperframeconsistsofsixteenequal-lengthslots,whichcanbefurtherdividedintoanactivepartandaninactivepart,duringwhichthecoordinatormayenterpowersavingmode,notneedingtocontrolitsnetwork.

Withinsuperframescontentionoccursbetweentheirlimits,andisresolvedbyCSMA/CA.Everytransmissionmustendbeforethearrivalofthesecondbeacon.Asmentionedbefore,applicationswithwell-definedbandwidthneedscanuseuptosevendomainsofoneormorecontentionlessguaranteedtimeslots,trailingattheendofthesuperframe.Thefirstpartofthesuperframemustbesufficienttogiveservicetothenetworkstructureanditsdevices.Superframesaretypicallyutilizedwithinthecontextoflow-latencydevices,whoseassociationsmustbekeptevenifinactiveforlongperiodsoftime.

Datatransferstothecoordinatorrequireabeaconsynchronizationphase,ifapplicable,followedbyCSMA/CAtransmission(bymeansofslotsifsuperframesareinuse);acknowledgmentisoptional.Datatransfersfromthecoordinatorusuallyfollowdevicerequests:ifbeaconsareinuse,theseareusedtosignalrequests;thecoordinatoracknowledgestherequestandthensendsthedatainpacketswhichareacknowledgedbythedevice.Thesameisdonewhensuperframesarenotinuse,onlyinthiscasetherearenobeaconstokeeptrackofpendingmessages.

Point-to-PointnetworksmayeitheruseunslottedCSMA/CAorsynchronizationmechanisms;inthiscase,communicationbetweenanytwodevicesispossible,whereasin"structured"modesoneofthedevicesmustbethenetworkcoordinator.

Ingeneral,allimplementedproceduresfollowatypicalrequest-confirm/indication-responseclassification.

5.Reliabilityandsecurity

ThephysicalmediumisaccessedthroughaCSMA/CAprotocol.Networkswhicharenotusingbeaconingmechanismsutilizeanunslottedvariationwhichisbasedonthelisteningofthemedium,leveragedbyarandomexponentialbackoffalgorithm;acknowledgmentsdonotadheretothisdiscipline.Commondatatransmissionutilizesunallocatedslotswhenbeaconingisinuse;again,confirmationsdonotfollowthesameprocess.

Confirmationmessagesmaybeoptionalundercertaincircumstances.Whateverthecase,ifadeviceisunabletoprocessaframeatagiventime,itsimplydoesnotconfirmitsreception:timeout-basedretransmissioncanbeperformedanumberoftimes,followingafterthatadecisionofwhethertoabortorkeeptrying.

Becausethepredictedenvironmentofthesedevicesdemandsmaximizationofbatterylife,theprotocolstendtofavorthemethodswhichleadtoit,implementingperiodicchecksforpendingmessages,thefrequencyofwhichdependsonapplicationneeds.

Regardingsecurecommunications,theMACsublayeroffersfacilitieswhichcanbeharnessedbyupperlayerstoachievethedesiredlevelofsecurity.Higher-layerprocessesmayspecifykeystoperformsymmetriccryptographytoprotectthepayloadandrestrictittoagroupofdevicesorjustaPoint-to-Pointlink;thesegroupsofdevicescanbespecifiedinaccesscontrollists.Furthermore,MACcomputesfreshnesschecksbetweensuccessivereceptionstoensurethatpresumablyoldframes,ordatawhichisnolongerconsideredvalid,doesnottranscendtohigherlayers.

Inadditiontothissecuremode,thereisanother,insecureMACmode,whichallowsaccesscontrollistsmerelyasameanstodecideontheacceptanceofframesaccordingtotheir(presumed)source.

ZigBeeisaspecificationforasuiteofhighlevelcommunicationprotocolsusingsmall,low-powerdigitalradiosbasedonanIEEE802standardforpersonalareanetworks.Applicationsincludewirelesslightswitches,electricalmeterswithin-home-displays,ZigBeeandotherconsumerandindustrialequipmentthatrequiresshort-rangewirelesstransferofdataatrelativelylowrates.ThetechnologydefinedbytheZigBeespecificationisintendedtobesimplerandlessexpensivethanotherWPANs,suchasBluetooth.ZigBeeistargetedatRadio-Frequency(RF)applicationsthatrequirealowdatarate,longbatterylife,andsecurenetworking.ZigBeehasadefinedrateof250kbpsbestsuitedforperiodicorintermittentdataorasinglesignaltransmissionfromasensororinputdevice.(SeeFigure9.4)

Thenamereferstothewaggledanceofhoneybeesaftertheirreturntothebeehive.

The€

1coin,shownforsizereference,

isabout23mm(0.9inch)indiameter.Firgure9.4ZigBeemodule.

1.Technicaloverview

ZigBeeisalow-cost,low-power,wirelessmeshnetworkstandard.Thelowcostallowsthetechnologytobewidelydeployedinwirelesscontrolandmonitoringapplications.Lowpower-usageallowslongerlifewithsmallerbatteries.Meshnetworkingprovideshighreliabilityandmoreextensiverange.ThetechnologyisintendedtobesimplerandlessexpensivethanotherWPANssuchasBluetooth.ZigBeechipvendorstypicallysellintegratedradiosandmicrocontrollerswithbetween60KBand256KBflashmemory.

ZigBeeoperatesintheIndustrial,ScientificandMedical(ISM)radiobands;868MHzinEurope,915MHzintheUSAandAustralia,and2.4GHzinmostjurisdictionsworldwide.Datatransmissionratesvaryfrom20to250kilobits/second.

TheZigBeenetworklayernativelysupportsbothstarandtreetypicalnetworks,andgenericmeshnetworks.Everynetworkmusthaveonecoordinatordevice,taskedwithitscreation,thecontrolofitsparametersandbasicmaintenance.Withinstarnetworks,thecoordinatormustbethecentralnode.BothtreesandmeshesallowstheuseofZigBeerouterstoextendcommunicationatthenetworklevel.

ZigBeebuildsuponthephysicallayerandmediumaccesscontroldefinedinIEEEstandard802.15.4(2003version)forlow-rateWPAN's.Thespecificationgoesontocompletethestandardbyaddingfourmaincomponents:networklayer,applicationlayer,ZigBeeDeviceObjects(ZDO's)andmanufacturer-definedapplicationobjectswhichallowforcustomizationandfavortotalintegration.(SeeFigure9.5)

Besidesaddingtwohigh-levelnetworklayerstotheunderlyingstructure,themostsignificantimprovementistheintroductionofZDO's.Theseareresponsibleforanumberoftasks,whichincludekeepingofdeviceroles,managementofrequeststojoinanetwork,devicediscoveryandsecurity.

Figure9.5ZigBeeprotocolstack

ZigBeeisnotintendedtosupportpowerlinenetworkingbuttointerfacewithitatleastforsmartmeteringandsmartappliancepurposes.

BecauseZigBeenodescangofromsleeptoactivemodein30msecorless,thelatencycanbelowanddevicescanberesponsive,particularlycomparedtoBluetoothwake-updelays,whicharetypicallyaroundthreeseconds.BecauseZigBeenodescansleepmostofthetime,averagepowerconsumptioncanbelow,resultinginlongbatterylife.

2.Uses

ZigBeeprotocolsareintendedforembeddedapplicationsrequiringlowdataratesandlowpowerconsumption.Theresultingnetworkwilluseverysmallamountsofpower—individualdevicesmusthaveabatterylifeofatleasttwoyearstopassZigBeecertification.

Typicalapplicationareasinclude:

·HomeEntertainmentandControl—Homeautomation,smartlighting,advancedtemperaturecontrol,safetyandsecurity,moviesandmusic;

·WirelessSensorNetworks'—StartingwithindividualsensorslikeTelosb/TmoteandIrisfromMemsic;

·Industrialcontrol;

·Embeddedsensing;

·Medicaldatacollection;

·Smokeandintruderwarning;

·Buildingautomation.

3.Devicetypes

TherearethreedifferenttypesofZigBeedevices:

·ZigBeeCoordinator(ZC):Themostcapabledevice,thecoordinatorformstherootofthenetworktreeandmightbridgetoothernetworks.ThereisexactlyoneZigBeeCoordinatorineachnetworksinceitisthedevicethatstartedthenetworkoriginally.Itisabletostoreinformationaboutthenetwork,includingactingastheTrustCenter&repositoryforsecuritykeys.

·ZigBeeRouter(ZR):Aswellasrunninganapplicationfunction,aroutercanactasanintermediaterouter,passingondatafromotherdevices.

·ZigBeeEndDevice(ZED):Containsjustenoughfunctionalitytotalktotheparentnode(eitherthecoordinatororarouter);itcannotrelaydatafromotherdevices.Thisrelationshipallowsthenodetobeasleepasignificantamountofthetimetherebygivinglongbatterylife.AZEDrequirestheleastamountofmemory,andthereforecanbelessexpensivetomanufacturethanaZRorZC.

4.Protocols

Theprotocolsbuildonrecentalgorithmicresearch(Ad-hocOn-demandDistanceVector,neuRFon)toautomaticallyconstructalow-speedad-hocnetworkofnodes.Inmostlargenetworkinstances,thenetworkwillbeaclusterofclusters.Itcanalsoformameshorasinglecluster.ThecurrentZigBeeprotocolssupportbeaconandnon-beaconenablednetworks.

Innon-beacon-enablednetworks,anunslottedCSMA/CAchannelaccessmechanismisused.Inthistypeofnetwork,ZigBeeRouterstypicallyhavetheirreceiverscontinuouslyactive,requiringamorerobustpowersupply.However,thisallowsforheterogeneousnetworksinwhichsomedevicesreceivecontinuously,whileothersonlytransmitwhenanexternalstimulusisdetected.Thetypicalexampleofaheterogeneousnetworkisawirelesslightswitch:TheZigBeenodeatthelampmayreceiveconstantly,sinceitisconnectedtothemainssupply,whileabattery-poweredlightswitchwouldremainasleepuntiltheswitchisthrown.Theswitchthenwakesup,sendsacommandtothelamp,receivesanacknowledgment,andreturnstosleep.InsuchanetworkthelampnodewillbeatleastaZigBeeRouter,ifnottheZigBeeCoordinator;theswitchnodeistypicallyaZigBeeEndDevice.

Inbeacon-enablednetworks,thespecialnetworknodescalledZigBeeRouterstransmitperiodicbeaconstoconfirmtheirpresencetoothernetworknodes.Nodesmaysleepbetweenbeacons,thusloweringtheirdutycycleandextendingtheirbatterylife.Beaconintervalsdependondatarate;theymayrangefrom15.36millisecondsto251.65824secondsat250kbit/s,from24millisecondsto393.216secondsat40kbit/sandfrom48millisecondsto786.432secondsat20kbit/s.However,lowdutycycleoperationwithlongbeaconintervalsrequiresprecisetiming,whichcanconflictwiththeneedforlowproductcost.

Ingeneral,theZigBeeprotocolsminimizethetimetheradioison,soastoreducepoweruse.Inbeaconingnetworks,nodesonlyneedtobeactivewhileabeaconisbeingtransmitted.Innon-beacon-enablednetworks,powerconsumptionisdecidedlyasymmetrical:somedevicesarealwaysactive,whileothersspendmostoftheirtimesleeping.

ExceptfortheSmartEnergyProfile2.0,ZigBeedevicesarerequiredtoconformtotheIEEE802.15.4-2003Low-RateWirelessPersonalAreaNetwork(LR-WPAN)standard.Thestandardspecifiesthelowerprotocollayers—thePhysicalLayer(PHY),andtheMediaAccessControlportionoftheDataLinkLayer(DLL).Thebasicchannelaccessmodeis"CarrierSense,MultipleAccess/CollisionAvoidance"(CSMA/CA).Thatis,thenodestalkinthesamewaythatpeopleconverse;theybrieflychecktoseethatnooneistalkingbeforetheystart.TherearethreenotableexceptionstotheuseofCSMA.Beaconsaresentonafixedtimingschedule,anddonotuseCSMA.MessageacknowledgmentsalsodonotuseCSMA.Finally,devicesinBeaconOrientednetworksthathavelowlatencyreal-timerequirementsmayalsouseGuaranteedTimeSlots(GTS),whichbydefinitiondonotuseCSMA.

IEEE802.15.4是一个标准，它为低速率无线个人局域网(LR-WPANs)中物理层和介质访问控制提供规范，它由IEEE802.15工作组维护。它是ZigBee、ISA100.11a、WirelessHART以及MiWi规范的基础，这些规范都进一步扩展了该标准，方法是开发802.15.4没有定义的上层。另外一个选择是将IEEE802.15.4和6LoWPAN以及标准的因特网协议一起使用，建立一个无线嵌入式因特网。IEEE802.15.4

1.概论

IEEE802.15.4标准打算为无线个人局域网(WPAN)提供基础较低的网络层。WPAN着重在低成本、低速设备之间广泛通讯(与之相对的是其他更面向终端用户的方法，如WiFi)，重点是近距离的、有很少或无底层基础设施的设备之间的低成本通讯，且打算用它来降低功耗。

基本框架设想在10米的通信范围内，传输率为250kbit/s，也可以折衷传输率来支持更多功耗更低的嵌入设备，方法是定义多个而不是一个物理层。初期定义的传输率更低，在20kbit/s到40kbit/s之间，最近的修订版中的传输率已经增加了100kbit/s。使用低传输率主要是为了降低功耗。如上所述，WPAN中802.15.4的主要标志性特点在于制造和运行成本低，而且技术简单，不会牺牲灵活性和通用性。

实时适应性也是IEEE802.15.4的主要特色，方法是保留确定的时隙、通过CSMS/CA避免冲突并完全支持安全通信。802.15.4设备也包括电源管理功能，如链接质量和电能检查。

802.15.4兼容设备使用三种频段中的一种来运行。

2.协议体系

802.15.4设备可以通过概念简单的无线网络实现相互结合。网络层的定义基于OSI模型；虽然在该标准中只定义了低层，但如果打算与高层交互的话，则可使用IEEE802.2逻辑链路控制子层并通过汇聚子层来访问MAC。此访问可依赖外部设备或者纯嵌入的、自运行设备来实现。

2.1物理层

物理层(PHY)总的来说可提供数据传输服务，也可以作为物理层管理实体的接口，管理每层并维护相关个人局域网的信息库。因此，PHY管理物理RF收发器并选择通道、管理能源和信号。它运行在下面三个可能未经许可的波段之一：

868.0MHz～868.6MHz：欧洲，允许一个信道(2003,2006)；

902MHz～928MHz：北美，高达10个通道(2003)，已扩展到30个(2006)；

2400MHz～2483.5MHz：全球使用，高达60通道(2003,2006)。

该标准的2003年版本原来指定了基于直接序列扩频(DSSS)技术的两个物理层：一个工作在传输率为20kbit/s～40kbit/s的868/915MHz波段，另一个工作在传输率为250kbit/s的2450MHz波段。

2006年版本增大了868/915MHz波段的数据传输率，上调到支持100kbit/s和250kbit/s的传输率。更重要的是，它进一步定义了基于所使用的调制模式的四个物理层。其中三个层继续使用DSSS方法：在868/915MHz波段，使用二相或偏移四相移相键控(其中第二个是一个备选项)；在2450MHz波段，使用偏移四项移相键控。另外的选择是，用二相键控和幅移键控组合定义868/915MHz层(因此这就基于平行，而不是序列扩展频谱，PSSS)。在支持的868/915MHzPHY之间动态切换是可能的。

除了这三个波段外，IEEE802.15.4c研究组正在考虑使用最新在中国开放的314MHz～316MHz、430MHz～434MHz以及779MHz～787MHz波段，而IEEE802.15TaskGroup4d正在改进现有的802.15.4-2006标准以便支持日本新的950MHz～956MHz