48thInternationalSymposiumELMAR-2006,07-09June2006,Zadar,CroatiaZigBeewirelessstandardStanislavSafaric,KresimirMalaricFacultyofElectricalEngineeringandComputing,Unska3,HR-10000Zagreb,CroatiaE-mail:stanislav.safaricgfer.hr,kresimir.malaricgfer.hrAbstract-InthisarticleZigBeetechnologyisdescribed.Itisanewwirelessnetworkstandard.Theprincipleofworkandcharacteristicsareexplained.Possiblenetworktopologiesanddevicetypesareshown.Finally,theapplicationofZigBeedevicesineverydaylifewasproposed.Keywords-ZigBee,IEEE802.15.4,wireless1.INTRODUCTIONWirelesssensornetworkingisoneofthemostexcitingtechnologymarketstoday.Overthenextfivetotenyears,wirelesssensorswillhaveasignificantimpactonalmostallmajorindustriesaswellasourhomelives.ZigBeegotitsnamefromthewaybeeszigandzagwhiletrackingbetweenflowersandrelayinginformationtootherbees aboutwheretofindresources.ZigBeeisanewglobalstandardforwirelessconnectivity,focusingonstandardizingandenablinginteroperabilityofproducts.ZigBeeisacommunicationsstandardthatprovidesashort-rangecosteffectivenetworkingcapability.Ithasbeendevelopedwiththeemphasisonlow-costbatterypoweredapplications.ZigBeehasbeenintroducedbyIEEEwithIEEE802.15.4standardandtheZigBeeAlliancetoprovidethefirstgeneralstandardfortheseapplications.TheZigBeeallianceincludessuchcompaniesasInvensys,Honeywell,MitsubishiElectric,Motorola,andPhilips.ZigBeeisbuiltontherobustradio(PHY)andmediumattachmentcontrol(MAC)communicationlayersdefinedbytheIEEE802.15.4standard.AbovethisZigBeedefinesmesh,starandclustertreenetworktopologieswithdatasecurityfeaturesandinteroperableapplicationprofiles.Thereareamultitudeofstandards(Table1.)likeBluetoothandWiFithataddressmidtohighdataratesforvoice,PCLANs,video,etc.However,uptillnowtherehasn'tbeenawirelessnetworkstandardthatmeetstheuniqueneedsofsensorsandcontroldevices.Sensorsandcontrolsdon'tneedhighbandwidthbuttheydoneedlowlatencyandverylowenergyconsumptionforlongbatterylivesandforlargedevicearrays.ZigBeelooksratherlikeBluetoothbutissimpler,hasalowerdatarateandspendsmostofitstimesnoozing.ItisnowwidelyrecognizedthatstandardssuchasBluetoothandWLANarenotsuitedforlowpowerapplications,whichisduetothesestandards'highnodecostsaswellascomplexandpowerdemandingRF-ICsandprotocols.WithZigbee,thecaseisdifferent,itistheonlystandardthatspecificallyaddressestheneedsofwirelesscontrolandmonitoringapplications.Ithaslargenumberofnodes/sensorsnecessitateswirelesssolutions,verylowsystem/nodecosts,needtooperateforyearsoninexpensivebatteries;thisrequireslowpowerRF-ICsandprotocols,reliableandsecurelinksbetweennetworknodes,easydeploymentandnoneedforhighdatarates[1].Table1.WirelessstandardcomparisonsStandardZigBeeBluetoothWi-FiGPRS/GSM802.15.4. 802.15.1.802.11bApplicationMonitoring&CableWeb,WAN,Controlreplacementvideo,voice/datae-mailSystem4kb-32kb250kb+1Mb+16Mb+resourceBatterylife100-1000+1-70.1-51-7(days)Nodesper256/65k+730 1000networkBandwidth20-25072011000+64-128(kbps)Range(m)1-75+1-10+1-1001000+Keyreliable,cost,speed,reach,attributeslowpower,convenienceflexibilityqualitycostffective2.GENERALCHARACTERISTICSIEEE802.15.4-2003standarddefinestheprotocolandinterconnectionofdevicesviaradiocommunicationinapersonalareanetwork(PAN).Thestandardusescarriersensemultipleaccesswithacollisionavoidancemediumaccessmechanismandsupportsstaraswellaspeer-to-peertopologies.Themediaaccessiscontentionbased.Thephysicallevel(PHY)ofthe802.15.4standardspecifiesthreefrequencybands,thoughanimplementationneedonlyoperateononeofthethree.25948thInternationalSymposiumELMAR-2006,07-09June2006,Zadar,CroatiaFig.1.PHYLayersTable2.GeneralCharacteristicsThebands(showninTable2.)are:868MHz-forEuropeanapplications,902-928MHz-forNorthAmericanapplications,2.400GHz-forworldwideapplications.Thereisasinglechannelbetween868and868.6MHz,10channelsbetween902.0and928.0MHz,and16channelsbetween2.4and2.4835GHzasshowninFigure1.Severalchannelsindifferentfrequencybandsenablestheabilitytorelocatewithinspectrum.Thestandardalsoallowsdynamicchannelselection,ascanfunctionthatstepsthroughalistofsupportedchannelsinsearchofbeacon,receiverenergydetection,linkqualityindication,channelswitching.Lowerfrequencyprovidelongerrangeduetolowerpropagationlosses.Lowratecanbetranslatedintobettersensitivityandlargercoveragearea.Higherratemeanshigherthroughput,lowerlatencyorlowerdutycycle.The2450MHzPHYsupportsanover-the-airdatarateof250kb/s,andthe868/915MHzPHYsupportsover-the-airdataratesof20kb/sand40kb/s.ThePHYchosendependsonlocalregulationsanduserpreference.Inallbands,themodulationschemeisdirectsequencespreadspectrum.Inthe868and902-928MHzbands,thetransmitterismodulatedusingBPSK.Inthe2.450GHzband,thetransmitterismodulatedusingoffset-QPSK,whichismorebandwidthefficientthanBPSK.Forthe2.4GHzPHY,thestandardspecifieshowthedatacoding,spreadingandmodulationmustbeperformed.Startingfromtherawbasebandbitstream,bitsareexaminedbygroupsoffourbits.Eachfour-bitsequenceismappedtoonesymboloutof16possiblesymbols.Eachsymbolisinturnmappedtoa32-chipsequence.Thesesequencesarepseudo-randomandtheyarenearlyorthogonal.ThechipstreamitselfisOQPSK(OffsetQuadraturePhaseShiftKeying)modulatedwithhalf-sinepulse-shaping.ThismodulationformatisalsoknownasMSK(MinimumShiftKeying).OddandevenchipstreamsaregeneratedforstandardQPSK,butforOQPSKtheyareshiftedbyonechipperiod.TheshiftingavoidshavingIandQsimultaneouslycrossingthe0value,whichcouldcauselargeamplitudevariationsintheenvelope.ThefeaturesofthePHYareactivationanddeactivationoftheradiotransceiver,energydetection(ED),linkqualityindication(LQI),channelselection,clearchannelassessment(CCA)andtransmittingaswellasreceivingpacketsacrossthephysicalmedium.PHYFrequencySpreadinparametersDataparameters(MHz)bandChipModulationBitrateSymbolSymbols(MHz)rate(kb/s)rate(kchip/s)(ksymbols/s)868868-868.6300BPSK20 20Binary&915902-928600BPSK40
View Full Document
Unlocking...