48thInternationalSymposiumELMAR-2006,07-09June2006,Zadar,Croatia
ZigBeewirelessstandard
StanislavSafaric,KresimirMalaric
FacultyofElectricalEngineeringandComputing,Unska3,HR-10000Zagreb,Croatia
E-mail:stanislav.safaricgfer.hr,kresimir.malaricgfer.hr
Abstract-InthisarticleZigBeetechnologyisdescribed.Itisanewwirelessnetworkstandard.Theprincipleof
workandcharacteristicsareexplained.Possiblenetworktopologiesanddevicetypesareshown.Finally,the
applicationofZigBeedevicesineverydaylifewasproposed.
Keywords-ZigBee,IEEE802.15.4,wireless
1.INTRODUCTION
Wirelesssensornetworkingisoneofthemost
excitingtechnologymarketstoday.Overthenext
fivetotenyears,wirelesssensorswillhavea
significantimpactonalmostallmajorindustriesas
wellasourhomelives.
ZigBeegotitsnamefromthewaybeeszigand
zagwhiletrackingbetweenflowersandrelaying
informationtootherbeesaboutwheretofind
resources.
ZigBeeisanewglobalstandardforwireless
connectivity,focusingonstandardizingand
enablinginteroperabilityofproducts.ZigBeeisa
communicationsstandardthatprovidesashort-
rangecosteffectivenetworkingcapability.Ithas
beendevelopedwiththeemphasisonlow-cost
batterypoweredapplications.
ZigBeehasbeenintroducedbyIEEEwithIEEE
802.15.4standardandtheZigBeeAllianceto
providethefirstgeneralstandardforthese
applications.TheZigBeeallianceincludessuch
companiesasInvensys,Honeywell,Mitsubishi
Electric,Motorola,andPhilips.
ZigBeeisbuiltontherobustradio(PHY)and
mediumattachmentcontrol(MAC)communication
layersdefinedbytheIEEE802.15.4standard.
AbovethisZigBeedefinesmesh,starandcluster
treenetworktopologieswithdatasecurityfeatures
andinteroperableapplicationprofiles.
Thereareamultitudeofstandards(Table1.)
likeBluetoothandWiFithataddressmidtohigh
dataratesforvoice,PCLANs,video,etc.
However,uptillnowtherehasn''tbeenawireless
networkstandardthatmeetstheuniqueneedsof
sensorsandcontroldevices.
Sensorsandcontrolsdon''tneedhighbandwidth
buttheydoneedlowlatencyandverylowenergy
consumptionforlongbatterylivesandforlarge
devicearrays.
ZigBeelooksratherlikeBluetoothbutis
simpler,hasalowerdatarateandspendsmostofits
timesnoozing.Itisnowwidelyrecognizedthat
standardssuchasBluetoothandWLANarenot
suitedforlowpowerapplications,whichisdueto
thesestandards''highnodecostsaswellascomplex
andpowerdemandingRF-ICsandprotocols.
WithZigbee,thecaseisdifferent,itistheonly
standardthatspecificallyaddressestheneedsof
wirelesscontrolandmonitoringapplications.
Ithaslargenumberofnodes/sensorsnecessitates
wirelesssolutions,verylowsystem/nodecosts,
needtooperateforyearsoninexpensivebatteries;
thisrequireslowpowerRF-ICsandprotocols,
reliableandsecurelinksbetweennetworknodes,
easydeploymentandnoneedforhighdatarates[1].
Table1.Wirelessstandardcomparisons
StandardZigBeeBluetoothWi-FiGPRS/GSM
802.15.4.802.15.1.802.11b
ApplicationMonitoring&CableWeb,WAN,
Controlreplacementvideo,voice/data
e-mail
System4kb-32kb250kb+1Mb+16Mb+
resource
Batterylife100-1000+1-70.1-51-7(days)
Nodesper256/65k+7301000
network
Bandwidth20-25072011000+64-128(kbps)
Range(m)1-75+1-10+1-1001000+
Keyreliable,cost,speed,reach,
attributeslowpower,convenienceflexibilityquality
costffective
2.GENERALCHARACTERISTICS
IEEE802.15.4-2003standarddefinesthe
protocolandinterconnectionofdevicesviaradio
communicationinapersonalareanetwork(PAN).
Thestandardusescarriersensemultipleaccess
withacollisionavoidancemediumaccess
mechanismandsupportsstaraswellaspeer-to-peer
topologies.Themediaaccessiscontentionbased.
Thephysicallevel(PHY)ofthe802.15.4
standardspecifiesthreefrequencybands,thoughan
implementationneedonlyoperateononeofthe
three.
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48thInternationalSymposiumELMAR-2006,07-09June2006,Zadar,Croatia
Fig.1.PHYLayers
Table2.GeneralCharacteristics
Thebands(showninTable2.)are:868MHz-
forEuropeanapplications,902-928MHz-for
NorthAmericanapplications,2.400GHz-for
worldwideapplications.Thereisasinglechannel
between868and868.6MHz,10channelsbetween
902.0and928.0MHz,and16channelsbetween2.4
and2.4835GHzasshowninFigure1.Several
channelsindifferentfrequencybandsenablesthe
abilitytorelocatewithinspectrum.Thestandard
alsoallowsdynamicchannelselection,ascan
functionthatstepsthroughalistofsupported
channelsinsearchofbeacon,receiverenergy
detection,linkqualityindication,channel
switching.Lowerfrequencyprovidelongerrange
duetolowerpropagationlosses.Lowratecanbe
translatedintobettersensitivityandlargercoverage
area.Higherratemeanshigherthroughput,lower
latencyorlowerdutycycle.
The2450MHzPHYsupportsanover-the-air
datarateof250kb/s,andthe868/915MHzPHY
supportsover-the-airdataratesof20kb/sand40
kb/s.ThePHYchosendependsonlocalregulations
anduserpreference.
Inallbands,themodulationschemeisdirect
sequencespreadspectrum.Inthe868and902-928
MHzbands,thetransmitterismodulatedusing
BPSK.Inthe2.450GHzband,thetransmitteris
modulatedusingoffset-QPSK,whichismore
bandwidthefficientthanBPSK.
Forthe2.4GHzPHY,thestandardspecifies
howthedatacoding,spreadingandmodulation
mustbeperformed.Startingfromtherawbaseband
bitstream,bitsareexaminedbygroupsoffourbits.
Eachfour-bitsequenceismappedtoonesymbol
outof16possiblesymbols.Eachsymbolisinturn
mappedtoa32-chipsequence.Thesesequencesare
pseudo-randomandtheyarenearlyorthogonal.
ThechipstreamitselfisOQPSK(Offset
QuadraturePhaseShiftKeying)modulatedwith
half-sinepulse-shaping.Thismodulationformatis
alsoknownasMSK(MinimumShiftKeying).Odd
andevenchipstreamsaregeneratedforstandard
QPSK,butforOQPSKtheyareshiftedbyonechip
period.TheshiftingavoidshavingIandQ
simultaneouslycrossingthe0value,whichcould
causelargeamplitudevariationsintheenvelope.
ThefeaturesofthePHYareactivationand
deactivationoftheradiotransceiver,energy
detection(ED),linkqualityindication(LQI),
channelselection,clearchannelassessment(CCA)
andtransmittingaswellasreceivingpacketsacross
thephysicalmedium.
PHYFrequencySpreadinparametersDataparameters
(MHz)bandChipModulationBitrateSymbolSymbols
(MHz)rate(kb/s)rate
(kchip/s)(ksymbols/s)
868868-868.6300BPSK2020Binary
&915902-928600BPSK4040Binary
24002400-24832000O-QPSK25062.516-ary
I_I__I__I__I__th
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48thInternationalSymposiumELMAR-2006,07-09June2006,Zadar,Croatia
Table3.Zigbee802.15.4specifications
Receiversensitivities(Table3.)are-85dBmfor
2.4GHzand-92dBmfor868/915MHz.The
advantageof6-8dBcomesfromtheadvantageof
lowerrate.Theachievablerangeisafunctionof
receiversensitivityandtransmitpower.The
maximumtransmitpowershallconformwithlocal
regulations.Acompliantdeviceshallhaveits
nominaltransmitpowerlevelindicatedbythePHY
parameter[2,3].
3.DEVICETYPESANDNETWORK
TOPOLOGIES
TheZigBeenetworknodeisdesignedfor,
batterypoweredorhighenergysavings,searches
foravailablenetworks,transfersdatafromits
applicationasnecessary,determineswhetherdatais
pending,requestsdatafromthenetwork
coordinator,cansleepforextendedperiods.
Therearetwophysicaldevicetypesforthe
lowestsystemcostdefinedbytheIEEE.Full
functiondevice(FFD)canfunctioninany
topology,iscapableofbeingthenetwork
coordinatorandcantalktoanyotherdevice.
Reducedfunctiondevice(RFD)islimitedtostar
topology,cannotbecomeanetworkcoordinator,
talksonlytoanetworkcoordinatorhasverysimple
implementation.
AnIEEE802.15.4/ZigBeenetworkrequiresat
leastonefullfunctiondeviceasanetwork
coordinator,butendpointdevicesmaybereduced
functionalitydevicestoreducesystemcost.
TheFFDcanoperateinthreemodes(Fig.2.)
servingasapersonalareanetwork(PAN)
coordinator,acoordinator,oradevice.AnRFDis
intendedforapplicationsthatareextremelysimple,
suchasalightswitchorapassiveinfraredsensor;
theydonothavetheneedtosendlargeamountsof
dataandmayonlyassociatewithasingleFFData
time.Consequently,theRFDcanbeimplemented
usingminimalresourcesandmemorycapacity.
TheIEEE802.15.4MACisflexibleenoughto
handleeachofthesetypes.
Periodicdatacanbehandledusingthe
beaconingsystemwherebythesensorwillwakeup
forthebeacon,checkforanymessagesandthengo
backtosleep.
Intermittentdatacanbehandledeitherina
beaconlesssystemorinadisconnectedfashion.Ina
disconnectedoperationthedevicewillonlyattach
tothenetworkwhenitneedstocommunicate
savingsignificantenergy.
Lowlatencyapplicationsmaychoosetothe
guaranteedtimeslot(GTS)option.GTSisa
methodofQoSinthatitallowseachdevicea
specificdurationoftimeeachSuperframetodo
whateveritwishestodo.
Meshnetworkingmakesupforthelimited
powerofeachindividualnodebyleveragingthe
abilitytorelaydatathroughnearbycooperating
nodes.Thishappenstransparentlyandprovides
redundancyandreliability,assumingthedensityof
nodesishighenough.It''sacaseofthevalueofthe
networkgrowingatagreaterratethantherateat
whichyouaddnodestoit.Theoverheadof
occasionalnetworkreconfigurationtakesonlya
fewtensofmilliseconds.
TheZigBeenetworkcoordinator(Fig.3.)sets
upanetwork,transmitsnetworkbeacons,manages
networknodes,storesnetworknodeinformation,
routesmessagesbetweenpairednodes,typically
operatesinthereceivestate.AnFFDusedasa
coordinatorneedssufficientmemorytoholdthe
networkconfiguration,data,andprocessingpower
toself-configurethenetworkinadditiontoits
applicationtask.Arouterstoresandforwards
messagestoandfromdevicesthatcan''tdirectly
swapmessages.Acoordinatorwouldusealotmore
powerthanasimplenodeattheedgeofthe
networkandmayrequirelinepowerorbepowered
fromadevicewithasubstantialpowersupply.
Sta,r\/
ClusterTree\CPANcoor:dinatorClusterTeFUlIFunctionDevice
ReducedFunctionDevice
Fig2.TopologyModels
261
868MHz902-928MHz2.450GHz
Datarate20kbps40kbps250kbps
#channels11016
TXpower-3dBm-3dBm-3dBm
RX-92dBm-92dBm-85dBm
sensitivity
Linkbudget89dB89dB82dB
Adjacent
channel0dB0dB0dB
rejection
Alternate
channel30dB30dB30dB
rejection
48thInternationalSymposiumELMAR-2006,07-09June2006,Zadar,Croatia
ZigBeeusesdirectsequencespreadspectr
(DSSS)modulationinmixedmesh,star,andpe
to-peertopologies(includingcluster-free)todeli
areliabledataservicewithoptio
acknowledgments.
Therangepernodeisanominal10m,
popularimplementationshaveasingle-hoprange
upto100mpernodelineofsight(andfarthei
relayingthroughothernodes).ZigBeeemploysi
bitIEEEaddressesandshorter16-bitonesforlo
addressing,whichallowsthousandsofnodes
network.
Mesh
0"
um
3er-
iver
nal
but
Zof
rif
ZigBeedevicescanbeusedforbuilding
automationandindustrialcontrolandmonitoring,
containersecurity/tracking,commercialcontrols,
marinewirelessandmanyother.
4.CONCLUSION
64-ZigBeemightbeabestoptionifthefollowingis
calrequired:smallsize,costsensitivity,lowlatency,
perlowpower,andinteroperability.Butthebiggest
reasontochooseZigBeeisbyfarthe
implementationofthecutting-edgetechnology.It
zigzagsitswayaroundtheotherwirelessoptions.
Althoughitisinferiortoalmostalloftheothersin
datarate,itsurpassestheminthetermsof
probabilityinsophisticatedequipmentanddatacontrol.ZigBeeisthebestsolutionforlowdata
0Jtg1rate,shortrangecommunications(Fig.5.).
(ZigbeeCoordinator
ZigbeeRouter-FullFunctionDevice(FFD)
0ZigbeeEndDevice-ReducedFunctionDevice(RFD)
Fig3.Zigbeenetworkmodel
WhensecurityofM\AClayerframesisdesired,
ZigBeeusesM\AClayersecuritytosecureM\AC
command,beacon,andacknowledgementframes[4,5].
3.1.ApplicationofZigBeedevices
Thistechnologyincludesapplicationsegments
inhomecontrol(Fig.4.):wirelesshomesecurity,
remotethermostats,remotelighting,drape
controller,automatedmeterreading,personal
healthcareandadvancedtagging,callbuttonfor
elderlyanddisabled,universalremotecontrollerto
TVandradio,lighting,wirelesskeyboard,mouse
andgamepads,wirelesssmoke,COdetectors,etc.
LDU2WHIG>H
Fig5.ZigBeepositioninwirelessstandard
spectrum
REFERENCES:
[1]TomaszAugustynowicz,"ZigBeeIEEE802.15.4"
URL:http://www.cs.tut.fi/kurssit/8304700/sem
7talkl.pdf
[2]IEEE,"Std802.15.4[2003]"
URL:http:Hstandards.ieee.org/getieee802/dow
nload/802.15.4-2003.pdf
[3]SteveMontgomery,"Wi.232DTSvs.ZigBee"
URL:http://www.radiotronix.com/support/clic
k_download.asp?Contentld=184&FileURL=../
datasheets/Wi232_vsZigbee.pdf
[4]ZigBeeAlliance,"Tutorial"
URL:http:Hgrouper.ieee.org/groups/802/15/pu
b/03/15-03-0305-00-0040-zigbee-tutorial.ppt
[5]MarkCoates,MikeRabbat,"SensorNetworks
Part2:ZigBeeandIEEE802.15.4"
URL:http:www.ece.mcgill.ca/coates/public
ations/shortcourse-part2.pdf
Fig4.Useinhome
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