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A Power Graded Data Gathering Mechanism for Wireless Sensor Networks

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A Power Graded Data Gathering Mechanism for Wireless Sensor Networks

    A Power Graded Data Gathering

    Mechanism for Wireless Sensor Networks Vo1.32.No.6ACTAAUT0MATICASINICANovember,2006

    APowerGradedDataGatheringMechanismforWirelessSensor

    Networks1)

    BIYan-Zhong,YANTing-Xin,-SUNLiMinWUZhiMei

    (InstituteD,Software,ChineseAcademyolSciences,Beijing100080)

    .(GraduateSchoololChineseAcademyolSciences,Beijing100039)

    (E-mail:yanzhongO2~ios.an,tingxin03~ios.an)

    AbstractThedatagatheringmannerofwirelesssensornetworks.inwhichdataisforwarded towardsthesinknode,wouldcausethenodesnearthesinknodetotransmitmoredatathanthose

    farfromit.Mostdatagatheringmechanismsnowdonotdowellinbalancingtheenergyconsumption

    amongnodeswithdifierentdistancestothesink,thustheycanhardlyavoidtheproblemthatnodes

    nearthesinkconsumeenergYmorequickly,whichmaycausethenetworkrupturefromthesinknode.

    ThispaperpresentsadatagatheringmechanismcalledPODA.whichgradestheoutputpowerof

    nodesaccordingtotheirdistancesfromthesinknode.P0DAbalancesenergyconsumptionbysetting

    thenodesnearthesinkwithloweroutputpowerandthenodesfarfromthesinkwithhigheroutput

    power.SimulationresultsshowthatthePODAmechanismcanachieveevenenergyconsumptionin

    theentirenetwork,improveenergYemciencyandprolongthenetworklifetime.

    KeywordsWirelesssensornetwork,energybalance,powergrade,datagathering 1Introduction

    Recentadvancesinmicro-electromechanicalsystems(MEMS)haveledtothedevelopmentof

    large-scalesensornetworksformilitaryaffairs,environmentmonitoringandsoontI1. Sensornodesare

    deployeddenselynearorinthesensingareatocollectandtransmitinformationtothesinknodeina

    multi

    hopfashion.Sensornodesusuallyhavenon-replenishableenergyresource,whichcausesenergy

    emciencytobeanimportantconsiderationforsensornetworkdesign.

    Inthesensornetworksfordatagatheringapplications,datacongregatestothesinknodeand thismakesthenodesnearthesinkbecomehotspotsinthenetwork.Asdatatransmissionconsumes

    mostenergyofanode,thiswouldrupturethenetworkandstopdatatransmissiontothesink,and

    thenetworklifetimeisreducedthereby.Inanotheraspect.wenoticedthattheenergyconsumptionis

    proportionaltothedistanceofcommunication.Wecanadjusttheenergyconsumptionforthenode

    totransferthesameamountofdatabychangingthenodescommunicationradius.Atthesametime,

    themodernwirelesscommunicationtechnologieshavemadeiteasyfornodestoadjusttheiroutput

    powerinmultipleleve1.Thus,themethodofchangingasensornodescommunicationradiusby

    adjustingitsoutputpowerhasbeenadoptedbymanyresearcherstobalancetheenergyconsumption

    ofsensorsnodest.

    However,mostoftheresearchersonlyconsideredatnodeleve1.withoututilizing theadvantageofadjustablecommunicationradiusofnodesadequately.

    ThispaperpresentsanewdatagatheringmechanismcalledPODA(Power

    gradeddatagathering),

    whichtakestheadjustmentofoutputpoweratsystemlevelinconsiderationtotacklethehotspot

    probleminwirelesssensornetworksforgatheringdatainlargeareas.Makingnodesfarfromthesink

    usehigheroutputpowerthanthosenearthesink,allthenodesinthenetworkcanconsumeenergy

    evenlysoastoimprovetheenergyefficiencyandprolongthenetworklifetime.PODAprotocolhasthe

    followingcharacters.Firstly,energyconsumptionofnodesiseveninthewholenetwork.Secondly,the

    protocolissimplewithlowprotocolcost,andeasytoimplement.

    Therestofthepaperisorganizedasfollows.Section2presentssomepreviousworkaboutdata gatheringprotocolforwirelesssensornetworks.Section3describesourmechanismindetail.Section

    4givesouttheexperimentalresults.Section5discussessomeissuesinimplementation.Finally.we

    concludethispaperinSection6.

    2Relatedwork

    Manypreviousdatagatheringmechanismsadoptdifferentmeanstosavenodeenergyandprolong

    thenetworklifetime.DirectedDiffusionL5Jisatypicalgradient

    baseddataforwardingmechanism

    thatcanformadata-reportingtreeinthenetwork.Itreducestheunnecessarydatatransmission 1)SupportedbyNationalNaturalScienceFoundationofP.R.China(60434030,606731781 ReceivedNovember10,2004;inrevisedforEMarch7,2006

882ACTAAUToMATICASINICAVo1.32

    bysuppressingtheredundantdatapackets.Directeddiffusionhasarelativelyheavycommunication

    cost,asitnotonlyneedstorebuildthetopologyperiodicallytomaintainthegradient,butalsohas

    tomaintainmorethanonepathtosinknodeforeachdatasourcetotransfermulti

    copymessages.

    EnergyawareroutingrEAR)jbuildsmultiplepathsfromthedatasourcetothesinknode.Usinga

    stochasticapproach,itselectssub

    optimalnexthopforeachnode,soitcanonlygainenergybalance

    locally.Thoughdynamicenergyawarerouting(DEAR)

    lcanconsumeenergymoreevenlythanEAR,

    itcannotavoidbringinghotspotnearthesinknodeeither.Theauthorsof

    8]triedtofindanenergy

    balancedsolutionfordatapropagationinwirelesssensornetworks,buttheydidnotadequatelymake

    useoftheoutputpoweradjustingfulnctionofnodes.Besides.theiralgorithmistoocomplextotake

    intopractice.Inf41,theauthorsgaveare

    clusteringstrategyandaredirectionschemeforcluster-based

    wirelesssensornetworksThemethodofdynamictransmissionpoweradjustmentisintroducedintotheir

    protocoltocontrolthenumberofneighborsforeachnode,yettheirprotocolcanonlyguaranteethe

    localenergybalancewithinacluster.Withoutconsideringthetrafficcharacteristieofthewholenetwork

    inadatagatheringapplication,alltheseprotocolscanhardlymeettherequirementofenergybalance

    onallthenodesinthenetworks.Basedontheanalysisofthetraffic,wepresentanewdatagather

ing

    mechanisminthispapertoachievethisgoalbyexertingthefunctionofoutputpoweradjustmenton

    nodesadequately.

    3Power-gradeddatagathering

    Inthispaper.weassumeawirelesssensornetworkmode1.whichissimilartodatagathering applicationssuchasenvironmentmonitoring,withthefollowingproperties: 11A1argernumberofenergy

    constrainedsensornodesaredeployeduniformlyinthenetworkarea

    andareequippedwithpowercontrolcapabilitiestovarytheiroutputpower. 21Afixedsinknodeislocatedinthecenterofthenetworkarea.

    31Eachsensornodesendsfixedlengthdatapacketstothesinknodeperiodically.

    Insuchasensornetwork,mostsensingdatagatherstothesinknodehopbyhop,asitisenergy inefficienttotransmitdatatothesinkdirectly.Nevertheless,thenodesnearthesinkhavetoforward

    dataforothernodesbesidestheirowndatareporting.Theclosertothesink.themoredatatheyhave

    toforward.Sincetheenergyconsumptionofasensornodedependsmainlyoncommunicationandis

    proportionalthedistanceofcommunication.ifallthenodesinthenetworkuseasamecommunication

    radius,theywillhavethesameenergyconsumptionintransmittingadatapacket.Therefore,nodes

    nearthesinkconsumemoreenergybecausetheyhavetotransmitmoredata,andthisdecreasestheir

    lifetimedramatically.

    Fig.1(a)illustratesatraditionalnetworkusingauniformoutputpower.Allthenodesthat haveasamehop.counttothesinkformanodesset.whichwecallahop

    grade.Thenodeswithin

the1-hop

    gradetakechargeoftransmittingthedataofnodesinallothersectionsofthenetwork.In

    PODA.nodesnearthesinkadoptashortradiusforcommunication.whilenodesfarfromthesi

    nk

    adoptalongerone.Fig.1(b)showsanetworkusingtheproposedPODAmechanismofclassify

    ing

    outputpower,andthewidthofeachgradedringincreasesalongwithhop

    counts.Forthenodesin

    higherhop

    gradesalthoughtheyconsumemoreenergytotransmitadatapacketthanthoseinlower

    hop.grades,theamountofdataneededtotransmitismuchsmaller.Asaresult,thismakestheen

    ergy

    sink

    ……-=7:一一-I?#??',,.?0..??..-'??.?,.''?

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    2-hopgrade

    sink

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    1-hopgrade

    2-hopgrade

    3-hopgrade

    (a)Asensornetworkusingauniformradioradius(b)AsensornetworkwithPODAmechanism

    Fig.1Hop-countgradesinwirelesssensornetwork

    No.6BIYanZhongeta1.:APowerGradedDataGatheringMechanismforWireless???883 consumptionalmostequalamongnodesindifferenthop

    gradesinalongtimerunningnetwork.which

    canimprovetheenergyemciencyandprolongthenetworklifetimebyavoidingmakingthenodesnear

    thesinka8hotspots.

    AnotheradvantageprovidedbyPODAmechanismisthatitcanshortenthedelayincurredin gatheringdatawithamulti

    hoppattern.Therealwaysexistsatradeoffbetweendelayandenergy

    consumptionduringgatheringdatainwirelesssensornetworks[9~11J.Withthenetworktrafficmodel

    weassumed,thebiggerthecommunicationradiiofthenodes,theshorterthedelayofthedata,butthe

    higherenergycostfortransmittingadatapacket.InPODAmechanism,communicationradiiofthe

    nodesincreasealongwithhop

    countfromthesink,thusthedatapacketscanarriveatthesinkwith

    lesshopcount,butwithoutwastingenergy.

    3.1Output-power-grade

    Inthissection,wedescribethenetworktrafficmodel,whichisusedinPODAmechanism,based

    onthesensornetworkmodelmentionedabove.

    InPODA.weassignanoutputpowergradetoeachhopgrade.Thenodesinasameoutputpower gradetransmitdatausingthesameoutputpower,sotheyhavethesamecommunicationradius.

    Aiming

    atbalancingtheenergyconsumptionofallthenodesinthenetwork,weneedtocarefullydesig

    nthe

    communicationradiususedbynodesineachhopcountgradetogetatableofoutputpowergrades

    correspondingtohopcount.

    InFig.2(a),thesinknodeusesRoasitscommunicationradiusandinformsthenodeswithin

    thisareaas1-hopgradenodes.Allthe1-hopgradenodes(e.g.NodeAinFig.2)useR1astheir communicationradius.andthentheyannouncetheirhopgradesinformationtothenodeswithintheir communicationrangetomakethem2-hopgradenodes.Similarly,allthe2-hopgradenodes(e.g.Node

    B)useR2astheircommunicationradius,andsoforth.Assumingthenodesdistributeuniforml

    y,Fig.2

    (a)canbepredigestedtoFig.2(b)inwhichnodesthathavethesamehopcountformaringarea.w_e

    calleachringareaanoutputpowergradeanddenotethemas{G.).Especially,thefirstoutputpower

    gradeGoisaroundareawiththesinknodeasitscenter.canseethatthehopcountfromnodes

    inthei-thgrade,G,tothesinknodeisi+1. 旗懑o'e.:一,;sinkwidthG_?5.Rowidtha1?5.R1

    widtha2?5.R2

    (a)fb)

    Fig.2Outputpowergradesinawirelesssensornetwork

    LetdenotethecommunicationradiususedbynodesingradeGi.InPODA.startingfromthe sink,eachnodeshop

    gradeisconfirmedhopbyhop.Tomakethenodescommunicatewiththatin

    neighboringgradesinbothdirections,weshouldhave

    Ri+l?兄,i?0(1)

    AsshowninFig.2(b),thecommunicationradiusisRi+IofnodesingradeGi.Therefore,the widthoftheringareaofGiisdecidedby:

    ,G:5?,i?0(2)

    where5isaparameterin(0,1],whichisdecidedbythedeploymentdensityofnodes,communication

    chmqnelqualityandtopologybuildingalgorithminthespecifiednetwork.

884ACTAAUToMATICASINICAVo1.32

    Letusconsideradata-gatheringnetworkthatcoversaroundareaandhasasinknodeatthe centre.LetRdenotetheradiusoftheentirenetwork.Then

    R=?WG?见,i?0(3)

    AssumingthenodesaredeployeduniformlyandthedeploymentdensityisP,theamountofnodes

    inthenetworkisP?7r.R.AllthesensornodesperiodicallysenddatapacketshavingalengthofLbit

    tothesink.Especially,inonereportperiod,theamountofpacketsgeneratedbynodesingradeGois

    Dao:P.7r.Wg0(4)

    Duetof21,wehave

    DG0=P.7r.(.Ro)=P.7r..(5)

    NodesingradeGocommunicatewiththesinkdirectly,thustheyhavetotransmitdatagenerated

    bynodesinalltheothergrades

    Ta0=P.7r.RDG0=P.7r.RP.7r..(6)

    FornodesingradeGi,theamountofpacketsgeneratedineachreportperiod,whichisalsothe

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