11552011968046 Research Article CARNIVORE A DisruptionTolerant System for Studying Wildlife Matthew Rutishauser Vladislav Petkov Jay Boice Katia Obraczka Patrick Mantey Terrie M Williams and Christopher C Wilmers Department of Computer Engineering Un ID: 49891
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intheirnaturalenvironment.However,manyspeciesare TheCARNIVOREmobile,animal-borne,sensingnodes,orCSNsarelimitedinweightyetcontaintherequiredsensors(3-axisaccelerometerandGPS),processing,storage, thefunctiontobecalled,therequiredcountervalueisstoredinacapture-compareregister,andtheinterruptisenabled.Whenthesystemclockadvancesthecountertotherequiredvalue,thefunctionpointerisdereferencedandthespeciÞedfunctioniscalled.3.2.DataStorage.DuringinitialdebuggingoftheÞrmware,anFATÞlesystemontheSDcardwasvaluablefortestingsensordataacquisition.However,troubleshootingÞlesystemerrorsbecamedi dataProcessframesGPSmachinetaskElectiontaskNeighbordiscoverytaskTransmitTxframeMAClayerTasksab 3.3.ReceiveBu!er.Weimplementedahigh-prioritytaskthatprocessesframesandareceivebu e"ects.3.5.GPSFirmware.TheGPSÞrmwareallowsfornetworktimingbyupdatingthenodessystemtimeandmaintaininganaccuratereal-timeclockforsensorsampling.Inaddition,theGPSÞrmwareensuresthatthealmanacisalwayscurrent.TheLasseniQ[23]onacoldstartmustdownloadthesatellitealmanac,whichdescribescurrentsatellitelocations.Thisrequires15minutesofcontinuoussignalfromonesatellite.Also,thealmanacwillexpireafter8Ð10weeksandrequireanewdownload.IfthestatuspacketfromtheGPSmoduleindicatesthatthealmanacisneeded,theGPStimeoutisincreasedto18minutestoallowforthedownload.Time,latitude,longitude,altitude,andvelocityarerecordedforeachlocationandtakeup30bytesofspace.16suchlocationscanÞtintoonecollardatasegment(Figure5).TheÞrmwareiscapableofloggingonelocationpersecond,buttheenergycostofdoingthisisprohibitive.CommercialtrackingcollarsavailablefromTelemetrySolutionstypicallyloganywherefrom1to48locationsperday.Dependingonthespeciesbeingtracked,biologistsmaybeabletosettleforlowertemporalresolutiononthelocationdata.Wechosetodo72locationsperday,givingusslightlyhighertemporalresolution.4.NetworkProtocolTheCARNIVOREnetworkcanbeconsideredtobeahighly-disconnectednetworkorausually-disconnectednetworkbecausepredatorswearingtheCSNsaretypicallynotwithinwirelessrangeofeachother.Timelyorcompleterecoveryofthedataatabasestationisnotrequired;however,asmuchdataaspossibleshouldbecaptured.Therearethreetaskswhichsetuptheinter-CSNorCSN-to-SRNconnections:neighbordiscovery,election,anddatatransfer(Figure6).EachoftheseutilizestheMAClayertosendandreceivedata.AsingleMAClayertaskparsesframesrapidlyandupdatesthestatevariablesforeachtask.AneighbortableismaintainedateachCSNthatstorestheneighborIDandarankingmetric.ThecompleteCARNIVOREprotocolrequiressixdi"erentCARNIVOREpackettypes(Table1).Whentwoormorenodescometogether,theyformastar-shapednetwork,wherethecentralnodeischosentoreceivethedatafromalltheothernodes(Figure7).Ifpresent,anSRNisalwayschosentoreceivedata.Thechosenreceivermediatestheround-robinschemeandminimizescompetitionforthechannel,givingeachnodearequestfordatainturn(seeSections4.4and4.5 SenderDataFigure7:Roundrobinstarnetwork.Thereceivermediatestheround-robindatatransfer,acceptingdatafromthesenders.Eithersenderorreceivercanendthetransfer.base-linepoweruse,caremustbetakentousetheavailablebandwidthe!ciently.UsingtheQualnet[28]networksimulator,westudieddi"erentdatarouting/forwardingalgorithms.Resultsfromthisstudy(showninSection5.3)comparingepidemic,controlledepidemic,single-copyforwarding,andmulticopyforwardingshowthatthelatterdeliversthebestperformanceintermsofdeliveryratioandbandwidthusage.Inourmulticopyforwarding,implementationCSNssendmessagestothoseCSNswithamorerecenttimestampfromasink.Thesourcecoyote(theonewhoproducesthedata)keepsthemessagesandwillresendthemagain,thoughonlydirectlytoabasestation.Thesemessagesarealsomarkedinthebu"ertobedeletedÞrst.4.2.MACLayer.ThecurrentversionoftheCARNIVORECSNutilizesacustomnetworkprotocolstackandimple-mentsthe802.15.4MAClayer[29].TheMAClayerusesCSMA/CA(CarrierSenseMultipleAccesswithCollisionAvoidance).Anodewishingtotransmitlistenstothe SimilartoEpidemic,exceptthatacoyoteonlysendsmessagestothosecoyoteswhohavemorerecentlybeenincontactwithabasestation.Thesendingcoyotekeepsthemessagesandwillsendthemagaintoothercoyotesiftheopportunityarises.SingleCopy.Coyotessendmessagesonlytocoyoteswithamorerecenttimestampfromasinkthendeletethemessagesfromtheirownbu"er.MulticopyForwarding.Coyotessendmessagestothosecoy-oteswithamorerecenttimestampfromasink.Thesourcepredator(theonewhoproducesthedata)keepsthemessagesandwillresendthemagain,thoughonlydirectlytoabasestation.Thesemessagesarealsomarkedinthebu"ertobedeletedÞrst.Althoughstudyingthemobilityofpredatorsintheirnativehabitatisoneofthegoalsofthesensornetwork,wegeneratedasimplemodeltoevaluateourproposedroutingprotocols.Wechosetosimulatethenetworkwitharelativelysocialpredator,theCoyote(Canislatrans)toallowforbothCSN-CSNandCSN-SRNdatatransfer.AQualnet[28]simulationmodelwasrunforsevendaysofrealtimewith16collaredcoyotesandfourrandomlyplacedbasestationsinanareaof64squarekilometers.Thesimulationwasrunwith10randomseedsfordenlocation,SRNlocation,andcoyotemovement.Theresultswereaveragedoverthe10seeds.Each .2004006008001000120014001600AMDF00.10.20.30.40.50.60.70.80.91