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简介:本文档为《s Thesis Localisation in Large-Scale Outdoor Wirelesspdf》,可适用于IT/计算机领域

LocalisationinLargeScaleOutdoorWirelessSensorNetworksOttoWilbertVisserLocalisationinLargeScaleOutdoorWirelessSensorNetworksMaster’sThesisinComputerScienceParallelandDistributedSystemsgroupFacultyofElectricalEngineering,Mathematics,andComputerScienceDelftUniversityofTechnologyOttoWilbertVisserAugustth,AuthorOttoWilbertVisserTitleLocalisationinLargeScaleOutdoorWirelessSensorNetworksMScpresentationAugustth,GraduationCommitteeprofdrirHJSips(chair)DelftUniversityofTechnologydrKGLangendoenDelftUniversityofTechnologydrirRFHanssenDelftUniversityofTechnologyAbstractWirelesssensornetworksarenetworksconsistingofnumeroussmallcomputersequippedwithsensorstodetecteventslikehumanmotionwithinfraredsensorsordeterminethecurrentstateofcertainvariablesliketemperatureThesesensornodesareequippedwitharadiotocommunicatewitheachotherandtosenddatatoacentralcomputerwherethisdatacanbeparsedandviewedItisusefultohavethelocationanodeinordertoknowtheoriginofnewdataorneweventsResearchinlocalisationforwirelesssensornetworkshaslargelybeenbasedonsimulationbecauseofthecostsassociatedwithrealworlddeploymentsThisthesisinvestigatestheperformanceoflocalisationalgorithmintherealworldanddoesacomparisonwithsimulationThesetupofthetestenvironmentonapotatofield,usedascomparisontosimulation,isdescribedAnumberofexistinglocalisationalgorithmsisexplainedandtheseareusedbothwithrealworlddataandwithsimulateddataThisthesisshowsthatrealworldexperimentsdiffersignificantlyfromsimulationandindicatesstepsthatcouldbemadetoimprovesimulationsaswellasperformanceintherealworldiv“I’msorrybutIdon’tneedsomeremotesensordeviceusingWiFitellingmethatitisraininghailstones,thepainfromthefracturestomycraniumwillbemorethanenough”–ArashPartowCommentingonSlashdot(wwwslashdotorg)onourexperimentsonthepotatofieldPrefaceWhenlookingforasubjectformymaster’sthesisIwasofferedtheopportunitytohelponanewandexcitingprojectcalledLofarAgroAlthoughthisprojectwasprimarilyfocusedongettingagriculturalresults,IwasallowedtopiggybackmyowndataandperformmyownexperimentsonlocalisationGoingfromsimulationstotherealworldandgoingfromafewnodestooverahundrednodesarenottrivialstepsyetRealworldbringsnewproblemsor“challenges”theoutdoorsdoesnothavearoofoveritandthismeansprotectingthefragilenodefromthebadoutdoorsOncesealed,thenodeanditspowersupplyaresafefromrainandsmallanimals,butquicklyreplacingabatterysuddenlynolongertakessecondsasinthelab,butatleastminutesforbreakingtheseal,openingthecase,disconnectingtheindustrialstrengthbatteryclamps,connectingthenewbatterywiththeappropriatetools,usingbruteforcetoclosethecaseagainandreapplyingsealantThendoaquickprayertoyourdeityofchoice,becausewedecidedtoswitchofftheLEDstopreservepower,sothereisnowaytotellwhetheritisworkingagainunlessyouwalkordriveafewhundredmeterstoacomputerandwaitforamessagefromthatparticularnodeAndallofthisrequireshoursofdrivingtogettothatnodeandminutesofsearchingforthenode,whichisthankstoMurphytocmshorterthenthepotatocropssurroundingitandcompletelyhiddenNottomentionthefactthatyoufirstneedtoconvincesomeonetogotothebatteryfactoryandloadexplosivebatteriesintohisorhertrunkDespitealltheproblemswithbatteriesandgettingallthedata,itwasdefinitelyaninterestingprojecttoworkonWhowouldhavethoughtthepotatosensorswouldhavemadeitontointernationaltelevisionIwouldliketousethisopportunitytothankafewpeoplefortheirhelpandsupportinnoparticularorder:DaanvanYperenforcreatingthespiffyFlashapplicationtodisplaythecurrentpotatofieldstatusKoenLangendoenforhissupervision,GertjanHalkes“thiscanbedonemoreeasily”andTomParker“Itshouldbeworkingnow”fortheirhackingonTMAC,IvayloHaratchevforhisinsightsonradiosandRSSI“Thiscouldbeduetoducks”,MichielKonstapelforhelpingmeflash,packageandplacenodes,KatelijneVandenbusscheforhelpingmeoutonvariousoccasionslikegettingserversintheairfiveminutesbeforeapressconferenceandallpeopleintheaquariumfortheinterestingconversations,feedback,coffeebreaksandlunchesOttoVisserDelft,TheNetherlandsAugustviiviiiContentsPrefaceviiIntroductionThesisstructureWirelesssensornetworksAvailablesensornodesDeploymentsAstronLofarLofarAgroLocalisationalgorithmsDeterminingdistanceLaserTimeofFlightRSSIDerivelocationLaterationMinmaxRefinementImplementationNhopmultilaterationAdhocpositioningRobustpositioningExperimentalsetupThefieldHardwareGatewaySensornodesSoftwareSoftwareonthesensornodesSoftwareontheStargateandserverixOfflinelocalisationResultsPreprocessingthedataMissingandunknownnodesNodelifeRSSIdistributionandinfluencesRSSIdistributionReconstructingthespanningtreeRSSItodistancemappingImprovingtheRSSItodistancemappingMissingandunknownnodesRealworldversussimulationNhopmultilaterationAdhocpositioningRobustpositioningDiscussionConclusionsandFutureWorkADetaileddescriptionofthepotato�eldBRSSImappingstatisticsxChapterIntroductionWirelesssensornetworksarerapidlygrowinginpopularityTheyseemedtobeasolutionlookingforaproblemandwereanewtoyforresearchersandstudentsattechnicaluniversities,butwirelesssensornetworksarenowleavingthesafeplaygroundsinsideuniversitybuildingsandarebeingplacedintherealandharshoutdoorsWirelesssensornetworkswillbediscussedinmoredetailinChapterMostapplicationsforwirelesssensornetworksrequiresomeknowledgeofthelocationsofthenodesTherehavealreadybeenquiteanumberofpeopledoingresearchonlocalisationinwirelesssensornetworksMostofthemshareafewcommonpoints,forinstance:theystartbysaying:“Supposethatwewanttothrownodesoutofanairplanehowdoweknowwhereeachnodelanded”andtheyendupwithasimulationoftonodesuniformlydistributedinasquareareaThoseexperimentsthataredonewithrealnodesaremostlyperformedinsideandiftheyaredoneoutside,theyareeitherwithveryfewnodesonanopenfieldortheyareallcooperatingtolocateonemovingnodeAlgorithmsfordoinglocalisationinwirelesssensornetworkscanbefoundinChapterThegoalofthisthesisistotakesomelocalisationalgorithmspreviouslyevaluatedinsimulationandtesttheirperformanceinarealworldenvironmentDothesealgorithmsproducelocalisationinformationthatisusableAnothergoalistoseewhatcouldbechangedtosimulationstomakethemmoreaccurateTherealworlddatagatheredforthisthesiscanalsobeusedbyotherstotestcompletelynewalgorithmsagainstrealdataAnothergoalforTUDelftwastotryoutthenewMAClayer,TMAC,andseehowitwouldperformwithoverahundrednodesTMACwasdesignedtobeenergyefficientwhichisaverywelcomefeaturewiththisnumberofnodesandtheamountoftimethenodesaresupposedtoberunningThesisstructureThisthesisisaproductofthecooperationoftheUniversityofWageningen,TUDelftandAstroninaprojectcalledLofarAgroThegoalofthisprojectistofightfungaldiseasesinpotatocropsbymeansofasensornetworkmonitoringthemicroclimateAmoredetaileddescriptionofthisprojectandthesetupcanbefoundinChapterPartofthelocalisationalgorithmsdiscussedinChapterwereappliedtothedatagatheredonthepotatofieldwhichgivesresultsthatcanbefoundinChapterFinally,inChaptertherearesomeconclusionsresultingfromtheexperimentsperformedandsomesuggestionsforimprovementsandfutureworkChapterWirelesssensornetworksAccordingtoWikipediawirelesssensornetworkscanbedescribedasfollows:Awirelesssensornetwork(WSN)isanetworkmadeofnumeroussmallindependentsensornodesThesensornodes,typicallythesizeofammfilmcanister,areselfcontainedunitsconsistingofabattery,radio,sensors,andaminimalamountofonboardcomputingpowerThisdefinitionalreadydepictsthefactthatsensornodesarelimitedincomputingpowerThisishowevernottheonlyresourcethatislimited,alsotheamountofmemoryandstorageareverylimitedTheamountofRAMavailableisingeneralintheorderofKBandanodetypicallydoesnothavemorethanonemegabyteofEEPROMstorageThisplacesanupperboundonthecapabilitiesforasensornodeanddatageneratedinasensornetworkisthereforetypicallyforwardedtoaPCforprocessingAsensornodeisequippedwithabatteryforitspowerSensornodesaremadeassmallaspossibleandtheygenerallydonotcarryabatterymuchlargerthanthenodeitselfThisbringsanotherlimitation:theamountofpoweranodeisallowedtoconsumeThisshouldbeaslowaspossible,tomakesurethenodelastsaslongaspossibleAnodemightconsumeuptoafewmAwhileactive,butonlyafewµAwhileasleepSopreferablyanodeisasleepforthemajorityoftimeAnotherlimitationcanbefoundintheradioTheradioisbyfarthebiggestpowerconsumeronanodeandshouldbeturnedoffasmuchaspossibleItisthereforeagoodideatodoalittleextracomputationifthatavoidsanextraradiomessageAvailablesensornodesAlotofresearchinstitutesmaketheirownnodesfortheirresearch,forinstancetheEyesnodes,buttherearealsonodesforsaleatcommercialcompanieshttp:enwikipediaorgFigure:CollectionofnodesavailablefromCrossbow©CrossbowCrossbowisacompanythatsellsanumberofdifferentnodetypes(seeFigure)withdifferentspecificationsandsizesfordifferentgoalsOneoftheirmostpopularmodelsistheMicawhichisthesizeofAAsizedbatteriesandwhichcanbeenhancedbyattachingavarietyofsensorboardsThereisalsoaMicadot,whichisthesizeofatwoeurocoinTNOmadeanodebasedontheMicadot,calledaTNOdeDeploymentsBecauseofthelimitationsthatneedtobedealtwithandtheassociatedcosts,therearenotalotoflargerealworlddeploymentsyetOneofthebestknownrealworldexperimentsisGreatDuckIslandinwhichtheyusednodestomonitorthebreedinghabitsofpetrelsThesenodescouldnotbeservicedduringtheprojectbecausedisturbanceduringthebreedingseasonincreasesthedeathrateofeggsandchicksseverelyThisthesistakesadvantageofthedeploymentofsensornodesinapotatofieldfortheLofarAgroprojectLofarAgroisasubprojectofLofar,whichisinturnaprojectofAstronLOFARAgroisajointprojectofthefollowinginstitutesandcompanies:ASTRON,KvernelandMechatronics,Vertis,Opticrop,AgrotechnologyFoodInnovationsandPlantResearchInternational(fromWageningenUniversity,FarmTechnologygroup)andfinallytheTUDelftAstronAstronisafoundationforresearchinastronomyintheNetherlands(ASTRON=StichtingASTRonomischOnderzoekinNederland)TheirgoalistoenablediscoveryinastronomybyprovidingfrontlineobservingcapabilitiestoastronomerswithabroadrangeoftechniquesTheyhaveanarrayofverysensitiveradiotelescopesinWesterborkwhichenablesthemtostudyawiderangeofastrophysicalphenomena:frompulsarstokinematicsofnearbygalaxiestothephysicsofblackholesAstronhasaveryactiveresearchanddevelopmentdepartmentfordesigningwithnew(astronomical)instruments,microchipsandsoftwareFigure:ArrayofradiotelescopesnearWesterbork©AstronLofarAspartofAstron’scontinuingefforttogetabetterinsightintheuniversearoundustheyplannedonmakingatelescopethatcouldlookfurtherToaccomplishthis,averylargetelescopewouldbeneededandthereforeAstroncameupwithabetteridea:asoftwaretelescopebuiltontopof,smallradioantennasTomakeradiopicturesoftheskywithadequatesharpness,theseantennasaretobearrangedinclustersthatarespreadoutoveranareaofkmindiameterThisresultsinanenormousdatastream(manyTerabitspersecond)thatneedstobeprocessedintheLofarCentralProcessor(CEP)whichhasaIBMBlueGeneLasitscoremachineThenameofthisprojectisLofarwhichstandsforLOwFrequencyARray,sincethistelescopewillonlydomeasurementsintherangeoftoMHzThecentreofthistelescopeislocatedinafieldnearExloo(Drenthe)withanelectromagneticallyshieldedcontainerinthecentreforpreprocessingthedataandforwardingittoCEPAlthoughLofar’sprimarygoalistoenhanceknowledgeabouttheuniverse,asecondarygoalistosupportotherresearchthatcouldmakeuseofthishighbandwidthnetworkThereisnowasensornetworkforgeophysicistswithseismicsensorswithwhichtheyhopetolearnmoreabout(ground)watermanagement,effectsofgasextractionanddetectinginfrasoundwavesasgeneratedbynuclearblastsandvolcaniceruptionsFigure:AfewoftheantennasinthefieldinExlooLofarAgroTheothersensornetworkthatispartofLofaristheagriculturalsensornetworkinanearbypotatofieldTheuniversityofWageningenwaslookingforanideatoprotectpotatocropsfromthephytophthoradiseasePhytophthoraisafungaldiseaseinpotatoes,whichcanenterafieldthroughavarietyofsourcesThedevelopmentandassociatedattackofthecropdependsstronglyontheclimatologicalconditionswithinthefieldThefactorsthataremostimportantindicatorsforthedevelopmentofphytophthoraare:temperature,humidityandthemoisturelevelsoftheleavesTheuniversityofWageningenwaslookingforasolutiontomeasurethemicroclimateinthepotatofieldandtheTUDelftwasabletoprovideoneintheformofawirelesssensornetworkChapterLocalisationalgorithmsAlargenumberofwirelessapplicationsrequiressomesortoflocationknowledgeDetectingenemysoldiersandtanksorotherunwelcomevisitorsonlymakessenseiftheuserofthisapplicationcanbeinformedofthelocationofsuchaneventThereareafewwaystoaccomplishthisFirstofall,thesimplestsolutionavailable:tellthenodeitslocationThiscanbedonebyhardcodingthislocationinthenodeandplacingthisnodeonthatspecificplaceorbylocatingthenodewithsomeotherdeviceandthentellingthenodeitslocationTheidealsituationwouldbetoplaceanodeonarandomlocationandhavethenodefigureoutitsownpositionwithoutanyfurtheruserinterventionThisdoesofcourserequiresomeextrasoftwareandmaybeevensomeextrahardwareaswellMostadhoclocalisationalgorithmsworkinacomparablefashionThemajorityofthenodesstartswithoutknowledgeoftheirlocationandthereareafewnodesamongstthemthatdoknowtheirlocationThesenodeshaveeitherextrahardwaretoderivetheirlocationfrom,theygottheirlocationfrom,forinstance,ahumanbeingthatdeterminedtheirlocation,ortheirlocationishardcodedandtheymustbeplacedatthathardcodedlocationThesenodeswithknownlocationarecalledanchornodesLocalisationisinmostcasesathreestageprocess:determinedistancetoanchorsderivecurrentlocationrefinewithinformationfromothernodesDeterminingdistanceDuringthefirststepdeterminingdistancetoanchorsnodesmeasurethedistancebetweenthemselvesandanchorswithinradiorangeThiscanbeaccomplishedwithanumberofdifferentmethodsLaserAratherexpensiveoptionwouldbemeasuringdistancewithalaserThisrequiresaclearlineofsightandsomemechanicsforaimingItisextremelyaccurateatdeterminingthedistancebetweentwonodes,butthedrawbacksmakeitimpracticaltouseInthespotlightsystem,asinglelaserisusedtogeneratelighteventswhichcanbedetectedbythenodesThenodesreportthedetectionofthelighttothenodeconnectedtothelaser,whichinturntellsthenodeitslocationTimeofFlightBysimultaneouslysendingoutaradiopacketandanothersignalsuchas(ultra)soundandmeasuringthedifferenceintimeittakesforbothsignalstoarriveatanothernode,thedistancebetweenthemcanbedeterminedbydividingthetimeofflightbythespeedofsoundThisrequiresextrahardwarelikeamicrophoneandasounderGPSGPSisanexampleoftimeofflightmeasurementsAGPSreceiverusesthetimeasignalneedstogetfromasatellitetothereceivertodetermineitsdistancetothissatelliteAGPSreceiverhoweverdoesnotonlydeterminethetimeofflighttoanumberofsatellites,italsodoesthenextstage:triangulation,andreturnsthecurrentlocationonearthThisprovidesthenodewithitslocationwithinafewmetersAnaccuracyofafewcentimetresispossibleifthereisaadditionalg

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