英文翻译采用红外传感器网络对移动目标的计数英文翻译.docx
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英文翻译采用红外传感器网络对移动目标的计数英文翻译.docx
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英文翻译采用红外传感器网络对移动目标的计数英文翻译
MovingObjectCountingwithanInfrared
SensorNetwork
ByChi-KeungKi
Abstract
WirelessSensorNetwork(WSN)hasbecomeahotresearchtopicrecently.GreatbenefitcanbegainedthroughthedeploymentoftheWSNoverawiderangeofapplications,coveringthedomainsofcommercial,militaryaswellasresidential.Inthisproject,wedesignacountingsystemwhichtrackspeoplewhopassthroughadetectingzoneaswellasthecorrespondingmovingdirections.Suchasystemcanbedeployedintrafficcontrol,resourcemanagement,andhumanflowcontrol.Ourdesignisbasedonourself-madecost-effectiveInfraredSensingModuleboardwhichco-operateswithaWSN.ThedesignofoursystemincludesInfraredSensingModuledesign,sensorclustering,nodecommunication,systemarchitectureanddeployment.WeconductaseriesofexperimentstoevaluatethesystemperformancewhichdemonstratestheefficiencyofourMovingObjectCountingsystem.
KeywordsInfraredradiation;WirelessSensorNode
1WirelessSensorNetwork
1.1IntroductiontoInfrared
Infraredradiationisapartoftheelectromagneticradiationwithawavelengthlyingbetweenvisiblelightandradiowaves.Infraredhavebewidelyusednowadaysincludingdatacommunications,nightvision,objecttrackingandsoon.Peoplecommonlyuseinfraredindatacommunication,sinceitiseasilygeneratedandonlysufferslittlefromelectromagneticinterference.TaketheTVremotecontrolasanexample,whichcanbefoundineveryone'shome.Theinfraredremotecontrolsystemsuseinfraredlight-emittingdiodes(LEDs)tosendoutanIR(infrared)signalwhenthebuttonispushed.Adifferentpatternofpulsesindicatesthecorrespondingbuttonbeingpushed.ToallowthecontrolofmultipleappliancessuchasaTV,VCR,andcablebox,withoutinterference,systemsgenerallyhaveapreambleandanaddresstosynchronizethereceiverandidentifythesourceandlocationoftheinfraredsignal.Toencodethedata,systemsgenerallyvarythewidthofthepulses(pulse-widthmodulation)orthewidthofthespacesbetweenthepulses(pulsespacemodulation).Anotherpopularsystem,bi-phaseencoding,usessignaltransitionstoconveyinformation.EachpulseisactuallyaburstofIRatthecarrierfrequency.A'high'meansaburstofIRenergyatthecarrierfrequencyanda'low'representsanabsenceofIRenergy.Thereisnoencodingstandard.However,whileagreatmanyhomeentertainmentdevicesusetheirownproprietaryencodingschemes,somequasi-standardsdoexist.TheseincludeRC-5,RC-6,andREC-80.Inaddition,manymanufacturers,suchasNEC,havealsoestablishedtheirownstandards.
1.2Wirelesssensornetwork
Wirelesssensornetwork(WSN)isawirelessnetworkwhichconsistsofavastnumberofautonomoussensornodesusingsensorstomonitorphysicalorenvironmentalconditions,suchastemperature,acoustics,vibration,pressure,motionorpollutants,atdifferentlocations.Eachnodeinasensornetworkistypicallyequippedwithawirelesscommunicationsdevice,asmallmicrocontroller,oneormoresensors,andanenergysource,usuallyabattery.Thesizeofasinglesensornodecanbeaslargeasashoeboxandcanbeassmallasthesizeofagrainofdust,dependingondifferentapplications.Thecostofsensornodesissimilarlyvariable,rangingfromhundredsofdollarstoafewcents,dependingonthesizeofthesensornetworkandthecomplexityrequirementoftheindividualsensornodes.Thesizeandcostareconstrainedbysensornodes,therefore,haveresultincorrespondinglimitationsonavailableinputssuchasenergy,memory,computationalspeedandbandwidth.Thedevelopmentofwirelesssensornetworks(WSN)wasoriginallymotivatedbymilitaryapplicationssuchasbattlefieldsurveillance.Duetotheadvancementinmicro-electronicmechanicalsystemtechnology(MEMS),embeddedmicroprocessors,andwirelessnetworking,theWSNcanbebenefitedinmanycivilianapplicationareas,includinghabitatmonitoring,healthcareapplications,andhomeautomation.
1.3TypesofWirelessSensorNetworks
Wirelesssensornetworknodesaretypicallylesscomplexthangeneral-purposeoperatingsystemsbothbecauseofthespecialrequirementsofsensornetworkapplicationsandtheresourceconstraintsinsensornetworkhardwareplatforms.Theoperatingsystemdoesnotneedtoincludesupportforuserinterfaces.Furthermore,theresourceconstraintsintermsofmemoryandmemorymappinghardwaresupportmakemechanismssuchasvirtualmemoryeitherunnecessaryorimpossibletoimplement.TinyOSispossiblythefirstoperatingsystemspecificallydesignedforwirelesssensornetworks.Unlikemostotheroperatingsystems,TinyOSisbasedonanevent-drivenprogrammingmodelinsteadofmultithreading.TinyOSprogramsarecomposedintoeventhandlersandtaskswithruntocompletion-semantics.Whenanexternaleventoccurs,suchasanincomingdatapacketorasensorreading,TinyOScallstheappropriateeventhandlertohandletheevent.TheTinyOSandprogramsarebothwritteninaspecialprogramminglanguagecalledNesCwhichisanextensiontotheCprogramminglanguage.NesCisdesignedtodetectraceconditionsbetweentasksandeventhandlers.TherearealsooperatingsystemsthatallowprogramminginC.ExamplesofsuchoperatingsystemsincludeContiki,andMANTIS.Contikiisdesignedtosupportloadingmodulesoverthenetworkandrun-timeloadingofstandardELFfiles.TheContikikernelisevent-driven,likeTinyOS,butthesystemsupportsmultithreadingonaper-applicationbasis.Unliketheevent-drivenContikikernel,theMANTISkernelisbasedonpreemptivemultithreading.Withpreemptivemultithreading,applicationsdonotneedtoexplicitlyyieldthemicroprocessortootherprocesses.
1.4IntroductiontoWirelessSensorNode
Asensornode,alsoknownasamote,isanodeinawirelesssensornetworkthatiscapableofperformingprocessing,gatheringsensoryinformationandcommunicatingwithotherconnectednodesinthenetwork.Sensornodeshouldbeinsmallsize,consumingextremelylowenergy,autonomousandoperatingunattended,andadaptivetotheenvironment.Aswirelesssensornodesaremicro-electronicsensordevice,theycanonlybeequippedwithalimitedpowersource.Themaincomponentsofasensornodeincludesensors,microcontroller,transceiver,andpowersource.Sensorsarehardwaredevicesthatcanproducemeasurableresponsetoachangeinaphysicalconditionsuchaslightdensityandsounddensity.ThecontinuousanalogsignalcollectedbythesensorsisdigitizedbyAnalog-to-Digitalconverter.Thedigitizedsignalisthenpassedtocontrollersforfurtherprocessing.MostofthetheoreticalworkonWSNsconsidersPassiveandOmnidirectionalsensors.PassiveandOmnidirectionalsensorssensethedatawithoutactuallymanipulatingtheenvironmentwithactiveprobing,whilenonotionof“direction”isinvolvedinthesemeasurements.Commonlypeopledeploysensorfordetectingheat(e.g.thermalsensor),light(e.g.infraredsensor),ultrasound(e.g.ultrasonicsensor),orelectromagnetism(e.g.magneticsensor).Inpractice,asensornodecanequipwithmorethanonesensor.Micro-controllerperformstasks,processesdataandcontrolstheoperationsofothercomponentsinthesensornode.Thesensornodeisresponsibleforthesignalprocessinguponthedetectionofthephysicaleventsasneededorondemand.Ithandlestheinterruptionfromthetransceiver.Inaddition,itdealswiththeinternalbehavior,suchasapplication-specificcomputation.
Thefunctionofbothtransmitterandreceiverarecombinedintoasingledeviceknownastransceiversthatareusedinsensornodes.Transceiversallowasensornodetoexchangeinformationbetweentheneighboringsensorsandthesinknode(acentralreceiver).TheoperationalstatesofatransceiverareTransmit,Receive,IdleandSleep.Powerisstoredeitherinthebatteriesorthecapacitors.Batteriesarethemainsourceofpowersupplyingforthesensornodes.Twotypesofbatteriesusedarechargeableandnon-rechargeable.TheyarealsoclassifiedaccordingtoelectrochemicalmaterialusedforelectrodesuchasNickel-cadmium,Nickel-zinc,Nickelmetalhydride,andLithium-Ion.Currentsensorsaredevelopedwhichareabletorenewtheirenergyfromsolartovibrationenergy.TwomajorpowersavingpoliciesusedareDynamicPowerManagementandDynamicVoltageScaling.DPMtakescareofshuttingdownpartsofsensornodewhicharenotcurrentlyusedoractive.DVSschemevariesthepowerlevelsdependingonthenon-deterministicworkload.Byvaryingthevoltagealongwiththefrequency,itispossibletoobtainquadraticreductioninpowerconsumption.
1.5Challenges
Themajorchallengesinthedesignandimplementationofthewirelesssensornetworkaremainlytheenergylimitation,hardwarelimitationandtheareaofcoverage.EnergyisthescarcestresourceofWSNnodes,anditdeterminesthelifetimeofWSNnodes.WSNnodesaremeanttobedeployedinlargenumbersinvariousenvironments,includingremoteandhostileregions,withad-hoccommunicationsaskey.Forthisreason,algorithmsandprotocolsneedtobelifetimemaximization,robustnessandfaulttoleranceandself-configuration.Thechallengeinhardwareistoproducelowcostandtinysensornodes.Withrespecttotheseobjectives,currentsensornodesusuallyhavelimitedcomputationalcapabilityandmemoryspace.Consequently,theapplicationsoftwareandalgorithmsinWSNshouldbewell-optimizedandcondensed.Inordertomaximizethecoverageareawithahighstabilityandrobustnessofeachsignalnode,multi-hopcommunicationwithlowpowerconsumptionispreferred.Furthermore,todealwiththelargenetworksize,thedesignedprotocolforalargescaleWSNmustbedistributed.
1.6ResearchIssues
Researchersareinterestedinvarious
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