搜索
DataCollectioninVehicularNetworksIsmailSalhi,MohamedCherif,andSidiMohammedSenouciOrangeLabs,2AvenuePierreMarzin,22307,LannionCedex,FranceVehicularSensorsNetworks(VSNs)areanemergingparadigminvehicularnetworks.Thisnewtechnologyusesdifferentkindofsensingdevicesavailableinnewvehicles,togatherinformationaboutthedriver’senvironment(speed,acceleration,temperature,seatsoccupations,etc.)inordertoprovideasafer,moreefficientandmorecomfortabledrivingexperience.Inthispaper,wefocusonaparticularVSNarchitecture,wheretheadhocnetworkisoperatedbyatelecommunication/serviceprovider(WiMaxaccesspoint,2.5/3Gbasestation)tocombinenon-valuableindividualsenseddataandextractfromthemeffectivefeedbacksaboutthesituationoftheroadinageographicalarea(trafficdensity,unusualtrafficbehaviour,etc.).InoperatedVSNs,providerstendtoreducethetrafficloadontheirnetwork,usingthefree-frequencycommunicationmedium(IEEE802.11p,forexample).Todoso,weproposeCGP(ClusteredGatheringProtocol),acrosslayerprotocolbasedonhierarchicalandgeographicaldatacollection,aggregationanddisseminationmechanisms.Weanalyzetheperformancesofoursolutionusingasimulationenvironmentandrealisticmobilitymodels.WedemonstratethefeasibilityofsuchsolutionandshowthatCGPofferstheoperatorpreciousinformationwithoutoverloadinghisnetwork.IndexTerms—VSN,VANET,dissemination,ITS,datacollection,dataaggregation,hybridarchitecture,operatednetwork.I.INTRODUCTIONVERTHELASTDECADE,thenatureofwirelesscommunicationshasevolvedrapidly.Theintroductionof3GandWLANtechnologiesandtherecentstandardisationofWiMaxhavehelpedtorealisethevisionofubiquitousconnectivity.Currently,muchresearcheffortisfocusingonexploitingthisalways-onfeatureforuseinTransportationSystems.TheprimaryobjectiveofITS(IntelligentTransportationSystems)istoimprovetrafficsafety,efficiency,andtravellingcomfort.Inthiswork,wefocusonthemaincomponentinIntelligentTransportationSystems,whichisvehicularcommunication.Indeed,manycarmanufacturersareinstallingwirelessconnectivityequipmentsintheirvehiclestoenablecommunicationbetweenvehiclesandalsowiththeinfrastructure.VehicularSensorNetworks(VSNs)canbebuiltontopofthesevehicularnetworksbyequippingvehicleswithonboardsensingdevices.Insuchcase,sensorscangatherasetofinformationlikevideodata,speed,localisation,acceleration,temperature,seatoccupation,etc.Comparedtotraditionalsensornetworks,thisrecentlyemergedsensornetworkisnotrestrictedbythepowersupplyandthestoragespace.However,thetypicalscaleofaVSNoverwidegeographicareas(e.g.,millionsofnodes),thevolumeofgenerateddata(e.g.,streamingdata),andmobilityofvehiclesmakeitinfeasibletoadopttraditionalsensornetworksolutionswheresenseddatatendstobesystematicallydeliveredtosinksusingdata-centricprotocolssuchasDirectedDiffusion[1].Undersuchenvironment,aneffectiveandefficientarchitecturefordatacollectionanddataexchangeismoreimportant.Thisworkdealswithsuchasystemframeworkconsistingofmobilevehicularsensorsandroad-side-unitsoperatedbyanoperatororaserviceprovider(WiMaxaccesspoint,2.5/3Gbasestation).Road-side-unitsaredistributedovertheroadforcollectingdatafrommobilevehicularsensorspassingby.Whilemobilesensorsonvehiclessenseandsendtheinformationtoroadsideunits.Inourstudy,theVSNwillbeusedbyaninfrastructurewirelessnetworkowner(telecomorInternetprovider,forexample)togatheruselessindividualinformation(thatcannotbeusedtodeduceaglobalviewoftheroadtraffic)fromeachvehicleandtoaggregatetheminsideanadhocwirelessnetworkusingfreefrequency(IEEE802.11,forexample),togetaglobalviewofthestateoftheroadinageographicalareaataspecifictime,ortousetheseinformationasadatabaseforaposteriortreatment(seefigure1).Figure1–OperatedvehicularsensorsnetworkInourstudy,theVSNwillbeusedtocollectindividualinformationfromeachvehicleandaggregatetheminsidetheadhocwirelessnetwork(freefrequency).Theaggregatedinformationwillbesenttotheroadsideunitownedbytheoperatorviaanon-freefrequency(WiMaxor2.5/3G).Infact,thesesensorscangeneratemassiveamountsofsenseddataandthereisaneedtocollect,store,andretrievethem.Theobjectiveinsucharchitecturesforanoperator/serviceprovideristoreducetheuseofitshigh-costlinks.Todoso,wepresentCGP(ClusteredGatheringProtocol):across-layeredprotocolbasedonhierarchicalandgeographicaldatagathering,aggregationanddissemination.ThegoalofCGPistogatherdatafromallnodesinthevehicularadhocnetworkinordertoofferdifferentkindofITSservices.Forexample,atelecommunication/serviceprovidercanuseCGPtoprovide:-Areal-timetrafficinformationservice,bygatheringallOnode’spositionsandvelocities,[2]-Ageographicallocalizationserviceforcustomerswhowanttofollowtheirvehiclesmobility(fleetmanagement),-Aparkinglotsavailabilityservice,bydetectingemptyspacesinparkinglots,[3]-Warningsmessagesinaspecificarea,whenanunusualeventhappens(asuddenspeeddecreaseofseveralvehicles,forexample),[4]-Areal-timefuelconsumptionandpollutionindicators,[5]-Surveillanceapplicationssuchasproposedin[2]wherenodesmakevideosoftheroadanddetectandsavetheregistrationplatesofvehiclesaround.Therestofthispaperisorganizedasfollows.SectionIIpresentsvehicularsensornetworkspropertiesandther