无线传感器网络中英文对照外文翻译文献.docx

无线传感器网络中英文对照外文翻译文献.docx

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无线传感器网络中英文对照外文翻译文献

中英文对照外文翻译文献

（文档含英文原文和中文翻译）

原文：

Distributedlocalizationinwirelesssensornetworks:

aquantitativecomparison

ABSTRACT

Thispaperstudiestheproblemofdeterminingthenodelocationsinad-hocsensornetworks.Wecomparethreedistributedlocalizationalgorithms（Ad-hocpositioning,Robustpositioning,andN-hopmultilateration）onasinglesimulationplatform.Thealgorithmsshareacommon,three-phasestructure:

（1）determinenode–anchordistances,

（2）computenodepositions,and（3）optionallyrefinethepositionsthroughaniterativeprocedure.Wepresentadetailedanalysiscomparingthevariousalternativesforeachphase,aswellasahead-to-headcomparisonofthecompletealgorithms.Themainconclusionisthatnosinglealgorithmperformsbest;whichalgorithmistobepreferreddependsontheconditions（rangeerrors,connectivity,anchorfraction,etc.）.Ineachcase,however,thereissignificantroomforimprovingaccuracyand/orincreasingcoverage

1INTRODUCTION

Wirelesssensornetworksholdthepromiseofmanynewapplicationsintheareaofmonitoringandcontrol.Examplesincludetargettracking,intrusiondetection,wildlifehabitatmonitoring,climatecontrol,anddisastermanagement.Theunderlyingtechnologythatdrivestheemergenceofsensorapplicationsistherapiddevelopmentintheintegrationofdigitalcircuitry,whichwillbringussmall,cheap,autonomoussensornodesinthenearfuture.

Newtechnologyoffersnewopportunities,butitalsointroducesnewproblems.Thisisparticularlytrueforsensornetworkswherethecapabilitiesofindividualnodesareverylimited.Hence,collaborationbetweennodesisrequired,butenergyconservationisamajorconcern,whichimpliesthatcommunicationshouldbeminimized.Theseconflictingobjectivesrequireunorthodoxsolutionsformanysituations.

ArecentsurveybyAkyildizetal.discussesalonglistofopenresearchissuesthatmustbeaddressedbeforesensornetworkscanbecomewidelydeployed.Theproblemsrangefromthephysicallayer（low-powersensing,processing,andcommunicationhardware）allthewayuptotheapplicationlayer（queryanddatadisseminationprotocols）.Inthispaperweaddresstheissueoflocalizationinad-hocsensornetworks.Thatis,wewanttodeterminethelocationofindividualsensornodeswithoutrelyingonexternalinfrastructure（basestations,satellites,etc.）.

Thelocalizationproblemhasreceivedconsiderableattentioninthepast,asmanyapplicationsneedtoknowwhereobjectsorpersonsare,andhencevariouslocationserviceshavebeencreated.Undoubtedly,theGlobalPositioningSystem（GPS）isthemostwell-knownlocationserviceinusetoday.TheapproachtakenbyGPS,however,isunsuitableforlow-cost,ad-hocsensornetworkssinceGPSisbasedonextensiveinfrastructure（i.e.,satellites）.Likewisesolutionsdevelopedintheareaofroboticandubiquitouscomputingaregenerallynotapplicableforsensornetworksastheyrequiretoomuchprocessingpowerandenergy.

Recentlyanumberoflocalizationsystemshavebeenproposedspecificallyforsensornetworks.Weareinterestedintrulydistributedalgorithmsthatcanbeemployedonlarge-scalead-hocsensornetworks（100+nodes）.Suchalgorithmsshouldbe:

•self-organizing（i.e.,donotdependonglobalinfrastructure）,

•robust（i.e.,betoleranttonodefailuresandrangeerrors）,

•energyefficient（i.e.,requirelittlecomputationand,especially,communication）.

Theserequirementsimmediatelyruleoutsomeoftheproposedlocalizationalgorithmsforsensornetworks.Wecarriedoutathoroughsensitivityanalysisonthreealgorithmsthatdomeettheaboverequirementstodeterminehowwelltheyperformundervariousconditions.Inparticular,westudiedtheimpactofthefollowingparameters:

rangeerrors,connectivity（density）,andanchorfraction.Thesealgorithmsdifferintheirpositionaccuracy,networkcoverage,inducednetworktraffic,andprocessorload.Giventhe（slightly）differentdesignobjectivesforthethreealgorithms,itisnosurprisethateachalgorithmoutperformstheothersunderaspecificsetofconditions.Undereachcondition,however,eventhebestalgorithmleavesmuchroomforimprovingaccuracyand/orincreasingcoverage.

Themaincontributionsofourworkdescribedinthispaperare:

•weidentifyacommon,three-phase,structureinthedistributedlocalizationalgorithms.

•weidentifyagenericoptimizationapplicabletoallalgorithms.

•weprovideadetailedcomparisononasingle（simulation）platform.

•weshowthatthereisnoalgorithmthatperformsbest,andthatthereexistsroomforimprovementinmostcases.

Section2discussestheselection,genericstructure,andoperationofthreedistributedlocalizationalgorithmsforlarge-scalead-hocsensornetworks.Thesealgorithmsarecomparedonasimulationplatform,whichisdescribedinSection3.Section4presentsintermediateresultsfortheindividualphases,whileSection5providesadetailedoverallcomparisonandanin-depthsensitivityanalysis.Finally,wegiveconclusionsinSection6.

2LOCALIZATIONALGORITHMS

Beforediscussingdistributedlocalizationindetail,wefirstoutlinethecontextinwhichthesealgorithmshavetooperate.Afirstconsiderationisthattherequirementforsensornetworkstobeself-organizingimpliesthatthereisnofinecontrolovertheplacementofthesensornodeswhenthenetworkisinstalled（e.g.,whennodesaredroppedfromanairplane）.Consequently,weassumethatnodesarerandomlydistributedacrosstheenvironment.Forsimplicityandeaseofpresentationwelimittheenvironmentto2dimensions,butallalgorithmsarecapableofoperatingin3D.Fig.1showsanexamplenetworkwith25nodes;pairsofnodesthatcancommunicatedirectlyareconnectedbyanedge.Theconnectivityofthenodesinthenetwork（i.e.,theaveragenumberofneighbors）isanimportantparameterthathasastrongimpactontheaccuracyofmostlocalizationalgorithms（seeSections4and5）.Itcanbesetinitiallybyselectingaspecificnodedensity,andinsomecasesitcanbesetdynamicallybyadjustingthetransmitpoweroftheRFradioineachnode.

Insomeapplicationscenarios,nodesmaybemobile.Inthispaper,however,wefocusonstaticnetworks,wherenodesdonotmove,sincethisisalreadyachallengingconditionfordistributedlocalization.Weassumethatsomeanchornodeshaveaprioriknowledgeoftheirownpositionwithrespecttosomeglobalcoordinatesystem.Notethatanchornodeshavethesamecapabilities（processing,communication,energyconsumption,etc.）asallothersensornodeswithunknownpositions;wedonotconsiderapproachesbasedonanexternalinfrastructurewithspecializedbeaconnodes（accesspoints）asusedin,forexample,theGPS-lesslocationsystemandtheCricketlocationsystem.Ideallythefractionofanchornodesshouldbeaslowaspossibletominimizetheinstallationcosts,andoursimulationresultsshowthat,fortunately,mostalgorithmsareratherinsensitivetothenumberofanchorsinthenetwork.

Thefinalelementthatdefinesthecontextofdistributedlocalizationisthecapabilitytomeasurethedistancebetweendirectlyconnectednodesinthenetwork.FromacostperspectiveitisattractivetousetheRFradioformeasuringtherangebetweennodes,forexample,byobservingthesignalstrength.Experiencehasshown,however,thatthisapproachyieldspoordistanceestimates.Muchbetterresultsareobtainedbytime-of-flightmeasurements,particularlywhenacousticandRFsignalsarecombined;accuraciesofafewpercentofthetransmissionrangearereported.Oursimulationresultsprovideinsightintotheeffectoftheaccuracyofthedistancemeasurementsonthelocalizationalgorithms.

Itisimportanttorealizethatthemainthreecontextparameters（connectivity,anchorfraction,andrangeerrors）aredependent.Poorrangemeasurementscanbecompensatedforbyusingmanyanchorsand/orahighconnectivity.Thispaperprovidesinsightinthecomplexrelationbetweenconnectivity,anchorfraction,andrangeerrorsforanumberofdistributedlocalizationalgorithms.

2.1GENERICAPPROACH

Fromtheknownlocalizationalgorithmsspecificallyproposedforsensornetworks,weselectedthethreeapproachesthatmeetthebasicrequirementsforself-organization,robustness,andenergy-efficiency:

•Ad-hocpositioningbyNiculescuandNath,

•N-hopmultilaterationbySavvidesetal,and

•RobustpositioningbySavareseetal.

Theotherapproachesoftenincludeacentralprocessingelement,relyonanexternalinfrastructure,orinducetoomuchcommunication.Thethreeselectedalgorithmsarefullydistributedanduselocalbroadcastforcommunicationwithimmediateneighbors.Thislastfeatureallowsthemtobeexecutedbeforeanymultihoproutingisinplace,hence,theycansupportefficientlocation-basedroutingschemeslikeGAF.

Althoughthethreealgorithmsweredevelopedindependently,wefoundthattheyshareacommonstructure.Wewereabletoidentifythefollowinggeneric,three-phaseapproach1for

determiningtheindividualnodepositions：

1.Determinethedistancesbetweenunknownsandanchornodes.

2.Deriveforeachnodeapositionfromitsanchordistances.

3.Refinethenodepositionsusinginformationabouttherange（distance）to,andpositionsofneighboringnodes.

Theoriginaldescriptionsofthealgorithmspresentthefirsttwophasesasasingleentity,butwefoundthatseparatingthemprovidestwoadvantages.First,weobtainabetterunderstandingofthecombinedbehaviorbystudyingintermediateresults.Second,itbecomespossibletomix-and-matchalternativesforbothphasestotailorthelocalizationalgorithmtotheexternalconditions.Therefinementp