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Unit8WirelessSensorNetworkandIt'sApplication[137]
TextA
WirelessSensor
Network[148]
TextB
TheApplicationof
WirelessSensorNetwork[152]参考译文无线传感器网络
AWirelessSensorNetwork(WSN)consistsofspatiallydistributedautonomoussensorstomonitorphysicalorenvironmentalconditions,suchastemperature,sound,vibration,pressure,motionorpollutantsandtocooperativelypasstheirdatathroughthenetworktoamainlocation.WirelessSensorNetworkThemoremodernnetworksarebidirectional,alsoenablingcontrolofsensoractivity.Thedevelopmentofwirelesssensornetworkswasmotivatedbymilitaryapplicationssuchasbattlefieldsurveillance;todaysuchnetworksareusedinmanyindustrialandconsumerapplications,suchasindustrialprocessmonitoringandcontrol,machinehealthmonitoring,andsoon.
TheWSNisbuiltof"nodes"—fromafewtoseveralhundredsoreventhousands,whereeachnodeisconnectedtoone(orsometimesseveral)sensors.Eachsuchsensornetworknodehastypicallyseveralparts:aradiotransceiverwithaninternalantennaorconnectiontoanexternalantenna,amicrocontroller,anelectroniccircuitforinterfacingwiththesensorsandanenergysource,usuallyabatteryoranembeddedformofenergyharvesting.Asensornodemightvaryinsizefromthatofashoeboxdowntothesizeofagrainofdust.Thecostofsensornodesissimilarlyvariable,rangingfromafewtohundredsofdollars,dependingonthecomplexityoftheindividualsensornodes.Sizeandcostconstraintsonsensornodesresultincorrespondingconstraintsonresourcessuchasenergy,memory,computationalspeedandcommunicationsbandwidth.ThetopologyoftheWSNscanvaryfromasimplestarnetworktoanadvancedmultihopwirelessmeshnetwork.Thepropagationtechniquebetweenthehopsofthenetworkcanberoutingorflooding.
Incomputerscienceandtelecommunications,wirelesssensornetworksareanactiveresearchareawithnumerousworkshopsandconferencesarrangedeachyear.
1.Characteristics
ThemaincharacteristicsofaWSNinclude(SeeFigure8.1):
·Powerconsumptionconstrainsfornodesusingbatteriesorenergyharvesting;
·Abilitytocopewithnodefailures;
·Mobilityofnodes;
·Dynamicnetworktopology;
·Communicationfailures;
·Heterogeneityofnodes;
·Scalabilitytolargescaleofdeployment;
·Abilitytowithstandharshenvironmentalconditions;
·Easeofuse;
·Unattendedoperation;
·Powerconsumption.
Figure8.1Typicalmulti-hopwirelesssensornetworkarchitecture
Sensornodescanbeimaginedassmallcomputers,extremelybasicintermsoftheirinterfacesandtheircomponents.Theyusuallyconsistofaprocessingunitwithlimitedcomputationalpowerandlimitedmemory,sensorsorMEMS(includingspecificconditioningcircuitry),acommunicationdevice(usuallyradiotransceiversoralternativelyoptical),andapowersourceusuallyintheformofabattery.Otherpossibleinclusionsareenergyharvestingmodules,secondaryASICs,andpossiblysecondarycommunicationdevices(e.g.RS-232orUSB).
ThebasestationsareoneormorecomponentsoftheWSNwithmuchmorecomputational,energyandcommunicationresources.TheyactasagatewaybetweensensornodesandtheenduserastheytypicallyforwarddatafromtheWSNontoaserver.Otherspecialcomponentsinroutingbasednetworksarerouters,designedtocompute,calculateanddistributetheroutingtables.Manytechniquesareusedtoconnecttotheoutsideworldincludingmobilephonenetworks,satellitephones,radiomodems,long-rangeWiFilinksetc.ManybasestationsareARM-basedrunningaformofEmbeddedLinux.
2.Platforms
2.1StandardsandSpecifications
Severalstandardsarecurrentlyeitherratifiedorunderdevelopmentforwirelesssensornetworks.ThereareanumberofstandardizationbodiesinthefieldofWSNs.TheIEEEfocusesonthephysicalandMAClayers;theInternetEngineeringTaskForceworksonlayers3andabove.Inadditiontothese,bodiessuchastheInternationalSocietyofAutomationprovideverticalsolutions,coveringallprotocollayer.Finally,therearealsoseveralnon-standard,proprietarymechanismsandspecifications.
StandardsareusedfarlessinWSNsthaninothercomputingsystemswhichmakesmostsystemsincapableofdirectcommunicationbetweendifferentsystems.HoweverpredominantstandardscommonlyusedinWSNcommunicationsinclude:
·WirelessHART
·ISA100
·IEEE1451
·ZigBee/802.15.4
2.2Hardware
OnemajorchallengeinaWSNistoproducelowcostandtinysensornodes.ThereareanincreasingnumberofsmallcompaniesproducingWSNhardwareandthecommercialsituationcanbecomparedtohomecomputinginthe1970s.Manyofthenodesarestillintheresearchanddevelopmentstage,particularlytheirsoftware.Alsoinherenttosensornetworkadoptionistheuseverylowpowermethodsfordataacquisition.
2.3Software
EnergyisthescarcestresourceofWSNnodes,anditdeterminesthelifetimeofWSNs.WSNsaremeanttobedeployedinlargenumbersinvariousenvironments,includingremoteandhostileregions,whereadhoccommunicationsareakeycomponent.Forthisreason,algorithmsandprotocolsneedtoaddressthefollowingissues:
·Lifetimemaximization;
·Robustnessandfaulttolerance;
·Self-configuration.
SomeoftheimportanttopicsinWSNsoftwareresearchare:
·Operatingsystems;
·Security;
·Mobility;
·Usability—humaninterfacefordeploymentandmanagement,debuggingandend-usercontrol;
·Middleware—thedesignofmiddle-levelprimitivesbetweenhighlevelsoftwareandthesystems.
2.3.1Operatingsystems
Operatingsystemsforwirelesssensornetworkaretypicallylesscomplexthangeneral-purposeoperatingsystems.Theymorestronglyresembleembeddedsystems,fortworeasons.First,wirelesssensornetworksaretypicallydeployedwithaparticularapplicationinmind,ratherthanasageneralplatform.Second,aneedforlowcostsandlowpowerleadsmostwirelesssensornodestohavelow-powermicrocontrollersensuringthatmechanismssuchasvirtualmemoryareeitherunnecessaryortooexpensivetoimplement.
ItisthereforepossibletouseembeddedoperatingsystemssuchaseCosoruC/OSforsensornetworks.However,suchoperatingsystemsareoftendesignedwithreal-timeproperties.
TinyOSisperhapsthefirstoperatingsystemspecificallydesignedforwirelesssensornetworks.TinyOSisbasedonanevent-drivenprogrammingmodelinsteadofmultithreading.TinyOSprogramsarecomposedofeventhandlersandtaskswithrun-to-completionsemantics.Whenanexternaleventoccurs,suchasanincomingdatapacketorasensorreading,TinyOSsignalstheappropriateeventhandlertohandletheevent.EventhandlerscanposttasksthatarescheduledbytheTinyOSkernelsometimelater.
LiteOSisanewlydevelopedOSforwirelesssensornetworks,whichprovidesUNIX-likeabstractionandsupportfortheCprogramminglanguage.
3.SimulationofWSNs
Ingeneral,therearetwowaystodevelopsimulationsofWSNs.Eitheruseacustomplatformtodevelopthesimulation.Andthesecondoptionistodevelopone'sownsimulation.
3.1Simulators
Assuch,atpresentAgent-basedModelingandSimulationistheonlyparadigmwhichallowsthesimulationofevencomplexbehaviorintheenvironmentsofWirelesssensors(suchasflocking).
NetworkSimulatorslikeQualNet,NetSim,andNS2canbeusedtosimulateWirelessSensorNetwork.
3.2Agent-basedsimulationofWSN
Agent-basedsimulationofwirelesssensorandadhocnetworksisarelativelynewerparadigm.Agent-basedmodellingwasoriginallybasedonsocialsimulation.Arecentarticleonagent-basedsimulationpublishedintheIEEECommunicationsmagazinegivesexamplesandtutorialsonhowtodevelopcustomagent-basedsimulationmodelsforwirelesssensors,mobilerobotsandP2Pnetworksinashortperiodoftime(fewhours).Aformalagent-basedsimulationframeworkusingformalspecificationusingZnotationdemonstratingtheuseofagent-basedmodelingtorepresentsimulationofcomplexbehaviorintheenvironmentofsensorsisgivenin.Agent-basedsimulationhasalsobeenshowntobeusefulformodelingandsimulationforquantifyingemergentbehaviorinthevicinityofWSNnodes.
4.Otherconcepts
4.1Distributedsensornetwork
Ifacentralisedarchitectureisusedinasensornetworkandthecentralnodefails,thentheentirenetworkwillcollapse,howeverthereliabilityofthesensornetworkcanbeincreasedbyusingadistributedcontrolarchitecture.
DistributedcontrolisusedinWSNsforthefollowingreasons:
·Sensornodesarepronetofailure;
·Forbettercollectionofdata;
·Toprovidenodeswithbackupincaseoffailureofthecentralnode.
Thereisalsonocentralisedbodytoallocatetheresourcesandtheyhavetobeselforganised.
4.2Dataintegrationandsensorweb
Thedatagatheredfromwirelesssensornetworksisusuallysavedintheformofnumerical
datainacentralbasestation.Additionally,theOpenGeospatialConsortium(OGC)isspecifyingstandardsforinteroperabilityinterfacesandmetadataencodingsthatenablerealtimeintegrationofheterogeneoussensorwebsintotheInternet,allowinganyindividualtomonitororcontrolWirelessSensorNetworksthroughaWebBrowser.
4.3In-networkprocessing
Toreducecommunicationcostssomealgorithmsremoveorreducenodesredundantsensorinformationandavoidforwardingdatathatisofnouse.Asnodescaninspectthedatatheyforwardtheycanmeasureaveragesordirectionality,forexample,ofreadingsfromothernodes.
4.4Informationfusion
Inwirelesssensornetworks,informationfusion,alsocalleddatafusion,hasbeendevelopedforprocessingsensordatabyfiltering,aggregating,andmakinginferencesaboutthegathereddata.Informationfusiondealswiththecombinationofmultiplesourcestoobtainimprovedinformation:cheaper,greaterqualityorgreaterrelevance.Withinthewirelesssensornetworksdomain,simpleaggregationtechniquessuchasmaximum,minimum,andaverage,havebeendevelopedforreducingtheoveralldatatraffictosaveenergy.TextB
TheApplicationofWirelessSensorNetwork
1.Areamonitoring
AreamonitoringisacommonapplicationofWSNs.Inareamonitoring,theWSNis
deployedoveraregionwheresomephenomenonistobemonitored.Amilitaryexampleistheuseofsensorstodetectenemyintrusion;acivilianexampleisthegeo-fencingofgasoroilpipelines.
Whenthesensorsdetecttheeventbeingmonitored(heat,pressure),theeventisreportedtooneofthebasestations,whichthentakesappropriateaction(e.g.,sendamessageontheinternetortoasatellite).Similarly,wirelesssensornetworkscanusearangeofsensorstodetectthepresenceofvehiclesrangingfrommotorcyclestotraincars.
2.Environmentalsensing
ThetermEnvironmentalSensorNetworkshasevolvedtocovermanyapplicationsofWSNs
toearthscienceresearch.Thisincludessensingvolcanoes,oceans,glaciers,forests,etc.
3.Airpollutionmonitoring
Wirelesssensornetworkshavebeendeployedinseveralcitiestomonitortheconcentrationofdangerousgasesforcitizens.Thesecantakeadvantageofthead-hocwirelesslinksratherthanwiredinstallations,whichalsomakethemmoremobilefortestingreadingsindifferentareas.
4.Forestfiresdetection
AnetworkofSensorNodescanbeinstalledinaforesttodetectwhenafirehasstarted.Thenodescanbeequippedwithsensorstomeasuretemperature,humidityandgaseswhichareproducedbyfiresinthetreesorvegetation.Theearlydetectioniscrucialforasuccessfulactionofthefirefighters;thankstoWirelessSensorNetworks,thefirebrigadewillbeabletoknowwhenafireisstartedandhowitisspreading.
5.Greenhousemonitoring
Wirelesssensornetworksarealsousedtocontrolthetemperatureandhumiditylevelsinsidecommercialgreenhouses.Whenthetemperatureandhumiditydropsbelowspecificlevels,thegreenhousemanagermustbenotifiedviaE-mailorcellphonetextmessage,orhostsystemscantriggermistingsystems,openvents,turnonfans,orcontrolawidevarietyofsystemresponses.
6.Landslidedetection
Alandslidedetectionsystemmakesuseofawirelesssensornetworktodetecttheslightmovementsofsoilandchangesinvariousparametersthatmayoccurbeforeorduringalandslide.Andthroughthedatagathereditmaybepossibletoknowtheoccurrenceoflandslideslongbeforeitactuallyhappens.
7.Industrialmonitoring
7.1Machinehealthmonitoring
WSNshavebeendevelopedformachineryCondition-BasedMaintenance(CBM)asthey
offersignificantcostsavingsandenablenewfunctionalities.Inwiredsystems,theinstallationofenoughsensorsisoftenlimitedbythecostofwiring.Previouslyinaccessiblelocations,rotatingmachinery,hazardousorrestrictedareas,andmobileassetscannowbereachedwithwirelesssensors.
7.2Water/wastewatermonitoring
Therearemanyopportunitiesforusingwirelesssensornetworkswithinthewater/wastewaterindustries.FacilitiesnotwiredforpowerordatatransmissioncanbemonitoredusingindustrialwirelessI/Odevicesandsensorspoweredusingsolarpanelsorbatterypacksandalsousedinpollutioncontrolboard.
7.3Agriculture
UsingWSNswithintheagriculturalindustryisincreasinglycommon;usingawirelessnetworkfreesthefarmerfromthemaintenanceofwiringinadifficultenvironment.Gravityfeedwatersystemscanbemonitoredusingpressuretransmitterstomonitorwatertanklevels,pumpscanbecontrolledusingwirelessI/Odevicesandwaterusecanbemeasuredandwirelesslytransmittedbacktoacentralcontrolcenterforbilling.Irrigationautomationenablesmoreefficientwateruseandreduceswaste.
7.4Structuralmonitoring
Wirelesssensorscanbeusedtomonitorthemovementwithinbuildingsandinfrastructuresuchasbridges,flyovers,embankments,tunnels,etc.enablingengineeringpracticestomonitorassetsremotelywithouttheneedforcostlysitevisits,aswellashavingtheadvantageofdailydata,whereastraditionallythisdatawascollectedweeklyormonthly,usingphysicalsitevisits,involvingeitherroadorrailclosureinsomecases.Itisalsofarmoreaccuratethananyvisualinspectionthatwouldbecarriedout.
一个无线传感器网络(WSN)由分布在不同空间的自治传感器组成,以便监控物质或环境条件,如温度、声音、振动、压力、运动或污染物质,并且协作地把数据传输到主要地点。更现代的网络是双向的,其也能控制传感器的行为。曾经,无线传感器网络的发展是由军事应用推动的,如战场监控。今天,这些网络已经用于许多工业领域和消费领域,如工业过程的监控、机器的健康监控等。无线传感器网络无线传感器网络由许多“节点”构成—从几个节点到几百节点甚至几千节点,每个节点都连接着一个(或有时数个)传感器。这样的传感器网络节点通常包含以下几部分:一个带有内置天线或可连接外部天线的无线电收发器、一个微型控制器、一个连接传感器和电源的电路、常用电池或内嵌的能量采集器。传感器节点的大小各异,从鞋盒大小到尘粒大小不等。传感器节点的成本也有多种,从几美元到几百美元不等,这取决于每个节点的复杂性。传感器节点的大小和成本决定其资源,如能量、内存、计算速度和通信带宽。无线传感器网络的拓扑也有多种,从简单的星型网络到高级的多跳跃无线掩膜网络。网络跳跃之间的传播技术在迅速发展。在计算机科学和电信学中,无线传感器网络是众多研究机构积极研究的领域,也是每年会议的热点。
1.特点
无线传感器网络的主要特点包括:
能够对节点所用电池或能量采集器的能源消耗进行约束;
能够应付节点失效;
节点可迁移;
动态的网络拓扑;
(可处理)通信故障;
大规模部署的可测量性;
能经受严酷环境的考验;
易用;
自主运行;
能源消耗(即节能)。
可以把传感器节点想像成小型计算机,其接口和部件非常简单。它们通常由以下几部分组成:计算能力有限的处理器和有限的内存、传感器或MEMS(包括特定条件的电路)、通信设备(通常是无线电收发器或光收发器)以及一般为电池形式的电源,还可能包括能源采集模块、辅助的ASIC以及辅助的通信设备(如RS-323或USB)。基站带有一个或多个WSN部件,还带有许多可计算的、有能量的及通信的资源。它们通常把WSN上的数据转发到服务器,起传感器节点与终端用户之间的网关的作用。路由网络的其他特殊部件是路由器,是为计算、规划以及分配路由表而设计的。用于外部连接的技术有很多,包括手机网络、卫星电话、无线电调制解调器、远程WiFi链接等。许多基站基于ARM并运行于嵌入式Linux系统中。
2.平台
2.1标准和规范
用于无线传感器网络的几个流行标准要么已经认可,要么正在开发中。在WSN领域有许多标准化团体。IEEE关注物理和MAC层。互联网工程任务组从事第三层及以上的标准研究。除此之外,像美国国际自动化协会这样的团体提供垂直解决方案,覆盖了全部协议层。当然,还有几种非标准的、专有机制和规范。用于WSN的标准比用于其他计算系统的少得多,这些标准使得大多数系统不能够在不同系统之间直接通信。WSN通信中常用的标准包括:
WirelessHART
ISA100
IEEE1451
ZigBee/802.15.4
2.2硬件
WSN中的一个主要挑战是生产低成本和微小的传感器节点。生产WSN硬件的小公司数量不断增加,商业境况与上世纪七十年代的家庭计算相仿。许多节点仍然处于研发阶段,其相关软件的研发更明显。同样,传
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