《物联网专业英语教程》课件第8章

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