WhitePaper

?

InternetofThings:WirelessSensorNetworks

PAGE

3

Executivesummary

Today,smartgrid,smarthomes,smartwaternetworks,intelligenttransportation,areinfrastruc-turesystemsthatconnectourworldmorethanweeverthoughtpossible.Thecommonvisionofsuchsystemsisusuallyassociatedwithonesinglecon-cept,theinternetofthings(IoT),wherethroughtheuseofsensors,theentirephysicalinfrastructureiscloselycoupledwithinformationandcommunica-tiontechnologies;whereintelligentmonitoringandmanagementcanbeachievedviatheusageofnet-workedembeddeddevices.Insuchasophisticat-eddynamicsystem,devicesareinterconnectedtotransmitusefulmeasurementinformationandcon-trolinstructionsviadistributedsensornetworks.

Awirelesssensornetwork(WSN)isanetworkformedbyalargenumberofsensornodeswhereeachnodeisequippedwithasensortodetectphysicalphenomenasuchaslight,heat,pressure,etc.WSNsareregardedasarevolutionaryinformationgatheringmethodtobuildtheinformationandcommunicationsystemwhichwillgreatlyimprovethereliabilityandefficiencyofinfrastructuresystems.Comparedwiththewiredsolution,WSNsfeatureeasierdeploymentandbetterflexibilityofdevices.Withtherapidtechnologicaldevelopmentofsensors,WSNswillbecomethekeytechnologyforIoT.

InthisWhitePaperwediscusstheuseandevolutionofWSNswithinthewidercontextofIoT,andprovideareviewofWSNapplications,whilealsofocusingtheattentiononinfrastructuretechnologies,applicationsandstandardsfeaturedinWSNdesigns.ThisWhitePaperisthesixthinaserieswhosepurposeistoensurethattheIECcancontinuetocontributewithitsInternationalStandardsandConformityAssessmentservicestosolveglobalproblemsinelectrotechnology.

Section2startswiththehistoricalbackgroundofIoTandWSNs,thenprovidesanexamplefromthepowerindustrywhichisnowundergoingpowergridupgrading.WSNtechnologiesareplayinganimportantroleinsafetymonitoringoverpowertransmissionandtransformationequipmentandthedeploymentofbillionsofsmartmeters.

Section3assessesthetechnologyandcharac-teristicsofWSNsandtheworldwideapplicationneedsforthem,includingdataaggregationandsecurity.

Section4addressesthechallengesandfuturetrendsofWSNsinawiderangeofapplicationsinvariousdomains,includingultralargesensingdeviceaccess,trustsecurityandprivacy,andservicearchitecturestonameafew.

Section5providesinformationonapplications.ThevarietyofpossibleapplicationsofWSNstotherealworldispracticallyunlimited.Ononehand,WSNsenablenewapplicationsandthusnewpossiblemarkets;ontheotherhand,thedesignisaffectedbyseveralconstraintsthatcallfornewparadigms.ThissectionoutlinesWSNusesforthesmartgrid,smartwater,intelligenttransportationsystems,andsmarthomedomains.

Section6offersanalysisofstandardizationbeingamajorprerequisiteinachievingtheinteroperabilityofWSNs,notonlybetweenproductsofdifferentvendors,butalsobetweendifferentsolutions,applicationsanddomains.

Section7concludeswithanumberofkeyrecommendationsforindustry,regulators,theIEC,andgeneralobservationsonWSNsecurityanddatatopics.

Executivesummary

Acknowledgments

ThisWhitePaperhasbeenpreparedbytheWirelessSensorNetworksprojectteam,intheIECMarketStrategyBoard.Theprojectteamincludes:

Dr.ShuYinbiao,ProjectLeader,MSBMember,SGCC

Dr.KangLee,ProjectPartner,NISTMr.PeterLanctot,IEC

Dr.FanJianbin,SGCCDr.HuHao,SGCC

Dr.BruceChow,CorningIncorporated

Mr.Jean-PierreDesbenoit,SchneiderElectricMr.GuidoStephan,Siemens

Mr.LiHui,Siemens

Mr.XueGuodong,HaierMr.SimonChen,SAPMr.DanielFaulk,SAPMr.TomasKaiser,SAPMr.HirokiSatoh,Hitachi

Prof.OuyangJinsong,ITEIChinaMr.WangLinkun,ITEIChina

Ms.WangShou,ITEIChina

Dr.ZhenYan,NariGroupCorporationDr.SunJunping,China-EPRI

Prof.YuHaibin,SIADr.ZengPeng,SIADr.LiDong,SIA

Dr.WangQin,UniversityofScienceandTechnology,Beijing

Tableofcontents

Listofabbreviations 9

Glossary 12

Section1 Introduction 13

Overview 13

ScopeofthisWhitePaper 14

Section2 HistoryandindustrialdriversofWSNs 15

Section3 WSNtechnology 19

CharacteristicfeaturesofWSNs 19

Sensornodes 20

MiniaturizationtechnologyofsensorbasedonMEMS 20

Ambientenergyharvestingtechnology 21

Accessnetworktechnologies 22

Topology 24

Self-organizingandreliablenetworkingtechnology 25

LowcostIPinterconnectiontechnology 25

Self-adaptiveflowcontroltechnology 27

Dataaggregation 28

Security 29

Trust,securityandprivacy 29

Cryptoalgorithms 30

KeymanagementofWSNs 31

SecureroutingofWSNs 31

SecuredataaggregationofWSNs 32

Section4 ChallengesofWSNs 33

Systemqualities,architecturedivergence,andtheneedforanarchitectureframework 33

Ultra-largesensingdeviceaccess 35

Massiveheterogeneousdataprocessing 35

Intelligentcontrolandservicestodynamicchanges 35

Sensornetworkarchitecture 36

Highconcurrentaccess 36

Highconcurrentaccesswithfrequencydivisionmultiplexing 37

Highconcurrentaccesswithdistributedantennasystems 37

Highreal-timetransmission 37

Distributedsolution 38

Centralizedsolution 38

Semanticrepresentationandprocessing 40

MoresecureWSNs 40

Protocolsecurityframework 41

Trust,securityandprivacy 41

Section5 WSNapplicationsintheinfrastructuresystems 43

WSNapplicationinthesmartgrid 43

Onlinemonitoringsystemfortransmissionlines 43

Intelligentmonitoringandearlywarningsystemforsubstations 44

Onlinemonitoringandearlywarningsystemfordistributionnetworks 46

Smartelectricityconsumptionservices 47

WSNapplicationinsmartwaternetworks 48

Sustainability(waterresourcefocus) 48

WSNapplicationinintelligenttransportation 50

Sensingoftrafficflows 50

Citylogistics 51

On-boardWSNs 51

WSNintrafficinfrastructures 52

WSNapplicationinsmarthomes 52

Theenergychallenge 52

Energyefficiencyinbuildings–Casestudy 53

Activecontrolinbuildings 54

WSNsarekeyforimprovingtheenergyefficientperformancesofexistingbuildings 55

AdditionalapplicationbenefitsofWSN 57

Improveenergyefficiency 57

Contributetoenvironmentalmonitoring 57

Enhancesocialservices 57

Section6 StandardsofWSNsandsystems 59

General 59

Presentstatus 59

Standardizationneedsandoutlook 67

Challengesandfuturestandardizationneeds 68

Section7 Conclusionsandrecommendations 69

Generalrecommendations 69

RecommendationsaddressedtotheIECanditscommittees 70

AnnexA Accesstechnologies 71

Developingtrendofaccesstechnologies 71

Bluetooth4.0 71

IEEE802.15.4e 72

WLANIEEE802.11? 73

References 75

9

Listofabbreviations

Technicaland

ABS

anti-lockbrakingsystem

AMI

advancedmeteringinfrastructure

CAPEX

capitalexpenditure

CoAP

constrainedapplicationprotocol

COSEM

companionspecificationforenergymetering

CPU

controlprocessingunit

DLMS

devicelanguagemessagespecification

DSN

distributedsensornetwork

ESC

electronicstabilitycontrol

FCD

floatingcardata

FDM

frequency-divisionmultiplexing

FH

frequencyhopping

GHG

greenhousegases

GPS

globalpositioningsystem

ICT

informationandcommunicationtechnologies

IoT

internetofthings

KPI

keyperformanceindicator

M2M

machinetomachine

MAC

mediaaccesscontrol

MEMS

microelectromechanicalsystems

MIMO

multiple-inputmultiple-output

OEM

originalequipmentmanufacturer

OFDM

orthogonalfrequency-divisionmultiplexing

OPEX

operationalexpenditure

PHY

physicallayer

PV

photovoltaic

QoS

qualityofservice

RES

renewableenergysource

scientificterms

Listofabbreviations

RFID radio-frequencyidentification

SOA serviceorientedarchitecture

SOAP serviceorientedarchitectureprotocol

TDMA timedivisionmultipleaccess

TSMP timesynchronizedmeshprotocol

TSP trust,securityandprivacy

UCC urbanconsolidationcentre

USN ubiquitoussensornetwork

WIA-FA wirelessnetworksforindustrialautomation–factoryautomationWIA-PA wirelessnetworksforindustrialautomation–processautomationWISA wirelessinterfaceforsensorsandactuators

WLAN wirelesslocalareanetwork

WMAN wirelessmetropolitanareanetworkWPAN wirelesspersonalareanetworkWSN wirelesssensornetwork

WWAN wirelesswideareanetwork

XFCD extendedfloatingcardata

Organizations,institutionsandcompanies

ABB ABBGroup

ARPANET AdvancedResearchProjectsAgencyNetwork

BBF BroadbandForum

CAB ConformityAssessmentBoard(oftheIEC)

China-EPRIChinaElectricPowerResearchInstitute

DARPA DefenseAdvancedResearchProjectsAgency(USA)

ETSI EuropeanTelecommunicationsStandardsInstitute

IEC InternationalElectrotechnicalCommission

IEEE InstituteofElectricalandElectronicsEngineers

IETF InternetEngineeringTaskForce

ISO InternationalOrganizationforStandardization

ITEI InstrumentationTechnologyandEconomyInstitute(China)

Listofabbreviations

PAGE

11

ITU-T

InternationalTelecommunicationUnion–

TelecommunicationStandardizationSector

MSB

MarketStrategyBoard(oftheIEC)

NIST

NationalInstituteofStandardsandTechnology

OGC

OpenGeospatialConsortium

OMA

OpenMobileAlliance

SGCC

StateGridCorporationofChina

SIA

ShenyangInstituteofAutomation(China)

SMB

StandardizationManagementBoard(oftheIEC)

UCB

UniversityofCaliforniaBerkeley(USA)

W3C

WorldWideWebConsortium

PAGE

12

Glossary

internetofthingsIoT

referstotheinterconnectionofuniquelyidentifiableembeddedcomputing-likedeviceswithintheexistinginternetinfrastructure

mediaaccesscontrollayerMAClayer

partofthedatalinkprotocolthatcontrolsaccesstothephysicaltransmissionmediuminIEEE802networks(LANs)

systemonachipSoC

integratedcircuit(IC)thatintegratesallcomponentsofacomputerorotherelectronicsystemintoasinglechip

timesynchronizedmeshprotocolTSMP

anetworkingprotocolthatformsthefoundationofreliable,ultralow-powerwirelesssensornetworking

wirelesslocalareanetworkWLAN

localareanetworkinwhichdataaretransferredwithouttheuseofwires

wirelessmetropolitanareanetworkWMAN

alsoknownasawirelesslocalloop(WLL).WMANsarebasedontheIEEE802.16standard.Wirelesslocalloopcanreacheffectivetransferspeedsof1to10Mbpswithinarangeof4to10kilometres

wirelesspersonalareanetworkWPAN

alow-rangewirelessnetworkwhichcoversanareaofonlyafewdozenmetres

wirelesssensornetworkWSN

self-organizing,multi-hopnetworksofwirelesssensornodesusedtomonitorandcontrolphysicalphenomena

wirelesswideareanetworkWWAN

wirelessnetworkthatprovidescommunicationservicestoageographicarealargerthanasingleurbanarea.Themostcommonofallwirelessnetworks

Section1

Introduction

Overview

Todaysensorsareeverywhere.Wetakeitforgranted,buttherearesensorsinourvehicles,inoursmartphones,infactoriescontrollingCO2emissions,andeveninthegroundmonitoringsoilconditionsinvineyards.Whileitseemsthatsensorshavebeenaroundforawhile,researchonwirelesssensornetworks(WSNs)startedbackinthe1980s,anditisonlysince2001thatWSNsgeneratedanincreasedinterestfromindustrialandresearchperspectives.Thisisduetotheavailabilityofinexpensive,lowpoweredminiaturecomponentslikeprocessors,radiosandsensorsthatwereoftenintegratedonasinglechip(systemonachip(SoC)).

Theideaofinternetofthings(IoT)wasdevelopedinparalleltoWSNs.TheterminternetofthingswasdevisedbyKevinAshtonin1999[1]andreferstouniquelyidentifiableobjectsandtheirvirtualrepresentationsinan“internet-like”structure.Theseobjectscanbeanythingfromlargebuildings,industrialplants,planes,cars,machines,anykindofgoods,specificpartsofalargersystemtohumanbeings,animalsandplantsandevenspecificbodypartsofthem.

WhileIoTdoesnotassumeaspecificcommuni-cationtechnology,wirelesscommunicationtech-nologieswillplayamajorrole,andinparticular,WSNswillproliferatemanyapplicationsandmanyindustries.Thesmall,rugged,inexpensiveandlowpoweredWSNsensorswillbringtheIoTtoeventhesmallestobjectsinstalledinanykindofenvi-ronment,atreasonablecosts.IntegrationoftheseobjectsintoIoTwillbeamajorevolutionofWSNs.

AWSNcangenerallybedescribedasanetworkofnodesthatcooperativelysenseandmaycontroltheenvironment,enablinginteractionbetweenpersonsorcomputersandthesurroundingenvironment[2].Infact,theactivityofsensing,processing,andcommunicationwithalimitedamountofenergy,ignitesacross-layerdesignapproachtypicallyrequiringthejointconsiderationofdistributedsignal/dataprocessing,mediumaccesscontrol,andcommunicationprotocols[3].

ThroughsynthesizingexistingWSNapplicationsaspartoftheinfrastructuresystem,potentialnewapplicationscanbeidentifiedanddevelopedtomeetfuturetechnologyandmarkettrends.ForinstanceWSNtechnologyapplicationsforsmartgrid,smartwater,intelligenttransportationsystems,andsmarthomegeneratehugeamountsofdata,andthisdatacanservemanypurposes.

Additionally,asthemodernworldshiftstothisnewageofWSNsintheIoT,therewillbeanumberoflegalimplicationsthatwillhavetobeclarifiedovertime.Oneofthemostpressingissuesistheownershipanduseofthedatathatiscollected,consolidated,correlatedandminedforadditionalvalue.Databrokerswillhaveaflourishingbusinessasthepoolingofinformationfromvarioussourceswillleadtonewandunknownbusinessopportu-nitiesandpotentiallegalliabilities.TherecentUSNationalSecurityAdministrationscandalandotherindignitieshaveshownthatthereiswideinterestingatheringdataforvarieduses.

Oneofthemorecomplexissueswhicharisewithinthisnewworldisthethoughtofmachinesmakingautonomousdecisions,withunknownimpactontheenvironmentorsocietywithinwhich

Introduction

itfunctions.Thiscanbeassimpleasarefrigeratorrequestingreplenishmentformilkandbutteratthelocalstoreforitsowner,orascomplexasarobotthathasbeenprogrammedtosurviveinaharshenvironmentthatoriginallydidnotforeseehumaninteraction.Itcanalsobeassimpleasavehiclethatrecordsitsusage,asdoestheblackboxintheaerospaceindustry,butthennotonlyusingtheinformationtounderstandthecauseofanaccident,butalsotoprovideevidenceagainsttheownerandoperator.Forexample,amachinethatnotifieslegalauthoritiesifitwasusedagainstthelaw.

Itcomestothepointwhereamachinestartsactingasifitwerealegalentity.Thequestionofliabilitystartstogetfuzzyandtheliabilityquestionforthe“owner”and“operator”ofthemachinegetsmoredifficulttoarticulateifthereislittletonorealhumaninterventionintheactionsofthemachineorrobot.Thisiscertainlytheworstcasescenario,butthequestionishowtobalancethecostofpotentialliabilitieswiththebenefitsofIoTsolutions?Thisquicklystartstobecomemoreofasocietalorethical,andmoraldiscussion.Thatiswhatweusuallyrefertoasgenerationalshiftsinvalues–buttheIoTtrendwillnotwaitageneration.

ScopeofthisWhitePaper

ThisWhitePaperisthesixthinaserieswhosepurposeistoensurethattheIECcancontinuetocontributethroughitsInternationalStandardsandConformityAssessmentservicessolvingglobalproblemsinelectrotechnology.TheWhitePapersaredevelopedbytheIECMSB(MarketStrategyBoard),responsibleforanalyzingandunderstandingtheIEC’smarketsoastopreparetheIECtostrategicallyfacethefuture.

Section2

HistoryandindustrialdriversofWSNs

ThedevelopmentofWSNswasinspiredbymilitaryapplications,notablysurveillanceinconflictzones.Today,theyconsistofdistributedindependentdevicesthatusesensorstomonitorthephysicalconditionswiththeirapplicationsextendedtoindustrialinfrastructure,automation,health,traffic,andmanyconsumerareas.

ResearchonWSNsdatesbacktotheearly1980swhentheUnitedStatesDefenseAdvancedResearchProjectsAgency(DARPA)carriedoutthedistributedsensornetworks(DSNs)programmefortheUSmilitary.Atthattime,theAdvancedResearchProjectsAgencyNetwork(ARPANET)hadbeeninoperationforanumberofyears,withabout200hostsatuniversitiesandresearchinstitutes[4].DSNswereassumedtohavemanyspatiallydistributedlow-costsensingnodes,collaboratingwitheachotherbutoperatedautonomously,withinformationbeingroutedtowhichevernodethatcanbestusetheinformation.EventhoughearlyresearchersonsensornetworkshadthevisionofaDSNinmind,thetechnologywasnotquiteready.Morespecifically,thesensorswereratherlarge(i.e.thesizeofashoeboxandbigger),andthenumberofpotentialapplicationswasthuslimited.Furthermore,theearliestDSNswerenottightlyassociatedwithwirelessconnectivity.

Recentadvancesincomputing,communicationandmicro-electromechanicaltechnologyhaveresultedinasignificantshiftinWSNresearchandbroughtitclosertotheoriginalvision.ThenewwaveofresearchonWSNsstartedaround1998andhasbeenattractingmoreandmoreattentionandinternationalinvolvement.Thenewwaveofsensornetworkresearchputsitsfocusonnetworkingtechnologyandnetworkedinformationprocessing

suitableforhighlydynamicadhocenvironmentsandresource-constrainedsensornodes.Further-more,thesensornodeshavebeenmuchsmallerinsize(i.e.fromthatofapackofcardstodustparticle)andmuchcheaperinprice,andthusmanynewcivilianapplicationsofsensornetworkssuchasenvironmentmonitoring,vehicularsensornetworkandbodysensornetworkshaveemerged.

Again,DARPAactedasapioneerinthenewwaveofsensornetworkresearchbylaunchinganinitiativeresearchprogrammecalledSensIT[5]whichprovidedthepresentsensornetworkswithnewcapabilitiessuchasadhocnetworking,dynamicqueryingandtasking,reprogrammingandmulti-tasking.Currently,WSNshavebeenviewedasoneofthemostimportanttechnologiesforthe21stcentury[6].ChinaforexamplehasincludedWSNsintheirnationalstrategicresearchprogrammes[7].Asaresult,thecommercializationofWSNsisacceleratingandmanynewtechnologycompaniesareemergingsuchasCrossbowTechnology(connectingthephysicalworldtothedigitalworld)andDustNetworks.

Today,industrialautomationisoneofthemostimportantareasofWSNapplications.AccordingtoFreedoniaGroup,theglobalmarketshareofsensorsforindustrialuseis11billionUSD,whilethecostofinstallation(mainlycablingcosts)andusageisuptomorethan100billionUSD.Thishighcostisthemainissuehinderingthedevelopmentofindustrialcommunicationtechnology.WSNtechnology,allowing“ubiquitoussensing”overthewholeindustrialprocess,cansecuretheimportantparameterswhicharenotavailablebyonlinemonitoringduetothecostreasonsstatedabove.Theseparametersareimportantfoundationsfor

HistoryandindustrialdriversofWSNs

PAGE

16

theimplementationofoptimalcontrolinordertoachievetheobjectiveofimprovingproductquality,andreducingenergyconsumption.

AccordingtoONWorld[8],wirelessdevicestobeinstalledinindustrialfieldswillincreaseby553%between2011and2016whentherewillbe24millionwireless-enabledsensorsandactuators,orsensingpoints,deployedworldwide.Amongthese,39%willbeusedfornewapplicationsthatareonlypossiblewithwirelesssensornetworking.By2014,thenumberofWSNdeviceswillaccountfor15%oftheentireindustrialmeasurementandcontrolequipmentsensingpoints,and33%by2016.

Intoday’smarket,three-fourthsoftheindustrialWSNincomecomesfromtheprocessindustry;withtheoilandpowerindustrybeingthefastestgrowingones.Forexample,PetroChinaiscarryingoutIoTprojectsinitsoilfields,withthepurposetoreconstruct200000oilwells.WSNtechnologyappliedinthedigitalconversionsoftheoilwellswillmakeuseofonlinemonitoringtomeasureoilwellproductionandensureproductionsafety.

Inthepowerindustrywhichisnowundergoingthepowergridupgrading,WSNtechnologyisalsoplayinganimportantroleinsafetymonitoringoverpowertransmissionandtransformationequipmentandthereconstructionofbillionsofsmartmeters.

Figure2-1|Globalinstalledindustrialwirelesssensingpoints[8]

HistoryandindustrialdriversofWSNs

PAGE

17

Figure2-2|Globalindustrialfieldinstrumentshipments,wiredandwireless[8]

In-plantprocessOilandgas

PowertransmissionVerticalmarketsFactoryautomation

$7500

$5000

$2500

$

$Millions

2011 2012 2013 2014 2015 2016

Source:ONWorld

Figure2-3|WSNrevenuegrowthinallindustries[8]

PAGE

19

Section3

WSNtechnology

CharacteristicfeaturesofWSNs

AWSNcangenerallybedescribedasanetworkofnodesthatcooperativelysenseandcontroltheenvironment,enablinginteractionbetweenpersonsorcomputersandthesurroundingenvironment[2].WSNsnowadaysusuallyincludesensornodes,actuatornodes,gatewaysandclients.Alargenumberofsensornodesdeployedrandomlyinsideofornearthemonitoringarea(sensorfield),formnetworksthroughself-organization.Sensornodesmonitorthecollecteddatatotransmitalongtoothersensornodesbyhopping.Duringtheprocessoftransmission,monitoreddatamaybehandledbymultiplenodestogettogatewaynodeaftermulti-

hoprouting,andfinallyreachthemanagementnodethroughtheinternetorsatellite.ItistheuserwhoconfiguresandmanagestheWSNwiththemanagementnode,publishmonitoringmissionsandcollectionofthemonitoreddata.

Asrelatedtechnologiesmature,thecostofWSNequipmenthasdroppeddramatically,andtheirapplicationsaregraduallyexpandingfromthemilitaryareastoindustrialandcommercialfields.Meanwhile,standardsforWSNtechnologyhavebeenwelldeveloped,suchasZigbee?1,

1Zigbee?isanexampleofasuitableproductavailablecommercially.ThisinformationisgivenfortheconvenienceofusersofthisstandardanddoesnotconstituteanendorsementbyIECofthisproduct.

Figure3-1|Wirelesssensornetworks

WSNtechnology

PAGE

20

Figure3-2|MarketsizeofWSNapplications[9]

WirelessHart,ISA100.11a,wirelessnetworksforindustrialautomation–processautomation(WIA-PA),etc.Moreover,withnewapplicationmodesofWSNemerginginindustrialautomationandhomeapplications,thetotalmarketsizeofWSNapplicationswillcontinuetogrowrapidly.

Sensornodes

ThesensornodeisoneofthemainpartsofaWSN.Thehardwareofasensornodegenerallyincludesfourparts:thepowerandpowermanagementmodule,asensor,amicrocontroller,andawirelesstransceiver,seeFigure3-3.Thepowermoduleoffersthereliablepowerneededforthesystem.ThesensoristhebondofaWSNnodewhichcanobtaintheenvironmentalandequipmentstatus.Asensorisinchargeofcollectingandtransformingthesignals,suchaslight,vibrationandchemicalsignals,intoelectricalsignalsandthentransferringthemtothemicrocontroller.Themicrocontrollerreceivesthedatafromthesensorandprocessesthedataaccordingly.TheWirelessTransceiver(RF

module)thentransfersthedata,sothatthephysicalrealizationofcommunicationcanbeachieved.

ItisimportantthatthedesignoftheallpartsofaWSNnodeconsidertheWSNnodefeaturesoftinysizeandlimitedpower.

MiniaturizationtechnologyofsensorbasedonMEMS

TheminiaturizationtechnologyofWSNnodesbasedonmicroelectromechanicalsystems(MEMS)hasmaderemarkableprogressinrecentyears.ThecoretechnologyofMEMSistorealizethecombinationofmicroelectronicstechnology,micro-machiningtechnologyandthepackagingtech-nology.Differentlevelsof2Dand3Dmicro-sensitivestructurescanbeproducedbasedonmicroelectronicsandmicro-machiningtechnology,whichcanbetheminiaturesensingelements.Theseminiaturesensingelements,associatedpowersupplyandsignalconditioningcircuitscanbeinte-gratedandpackagedasaminiatureMEMSsensor.

Powerandpowermanagement

Sensor

Microcontroller

Transceiver

Figure3-3|HardwarestructureofaWSNsensornode

Atpresent,therearealreadymanytypesofminiatureMEMSsensorsinthemarketwhichcanbeusedtomeasureavarietyofphysical,chemicalandbiomasssignals,includingdisplacement,velocity,accelera-tion,pressure,stress,strain,sound,light,electric-ity,magnetism,heat,pHvalue,etc.[10].In2003,researchersattheUniversityofCaliforniaBerkeley(UCB)developedaWSNsensornode(mote)withamicrosensor.TheactualsizeofitsMEMSsensingmodulewasonly2.8mm×2.1mm[11].

Ambientenergyharvestingtechnology

Nodesneedanenergysource,andambientenergyharvestingfromexternalsourcesareusedtopowersmallautonomoussensorssuchasthosebasedonMEMStechnology.Thesesystemsareoftenverysmallandrequirelittlepower,howevertheirapplicationsarelimitedbytherelianceonbatterypower.

Ambientenergyharvestingcannotonlyberealizedbyconventionalopticalcellpowergeneration,butalsothroughminiaturepiezoelectriccrystals,microoscillators,thermoelectricpowergenerationelements,orelectromagneticwavereceptiondevices[12][13].

Somecompanieshavebeguntocommercializesensornetworkapplicationsusingenergyacqui-sitiondevices.Forexample,theGermancompa-nyEnOceanhasprovidedlightenergyharvestingdevices,vibrationenergyharvestingdevicesandtemperature-basedenergyharvestingdevicesforsmartbuildinglightingandairmonitoringappli-cations.Forequipmentandconstructionhealthmonitoringapplications,avarietyofpiezoelectricvibrationenergyharvestingproductshaveenteredthemarket.TheBritishcompanyofPerpetuumprovidesaseriesofproductsthatconvertsmechan-icalvibrationintoelectricalenergyusedtoperpetu-allypowerautonomous,maintenance-freeindustrialwirelesssensornodes.Forthesesensornodesthe