无线微传感器中英文对照外文翻译文献.docx

无线微传感器中英文对照外文翻译文献.docx

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无线微传感器中英文对照外文翻译文献

无线微传感器中英文对照外文翻译文献

（文档含英文原文和中文翻译）

ASimpleEnergyModelforWirelessMicrosensorTransceivers

Abstract—Thispaperdescribesthemodellingofshortrangetransceiversformicrosensorapplications.Asimpleenergymodelisderivedandusedtoanalyzethetransceiverbatterylife.Thismodeltakesintoaccountenergydissipationduringthestart-up,receive,andtransmitmodes.Itshowsthatthereisasignificantfixedcostinthetransceiverenergyconsumptionandthisfixedcostcanbedrivendownbyincreasingthedatarateofthetransceiver.

I.Introduction

Wirelessmicrosensornetworkscanprovideshort-rangeconnectivitywithsignificantfaulttolerances.Thesesystemsfindusageindiverseareassuchasenvironmentalmonitoring,industrialprocessautomation,andfieldsurveillance.Asanexample,TableIshowsadetailedspecificationforasensorsystemusedinafactorymachinemonitoringenvironment.

Themajorcharacteristicsofamicrosensorsystemarehighsensordensity,shortrangetransmissions,andlowdatarate.Dependingontheapplication,therecanalsobestringentBERandlatencyrequirements.Duetothelargedensityandtherandomdistributednatureofthesenetworks,batteryreplacementisadifficulttask.Infact,aprimaryissuethatpreventsthesenetworkstobeusedinmanyapplicationareasistheshortbatterylife.Therefore,maximizingthebatterylifetimeofthesensornodesisimportant.Figure1showsthepeakcurrentconsumptionlimitwhena950mAhbatteryisusedastheenergysource.Asseeninthefigure,batterylifecanvarybyordersofmagnitudedependingonthedutycycleofeachoperation.Toallowforhighermaximumpeakcurrent,itisdesirabletohavethesensorremainintheoff-stateforaslongaspossible.However,thelatencyrequirementofthesystemdictateshowoftenthesensorneedstobeactive.Fortheindustrialsensorapplicationdescribedabove,thesensorneedstooperateevery5mstosatisfythelatencyrequirement.Assumingthatthesensoroperatesfor100µsevery5ms,

thedutycycleis2%.Toachieveaone-yearbatterylife,thepeakcurrentconsumptionmustbekeptunder5.4mA,whichtranslatestoapproximately10mWat2Vsupply.Thisisadifficulttargettoachieveforsensorsthatcommunicateatgiga-Hertzcarrierfrequencies.

Therehasbeenactiveresearchinmicrosensornetworksoverthepastyears.Gupta[1]andGrossglauser[2]establishedinformationtheoreticboundsonthecapacityofad-hocnetworks.Chang[3]andHeinzelman[4]suggestedalgorithmstoincreaseoverallnetworklife-timebyspreadingworkloadsevenlyamongallsensors.Muchoftheworkinthisarea,especiallythosethatdealwithenergyconsumptionofsensornetworks,requireanenergymodel[5].ThispaperdevelopsarealisticenergymodelbasedonthepowerconsumptionofastateoftheartBluetooth

transceiver[6].Thismodelprovidesinsightsintohowtominimizethepowerconsumptionofsensornetworksandcanbeeasilyincorporatedintoworkthatstudiesenergylimitedwirelesssensornetworks.Theoutlineofthispaperisasfollows.SectionIIderivesthetransceivermodel.SectionIIIappliesthismodeltoanalyzingthebatterylifetimeoftheBluetoothtransceiver.SectionIVinvestigatesthedependenciesinthemodelandshowshowtomodifythedesignoftheBluetoothtransceivertoimprovethebatterylife.SectionVshowsthebatterylifeimprovementrealizedbyapplyingtheresultsinSectionIV.SectionVIsummarizesthepaper.

II.MicrosensorTransceiverModelling

Thissectionderivesasimpleenergymodelforlowpowermicrosensors.Figure2showsthemodelofthesensornode.Itincludesasensor/DSPunitfordataprocessing,D/AandA/Dfordigital-to-analogandanalog-to-digitalconversion,andawirelesstransceiverfordatacommunication.Thesensor/DSP,D/A,andA/Doperateatlowfrequencyandconsumelessthan1mW.Thisisoveranorderofmagnitudelessthanthepowerconsumptionofthetransceiver.Therefore,theenergymodelignoresthecontributionsfromthesecomponents.Thetransceiverhasthreemodesofoperation:

start-up,receive,andtransmit.Eachmodewillbedescribedandmodelled.

A.Start-upMode

Whenthetransceiverisfirstturnedon,ittakessometimeforthefrequencysynthesizerandtheVCOtolocktothecarrierfrequency.Thestart-upenergycanbemodelledasfollows:

wherePLOisthepowerconsumptionofthesynthesizerandtheVCO.Thetermtstartistherequiredsettlingtime.RFbuildingblocksincludingPA,LNA,andmixerhavenegligiblestart-uptimeandthereforecanremainintheoff-stateduringthestart-upmode.

B.ReceiveMode

Theactivecomponentsofthereceiverincludesthelownoiseamplifier（LNA）,mixer,frequencysynthesizer,VCO,intermediate-frequency（IF）amplifier（amp）,anddemodulator（Demod）.Thereceiverenergyconsumptioncanbemodelledasfollows:

wherePRXincludesthepowerconsumptionoftheLNA,mixer,IFamplifier,anddemodulator.Thereceiverpowerconsumptionisdictatedbythecarrierfrequencyandthenoiseandlinearityrequirements.Oncetheseparametersaredetermined,tothefirstorderthepowerconsumptioncanbeapproximatedasaconstant,fordataratesupto10’sofMb/s.Inotherwords,thepowerconsumptionisdominatedbytheRFbuildingblocksthatoperateatthecarrierfrequency.TheIFdemodulatorpowervarieswithdatarate,butitcanbemadesmallbychoosingalowIF.

C.TransmitMode

Thetransmitterincludesthemodulator（Mod）,frequencysynthesizerandVCO（sharedwiththereceiver）,andpoweramplifier（PA）.ThedatamodulatestheVCOandproducesaFSKsignalatthedesireddatarateandcarrierfrequency.AsimpletransmitterenergymodelisshowninEquation（3）.Themodulatorconsumesverylittleenergyandthereforecanbeneglected.

PLOcanbeapproximatedasaconstant.PPAdependsonadditionalfactorsandneedstobemodelledmorecarefullyasfollows:

whereηisthePAefficiency,risthedatarate,disthetransmissiondistance,andnisthepathlossexponent.γPAisafactorthatdependsonEb/NO,noisefactorFofthereceiver,linkmarginLmar,wavelengthofthecarrierfrequencyλ,andthetransmit/receiveantennagainsGT,GR:

FromEquations（3）and（4）,thetransmitterpowerconsumptioncanbewrittenasaconstanttermplusavariableterm.Theenergymodelthusbecomes

III.BluetoothTransceiver

HerewedemonstratehowtheabovemodelcanbeusedtocalculatethebatterylifetimeofaBluetoothtransceiver[6].ThisisoneofthelowestpowerBluetoothtransceiversreportedinliterature.Theenergyconsumptionofthetransceiverdependsonhowitoperates.Assuminga100-bitpacketisreceivedanda100-bitpacketistransmittedevery5ms,Figure3shows

thetransceiveractivitywithinonecycleofoperation.Thetransceivertakes120µstostartup.Operatingat1Mb/s,thereceivertakes100µstoreceivethepacket.Thetransceiverthenswitchestothetransmitmodeandtransmitsasame-lengthpacketatthesamerate.A10µsinterval,tswitch,betweenthereceiveandthetransmitmodeisallowedtoswitchchannelortoabsorbanytransientbehavior.Therefore,theenergydissipatedinonecycleofoperationissimply

BoththeaveragepowerconsumptionandthedutycyclecanbefoundFromFigure3.Knowingthatthetransceiveroperatesat2V,thelifetimefora950mAhbatteryiscalculatedtobeapproximately2-months.

IV.EnergyOptimization

ThemicrosensorsystemdescribedinSectionIrequiresabatterylifeofoneyearorbetter.AlthoughtheBluetoothtransceiverdescribedinthelastsectionfallsshortofthisrequirement,itservesasastartingpointformakingimprovements.ThissectionexaminesEopindetailandsuggestswaystoincreasethebatterylifebyconsideringbothcircuitandsystemimprovements.

A.Start-upEnergy

Thestart-upenergycanbeasignificantpartofthetotalenergyconsumption,especiallywhenthetransceiverisusedtosendshortpacketsinburstmode.FortheBluetoothtransceiver,Estartaccountsfor20%ofEop.Thestart-upenergybecomesnegligibleifthefollowingconditionisheldtrue:

Forthereceive/transmitschemeshowninFigure3,therighthand-sideofEquation（8）isevaluatedtobeapproximately450µs.TokeepEstartanorderofmagnitudebelowEop,itisdesirabletohaveastart-uptimeoflessthan45µs.Chohasdemonstrateda5.8GHzfrequencysynthesizerim-

plementationwithastart-uptimeunder20µs[7].

B.PowerAmplifier

ThePApowerconsumptionisgivenby

whereηisthepowerefficiencyandPoutistheRFoutputpower.Poutcanbedeterminedbylink-budgetanalysis.ForaBluetoothtransceiver,therequiredPoutis1mW[8].

Thisenablesamaximumtransmissiondistanceof10meters,whichisadequateformicrosensorapplications.NotethatPoutissmallascomparedtoPLO.TheBluetoothtransceiverdiscussedinSectionIIhasamaximumRFoutputpowerof1.6mWandaPApowerconsumptionof10mW,sotheefficiencyisat16%.Atfrequenciesaround2GHz,thePAefficiencycanvaryfrom10%[9]to70%[10]dependingonlinearity,circuittopology,andtechnology.SinceFSKsignalhasaconstantenvelope,nonlinearPA’scanbeusedsothatbetterefficiencycanbeachieved.Aswillbeshowninthenextsection,PAefficiencyhasasignificantimpactonthebatterylife.

C.DataRate

AssumingapacketoflengthLpktistransmittedatdatrater,thenthetransmittimeis

Thetransmitterenergyconsumptioncanbere-writtenas

Equation（12）showsthatthecontributionofthefixedcostPLOcanbereducedbyincreasingthedatarate.Theenergyperbit,Ebit,isdefinedasEopdividedbythetotalnumberofbitsreceivedandsentduringonecycleofope