文献翻译——最大范围的低成本的无线网络

第1页外文文献资料MaximizingRangeinLow-CostWirelessNetworksTheproliferationofcost-effectivewirelesstechnologyhasledtotheriseofentirelynewtypesofnetworksacrossawiderangeofapplicationsincludingsecurity,homeandbuildingautomation,smartmetersandpersonalmedicaldevices.Manyofthesenetworkscomprisesimplenodesthatcollectandtransmitalimitedamountofdatatoacentralcontroller.Thegoalforwirelesssystemmanufacturersistoproviderobustnodesthatmaximizebatterylifewhileextendingtherangeofthenetworkasfaraspossible.Giventhehighprofileofseveral2.4GHzwirelessstandards,namelyBluetoothandWi-Fi,manymanufacturersassumetheyhavetouseastandardprotocolandthat2.4GHzisthedefactotransceiverfrequencyofchoice.Thisistrueforsomeapplicationswhenusinganestablishedprotocolisamarket-drivenchoice.Forexample,Wi-FiprovidesuniversalhighdatarateconnectivitywhileBluetoothoffersdevicecompatibilityinhigh-volumeconsumermarketssuchascellphoneandPCaccessories.Manyapplications,however,haverelativelylowdataraterequirementsandoperatewithinaclosedwirelessnetwork.Inthesecases,aproprietaryprotocolcanreducesystemcostsignificantlybystreamlininganimplementation,thusminimizingtheprocessorresourcesrequiredaswellasavoidingthecostsassociatedwithcompliancetestingandlogolicensing.Forexample,aZigBeeradionodecostsontheorderof$2(USD)andrequiresthesystemtosupporta128KBstack.Asub-GHzradionodeusingaproprietaryprotocolcancostlessthan$1.2andrequiresonlyan8KBstack.Manyapplicationsuseproprietaryprotocolsforcostreasonssincefewmarketsrequirevendorinteroperability.WirelessdeWhilecertainmarketsmaynotuseastandardwirelessprotocol,theyhaveconsolidatedaroundaparticularfrequency.Forexample,wirelessgame第2页controllersuse2.4GHzwhileautomotiveremotekeylessentry(RKE)systemsusesub-GHzfrequencies.SomemarketsusemultipleSiliconLaboratories,Inc.Rev1.02wirelesstechnologies.Automatedutilitymeters,forexample,usesub-GHzasalong-rangewirelessbackhaulnetworkand2.4GHzformeter-to-homecommunications.Homesecuritysystemsusesub-GHzforlowdataratesensorsand2.4GHzforhighdataratevideocameras.Somemarketsremainundecidedwhenitcomestowirelessprotocols.Forexample,existinghomeautomationsystemsusesub-GHzfrequencieswhileemerging2.4GHz/ZigBeedevicesareenteringthemarket.velopersmustdeterminewhetherasub-GHzor2.4GHztransceiverwillbestservetheirapplicationneeds.Transceiversbasedon2.4GHzofferhighdatarates(greaterthan1Mbps)andasmallantenna(lessthanone-thirdthesizeofa900MHzantenna),whichmakesforagoodfitwithshort-rangeconsumerelectronicsdevices.However,a2.4GHzradiohaslimitedrangeenvironmentallossesare9dBmorethanat900MHz.Thehighdataratesrequireawiderreceiverchannelbandwidth,whichfurtherlimitsthesensitivityandrange.A2.4GHzradioalsohashigherpowerconsumptionduetoreducedcircuitefficiencies.Inaddition,the2.4GHzspectrumiscrowdedandsubjecttosignificantinterferencefromWi-Fidevices,Bluetoothnodesandmicrowaveovens.Incontrast,sub-GHzradiosoffersubstantiallyhigherrangethan2.4GHzradios,ontheorderofkilometers.Sub-GHzradiosalsoenablelowpowerconsumptionandcanoperateforyearsonasinglebattery.Thesefactors,combinedwithlowsystemcost,makesub-GHztransceiversidealforlowdatarateapplicationsthatneedmaximumrangeandmulti-yearoperatinglife.Oneofthedisadvantagesoftenaimedatsub-GHzwirelessdesignsisthattheantennasarelargerthanthoseusedin2.4GHzdesigns.Theantennasizefor433MHzapplications,forinstance,canbeuptosevenincheslong.AntennasizeandfrequencyareinverselyproportionalasshowninFigure2.Ifnodesizeisanimportantdesignconsideration,developerscanraisethefrequency(upto950MHz,forexample)andemployasmallerantenna.第3页ThefirstwirelessnetworksweredevelopedinthePre-industrialage.Thesesystemstransmittedinformationoverline-of-sightdistances(laterextendedbytelescopes)usingsmokesignals,torchsignaling,flashingmirrors,signalflares,orsemaphoreflags.Anelaboratesetofsignalcombinationswasdevelopedtoconveycomplexmessageswiththeserudimentarysignals.Observationstationswerebuiltonhilltopsandalongroadstorelaythesemessagesoverlargedistances.Theseearlycommunicationnetworkswerereplacedfirstbythetelegraphnetwork(inventedbySamuelMorsein1838)andlaterbythetelephone.In1895,afewdecadesafterthetelephonewasinvented,MarconidemonstratedthefirstradiotransmissionfromtheIsleofWighttoatugboat18milesaway,andradiocommunicationswasborn.Radiotechnologyadvancedrapidlytoenabletransmissionsoverlargerdistanceswithbetterquality,lesspower,andsmaller,cheaperdevices,therebyenablingpublicandprivateradiocommunications,television,andwirelessnetworking.Earlyradiosystemstransmittedanalogsignals.Todaymostradiosystemstransmitdigitalsignalscomposedofbinarybits,wherethebitsareobtaineddirectlyfromadatasignalorbydigitizingananalogsignal.Adigitalradiocantransmitacontinuousbitstreamoritcangroupthebitsintopackets.Thelattertypeofradioiscalledapacketradioandischaracterizedbyburstytransmissions:theradioisidleexceptwhenittransmitsapacket.Thefirstnetworkbasedonpacketradio,ALOHANET,wasdevelopedattheUniversityofHawaiiin1971.ThisnetworkenabledcomputersitesatsevencampusesspreadoutoverfourislandstocommunicatewithacentralcomputeronOahuviaradiotransmission.Thenetworkarchitectureusedastartopologywiththecentralcomputeratitshub.Anytwocomputerscouldestablishabi-directionalcommunicationslinkbetweenthembygoingthroughthecentralhub.ALOHANETincorporatedthefirstsetofprotocolsforchannelaccessandroutinginpacketradiosystems,andmanyoftheunderlyingprinciplesintheseprotocolsarestillinusetoday.TheU.S.militarywasextremelyinterestedinthecombinationofpacketdataandbroadcastradioinherenttoALOHANET.第4页TheintroductionofwiredEthernettechnologyinthe1970ssteeredmanycommercialcompaniesawayfromradio-basednetworking.Ethernets10Mbpsdataratefarexceededanythingavailableusingradio,andcompaniesdidnotmindrunningcableswithinandbetweentheirfacilitiestotakeadvantageofthesehighrates.In1985theFederalCommunicationsCommission(FCC)enabledthecommercialdevelopmentofwirelessLANsbyauthorizingthepublicuseoftheIndustrial,Scientific,andMedical(ISM)frequencybandsforwirelessLANproducts.TheISMbandwasveryattractivetowirelessLANvendorssincetheydidnotneedtoobtainanFCClicensetooperateinthisband.However,thewirelessLANsystemscouldnotinterferewiththeprimaryISMbandusers,whichforcedthemtousealowpowerprofileandaninefficientsignalingscheme.Moreover,theinterferencefromprimaryuserswithinthisfrequencybandwasquitehigh.AsaresulttheseinitialwirelessLANshadverypoorperformanceintermsofdataratesandcoverage.Thispoorperformance,coupledwithconcernsaboutsecurity,lackofstandardization,andhighcost(thefirstwirelessLANaccesspointslistedfor$1,400ascomparedtoafewhundreddollarsforawiredEthernetcard)resultedinweaksales.Fewofthesesystemswereactuallyusedfordatanetworking:theywererelegatedtolow-techapplicationslikeinventorycontrol.ThecurrentgenerationofwirelessLANs,basedonthefamilyofIEEE802.11standards,havebetterperformance,althoughthedataratesarestillrelativelylow(maximumcollectivedataratesoftensofMbpsandthecoverageareaisstillsmall(around150m.).WiredEthernetstodayofferdataratesof100Mbps,andtheperformancegapbetweenwiredandwirelessLANsislikelytoincreaseovertimewithoutadditionalspectrumallocation.Despitethebigdataratedifferences,wirelessLANsarebecomingthepreferedInternetaccessmethodinmanyhomes,offices,andcampusenvironmentsduetotheirconvenienceandfreedomfromwires.However,mostwirelessLANssupportapplicationssuchasemailandwebbrowsingthatarenotbandwidth-intensive.ThechallengeforfuturewirelessLANswillbetosupportmanyuserssimultaneouslywithbandwidth-intensiveanddelay-constrainedapplicationssuchasvideo.RangeextensionisalsoacriticalgoalforfuturewirelessLANsystems.第5页Formanyapplications,433MHzisaviablealternativeto2.4GHzformostoftheworld,anddesignsbasedon868and915MHzradioscanservetheUSandEuropeanmarketswithasingleproduct.Ingeneral,highdatarateapplicationswillneeda2.4GHzradio.Forlong-range,low-powerapplications,asub-GHztransceiveroftenprovidestheoptimalapproach.Batterylifetimeisacriticaldesignconstraintinmanywirelessnetworkingapplicationssincemanywirelessnodesaretypicallybattery-operatedandneedtooperateformonthsoryearswithoutmaintenance.Optimizingbatterylife,however,requiresthatdeveloperslookbeyondtheefficiencyofthetransceiver.Operatinglifeforasensornodealsodependsonthenodesrange,radiosensitivity,datarateandthenumberofnodesinthenetwork.Formanysub-GHzapplications,rangeisunquestionablythemostimportantdesignconstraint,makingthisastraightforwarddetermination.Increasingthetransmitoutputpowerextendstherangeandcoveragebutconsumersmorebatterypower.Greaterrangecanresultinlowersystemcostsincethelongeranodesrange,thefewernodesthereneedtobeinthesystemtoprovidecompletecoverageofanarea.Forexample,inalightingautomationsystem,nodesmustbeabletocommunicatewiththecentralcontrollerfromanyroominthehouseorbuilding.Anodewithlimitedrangewillpresentdeploymentissues,whichcouldincreaseinstallationdifficultiesthatresultinexpensivecustomerservicesupportcalls,productreturnsandlostrevenue.Toachievesufficientbuildingcoverage,anodemustbeabletotransmitatmorethan10dBm.Forlargerlocationssuchaswarehousesandcampuses,10dBmwillbeinsufficienttoreachacrosstheentiretargetsite.Asaresult,morenodeswillberequiredtoachievecompletecoverage.Inaddition,multiplecontrollersmaybeneededthroughoutthesite,significantlyincreasingsystemcomplexityandrequiringexpensivemanualconfigurationduringinstallation.Sub-GHztransceiverssuchasSiliconLabsEZRadioPROICsprovidegreateroutputpowertosupporttransmissionsupto20dBm.Whiletheoutputpowercanbescaleddownfrom20dBmtomatchtheoptimalrange,increasingthemaximum第6页outputpoweravailableateachnodecanensurethatthereissufficientmargintoprovidethedesiredrange.Afterall,ifanodecannotreachthecentralcontroller,itdoesntmatterhowpowerefficientitis.Inaddition,greaterrangepotentiallyreducesthenumberofnodesrequiredinameshnetworktoachievecompletecoverage.Theneedforfewernodesinturnminimizessystemcostwhileincreasingsystemrobustnessandefficiencybyreducingcontentionforsharedbandwidthbetweennodes.Evenifrangeisnotanissue,manywirelesssystemmanufacturerswillconsideroperatingatahigheroutputpowertooverdrivetheantenna.Inthisway,therangerequirementsofanapplicationcanbemetwithalessexpensive,inefficientantenna,resultinginlowersystemcost.Havinghighoutputpowerasanoptiongivesmanufacturerstheflexibilitytodecidethistradeoffforthemselves.Simplewirelessdatatransmissionusestheresonanceofacapacitorandaninductor.DatacanbeconvertedtotheresonancefrequencyorQvalue.Toenhancethefunctionofdatatransmission,mostwirelesstransmissionusesanintegratedcircuitwirelesstransmitter.MostcasestakeadvantageoftheunlicensedISM(industrial,scientific,andmedical)bands,andusecommunicationprotocolssuchasBluetooth,ZigBee,andIEEE802.11.Basically,thesewirelesscommunicationsrequireapowersupplytosendaradiosignal.developedalow-powersensorfortirepressuremonitoringusinglow-poweroscillators.ItconsistsoffourtiremodulestransmittingtheirdataviaanHF-linktoacentralreceiver,thehardwareofwhichissharedwiththeremotekeylessentryreceiversystem.However,abatterylimitstheoperationtimeofthesensorandwirelesscommunication.Toguaranteeaneffectivelifetimeof510years,thebatteryneedstohaveacapacityofseveralhundredmAh,whichincreasestheweightandsizeofthesensingsystem.Insteadofembeddingbatteries,mechanicalvibrationenergycanbeconvertedintoelectricitybycapacitive,electromagneticandpiezoelectricgenerators.Harvestingenergyfromarotatingtireisapossiblemethodofpoweringwirelessdevicesimplantedinthesurfaceofthevehicle.Scientistproposedcapacitivegeneratorsforconvertingambientmechanicalvibrationintoelectricalenergyusingan第7页MEMSvariablecapacitor.Byplacingchargeonthecapacitorplatesandthenmovingtheplatesapart,mechanicalenergycanbeconvertedintoelectricalenergy,whichcanthenbestored.Theenergyincreasesasmorechargeisloadedontothecapacitor.However,thecapacitivegeneratorsneedaninitialvoltagebeforetheycanproducepower.Scientistproposedanelectromagneticgeneratorthatconsistsofamagnetonapolyimidespring.Whenthegeneratorisvibrated,thereisanetmovementbetweenthemagnetandhousing.Thisrelativedisplacementgenerateselectricalenergybytheinteractionofthemagnetwithaplanarpick-upcoil.Scientistintroducedaself-poweredmethodofsensingandcommunicatingusingpiezoelectricmaterial.Thepowerisgeneratedsolelyfromtheconversionofmechanicalstrainenergyintoelectricalenergy,whichisthenusedtopowerawirelesslinktoareceiveranddataprocessingunit.Jeongetal.developedbender-typepiezoelectricdevicesforpowergenerator.Batterylifetimecanalsobeaffectedbythetotalnumberofnodesinthenetwork.Iftherearehundredsofnodescompetingwitheachothertocommunicatewiththecontroller,therewillbeasignificantnumberofcollisionsandretriesdependinguponthefrequencyofcommunication.Evenifthereissufficientbandwidthtocarryallofthedatathesenodeshavetotransmit,thewastedpowerexpendeduponretriescanexceedthepowerrequiredtosendthedataitself.Evaluatingcontentionissuesisanimportantstepindesigningarobustsensornodenetwork.Forexample,ifeachnodeonlyneedstosendafewbytestwiceperday,thetransmissionsofhundredsofnodescanbestaggeredtoresultinlittletonocontention.However,ifeachnodeneedstoconstantlyupdatethecontrollerwithalongstreamofdata,evenafewnodeswillgeneratesubstantialcontentionifthedatarateistoolow.Contentioncanbealleviatedinanumberofways.Reducingthetransmissionfrequency,possiblybybufferingdataforlongerperiodsoftime,caneliminatecontentionsinceeachnodewillattempttotransmitlessfrequently.Alternatively,datapacketsizecanbereducedthroughvariouscompressiontechniques(i.e.,senda4-bitdeltabasedonthelastvaluesentratherthananabsolute8-bitvalue)orbyemploying第8页moreintelligenceinthenodethroughamicrocontroller(MCU).Forexample,whencapturedsensorvaluesarewithinanacceptablerange,onlyasimplestatusflagissent.Contentioncanalsobereducedbyincreasingthedataratewhenothermethodsareinsufficient.Thenetworktopologyalsoimpactsthebatterylife.Considerastarnetworkwhereeverynodetalksdirectlytothecentralcontroller.Thisisaneffectiveandrobustwirelessnetworktopologysinceeverynodeiswithinrangeofthemaster.Thedisadvantageofthistypeofnetworkisthatasitbecomeslarger,thecontrollercanbecomeabottleneck.Inaddition,thedatarateneedstobehighenoughtoaccommodatedatatransmissionsfromeverynodeaswellasaccountforcontentionthatarises.Atsomepoint,contentioncanoverwhelmthenetwork.Dependinguponthenetwork,thisnumbercouldbeaslowas16to32nodes.Ameshnetworkwherenodesinterconnectwitheachotheranddatacanpassthroughseveralnodestoreachthecentralcontrolleroffersthemostflexibilityandcansupportalargernetworkoveragreaterphysicalarea.Importantattributesofanymeshnetworkincludeautomaticrecognitionofnodesastheyareaddedtothenetworkandself-healingasnodesaretakenoutofservice.Ingeneral,transceiversaresoftwareandprotocolagnosticsincetheradiodriverontheMCUcanbeadjustedtosupportmostexistingsoftwarestacks.Withitswidespectrumofoptions,controlsoftwareshouldbeselectedbasedonrange,thesizeofnetwork,andtheapplicationfunctionalitythatneedstobesupported.Siliconvendor-suppliedcodewillsufficeforsmall,simplenetworksregardlessoftopology.Forexample,SiliconLabsofferscomplementary,royalty-freeEZMaccontrolsoftwaretosupportbasicsensornetworksupto128nodes.Forlargernetworksofhundredstothousandsofnodes,robustsoftwareisavailablefromthirdpartiesofferingawiderangeofadvancedfeatures.Forsimplesensor-basednetworks,wirelessMCUssuchasSiliconLabsSi10xxdevices,whichintegrateasub-GHztransceiverwithanMCU(seeFigure5),enabledeveloperstoimplementtheentiresystemwithasingleSoC,resultinginlongerbatterylife,lowersystemcostandamorecompactformfactorcomparedto第9页multi-chipimplementations.Fornewdesigns,awirelessMCUenablesdeveloperstooptimizeboththeradioandcontrolcodeusingthesamesetoftools,simplifyingdesignandspeedingtime-to-market.Tosimplifymanufacturing,meshnetworkprotocolcodecanbeembeddeddirectlyintothewirelessMCUsflashmemory.Whenaddingwirelesscapabilitiestoanexistingdesign,itmaybethecasethatatransceiver-onlydeviceismorecost-effective.Ratherthanhavingtoportorredesignapplicationcode,developerscanimplementaprotocolstackandinterfacetotheradioontothesystemCPUwithinasmallfootprint.TodaysdevelopershaveawiderangeofRFtechnologychoiceswhendevelopinglow-costwirelessnetworks.Theavailabilityof2.4GHzradiosusingstandardprotocolsfacilitatesinteroperabilityforapplicationswithopennetworkswhilesub-GHzradiosprovideacost-effectiveapproachprovidinglongrangeandoptimalbatterylifetime.Thecombinationofhighpoweroutput,radiosensitivityandconfigurabledatarateprovidesdeveloperswiththeflexibilitytooptimizetheirimplementationforrange,cost,operatinglifeandeaseofinstallation.Inaddition,withavarietyofnetworktopologiesandintelligentnodefirmwareavailable,networksfromahandfultothousandsofnodescanbesupportedinasimpleandrobustmanner.第10页中文翻译稿最大范围的低成本的无线网络低成本无线技术的扩散导致导致完全新类型的网络在大范围的应用，包括安全，家庭和楼宇自动化，智能电表以及个人医疗设备。这些网络包括简单的节点，收集和传送有限的数据量到一个中央控制器。无线系统制造商的目标是提供强大的节点，最大限度地延长电池寿命，尽可能地扩展网络的距离。鉴于一些2.4GHz无线标准的高姿态，即蓝牙和无线，许多制造商认为他们必须使用标准的协议，即2.4GHz的是事实上的收发频率的选择。对一些应用程序来说利用市场驱动选择的建立协议是正确的。例如，无线网络提供了通用的高数据速率的连接，而蓝牙提供了大批量消费市场，如手机和电脑配件设备的兼容性。然而，许多应用程序，具有相对低的数据速率要求和操作一个封闭的无线网络。在这些情况下，一个专用协议可以通过简化的实施显著降低系统成本，从而最大限度地减少处理器所需的资源，以及避免与符合性测试和标识牌相关的成本。例如，一个低功耗局域网协议无线电节点的成本大约在2元（美元），并要求该系统支持一个128千字节的栈。使用私有协议的子-GHz无线节点可以花费少于$1.2和只需要8千字节的堆栈。因为很少的市场需要供应商的互用性，由于成本的原因许多应用程序使用专有协议。而某些市场可能无法使用标准无线协议，他们已经合并围绕一个特定的频率。例如，无线游戏控制器使用的2.4GHz而汽车远程无钥匙进入系统使用的子吉赫兹的频率。一些市场使用多个硅实验室公司1.02版的无线技术。例如，自动化仪表，使用的子吉赫兹的长距离无线回程网络和2.4GHz的水表到户通信。家庭安全系统使用子吉赫兹的低数据速率传感器和2.4GHz的高数据速率视频摄像机。当涉及到无线协议，有些市场仍犹豫不决。例如，现有的家庭自动化系统使用的子吉赫兹的频率，而新兴的2.4GHz设备正在进入市场。无线开发者必须确定是否子吉赫或2.4GHz收发器将最好地满足其应用需求。基于2.4GHz的收发器提供高的数据速率（大于1兆比特/秒）和一个小天线（一个尺寸小于三分之一的900兆赫的天线），这是短程消费电子设备的一个不错的选择。然而，一个2.4GHz的无线电有无限的范围，环境损失在9dB，大于900兆赫。高的数据速率要求更宽的接收机的信道带宽，这进一步限制了灵敏度和范围。一个2.4GHz无线电由于减少了电路的效率，还第11页具有更高的功耗。此外，在2.4GHz频谱是拥挤的，受到来自无线设备，蓝牙节点和微波炉显著干扰。与此相反，子吉赫兹无线电提供基本上比2.4GHz无线电更高的千米级范围。子吉赫无线电也使低功耗和在单电池多年来都可以操作。这些因素，再加上较低的系统成本，使吉兆赫收发器，适用于需要最大范围和多年的工作寿命的低数据速率应用。一个经常针对子吉赫无线设计的缺点之一是，该天线是比2.4GHz的设计中天线的尺寸要大。例如，433兆赫的应用，。天线的尺寸最多可以达到七英寸长。天线的尺寸和频率成反比，如果节点大小是一个重要的设计考虑因素，开发者可以提高频率（高达950兆赫，例如），并采用一个较小的天线。另一个需要考虑的因素就是产品将被出售和部署。2.4GHz频带具有使一台设备向所有主要市场服务于全世界自2.4GHz频带是一个全球性的频谱的优点。然而在现实中，这种优势往往是夸大了。每个国家都有不同的规定，可以迫使制造商为特定国家和地区的产品提供SKU。开发人员需要在设计过程的早期了解这些规定，以避免昂贵的重新设计的周期。第一个无线网络是在工业化前的时代发展起来的。这些系统使用烟信号、火炬信号、闪动的镜子、信号火箭或者信号旗子在可视范围内传送信息(后来被望远镜取代)。一个信号组合精心制定了一套初步的转达这些复杂的信号信息。