FM毕设英文资料文档格式.docx
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FM毕设英文资料文档格式.docx
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1DepartmentofElectrical&
ComputerEngineering
RiceUniversity,Houston,Texas,USA
{hang.yu,rahman,andaman,zhang}@rice.edu
AppliedResearchCenter
MotorolaMobility,Libertyville,Illinois,USA{jehan,venu}@
ABSTRACT
Inthiswork,weofferanovelsystem,MicroStation(μStation)thatallowsubiquitousdatabroadcastingapplicationsusingtheFMradioonmobiledevicessuchassmartphones.μStationincludestwokeymodulestoenabledatabroadcastingbasedonexistingmobileFMradiohardware.ChannelSelectorassignsdifferentFMchannelstoneighboringμStationbroadcasterstoavoidcollisionandguidesμStationlistenerstofindtheirbroadcastingofinterest.DataCodecrealizesbit-levelcommunicationbetweenmobiledevicesthroughexistingFMradiohardware.WedescribeanimplementationofμStationontheNokiaN900smartphone,andprovidelow-levelAPIsandservicestosupportapplicationdevelopment.Wealsodemonstratetworepresentativeapplications:
Facebook-FMandSync-Flash.TheseapplicationsdemonstratethecapabilityofμStationtoreadilyenableanewclassofubiquitousdatabroadcastingapplicationsonmobiledevices.
AuthorKeywords:
FMradio,databroadcasting,mobiledevices.
ACMClassificationKeywords:
C2.0Computer-CommunicationNetworks:
Datacommunications
GeneralTermsDesign,Experimentation,Measurement.
INTRODUCTION
Peer-to-peer(P2P)andlocation-basedmobileapplicationshavelongbeenanimportantfocusoftheubiquitouscomputingcommunity.AfewrecentindicativeapplicationsincludeColor[1]whichallowsausertosharephotoswithothersintheirvicinity,andCiscoStadiumVision[2]whichdeliverslocation-basedcontentandserviceforsportsvenues.Theproliferationofsuchapplicationsrequirespower-efficientandoverhead-freemobilebroadcastingtechnologies.
Inthiswork,weexploittheFMradiothatisincreasinglyavailableonmobiledevicestoprovideadatabroadcastingsystemforP2Pandlocation-basedapplications.Wearemotivatedbyarecentandimportanthardwaretrendonmobiledevices:
duetoitscontinuouslyreducedcostandintegrationwithotherwirelesstechnologies(e.g.,Wi-FiandBluetooth)onasinglechipset,theFMradioisbecomingincreasinglyavailableonmobiledevicessuchassmartphones,tabletsandmediaplayers.TestimonytothistrendincludesthehardwarerequirementsoftheWindowsPhone7Platform,whichembracestheFMradio[3].Asanotherexample,theAppleiPhoneandiPodTouchalreadyincorporatetheFMreceiverandtransmitterhardware,andthesoftwaretoenablethemisreportedlyunderdevelopment[4].ThemobileFMreceiverandtransmitterareintendedtoallowuserstolistentothebroadcastedprograms,andstreammusictoshort-rangehomeandautomobilestereos,respectively.However,wegobeyondsuchintendedusesofthemobileFMradioandenabledatabroadcastingapplicationsbasedonexistinghardware.
Werevealtwochallengestowardenablingpracticalanddeployabledatabroadcastingapplications.First,simultaneousbroadcastersmustnotcollide.Therefore,theyshouldcoordinatewitheachothertousetheavailableFMchannelswhileremainingquicklyidentifiablebyinterestedlisteners.Unlikeradiosinwhitespace,FMradiohasamuchshorterrange(~5meters)andmultipleorthogonalchannelssothatthesolutionrequiresspecialtreatmenttowardthehidden-nodeproblemandchannelallocation.Second,thesolutionmustnotmodifytheFMradiohardware,buthastorelyonthedevice’saudiointerfacetorealizedatabroadcasting.Therefore,binarydatamustbeproperlyconvertedintoaudio,andthebroadcasterandlistenermustbesymbol-synchronizedusingsoftware.
WeaddressthesechallengeswithμStation,asoftwaresolutionthatoperateswithoutmodificationtodevicePaperSession:
DIYandDesignhardware,operatingsystem,andtheFMradiodriver.μStationhastwokeymodules:
ChannelSelectorandDataCodec.First,ChannelSelectorenablesautomaticandefficientFMchannelallocation,sothatnearbybroadcastersuseorthogonalchannelswithhighprobability.Meanwhile,itensureslistenerstofindthechannelwithbroadcastingofinteresttimely,bylettingbroadcastersperiodicallyannouncetheirpresence.Second,DataCodecperformsconversionbetweenbinarydataandaudiotocompatiblyworkwiththeFMradiohardware.Moreimportantly,iteffectivelyachievessymbolsynchronizationinsoftwarebyleveragingdifferentsamplingfrequenciesintheFMtransmitterdigital-to-analogconverter(DAC)andFMreceiveranalog-to-digitalconverter(ADC).
WehaveimplementedμStationontheNokiaN900smartphoneandprovidedbothlow-levelAPIsandservicestosupportalargesetofmobileapplications.WehavealsodevelopedtworepresentativeapplicationsusingμStationtodemonstrateitseffectiveness.First,Facebook-FMbroadcastsauser’sFacebookIDsothatnearbyuserscanloadthecorrespondingFacebookprofiletofacilitatesocialinteraction.Second,Sync-Flashrealizesasynchronizedflashingpatternusingmanysmartphonescreensfromusersphysicallyclosetoeachother,e.g.,theaudienceofaconcertorasportsgame.
AsthefirstpubliclyreportedsystemthataimstoenableubiquitousdatabroadcastingapplicationsusingexistingmobileFMradiohardware,μStationhasofferedtheFMradio,whichpossiblyobtainslittleattentionbefore,significantpotentialtofacilitatetheinteractionbetweenphysicallyadjacentmobiledevices.WehopeourinitialendeavorwithμStationcanenlightenmoreinnovativewaystoleveragetheFMradioasanimportanthardwarefeatureoncurrentandemergingmobiledevices.
BACKGROUNDOFMOBILEFMRADIO
WenextprovidebackgroundofthemobileFMradio.
SpectrumUsage
ThespectrumusageofFMradiofallsintotheUHFbandandspansfrom87.5MHzto107.9MHzintheU.S.Inthiscase,thespectrumisequallydividedinto103orthogonalchannels,eachofwhichis200KHzapartfromitsneighbors.AFMchannelcanbeidentifiedbyitscenterfrequency,orbyauniquenumber(e.g.,Channel#1forthechannelat87.5MHz).IneachFMchannel,FMradiouses15KHzand30KHzbandwidthforbroadcastingmonauralandstereoaudiosrespectively.TheremainingbandwidthisusedforsidebandapplicationssuchastheRadioBroadcastDataSystem(RBDSotherwiseknownasRDSinEurope)[5],andthecurrentlyobsoleteMicrosoftDirectBand[6].
BothlicensedandunlicensedFMbroadcastingusethesamesetofchannels.Licensedbroadcastingusuallycomesfromradiostationsownedbycommercialorganizationsoreducationalinstitutions,withafixedcoverageandschedule.
Figure1:
FMradiohardwarearchitectureonmobiledevices
Asaresult,giventimeandlocation,licensedbroadcastingsareoftenhighlypredictable,asindicatedby[7].
RegulationsforUnlicensedBroadcasting
MostcountriesallowunlicensedFMbroadcasting.TheUSFCCregulatestheoutputpowerandmandatesthatthefieldstrengthofanyunlicensedFMemissionsmustnotexceed250microvolt/meterat3meters,leadingtoamaximumoutputpowerofapproximately15nW.TheEUregulationissimilarlyenactedbutthemaximumallowedoutputpoweris50nW.Australiaallowsoutputpowerashighas10μW,butonlyiftheunlicensedtransmissiondoesnotinterferewithpresentlicensedbroadcastings.WenotethatafewcountriessuchasChinadonotyetallowunlicensedFMbroadcasting;
mobiledevicesusedinthesecountriesusuallyhavetheFMtransmitterdisabled.Duetoourimplementationandexperimentalconstraints,weworkundertheUSFCCregulations.
WedefineavailableFMchannelsinthefollowingway:
aFMchannelisavailableifthechannelRSSIunderlicensedbroadcastingisbelowcertainthreshold(e.g.,-110dBminourimplementation).WenotethataFMchannelcanbeavailableevenwithpresentlicensedbroadcastings,aslongasthelicensedbroadcastingissufficientlyweak.Asaresult,checkingtheavailabilityofaFMchannelcanbesimplydonebymeasuringthechannelRSSI,whichissupportedbymobileFMradio.OurRSSIbaseddefinitionensuresthequalityofunlicensedbroadcastings,yettherecanbealternativewaystodefineavailableFMchannelssuchasusingthehumanperceivablequalityoflicensedbroadcasting.Nonetheless,μStationisagnosticofthedefinitionofchannelavailability,aswewillshowlater.
HardwareArchitecture
WeshowthehardwarearchitectureofmobileFMradioinFigure1.WenotethattheFMtransmitterandreceivermaybeinthesameorseparateintegratedcircuits,e.g.,theNokiaN900usestheSiliconLabSi4713forthetransmitterandBroadcomBCM2048forthereceiver,whiletheiPhone4utilizestheBroadcomBCM4329includingboththetransmitterandreceiver.Furthermore,someFMradiochipsetshaveaninternalDACforconvertingdigitalaudiointoanalogaudio,andanADCfortheoppositeconversion.Otherchipsetsonlyprovideananalogaudiointerface;
anaudiocodecchipprovidesthenecessaryADCandDAC,andeffectivelybridgestheFMradiohardwarewiththerestofthesystemthroughadigitalaudiointerface.μStationisindependentontheseimplementationissuesbyinterfacingwiththedigitalaudiointerfaceprovidedbyeithertheFM
Figure2:
Theheadphone,earphoneandthewindingcaseusedinourexperiments
radiochipsetsortheaudiocodec.Forgenerality,weusethetermFMradiohardwaretorefertotheFMtransmitter,FMreceiverandaudiocodecifexisting.
CurrentmobileFMtransmittersandreceiversemploydifferentantennas.Toachievesmallantennaloss,theantennalengthshouldbeatleastatenthofthecarrierwavelength,i.e.,about30cmf
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