Lesson8WirelessTechnologiesKeywordswirelessLANs無線局域顧bluetooth藍牙satellite衛(wèi)星thewirelessweb無線網(wǎng)站approx大約terrestrialmicrowave地面微波communicationssatellites通信衛(wèi)星microwaveantennas微波天線personalcommunicationsservice個人通信系統(tǒng)下一頁返回Lesson8WirelessTechnologiesTerrestrialMicrowaveTerrestrialmicrowavesuseearthbasedtransmitterandreceiver,asshowninFig8-1andFig8-2TheequipmentlookssimilartosatellitedishesTerrestrialmicrowavesuselowgigahertzrange,whichlimitsallcommunicationstolineofsight.Thedistancebetweentworelaystationsapproximatesto30milesMicrowaveantennasareusuallyplacedonthetopofbuildings,towers,hills,andmountainpeaks下一頁上一頁返回Lesson8WirelessTechnologiesCommunicationsSatellitessatellitesusemicrowaveradioastheirtelecommunicationsmediumwhicharenotdeflectedbytheearth’satmosphereThesatellitesarestationedinspace,typically22000miles(forgeosynchronoussatellites)abovetheequatorTheseearth-orbitingsystemsarecapableofreceivingandrelayingvoice,data,andTVsignals,asshowninFig8-3Thecommunicationssatellitessystem,dicty-netandstellatenetasshowninFig8-4toFig8-6

下一頁上一頁返回Lesson8WirelessTechnologiesCellularandPCSsystemsItusesseveralradiocommunicationstechnologiesThesystemsaredividedintodifferentgeographicareasEachareahaslowpowertransmitterorradiorelayantennadevicetorelaycallsfromoneareatothenextarea下一頁上一頁返回Lesson8WirelessTechnologiesWirelessLANsAsshowninFig8-7,wirelesslocalareanetworkusesahighfrequencyradiotechnologysimilartodigitalcellularandalowfrequencyradiotechnologyWirelessLANsusespreadspectrumtechnologytoenablecommunicationbetweenmultipledevicesinalimitedareaAnexampleofopenstandardswirelessradiowavetechnologyisIEEE802.11b.下一頁上一頁返回Lesson8WirelessTechnologiesBluetoothTheapplicationofbluetoothasshowninFig8-8It’sashortrangewirelesstechnology.Operateatapprox1Mbit/swithrangefrom10mto100m.Bluetoothisanopenwirelessprotocolfordataexchangeovershortdistances.下一頁上一頁返回Lesson8WirelessTechnologiesThewirelesswebThewirelesswebreferstotheuseoftheWorldWideWebthroughequipmentslikecellularphones,pagers,PDAs,andotherportablecommunicationsdevices.Thewirelesswebserviceoffersanytime/anywhereconnection,asshowninFig8-9.上一頁返回Lesson9CellphoneCommunicationKeywordsantenna天線mobile移動的wireless無線的wavelength波長modulation調(diào)制propagation傳播attenuation衰減spectrum頻譜下一頁返回transmit傳愉phase相位amplitude幅度amplify放大ADC模數(shù)轉(zhuǎn)換器DAC數(shù)模轉(zhuǎn)換器communication通信demodulation解調(diào)Lesson9CellphoneCommunicationHowtomakecommunicationbetweentwomobilephonescometrue？

Therearetwomobilephoneswhichareindifferentcities.AsshowninFig9-1,howdotheyachievecommunicationsToachievewirelesscommunications,antennaisanecessary.Inmobilephones,theantennaisverysmalljustlikethis,asshowninFig9-2

下一頁上一頁返回Lesson9CellphoneCommunicationFromthepicturewecanseethatthesizeoftheantennaisverysmall.Asweallknow,thefrequencyofouraudiosignalsis20-200kHz.Andatthesametime,inordertobetteremittingsignals,thelengthofantennasmustbelongerthanthewavelengthofsignalsby10percent.Soifwewanttodirectlyemitaudiosignals,thesizeofantennasishardtothinkforcommonmobilephonesSolution：Modulationisjustspectrumshifting.Thatistosay,modulationistheprocessofshiftingspectrumofonecenterfrequencytoanother.ThespectrumshiftingisasshowninFig9-3

下一頁上一頁返回Lesson9CellphoneCommunicationModulationistheadditionofinformation(orthesignal)toanelectronicoropticalsignalcarrierCommonmodulationmethodsinclude:AmplitudeModulation(AM),inwhichtheamplitudeofthecarrierisvariedovermodulatesignalsFrequencyModulation(FM),inwhichthefrequencyofthecarrierwaveformisvariedovermodulatesignalsPhaseModulation(PM),inwhichthephaseofthecarrierwaveformisvariedovermodulatesignals下一頁上一頁返回Lesson9CellphoneCommunicationAftertheemittingofantenna，modulatedsignalstransmitintheairGenerallyspeaking，therearethreepropagationmodes,asshowninFig9-4toFig9-6SkywavepropagationLineofsightpropagationGroundwavepropagation下一頁上一頁返回Lesson9CellphoneCommunicationAttenuationfactorsforunguidedmedia:Receivedsignalsmusthavesufficientstrengthsothatcircuitryinthereceivercaninterpretthem.Signalsmustmaintainalevelsufficientlyhigherthannoisetobereceivedwithouterror.Attenuationisgreaterathigherfrequencies，causingdistortion.Inordertobetterreceivedsignalsforreceivingantennasattenuationandconsideringthenoise,weshouldproperlyenhancethetransmittedpower.下一頁上一頁返回Lesson9CellphoneCommunicationBecausetheantennaofreceivingmobilephonesreceivesthesignalswhichareusuallypoor,weshouldamplifythereceivedsignals.Then,changetheanalogsignalstodigtaldatathroughanADC.Afterthat,weshoulddemodulatethesignalsDemodulationistheactofextractingtheoriginalinformationbearingsignalfromamodulatedcarrierwave.TakethedemodulationofAMforexample,asshowninFig9-7

下一頁上一頁返回Lesson9CellphoneCommunicationAdemodulatorisanelectroniccircuitusedtorecovertheinformationcontentfromthemodulatedcarrierwave.Thesetermsaretraditionallyusedinconnectionwithradioreceivers,butmanyothersystemsusemanykindsofdemodulators.Anothercommononeisinamodem,whichisacontractionofthetermsmodulator/demodulator.Andthenthedecoderrecoverstheinputdatabitsfromtheoutputcodebits.ThesedigtaldatacanbechangedtoanalogsignalsthroughaDAC,asshowninFig9-8

下一頁上一頁返回Lesson9CellphoneCommunicationSotwomobilephonesachievescommunicationsWecansumthewholeprocesslikethis,asshowninFig9-9

上一頁返回Lesson10ImageSensorsKeyWordsimage圖像sensor傳感器digital數(shù)字的camera照相機aperture光圈bright明亮的CCD電藕合器件CMOS互補氧化物半導(dǎo)體silicon硅diode二極管shutter快門下一頁返回photon光子pixel像素bottom底部microlens微型透鏡amplifier放大器convert轉(zhuǎn)換astronomical天文學的telescope望遠鏡camcorder便攜式攝像機manufacture制造fabricate制造Lesson10ImageSensorsIntroductionAsshowninFig10-1,digitalcamerashaverootsgoingbackalmost200yearsBeginningwiththeveryfirstcameraallhavebeenbasicallyblackboxeswithalenstofocustheimage,anaperturethatdetermineshowbrightthelightis,andashutterthatdetermineshowlongthelightenters.下一頁上一頁返回Lesson10ImageSensorsThebigdifferencebetweentraditionalfilmcamerasanddigitalcamerasishowtheycapturetheimageInsteadoffilm,digitalcamerasuseasolidstatedevicecalledanimagesensor.Insomedigitalcamerastheimagesensorisachargecoupleddevice(CCD),asshowninFig10-2,whileinothersit’saCMOSsensor.Onthesurfaceofthesefingernailsizedsiliconchipsaremillionsofphotosensitivediodes,calledphotosites,eachofwhichcapturesasinglepixelinthephotographtobe下一頁上一頁返回Lesson10ImageSensorsWhenyoutakeapicture,thecamera’sshutteropensbrieflyandeachphotositeontheimagesensorrecordsthebrightnessofthelightthatfallsonitbyaccumulatingphotons.Themorelightthathitsaphotosite,themorephotonsitrecordsThenumberofphotonsfromeachphotositerepresentsthecolorofasinglepixelanditalongwithpixelscapturedbyalloftheotherphotositesonthesensorisusedtoreconstructtheimagebysettingthecolorandbrightnessofmatchingpixelsonthescreenorprintedpage下一頁上一頁返回Lesson10ImageSensorsTypesofimagesensorsTheCCDimagesensorasshowninFig10-3

AsshowninFig10-4,aCCDislikeathreedeckersandwich.Thebottomlayercontainsthephotosites.Abovethemisalayerofcoloredfiltersthatdetermineswhichcoloreachsiterecords.Finally,thetoplayercontainsmicrolensesthatgatherlight下一頁上一頁返回Lesson10ImageSensorsChargecoupleddevices(CCDs)havealreadybeenwelldevelopedthroughtheiruseinastronomicaltelescopes,scanners,andvideocamcordersHowever,thereisnowawellestablishedalternative,theCMOSimagesensor,asshowninFig10-5.BothCCDandCMOSimagesensorscapturelightusingagridofsmallphotositesontheirsurfaces.It’showtheyprocesstheimageandhowtheyaremanufacturedwheretheydifferfromoneanother下一頁上一頁返回Lesson10ImageSensorsImagesensorsaremanufacturedinfactoriescalledwaferfoundriesorfabswherethetinycircuitsanddevicesareetchedontosiliconchips,asiliconwaferusedtomakeimagesensorsasshowninFig10-6.CMOSisbyfarthemostcommonandhighestyieldingchipmakingprocessintheworld.Asaresultoftheseeconomiesofscale,thecostoffabricatingaCMOSwaferissignificantlylessthanthecostoffabricatingasimilarwaferusingthespecializedCCDprocess.CostsareloweredevenfartherbecauseCMOSimagesensorscanhaveprocessingcircuitscreatedonthesamechipWithCCDs,theseprocessingcircuitsmustbeonseparatechips下一頁上一頁返回Lesson10ImageSensorsPixelThepixelsasshowninFig10-7,squarepixelsarearrangedinpatternstoformcurvedlinesandedgesinaphotoThemorepixelsused,thesmootherthesecurveswillbe.Herethesameredballisrepresentedby4,12,andthen24squarepixels.Asmorepixelsareadded,edgesbecomemorerefinedandtheshapebecomesmoreliketheoriginalImagesizesareexpressedasdimensionsinpixels(4368×2912)orbythetotalnumberofpixels(12,719,616),asshowninFig10-8

下一頁上一頁返回Lesson10ImageSensorsWhenadigitalimageisdisplayedorprint