UnitThree■

主要內容：與電子相關的學科及領域的知識，如傳感器，計算機，通信，數控等等技術。■學習目標：了解與電子相關的學科及領域的知識，如通信，衛星，數控等方面。■素質目標：啟發探索興趣，樹立科學自信，虛擬交互現實，增強文化自信；樹立正確的勞動觀，崇尚勞動、尊重勞動、熱愛勞動。Lesson7cellphonecommunicationKeywords■communication[k?,mjuni’kei??n]

通信■antenna[?n’ten?]天線■mobile[’m?ubail]移動的■wireless[’wa??l?s]無線的■wavelength

[’we?v,le?kθ]波長■modulation[,m?dju’lei??n]

調制■demodulation[’di:,m?dju:’lei??n]

解調■propagation[,pr?p?’ge???n]

傳播■attenuation[??tenju?ei??n]衰減■spectrum[‘spektr?m]頻譜■transmit[tr?nz’mit]傳輸■phase[feiz]

相位■amplitude[,?mpl?’tu:d]

幅度■amplify[‘?mplifai]

放大■ADC模數轉換器■DAC數模轉換器■工作任務：如何實現兩個手機的通信？■學習目標：掌握基本的調制解調技術，以及在通信系統中的應用。■重點難點：調制解調技術在各種通信系統中的應用■推薦學時：6學時■任務：Howtomakecommunicationoftwomobilephonescometrue？Communications

Toachievewirelesscommunications,antennaisanecessary.Inmobilephone,antennaisverysmalljustlikethis:Fromthepicturewecanseethatthesizeoftheantennaisverysmall.

Asweallknown,thefrequencyofouraudiosignalsis20~200KHZ.Andatthesametime,inordertobetteremittingsignals,thelengthofantennasmustbiggerthan10percentofthewavelengthofsignals.Soifwewanttodirectlyemitaudiosignals,thesizeofantennasishardtothinkforcommonmobilephones.Solution:modulation.modulationisjustspectrumshifting.Thatistosay,modulationistheprocessofshiftingspectrumofonecenterfrquencytoanother.Modulationistheadditionofinformation(orthesignal)toanelectronicoropticalsignalcarrier.Commonmodulationmethodsinclude:Amplitudemodulation(AM),inwhichtheamplitudeofthecarrierisvariedovermodulatesignals.Frequencymodulation(FM),inwhichthefrequencyofthecarrierwaveformisvariedovermodulatesignalsPhasemodulation(PM),inwhichthephaseofthecarrierwaveformisvariedovermodulatesignals.Aftertheemittingofantenna，modulatedsignalstransmitintheair.Generallyspeaking，therearethreepropagationmodes：Sky-wavepropagationLine-of-sightpropagationGround-wavepropagationFig7-5Sky-wavepropagationFig7-6Line-of-sightpropagationFig7-7Ground-wavepropagationBecauseantennaofreceivemobilephonereceivesthesignalswhichareusuallypoor,weshouldamplifythereceivedsignals.Then,changetheanalogsignalstodigtaldatasthroughanADC.Afterthat,weshoulddemodulatethesignals.

Demodulationistheactofextractingtheoriginalinformation-bearingsignalfromamodulatedcarrierwave.TakethedemodulationofAMforexample:microphoneA/DCodingmodulationAntenna1信道噪聲Antenna2AmplifyDemodulaitionDecodin