无线通信与网络ppt课件.ppt

《无线通信与网络ppt课件.ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、SignalEncodingTechniquesChapter6ReasonsforChoosingEncodingTechniquesDigitaldata,digitalsignalEquipmentlesscomplexandexpensivethandigital-to-analogmodulationequipmentAnalogdata,digitalsignalPermitsuseofmoderndigitaltransmissionandswitchingequipmentReasonsforChoosing

2、EncodingTechniquesDigitaldata,analogsignalSometransmissionmediawillonlypropagateanalogsignalsE.g.,opticalfiberandunguidedmediaAnalogdata,analogsignalAnalogdatainelectricalformcanbetransmittedeasilyandcheaplyDonewithvoicetransmissionovervoice-gradelinesSignalEncodin

3、gCriteriaWhatdetermineshowsuccessfulareceiverwillbeininterpretinganincomingsignal?Signal-to-noiseratioDatarateBandwidthAnincreaseindatarateincreasesbiterrorrateAnincreaseinSNRdecreasesbiterrorrateAnincreaseinbandwidthallowsanincreaseindatarateFactorsUsedtoCompareE

4、ncodingSchemesSignalspectrumWithlackofhigh-frequencycomponents,lessbandwidthrequiredWithnodccomponent,accouplingviatransformerpossibleTransferfunctionofachannelisworsenearbandedgesClockingEaseofdeterminingbeginningandendofeachbitpositionFactorsUsedtoCompareEncodin

5、gSchemesSignalinterferenceandnoiseimmunityPerformanceinthepresenceofnoiseCostandcomplexityThehigherthesignalratetoachieveagivendatarate,thegreaterthecostBasicEncodingTechniquesDigitaldatatoanalogsignalAmplitude-shiftkeying(ASK)AmplitudedifferenceofcarrierfrequencyF

6、requency-shiftkeying(FSK)FrequencydifferencenearcarrierfrequencyPhase-shiftkeying(PSK)PhaseofcarriersignalshiftedBasicEncodingTechniquesAmplitude-ShiftKeyingOnebinarydigitrepresentedbypresenceofcarrier,atconstantamplitudeOtherbinarydigitrepresentedbyabsenceofcarrie

7、rwherethecarriersignalisAcos(2πfct)Amplitude-ShiftKeyingSusceptibletosuddengainchangesInefficientmodulationtechniqueOnvoice-gradelines,usedupto1200bpsUsedtotransmitdigitaldataoveropticalfiberBinaryFrequency-ShiftKeying(BFSK)Twobinarydigitsrepresentedbytwodifferentf

8、requenciesnearthecarrierfrequencywheref1andf2areoffsetfromcarrierfrequencyfcbyequalbutoppositeamountsBinaryFrequency-ShiftKeying(BFSK)Lesssuscept