同济大学通信系统原理英文班练习题附答案.docx
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同济大学通信系统原理英文班练习题附答案
Chapter1
Homework:
Fill-inQuestions:
1.InaM-arycommunicationsystem,eachsymbolcontains（
）bitsinformationcontent.
2.Thepurposeofcommunicationisto（transferinformation）.Efficiencyofthedigitalcommunicationsystemcanbemeasuredbythespecificationssuchas（
）,（
）,（
）.Andreliabilitycanbemeasuredby（
）,（
）.
3.Thebasicfactorsformeasuringthemeritofacommunicationsystemare（efficiency）,and（reliability）.
4.Themaininfluenceofconstantparameterchannelonsignaltransmissionareusuallydescribedbytheir（Amplitude-Frequency）and（Phase-Frequency）characteristics.
5.Commoncharacteristicsofrandomparameterchannelsare（transmissionattenuationofthesignalisvaryingwithtime）,（transmissiondelayofthesignalvarieswithtime）,and（signalarrivesatthereceiveroverseveralpaths）.
Multiple-ChoiceQuestions:
1.Foranaloganddigitalcommunications,whichis（are）true?
（ABCD）.
A.digitalcommunicationtypicallyusesmorebandwidth.
B.analogcommunicationcaresmoreaboutfidelity
C.digitalcommunicationcaresmoreaboutprobabilityforcorrectdecision
D.digitalcommunicationtypicallyusesanalogcarriertocarrybasebandsignals
Single-ChoiceQuestions:
1.Thesymbolrateof16-arydigitalsignalis1200Bd,thenthecorrespondinginformationrateis（D）;Ifwiththesameinformationrate,thesymbolrateof8-arydigitalsignalis（D）.
A.1600b/s,1200BdB.1600b/s,3200Bd
C.4800b/s,2400BD.4800b/s,1600B
2.Assumethedelaydifferenceoftwopathsinarandomparameterchannelis
thefrequenciesofmaximumtransmissionlossare（B）,thefrequenciesofminimumtransmissionlossare（B）.
A.
kHz,
kHzB.
kHz,
kHz
C.
kHz,
kHzC.
kHz,
kHz
TrueorFalse
Whenthereisnoinputsignal,theadditiveinterferencedoesn’texist,butthemultiplicativeinterferencestillexists.（F）
Chapter2
Homework:
2.1,2.4,2.5,2.6,2.8,2.11
Fill-inQuestions:
1.AWGNnoiseisshorttermfor（AdditiveWhiteGaussianNoise）.
2.Thepowerspectraldensityand（theautocorrelationfunction）ofastationaryrandomprocessareapairofFouriertransform.
3.Ifbandwidthis10MHz,signal-to-noiseratiois20dB,theShannoncapacityisC=（66.6Mbps）.
Single-ChoiceQuestions:
1.Assume
isageneralizedstationaryrandomprocesswithzeromathematicalexpectation,thentheaveragepowerof
is（D）.
A.
B.
C.
D.
2.Foranarrowbandrandomprocess
if
isaGaussianprocess,then（A）.
（A）
and
arealsoGaussianprocesses;（B）Only
isalsoGaussianprocess;
（C）
and
arenotGaussianprocesses;（D）Only
isalsoGaussianprocesses.
Chapter3
1.ComparisonofAM,DSB,SSBandFMthesefourcommunicationsystem,whichhasthebestefficiency?
Whichhasthebestreliability?
Whichhavethesameefficiency?
SSBhasbestefficiency.FMhasthebestreliability.AMandDSBhavethesameefficiency.
2.WhatistherequirementonthecharacteristicsofthefilterforproducingtheVSBsignal?
3.WhatkindofbasebandsignalissuitableforVSBmodulation?
TheanalogbasebandsignalwithD.C.componentandlowfrequencycomponentissuitableforVSBmodulation.
4.LettheexpressionofaFMmodulatedsignalbe
Find:
（1）themaximumfrequencydeviationofthemodulatedsignal.
（2）thefrequencyofthecarrier.
（3）thebandwidthandtheaveragepowerofthemodulatedsignal.
（4）iftheFMcircuitconstantis
kHz/V,thentheexpressionofthebasebandsignalcanbewrittenas:
（1）∵
（2）
Hz
（3）
Hz
W
（4）∵
∴
V
∴thebasebandsignalcanbewrittenas:
5.AssumetheamplitudeofaFMmodulatedsignalis10V,theinstantaneousfrequencyoftheFMsignalis:
Find:
（1）theexpressionoftheFMmodulatedsignal.
（2）themaximumfrequencydeviation,themodulationindex,andthebandwidthofthemodulatedsignal.
（1）
（2）
kHz
Fill-inQuestions:
1.AssumetheexpressionofaFMsignalis
thecarrierfrequencyofthisFMsignalis（
）Hz,themaximumfrequencydeviationis（5000）Hz,thebandwidthofthisFMsignalis（
）Hz，theaveragepoweris（12.5）W.
Single-ChoiceQuestions:
1.Whichanalogmodulationhasthehighestspectrumefficiency?
（C）
（A）AM（B）DSB
（C）SSB（D）VSB
CalculationQuestions:
1.Letabasebandmodulatingsignalbeasinusoidalwavewiththefrequency10kHz,andtheamplitude1V.Itmodulatesthephaseofacarrierwithfrequency10MHz,andthemaximumphasedeviationofmodulationis10rad.
（1）Calculatetheapproximatebandwidthofthephasemodulatedsignal.
（2）Ifthefrequencyofthemodulatingsignalischangedto5kHz,calculatethebandwidthofthephasemodulatedsignal.
Answer:
（1）Wehasknownthat:
andmaximumphasedeviation
.
Theinstantaneousphaseofthecarriercanberepresentedas:
where
.
Then,theinstantaneousfrequencydeviationofthecarriercanberepresentedas:
d
andmaximumfrequencydeviationis
.
Hence,thefrequencymodulationindexis:
Thus,theapproximatebandwidthofthephasemodulatedsignalis
（2）Ifthefrequencyofthemodulatingsignalischangedto5kHz,thentheapproximatebandwidthofthephasemodulatedsignalis:
.
Chapter4
Fill-inQuestions:
1.Thebasicprocess,from（Samplingtheanalogsignal）,（thequantization）,and（convertingtobinarysymbols）,isusuallycalledaspulsecodemodulation（PCM）.
Single-ChoiceQuestions:
1.Thepurposeofnonuniformquantizationis（B）.
A.ProtectbigsignalB.Protectsmallsignal
C.removequantizationnoiseD.Increasequantizationlevels
2.InDeltamodulation,thebestwaytoavoidoverloadquantizationnoiseis（A）.
A.IncreasesamplingfrequencyB.Increasequantizationstep
C.ReducesamplingfrequencyD.Reducequantizationstep
3.Thesamplingtheorempointsoutthatifthehighestfrequencyofalow-passanalogsignalis
thenthesignalcanberepresentedbyitssampleswhenthesamplingfrequencynolessthan（B）.
（A）
（B）
（C）
（D）
4.Ifthesamplesobeyuniformdistributionover
thenthequantizationnoisepowerisdeterminedby（C）
（A）
（B）
andquantizationinterval
（C）quantizationinterval
（D）otherparameters.
Multiple-ChoiceQuestions:
1.Digitizationofanalogsignalsincludes（B、D、E）
（A）.Modulation（B）.Quantization（C）.Multiplexing（D）.Sourcecoding（E）.Sampling
Short-AnswerQuestions:
1.InDeltamodulationsystem,whyweincreasesamplingfrequency
ratherthanquantizationstep
toavoidoverloadquantizationnoise?
Answer:
Giventhesamplingfrequencyandthequantizationstep
thentheslopeofastepis:
Itisthemaximumpossibleslopeofastep-shapedwave,oritiscalledthemaximumtrackingslopeofthedecoder.Whentheslopeoftheinputsignalofthedeltamodulatorexceedsthismaximum,overloadquantizationnoisewillbegenerated.Therefore,inordertoavoidoverloadquantizationnoise,itisnecessarytomaketheproductof
and
largeenough,sothattheslopeofthesignalcannotexceedthisproduct.Onetheotherhand,thevalueof
isdirectlyrelatedtothemagnitudeofthebasicquantizationnoise.Ifthevalueof
islarge,thenthebasicquantizationnoisemustalsobelarge.Therefore,onlythemethodofincreasing
toincreasetheproduct
canensurethatthebasicquantizationnoiseandtheoverloadquantizationnoisedonotexceedthelimit.
Fill-inQuestions:
1.
（2）Baud/Hzisthehighestpossibleunitbandwidthrate,andisalsocalledastheNyquistrate.
2.Thetime-domainequalizerisusedtoovercome（intersymbolinterference（ISI））.
3.Thebasicprocess,from（Samplingtheanalogsignal）,（thequantization）,and（convertingtobinarysymbols）,isusuallycalledaspulsecodemodulation（PCM）.
Single-ChoiceQuestions:
1.Ifthesamplesobeyuniformdistributionover
thenthequantizationnoisepowerisdeterminedby（C）
（A）
（B）
andquantizationinterval
（C）quantizationinterval
（D）otherparameters.
Multiple-ChoiceQuestions:
1.Digitizationofanalogsignalsincludes（B,E）
（A）.Modulation（B）.Quantization（C）.Multiplexing（D）.Sourcecoding（E）.Sampling
2.Whicharesymbolcodetypeforbasebanddigitalsignals?
（A,B,C,D,E）
（A）.HDB3（B）.AMI（C）.CMI（D）.Biphasiccode（E）.5B6B（F）.BPSK（G）.MSK
Short-AnswerQuestions:
1.Whicharethedesignprinciplesofcodefordigitalbasebandsignal?
Asweknow,theperformanceofapracticalbasebandtransmissionsystemcanbefoundinitseyepattern（refertothefigurebelow）.Pleasefindoutthecharacteristicsinthefigure1,andpointouttheirimpactsontransmissionperformance.
Answer:
（1）Thelocationofthecentralperpendicularlineistheoptimumsamplinginstant.
（2）Themiddlehorizontallinerepresentstheoptimumdecisionthresholdlevel.
（3）Theperpendicularheightoftheshadowregionrepresentsthedistortionrangeofthereceivedsignal.
（4）Theslopeofthebeveledgeofthe“eye”representssensitivityofthesamplinginstanttothetimingerror.
（5）Undernonoisesituation,thedegreeoftheopeningofthe“eyeisthenoisetolerance;ifnoiseatthesamplinginstantexceedsthistolerance,thenerrordecisionmayhappen.
CalculationQuestions:
1.Assumethereare4overalltransfercharacteristicsofbasebandtransmissionsystemsshowninFigure2.Ifsymbolrateis2000Bd,pleaseillustratewhethertheycantransmitinformationwithoutISI?
Whichsystemhasbettertransmissioncharacteristic?
Solution:
∵symbolrateis2000Bd,
∴ISIexistsinsystem（a）and（c）,ISIdoesnotexistinsystem（b）and（d）.
Sincesystem（b）canberealizedphysically,andits
system（d）can’tberealized
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