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.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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