同济大学通信系统原理英文班练习题附答案Word格式文档下载.docx

同济大学通信系统原理英文班练习题附答案Word格式文档下载.docx

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（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

C.

kHzC.

TrueorFalse

Whenthereisnoinputsignal,theadditiveinterferencedoesn’texist,butthemultiplicativeinterferencestillexists.（F）

Chapter2

2.1,2.4,2.5,2.6,2.8,2.11

1.AWGNnoiseisshorttermfor（AdditiveWhiteGaussianNoise）.

2.Thepowerspectraldensityand（theautocorrelationfunction）ofastationaryrandomprocessareapairofFouriertransform.

3.Ifbandwidthis10MHz,signal-to-noiseratiois20dB,theShannoncapacityisC=（66.6Mbps）.

1.Assume

isageneralizedstationaryrandomprocesswithzeromathematicalexpectation,thentheaveragepowerof

is（D）.

B.

C.

D.

2.Foranarrowbandrandomprocess

if

isaGaussianprocess,then（A）.

（A）

and

arealsoGaussianprocesses;

（B）Only

isalsoGaussianprocess;

（C）

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）

W

（4）∵

∴

V

∴thebasebandsignalcanbewrittenas:

5.AssumetheamplitudeofaFMmodulatedsignalis10V,theinstantaneousfrequencyoftheFMsignalis:

（1）theexpressionoftheFMmodulatedsignal.

（2）themaximumfrequencydeviation,themodulationindex,andthebandwidthofthemodulatedsignal.

（1）

1.AssumetheexpressionofaFMsignalis

thecarrierfrequencyofthisFMsignalis（

）Hz,themaximumfrequencydeviationis（5000）Hz,thebandwidthofthisFMsignalis（

）Hz，theaveragepoweris（12.5）W.

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

1.Thebasicprocess,from（Samplingtheanalogsignal）,（thequantization）,and（convertingtobinarysymbols）,isusuallycalledaspulsecodemodulation（PCM）.

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）

andquantizationinterval

（C）quantizationinterval

（D）otherparameters.

1.Digitizationofanalogsignalsincludes（B、D、E）

（A）.Modulation（B）.Quantization（C）.Multiplexing（D）.Sourcecoding（E）.Sampling

Short-AnswerQuestions:

1.InDeltamodulationsystem,whyweincreasesamplingfrequency

ratherthanquantizationstep

toavoidoverloadquantizationnoise?

Giventhesamplingfrequencyandthequantizationstep

thentheslopeofastepis:

Itisthemaximumpossibleslopeofastep-shapedwave,oritiscalledthemaximumtrackingslopeofthedecoder.Whentheslopeoftheinputsignalofthedeltamodulatorexceedsthismaximum,overloadquantizationnoisewillbegenerated.Therefore,inordertoavoidoverloadquantizationnoise,itisnecessarytomaketheproductof

and

largeenough,sothattheslopeofthesignalcannotexceedthisproduct.Onetheotherhand,thevalueof

isdirectlyrelatedtothemagnitudeofthebasicquantizationnoise.Ifthevalueof

islarge,thenthebasicquantizationnoisemustalsobelarge.Therefore,onlythemethodofincreasing

toincreasetheproduct

canensurethatthebasicquantizationnoiseandtheoverloadquantizationnoisedonotexceedthelimit.

1.

（2）Baud/Hzisthehighestpossibleunitbandwidthrate,andisalsocalledastheNyquistrate.

2.Thetime-domainequalizerisusedtoovercome（intersymbolinterference（ISI））.

3.Thebasicprocess,from（Samplingtheanalogsignal）,（thequantization）,and（convertingtobinarysymbols）,isusuallycalledaspulsecodemodulation（PCM）.

1.Ifthesamplesobeyuniformdistributionover

thenthequantizationnoisepowerisdeterminedby（C）

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

1.Whicharethedesignprinciplesofcodefordigitalbasebandsignal?

Asweknow,theperformanceofapracticalbasebandtransmissionsystemcanbefoundinitseyepattern（refertothefigurebelow）.Pleasefindoutthecharacteristicsinthefigure1,andpointouttheirimpactsontransmissionperformance.

（1）Thelocationofthecentralperpendicularlineistheoptimumsamplinginstant.

（2）Themiddlehorizontallinerepresentstheoptimumdecisionthresholdlevel.

（3）Theperpendicularheightoftheshadowregionrepresentsthedistortionrangeofthereceivedsignal.

（4）Theslopeofthebeveledgeofthe“eye”representssensitivityofthesamplinginstanttothetimingerror.

（5）Undernonoisesituation,thedegreeoftheopeningofthe“eyeisthenoisetolerance;

ifnoiseatthesamplinginstantexceedsthistolerance,thenerrordecisionmayhappen.

1.Assumethereare4overalltransfercharacteristicsofbasebandtransmissionsystemsshowninFigure2.Ifsymbolrateis2000Bd,pleaseillustratewhethertheycantransmitinformationwithoutISI?

Whichsystemhasbettertransmissioncharacteristic?

Solution:

∵symbolrateis2000Bd,

∴ISIexistsinsystem（a）and（c）,ISIdoesnotexistinsystem（b）and（d）.

Sincesystem（b）canberealizedphysically,andits

system（d）can’tberealizedph