雨课堂学堂在线学堂云《Wireless Communications（西安电子科技）》单元测试考核答案

第1题Inlearningthecourse,weassumethelearnerhasthefundamentalknowledgeofmodulation,channelcodingandsynchronization,whichiscoveredinCommunicationPrinciples第1题WhatarethemainproblemsofthefirstgenerationWlan?

A

poorperformanceBsecurityproblemsChighcostDfastdatarate正确答案：ABChomework1.3第1题Themainchallengesofwirelesscommunicationscomefromthe___betweenthetransmitterandreceiver.AmodulationanddemodulationdesignBchannelCspectrumallocationDdopplerhomework1.4第1题Inthefollowingdescriptiononthecellconcept，whichisincorrect?AThegeographicregionisdividedintocellsandthesecellsarenonoverlapping.BThechannelsetssuchasfrequencies/timeslots/codescanbereusedatspatially-separatedlocations.CShrinkingthecellsizecanincreasethecapacity.DThebigcellsizemaycausefrequenthandoffproblems.homework1.5第1题Bluetoothisaopenwirelesstechnologystandardforexchangingdataovershortdistances，whichcoveragecanbeextendedto1km.Testforchapter1第1题ThefirstwirelesscommunicationnetworksinthePre-industrialagetransmittedinformationbyusingsomesimplesignals,suchlike__signals,__signal,signal___,orbeatingdrums.

AsmokeBfireCflaresDlaser正确答案：ABC第2题ThemobiletelephonenetworkinNewYorkcouldonlysupportsmallnumberofsubscribersmainlybecausethepowerofthebasestationistoolow.

第3题ThefirstgenerationWLANdeviceshadtouselowpowerdensityschemebecausehighpowerdevicesareveryexpensive.第4题__isnotthereasonthatwhythe1stgenerationWLANisnotwidelyused.ALackofmobilityBLowdatarateCShortcoverage.DLackofstandardization第5题

­__

and__

aretwomaindisadvantagesforhighaltitudeorbitssatellitecommunications.

AHighpathlossBsallcoverageCbigpropagationdelayDmultpathinterferrence正确答案：AChomework2.1第1题Whatarethemainmechanismsbehindelectromagneticwavepropagation?AreflectionBdiffractionCpolarizationDscattering正确答案：ABDhomework2.2第1题Thefrequencybandisaprimaryfactortotakeintoaccountwhenassessingeffectivenessofradiocommunicationlinks.homework2.3第1题Scatteringoccurswhenthesurfaceoftheobjectbetweenthetransmitterandreceiverisirregularorcoarse.homework2.4第1题TheHatamodelisanotherempiricalmodelusingthegraphicalpathlossdataprovidedbyOkumura.Inwhatfrequencyrangeisiteffective?A150-1500MHzB180-1920MHzC200-2020MHzD240-2100MHzhomework2.5第1题TheminimumtransmissionqualityisnotcorrespondingtoaminimumSignal-to-NoisepowerRatio(SNR)atthereceiver.Testforchapter2第1题Whatcancausepowervariationinthereceivedsignaloverthedistance?Afree-spacepropagationBconstantsignalsourcepowerCpathlossDshadowingeffects正确答案：CD第2题Whichfrequencybandisusedfortelevisioncommunicationsandradionavigationsystems?A3kHz-30kHzB3MHz-30MHzC30MHz-300MHzD300MHz-3GHz第3题PathlossandShadowingaregenerallyreferredaslargescalepropagationeffects.第4题Fresnelknifeedgediffractionmodeliscommonlyuseddiffractionmodel.第5题Shadowingiscausedbytheamplificationofthepowerradiatedbythetransmitterandthereflectiveeffectsofthepropagationchannel.homework3.1第1题Inthetelephone/cablenetworksystem,whatisthecauseofthemultipathmechanism?AAtmosphericrefractionandreflectionBGroundandbuildingreflectionCReflectionsfromterminationsDMultimodepropagationhomework3.2第1题Themeandelayspread,rmsdelayspread,ordelayspreaddeviationcanbeusedtodescribethedelayspread,andtheseparameterscanbemeasureddirectly.homework3.3第1题Ifthebandwidthofthesignalisfargreaterthanchannelcoherencebandwidth,theeffectofDopplerspreadwouldbenegligibleandthechanneliscalledfastfadingchannel.homework3.4第1题Whenthetimespreadingisfarlessthanthesymboltime,thechannelissaidtobeflatfadingchannel.homework3.5第1题____and

____ofaRayleighfadingsignalaretwoimportantstatisticsandarekeyfactorsinthedesignofchannelcodesanddiversityschemesinmobilecommunications.AThelevelcrossingrateBAveragefadedurationCSignal-to-noiseratioDCarrierfrequency正确答案：ABTestforchapter3第1题Therearemanyphysicalfactorsintheradiopropagationenvironmentinfluencesmall-scalefading，suchas____.AMultipathpropagationBThesignalbandwidthCRelativemotionofthereceiverandtransmitterDRelativemotionofthereceiverandsurroundingobjects正确答案：ABCD第2题Foramodulatedsignal,ifthesignalbandwidthislessthanthechannelcoherencebandwidth,thesignalthatpassesthechannelwillexperience____.Afrequency-selectivefadingBflatfadingCRayleighfadingDmultipathfading第3题TherelativemotionbetweenthereceiverandthetransmitterresultinrandomfrequencymodulationduetodifferentDopplershiftsoneachofthemultipathcomponents.第4题Whenthechannelrmsdelayspreadismuchmorethanthesymbolduration,thechannelisregardedasfrequency-selectivefadingchannelorwidebandchannel.第5题Inthelinkbudgetofmobilecommunications,fademarginisnotnecessarilyconsidered.homework4.1第1题Thefollowingaresomeofthemainreasonswhydigitalmodulationswereintroduced.AHighordermodulationtechniquescanbeused.BPowerfulchannelcoding,equalizationormulticarriertechniquescanbeusedtomitigatetheISIeffect.CSpreadspectrumtechniquesmodulationscanbeusedtoremoveorcombinemultipath,resistinterference,anddetectmultipleuserssimultaneously.D

Encryptioncanalsobeapplied.正确答案：ABCDhomework4.2第1题Thefundamentalofdemodulationistoconverttheconstellationpointintoasignalvectorinthesignalspaceandfindthenearestconstellationpointtothisvector.

homework4.3第1题TheprobabilityoferrorassociatedwithconstellationsattheminimumdistancedminmultipliedbythenumberofneighborsatthisdistanceMdminis____.A

theupperboundB

thenearneighborapproximationCthelooserupperboundDtheexactsolution.homework4.4第1题In__,theinformationiscarriedinamplitude.AMPAMBMPSKCMQAMDMFSKhomework4.5第1题Inπ/4-DQPSK,thein-phaseandthequadrature-phasecomponentsoccuratatimedifferenceofT/2,whereTisthesymboltime,andthis

mitigatetheamplitudefluctuationsofa180degreephaseshift.

homework4.6第1题In__,theinformationiscarriedinphaseandamplitude.

AMPAMBMPSKCMQAMDMFSKhomework4.7第1题

ForMFSK,theminimumfrequencyseparationis__toguaranteethatthebasisfunctionsondifferentfrequencyareorthogonal.A2△f

c.=1/(2Ts)B

2△f

c.=1/TsC2△f

c.=0.5/TsD

△f

c.=1/Tshomework4.8第1题__donotsatisfytheheprincipleofpulseshapingthatinter-symbolinterference(ISI)betweenpulsesinthereceivedsignalisnotintroduced.

AThe

rectangularpulseBThecosinepulseCTheraisedcosinepulsesDThe

Gaussianpulsehomework4.9第1题Assumethatthesymbolenergyisdividedequallyamongallbits,ifGrayencoding

isusedandthesystemisunderareasonableSNRsandthesizeofsymbolsetisM,thenrs=rblog2Mandps.=pblog2M

homework4.10第1题__applieswhenTs≈Tc,whichmeanstheSNRpersymbolγsisroughlyconstantoverasymboltimesothatonecanintegratetheerrorprobabilityinAWGNoverthefadingdistributiontoobtaintheaverageerrorprobability.

ABERB

Theoutageprobability,PoutCTheaverageerrorprobabilityDTheoutageandaverageerrorprobabilitycombinedhomework4.11第1题TheirreducibleerrorforDPSKRayleighfadingchannelisapproximatedas0.5*(πfdTb)2.IftheDopplershiftisdetermined,alargebittime,orequivalently,alowerbitratecanguaranteealowererrorfloor.Testforchapter4第1题Thefollowingarecomponentsofthetransmitterofacommunicationsystem.AsourcecoderBchannelcoderCmodulatorDequalizer正确答案：ABC第2题Atreceiver,thelocaloscillator(LO)whichisgeneratedandtrackedbyacarrierfrequencyrecoverycomponentprovidesanunmodulatedsinusoidalsignal,toconverttheradiofrequencysignalintoabasebandsignal.第3题IfthereareMsymbolandeachsymbolhasKbits,i.e.M=2K.AssumethesymboldurationisT,thedatarateofthesystemis__.AM/TBK*TClog2M/TbpsDK/Tbps正确答案：CD第4题Indemodulation,minimizingthesymbolerrorprobabilitycorrespondstofindtheconstellationsithatmaximizesp(si|r),whereristhereceivedvector.第5题___are

performancecriteriawhichareusedtodescribetheperformanceofdigitalmodulationsoverfadingchannelsdependsontherateofchangeoffading.ABERBTheoutageprobability,PoutCTheaverageerrorprobabilityDTheoutageandaverageerrorprobabilitycombined正确答案：BCDhomework5.1第1题ForDiversity,theindependentpathsmaybeimplementedinthe_domain.

A

polarizationBtimeC

spaceD

frequency正确答案：BCDAhomework5.2第1题WhatisMaximalRatioCombining(MRC)?AAsystemthatcombinessignalsfrommultiplebranchesbyoptimallyweightingtheiramplitudesandphases.BAsystemthatonlyoutputsonebranchofsignalstothedemodulator.CAsystemthatswitchesbetweenbranchesbasedonRSSI.D

Asystemthatcombinessignalsfrommultiplebranchesbyequallyweightingthem.homework5.3第1题ChannelcodingreducethebandwidthefficiencyinhighSNRconditions.

homework5.4第1题Whatisthepurposeoftheparitycheckbitsinasystematiccode?

A

Toensurethatthecodewordisunique.B

Todetecterrorsinthecodeword.CToincreasethestorageefficiencyofthecode.DTomaptheinformationbitstothecodeword.homework5.5第1题Inthedecodingprocedureofblockcoding,thefirststepistocheckifareceivedcodewordisvalidornot.homework5.6第1题Theoutputofaconvolutionalencoderdependsonlyonthecurrentinputandnotonthepreviousinputs.homework5.7第1题Whichofthefollowingstatementsaboutblockcodingwithinterleavingistrue?A

Theinterleaverisappliedbeforethechannelencoder.BThebitsareputintothedemodulatorafterde-interleaver.CDe-interleaverisappliedafterdemodulator,theresultisthenputintothechanneldecoder.D)Theinterleaverisappliedafterthemodulator.DTheinterleaverisappliedafterthemodulator.homework5.8第1题Whatisthemainpurposeofequalizationinwirelesscommunications?(A)Toreducenoise(B)Toincreasesignalstrength(C)ToalleviateInterSymbolInterference(ISI)(D)ToimprovemodulationefficiencyAToreducenoiseBToincreasesignalstrengthCToalleviateInterSymbolInterference(ISI)DToimprovemodulationefficiencyhomework5.9第1题Thecomplexityoftimedomainequalizergrowasthedatarateincreases.Testforchapter5第1题_，_and_aretechniqueswhichcanbeusedtoimprovethelinkqualityofwirelesschannelsASourcecodingBDiversityCChannelcodingDEqualization正确答案：BCD第2题__selectsthebranchwiththehighestSNRastheresultdiversityoutputanddiscardsotherbranches.ASelectioncombiningBThresholdcombiningCMaximalRatiocombiningDEqualgaincombing第3题Whichofthefollowingstatementsistrueaboutchannelcoding?AItcanonlydetecterrors,notcorrectthem.BItcanonlycorrecterrors,notdetectthem.CItcanbothdetectandcorrecterrors.DIthasnoeffectonerrorcorrectioninwirelessfadingchannels.第4题Inthedecodingprocessofblockcoding,ifthesyndromevectorhasall-zeroentries,thereceivedcodewordisalwaysvalid.第5题Whatarethetwomaincategoriesoftimedomainequalization?ALinearandnonlinearBFrequencydomainandtimedomainCDecision-feedbackandmaximumlikelihoodsequenceestimationDSimpleandcomplexhomework6.1第1题ThefundamentalofspreadspectrumcommunicationcanbeexplainedbythefamousShannoncapacityformula.homework6.2第1题Forthepseudorandomsequenceinthespreadspectrumsystem,themostimportantthingisthecorrelationproperties,including:____.AautocorrelationBcrosscorrelationCpartialcorrelationDVariance正确答案：ABChomework6.3第1题Inspreadspectrumsystems,thestructureofmsequencegeneratorgenerallyhastwoforms:____and____.

ADSSSBMSRGCSSRGDFHSS正确答案：BChomework6.4第1题ARAKEreceiverisaclassicaldiversityreceiverdesignedfortheCDMAsystem.Testforchapter6第1题Inspreadspectrumcommunications,thesignalisspreadbyaPNcodeatthetransmitteranditiscorrelatedbythesamePNcodeatthereceiver,whichhasmanyadvantages,including:____.AStronganti-interferencecapabilityBStrongresistancetomultipathinterferenceCHighcapabilityofanti-fadingDLowprobabilityofinterception正确答案：ABCD第2题Toguaranteethespreadingcodegeneratedinthereceivercansynchronizewiththespreadingcodeinthereceivedsignal,____isneeded.AphasesynchronizationBfrequencysynchronizationCtimesynchronizationDpowersynchronization第3题Spreadspectrumcanbetakentoimproveperformanceofwirelesscommunications.第4题Spreadspectrumcommunicationisasingle-accesscommunicationmethodthatdistinguishescommunicationaddressesbyfrequencydifferences.第5题Awaytoimprovetheworkingspeedofpseudo-randomsequenceistoadoptMSRGstructure.homework7.1第1题WhatisthedifferencebetweentraditionalFDMandOFDMintermsofhowtheydividethefrequencyband?ATraditionalFDMdividestheentirefrequencybandintonon-overlappingsub-channels,whileOFDMdividesitintooverlappingsub-channelswithorthogonalcharacteristics.BTraditionalFDMdividestheentirefrequencybandintooverlappingsub-channels,whileOFDMdividesitintonon-overlappingsub-channels.C

TraditionalFDMdividesthefrequencybandintoequalparts,whileOFDMdividesitintounequalparts.

D

TraditionalFDMusescoherentdemodulation,whileOFDMusesnon-coherentdemodulation.homework7.2第1题WhatisthepurposeofaddingaguardintervalinanOFDMsystem?AToincreasethedatarateBToreducepowerconsumptionCTominimizeISIandmultipathinterferencecausedbydelayspreadofthechannelDToimprovesignalqualityhomework7.3第1题Whatisthetermusedtodescribemultipleantennasatbothtransmitterandreceiverinacommunicationsystem?AMultipleInputSingleOutput(MISO)BMultipleInputMultipleOutput(MIMO)CSingleInputSingleOutput(SISO)DSingleInputMultipleOutput(SIMO)homework7.4第1题WhatarethetwomainapplicationsofMIMOsystem?ASpatialmultiplexingandspatialdiversityBTimemultiplexingandfrequencydiversityCFrequencymultiplexingandtimediversityDChannelmultiplexingandsignaldiversityhomework7.5第1题Whenthenumberofantennaelementstendstobeverylarge(infinite),whathappenstothechannelsofMassiveMIMO?ATheybecomemorerandom.BTheybecomelesscertain.CTheytendtobeorthogonal.DTheybecomemorecertain.TestforChapter7第1题Whatisthepurposeofmulticarriermodulation?ATodivideahighspeeddatastreamintomanylowspeedsubstreamsBToimprovetheperformancethroughdiversityCTochangefrequencyselectivefadingintoflatfadingDToovercomeDopplershiftproblem正确答案：ABC第2题WhereisthecyclicprefixaddedinanOFDMsystem?ABeforetheOFDMsignalissenttothechannelfortransmissionBAftertheOFDMsignalisreceivedatthereceiverCDuringtheDFTdemodulationprocessDBeforetheIDFTmodulationprocess第3题WhatisthematrixHusedtorepresentinaMIMOchannelmodel?AThecomplexgainfactorfromeachtransmitantennatoreceiveantennapairBThechannelgainfromeachtransmitantennatoreceiveantennapairCThenumberoftransmittingandreceivingantennasinaMIMOsystemDTheestimatedaccuracyofthechannelatthereceiver第4题WhenboththereceiverandtransmitterknowtheCSI,howcanthecorrespondingpowerallocationpolicybeobtainedforthemaximumchannelcapacity?AItisobtainedbyaveragingthepowerallocationonthetransmittingantenna.BItisobtainedbyusingwaterfillingalgorithm.CItisobtainedbyequallyallocatingthepowerPi.DItisobtainedbyusingSVD.第5题WhatisthemainideaofspatialdiversityinMIMO?AToincreasethereliabilityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinforma