Wireless Communications知到智慧樹(shù)章節(jié)測(cè)試課后答案2024年秋西安電子科技大學(xué)

WirelessCommunications知到智慧樹(shù)章節(jié)測(cè)試課后答案2024年秋西安電子科技大學(xué)第一章單元測(cè)試

ThemobiletelephonenetworkinNewYorkcouldonlysupportsmallnumberofsubscribersmainlybecausethepowerofthebasestationistoolow.（）

A:對(duì)B:錯(cuò)

答案:錯(cuò)ThefirstgenerationWLANdeviceshadtouselowpowerdensityschemebecausehighpowerdevicesareveryexpensive.（）

A:對(duì)B:錯(cuò)

答案:錯(cuò)__isnotthereasonthatwhythe1stgenerationWLANisnotwidelyused.（）

A:Lowdatarate.B:Shortcoverage.C:Lackofmobility.D:Lackofstandardization.

答案:Lackofmobility.__and__aretwomaindisadvantagesforhighaltitudeorbitssatellitecommunications.（）

A:multipathinterference.B:HighpathlossC:smallcoverage.D:bigpropagationdelay

答案:Highpathloss；bigpropagationdelayThefirstwirelesscommunicationnetworksinthePre-industrialagetransmittedinformationbyusingsomesimplesignals,suchlike__signals,__signal,signal___,orbeatingdrums.（）

A:laserB:smokeC:fireD:flares

答案:smoke；fire；flares

第二章單元測(cè)試

Whatcancausepowervariationinthereceivedsignaloverthedistance?（）

A:shadowingeffectsB:constantsignalsourcepowerC:free-spacepropagationD:pathloss

答案:shadowingeffects；pathlossWhichfrequencybandisusedfortelevisioncommunicationsandradionavigationsystems?（）

A:300MHz-3GHzB:30MHz-300MHzC:3kHz-30kHzD:3MHz-30MHz

答案:3MHz-30MHzPathlossandShadowingaregenerallyreferredaslargescalepropagationeffects.（）

A:對(duì)B:錯(cuò)

答案:對(duì)Fresnelknifeedgediffractionmodeliscommonlyuseddiffractionmodel.（）

A:錯(cuò)B:對(duì)

答案:對(duì)Shadowingiscausedbytheamplificationofthepowerradiatedbythetransmitterandthereflectiveeffectsofthepropagationchannel.（）

A:錯(cuò)B:對(duì)

答案:錯(cuò)

第三章單元測(cè)試

Therearemanyphysicalfactorsintheradiopropagationenvironmentinfluencesmall-scalefading，suchas____.（）

A:RelativemotionofthereceiverandtransmitterB:ThesignalbandwidthC:RelativemotionofthereceiverandsurroundingobjectsD:Multipathpropagation

答案:Relativemotionofthereceiverandtransmitter；Thesignalbandwidth；Relativemotionofthereceiverandsurroundingobjects；MultipathpropagationForamodulatedsignal,ifthesignalbandwidthislessthanthechannelcoherencebandwidth,thesignalthatpassesthechannelwillexperience____.（）

A:flatfadingB:frequency-selectivefadingC:RayleighfadingD:multipathfading

答案:flatfadingTherelativemotionbetweenthereceiverandthetransmitterresultinrandomfrequencymodulationduetodifferentDopplershiftsoneachofthemultipathcomponents.（）

A:對(duì)B:錯(cuò)

答案:對(duì)Whenthechannelrmsdelayspreadismuchmorethanthesymbolduration,thechannelisregardedasfrequency-selectivefadingchannelorwidebandchannel.（）

A:對(duì)B:錯(cuò)

答案:對(duì)Inthelinkbudgetofmobilecommunications,fademarginisnotnecessarilyconsidered.（）

A:對(duì)B:錯(cuò)

答案:錯(cuò)

第四章單元測(cè)試

Thefollowingarecomponentsofthetransmitterofacommunicationsystem.（）

A:equalizerB:channelcoderC:sourcecoderD:modulator

答案:channelcoder；sourcecoder；modulatorAtreceiver,thelocaloscillator(LO)whichisgeneratedandtrackedbyacarrierfrequencyrecoverycomponentprovidesanunmodulatedsinusoidalsignal,toconverttheradiofrequencysignalintoabasebandsignal.（）

A:錯(cuò)B:對(duì)

答案:對(duì)IfthereareMsymbolandeachsymbolhasKbits,i.e.M=2K.AssumethesymboldurationisT,thedatarateofthesystemis__.（）

A:K*TB:K/TbpsC:log2M/TbpsD:M/T

答案:K/Tbps；log2M/TbpsIndemodulation,minimizingthesymbolerrorprobabilitycorrespondstofindtheconstellationsithatmaximizesp(si|r),whereristhereceivedvector.（）

A:對(duì)B:錯(cuò)

答案:對(duì)___areperformancecriteriaareusedtodescribetheperformanceofdigitalmodulationsoverfadingchannelsdependsontherateofchangeoffading.（）

A:BERB:Theoutageprobability,PoutC:TheoutageandaverageerrorprobabilitycombinedD:Theaverageerrorprobability

答案:Theoutageprobability,Pout；Theoutageandaverageerrorprobabilitycombined；Theaverageerrorprobability

第五章單元測(cè)試

___，___and___aretechniqueswhichcanbeusedtoimprovethelinkqualityofwirelesschannels.（）

A:SourcecodingB:ChannelcodingC:EqualizationD:Diversity

答案:Channelcoding；Equalization；Diversity___selectsthebranchwiththehighestSNRastheresultdiversityoutputanddiscardsotherbranches.（）

A:ThresholdcombiningB:MaximalRatiocombiningC:EqualgaincombingD:Selectioncombining

答案:SelectioncombiningWhichofthefollowingstatementsistrueaboutchannelcoding?（）

A:Itcanonlydetecterrors,notcorrectthem.B:Itcanbothdetectandcorrecterrors.C:Ithasnoeffectonerrorcorrectioninwirelessfadingchannels.D:Itcanonlycorrecterrors,notdetectthem.

答案:Itcanbothdetectandcorrecterrors.Inthedecodingprocessofblockcoding,ifthesyndromevectorhasall-zeroentries,thereceivedcodewordisalwaysvalid.（）

A:對(duì)B:錯(cuò)

答案:對(duì)Whatarethetwomaincategoriesoftimedomainequalization?（）

A:FrequencydomainandtimedomainB:LinearandnonlinearC:SimpleandcomplexD:Decision-feedbackandmaximumlikelihoodsequenceestimation

答案:Linearandnonlinear

第六章單元測(cè)試

Inspreadspectrumcommunications,thesignalisspreadbyaPNcodeatthetransmitteranditiscorrelatedbythesamePNcodeatthereceiver,whichhasmanyadvantages,including:____.（）

A:Highcapabilityofanti-fadingB:StrongresistancetomultipathinterferenceC:Stronganti-interferencecapabilityD:Lowprobabilityofinterception

答案:Highcapabilityofanti-fading；Strongresistancetomultipathinterference；Stronganti-interferencecapability；LowprobabilityofinterceptionToguaranteethespreadingcodegeneratedinthereceivercansynchronizewiththespreadingcodeinthereceivedsignal,____isneeded.（）

A:timesynchronizationB:powersynchronizationC:frequencysynchronizationD:phasesynchronization

答案:timesynchronizationSpreadspectrumcanbetakentoimproveperformanceofwirelesscommunications.（）

A:對(duì)B:錯(cuò)

答案:對(duì)Spreadspectrumcommunicationisasingle-accesscommunicationmethodthatdistinguishescommunicationaddressesbyfrequencydifferences.（）

A:對(duì)B:錯(cuò)

答案:錯(cuò)Awaytoimprovetheworkingspeedofpseudo-randomsequenceistoadoptMSRGstructure.（）

A:錯(cuò)B:對(duì)

答案:對(duì)

第七章單元測(cè)試

Whatisthepurposeofmulticarriermodulation?（）

A:ToovercomeDopplershiftproblemB:TodivideahighspeeddatastreamintomanylowspeedsubstreamsC:ToimprovetheperformancethroughdiversityD:Tochangefrequencyselectivefadingintoflatfading

答案:Todivideahighspeeddatastreamintomanylowspeedsubstreams；Toimprovetheperformancethroughdiversity；TochangefrequencyselectivefadingintoflatfadingWhereisthecyclicprefixaddedinanOFDMsystem?（）

A:BeforetheOFDMsignalissenttothechannelfortransmissionB:BeforetheIDFTmodulationprocessC:DuringtheDFTdemodulationprocessD:AftertheOFDMsignalisreceivedatthereceiver

答案:BeforetheOFDMsignalissenttothechannelfortransmissionWhatisthematrixHusedtorepresentinaMIMOchannelmodel?（）

A:ThechannelgainfromeachtransmitantennatoreceiveantennapairB:TheestimatedaccuracyofthechannelatthereceiverC:ThecomplexgainfactorfromeachtransmitantennatoreceiveantennapairD:ThenumberoftransmittingandreceivingantennasinaMIMOsystem

答案:ThecomplexgainfactorfromeachtransmitantennatoreceiveantennapairWhenboththereceiverandtransmitterknowtheCSI,howcanthecorrespondingpowerallocationpolicybeobtainedforthemaximumchannelcapacity?（）

A:Itisobtainedbyaveragingthepowerallocationonthetransmittingantenna.B:ItisobtainedbyusingSVD.C:Itisobtainedbyusingwaterfillingalgorithm.D:ItisobtainedbyequallyallocatingthepowerPi.

答案:Itisobtainedbyusingwaterfillingalgorithm.WhatisthemainideaofspatialdiversityinMIMO?（）

A:Todecreasethereliabilityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinformationonaparallelchannelinspace.B:Toincreasethereliabilityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinformationonaparallelchannelinspace.C:Todecreasethecomplexityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinformationonaparallelchannelinspace.D:Toincreasethecomplexityofcommunicationbyusing