【答案】《Wireless Communications(无线通信)》(西安电子科技大学)章节期末中国大学慕课答案

Chapter1WirelessCommunicatiosnsOverviewTestforchapter11.单选题：In1898,__demonstratedthewell-knownradiotransmissionfromtheIsleofWighttoatugboat18milesaway.

选项：

A、Tesla

B、Marconi

C、Edison

D、KarlFerdinandBraun

答案：【Marconi】2.单选题：__isnotthereasonthatwhythe1stgenerationWLANisnotwidelyused.

选项：

A、Lackofmobility

B、Lowdatarate

C、Shortcoverage

D、Lackofstandardization

答案：【Lackofmobility】3.多选题：__and__aretwomaindisadvantagesforhighaltitudeorbitssatellitecommunications

选项：

A、Highpathloss

B、sallcoverage

C、bigpropagationdelay

D、multpathinterferrence

答案：【Highpathloss;bigpropagationdelay】4.多选题：ThefirstwirelesscommunicationnetworksinthePre-industrialagetransmittedinformationbyusingsomesimplesignals,suchlike__signals,__signal,signal___,orbeatingdrums.

选项：

A、smoke

B、flares

C、fire

D、laser

答案：【smoke;flares;fire】5.单选题：ThemobiletelephonenetworkinNewYorkcouldonlysupportsmallnumberofsubscribersmainlybecausethepowerofthebasestationistoolow

选项：

A、正确

B、错误

答案：【错误】6.单选题：Thedevelopmentofsignalprocessingalgorithmhasnothingtodowiththedevelopmentofwirelessindustry

选项：

A、正确

B、错误

答案：【错误】Chapter2WirelessPropagationChannelModeling:Large-ScalePathLossandShadowingTestforchapter21.单选题：Whichfrequencybandisusedfortelevisioncommunicationsandradionavigationsystems?

选项：

A、3kHz-30kHz

B、3MHz-30MHz

C、30MHz-300MHz

D、300MHz-3GHz

答案：【30MHz-300MHz】2.多选题：Whatcancausepowervariationinthereceivedsignaloverthedistance?

选项：

A、free-spacepropagation

B、constantsignalsourcepower

C、pathloss

D、shadowingeffects

答案：【pathloss;shadowingeffects】3.单选题：PathlossandShadowingaregenerallyreferredaslargescalepropagationeffects.

选项：

A、正确

B、错误

答案：【正确】4.单选题：Fresnelknifeedgediffractionmodeliscommonlyuseddiffractionmodel.

选项：

A、正确

B、错误

答案：【正确】5.单选题：Shadowingiscausedbytheamplificationofthepowerradiatedbythetransmitterandthereflectiveeffectsofthepropagationchannel.

选项：

A、正确

B、错误

答案：【错误】Chapter3WirelessPropagationChannelModeling:Small-ScaleFadingandStatisticalMultipathChannelTestforchapter31.单选题：Foramodulatedsignal,ifthesignalbandwidthislessthanthechannelcoherencebandwidth,thesignalthatpassesthechannelwillexperience____.

选项：

A、frequency-selectivefading

B、flatfading

C、Rayleighfading

D、multipathfading

答案：【flatfading】2.多选题：Therearemanyphysicalfactorsintheradiopropagationenvironmentinfluencesmall-scalefading，suchas____.

选项：

A、Multipathpropagation

B、Thesignalbandwidth

C、Relativemotionofthereceiverandtransmitter

D、Relativemotionofthereceiverandsurroundingobjects

答案：【Multipathpropagation;Thesignalbandwidth;Relativemotionofthereceiverandtransmitter;Relativemotionofthereceiverandsurroundingobjects】3.单选题：Inthelinkbudgetofmobilecommunications,fademarginisnotnecessarilyconsidered.

选项：

A、正确

B、错误

答案：【错误】4.单选题：TherelativemotionbetweenthereceiverandthetransmitterresultinrandomfrequencymodulationduetodifferentDopplershiftsoneachofthemultipathcomponents.

选项：

A、正确

B、错误

答案：【正确】5.单选题：Whenthechannelrmsdelayspreadismuchmorethanthesymbolduration,thechannelisregardedasfrequency-selectivefadingchannelorwidebandchannel.

选项：

A、正确

B、错误

答案：【正确】Chapter4DigitalModulationsoverWirelessChannelsTestforchapter41.单选题：__isneededtoconvertortheanalogyinformationsourceintodigitalfordigitaltransmitter.

选项：

A、A/Dconvertor

B、D/Aconvertor

C、Sourcecoder

D、Channelcoder.

答案：【A/Dconvertor】2.单选题：__producesveryhighspectralsidelobes,whichmeansthatalargerbandwidthisoccupied.

选项：

A、Therectangularpulse

B、Thecosinepulse

C、Theraisedcosinepulses

D、TheGaussianpulse

答案：【Therectangularpulse】3.单选题：__isappliedwhenthesignalpowerischangingslowly(Ts＜＜Tc),whereTcisthechannelcoherencetime,andTsisthesymboltime.

选项：

A、BER

B、Theoutageprobability,Pout

C、Theaverageerrorprobability

D、Theoutageandaverageerrorprobabilitycombined

答案：【Theoutageprobability,Pout】4.单选题：__isappliedwhenthesignalpowerischangingslowly(Ts＜＜Tc),whereTcisthechannelcoherencetime,andTsisthesymboltime.(A)BER(B)Theoutageprobability,Pout(C)Theaverageerrorprobability(D)Theoutageandaverageerrorprobabilitycombined

选项：

A、BER

B、Theoutageprobability,Pout

C、Theaverageerrorprobability

D、Theoutageandaverageerrorprobabilitycombined

答案：【Theoutageprobability,Pout】5.单选题：AlthoughGaussianpulseshapedoesnotsatisfytheNyquistcriterion,itisstillusedinGSＭfor__

选项：

A、arelativelyhighPb≈10−3istolerableinvoicetransmition.

B、wedonothaveotherpulseforms.

C、otherpulseformsintroducehigherBER.

D、GSMdonotcareISI.

答案：【arelativelyhighPb≈10−3istolerableinvoicetransmition.】6.多选题：Thefollowingarecomponentsofthetransmitterofacommunicationsystem.

选项：

A、sourcecoder

B、channelcoder

C、modulator

D、equalizer

答案：【sourcecoder;channelcoder;modulator】7.多选题：___areperformancecriteriaareusedtodescribetheperformanceofdigitalmodulationsoverfadingchannelsdependsontherateofchangeoffading

选项：

A、BER

B、Theoutageprobability,Pout

C、Theaverageerrorprobability

D、Theoutageandaverageerrorprobabilitycombined

答案：【Theoutageprobability,Pout;Theaverageerrorprobability;Theoutageandaverageerrorprobabilitycombined】8.多选题：IfthereareMsymbolandeachsymbolhasKbits,i.e.M=2K.AssumethesymboldurationisT,thedatarateofthesystemis__

选项：

A、M/T

B、K*T

C、log2M/Tbps

D、K/Tbps

答案：【log2M/Tbps;K/Tbps】9.多选题：__maycauseintersymbolinterferenceandirreducibleerrorfloor.

选项：

A、AWGNnoise

B、Thedopplerspread

C、Thedelayspread

D、Pathlossandshadowing

答案：【Thedopplerspread;Thedelayspread】10.单选题：Atreceiver,thelocaloscillator(LO)whichisgeneratedandtrackedbyacarrierfrequencyrecoverycomponentprovidesanunmodulatedsinusoidalsignal,toconverttheradiofrequencysignalintoabasebandsignal.

选项：

A、正确

B、错误

答案：【正确】11.单选题：Indemodulation,minimizingthesymbolerrorprobabilitycorrespondstofindtheconstellationsithatmaximizesp(si|r),whereristhereceivedvector

选项：

A、正确

B、错误

答案：【正确】12.单选题：ThecoherentdemodulationofMFSKneedrecoverthecorrespondingphasereferenceforeachofthebranches,whichisgenerallydifficultandcostly.

选项：

A、正确

B、错误

答案：【正确】Chapter5Diversity,ChannelCodingandEqualizationTestforchapter51.单选题：__selectsthebranchwiththehighestSNRastheresultdiversityoutputanddiscardsotherbranches.

选项：

A、Selectioncombining

B、Thresholdcombining

C、MaximalRatiocombining

D、Equalgaincombing

答案：【Selectioncombining】2.单选题：Whichofthefollowingstatementsistrueaboutchannelcoding?

选项：

A、Itcanonlydetecterrors,notcorrectthem.

B、Itcanonlycorrecterrors,notdetectthem.

C、Itcanbothdetectandcorrecterrors.

D、Ithasnoeffectonerrorcorrectioninwirelessfadingchannels.

答案：【Itcanbothdetectandcorrecterrors.】3.单选题：Whatarethetwomaincategoriesoftimedomainequalization?

选项：

A、Linearandnonlinear

B、Frequencydomainandtimedomain

C、Decision-feedbackandmaximumlikelihoodsequenceestimation

D、Simpleandcomplex

答案：【Linearandnonlinear】4.多选题：_，_and_aretechniqueswhichcanbeusedtoimprovethelinkqualityofwirelesschannels

选项：

A、Sourcecoding

B、Diversity

C、Channelcoding

D、Equalization

答案：【Diversity;Channelcoding;Equalization】5.多选题：Channelcodingwillgenerally__or__.

选项：

A、keepthedatarateandbandwidth

B、lowertherawdatatransmissionrate

C、expandtheoccupiedbandwidthwithaparticulardatarate

D、increasetherawdatarate

答案：【lowertherawdatatransmissionrate;expandtheoccupiedbandwidthwithaparticulardatarate】6.单选题：Theconvolutionalcodeisatypeofchannelcodethatgroupsthesourcedatablocksbeforeencoding.

选项：

A、正确

B、错误

答案：【错误】7.单选题：Inthedecodingprocessofblockcoding,ifthesyndromevectorhasall-zeroentries,thereceivedcodewordisalwaysvalid.

选项：

A、正确

B、错误

答案：【正确】Chapter6SpreadSpectrumSystemsandSpreadSpectrumwithRakeReceiverTestforchapter61.单选题：Toguaranteethespreadingcodegeneratedinthereceivercansynchronizewiththespreadingcodeinthereceivedsignal,____isneeded.

选项：

A、phasesynchronization

B、frequencysynchronization

C、timesynchronization

D、powersynchronization

答案：【timesynchronization】2.多选题：Inspreadspectrumcommunications,thesignalisspreadbyaPNcodeatthetransmitteranditiscorrelatedbythesamePNcodeatthereceiver,whichhasmanyadvantages,including:____.

选项：

A、Stronganti-interferencecapability

B、Strongresistancetomultipathinterference

C、Highcapabilityofanti-fading

D、Lowprobabilityofinterception

答案：【Stronganti-interferencecapability;Strongresistancetomultipathinterference;Highcapabilityofanti-fading;Lowprobabilityofinterception】3.单选题：Spreadspectrumcanbetakentoimproveperformanceofwirelesscommunications.

选项：

A、正确

B、错误

答案：【正确】4.单选题：Spreadspectrumcommunicationisasingle-accesscommunicationmethodthatdistinguishescommunicationaddressesbyfrequencydifferences.

选项：

A、正确

B、错误

答案：【错误】5.单选题：Awaytoimprovetheworkingspeedofpseudo-randomsequenceistoadoptMSRGstructure.

选项：

A、正确

B、错误

答案：【正确】Chapter7MulticarrierModulationandMulti-antennaSystemsTestforchapter71.单选题：WhenboththereceiverandtransmitterknowtheCSI,howcanthecorrespondingpowerallocationpolicybeobtainedforthemaximumchannelcapacity?

选项：

A、Itisobtainedbyaveragingthepowerallocationonthetransmittingantenna.

B、Itisobtainedbyusingwaterfillingalgorithm.

C、ItisobtainedbyequallyallocatingthepowerPi.

D、ItisobtainedbyusingSVD.

答案：【Itisobtainedbyusingwaterfillingalgorithm.】2.单选题：WhatisthemainideaofspatialdiversityinMIMO?

选项：

A、Toincreasethereliabilityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinformationonaparallelchannelinspace.

B、Todecreasethereliabilityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinformationonaparallelchannelinspace.

C、Toincreasethecomplexityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinformationonaparallelchannelinspace.

D、Todecreasethecomplexityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinformationonaparallelchannelinspace.

答案：【Toincreasethereliabilityofcommunicationbyusingspatialredundancytotransmitdatacontainingthesameinformationonaparallelchannelinspace.】3.单选题：WhereisthecyclicprefixaddedinanOFDMsystem?

选项：

A、BeforetheOFDMsignalissenttothechannelfortransmission

B、AftertheOFDMsignalisreceivedatthereceiver

C、DuringtheDFTdemodulationprocess

D、BeforetheIDFTmodulationprocess

答案：【BeforetheOFDMsignalissenttothechannelfortransmission】4.单选题：WhatisthematrixHusedtorepresentinaMIMOchannelmodel?

选项：

A、Thecomplexgainfactorfromeachtransmitantennatoreceiveantennapair

B、Thechannelgainfromeachtransmitantennatoreceiveantennapair

C、ThenumberoftransmittingandreceivingantennasinaMIMOsystem

D、Theestimatedaccuracyofthechannelatthereceiver

答案：【Thecomplexgainfactorfromeachtransmitantennatoreceiveantennapair】5.多选题：WhatisthedisadvantageofOFDMsystem?

选项：

A、Itissensitivetofrequencyoffset.

B、Itallowsoverlappingofsubchannels.

C、Ithasahighpeak-to-averagepowerratio(PAR).

D、ItcanbeachievedbyFFT.

答案：【Itissensitivetofrequencyoffset.;Ithasahighpeak-to-averagepowerratio(PAR).】6.多选题：Whatisthepurposeofmulticarriermodulation?

选项：

A、Todivideahighspeeddatastreamintomanylowspeedsubstreams

B、Toimprovetheperformancethroughdiversity

C、Tochangefrequencyselectivefadingintoflatfading

D、ToovercomeDopplershiftproblem

答案：【Todivideahighspeeddatastreamintomanylowspeedsubstreams;Toimprovetheperformancethroughdiversity;Tochangefrequencyselectivefadingintoflatfading】7.单选题：BLAST(BellLaboratoriesLayeredSpaceTime)isanalgorithmproposedbyBelllaboratoryforspatialmultiplexing,whichinvolvestransmittingdifferentdatastreamsondifferentantennasatthesametimeandthesamefrequencyband.

选项：

A、正确

B、错误

答案：【正确】Chapter8Duplexing,MultipleAccess,andCellularDesignFundamentalsTestforchapter81.单选题：Whichofthefollowingisthecorrectcellularnetworkgroupsize?

选项：

A、two

B、four

C、six

D、eight

答案：【four】2.单选题：____worksatburstsmode,thesynchronizationisneededforeachofthetimeslot.

选项：

A、OFDMA

B、SDMA

C、PDMA

D、TDMA

答案：【TDMA】3.多选题：Whatarethemainpartsofsimplifiedcellularprotype?

选项：

A、MSU

B、BSS

C、MSC

D、OMC

答案：【MSU;BSS;MSC;OMC】4.单选题：ThebandwidthofeachFDMAsubchannelisrelativelynarrow,whichislessthanthechannelcoherencebandwidth,thusthechannelisflatfadingchannelandnoseriousinter-symbolinterferenceoccurs.

选项：

A、正确

B、错误

答案：【正确】5.单选题：InFDMAsystems,thespectrumisdividedintimeslotsanddifferentusersareassigneddifferentones.

选项：

A、正确

B、错误

答案：【错误】期末考试期末考试1.单选题：InordertofindabalancedGoldcode,the____isfirstdetermined.

选项：

A、characteristicamplitude

B、characteristicphase

C、characteristicfrequency

D、characteristicperiod

答案：【characteristicperiod】2.单选题：Whichofthefollowingisnotarequirementfortheaddresscode?

选项：

A、Theyhavegoodcross-correlationandpartial-correlationproperties.

B、Thereisanuncertainlength.

C、Theacquisitiontimeisshort.

D、Theyhavegoodautocorrelation.

答案：【Thereisanuncertainlength.】3.单选题：Theminimumallowedgroupsizeforacellularnetworkis____inFDMAsystem.

选项：

A、one

B、two

C、three

D、four

答案：【three】4.单选题：IfTDDisusedinconjunctionwithTDMA,thetimeslotnumberisgenerally____,whereeachoftheNusersisassignedonetimeslotfortheuplink,andoneforthedownlink.

选项：

A、N

B、2N

C、3N

D、4N

答案：【2N】5.单选题：Whenradiowavesareprojectedontoaroughsurface,____occurs.

选项：

A、refraction

B、diffraction

C、reflection

D、scattering

答案：【scattering】6.单选题：InthediffuseInfra-redsystem,themultipathmechanismis____.

选项：

A、Reflectionfrommultipleionospherelayers

B、Reflectionfromwalls

C、Reflectionsfromterminations

D、Multimodepropagation

答案：【Reflectionfromwalls】7.单选题：WhichofthefollowingsystemcanuseRAKEreceiver?

选项：

A、GSM

B、WIFI

C、NR

D、WCDMA

答案：【WCDMA】8.单选题：ISImeans____.

选项：

A、Co-channelinterference

B、Adjacent-channelinterference

C、Inter-symbolinterference

D、Inter-modulationinterference

答案：【Inter-symbolinterference】9.单选题：Differentfromtheaccessmethodsforcellularphonenetwork,____doesnotallocateadedicatedchannelforeachuser.

选项：

A、packetradio

B、CDMA

C、TDMA

D、FDMA

答案：【packetradio】10.单选题：ForaBPSKmodulation,supposethesignaltonoisepowerratioperbitγbis16dBin25%oftimeandis-∞intherestoftime,thentheaveragesignaltonoisepowerratioperbitis10dB.theaveragebiterrorprobabilityisapproximately_

选项：

A、0.125

B、0.25

C、0.375

D、0.5

答案：【0.375】11.单选题：__isatechniqueusedtocompensateforthefadingchannelimpairments,whichisimplementedbytwoormoreindependentpaths.

选项：

A、Sourcecoding

B、Diversity

C、Channelcoding

D、Equalization

答案：【Diversity】12.单选题：__istechniquetoimprovethewirelesslinkperformancebyaddingerrordetectionorerrorcorrectionbitsinthetransmittedmessage.

选项：

A、Sourcecoding

B、Diversity

C、Channelcoding

D、Equalization

答案：【Channelcoding】13.单选题：Whatisthepurposeofinterleavinginchannelcodingforfadingchannels?

选项：

A、Toincreasethebandwidthefficiency.

B、Todecreasethebandwidthefficiency.

C、Torandomizeerrorburstssothattheycanbehandledbychannelcoding.

D、Toreducetheprobabilityofbitorblockerror.

答案：【Torandomizeerrorburstssothattheycanbehandledbychannelcoding.】14.单选题：In1898,__demonstratedthewell-knownradiotransmissionfromtheIsleofWighttoatugboat18milesaway.

选项：

A、Tesla

B、Marconi

C、Edison

D、KarlFerdinandBraun

答案：【Marconi】15.单选题：_isnon-linearmodulationformat.

选项：

A、MPAM

B、MPSK

C、MQAM

D、MFSK

答案：【MFSK】16.单选题：In__,theinformationiscarriedinfrequency

选项：

A、MPAM

B、MPSK

C、MQAM

D、MFSK

答案：【MFSK】17.单选题：__producesveryhighspectralsidelobes,whichmeansthatalargerbandwidthisoccupied

选项：

A、Therectangularpulse

B、Thecosinepulse

C、Theraisedcosinepulses

D、TheGaussianpulse

答案：【Therectangularpulse】18.单选题：Whatdoesspatialmultiplexingreferto?

选项：

A、Transmittingdifferentdatastreamsondifferentantennas

B、Usingthesamefrequencybandforallsignals

C、Sendingsignalsatthesametimeonthesamefrequencyband

D、Distinguishingtheirdatastreamsbyusingthedifferenceofspatialparallelsubchannels

答案：【Transmittingdifferentdatastreamsondifferentantennas】19.单选题：CanMIMOimprovethesystemcapacitywithoutsacrificingtimeandfrequencyresources?

选项：

A、Yes,itcangreatlyimprovethesystemcapacityandspectrumutilizationwithoutsacrificingtimeandfrequencyresources.

B、No,itcannotimprovethesystemcapacitywithoutsacrificingtimeandfrequencyresources.

C、Itdependsonthespecificsituation.

D、Itcanonlyimprovethesystemcapacityifotherresourcesaresacrificed.

答案：【Yes,itcangreatlyimprovethesystemcapacityandspectrumutilizationwithoutsacrificingtimeandfrequencyresources.】20.单选题：WhatisthemainideaofmassiveMIMO?

选项：

A、Ituseslargeantennaarraysandtosimultaneouslyservemanyautonomousterminalsbyusingprincipleofspacedivisionmultiplexingandbeamforming.

B、Itusessmallantennaarraysandtosimultaneouslyservefewautonomousterminalsbyusingprincipleoftimedivisionmultiplexingandbeamforming.

C、Itusesmediumantennaarraysandtosimultaneouslyservesomeautonomousterminalsbyusingprincipleoffrequencydivisionmultiplexingandbeamforming.

D、Ituseslargeantennaarraysandtosimultaneouslyservefewautonomousterminalsbyusingprincipleoffrequencydivisionmultiplexingandbeamforming.

答案：【Ituseslargeantennaarraysandtosimultaneouslyservemanyautonomousterminalsbyusingprincipleofspacedivisionmultiplexingandbeamforming.】21.单选题：Whichfrequencybandisveryeffectiveforwirelessmicrowavelinks,andmobile–satellitecommunicationchannels?

选项：

A、3kHz-30kHz

B、3MHz-30MHz

C、30MHz-300MHz

D、300MHz-3GHz

答案：【300MHz-3GHz】22.单选题：Whichequalizerprovidesbetterperformance,linearornonlinearequalizers?

选项：

A、Linearequalizers

B、Nonlinearequalizers

C、Bothprovidethesameperformance

D、Itdependsontheapplication

答案：【Nonlinearequalizers】23.单选题：WhatistheroleofcyclicprefixinOFDMsystems?

选项：

A、Toincreasethelengthoftheguardinterval

B、ToeliminateInter-CarrierInterference(ICI)causedbymultipathpropagation

C、Toreducethedelayspreadofthechannel

D、Toimprovetheorthogonalitybetweensubcarriers

答案：【ToeliminateInter-CarrierInterference(ICI)causedbymultipathpropagation】24.单选题：HowisthenumberofbitsthateachOFDMsymbolshouldtransmitdetermined?（

选项：

A、BytherequiredbitrateofthesystemandthedurationofeachOFDMsymbol

B、Bythenumberofsubcarriersandthecodingscheme

C、Bythemaximumdelayspreadofthechannelandthesymbolperiod

D、BythenumberofIFFTpointsandthedurationofeachOFDMsymbol

答案：【BytherequiredbitrateofthesystemandthedurationofeachOFDMsymbol】25.单选题：WhatarethetwomainapplicationsofMIMOsystem?

选项：

A、Spatialmultiplexingandspatialdiversity

B、Timemultiplexingandfrequencydiversity

C、Frequencymultiplexingandtimediversity

D、Channelmultiplexingandsignaldiversity

答案：【Spatialmultiplexingandspatialdiversity】26.单选题：Incellularsystem,twouserscanoperateonthesamefrequencybecause__

选项：

A、theyareadjacentcells.

B、thesignalpowerfallsoffquicklywithdistancesothattheywillnotinterferencewitheachother.

C、thecellisbigenough.

D、thecellissmallenough.

答案：【thesignalpowerfallsoffquicklywithdistancesothattheywillnotinterferencewitheachother.】27.单选题：__sattelitesaremostsuitablefortwo-wayrealtimevoicecommunitions.

选项：

A、LEO

B、MEO

C、GEO

D、Noneoftheabove

答案：【LEO】28.多选题：WhichofthefollowingarethemainfeaturesofWLAN?

选项：

A、TheWLANsconnect“local”computers,thetypicalrangeisabout100m.

B、WLANispacket-basedradio.

C、ThechannelaccessofWLANisshared,ituserandomaccesspolicy.

D、ThebackboneofWLANprovidesbest-effortservice.

答案：【TheWLANsconnect“local”computers,thetypicalrangeisabout100m.;WLANispacket-basedradio.;ThechannelaccessofWLANisshared,ituserandomaccesspolicy.】29.多选题：Thefollowingarecomponentsofthereceiverofacommunicationsystem.

选项：

A、channeldecoder

B、sourcedecoder

C、demodulator

D、channelencoder

答案：【channeldecoder;sourcedecoder;demodulator】30.多选题：___arethereasonswhydigitalmodulationswereintroduced.

选项：

A、Theadvancementsinhardwareanddigitalsignalprocessinghavemadedigitaltransceiversmuchcheaper

B、Thecurrentdigitaltransceiversaremuchfaster

C、Thedigitaltransceiversaremorepower-efficient.

D、Encryptioncanbeappliedindigitalsystem.

答案：【Theadvancementsinhardwareanddigitalsignalprocessinghavemadedigitaltransceiversmuchcheaper;Thecurrentdigitaltransceiversaremuchfaster;Thedigitaltransceiversaremorepower-efficient.;Encryptioncanbeappliedindigitalsystem.】31.多选题：___arethemethodscanbeusedindigitalmodulationsystemtoovercomeISI.

选项：

A、Spreadspectrum

B、Powerfulchannelcoding

C、Equalization

D、multicarriertechniques

答案：【Spreadspectrum;Powerfulchannelcoding;Equalization;multicarriertechniques】32.多选题：Whichofthefollowingdescriptionsarecorrectinthefirstwirelessnetworks?

选项：

A、Theytransmittedinformationoverline-of-sightdistance.

B、Theyusedsimplesignalssuchassmoke,fire,orbeatingdrumstotransmitinformation.

C、Thesesignalscanberelayedbyobservationstations,suchasbeacontowertolargedistances.

D、Thesemodeswerereplacedbytelegraphandtelephone.

答案：【Theytransmittedinformationoverline-of-sightdistance.;Theyusedsimplesignalssuchassmoke,fire,orbeatingdrumstotransmitinformation.;Thesesignalscanberelayedbyobservationstations,suchasbeacontowertolargedistances.;Thesemodeswerereplacedbytelegraphandtelephone.】33.多选题：Whichofthefollowingarethesecondgenerationstandard?

选项：

A、GSM

B、TDS-CDMA

C、WCDMA

D、IS-95

答案：【GSM;IS-95】34.多选题：___arethemainapplicationscenariosofthe5G

选项：

A、.eMMB，EnhanceMobileBroadband

B、.uRLLC,UltraReliable&LowLatencyCommunication

C、CDRVCConstantDataRateVoiceCommunications

D、.mMTCMassiveMachineTypeCommunication.

答案：【.eMMB，EnhanceMobileBroadband;CDRVCConstantDataRateVoiceCommunications】35.多选题：Whatisthepurposeofusingmultipleantennasinacommunicationsystem?

选项：

A、Toincreasethedataratethroughmultiplexing

B、Toimprovethesystemperformancethroughdiversity

C、Todetectandcorrecterrors

D、ToalleviatetheISIeffect

答案：【Toincreasethedataratethroughmultiplexing;Toimprovethesystemperformancethroughdiversity】36.多选题：Whatmightaffecttransmissionbetweenthetransmitterandthereceiver?

选项：

A、noise

B、interference

C、Otherobstructionsfrombuildingsandmountains

D、Idealatmosphericconditions

答案：【noise;interference;Otherobstructionsfrombuildingsandmountains】37.多选题：Okumuramodelisoneofthemostwidelyusedmodelfforsignalpredictioninlargeurbanmacrocells.WhichofthefollowingstatementsabouttheOkumuramodelaretrue?

选项：

A、Thismodelisapplicableoverdistancesof1-100km.

B、Thismodelisapplicableoverfrequencyrangesof150-1920MHz.

C、Thefrequencybandcanbeextrapolatedto3GHz.

D、Thebasestationheightsforthismodelwere30-1000m.

答案：【Thismodelisapplicableoverdistancesof1-100km.;Thismodelisapplicableoverfrequencyrangesof150-1920MHz.;Thefrequencybandcanbeextrapolatedto3GHz.;Thebasestationheightsforthismodelwere30-1000m.】38.多选题：Itisdifficultfor____and____toaccuratelycharacterizethepathlossinirregularenvironmentswheremostmobilecommunicationsystemsoperate.

选项：

A、Empiricaloutdoorpath-lossmodels

B、Freespacepropagationmodel

C、Raytracingmechanismsandmodels

D、Indoorpathlossmodels

答案：【Freespacepropagationmodel;Raytracingmechanismsandmodels】39.多选题：WhatisthedisadvantageofSC(selectioncombining)?

选项：

A、ItrequiresadedicatedreceiveroneachbranchtomonitorRSSI.

B、Itmakescomparisonscontinuouslyandcontroltheswitchingwhenthebestbranchchanges.

C、ItscanseachofthebranchesinsequentialorderandoutputthefirstsignalwithRSSIaboveagiventhreshold.

D、Itselectsthebestbranch.

答案：【ItrequiresadedicatedreceiveroneachbranchtomonitorRSSI.;Itmakescomparisonscontinuouslyandcontroltheswitchingwhenthebestbranchchanges.】40.多选题：WhichdescriptiononThresholdCombining(TC)iscorrect?

选项：

A、Itisasimplerversionofselectioncombining.

B、ItscanseachofthebranchesinsequentialorderandoutputthefirstsignalwithRSSIaboveagiventhreshold.

C、Itmakescomparisonscontinuouslyandcontroltheswitchingwhenthebestbranchchanges.

D、Itisaweightedsumofallbranches.

答案：【Itisasimplerversionofselectioncombining.;ItscanseachofthebranchesinsequentialorderandoutputthefirstsignalwithRSSIaboveagiventhreshold.】41.多选题：Whichofthefollowingstatementsistrueaboutcodinggain?

选项：

A、CodinggainisdefinedastheamountofSNRthatcanbereducedunderacertaincodingtechniqueforagivenbiterrorprobabilityorblock(frame)errorprobability.

B、CodinggaindecreasesasSNRdecreases.

C、CodinggainisnotaffectedbySNR.

D、ThecodinggainatlowSNRconditionsmaydecreasesignificantlyduetotheincreasedprobabilityofbitorblockerror

答案：【CodinggainisdefinedastheamountofSNRthatcanbereducedunderacertaincodingtechniqueforagivenbiterrorprobabilityorblock(frame)errorprobability.;ThecodinggainatlowSNRconditionsmaydecreasesignificantlyduetotheincreasedprobabilityofbitorblockerror】42.多选题：WhatisthedisadvantageofOFDMsystem?

选项：

A、Itissensitivetofrequencyoffset.

B、Itallowsoverlappingofsubchannels.

C、Ithasahighpeak-to-averagepowerratio(PAR).

D、ItcanbeachievedbyFFT.

答案：【Itissensitivetofrequencyoffset.;Ithasahighpeak-to-averagepowerratio(PAR).】43.多选题：TheCSMAalgorithmdefinesthefollowinguseractionsorresponses:____.

选项：

A、delay

B、transmission

C、interruption

D、backoff

答案：【delay;transmission;interruption;backoff】44.多选题：Weneedtwootherparameters____and____tocharacterizethetimevarying