移动通信试题库.docx

移动通信试题库.docx

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移动通信试题库

名词解释

1．Explainthedifferencebetweenhardandsofthandoff.

Answers：

Thehardhandoffisthatwhenthesignalstrengthofaneighboringcellexceedsthatofthecurrentcell,plusathreshold,themobilestationisinstructedtoswitchtoanewfrequencybandthatiswithintheallocationofthenewcell.

Thesofthandoffisthatamobilestationistemporarilyconnectedtomorethanonebasestationsimultaneously.Amobileunitmaystartoutassignedtoasinglecell.Iftheunitentersaregioninwhichthetransmissionsfromtwobasestationsarecomparable,themobileunitentersthesofthandoffstateuntilwhichitisconnectedtothetwobasestations.

2．WhatarethecorestechniquesofWCDMA?

Answers:

TheWCDMAkeytechniquesmostlyconsistofthepowercontroltechnique,PNcodetechnique,RSKE,SoftHandoff,andSpeechcoding.

3．Whatisattenuation?

4．Whattwofunctionsareperformedbyanantenna?

5．WhataretheadvantagesofusingCDMAforacellularnetwork?

Answers:

（1）Frequencydiversity;

（2）Multipathresistance;（3）Privacy;（4）Gracefuedegradation.

6.Whatarethekeydifferencesbetweenfirstandsecondgenerationcellularsystem?

Answers:

Thekeydifferencesbetweenthetwogenerations:

（1）.Digitaltrafficchannels;

（2）.Encryption;（3）.Errordetectioncorrection;

（4）.Channelaccess.

7.WhatarethecorestechniquesofTD-SCDMA?

Answers:

ThecorestechniquesofTD-SCDMAaresmartantenna（intelligentantenna）,jointexaminationtechnique,SCDMAtechnique,softwarewirelesstechnique,anddynamicchannelallocationtechnique

8.Whatisdirectbroadcastsatellite（DBS）?

Answers:

Thesatellitevideosignalsaretransmissiondirectlytothehomeuser.

9.Whatisanisotropicantenna?

Answers:

Anisotropicantennaisapointinspacethatradiatespowerinalldirectionequally.

10.WhatisCDMA?

Answers:

CDMAisamultiplexingtechniqueusedwithspreadspectrum

11.Whatisfrequencyhoppingspreadspectrum?

Answers:

Thesignalisbroadcastoveraseeminglyrandomseriesofradiofrequency,hoppingfromfrequencytofrequencyatfixedintervals

12．Whataretheprimarycausesofatmosphericattenuationforsatellitecommunications?

Answers:

Theprimarycausesofatmosphericattenuationareoxygenandwater

13．WhatisaSIR?

Answers:

Thisratioisdefinedtobetheratioofthedesiredaveragesignalpoweratareceivertothetotalaverageinterferencepower.

14．WhatarefeaturesofCDMA?

Answers:

（1）Highspectrumefficiency

（2）Releasefromfrequencymanagement

（3）Lowmobilestationtransmitpower（4）Soft-handover（5）PathDiversity（RAKEFingers）（6）Security（7）Anti-jammingcapability

15．Ingeneral,physicalmodelsincludethreebasicmodesofpropagation.

Answers：

（1）Free-spaceorlink-of-signaltransmission;

（2）Reflection；（3）Diffraction.

16．Intime,asmorecustomersusethethesystem,trafficmaybuildupsothattherearenotenoughfrequencybandsassignedtoacelltohandleitscalls.Anumberofapproacheshavebeenusedtocopewiththissituation,includingthefollowing。

Answers:

（1）Addingnewchannels；

（2）Frequencyborrowing；（3）Cellsplitting；（4）Cellsectoring；（5）Microcells。

17．Explainthedifferencebetweenopen-loopandclosed-looppowercontrol.

Answers:

Open-looppowercontroldependssolelyonthemobileunit,withnofeedbackfromtheBS.

Closed-looppowercontroladjustssignalstrengthinthereversechannelbasedonsomemetricofperformanceinthatreversechannel.

18．Definechannelcapacity.

Answers:

Themaximumrateatwhichdatacanbetransmittedoveragivencommunicationpath,orchannel,undergivenconditionsisreferredtothechannelcapacity.

填空题

1．Antennacharacteristicsareessentiallythesamewhetheranantennaissending

orreceivingelectromagneticenergy.

2．Thebasisforanalogsignalingisacontinuousconstantfrequencysignalknownasthecarriersignal.

3．NikolaTeslainventedthewirelesstelegraphin1893.

4．Atransmissionfromearthstationtosatelliteisreferredtoasuplinkinthesatellitecommunication.

5．Theessenceofacellularnetworkistheuseofmultiplelow-powertransmitters,onorder

of100Worless.

6．ThirdgenerationsystemgenerallycallWCDMAorUMTS.

7．Adjacentcellsareassigneddifferentfrequenciestoavoidinterferenceorcrosstalk.

8.Viewedasafunctionof,anelectromagneticsignalcanbeeitheranalogordigital.

Ananalogsignalisoneinwhichthesignalintensityvariesinasmoothfashionovertime.

9．Thedatasignalingrate,orjustdatarate,ofasignalistherate,inbitspersecond,thatdataaretransmitted.

10TheTD-SCDMAisamultipleconnectintoincludetheFCDMA/TDMA/CDMA

11．NikolaTeslainventedthewirelesstelegraphin1893.

12．Adigitalsignalisoneinwhichthesignalintensitymaintainsaconstantlevelforsomeperiodoftimeandthenchangestoanotherconstantlevel.

13.Reflectionoccurswhenanelectromagneticsignalencountersasurfacethatislargerelativetothewavelengthofthesignal.

14．Ifthesizeofanobstacleisontheorderofthewavelengthofthesignalor

lessscatteringoccurs.

15.Foradataof

thedurationofabitis

secondsandthedurationofasignalelementis

seconds.If

isgreaterthenorto

thespreadingmodulationisreferredtoasslow-frequency-hopspreadspectrum;otherwiseitisknownasfast-frequency-hopspreadspectrum.

16．Atransmissionfromsatellitestationtoearthisreferredtoasdownlinkinthesatellitecommunication.

17．Thecellssufficientlydistantfromeachothercanusethesamefrequencyband

18．Codedivisionmultipleaccessisaspreadspectrumbasedtechniqueformultiplexing.

19．Theobjectiveofthethirdgenerationofwirelesscommunicationistoprovidefairlyhighspeedwirelesscommunicationstosupportmultimedia,data,andvideoinadditiontovoice.

20．PowercontroltechniqueiscoreintheCDMA.

21．Onepurposeofthedata-layeristoperformerrorcorrectionordetection.

22．Thechannelprovidesthephysicalmeansfortransportingthesignalproducedbythe

transmitteranddeliveringittothereceiver.

24．Thekeyphysicalresourceistheradiospectruminwirelesssystem.

24．Adigitalsignalisoneinwhichthesignalintensitymaintainsaconstantlevelforsomeperiodoftimeandthenchangestoanotherconstantlevel.

25．Thefrequencyistherateatwhichthesignalrepeats.

26．Anantennathattransmitsequallyinalldirectionscalledtheisotropicradiatio.

27．Noisecanbedefinedasunwantedelectricalsignalsinterferencewiththedesiredsignal.

28．Thebasicideawithcellularsystemistoreusechannelindifferentcell,increasingthecapacity

29．Duringtheperiodfrom1895to1901,GuglielmoMarconidevelopedanapparatusfortransmittingradiowavesoverlongerdistances.

30．Anelectromagneticsignalcanbeeitheranalogordigital.Ananalogsignal

isoneinwhichthesignalintensityvariesinasmoothfashionovertime.

31．Thespectrumofasignalistherangeoffrequenciesthatitcontains.

1.32．Thesamefrequencyassignmentscannotbemadeinadjacentcellbecauseofinter-channelinterference.

33．Handoffmaybenetworkinitiated.

34．ThateachuseroccupiesacyclicallyrepeatingtimeslotintheTDMAsystem.

35．AllusersinaCDMA,usethesamecarrierfrequencyandmaytransmitsimultaneously.

36．Self-jammingisaprobleminCDMAsystem.

37．TheGSMkeytechniqueconsistofeightparts

38.Reflectionoccurswhenanelectromagneticsignalencountersasurfacethatislargerelativetothewavelengthofthesignal.

判断题

1.Thermalnoisecanbeeliminated.（N）

2.Thetime-selectivechannelsaretime-invariantchannels.（N）

3.AhighSNRwillmeanahigh-qualitysignal.（Y）

4.Free-spacepropagation,inwhichthereceivedpowerdecreasesasthesquareofthedistancefromthetransmitter.（Y）

5.Fastfadingistherapidvariationofsignallevelswhentheuserterminalmovesshortdistances.（Y）

6.Trafficchannelsareusedtoexchangeinformation.（N）

7.Multipleaccessschemesareusedtoallowmanymobileuserstosharesimultaneouslyafiniteamountofradiospectrum.（Y）

8.Directsequencemultipleaccessisalsocalledcodedivisionmultipleaccess（CDMA）.（Y）

9.ThemostpopularsecondgenerationstandardsincludethreeTDMAstandardsandoneCDMAstandard.（Y）

10.TheNScontrolshandoffbetweencellindifferentBSSs,authenticatesusersandvalidatestheiraccounts,andincludesfunctionsforenablingworldwideroamingofmobileusers.（Y）

11.Thermalnoisecannotbeeliminated.（Y）

12.Frequency-SelectiveChannelsistime-invariantchannels.（N）

13.Thegreaterthebandwidth,thehighertheinformation-carryingcapacity..（Y）

14.Reflection,wherein,fortheplane-Earthmodel,thereceivedpowerdecreasesasthefourthpowerofdistance.（Y）

15.Slowfadingarisesfromthefactthatmostofthelargereflectorsanddiffractingobjectsalongthetransmissionpatharedistantfromtheterminal.（Y）

16.Controlchannelsareusedtoexchangeinformation.（Y）

17.ThateachuseroccupiesacyclicallyrepeatingtimeslotintheFDMAsystem.（N）

18.ManyusersofaCDMAsystemsharethesametime-slot.（N）

19.LikeTDMAorFDMA,CDMAhasasoftcapacitylimit..（N）

20.TheNScontrolshandoffbetweencellindifferentBSSs,authenticatesusersandvalidatestheiraccounts,andincludesfunctionsforenablingworldwideroamingofmobileusers.（Y）

选择题

Foreachsentencetherearefourchoices.ChoosetheONEanswerthatbestcompletesthesentence.

1.Ageneralsinewavecanberepresentedbythreeparameters,theyare（A）.

A.peakamplitude,frequency,andphase;B.speed,frequency,andphase;

C.peakamplitude,speed,andphase;D.peakamplitude,frequency,ands