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,anddynamicchannelallocationtechnique8.Whatisdirectbroadcastsatellite(DBS)?Answers:Thesatellitevideosignalsaretransmissiondirectlytothehomeuser.9.Whatisanisotropicantenna?Answers:Anisotropicantennaisapointinspacethatradiatespowerinalldirectionequally.10.WhatisCDMA?Answers:CDMAisamultiplexingtechniqueusedwithspreadspectrum11.Whatisfrequencyhoppingspreadspectrum?Answers:Thesignalisbroadcastoveraseeminglyrandomseriesofradiofrequency,hoppingfromfrequencytofrequencyatfixedintervals12．Whataretheprimarycausesofatmosphericattenuationforsatellitecommunications?Answers:Theprimarycausesofatmosphericattenuationareoxygenandwater13．WhatisaSIR?Answers:Thisratioisdefinedtobetheratioofthedesiredaveragesignalpoweratareceivertothetotalaverageinterferencepower.14．WhatarefeaturesofCDMA?Answers:(1)Highspectrumefficiency(2)Releasefromfrequencymanagement(3)Lowmobilestationtransmitpower(4)Soft-handover(5)PathDiversity(RAKEFingers)(6)Security(7)Anti-jammingcapability15．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．Antennacharacteristicsareessentiallythesamewhetheranantennaissendingorreceivingelectromagneticenergy.2．Thebasisforanalogsignalingisacontinuousconstantfrequencysignalknownasthecarriersignal.3．NikolaTeslainventedthewirelesstelegraphin1893.4．Atransmissionfromearthstationtosatelliteisreferredtoasuplinkinthesatellitecommunication.5．Theessenceofacellularnetworkistheuseofmultiplelow-powertransmitters,onorderof100Worless.6．ThirdgenerationsystemgenerallycallWCDMAorUMTS.7．Adjacentcellsareassigneddifferentfrequenciestoavoidinterferenceorcrosstalk.8.Viewedasafunctionof,anelectromagneticsignalcanbeeitheranalogordigital.Ananalogsignalisoneinwhichthesignalintensityvariesinasmoothfashionovertime.9．Thedatasignalingrate,orjustdatarate,ofasignalistherate,inbitspersecond,thatdataaretransmitted.10TheTD-SCDMAisamultipleconnectintoincludetheFCDMA/TDMA/CDMA11．NikolaTeslainventedthewirelesstelegraphin1893.12．Adigitalsignalisoneinwhichthesignalintensitymaintainsaconstantlevelforsomeperiodoftimeandthenchangestoanotherconstantlevel.13.Reflectionoccurswhenanelectromagneticsignalencountersasurfacethatislargerelativetothewavelengthofthesignal.14．Ifthesizeofanobstacleisontheorderofthewavelengthofthesignalorlessscatteringoccurs.15.ForadataofR,thedurationofabitisRT1secondsandthedurationofasignalelementisLTTSseconds.IfCTisgreaterthenortoST,thespreadingmodulationisreferredtoasslow-frequency-hopspreadspectrum;otherwiseitisknownasfast-frequency-hopspreadspectrum.16．Atransmissionfromsatellitestationtoearthisreferredtoasdownlinkinthesatellitecommunication.17．Thecellssufficientlydistantfromeachothercanusethesamefrequencyband18．Codedivisionmultipleaccessisaspreadspectrumbasedtechniqueformultiplexing.19．Theobjectiveofthethirdgenerationofwirelesscommunicationistoprovidefairlyhighspeedwirelesscommunicationstosupportmultimedia,data,andvideoinadditiontovoice.20．Powercontroltechniqueisco