mobile example paper

H64MOB/H64MOCH64MOB,H64MOCTurnOverTheUniversityofNottinghamDEPARTMENTOFELECTRICALANDELECTRONICENGINEERINGALEVEL4MODULE,SPRINGSEMESTER2009MOBILECOMMUNICATIONSTimeallowedTWOhoursCandidatesmaycompletethefrontcoveroftheiranswerbookandsigntheirdeskcardbutmustNOTwriteanythingelseuntilthestartoftheexaminationperiodisannouncedAnsweranyFOURquestionsOnlysilent,selfcontainedcalculatorswithaSingle-LineDisplayoraDual-LineDisplayarepermittedinthisexamination.Dictionariesarenotallowedwithoneexception.ThosewhosefirstlanguageisnotEnglishmayuseastandardtranslationdictionarytotranslatebetweenthatlanguageandEnglishprovidedthatneitherlanguageisthesubjectofthisexamination.Subjectspecifictranslationdictionariesarenotpermitted.Noelectronicdevicescapableofstoringandretrievingtext,includingelectronicdictionaries,maybeused.DONOTturntheexaminationpaperoveruntilinstructedtodosoADDITIONALINFORMATION:HandoutH64MOB/H64MOCH64MOB/H64MOC1.Oneofthechallengesinmobilecommunicationsystemsisovercomingtheharshenvironmentacrosstheairinterface.AdiagramoftwoantennaeisshowninfigureQ1below.ThepoweremittedbyantennaA1is30W,h1=30mandh2=2m.ThegainsoftheantennaeareGA1,dB=10dBandGA2,dB=5dBandthemodulationfrequencyoftheradiowavesis950MHz.a.Listthethreetypesoffadingthatoccuranddescribewhytheyoccur.[5marks]b.Neglectingreflectionsfromtheground,calculatetheaveragepowerreceivedattheantennaA2ifd1=1km.[5marks]c.Includingreflectionsfromtheground,calculatetheaveragepowerreceivedatantennaA2.(Youshouldassumethatdhandthatthepowerattenuatesas1/d4)[5marks]d.Differentmodulationtechniquescanbeusedtotransmitdigitaldatabetweentheantennae.Inthiscaseoffsetquadraturephaseshiftkeying(OQPSK)isusedonthedownlinkandphaseshiftkeying(PSK)isusedontheuplink.Forthedatasequence(1,0,0,1,1,1,0,0);i.Plotthedataoutputfromthemodulatoragainsttimeforthetwotechniques[5marks]ii.Showthesamesequenceonaconstellationplot[3marks]iii.WhataretheadvantagesofOQPSKoverPSK[2marks]FigureQ1d1h1dh2A1A2H64MOB/H64MOCH64MOB/H64MOC2.Cellsareanessentialpartofmobilecommunicationnetwork.Inaparticularmobilecommunicationssystemthereare700channelsavailabletobedistributedamongstthecells.Inthegeographicalareaoccupiedbythecells,theattenuationfactornhasbeenmeasuredas3.a.describethecellularconcept,includeadiscussionofcellreuseandhandoff[5marks]b.AlineofcellswithacellreusefactorC=3isshowninFigureQ2.1below.Thewidthofeachcellis10kmandtheattenuationfactorn=3.Calculatethesignaltointerferenceratio(SIR)atthepointPattheedgeofcell1ifonlythefirsttierofinterferingcellsinthefigurecontributetotheSIR.[5marks]c.Forthe2DhexagonalcellstructureshowninFigureQ2.2withacellularreusefactorC=3,assumingthatonlyfirsttierinterfererscontributetotheinterferencesignal,calculatetheSIRatthebase-stationB.[5marks]d.ConsiderthepositionPattheedgeofcell1inFigureQ2.2(C=3,n=3).Assumingthatonlyfirsttierinterfererscontributetotheinterferencesignal,calculatetheSIRatP.[5marks]e.ItisknownthatanSIR10atpointPisacceptabletousersi.CalculatethecellreusefactorCthatwillachieveacceptableperformance[3marks]ii.Howmanyuserscanbeaccommodatedwithinacell?[2marks]FigureQ2.1B1233322111111P1231231DRPH64MOB/H64MOCH64MOB/H64MOCFigureQ2.23.Sharingoftheavailablebandwidthcanbeobtainedusingfrequencydivisionmultipleaccess(FDMA),timedivisionmultipleaccess(TDMA)andcodedivisionmultipleaccess.a.DescribethebasicprinciplesofFDMA,TDMAandCDMA.[3marks]b.ACDMAbasedmobilecommunicationssystemusescodevectorsc1=(-1-1-1-1)andc2=(-111-1)i.Demonstratethatthetwocodesgivenbythevectorsc1andc2areorthogonal.[1mark]ii.Twousersneedtosendthedatad1=(1001)andd2=(1100).Demonstratetheprocessofmodulationanddemodulationusingthecodesc1andc2.[7marks]c.The2x2Walshmatrixisgivenby10002W.UsethismatrixtoobtaintheW16Walshmatrixanddemonstrateusingoneexamplethattherowsareorthogonal.[5marks]d.WhyisCDMAknownasaspreadspectrummethod?WhyishavingahighspreadinggainausefulpropertyofaCDMAsystem?[3marks]e.SatisfactoryperformanceofaparticularCDMAbasedsystemcanbeachievediftheenergy/bittotheinterferencefromotherusersis10.Forasystemwithaspreadinggainof200,howmanyuserscanbeaccommodatedif;i.Interferenceisonlyfromuserswithinthecell[3marks]ii.Interferenceisfromusersoutsidethecell[3marks]H64MOB/H64MOCH64MOB/H64MOC4.a.WhatisTrafficIntensity?[2marks]b.TheErlangBtablesprovidedshowtheErlangloadfordifferentnumbersof‘usersblockingprobabilities’.Usethetablestoobtain;i.TheallowableErlangloadwhentherequiredblockingprobabilityis0.005andthereare10channelsavailable[1mark]ii.TheallowableTrafficIntensitywhenthedesiredblockingprobabilityis0.001andthereare40channelsavailable[1mark]iii.TheminimumnumberofchannelsrequiredtosupportanErlangloadof14ifthedesiredblockingprobabilityis0.004[1mark]c.Amobilecommunicationsystemhas50channelsavailabletousersineachcell.Tomaintainaspecifiedqualityofserviceacallblockingprobabilityof0.0001isrequired.Usersonaverageusetheirphonesonceevery5minutes,eachcalltypicallylasting4minutes.Thesystemiswithinadenseurbanareawith500usersperkm2.Calculatetherequiredcellradiusifhexagonalcellsareassumed.[6marks]d.WhatistheHammingdistancebetweenthec