无线通信基础(双语)_教学课件_11

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1、Chapter2:TheCellularConcept-SystemDesignFundamentalsLecture27/19/202112.1TheConcept:CellularNetworks7/19/20212geometricshapesCircle:Equilateraltriangle:Square:Hexagon:7/19/20213Cellularcoveragerepresentation7/19/20214Macrocelllarge,coveringawidearerangeo

2、fseveralhundredkilometres(km)totenkmmostlydeployedinruralandsparselypopulatedareasMicrocellmediumcell,coverageareasmallerthaninmacrocellsrangeofseveralhundredmeterstoacoupleofmetresdeployedmostlyincrowdedareas,stadiums,shoppingmallsPicocellsmall,coveringa

3、verysmallarearangeofseveraltensofmetreslowpowerantennas,indoorThesizeofacell7/19/20215Threedifferentkindsofcells7/19/20216BasestationtransmittersInhexagonalcells,basestationstransmittersareeither:centre-excited,basestationisatthecentreofthecelledge-excite

4、d,basestationat3ofthe6cellverticescentre-excitededge-excited7/19/20217Ccanbeusedasameasureofcapacity2.2FrequencyReuseandCapacity7/19/20218Amobilecommunicationsystemusesafrequencyreusefactorof1/7and416channelsavailable.If21channelsareallocatedascontrolchan

5、nels,computeitssystemcapacity.Assumeachannelsupports8usersChannelsavailableforallocation=416-21=395ChannelNumberofacell=395/7=57Numberofsimultaneoususerspercell=8x57=456Numberofsimultaneoususersinsystem=7x456=3192Example17/19/20219Methodoflocatingco-chann

6、elcells7/19/202110ChannelAssignmentStrategies:TwoassignmentapproachesFixedandstatic(mostcommon)DynamicFixedchannelassignmentallchannelsinacellcouldbeinuseallthetimenewcallsarethenblocked(nochannelsleft)maybesolvedbyborrowingsparechannelsfromnearbycells2.3

7、ChannelAssignmentandhandoff7/19/202111DynamicchannelassignmentMSCallocatesfrequencieswhenacallismadeProvideshighchannelutilizationTodothisitneedsreal-timeinformationonchanneloccupancytrafficdistributionradiosignalstrengthindication(RSSI)highcomputational

8、loadandincreasedstorage7/19/202112Handover(Handoff)ProvidescontinuityofcommunicationacrosscellsDifficultydroppingacallbeforereconnectingisunacceptabledifferentcellsusedifferentfrequenciesmobilephoneusersusuallymovef