蜂窩系統(tǒng)切換技術(shù)中英文對照外文翻譯文獻

-PAGE54-中英文資料對照外文翻譯 原文：HandoffinCellularSystemsCellularSystemDeploymentScenariosTheradiopropagationenvironmentandrelatedhandoffchallengesaredifferentindifferentcellularstructures.Ahandoffalgorithmwithfixedparameterscannotperformwellindifferentsystemenvironments.Specificcharacteristicsofthecommunicationsystemsshouldbetakenintoaccountwhiledesigninghandoffalgorithms.Severalbasiccellularstructures(e.g.,macrocells,microcells,andoverlaysystems)andspecialarchitectures(e.g.,underlays,multichannelbandwidthsystems,andevolutionaryarchitectures)aredescribednext.Integratedcordlessandcellularsystems,integratedcellularsystems,andintegratedterrestrialandsatellitesystemsarealsodescribed.MacrocellsMacrocellradiiareinseveralkilometers.Duetothelowcellcrossingrate,centralizedhandoffispossibledespitethelargenumberofMSstheMSChastomanage.Thesignalqualityintheuplinkanddownlinkisapproximatelythesame.ThetransitionregionbetweentheBSsislarge;handoffschemesshouldallowsomedelaytoavoidflip-flopping.However,thedelayshouldbeshortenoughtopreservethesignalqualitybecausetheinterferenceincreasesastheMSpenetratesthenewcell.Thiscellpenetrationiscalledcelldragging.Macrocellshaverelativelygentlepathlosscharacteristics.Theaveraginginterval(i.e.,thetimeperiodusedtoaveragethesignalstrengthvariations)shouldbelongenoughtogetridoffadingfluctuations.First-andsecond-generationcellularsystemsprovidewide-areacoverageevenincitiesusingmacrocells.Typically,aBStransceiverinamacrocelltransmitshighoutputpowerwiththeantennamountedseveralmetershighonatowertoilluminatealargearea.MicrocellsSomecapacityimprovementtechniques(e.g.,largerbandwidths,improvedmethodsforspeechcoding,channelcoding,andmodulation)willnotbesufficienttosatisfytherequiredservicedemand.Theuseofmicrocellsisconsideredthesinglemosteffectivemeansofincreasingthecapacityofcellularsystems.Microcellsincreasecapacity,butradioresourcemanagementbecomesmoredifficult.Microcellscanbeclassifiedasone-,two-,orthreedimensional,dependingonwhethertheyarealongaroadorahighway,coveringanareasuchasanumberofadjacentroads,orlocatedinmultilevelbuildings,respectively.Microcellscanbeclassifiedashotspots(serviceareaswithahighertrafficdensityorareasthatarecoveredpoorly),downtownclusteredmicrocells(contiguousareasservingpedestriansandmobiles),andin-building3-Dcells(servingofficebuildingsandpedestrians).Typically,aBStransceiverinamicrocelltransmitslowoutputpowerwiththeantennamountedatlamppostlevel(approximately5maboveground).TheMSalsotransmitslowpower,whichleadstolongerbatterylife.SinceBSantennashavelowerheightscomparedtothesurroundingbuildings,RFsignalspropagatemostlyalongthestreets.Theantennamaycover100–200mineachstreetdirection,servingafewcityblocks.Thispropagationenvironmenthaslowtimedispersion,whichallowshighdatarates.Microcellsaremoresensitivetothetrafficandinterferencethanmacrocellsduetoshort-termvariations(e.g.,trafficandinterferencevariations),medium/long-termalterations(e.g.,newbuildings),andincrementalgrowthoftheradionetwork(e.g.,newBSs).Thenumberofhandoffspercellisincreasedbyanorderofmagnitude,andthetimeavailabletomakeahandoffisdecreased.Usinganumbrellacellisonewaytoreducethehandoffrate.Duetotheincreaseinthemicrocellboundarycrossingsandexpectedhightrafficloads,ahigherdegreeofdecentralizationofthehandoffprocessbecomesnecessary.Microcellsencounterapropagationphenomenoncalledthecornereffect.Thecornereffectischaracterizedbyasuddenlargedrop(e.g.,20–30dB)insignalstrength(e.g.,at10–20mdistance)whenamobileturnsaroundacorner.Thecornereffectisduetothelossofthelineofsight(LOS)componentfromtheservingBStotheMS.Thecornereffectdemandsafasterhandoffandcanchangethesignalqualityveryfast.Thecornereffectishardtopredict.Alongmeasurementaveragingintervalisnotdesirableduetothecornereffect.MovingobstaclescantemporarilyhinderthepathbetweenaBSandanMS,whichresemblesthecornereffect.ReferencestudiesthepropertiesofsymmetricalcellplansinaManhattan-typeenvironment.Cellplansaffectsignal-to-interferenceratio(SIR)performanceintheuplinkanddownlinksignificantly.Symmetricalcellplanshavefournearestco-channelBSslocatedatthesamedistance.Suchcellplanscanbeclassifiedintohalf-square(HS),full-square(FS),andrectangular(R)cellplans.Thesecellplansaredescribednext.Half-SquareCellPlan—ThiscellplanplacesBSswithomnidirectionalantennasateachintersection,andeachBScovershalfablockinallfourdirections.Thiscellplanavoidsthestreetcornereffectandprovidesthehighestcapacity.ThiscellplanhasonlyLOShandoffs.Figure2showsanexampleofahalf-squarecellplaninamicrocellularsystem.Full-SquareCellPlan—ThereisaBSwithanomnidirectionalantennalocatedateveryotherintersection,andeachBScoversablockinallfourdirections.ItispossibleforanMStoexperiencethestreetcornereffectforthiscellplan.TheFScellplancanhaveLOSorNLOShandoffs.Figure3showsanexampleofafullsquarecellplaninamicrocellularsystem.RectangularCellPlan—EachBScoversafractionofeitherahorizontalorverticalstreetwiththeBSlocatedinthemiddleofthecell.Thiscellplancaneasilybeadaptedtomarketpenetration.FewerBSswithhightransmitpowercanbeusedinitially.Asuserdensityincreases,newBSscanbeaddedwithreducedtransmitpowerfromappropriateBSs.Thestreetcornereffectispossibleforthiscellplan.TheRcellplancanhaveLOSorNLOShandoffs.Figure4showsanexampleofarectangularcellplaninamicrocellularsystem.Macrocell/MicrocellOverlaysCongestionofcertainmicrocells,thelackofserviceofmicrocellsinsomeareas,andhighspeedofsomeusersaresomereasonsforhigherhandoffratesandsignalingloadformicrocells.Toalleviatesomeoftheseproblems,amixed-cellarchitecture(calledanoverlay/underlaysystem)consistingoflargesizemacrocells(calledumbrellacellsoroverlaycells)andsmall-sizemicrocells(calledunderlaycells)canbeused.Figure5illustratesanoverlaysystem.Themacrocell/microcelloverlayarchitectureprovidesabalancebetweenmaximizingthenumberofusersperunitareaandminimizingthenetworkcontrolloadassociatedwithhandoff.Macrocellsprovidewide-areacoveragebeyondmicrocellserviceareasandensurebetterintercellhandoff.Microcellsprovidecapacityduetogreaterfrequencyreuseandcoverareaswithhightrafficdensity(calledhotspots).Examplesofhotspotsincludeanairport,arailwaystation,oraparkinglot.Inlesscongestedareas(e.g.,areasbeyondacitycenteroroutsidethemainstreetsofacity)trafficdemandisnotveryhigh,andmacrocellscanprovideadequatecoverageinsuchareas.MacrocellsalsoservehighspeedMSsandtheareasnotcoveredbymicrocells(e.g.,duetolackofchannelsortheMSbeingoutofthemicrocellrange).Also,afterthemicrocellularsystemisusedtoitsfullestextent,theoverflowtrafficcanberoutedtomacrocells.Oneoftheimportantissuesfortheoverlay/underlaysystemisthedeterminationofoptimumdistributionofchannelsinthemacrocellsandmicrocells.Referenceevaluatesfourapproachestosharingtheavailablespectrumbetweenthetwotiers.Approach1usesTDMAformicrocellandCDMAformacrocell.Approach2usesCDMAformicrocellandTDMAformacrocell.Approach3usesTDMAinbothtiers,whileapproach4usesorthogonalfrequencychannelsinbothtiers.Theoverlay/underlaysystemhasseveraladvantagesoverapuremicrocellsystem:?TheBSsarerequiredonlyinhightrafficloadareas.Sinceitisnotnecessarytocoverthewholeserviceareawithmicrocells,infrastructurecostsaresaved.?Thenumberofhandoffsinanoverlaysystemismuchlessthaninamicrocellsystembecausefast-movingvehiclescanbeconnectedtotheoverlaymacrocell.?BothcallingfromanMSandlocationregistrationcaneasilybedonethroughthemicrocellsystem.Thereareseveralclassesofumbrellacells.Inoneclass,orthogonalchannelsaredistributedbetweenmicrocellsandmacrocells.Inanotherclass,microcellsusechannelsthataretemporarilyunusedbymacrocells.Inyetanotherclass,microcellsreusethechannelsalreadyassignedtomacrocellsanduseslightlyhighertransmitpowerlevelstocounteracttheinterferencefromthemacrocells.Withintheoverlay/underlaysystemenvironment,fourtypesofhandoversneedtobemanaged[19]:microcelltomicrocell,microcelltomacrocell,macrocelltomacrocell,andmacrocelltomicrocell.Referencedescribescombinedcellsplittingandoverlaying.Reuseofchannelsinthetwocellsisdonebyestablishinganoverlaidsmallcellservedbythesamecellsiteasthelargecell.Smallcellsreusethesplitcell’schannelsbecauseofthelargedistancebetweenthesplitcellandthesmallinnercell,whilethelargecellcannotreusethesechannels.Overlaidcellsareapproximately50percentmorespectrallyefficientthansegmenting(theprocessofdistributingthechannelsamongthesmall-andlargesizecellstoavoidinterference).Apracticalapproachforimplementationofamicrocellsystemoverlaidwithanexistingmacrocellsystemisproposedin.Thisreferenceintroduceschannelsegregation(aself-organizeddynamicchannelassignment)andautomatictransmitpowercontroltoobviatetheneedtodesignchannelassignmentandtransmitpowercontrolforthemicrocellsystem.Theavailablechannelsarereusedautomaticallybetweenmicrocellsandmacrocells.Aslightincreaseoftransmitpowerforthemicrocellsystemcompensatesforthemacrocell-to-microcellinterference.Simulationresultsindicatethatthelocaltrafficisaccommodatedbythemicrocellslaidundermacrocellswithoutanysignificantchannelmanagementeffort.ThemethodologyoftheGlobalSystemforMobileCommunications(GSM)-basedsystemisextendedtothemacrocell/microcelloverlaysystemin.Theuseofrandomfrequencyhoppingandadaptivefrequencyplanningisrecommended,anddifferentissuesrelatedtohandoffandfrequencyplanningforanoverlaysystemarediscussed.Fourstrategiesaredesignedtodetermineasuitablecellforauserforanoverlaysystem.Twostrategiesarebasedonthedwelltime(thetimeforwhichacallcanbemaintainedinacellwithouthandoff),andtheothertwostrategiesarebasedonuserspeedestimation.Aspeedestimationtechniquebasedondwelltimesisalsoproposed.ACDMAcellularsystemcanprovidefullconnectivitybetweenthemicrocellsandtheoverlayingmacrocellswithoutcapacitydegradation.Referenceanalyzesseveralfactorsthatdeterminethecellsize,thesofthandoff(SHO)zone,andthecapacityofthecellclusters.Severaltechniquesforoverlay-underlaycellclusteringarealsooutlined.ApplicationofCDMAtomicrocell/macrocelloverlayhavethefollowingmajoradvantages:?Aheterogeneousenvironmentcanbeilluminateduniformlybyusingadistributedantenna(withaseriesofradiatorswithdifferentpropagationdelays)whilestillmaintainingahigh-qualitysignal.?SHOobviatestheneedforcomplexfrequencyplanning.ReferencestudiesthefeasibilityofaCDMAoverlaythatcansharethe1850–1990MHzpersonalcommunicationsservices(PCS)bandwithexistingmicrowavesignals(transmittedbyutilitycompaniesandstateagencies).TheresultsofseveralfieldtestsdemonstratetheapplicationofsuchanoverlayforthePCSband.TheissueofuseofaCDMAmicrocellunderlayforanexistinganalogmacrocellisthefocusof.Itisshownthathighcapacitycanbeachievedinamicrocellattheexpenseofaslightdegradationinmacrocellperformance.ReferencefindsthattransmitandreceivenotchfiltersshouldbeusedatthemicrocellBSs.ItshowsthatkeyparametersforsuchanoverlayarethepowersoftheCDMABSandMStransmittersrelativetothemacrocellBSsandtheMSsservedbythemacrocells.Reference[25]studiesspectrummanagementinanoverlaysystem.Anewcellselectionmethodisproposed,whichusesthehistoryofmicrocellsojourntimes.Aproceduretodetermineanoptimumvelocitythresholdfortheproposedmethodisalsooutlined.Asystematicapproachtooptimalfrequencyspectrummanagementisdescribed.SpecialArchitecturesThereareseveralspecialcellulararchitecturesthattrytoimprovespectralefficiencywithoutalargeincreaseininfrastructurecosts.Someofthesestructures,discussedhere,includeanunderlay/overlaysystem(whichisdifferentfromtheoverlay/underlaysystemdescribedearlier)andamultichannelbandwidthsystem.Manycellularsystemsareexpectedtoevolvefromamacrocellularsystemtoanoverlay/underlaysystem.Astudythatfocusesonsuchevolutionisdescribedin[26].AMultiple-Channel-BandwidthSystem—Multiplechannelbandwidthscanbeusedwithinacelltoimprovespectralefficiency.Inamultiple-channel-bandwidthsystem(MCBS),acellhastwoorthreering-shapedregionswithdifferentbandwidthchannels[28].Figure7showsanMCBS.Assumethat30kHzisthenormalbandwidthforasignal.Now,forathree-ringMCBS,30kHzchannelscanbeusedintheoutermostring,15kHzchannelsinthemiddlering,and7.5kHzchannelsintheinnermostring.Theareasoftheseringscanbedeterminedbasedontheexpectedtrafficconditions.Thus,insteadofusing30kHzchannelsthroughoutthecell,differentbandwidthchannels(e.g.,15kHzand7.5kHz)canbeusedtoincreasethenumberofchannelsinacell.TheMCBSusesthefactthatawide-bandwidthchannelrequiresalowercarrier-to-interferenceratio(C/I)thananarrow-bandwidthchannelforthesamevoicequality.Forexample,C/Irequirementsfor30kHz,15kHz,and7.5kHzchannelbandwidthsare18dB,24dB,and30dB,respectively,basedonsubjectivevoicequalitytests[28].Ifthetransmitpoweratacellciteisthesameforallthebandwidths,awidechannelcanservealargecellwhileanarrowchannelcanservearelativelysmallcell.Moreover,sinceawidechannelcantolerateahigherlevelofco-channelinterference(CCI),itcanaffordasmallerD/Rratio(theratioofco-channeldistancetocellradius).Thus,intheMCBSmorechannelsbecomeavailableduetomultiple-bandwidthsignals,andfrequencycanbereusedmorecloselyinagivenserviceregionduetodifferentC/Irequirements.IntegratedWirelessSystemsIntegratedwirelesssystemsareexemplifiedbyintegratedcordlessandcellularsystems,integratedcellularsystems,andintegratedterrestrialandsatellitesystems.Suchintegratedsystemscombinethefeaturesofindividualwirelesssystemstoachievethegoalsofimprovedmobilityandlowcost.IntegratedTerrestrialSystems—Terrestrialintersystemhandoffmaybebetweentwocellularsystemsorbetweenacellularsystemandacordlesstelephonesystem.ExamplesofsystemsthatneedintersystemhandoffsincludeGSM–DigitalEuropeanCordlessTelephone(DECT),CDMAinmacrocells,andTDMAinmicrocells.WhenacallinitiatedinacellularsystemcontrolledbyanMSCentersasystemcontrolledbyanotherMSC,intersystemhandoffisrequiredtocontinuethecall[29].InthiscaseoneMSCmakesahandoffrequesttoanotherMSCtosavethecall.TheMSCsneedtohavesoftwareforintersystemhandoffifintersystemhandoffistobeimplemented.CompatibilitybetweentheconcernedMSCsneedstobeconsidered,too.Thereareseveralpossibleoutcomesofanintersystemhandoff[29]:?Along-distancecallbecomesalocalcallwhenanMSbecomesaroamer.?Along-distancecallbecomesalocalcallwhenaroamerbecomesahomemobileunit.?Alocalcallbecomesalongdistancecallwhenahomemobileunitbecomesaroamer.?Alocalcallbecomesalong-distancecallwhenaroamerbecomesahomemobileunit.ThereisagrowingtrendtowardserviceportabilityacrossdissimilarsystemssuchasGSMandDECT[30].Forexample,itisnicetohaveintersystemhandoffbetweencordlessandcellularcoverage.Cost-effectivehandoffalgorithmsforsuchscenariosrepresentasignificantresearcharea.Thisarticleoutlinesdifferentapproachestoachievingintersystemhandoff.SimulationresultsarepresentedforhandoffbetweenGSMandDECT/WideAccessCommunicationsSystem(WACS).ThepapershowsthataminoradjustmenttotheDECTspecificationcangreatlysimplifytheimplementationofanMScapableofintersystemhandoffbetweenGSMandDECT.IntegratedTerrestrialandSatelliteSystems—Inanintegratedcellular/satellitesystem,theadvantagesofsatellitesandcellularsystemscanbecombined.Satellitescanprovidewideareacoverage,completionofcoverage,immediateservice,andadditionalcapacity(byhandlingoverflowtraffic).Acellularsystemcanprovideahigh-capacityeconomicalsystem.Someoftheissuesinvolvedinanintegratedsystemarediscussedin[31].Inparticular,theproceduresofGSMareexaminedfortheirapplicationtotheintegratedsystems.Thefuturepubliclandmobiletelecommunicationsystem(FPLMTS)willprovideapersonaltelephonesystemthatenablesapersonwithahandheldterminaltoreachanywhereintheworld[32].TheFPLMTSwillincludelowEarthorbit(LEO)orgeostationaryEarthorbit(GEO)satellitesaswellasterrestrialcellularsystems.WhenanMSisinsidethecoverageareaofaterrestrialcellularsystem,theBSwillactasarelaystationandprovidealinkbetweentheMSandthesatellite.WhenanMSisoutsidetheterrestrialsystemcoveragearea,itwillhaveadirectcommunicationlinkwiththesatellite.Differentissuessuchassystemarchitecture,callhandling,performanceanalysisoftheaccess,andtransmissionprotocolsarediscussedin[32].Thetwohandoffscenariosinanintegratedsystemaredescribedbelow.HandofffromtheLandMobileSatelliteSystemtotheTerrestrialSystem—Whileoperating,theMSmonitorsthesatellitelinkandevaluatesthelinkperformance.Thereceivedsignalstrengths(RSSs)areaveraged(e.g.,overa30stimeperiod)tominimizesignalstrengthvariations.IftheRSSfallsbelowacertainthresholdNconsecutivetimes(e.g.,N=3),theMSbeginsmeasuringRSSfromtheterrestrialcellularsystem.Iftheterrestrialsignalsarestrongenough,handoffismadetotheterrestrialsystem,providedthattheterrestrialsystemcanservetheMS.HandofffromtheTerrestrialSystemtotheLandMobileSatelliteSystem—WhenanMSisgettingservicefromtheterrestrialsystem,theBSsendsanacknowledgerequest(calledpage)atpredefinedintervalstoensurethattheMSisstillinsidethecoveragearea.IfanacknowledgerequestsignalfromtheMS(calledpageresponse)isnotreceivedattheBSforNconsecutivetimes,itishandedofftothelandmobilesatellitesystem(LMSS).Reference[33]focusesonpersonalcommunicationsystemswithhierarchicaloverlaysthatincorporateterrestrialandsatellitesystems.Thelowestlevelinthehierarchyisformedbymicrocells.Macrocellsoverlaymicrocellsandformthemiddlelevelinthehierarchy.Satellitebeamsoverlaymacrocellsandconstitutethetopmosthierarchylevel.Twotypesofsubscribersareconsidered,satellite-onlyanddualcellular/satellite.Callattemptsfromsatellite-onlysubscribersareservedbysatellitesystems,whilecallattemptsfromdualsubscribersarefirstdirectedtotheservingterrestrialsystemswiththesatellitestakingcareoftheoverflowtraffic.Ananalyticalmodelforteletrafficperformanceisdeveloped,andperformancemeasuressuchastrafficdistribution,blockingprobability,andforcedterminationprobabilityareevaluatedforlow-speedandhigh-speedusers.HandoffEvaluationMechanismsThreebasicmechanismsusedtoevaluatetheperformanceofhandoffalgorithmsincludetheanalytical,simulation,andemulationapproaches.Thesemechanismsaredescribedhere.TheAnalyticalApproachThisapproachcanquicklygiveapreliminaryideaabouttheperformanceofsomehandoffalgorithmsforsimplifiedhandoffscenarios.Thisapproachisvalidonlyunderspecifiedconstraints(e.g.,assumptionsabouttheRSSprofiles).Actualhandoffproceduresarequitecomplicatedandarenotmemoryless.Thismakestheanalyticalapproachlessrealistic.Forreal-worldsituations,thisapproachiscomplexandmathematicallyintractable.Someoftheanalyticalapproachesappearingintheliteraturearebrieflytouchedonbelow.

譯文：蜂窩系統(tǒng)切換技術(shù)蜂窩系統(tǒng)部署方案其無線電傳播環(huán)境和相關(guān)切換的難度是在于針對不同的單元結(jié)構(gòu)。在不同的系統(tǒng)環(huán)境中，固定參數(shù)切換算法不能發(fā)揮優(yōu)勢，。而通信系統(tǒng)的具體特點，應(yīng)考慮而設(shè)計的切換算法是：幾個基本的單元結(jié)構(gòu)（如宏蜂窩，微單元，并覆蓋系統(tǒng)）及（如：特殊結(jié)構(gòu)，多通道帶寬系統(tǒng)和演化架構(gòu)）是描述將來。集成的無線和蜂窩系統(tǒng)，蜂窩系統(tǒng)集成，綜合地面衛(wèi)星系統(tǒng)也作了相關(guān)說明。宏單元宏的定義是達數(shù)公里半徑。由于低單元傳輸率，集中式切換是可能的，盡管大量的各成員國已進行了海安管理。但是在上行和下行信號質(zhì)量大約是相同的?？紤]基地臺之間的過渡區(qū)，大切換計劃應(yīng)允許一些延遲，以避免信號不穩(wěn)定。然而，延誤應(yīng)足夠短，以保持信號的質(zhì)量，應(yīng)對新的穿透移動臺單元的干擾增加。這被稱為的“單元拖動”。宏單元有相對平緩的路徑損耗特性。在平均間隔（即使用一段時間的平均信號強度變化）應(yīng)得到足夠長的波動減少衰退。第一代和第二代蜂窩系統(tǒng)，即在城市大面積的報道。通常，在收發(fā)器宏單元傳輸與高輸出功率的天線安裝在塔高數(shù)米，覆蓋大片區(qū)域。微單元某些技術(shù)的提高（例如，更大的帶寬，編碼，改進方法，語音信道編碼和調(diào)制）將不足以滿足需要的服務(wù)需求。無線資源管理目前變得更加困難，因此微單元增加容量的能力被認為是增加單元系統(tǒng)的一個最有效的手段。微單元可分為一，二，或了三維，取決于他們是否沿著道路或公路這些區(qū)域進行覆蓋，如相鄰道路，或在多層建筑物內(nèi)分別編號。微單元可分為焦點（與通信密度較高或覆蓋不足地區(qū)服務(wù)的地區(qū)），市中心聚集微單元（行人和手機間的相鄰地區(qū)服務(wù)），并在建設(shè)3–D單元（在職辦公大樓和行人）。通常，在一個微蜂窩系統(tǒng)收發(fā)天線傳輸與低輸出功率在路燈水平（大約離地面5米）。安裝的移動臺轉(zhuǎn)送保持低功耗，從而延長電池壽命。使天線具有比周圍的建筑物更低的高度，射頻信號的天線大多集中在街區(qū).信號發(fā)射有可能包括在每個街道方向100-200米，服務(wù)幾個街區(qū)。此傳播環(huán)境具有較低的時間分散，這使得可以提高數(shù)據(jù)速率。微單元比宏單元通信更敏感。由于短期變化（如干擾，交通和干擾變化），中/長期變化（如新的建筑物），以及無線網(wǎng)絡(luò)（例如，新的增量增長基地臺）。每單元交接數(shù)目增加了一個數(shù)量級，以及可利用的時間作出交替下降。利用中轉(zhuǎn)單元是其中一個不錯方法，以減少切換率。由于微蜂窩接口要處理預(yù)期的高增長的通信負荷，讓切換過程中的權(quán)限下放程度較高成為一個必要。微單元遇到阻塞現(xiàn)象稱為拐角效應(yīng)。拐角效應(yīng)的特點是圍繞一個角落移動時信號處理突然大幅下降（例如，在20-30分貝信號強度（例如）在10-20米的距離）時。由于從服務(wù)基站組件到移動臺的視線丟失（LOS）。拐角效應(yīng)需要一個更快的切換和可以快速提高的信號質(zhì)量。角落里的效果是很難預(yù)測。測量平均間隔的不可取是由于拐角效應(yīng)。運動障礙可以暫時阻礙之間的信號傳遞，這類似于一個角落效應(yīng).參考了在曼哈頓式的環(huán)境對稱單元計劃的研究。單元計劃影響的信號來干擾比（SIR）的上行和下行的性能顯著。對稱單元計劃同時距離基地臺有四個最近的交流路徑。這種單元計劃可以分為半平方米（房協(xié)），全方（財經(jīng)事務(wù)），和矩形（R）的單元計劃。這些單元是描述未來的計劃。半廣場單元計劃此單元格計劃在每個路口基站全向天線的，并且每個微蜂窩占地50份在所有范圍的四個方向。此單元格計劃避免了街角的效果，并提供最高的容量。此計劃是穿透單元交接。圖2顯示了一半的系統(tǒng)計劃，其中在一平方單元微孔為例1。全區(qū)域單元計劃有其他的十字路口位于每個天線與全方位微蜂窩，微蜂窩的每塊覆蓋在所有四個方向。這是可能的移動臺體驗這個單元街道拐角效應(yīng)的計劃。計劃的全方位單元可以有一個例子，一個全方位的單元計劃計劃在微孔視角。從樓院或矩形單元的非視距切換。圖3顯示了每一個微蜂窩學(xué)位包括一小部分的水平或垂直的街道正中，及位于微蜂窩該單元格。此單元格圖可以很容易地適應(yīng)市場的需要。較少的基地臺發(fā)射功率高，可用于初步。隨著用戶密度的增加，可以添加新的基地臺與基地臺發(fā)射功率降低適當。街道拐角效應(yīng)是可能的這個單元的計劃。計劃的R單元可以有非視距或視線交接。圖4顯示矩形系統(tǒng)單元中的微孔計劃的一個例子。宏/微小區(qū)覆蓋微單元會擁塞缺乏某種服務(wù)的某些地區(qū)，而有些用戶的切換率過高等一些原因會令微單元負載[13]。為了減輕這些問題，一些單元的混合單元結(jié)構(gòu)（稱為覆蓋/襯底系統(tǒng)重疊）傘組成的大面積單元或宏單元（稱為）和小尺寸微單元（稱為襯底單元）都可以使用。圖5顯示了一覆蓋系統(tǒng)。在宏蜂窩/微蜂窩覆蓋架構(gòu)中提供了一個切換最大化之間的平衡，每個單位面積的用戶數(shù)量和減少社區(qū)間的網(wǎng)絡(luò)控制與負荷相關(guān)的切換。超出微蜂窩覆蓋面積宏單元提供廣泛的服務(wù)領(lǐng)域，并確保做得更好[14]。微小區(qū)的提供能力利用和覆蓋的地區(qū)，高密度的通信區(qū)（調(diào)用）有較大的頻率點。例如機場，火車站或停車場。在不太擁擠的通信需求地區(qū)（如城市以外地區(qū)的主要街道中心或市外）不是很高，宏單元可以提供足夠的覆蓋面等方面的研究。宏單元也為各成員國和高速微單元所覆蓋地區(qū)的不足（例如，由于缺乏渠道或范圍的移動臺正在走出微單元）。此外，在微孔系統(tǒng)用于溢出的通信其最充分的程度是可以路由到宏小區(qū)。覆蓋/襯墊系統(tǒng)是宏單元和微單元測定的最佳分配的渠道[15]。參考文獻[16]兩層之間的計算方法有四種共享的可用頻譜。方法1用于宏區(qū)域的TDMA和CDMA微蜂窩。方法2用于宏區(qū)域的CDMA和TDMA微蜂窩。愛他們使用在這兩個層次的TDMA中，且在這兩個辦法的第4層采用正交頻渠道。覆蓋/襯底系統(tǒng)微蜂窩系統(tǒng)的一些優(yōu)勢[17]：?基地臺只在需要高流量負荷的地區(qū)使用。因為它不是必需的，使該地區(qū)與微單元全程服務(wù)，同時基礎(chǔ)設(shè)施的成本節(jié)省。?在系統(tǒng)的覆蓋的數(shù)目遠遠低于宏微蜂窩系統(tǒng)，因為在快速移動的車輛可連接到覆蓋。?調(diào)用移動臺和通信位置可以很容易地做到通過微蜂窩系統(tǒng)。傘單元有幾類[17]。第一類在正交渠道分布微單元和巨單元之間。另一個類在微通道使用，微循環(huán)利用的巨單元的渠道已經(jīng)可以處理發(fā)射功率稍高的水平分配，抵消了宏單元的干擾。在環(huán)境中覆蓋/襯底系統(tǒng)中，有4種切換需要管理[19]：微單元，以微蜂窩，微蜂窩向宏，宏向宏，微蜂窩和宏蜂窩。參考文獻[20]描述了單元分裂和結(jié)合覆蓋。單元再利用