Indoorunit8.docx
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Indoorunit8.docx
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Indoorunit8
Unit8:
CDMAIndoorSystemDesign
Author
Department
PhoneNumber
ChuRuiChang
GlobalNetworkDesign(Dept.2779)
(972)685-7067
ESN445-7067
8.1Introduction
(1)UniqueFeaturesofIndoorEnvironment
IS-95CDMAsystemaremainlydesignedforoutdoorsystems.ThereareseveralspecialfeaturesofindoorenvironmentthatcouldreducetheadvantagesofCDMAtoindoorsystems.Theuniquefeaturesofindoorenvironmentare:
∙MuchShorterPropagationDistance:
Thedifferenceinmultipathdelay<<1chip,Rakefingerscannotdistinguishdifferentmultipathssonomultipathdiversity.Alsocoherencebandwidthisverywide,typically10to50MHz,thus1.25MHzisalmostlikenarrowbandandnofrequencydiversity.
∙MuchSlowerMovingSpeed:
Interleavinghasverylittleeffect.Ifnomultipathdiversityandnointerleave,highEb/Nocouldberequired,whichcouldhurtthecapacity.However,line-of-sight(LOS)conditionimprovesthingssignificantly.
∙DifferentBuildingshaveveryDifferentPropagationCondition:
Propagationenvironmentsignificantlydifferentfromonebuildingtoanother.Ifuseone“generic”indoorpropagationmodelforall,thesignalstandarddeviationcanbemorethan18dB.
∙Ifthesamefrequencyisusedastheoutdoorsystem,capacityishighlydependentontheBuildingPenetrationLoss:
Ifthebuildingisacomplete“metalbox”(penetrationloss=infinite),theindoorcapacityequalstothecapacityofonesingle,isolatedcell.Ontheotherextreme,ifthebuildingpenetrationlossiszero,theentireindoorareacouldbecomeasofthandoffzone(betweenindoormicrocellandoutdoormacrocell)andthecapacitygainbecomesalmostzero.
∙DifficultieswithHardhandoff:
UsingRTD,itisalmostimpossibletodohardhandoffbetweenindoorandoutdoor,sincetheuncertaintyofRTDusuallybiggerthentheentiredimensionofthebuilding.Itisveryexpensivetoputapairofpilotbeaconunits(1forenter,1forexit)ontheentranceofeverydoor.Otherhardhandoffmechanismsarealsonotreliable.Therefore,itisnoteasytodeploydifferentcarriersonlytoindoorarea.
Differentmethodsarebeenproposedtogetaroundthesepotentialissues.Wewilladdresstheminthefollowingsectors.
(2)GeneralDesignApproaches
Therearetwogeneralapproachestoprovideindoorcoverage:
(A)ForcetheRFwavepenetrateintothebuildings.ThisdesignapproachusesoutdoorBTSstoprovideindoorcoverage.Itrequiressufficientbuildingpenetrationmargintobefactoredintothelinkbudget.Themainadvantageissimplicity.Noneedtogetpermissionfromthebuildingownersandtowiretheentirebuilding.Thedisadvantageisitslowcoveragereliabilityandlowcapacity.Forsomebuildingareas(e.g.,undergroundbasement,tunnels),indoorcoveragecannotbeprovidednomatterhowmanydBofextramarginisgiventothelinkbudget.Additionally,toomuchextrabuildingpenetrationmargincouldresultinseverepilotpollutiontotheoutdoorcells.Buildingscanbetreatedas3-dimensionalhotspots.OutdoorBTSsprimarilydesignedforprovidingcoverageandcapacityfor2-dimensionalareas,cannotusuallyprovidesufficientcapacityfora3-dimensionalhotspot.
(B)GuideRFenergyintothebuildings.
∙Repeaters:
ArepeaterguidesRFenergyintothebuildingbypickinguptheRFenergyfromtheoutdoorBTS(mostlyovertheairfromitsdonorantenna),amplifyit,senditinthebuildingthroughcables,andreradiatetheenergyviaindoorantennas.Notethatrepeaterswillonlyenhancetheindoorcoverage,butwilldolittletoenhancetheoverallcapacitysincetheindoorcapacitymustcomefromtheoutdoorBTS.
∙Indoormicrocell:
AnindoormicrocellguidesRFenergyfromtheBTSintothebuildingeitherbyopticalfiberorcoaxialcables.TheBTSmaybeadedicatedBTSorsharedBTS(splitpartofitspower).Indoormicrocellwillprovidethebestindoorcoverageandsignificantlycapacitygain,ifdesignedproperly.Itisalsothemostexpensivesolution.Therefore,itismostlyusedinlargebuildingswithveryhighcapacityrequirements.Forcoverageonlyapplications,repeatershouldbeused.
8.2CoverageofIndoorAntennas
(1)EmpiricalPathLossFormula
Eq.(8.1)givesanempiricalformulafortheindoorpropagationpathlossbasedonlargenumberofmeasurementsondifferenttypesofbuildings.Thisformulaisforindoorantennasonly,andwillnotbeapplicableforleakycables.
Eq.(8.1)
Where
PL(xo)=pathlossat1meterfromtheindoorantenna;
PL(xo)=30-32dBfor800MHzsignals;
PL(xo)=38–40dBfor1900MHzsignals.
1.5<=n<=6,isthepathlossexponent;
=sumofallwall/floorpenetrationlosses
=variablewithzeromean,duetolognormalshadowing
Notethatthevalueofnisfrom1.5to6,whichmeansalthoughtheformatofthisformulaisgeneric,eachvariableintheformulacanbequitedifferentfordifferenttypesofbuildings.
NotethatEq.(8.1)onlyestimatesthepathloss.Theactualsignallevelataspecificpointischaracterizedbythreeterms:
Path_Loss(X)*Lognormal_fading(X)*Fast_fading(X).
Whenthelocationhasline-of-sightwiththeantenna,thefastfadingtypicallyobeysRiceandistribution.Whennoline-of-sightexist,ittypicallyfollowsReleighdistribution.
Thereareseveralspecialpropagationenvironmentswherethepathlossisalmostpredictable:
∙Alongalongcorridor,thepropagationconditionissimilartoawaveguide,thepathlosscanbelessthan2.Typicallybetween1.5to1.8.
∙IfthefirstFresnelzoneisnotobstructed,thepropagationalmostfollowfreespace(n=2).Examplesare:
Auditorium,openhallswithlineofsight.
∙Modernoffice(openspace+halfwallpartitions):
Intheopenarea,theindoorpropagationfollowsfreespacemodel,sinceitisnotdisturbeduntiltheFresnelellipsehitstheobstructionlayer.Belowthepartitions,thepropagationcanbeapproximatelymodeledbyasingleormultipleknife-edgediffractionmodel(e.g.,6dBextralosswhenthereisagrazingincidenceoveronesingleobstacle,etc.).
(2)GeneralRecommendations
Generally,coverageoftheindoorantennatothesamefloorismuchmorepredicablethanthecoveragetoadifferentfloor.Tothesamefloor,themainuncertaintiesofsignallevelcomefromanumberoffactors:
∙Differencesinwallmaterials,wallpenetrationlosscanbeanywherefrom1to10dB.Table8.1givessometypicalmeasuredwallpenetrationloss.
∙Differentsignalincidentanglecanproducemorethan15dBdifferenceinpathloss(normalandgrazingincidence)
∙Upto20dBchangeinsignalstrengthcouldbeexperiencedwhenturningacorner
∙Thesignalstandarddeviationforthesameflooristypicallybetween3to12dB.
Toadifferentfloor,theuncertaintiesaremuchbiggerandthecoverageismuchlesspredictable.Manydifferentfactorscanaffectthesignallevel:
∙Largedifferencesinfloorpenetrationlossduetodifferencesinfloorconstructionmaterials(8to30dB)
∙Morethan15dBdifferencesinfloorpenetrationlossbetweennormalandgazingincidence
∙Pathlossnotnecessarilyincreasesproportionaltothenumberoffloors.Onepossiblereasonisthataftertwotothreefloors,signalreflectedfromsurroundingbuildingsmaybecomedominantanddirectsignalbecomesinsignificant.
∙Ifuseonesinglepathlossmodelforcoveragetodifferentfloors,thestandarddeviationcanbe>18dB.Thiskindoferrorisusuallyunacceptable.
Table8.1TypicalMeasuredValuesforWallPenetrationLoss
MaterialType
PenetrationLoss[dB]
Frequency[MHz]
Lossfromonefloor
8-20
1300
ConcreteBlockWall
13-20
1300
1floor+1wall
40-50
1300
SheetRock(3/8in)
2
9600
ConcretePillar(diam=0.6m)
12-14
1300
Allmetal
26
815
Lossduetoturncorner
10-20
1300
Glass(notint)
0-2
?
?
TintGlass+metalmini-blind
10-15
?
?
Toaccuratelypredicttheindoorcoverage,measurementonseveraltypicalindoorenvironmentsarenecessary.Oncemeasurementsareperformedononekindofenvironment,thecoveragecanbeestimatedforadifferentbuildingwithsimilarenvironment,addorsubtractafewdBduetominorchanges(e.g.,anextrawallhere,apillarlessthere,etc).
Werecommenduseindoorantennasoneveryfloor.Thereasonsare:
∙Thecoveragewillbemuchmorereliable.IfoneusesarelativelylargenumberoflowpowerantennasperfloorsothatLOSconditioncanbemaintainedformostofareas,nearly100%ofindoorareareliabilitycouldbeachieved
∙Ifthecoverageisfromantennasatdifferentfloors,duetolargeuncertaintiesmeasurementsoneveryfloorarenecessarytoverifythecoverage.Thiscouldbeverytimeconsuming.
Howmanyindoorantennasperfloorwilldependsonanumberoffactors:
∙Thesizeofthebuilding
∙Theshapeofthefloorplan
∙Thepathlossslopeofthefloor
∙TxpowerlevelandRxnoisefigureoftheantennasystem
∙Therequired%ofin-buildingcoverage
Thefollowingfactorsincreasestherequirednumberofantennasperfloor:
∙largebuildingdimensions
∙irregularfloorplans
∙highpathloss
∙highreverselinknoisefigureoftheoverallindoorsystem
∙lowtheTxpowerlevelfromeachantenna
∙requirementofnearly100%ofindoorcoverage.
Notealsothatalargenumberoflowpowerantennaswillprovidemuchmoreuniformandreliablecoveragethanasmallnumberofhighpowerantennas.Distributingalargenumberoflowpowerantennasuniformlyacrossafloorwillprovidemacroscopicdiversity,andthussignificantdiversitygain.EachantennaprovidesanextraTx/Rxdiversity,becauseitisnotlikelythatalloftheseantennasareshadowedatthesametime.
Forthisreason,foranaveragesizedbuilding,werecommendusemultipledistributedanten
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