User Manual

Systemdesign
28
Downlink
Forthedownlinkyoucanusuallyjustusetheoutputpoweroftheremoteunitandthencalculateyourlinkbudget.
Rememberthatifyouhaveseveralcarriers,youneedtocalculateyourlinkbudgetwiththisinaccount.Foreach
newcarrieryouadd,thepowerpercarriergoesdownasthepow
erontheRemoteUnitisdividedontoallthe
(active)downlinkcarriers.
Tocal
culatethe“percarrier”outputpower, Table40 containsalistofmodifiersthatareappliedtotheoutput
powerofther
emoteunit.
Table 40 Per carrier loss
Asyoucanseethereisacorrelationthatwheneverthenumberofcarriersdoublethepercarrierpowerislowered
withanother3dB.Thustheformulaforanynumberofcarrierswillbe:
P
Carrier
P
Composite
10 10log N
Carriers
–=
Theoutputpowerforeachtypeofremoteunitandfrequencybandcanbefoundinthedatasheetsin "Rem o te
Un it(RU)"onpage18 wheretherelevantparametersforeachremotesystemarediscussed.
Remembertousethepercarr
ierpowerinyourlinkbudgetandnotthecompositebecauseifasyoukeepadding
carrierstothesystemthepowerpercarrierwillbelower.Ifyouareplanningonaddingadditionalcarriersinthe
futureyoushouldplanyoursystemforthemaximumfo
reseeablenumberofcarriers.
Followingisanex
ampleofalinkbudget.ThislinkbudgetisalsoincludedintheDASCalculatorpackage.Ifyoudo
nothavethispackagecontactDeltaNodeSolutionstoreceiveacopy.
Uplink
Uplinkcalculationsgenerallyrelyonhavingthenoisefigureathandbeforesothatthedesensitizationofthebase
stationcanbecalculated.Howeversincethenoisefigureisdependentonthelinkbudget,weshouldbeableto
calculateacrudelinkbudgetatfirst,getourgainstraightandthenwhenwear
edoneweshouldbeabletocalculate
thepropernoiseloadusingtheDASCalculatorTool(willbehandledin
Chapter6"RFCommissioning "on
page41 ).Thereforewewillassumeastandardnoisefigurefornow,properlyadjuste dtheDeltaNodeFiber‐DAS
solutionha
saNFoflessthan3dBperuplink.
Area
sonableassumptionfortheNFisaround3dB,ifweshouldgetabetterorworseNFlaterwhentheDAS
Calculatorisemployedwewilljustgobackandcorrectthelinkbudgetsforthis.
SystemU
plinkNetGain
Thene
tgainisthetotalgainintheuplinkfromtheRemoteUnitporttotheinputportonthebasestation.Thischain
lookssomethinglikethis:
Figure 15
Antenna
RU
RemoteUnit Fiber
FOI
FOICard
POI
POIunit
BIU
BIU
BTS
BaseStation
50dB ‐40dB 20dB ‐35dB 7dB
‐80dBm ‐30dBm ‐70dBm ‐50dBm ‐85dBm ‐78dBm
‐2dB
‐80dBm
Uplink Net Gain
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0 -3.0 -4.8 -6.0 -7.0 -7.8 -8.5 -9.0 -9.5 -10.0