User Manual

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Chapter 3 System design
Fiber‐DASisawayofdistributingradiosignalsfromabasestationtoaremotelylocatedantennawherethecoaxial
cablelosseswouldbetoohighoritisimpracticaltoinstallcoaxialcables.Fiber‐DAScanbeusedindoorstocover
largebuildingswhereoutsidepenetrationofradiosignals
isnotsufficient,itcanbeusedtocoverstructuressuchas
tunnelsforrail,orroads,airports,metrolinesandmanyotherplaces.
Thischapterprovidesthebasicsofsystemdesignandavoidingcommonpitfalls.Allfiber‐DASsharesomecommon
propertiesastheyareanextensionofanexistingsignalintoanareawherethereislittleornocoverage.
The Basics
Thereissomebasicknowledgeyoushouldbefamiliarwithwhendesigningasystem.Inthissectionwewilldiscuss
themostimportantelementsofdesigntohelpyoudesignyoursystem.
Alinkbudgetisawa yofcalculatingtherequiredsignallevelsforthebasestationandthemobilestationand
matchingthisagainstyoursystemdesign,thelossesinthecables,theantennafactorsandothersuchparametersgo
intoalinkbudget.
WhenyouhavedonearoughlinkbudgetyoushouldusetheDAScalculatorandcalculatethesettingsofeachuplink
anddownlinkinthesystem.
Example:Youhaveasystemwith3remoteunitsandtheyarealldualband850/1900forCDMAandGSM.Your
systemhas6uplinksand6downlinkswherethesignalmayproceedfromantennatobasestationorviceversa,in
unitonethereisone850RFstripand
one1900RFstripformingtwoRFchainswithuplinksanddownlinks.
TheDAScalculatormayyieldadifferentnoisefigurefromtheoneyouinitiallyassumed whenyoudidyourlink
budget.Thisisfine,youmayinsertthenewnoisefigureinyourlinkbudgetandobservetheresult.
Whenyouhavedoneyourcalculationsyoualreadyknowthesettingsofthesysteminprincipleandyoucannow
commissionit.UsingthesettingsfromtheDAScalculatorasabasisyoucanconnecttothesystemandsetitupone
unitatatime,moreaboutthatin
 Chapter5"Commissioning "onpage 40 .
Link Budgets
Thestartingpointistocreateaviable linkbudgetforyoursystem.Aslinkbudgetsarecalculateddifferentfor
differentsystemsyoumaywanttotakesometimeandstudytypicallinkbudgetcalculationsforthetypeofservices
youareusing.
Youdonotneedtocreatelinkbudgetsforallofyourremotesandallfrequencybands.Doitforthewors tcaseonly
foreachservice,thatshouldbeenough.Thisisthenormalprocedureanditisusuallynotdifficulttofindtheworst
casescenario.Lookforthe
highestlossbetweenthebasestationandtheantenna,includingthefiberlossbetween
MasterUnitandRemoteUnitandanysplitlossaftertheRemoteUnituntilyougettothelastantenna.
Ifyouareusingradiatingcables,thencalculatewiththelossoverthemaximumlengthofradiatingcableyouneed
tosupportandfindtheRemoteUnitthathasthehighesttotallossfromtheUserEquipment(mobilestation)tothe
BaseStationend.