User's Manual Part 1

Designing a Fusion Wideband Solution
Page 102 InterReach Fusion Wideband Installation, Operation, and Reference Manual
© 2013 TE Connectivity Ltd D-620616-0-20 Rev H • TECP-77-044 Issue 7 • May 2013
UplinkAttenuation
TheattenuationbetweentheMainHub’suplinkportandtheassociatedband’sbasestation
reducesboththenoiselevelandthedesiredsignalsoutofFusionWideband.Settingthe
attenuationontheuplinkisatrade‐offbetweenkeepingthenoiseandmaximumsignallevels
transmittedfromFusionWidebandtothebasestationreceiverlowwhilenotreducingtheSNR
(signal‐to‐noiseratio)ofthepathfromtheRAUinputstothebasestationinputs.ThisSNRcannot
bebetterthantheSNRofFusionWidebandbyitself,althoughitcanbesignificantlyworse.
Agoodruleofthumbistosettheuplinkattenuationsuchth
atthenoiseleveloutofFusion
Widebandiswithin10dBofthebasestation’ssensitivity.
RAUAttenuationandALC
TheRAUattenuationandALCaresetusingtheAdminBrowserEditUnitPropertiesscreen.
EmbeddedwithintheuplinkRFfront‐endofeachFusionWidebandRAU
bandisanALCcircuit.
ThisALCcircuitprotectstheFusionWidebandsystemfromoverloadandexcessive
intermodulationproductsduetohigh‐poweredmobilesorothersignalsourcesthatarewithin
thesupportedfrequencybandandareincloseproximitytotheRAU.
EachindividualBand(1or2)ofaFusionWidebandRAUhasanuplinkA
LCcircuitthatoperates
asafeedbackloop.Apowerdetectormeasuresthelevelofeachband’suplinkRFinputandifthat
levelexceeds–30dBm,anRFattenuatorisactivated.Thelevelofattenuationisequaltothe
amountthattheinputexceeds–30dBm.Thefollowingsequencedescribestheoperationofthe
ALCcircuit,asillustratedinFigure6‐2.
1 The
RFsignallevelintoeitherBandoftheRAUrisesabovetheactivationthreshold(–30
dBm),causingthatALClooptoenterintotheattackphase.
2 D
uringtheattackphase,theALCloopincreasestheattenuation(0to30dB)untilthedetector
readingisreducedtotheactivationthreshold.Thedurationofthisattackphaseiscalledthe
attacktime.
3 A
ftertheattacktime,theALCloopenterstheholdphaseandmaintainsafixedattenuationso
longasthehigh‐levelRFsignalispresent.
4 The
RFsignalleveldropsbelowthereleasethreshold(–45dBm)andtheALCloopentersthe
releasephase.
5 During
thereleasephase,theALCloopholdstheattenuationforafixedperiodthenquickly
releasestheattenuation.
AnimportantfeatureoftheALCloopisthatinStep3,theattenuation
ismaintainedatafixedlevel
untilthesignaldropsbyasignificantamount.ThispreventstheALCloopfromtrackingvariations
intheRFsignalitselfanddistortingthewaveformmodulation.