User's Manual

TrangoSystems,Inc. StrataLink24QuickStartGuide 14
CustomchannelsizeandT/Rspacing
The24GHzunlicensedspectrumistypicallyveryclearduetothenarrowantenna
beamwidthsrequired.However,ifcollocatedsystemsonthesamepatharerequired,
operationofeachlinkonanonoverlappingfrequencypairmaybeadvised.The
StrataLink24allowscustomTXandRXcenterfrequencytohelpwithco‐location.
Thesystemcansupportuserselectablechannelsizesof10,14,20,25,30,40,50,or60
MHz.
RecommendedsettingsforeachchannelsizeareshowninAppendix1
AdvancedAdaptiveCodingandModulation(AACM)
Adaptivecodingandmodulationprovideserror‐freehitlesschangingofthemodulation
levelforafixedchannelwidthtoallowthelinktobemaintainedduringheavyweather
relatedfadingconditions.Insteadofthelinkdroppingandnotrafficpassing,thelink
willbemaintainedwithalowercapacityuntilthefadingconditionisremoved,atwhich
timethelinkwillreturntothenormalmodulationlevel.
Thetransitionsbetweenmodulationlevelsarecontrolledbypre‐setMSEthresholdsand
eachtransitionismadewithoutdroppingpacketssincebothendsofthelinkcoordinate
thetransitionautomatically.Theavailablemodulationlevelsare1024QAM,512QAM,
256QAM,128QAM,64QAM,32QAM,16QAM,8PSK,andQPSK.
Theusercansetbothamaximumandminimummodulationlevelwhichtheradiowill
operatewithin.Bothsidesofthelinkshouldhavethesameminandmaxmodulation
levelsforproperoperation.TypicallyitisbesttoalwaysuseQPSKastheminimum
modulationleveltomaintainthelinkduringdeepfading.
AdaptiveChannelSize(ACS)
InadditiontotheAACM,uptoanadditional10dBofsystemgaincanbeobtainedby
enablingtheadaptivechannelsizefeature.
ACSwillsetthechanneltothesmaller,highlycoded10MHzbandwidthtopreservethe
linkduringextremefadingconditions.Inthecaseofa60MHzchanneldownshifting
from1024QAMtoQPSK,theprofilewillbesetto10MHzchannelsizeiftheMSEgoes
belowausersetdownshiftthreshold.This10MHzprofileisahighlycodedprofilethat
canoperatewithverylowSNR.Thesystemgainisincreasedby
upto10dBtopreserve
communicationacrossthechannelforaslongaspossible.Theswitchisnothitlessand
therewillbea1‐2secondbreakintrafficduringthedownshift.WhentheMSEimproves
aboveausersetupshiftthreshold,bothendsofthelinkwillreset
totheusersetACM
profile.
GPSCoordinates