AntSelDualpolunit6.docx
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AntSelDualpolunit6
Unit6:
AntennaSelectionConsiderations
Author
Department
PhoneNumber
ScottTran
CDMAGlobalNetworkDesign
(Dept.2779)
(972)6842796
ESN444-2796
6.AntennaSelectionConsiderationsandExperimentalResultsofDualPolarizationDiversityPerformance
Thissectionhastwomainsubections.Thefirstsubsectionisantennaselectionconsiderationsandthesecondsub-sectionistheexperimentalresultsofdualpolarizationdiversityperformanceatPCSBand.
6.1AntennaSelectionConsiderations
Thissub-sectioncoverswhatshouldbeconsideredwhenevaluatingorselectingbasestationantennasbasedonantennaspecificationsandtesting.Thissectionalsocovershowthehorizontalandverticalpatterncanimpactthesystemperformanceassociatedwithsofthandoffandsystemnoiseandhowtocombinemechanicaldowntiltandelectricaldowntiltforoptimizingthesystemperformance.ThissectionalsointroducesalistofantennavendorsthatisselectedbyNortelfortheantennausage.
6.1.1SelectionBaseStationAntennaperSpecificationandTestResults
ItisimportanttoconsiderthefollowingpointswhenselectingantennasforPCS(1900MHz)andDCS(800MHz)systems.
1.Electricaldesignspecifications
2.Mechanicaldesignspecifications
3.Environmentaldurabilitytestresults
6.1.1.1ElectricaldesignSelection
6.1.1.1.1HorizontalBeamwidthConsiderations
HorizontalbeamwidthtypicalusedonCDMA,TDMA,andAMPSsystemsare33o,65o,85o,and90o.
Fortri-sectorsiteapplication,ahorizontalbeamwidthof85o(atthe–3dBpoints)isusuallyspecifiedtoprovidetherightoverlapandcoverageareaforthesuburbanandruralareas.Forthedenseurban,urban,andinnercityareas,anantennabeamwidthof65oisconsideredtobeabetterchoicesincethecellradiusofdenseurbanandurbanareasisabout1Kmto2Km.Withthedeploymentof65ohorizontalbeamwidthantennafordenseurbanandurbansites,theexcessiveoverlapbetweensectorscanbereduced.Theseresultinreducingsofthandoff,channelelementusage,andsystemnoise.
Bi-sectorsitewithtwoantennasmountingbacktobackisnormallydeployedalongthehighwayintheruralareas.Anantennabeamwidthof65oisusuallyusedforhighwayinthesuburbanarea.Theusageof65ohorizontalbeamwidthinsteadof85obeamwidthcanincreasethelinkbudgetbyabout1.5dB.Forlongnarrowinterstatehighway,normallythecoverageisthemainconcern.Thelongerthecoveragecanextendalongthelongnarrowhighwaythelessrevenueneedtospendonthehardware(i.e.BTS).Thisresultsinusingantennaswith33ohorizontalbeamwidth.
6.1.1.1.1.2FronttoBackRatioConsideration
Thefront-to-backratioisalsoneededtobeconsidered.Thefront-to-backratioofhorizontalpatternnormallyvariesbetween20dBto35dB.Anantennawithfront-to-backratioof25dBistypicallybeenused.
6.1.1.1.1.3VerticalBeamwidthConsideration
Thehighergainthenarrowerverticalbeamwidthandthelongerlengthofanantennacanonlybedesigned.Averticalbeamwidthof4oisaboutasnarrowaverticalbeamwidthasshouldbeusedsinceantennawithverticalbeamwidthlessthan4oishardtolevelitaccuratelyandrequiresaverystablemountingstructurefortheantenna.Alsoantennawithverticalbeamwidthlessthan4oisveryeasysufferwinddeflectionandvibration.
Theselectionofverticalbeamwidthdependsonparticularapplications.Anantennawithverticalbeamwidthbetween7oto10oistypicallydeployedfordenseurban,urban,andinnercityareas.Anantennawithverticalbeamwidthbetween4oto7oisoftenusedforsuburbanandruralarea.
6.1.1.1.1.4UpperSidelobeConsideration
Almostanyoptimizednetworkrequiredsiteswithdowntilteitherwithmechanicalorelectricalorboth.Antennawithoutuppersidelobesuppressioncancreateunpredictableinterference,pilotpollution,systemnoiseincrease,andunnecessarysofthandtotheneighborsectororsometimesover-shoottothesecondtiercellsasaresultofmechanicaltilt.Therefore,allverticalsidelobeswithin20oofthemainbeamareoftenrequiredtosuppresstoatleast–19dBrelativetothemainbeam.
6.1.1.1.1.5VSWR(VoltageStandingWaveRatio)Consideration
VoltageStandingWaveRatio(VSWRorreturnloss)isanotherfactorneedtobeconsidered.ThetypicalvalueforVSWRisbetween1.2:
1to1.5:
1
issuggestusingbothmechanicaltiltandelectricaltilttogether.
6.1.1.1.1.6IntermodulationProductGenerationConsideration
Duplexingtransmittersandreceiversontothesameantennaareoftenbeendeployedtosaveantennaandmountingcostandtoimprovethevisualprofile.ThelevelofPassiveIntermodulationProduct(PIP)thatgeneratedbythemutiplexingofmultifrequencycarrierontransmissionandreceptiononanantennamustbeconsidered.
TypicallythePIPslevelisspecifiedtobeabout–110dBmfortwo+43dBm(20W)carriersformostantennamanufactures.ThePIPatthelevelof–110dBmissufficientforavoidinginterferenceintermodulationsincethe3rdintermodulationthataregeneratedbybasestationTXisfelloutthepass-bandofthemobileRXandviceversaforboth800MHzand1900MHz.Pleaserefertotables:
6.1and6.2belowforthedetails.
Table6.1:
3rdPIPgeneratedbyBaseStationandMobileStation(1900MHzSystem)
Table6.2:
3rdPIPgeneratedbyBaseStationandMobileStation(800MHzSystem)
6.1.1.2AntennaHardwareandEnvironmentaldurabilityConsideration
Alongwiththeseelectricalissues,mechanicalissuesarealsoimportanttoconsider.Theantennashouldhaslesscablesandsolderjointinthedesignsincethesolderedjointishardtocontrolandmaybreakdownoverlongperiodoftime.Thepassiveintermodulationisintroducedwhenthesesolderedjointsarelosingorbreakdown.
Anotherkeymechanicalissueistheantennaconnector.The7/16Dinconnectorshouldbeusedsinceitdurableandishardtohaveinnerpintobedamageduringtheinstallation.Iftheinnerpinispartialdamage,itcanhavepoorTxpowerandcreateintermodulation.
Downtiltclampsshouldbeconsidered.Theseclampsmustholdupto125-mphwind.Theantennamusthavethedrainhole.
Environmentaldurabilityalsoneedstobeconsidered.Whenselectingantennas,theenvironmentaltestingsuchastheIEC(InternationalElectroTechnical)testingmustbeobtainfromtheantennamanufacture.ThefollowingaretheminimalIECtestingamanufacturerneedtoperform.
IECTestCode
Description
IEC68-2-1
ColdTest:
16hoursat–40oC
IEC68-2-2
DryHeatTest:
16hoursat+70oC
IEC68-2-11
SaltMistTest:
48hoursinsalttank@5%saltsolution
IEC68-2-14
ChangeofTemperatureTest:
+70oCto–40oCtwocycles,2hoursdwell.ItshouldbedoneinconjunctionwithVSWRmeasurement.
IEC68-2-18
RainTest:
10mm/houratvariousangle
ICE68-2-26
Vibration:
Variedfrequenciesandmultipleaxes.
IEC-68-2-3
HumidityTest:
24hours@55oCand95%humidity,sixcycles.
6.1.2OptimizingSystemPerformancebydowntilting
Downtiltingbasestationantennaisakeyfactorfordesigningandoptimizingthesystemperformance.Asite(basestation)withantennalocatedinahighhillnormallycreatesindeadspotatdistanceclosetothebasestation.Onewaytocorrectthatistoapplysmall(2oto3o)mechanicaldowntilt.
DowntiltingthemainbeambelowthehorizoncanreduceRFsignalpropagatingbeyondthedesiredcoverageorreducetheRFpowerblastingtoadjacentsitesandtothesecondtiersites.Asaresult,systemnoise,unnecessarysofthandoff,pilotpollutioncanbereducedorcontrolled.
Downtiltingtheantennashouldbehandlewithcaresinceverysitehasspecificheightabovetheaverageterrain.Anestimatevalueofdowntiltcanbecalculatedbyusingthefollowingformula.
Mainbeamdistance=(H/tan(DT))/5280
Dmin=(H/tan(DT+0.5*VBW))/5280
Dmax=(H/tan(DT–0.5*VBW)/5280
WhereDT=downtiltangleandVBW=verticalbeamwidth.
Sitesthatrequiremechanicaltiltingwithmorethan6oshouldbeverifiedwhethertheboresideofthehorizontalpatternisdistorted.Electricaltiltcanbeusedinconjunctionwithmechanicaltiltforbetterresultsincemechanicaltiltonlyaffectonthehorizonbutnotthetwosidesofthehorizontalpattern.Thereforeifmechanicaltiltrequiresmorethan9o.Itissuggestusingbothmechanicaltiltandelectricaltilttogether.
6.1.3ListofAntennaVendorsSelectedbyNortelfortheantennausage
1.ALLGON
2.ANDREWS
3.COMSATRSI
4.CELWAVE
5.DAPA
6.DECIBLE(ALLENTELECOMGROUP)
7.
SCALA
6.1.4Appendices
6.2DualPolePolarizationAntenna
Dualpolarizationantennahasbeenpaidmuchattentionforitsdiversityperformancesincethesamesectorwhichisusedtwoantennasforspacediversitycannowbereplacedwithoneantennafordual-polepolarizationdiversity.
Dual-polepolarizationantennaisidealfordeployinginareaswithzoningrestrictionsindenseurban,urban,andsuburbansincethehighertheantennaofabasestationisthewidertheseparationoftwodiversityantennasisrequired.TheseparationDofthespacediversityschemecanbedeterminedwiththefollowing.
h/D=11,wherehistheantennaheight.
Theaboveequationhasbeendeterminedexperimentallythattheoptimumvalueis11asindicatedinLee[2].Forexample,iftheaverageantennaheightofbasestationsininnercityis30mor100feet,andthentheoptimumseparationDisabout3mor9feet.
Asmentionedabove,thedeploymentofdualpolarizationantennafordiversitywillreducetheantennacount.Atri-sectorsite(basestation)requires9antennas,3foreachsectorwhensimplexantennasystemconfigurationisusedandrequires6antennasforduplexantennaconfiguration.T