radiating cables cables dbm at 95% of the points in the vicinity of the cable end and at 6 m...
Post on 19-Jun-2018
213 Views
Preview:
TRANSCRIPT
CABL
ESrAdiAting CABL
ES
Application note
Link Budget
3.LINKBUDGET
The basic elements to calculate a link budget can be illustrated by considering the example showninFigure4.ItinvolvesaGSM900radiocoverageinadual-boretunnelthatis900minlength.Itshallbeassumedthat:
➔ thepowerperchannelavailableforthedownlinkis1W(+30dBm);➔ theRC ineachbore is fedviaapower splitter (“T-feed”configuration) the insertion lossofwhich
isequalto3.5dB;➔ jumper cables are used to connect the repeater, power splitter and the RCs. Their total insertion
lossisequalto1.5dB;➔ thespecification imposesa receivedsignal (measuredwithahalf-wavedipoleantenna)ofat least
-88dBmat95%ofthepointsinthevicinityofthecableendandat6mdistance.
It shall also be assumed that the RC has the following characteristics at 960 MHz (upper limit of theGSM900frequencyband):
➔ longitudinalattenuation:3.1dB/100m;➔ CL50%and equalto58and62dBrespectively.
Table1summarisesthelinkbudget.Thelastlineindicatesthatthespecificationissatisfied,i.e.aminimumreceivedsignal(measuredwithahalf-wavedipoleantenna)higherthan-88dBmat95%ofthepointsinthevicinityofthecableendandat6mdistance.Thevariouslinesofthislinkbudgetarecommentedhereafter.
Uplinkperformances(i.e.frommobilestationtobasestation)canbecomputedinthesameway.
Table1:Linkbudgetexample
Availablepowerperchannel +30dBm
Jumpercableloss -1.5dB
Powersplitterinsertionloss -3.5dB
RCinsertionloss:900mwith3.1dB/100m -28dB
CL95%at2m=62dB -62dB
Correctionforlongerdistance=20log(d/2)=20log(6/2)= -9.5dB
Penetrationloss* 0dB
Mobileantennalossrelativetodipole* 0dB
Safetymargin -10dB
Minimum received signal at 6 m from the RC (95% percentile) - 84.5 dBm
Figure4:Dual-boretunnel
withonebasestationandapowersplitter
*Note:Itresultsfromthespecificationofthisparticularexamplethatthepenetrationlossandmobileantennalossrelativetodipoleareequalto0dB.
RCinbore1
RCinbore2
RadiatingCablesApplicationnote03/2010
1.
3.1. RC insertion loss
The RC insertion loss is equal to the cable length multiplied by the longitudinal attenuation. Thislongitudinalattenuationissomewhatinfluencedbythestandoffdistance(betweentheRCandthewallorceilingtowhichitishung).Forexample,iftheRCisdirectlyagainstaconcretesurface,theimpactonthelongitudinalattenuationisfrequencydependentandisobviouslynotidenticalforallRCs.IftheIECstandardconditionsareconsideredasreferencevalues,measurementscarriedwithvariousEupenRMCsindicatethatinstallingtheRCdirectlyagainstaconcretesurfaceinvolvethefollowinglongitudinalattenuationincreases:
➔ below300MHz,theimpactisnegligibleandevensometimesnegative;➔ typicallyrangesfrom5to10%around450MHz;➔ typicallyrangesfrom10to20%around900MHz;➔ typicallyrangesfrom25to60%around2000MHz.
ThelongitudinalattenuationisalsoinfluencedbyhumidityanddustdepositontheRCjacket.Eveninrathersevereconditions,thelongitudinalattenuationincreaseneverexceeds10%.
3.2. RC Coupling loss
Some RC manufacturers use the free space method or specify the CLs for the antenna orientationcorrespondingtothebestresult.ThedifferencesofinterpretationinthemeaningoftheCLparametermayleadtosignificanterrorsinlinkbudgetorwhentheperformancesofdifferentproductshavetobecompared.
TheCL50%andCL95%specifiedintheEupendatasheetsaremeasuredwiththegroundlevelmethodaccordingthe IEC61196-4standard1.Thegroundlevelmethodhasbeenpreferredbecause itdefinesconditions which are closer to those actually met in practice. Indeed, in almost all the applications,theRCishungatshortdistancefromasurface(ceilingorwall).Adetailedanalysisofthisissueispresentedinsection4.
However,CLsmeasuredwiththefreespacemethodarealsoavailableforsomeEupenRCs.
TheCL50%andCL95%specifiedintheEupendatasheetsareaveragedoverthreeantennaorientations(radial,orthogonalandparallel).Asexplainedinsection4.2.,theCL50%orCL95%thatshouldbeusedforlinkbudgetcorrespondtothesymbolsCL50%-meanorCL95%-mean.
1IEC61196-4standard-Coaxialcommunicationcables-Part4:Sectionalspecificationforradiatingcables.
RadiatingCablesApplicationnote
03/2010
1.1.
1.2.
a)E.M.wavedepolarisationduetoreflectionsonobstacles
In thecaseofcommunicationswithhand-heldmobileequipmentonboard train,awavepenetratingintoacarriageexperiencesreflectionsonthecarriagewalls,ceiling,floor,seats,etc.Ateachpoint,thefieldstrengthisthevectoradditionofseveralwavesandthepolarisationofthesumcanbeconsideredaselliptical ratherthan linear.Figure5showsthesimplecasewhereadirectwaveradiatedbytheRCinterfereswithanotherwavewhichhasbeenreflectedbythecarriageceilingandwindow.Thedashedarrows(atrightanglewiththedirectionofpropagation)indicatethewavepolarisation.Ifweconsiderthedifferenceofpropagationdelay,itisclearthatthepolarisationoftheresultingE.M.fieldatthereceptionpoint R is very complex. Figure5 is a very simple casewithonlyone reflectedwave. Inpractice, thesituationsaremuchmorecomplexassuggestedinFigure6wherethedirectwavemaybeblockedbytravellersorbyanothertrain.
b)Mobileantennaorientation
Withhand-heldequipments,themobileantennaorientationisneitherperfectlyverticalnorhorizontalbutratheracombinationoftheseasshowninFigure7.Indeed,innormaluse,anhand-heldequipmentisslightlydown-tiltedandnotnecessarilyorientatedformaximumresponse.
Figure5:Wavedepolarisation
duetoreflections
Figure6:Propagationintocarriage
Figure7:Mobileantenna
orientation
Figure6 Figure7
RadiatingCablesApplicationnote03/2010
c)Mobilestationareratherinsensitivetoantennaorientation
Asexplainedinsection4.2,thedifferencebetweentheCLsinthedifferentantennaorientationisduetothedirectivityofthehalf-wavedipolewhichisusedforCLmeasurements.
Converselymobilestationantennas(suchasGSM,PCN,UMTS,etc.)aremoresophisticatedthatthesingledipoleormonopole(whichisillustratedinFigures6and7).Theirspatialresponseisdifferentandmuchmore“isotropic”thanquarter-wavemonopoleandhalf-wavedipoleantennas.Measurementsperformedwithvariousmobilestationsdemonstratethatthereceivedpowerisnearlyindependentoftheantennaorientation.So,mobilestationantennasbehaveasnearlyisotropicantennaswhichpickupthestrongestfieldcomponentwitharatherlowgain(about–10dB).
If the symbols CLr, CLp and CLo designate the coupling losses in the radial, parallel and orthogonalorientationrespectively(whichevertheprobabilitylevel)andifthesymbolCLmeancorrespondstothemeancoupling lossasdefined in the IEC61194-4standard, it is shown insection4.2thatCLmean isgenerally about 4 dB higher than the lowest coupling loss. It results that, for practice, the followingapproximationcanbemade:
CLmean = min (CLr, CLo, CLp) + 4
wherethe“min”symboldesignatestheminimumofthevaluesinbrackets.
This results means that calculating the link budget with the lowest coupling loss (CLr, CLp or CLo) instead of the average value (CLmean) is equivalent to a 4 dB decrease of the safety margin.
3.3. Correction for longer distance
With“classical”transmittingantennas,thereceivedpowerdecreasesasafunctionofthesquareofthedistanced,i.e.:
This is a consequence of the “spherical symmetry” (the radiated energy is contained in a sphere ofradiusequaltod.WithRCs,theradiatedenergyiscontainedinacylinderofradiusequaltod,hencea“cylindricalsymmetry”.Consequently,thereceivedpowerdecreasesasafunctionofthedistanced,i.e.:
1➔Prec÷— d2
1➔Prec÷— d
RadiatingCablesApplicationnote
03/2010
1.3.
TheCL50%isspecifiedat2moftheRCaccordingtotheIEC61196-4standard.Ifitisrequiredatanotherdistance,thefollowingcorrectionshouldbeapplied:
FortheCL95%,alongerdistanceinvolvesastrongerinfluenceofscatteredradiationsandreflectionsonwallsandceiling,henceafadingincrease.Thefollowingcorrectioncanbeapplied:
3.4. Penetration loss
For communications into vehicles, the link budget must take a penetration loss into account. Thispenetrationlossisstronglyinfluencedbythefrequency,thewidowsizes,theglasstype(singleordoublelayer) and the possible presence of metal coating (for thermal insulation). For example, at 900 MHz,penetrationlossmayrangefrom2or3dBforasinglelayerglass.Itreaches30dBinthecaseofmetalcoatedglasses.
3.5. Mobile antenna loss relative to dipole
Theantennasusedinmobilephones(suchasGSM,PCN,UMTS,etc.)haveanegativegainwithrespecttothehalfwavedipolenormallyusedtomeasuretheCLs.Theirspatialresponseishowevermore“isotropic”.A10dBmobileantennalossrelativetohalfwavedipoleseemsarealisticvalue.
3.6. Safety margin
A10dBsafetymarginisrecommendedtoaccountfor:
➔ thedifferencesbetweenthestandardconditionsinwhichtheCLsaremeasuredandthoseactuallymetinarealtunnelenvironment;
➔ thevariousfactorswhichmayimpairtheRCperformances.
As explained in section 3.2., a link budget based on a CL averaged over three antenna orientationsprovidesasafetymarginwhichis4dBsuperiortoabudgetcalculatedwiththevaluemeasuredinthebestorientation.
d➔CL50%(d)=CL50%+10log(——)
2
d➔CL95%(d)=CL50%+20log(——)
2
RadiatingCablesApplicationnote03/2010
1.4.
1.5.
1.6.
EUPEN CABLE
YourreliablePartnerforRFCommunications
Asaleadingsupplieroftransmissionlinesandaccessoriestoglobalwirelesscommunicationsmarkets,EUPENhastheexperienceandresourcestoeffectivelyservicecustomersintoday’schallengingwirelesscommunicationsmarkets.
Atatimewhenwirelesscommunicationinconfinedareas,suchasunderground,streetandservicetunnels,isimportanttothenetworkoperators,EUPENhighqualityradiatingcablesprovethatEUPENCableisyourreliablePartnerforRFCommunications!
DownloadyourowncopyofthelatestRadiatingCablecatalogueat:www.eupen.com
Tel. +3287597343Fax.+3287597060
www.eupen.comrf_sales@eupen.comrf-service@eupen.com
RadiatingCablesApplicationnote
03/2010
Malmedyer Str. 9 - B-4700 EUPEN - BELGIENTel.: +32(0)87.59.70.00 http://www.eupen.com Fax: +32(0)87.59.71.00 e-mail:info@eupen.com
ISO Certified Company
top related