EDX WP UseofClutterDatainRFPlanning Aug08 Web
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8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
1/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 12008EDXWireless www.edx.com
TechnologyWhitePaper
TheApplication
of
Land
Use/
LandCover(Clutter)Datato
WirelessCommunication
SystemDesign
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
2/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 22008EDXWireless www.edx.com
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
HarryAnderson,TedHicks,JodyKirtnerEDXWireless,LLC
Eugene,OregonUSA
Introduction
Landuse/landcover(LULC)datacanplayasignificantofroleindesigningwirelesscommunicationsystems. Itcan
beusedtoimprovepredictionsofsignalattenuationandotherradiopropagationeffectsandtoassistinfinding
theoptimallocationofnetworkbasestationsandotherwirelesssystemtransmitters. Itcanalsobeutilizedwhen
projectingusage(traffic)trendsinanytypeofmobileornomadicsystem.
Withliterallybillionsofdollarsbeingspentannuallyonbuildingwirelesscommunicationsystems,thereis
significantincentivetouseengineeringtoolsthatcanaccuratelyandefficientlydesignandplansuchsystems.
Therecurrentlyareanumberofsoftwaretoolsonthemarketintendedforjustthatpurpose. Consideringthata
wirelessnetworkforasingleurbanareacanbecomprisedofhundredsofbasestations,anefficientsystemdesign
processcan
easily
justify
the
expense
of
the
design
tool
and
the
effort
using
it.
As
the
wireless
system
grows
to
meetincreasingandchangingdemandsforservice,thedesigntoolisagainavaluableassetinplanningoptimum
modificationstothesystemtoaccommodategrowth.
Offundamentalimportancetothewirelesssystemdesigntoolistheabilitytoaccuratelypredictthestrengthof
radiosignalsfromthevarioustransmittersinthesystem.Themathematicalalgorithmsusedforthesepredictions
aregenerallyknownaspropagationmodels. Originally,propagationmodelsreliedonterrainelevationdataasthe
soleenvironmentparameteronwhichtobasepredictions. Substantialefforthasbeeninvestedoverthelast2030
yearsindevelopingaccurateDTEMs(digitalterrainelevationmodels)forallpartsoftheworld. Whileterrainhasa
profoundeffectonthepropagationofradiosignals(especiallyathigherfrequencies),morelocalizedfeaturesof
theenvironmentsuchastreesandstructures(buildings,houses,etc.)alsohaveasubstantialimpacton
propagation. Animportanttrendinwirelesssystemarchitectureistousesmallercellcoverageareas(socalled
microcells)and
much
higher
radio
frequencies
where
significantly
greater
transmission
bandwidth
is
available.
For
suchshortrangesystemarchitectureswherethecoverageradiusofthetransmittermayrangefrom0.5to5
kilometers,theterraincanoftenberegardedaslocallyflat. Undersuchconditions,signalpropagationis
dominatedbylocalobstructions("clutter")ratherthanbyterrain,makingthedescriptionandaccurate
classificationoflanduse/landcoverdataofprimaryimportance.
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
3/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 32008EDXWireless www.edx.com
WirelessSystemPropagationModeling
Radiowavepropagationisaphysicalphenomenonthatcanbedescribedusingelectromagneticwaveequations.
Likewavestravellingawayfromthespotwhereastonehasbeentossedintoapond,radiowavestravelawayfrom
thetransmittingantennainalldirections. Theoreticallyitispossibletoexactlypredictthestrengthofthesignal
fromanytransmitteratanyotherlocationifalltheelementsofthepropagationenvironmentarecorrectlytaken
intoaccount. Insocalledfreespace(actuallyavacuum),therearenoelementsinthepropagationenvironment
andthesignalstrengthatsomedistancefromthetransmittercanbeexactlycalculated. Radiowavetransmission
throughouterspaceisoneregionwheresuchasimpleformulationapplies. Fortransmitterslocatedonthe
earthssurfacetheproblemismuchmorecomplicated. Everyphysicalentityaradiosignalencountersafterit
leavesthetransmittingantennaaffectsthestrengthanddirectionofthesignal. Thephysicalentitiesthataffect
thesignalcanbegroupedintofourbroadcategories:
1. Theatmosphere(orothergaseousmedia)refracts(bends)anddiffracts(scatters)theradiowaves;
bendingchanges
the
direction
of
the
radio
wave
while
scattering
generally
weakens
the
wave.
2. Terrainfeatures(hillsandmountains)blocktheradiowaves,requiringthemtodiffractoverthetopor
aroundthesides,weakeningthesignalontheotherside. Radiowavesalsoreflectandscatteroffof
terrainsurfacescausingachangeinthedirectionoftheradiowave.
3. Muchliketerrain,structuressuchasbuildings,houses,towers,etc.blocktheradiowaves.Thewaves
diffract,reflect,scatterandtransmitthroughstructures.
4. Theleavesandbranchesoftreesandothertypesoffoliagealsoweakenradiowavesbyscatteringthem,whichhasasimilareffectasthatoftheblockingthemasterrainorbuildingscando
Asmentionedintheintroduction,theatmosphereandterrainhavebeenincludedformanydecadesinthe
propagationmodelswhicharedesignedtopredictthestrengthofradiosignals. Figure1showsarepresentation
ofaradiowavepropagatingfromatransmitter(ontheleft)toareceiverlocationintheopen(ontheright).
Figure1 RadioPathwithTree
Althoughthesignalarrivingatthereceiverwillincludesomereflectionsfromtheterrain,thedominantsignalis
theonethatarrivesdirectlyfromthetransmitter. Atreeislocatedalongthispathnearthereceiver. Becauseof
thetree,thesignalissome1020dBweakeratafrequencyof2.5GHz(atypicalWiMAXfrequency). Thisisdueto
theeffectsdescribedaboveinitemfourandisasimpleexampleoftheeffectofgroundcoveronsignal
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
4/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 42008EDXWireless www.edx.com
propagation. Onewaytoincludetheseeffectsistouseheuristicpropagationmodels. TheOkamuraHata,COST
231,IEEESUI,and"Pointslope"modelsareexamplesofthese. Thesedesignersofthesemodelsattemptto
integratethe
effects
of
clutter
by
making
many
measurements
of
the
signal
in
typical
environments
and
then
creatingsimpledistancevs.pathlossformulasthatincludenotonly"freespace"lossbutalsotheclutterloss
foundinthatenvironment. Forexample,theOkamuraHatamodelisbasedonmeasurementsdoneinandaround
Tokyo,Japan. Therefore,themodelisrepresentativeoflanduseenvironmentssimilartothatarea. Thesemodels
canbequiteusefulwhenonedoesnothaveaccesstogoodqualitydigitizedgroundcoverdata.
Figure2 ReceivedPowerusingRayTracingPropagationModel
However,itisobviousthatasimplemodelcannotfullyconsidertheactuallocalconditionsofeverystudy
situation. Asanexample,Figure2showsatypicalurbanbuildingenvironmentinwhichatransmitterhasbeen
located. Inreality,theradiosignalfromthetransmitterwillbepropagatedtothereceiverbydiffractingand
reflectingfromthevariousbuildingsshowninthisfigure. Becausethesignalsarriveatthereceiverviaanumber
ofradiopaths,thesignalatthereceiverisoftendescribedasamultipathsignal. Whenusingasingleantennaat
thetransmitterlocationandoneatthereceiveramultipathsignalcanhaveasignificantimpactonthesignal
qualityorintegrityofdatawhichissentbecausemanyversionsofthesamesignalarearrivingatthereceiverat
differenttimes. Ascanbeseen,thesignalatlineofsightreceiverlocationsalongthestreetstotheNorthandthe
Eastofthetransmitterareconsiderablydifferent. However,inthisstudyasimplepropagationmodelwouldshow
thesamesignalalongbothstreetsbecausethemodelwouldconsiderallstudypointsintheareahashavingonly
oneclass
of
clutter
rather
than
seeing
the
effect
each
of
the
individual
buildings
on
the
signal.
As
the
environment
becomesmorecomplex,asimplepropagationmodelisincapableofaccountingcompletelyforhowthe
environmentaffectsthesignal.
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
5/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 52008EDXWireless www.edx.com
ClassifyingGroundcoverData
Araytracingpropagationmodelhasbeenusedheretoshowtheeffectthatabuildingenvironmenthasonradio
waves. However,formanysystemslikeWiMAXorCellular/PCS,adetailedanalysisofanentiremarketwithray
tracingmaynotcomputationallyviable. Moreover,acquiringdatabasesdescribingthelocationandcharacteristics
ofeverytreeorbuildingmaybetimeorcostprohibitive. Therefore,tosimplifytheproblemofaccountingfor
cluttereffectsinpropagationprediction,itisusefultobroadlyclassifythedatainsomeway.Forexample,instead
ofconsideringeverytreeinaforest,awiderareacouldbeclassifiedasforestandanyreceiverlocatedwithin
thatareawouldexperienceanadditionalsignalstrengthlossbasedonfrequency. Ifsignallossdatawerealso
availablefordifferenttypesofforest,e.g.evergreenversusdeciduous,ortalltreesversusshorttrees,then
multiplegroundcoverclassificationsforforestswouldbeappropriate.
ManyGIS(GeographicalInformationSystem)landuseclassificationschemesprovideforalargenumberof
categoriesthatmaybeappropriateforlanduseplanningorzoning. However,forthepurposeofwirelesssystem
design,unless
there
are
calculations
or
measurements
that
demonstrate
astatistically
significant
difference
betweencategoriesintermsoftheirrelativeimpactonradiosignals,havingtheadditionalcategoriesdoesnot
necessarilyprovidemoreaccuratesignalpredictions. Theheight,extent,andlocationofgroundcoverelements
arethefactorswhichprimarilygoverntheimpactonradiosignals. Differentclassificationtypessuchas
industrialandcommercialmaybeusefulinurbanplanning,butifbothindicaterelativelylowbuildingsof
broadextent,thenthedistinctionisunimportantforwirelessengineeringbothwillaffectthesignalinsimilar
ways. Inthesamemanner,thegridpointspacingresolutionofthesedatabasesneedstobesmallenoughonlyto
allowtheRFplanningtooltoreasonablylocatetheboundarybetweenadjacentcluttertypes. 30mistypical.
ApplyingClutterDatatotheCalculation
Clutterdatacanbeusedinseveralwaystoenhancetheresolutionofthesignallevelcalculationtoreturnmore
accuratepointspecificresults. Themoststraightforwardapproachistousethemethodalludedtoabovewhere
theattenuationataparticularreceiverlocationisadirectfunctionofthecluttertypeatthatlocation. Iffor
example,aremoteunitislocatedinasuburbanareacontainingsinglestoryhousesandmaturetreesonemight
applyanadditionalattenuationof20dBat2.5GHz;forrelativelyopenParklands10dBmightbeused. Theongoing
challengeinusingclutterisdeterminingtheappropriateattenuationvaluesforeachcluttercategory. Oneoption
istousetheTelecommunicationsIndustryAssociationresources. Thisgrouphastypifiedclutterlossesbasedon
tencluttercategoriesappropriatetoRFplanninganddocumentedthemaspartoftheTSB881document.
Ultimatelythemostaccuratevaluewillbebasedonreceivedsignalmeasurements(i.e.drivetest)withineach
marketareathattakeintoaccountthetypeofvegetationandmanmadestructurespresentinthatarea.
Asecondapproachistoassumethattheclutterrepresentsahard,nontransparentblockagetotheradiosignal.
Theclutter
data
is
then
used
to
effectively
raise
the
terrain
elevation
used
by
the
planning
tool
so
that
the
propagationcalculationwillseetheclutterasobstaclesalongthepathratherthana"bareearth"condition. Here,
theclutterdataiscategorizedashavinganabovethegroundheightvaluerepresentingtheaverageheightfor
eachtypeofclutter. Thismethodismosteffectiveatthehigherfrequencies,especiallyabove5GHzwherealmost
anycluttertyperepresentsahighlossobstacletotheradiosignal. Thiscanbeextremelyusefulinurbanareas
wherebuildingsrepresenttheprimaryobstaclestothesignal. Ratherthaninvestinginahighcostvectordatabase
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
6/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 62008EDXWireless www.edx.com
describingeachindividualbuildingasa3Dpolygonwithindividuallydefinedwallsurfaces,onecancreateaclutter
databaseusingaveryfinegridpointspacing(15meters). Thisallowsthetransitionbetweenbuildingclutterand
othertypes
of
clutter
(such
as
streets)
to
be
sharply
defined.
Then,
by
organizing
the
buildings
into
anumber
of
clutterclassesbasedonaveragebuildingheightareasonablethreedimensionalrepresentationofthebuilding
environmentcanbecreated. Table1belowcontainsrepresentativevaluesfortypicalbuildingheights.
Finally,athird
method
acknowledges
that
for
most
clutter,
the
signal
propagation
mechanism
is
of
a"pass
through
attenuation"type. So,unlesstheclutteriscomposedofbuildingsmadeofreinforcedconcreteorsomeother
extremelyhighlossmaterial,arelationshipcanbemadebetweensignalattenuationandthedistancethatthe
signaltravelsthroughaclutterarea(i.e.dB/m). Thisismostusefulwheremuchifnotallofthesignalpasses
horizontallythroughtheclutterenvironment;anurbanWiFimeshnetworkisagoodexample. Here,theMesh
AccessPointsaretypicallyonlightpolesatabout8metersabovethegroundwhichisusuallylessthanheightof
thetreesand/orbuildingsinthearea. Thenodetonodesignalpathswillpassthroughtheclutterandby
determiningthelengthofpassagewithineachtypeofclutteragoodvaluecanbehadforthetotalattenuation
effect.
SignalStrengthStudies
Toillustratetheroleofgroundcoverdatainwirelesssystemdesign,threesignalstudiesareincludedtoshowthe
threemethodsforusingclutteraspreviouslydescribed.
Figure3showsthecoveragefromafoursiteWiMAXsystemoperatingat2.5GHz inamediumsizedurbanarea.
Thebaseantennaisat30mabovethegroundandtheremoteunitsareat1.5m. Inthisstudy,noclutterwas
used;terrainwastheonlyfactorindeterminingsignalstrength. Theareainthetophalfofthecoverageareais
relativelyflatsonotmuchvariationinsignalstrengthisseen freespacelossisthedominateattenuationfactor
here. Terrainbecomessignificantinthebottomhalfoftheareaasseenbythesharpreductionofsignalalongthe
southernedgeofthecoverage.
Table 1. Structure Height Classification
Classification Average block height
Residential < 2 meters
Low density urban 5 10 meters
Moderate density urban 10 25 meters
High density urban > 25 meters
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
7/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 72008EDXWireless www.edx.com
Figure3 ReceivedPower(TerrainDataonly)
ClutterdatawasthenaddedtothisareaandFigure4isamapindicatingthedifferenttypesofclutterbasedon
color. Theurbanandcommercial/industrialusesareshowninredandpinkrespectively;residentialisshownin
yellow. Asignalstudywasthenrunusingthefirstmethoddescribedabovewhereasimpleattenuationfactor(a
margin)wasappliedtothereceivedsignalstrengthbasedonthecluttertypeatthestudylocation. Thisisshown
inFigure
5.
The
correlation
between
additional
attenuation
and
clutter
type
can
be
clearly
seen.
Note
how
the
signalstrengthisnowshownasmuchlessinthebuiltupareaswhilethecoveragealongtheriver(lightbluearea
ontheClutterCategorymap)hasnotbeenaffected.
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
8/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 82008EDXWireless www.edx.com
Figure4 ClutterCategoryAreas
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
9/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 92008EDXWireless www.edx.com
Figure5 ReceivedPower TerrainplusClutterCategoryAttenuation
Figure6shows
the
second
way
to
use
clutter
data
where
the
height
of
each
clutter
type
is
taken
into
account
whenestablishingthepropagationpathbetweentransmitterandreceiver. Here,insteadofapplyingafixed
attenuationatthereceiverlocation,thesignalpropagationisinsteadaffectedbyshadowingfromthehigher
cluttertypes. Inthisinstance,thecommercial/industrialareas(Pink)aresetat20mheightandtheurbanarea
(Red)issetto15m. Themapshowshowthesignalisreducedintotheseareasduetotheirheights.
Figure6 ReceivedPowerwithTerrainplusClutterHeight
Finally,Figure7isanexampleofanumberofWiFiMeshnodeslocatedonlightpoles. Ahighresolutionclutter
database(3mpointspacing)wasusedheretobeabletodefinethestreetsfromothercluttertypes. Road
informationisalsodisplayedonthismaptoshowhowthesignalfromthemeshnodestravelsfurtherdownthe
streetcanyonsthanthroughtheclutteroneithersideofthestreets.
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
10/11
Technology White Paper
TheApplicationofLandUse/LandCover(Clutter)
DatatoWirelessCommunicationSystemDesign
The Power of Planning 102008EDXWireless www.edx.com
Figure7 WiFiMesh ClutterPassThroughAttenuation
Fromtheseexamplesitisclearthatclutterdataplaysanimportantroleinwirelesssystemdesign. Addingthis
informationprovidesacriticalrefinementtoasignalstudybytakingintoaccountamoreaccurateandrealistic
characteristicof
the
service
area
where
the
wireless
system
will
be
used.
UsingLandUseDatatoPredictServiceDemand(Traffic)
Thecoreofanywirelesscommunicationsystemisthenetworkoftowers,transmittersandantennasthatconvert
informationtoradiosignalsthatcanbereceivedandunderstoodbytheuser. Thenetworkmustbeconfiguredso
thatenoughsectorsandchannelsareallocatedtohandlethedemand. Considerationsinsystemdesignare:
locatingtransmitterstoprovideadequatesignallevelsthroughouttheservicearea,judgingwheresystemcapacity
maybeinsufficient(orunderutilized),andinthecaseofmultiusersystems,gauginghowthesystemmayhaveto
evolvetoaccommodatechangingusercallanddatatrafficpatterns.
Thesedynamictrafficpatternsrefertotimeandlocation. Peopleareusingthesystematvarioustimesthroughout
theday,
and
because
these
users
are
mobile,
they
may
be
located
anywhere
in
the
system
service
area.
For
example,duringmorningandeveningrushhour,trafficdensityforcellular/PCSphonesishighestalong
transportationroutes. Large,temporarygatheringsofusersconventioncenters,concerthalls,sportingevents
mustalsobeconsidered. Duringworkhourstrafficishighestinthecitycenters. Todeterminethecapacitythat
mustbeprovidedbyeachsector/siteinordertohandlethetraffic,itisnecessarytosomehowestablisha
8/8/2019 EDX WP UseofClutterDatainRFPlanning Aug08 Web
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