On accurate simulations of LTE femtocells using an open source simulator

Capozzi
etal.EURASIPJournalonWirelessCommunicationsandNetworking
2012,
2012
:328
http://jwcn.eurasipjournals.com/content/2012/1/328

RESEARCH

OpenAccess

OnaccuratesimulationsofLTEfemtocells
usinganopensourcesimulator
FrancescoCapozzi
1*
,GiuseppePiro
2
,LuigiAGrieco
2
,GennaroBoggia
2
andPietroCamarda
2

Abstract
Long-termevolution(LTE)femtocellsrepresentaverypromisinganswertotheevergrowingbandwidthdemandof
mobileapplications.Theycanbeeasilydeployedwithoutrequiringacentralizedplanning,toprovidehighdatarate
connectivitywithalimitedcoverage.Inthisway,theoverallcapacityofthecellularnetworkcanbegreatlyimproved.
Atthesametime,theuncoordinatedsetupoffemtocellsposesnewissuesthatrequireadeepandthoroughanalysis
beforespreadingthistechnologyworldwide.Unfortunately,tothebestofourknowledge,noaccuratesimulation
toolsarefreelyavailableforenablingthiskindofinvestigation.Thus,wepresentinthisstudyasimulationtoolforLTE
femtocells,implementedasamoduleoftheemergingopensourceLTE-simframework.Itencompasses
heterogeneousscenarioswithbothmacroandfemtocells,spectrumallocationtechniques,usermobility,femtocell
accesspolicies,andseveralotherfeaturesrelatedtothispromisingtechnology.Afterreviewingthestatusofthearton
LTEfemtocells,wedetailthedescriptionofthemodulethatweproposewithamajoremphasisonthenewlydevised
lossmodelsforindoorscenarios,thenewnetworktopologyobjects,andthemostsignificantenhancementstothe
simulatorprotocolstack.Furthermore,toprovideaclearunderstandingofthepracticalutilityofthisnewsimulator,
weinvestigatetwoindoorandurbanscenarios.Ascalabilitytestisalsopresentedtodemonstratetheefficiencyofthe
proposedtoolintermsofprocessingrequirements.Allpresentedresultssuggestthatthisnewmodulecanbevery
interestingfortheresearchcommunity,duetoitsgreatflexibilityandlimitedcomputationalcost.
Keywords:
Femtocells,3GPP,LTE,E-UTRA,Networksimulator,Performanceevaluation

1Introduction
theyensurethemaximumachievablephysicalrate.On
Thecapillarydiffusionofsmartphonesandtabletsandtheotherside,theamountofspectrumexpectedtobe
theintegrationofconnectivitycapabilitiesincommonlifelicensedduringnextyearsislessthanwhatrequestedby
objects(suchasTVs,domesticappliances,andvehicles)mobileoperators[4].Accordingtothisvision,thedeploy-
aregeneratingaveryfastgrowthofbandwidthdemandmentofsmallcellswithinthetypicalstructureofcellular
formobileapplications[1].Despiteemergingbroadbandnetworks,representsthesmartestsolutionforboosting
technologies(e.g.,WiMAX[2]andLTE[3])areabletoservicesinthesesystems[5].
enhancetheperformanceofcurrentlyused3Gsystems,Followingthisdirection,the3GPPhasintroduced,
theymightnotbeabletosustaintheexpectedraiseofthewithinthelong-termevolution-advanced(LTE-A)specifi-
trafficvolume.cations,thepossibilitytodeployaheterogeneousnetwork
Asaconsequence,notableimprovementsinbothcapac-(HetNet)composedbymacroandsmall-range(i.e.,micro,
ityandcoverageofmobilecommunicationsystemsarepico,andfemto)cells[6].Microandpicocellscouldbe
required,buttheycannotbefulfilledbyonlyenhancingexploitedforenhancingcoverageandcapacityinsome
the(PHY)layerand/orincreasingtheavailablespectrum.regionsinsidethemacrocell.Whereas,femtocellshave
Fromoneside,infact,latestinnovativePHYtechniquesbeendevisedforofferingbroadbandservicesinindoor
workveryclosetotheShannonlimit;inthismanner,(i.e.,homeandoffices)andoutdoorscenarioswithavery
limitedgeographicalcoverage.Amongthiskindofcells,
*Correspondence:francesco.capozzi@itia.cnr.it
theroleoffemtocellsbecomefundamental,becauseitis
1ITIA-CNR,v.PLembo,38F-70124,Bari,Italy
Fulllistofauthorinformationisavailableattheendofthearticle

©2012Capozzietal.;licenseeSpringer.ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommons
AttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,distribution,andreproduction
inanymedium,providedtheoriginalworkisproperlycited.

Capozzi
etal.EURASIPJournalonWirelessCommunicationsandNetworking
2012,
2012
:328
http://jwcn.eurasipjournals.com/content/2012/1/328

expectedthatinupcomingyearsthemostpartofvoice
callsanddatasessionswilltakeplaceinhomeorbusiness
environments[7].
Afemtocellcanbeeasilysetupwithoutanycentral-
izedcoordination,butsimplyenablingalow-powerand
small-rangeradiobasestation,whichisreferredtoas
homeevolvedNodeB(HeNB).Suchadevicehasplug-
and-playcapabilities,isconnectedtothecorenetwork
throughaDSLline,andoperatesinthespectrumlicensed
forcellularsystems[8].Theuncoordinatednatureof
femtocelldeploymentposesnovelandinterestingchal-
lengesonradioresourcemanagement(RRM).Infact,
classicalapproachesalreadyadoptedin3Gsystemsto
facefrequencyplanning,interferencecoordination,radio
resourcescheduling,andaccesspoliciescouldbenot
usefulanymoreinHetNetscenarios.
Startingfromthispremise,itisevidentthatthedevelop-
mentofnovelnetworkarchitecturesandtheoptimization
ofnextgenerationcellularsystemsbasedonfemtocells
aretopicsworthofinvestigationforbothindustryand
academiccommunities.
Inthisperspective,theavailabilityofaccuratesimu-
lationframeworksappearsoffundamentalimportance.
Severalopen-sourceandcommercialtoolsaretodayavail-
ableforsimulatingsomepartsoftheLTEsystem[9-14],
butnoneofthemprovidesmediaaccesscontrol(MAC)
andPHYmodelsforfemtocellarchitectures,handover
strategiesproperlyconceivedforHetNet,andspecific
propagationlossmodelsforindoorenvironments.Asys-
temlevelsimulatorforLTEfemtocellshasbeenproposed
in[15].However,itscodeisnotyetavailableand,forthis
reason,itcannotadequatelyservetheresearchcommu-
nity.Atthepresent,tothebestofourknowledge,the
onlyvaluabletoolistheonedevelopedforthenetwork
simulator3(NS-3)withintheLENAproject[16].Unfor-
tunately,despiteitprovidesstandardcompliantdefinition
oftheLTEnetworkarchitectureaswellasseveralprop-
agationlossmodelsforindoorscenarios,atthecurrent
statusitcannotbesufficientinhelpingresearchersdur-
ingthestudyoffemtocellrelatedissues.Infact,itdoes
notimplementanyhandoverstrategiesforHetNet,itdoes
notallowtheapplicationofdifferentaccesspoliciesto
theHeNB,itoffersonlyaweaksupportforthequal-
ityofservice(QoS)management[17](e.g.,onlysimple
schedulingstrategies,suchasMaximumThroughputand
ProportionalFair,havebeendevelopedattheMAClayer).
Inaddition,thesetupofarealisticsimulationscenariois
difficulttoaccomplish,especiallyforanon-expertNS-3
.ersuTobridgethisgap,thepresentstudyproposesamodule
thatextendsthefunctionsoftheemergingopensource
LTE-simframework[18],thusallowingalsothesimu-
lationofscenarioswithLTEfemtocells
a
.Itprovidesa
widerangeoffeaturesandhighscalability.Itencompasses

Page2of13

scenarioswithbothmacroandfemtocells,inmulti-cell
andmulti-userenvironments,andimplementsacomplete
LTEprotocolstackalongwithadvancedRRMtechniques,
suchasfrequencyreuseschemes,packetscheduling,and
QoSmanagement.Usermobilityisalsoconsideredand
severalconfigurationsofmobilitypatternsandhandover
mechanismsareconsidered.
Webelievethatthedevelopedtoolrepresentsagood
andusefulresearchtoolfortacklingseveralopenissues
suchas:(i)thedeploymentofheterogeneousLTEnet-
workscomposedbymacroandfemtocells;(ii)thedesign
ofsophisticatedtechniquesforbothradioresourceand
interferencemanagement;(iii)theimplementationof
novelcognitive-basedand/orself-organizedalgorithms,
protocols,andproceduresforthesetupofnextgeneration
broadbandnetworks,andsoon.
Inordertoshedsomelightonthepracticalutilityof
theproposedtool,inthisarticlewereportsomeexamples
aboutitsapplication.Inparticular,somereferenceindoor
andurbanscenariosareevaluated.Itisworthtonote
thatsuchananalysisisonlyintendedtodemonstratethe
generalagreementbetweenwhatisexpectedfromathe-
oreticalpointofviewandtheoutcomesofthesimulation
modulewepropose.
Furthermore,ascalabilityanalysistomeasurethecom-
putationalrequirementsofthedevelopedtool(i.e.,simu-
lationtimeandmemoryusage)hasbeenalsoprovided.
Therestofthearticleisorganizedasfollows:Section2
describesLTEfemtocells,highlightingprosandcons
relatedtothedevelopmentofthisnewtechnologyand
themostimportantopenissuesthatjustifytheneedofa
simulationframework.InSection3,thedevelopedmod-
uleisdescribed,withparticularemphasisonthenewly
implementedpropagationlossmodelsforindoorscenar-
ios,theintroductionofnewnetworktopologyobjects,
andtheenhancementsofsomemodulesoftheLTE-sim
framework.Section4providessomereferenceresultson
significantscenariosinordertoprovideaclearassessment
ofthepracticalutilityofthesimulatorandtodemon-
strateitsscalability.Finally,Section5drawsconclusions
andforecastsfutureworks.
2LTEfemtocells
TheLTEsystemismainlycomposedbytwoparts:theair
interface,i.e.,theevolved-universalterrestrialradioaccess
network(E-UTRAN),andthepacketswitchedcorenet-
work,knownasEvolvedPacketCore.Fromthenetwork
side,theevolvedNodeB(eNB)istheonlynodeofthe
E-UTRANanditisinchargeofprovidingnetworkcon-
nectivitythroughtheairinterfacetoalluserequipments
(UEs)inthecell,accordingtotheclassiccellularnetwork
paradigm.
Atthephysicallayer,theradiointerfacesupportsboth
frequencyandtimedivisionsduplexing.Channelaccess,

Capozzi
etal.EURASIPJournalonWirelessCommunicationsandNetworking
2012,
2012
:328
http://jwcn.eurasipjournals.com/content/2012/1/328

instead,isbasedonorthogonalfrequencydivisionmul-
tipleaccess(