On accurate simulations of LTE femtocells using an open source simulator

biomed - Capozzi Francesco , Piro Giuseppe , Grieco , Boggia Gennaro , Camarda , Camarda Pietro

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Description

Long-term evolution (LTE) femtocells represent a very promising answer to the ever growing bandwidth demand of mobile applications. They can be easily deployed without requiring a centralized planning, to provide high data rate connectivity with a limited coverage. In this way, the overall capacity of the cellular network can be greatly improved. At the same time, the uncoordinated setup of femtocells poses new issues that require a deep and thorough analysis before spreading this technology worldwide. Unfortunately, to the best of our knowledge, no accurate simulation tools are freely available for enabling this kind of investigation. Thus, we present in this study a simulation tool for LTE femtocells, implemented as a module of the emerging open source LTE-sim framework. It encompasses heterogeneous scenarios with both macro and femtocells, spectrum allocation techniques, user mobility, femtocell access policies, and several other features related to this promising technology. After reviewing the status of the art on LTE femtocells, we detail the description of the module that we propose with a major emphasis on the newly devised loss models for indoor scenarios, the new network topology objects, and the most significant enhancements to the simulator protocol stack. Furthermore, to provide a clear understanding of the practical utility of this new simulator, we investigate two indoor and urban scenarios. A scalability test is also presented to demonstrate the efficiency of the proposed tool in terms of processing requirements. All presented results suggest that this new module can be very interesting for the research community, due to its great flexibility and limited computational cost.

Sujets

3GPP

LTE

E-UTRA

Network simulator

Performance Evaluation

Informations

Publié par	biomed
Publié le	01 janvier 2012
Nombre de lectures	19
Langue	English
Poids de l'ouvrage	1 Mo

Extrait

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,