Analyzing Small-Cells and Distributed Antenna Systems from

DOI: 10.4018/IJWNBT.2017010104

International Journal of Wireless Networks and Broadband TechnologiesVolume 6 • Issue 1 • January-June 2017

Copyright©2017,IGIGlobal.CopyingordistributinginprintorelectronicformswithoutwrittenpermissionofIGIGlobalisprohibited.

Analyzing Small-Cells and Distributed Antenna Systems from Techno-Economic PerspectiveChristos Bouras, Computer Technology Institute and Press “Diophantus”, Patras, Greece & Computer Engineering and Informatics Dept., University of Patras, Patras, Greece

Vasileios Kokkinos, University of Patras, Patras, Greece

Anastasia Kollia, University of Patras, Patras, Greece

Andreas Papazois, University of Patras, Patras, Greece

ABSTRACT

Thenewgenerationsofmobilenetworkswillrequireeconomicalandviablesolutionsinordertomeetthepromisesraisedbyscientists.Inthisarticle,theauthorsoverviewtheavailableresearchactivitiesandpresentanarchitectureforDASandfemtocellsandamathematicalmodelanalyzingtheircosts,astheyareconsideredtechnologies,thatoffergreatadvantagesformobilenetworks.Theauthorspresentawideresearchinthesolutions’parametersandprices.Therearethoroughexperimentsincludingseveraldifferenttypesofcosts.Inparticular,Capital(CAPEX),Operational(OPEX)expendituresandTotalCostofOwnership(TCO)areexaminedforbothtechnologiesintermsofthebackhaulingtechnologies,ofthesizeofbuildingsthattheyareimplementedinandtheyearsofinvestmentfromatelecommunicationcompany.Themainresultsarethatfemtocellsareamoreappealingsolutionwhenitcomestosmallplaces,whilethealternativeismorefavorableforbiginfrastructures.

KEyWoRDS5G, DAS, Femtocells, Small-Cells, Techno-Economic Analysis, Ultra-Dense

1. INTRoDUCTIoN

Next-generationofmobiletechnologiesisexpectedtolargelyaugmentthesystem’speakdataratesandcutdownontheround-tripdelays.Themainideaofusingultra-densityorDAS(DistributedAntennaSystems)basedontheirproperties,isthattheyareabletoincreaseefficiencyandexpandnetworkcapacitywithouttheneedformorespectrumresourcesbyredistributingtheexistingones,depictthemasthekeysolutionsforthefuturemobilenetworks.SmallcellsandDASwerelaunchedmainlyforaddressingtheissueoflimitedconnectivityindoors.

Thereareseveralotherimportantbenefitsofthesetechnologies,whichconstitutethemasbasesforfuturegenerationsofmobilenetworks,suchas5G(5G-PPP,2014).Femtocells’benefitisthattheyprovideultra-density,whichisexpectedtobeoneoftheessentialfeaturesof5G.Ultra-densenetworkscoexistwiththeexistingmacrocellularonesformingaltogetherheterogeneousnetworksandfulfilltherequirementsandthenetwork’sfuturedemands.Scientistsandresearchershavedecidedtomovetowardsthisdirectionbyconductingresearchactivityinthearea(Networld2020ETP,2014;IWPC,2014).

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Thefuturemobilenetworksaregoingtodemandalargenetworkcoverage.DASwouldbeanidealsolutiontodealwiththelimitedspectrum,becauseitprovidesrepeaters,thatareconnectedtotheantennasystem.Italsoservestheaugmentingnumbersofthesmartdevices,thatinthefuturewillbeconnectedtotheInternetorthesmarthomedevicesoftheowner’shomenetworkaswemovedynamicallytotheInternetofThings.

Thispaperstudiesthetechno-economicaspectsofultra-denseandDASdeployments.Itpresentsthecharacteristicsandadvantagesforalltheirparts,aswellasatechno-economicmodelingofthesedeploymenttypes.Thedefinedmodelsareusedfortheinvestigationoftheuppertechnologiesfromaneconomicpointofview.Theyprovideaninsightinthefuturefinancialandpricingaspectsofthesesolutionsandconsistausefultoolforthedefinitionoffinancingandpricingpoliciestowardseconomicallyviabledeployments.The authors definemodels for selecting themost appropriatenetworkarchitecturalsolutionforpublicbuildings’ indoorcoverage.Cost, investment,materials,coverageandcapacityaretheparametersthataretakenintoaccountforthedefinitionoftheirmodels.Themainscientificcontributionofthispaperisthatitincludesmultiplecase-studyexamplesofthetechno-economicmodelsaswellasresultsofconductedexperiments.Italsoanalyzesandpresentsatechno-economicmodelandsummarizesthemainresearchactivityintheparticularfield.

Theremainingpartofthispaperisstructuredasfollows:thesecondsectionreferstotherelatedresearchthathasbeenconductedsofar.Thethirdsectionpresentsthearchitecturesofultra-denseandDASdeploymentsusedinthemodels.Inthefollowingsectionwedescribecostmodelsforultra-denseandDASdeployments.Inthenextsectionwedefinetheparameterizationofthecostmodels.Inthesixthsectionweconducesomeexperimentalscenariosandanalyzethecorrespondingresults.Finally,intheseventhsectionweconcludeourpaperwiththemostfundamentalconclusionsrealizedintheexperimentalprocedureandinthefinalsectionwelistsomeideasforfutureresearchworkinthefieldofmobilenetworktechnologies.

2. RELATED WoRK

Inthissection,itisofmajorimportancetopresentthemostvaluablestudiesthathavebeenconductedinthefield.Therecordofthemostvaluablepastresearchactivityisgoingtoindicatethepathsthatfuturescientificresearchshouldfollowdescribingmobilenetworkdeployments.

Inliterature,theDASsystem’smostvaluablestudiesare(Liu,2013;Liuetal.,2012),thatexaminetechnologicalandeconomicaspectsofthetechnologyandcomparetheTotalCostofOwnership(TCO)betweenDASandfemtocells,leadingtothefactthatfemtocelldeploymentsarecheaperthantheDASones.TherearenotanyothervitalstudiesinthefieldofDASdeployments,soitisimportanttopointouttheneedofinvestigatingit.

Thereexistssubstantialactivityinthefieldofsmallcells.Scientistshavealreadystudiedthetechnologicalaspects,suchascognitiveradio,self-organizednetworks,andradioresourcemanagementleadingtoasignificanttechnologicalbackground.Literaturereviewisindicatingthattechno-economicaspectsofsmallcellshavenotbeenfullyresearched,althoughtherearefundamentalworksthathavebeenpublishedsofar,like(Shettyetal.,2009)thatreferstotheeconomicadvantagesthatstemfromthecombinationofthemacrocellsandthefemtocellsfortheoperatorand(Claussenetal.,2007)thatadequatelyinvestigatesthecostofthenetworkforthepredecessoroffemtocell,thepicocell.Scientists,butmostly the telecommunicationandnetworkoperatorsare interested in the techno-economicaspects.Similarworksliketheonedescribedin(Nikolikjetal.,2014)examineseveraldeploymentstrategiesfromacostperspective.

Theauthorsofthispaperhavealsopresentedanintroductiontothepresentworkin(Bourasetal.,2014),wheretheyanalyzemodelsforfinancingandpricingsmallcellandmacrocellserviceandcomparewhichcaseisthemostfavorablefromtheperspectivesofusersandoperators.(Markendahletal.,2010)comparesthetwomaintechnologiesmacrocellsandfemtocellsconductingimportantconclusionsforthecostswhetherornotanewbasestationisformed.Accordingtothisresearch,if


47

abasestationisneeded,thenthemacrocellsremainaneffectivealternative.The(Fratuetal.,2014)referstoapurelytechnologicalanalysisofthefemtocelltechnology,analyzingtheinterference,energyefficiencyandspectrumefficiencyinheterogeneousnetworks.Thetechno-economicanalysis(Yunasetal.,2014)presentsathoroughinvestigationofsmallcells,microcellsandmacrocellsbytakingintoaccountfactors,suchasthecoverage,thecapacity,theenergyandthecostefficiency.Theresearchendsupconcludingthatultra-densityisthemainkeyto5G.In(5G-PPP,2014;Networld2020ETP,2014)arediscussedtheunderlyingdemandsoftheadventof5G.Themostimportantdemandsof5Gareaugmentednetworkcapacity,morecoverage,betterredistributionoftheavailableresources,safernetworkconnectionetc.

3. ALTERNATIVE DEPLoyMENTS

Inthissection,weanalyzethemostvaluablecharacteristics,thatsmallcellsandDASdeploymentspresentanddepicttheirbasicstructures:

3.1. Small CellsAccordingtoNetWorld2020in(Networld2020ETP,2014),5Gmobilenetworksshouldalsoprioritizetheprovisionofmethodsforflexiblepricingmechanismsandsmallcellsconstituteasuggestionthatoffersmanypossibilities.Inparallel,theInternationalWirelessIndustryConsortium(IWPC)stressesthevitalityofultra-densificationinnextgenerationofcellularsystems,i.e.,the5Gsystems(IWPC,2014).Itisconsideredthatultra-densificationFigure2isthefundamentalrequirementthat5Gsystemsshouldmeetinordertoachievefundamentalrequirements,suchas:

• 50xtimesmorecapacity(competentspectralefficiency,wideravailablespectrum)(IWPC,2014).• Peakdataratesexceeding10Gbit/s.• Ultra-lowlatencybelow1msec.

Thesetypesofdeploymentareexpectedtobecomeextremelyefficient,whentheyareaddressedinplaceswheretrafficpatternsarehighasdescribedinFigure1.

Ultra-densityoffersmanysignificantbenefits forsubscribersandmobilenetworkoperators.Onekeyevolutioninmobilenetworksistheshiftfromcellsofferinglargecoveragetoprogressively

Figure 1. The proximity of the cells in Ultra-dense deployments


48

smallercells,andultimatelyleadingtosuper-densedeployments.Ultra-densitybringsbasestationnexttothemobiledevice.Subsequently,itoffersthefollowingbenefitstoend-users:

• Higherthroughputaswellaslowerround-tripdelays.• Improvementinindoorcoverageduetointernalbasestationdeployment.• Seamlesshand-offs fromoutdoors (macrocellular access) to indoors (small cell access) and

viceversa.• Closedusergroupaccessibility.Onthecontrary,totheopenusergroupaccess,enablesthechoice

ofpre-decisedgroupofusersordevicesthatwillaccessaparticularcell.• Strictersecurityprotocolsandalgorithms.

Additionally, apart fromcustomers’ satisfaction, thereare several importantbenefits for themobiletelecommunicationoperators.Themostfundamentalonesarethefollowing:

• Lowerexpendituresforobtainingthebasicassetsandfortheoperationofthesystem.• De-congestionofthemacrocellnetworkbyreusingspectrumfromthesmallcellsperspective.• Thespectrumredistributionaugmentsthenetwork’scapacity.• Powerconsumptionandenergycostsdiminish,becausesmallcellsarewell-knownforbeinga

greentechnologicalsolution.• Degradeproblemsandissuesoflawandadministrationthatarisefromthemacrocells’use.

Ultra-densityhasseveralsignificantbenefitsforbothsubscribersandmobilenetworkoperatorsthatmakeitanappealingserviceandasolutionthatcompetesuccessfullyagainsttheconventionalsolutions.Subscribersinterferewithoutspecialknowledgeintheterminalofsmallcells.Anotherimportantproblemsolvedbytheadoptionofthemicrocellulartechnologyistheoneofthehandovers.Smallcellsaremoresecurecomparedtoothersolutions,becausetheyofferthepossibilitytolimittheaccesspermissionswithinapreselectedgroup.

Ontheotherhand,thereareseveralchallengesthatultra-densedeploymentsface.Basedontheanalysispresentedin(Fratuetal.,2014),theyaresummarizedasfollows:

• Self-organizingnetworkfeatures,sinceoperatorswillnotbeabletoperformconventionalnetworkplanningoverultra-densedeployments.

Figure 2. There are many antennas and cells inside the coverage area of a bigger cell in Ultra-dense deployments


49

• Inter-cellinterference,becauseoftheexistenceofthefemtocelltierovertheexistingmacrocellularinfrastructure.

• Energyefficiencyfeatures,sincethetotalenergyconsumptionwillbelikelytoincrease.• Spectral efficiency features, which will enable the high re-usage of the available spectrum

resources.• Costefficiency,whichisnotonlyatechnicalchallengebutalso,isthemaintopicofthispaper.

3.2. DASAnotherpossiblesolutioninordertoaugmentthenumberofusersconnectedtothenetworkistheuseofaDASdeployment.DASFigure3isanetworkofspatiallyseparatedantennanodesconnectedviaacommonsourceviaatransportmediumthatprovideswirelessservicewithinastructure.ThereareseveralassetsintheusageofDASrelatedtomoreefficientcoverage,lowerpowerconsumptionetc.AtypicalDASconsistsofthefollowingcomponents:

• AnumberofremoteDASnodes,eachoneincludesatleastoneantennaforthetransmissionandoneforthereceptionofwirelessprovider’sRadioFrequency(RF)signals(2antennas).Thisstructureisequivalenttotheexistingconventionalantenna,butinthiscase,itsfunctionalityispartedinsmallerantennastructures.Thereisalsoagreatneedinsupportingassetsandequipment,suchasamplifiers,remoteradioheads,signalconvertersandpowersupplies.

• Ahighcapacitysignaltransportmedium.Thedesiredmediumisfiberopticcable,becausedoesnotincursignallossunlikeothercheapermeansoftransmission.

• Agreatvarietyofradiotransceivers,thatprocessandcontrolthetransmittedsignal.

Abasicstructureincludestwoantennasandtwofeedersperfloor.ThecaseofindoorDASisimplementedinsidebuildingsandincludesallthecomponentsmentioned.Ineachdown-linkexistsapassivefeeder.Ifthenumberofdevicesservedaugments,morethanonestructuresineveryfloorareintroduced.DAStechnologyalsohasseveralsignificantbenefitsforbothsubscribersandmobilenetworkoperatorsthatmakeitanappealingsolutionsuchas:

• Betterdefinednetworkcoverageandredistributedcapacity.• Manycoverageholesthatenablenetworkstoovercomethecapacityproblems.• Offeringofthesamecoverage,butlesspowerconsumptioncomparedtoothersolutions.• Thedistributedantennasarenotplacedinsuchhighaltitudesastheequivalentsingleones.

Ontheotherhand,someoftheissuesraisedbyDASopponentsarethefollowing:

• Highcosts,duetotheadditionalinfrastructures,thathavealreadybeenreferred.• Possiblehealthconcerns,duetogreatervisualimpactonusers.• Differentnetworkdesignthanthemicrocellularsolutions.• Expertiseforengineersfordesigningandmaintainingthenetwork.

4. CoST ANALySIS

Inthissection,itisofvitalimportancetomathematicallyassessthecostsoftheprevioustechnologies.Weproposethreefinancialmodelsthatareusedforthecostestimationofthetechnologicalcasespresentedbelow:smallcells,macrocellsandDAS.


50

4.1. MethodologyForthetwobasictypesofdeploymentformacrocellsandsmallcells,weassumetwotypesofcoststhecapital(CAPEX)andtheoperationalexpenditure(OPEX).TheCAPEXistheamountofmoneyanetworkoperatorspendsinordertoobtainnewequipment,sites,etc.Ontheotherhand,theOPEXsumstheexpendituresthatarerelatedwiththecosts thatoccurduringthewholeyearandcoverthebudgetneededformaintenanceandoperation.Previousstudies,haveadoptedaunitedpatternofcomputingthesecostsandhavefollowedthesamereasoning.Themethodologyispresentedin(Claussenetal.,2007),thatpointsouthowimportantistoestimatetheCAPEXandOPEXannually.CAPEXisforeseenforthenewequipmentbyusinganimportantassumption.CAPEXisconsideredtobealoan,soCAPEXisvaluedasthecapitalthatisacquiredthroughtheloan.Finally,theannualpaymentsfortheinstallationanddeploymentofthenewequipmentarethebudgetneededtorepaytheloan.

Figure 3. Description of the DAS system architecture of a building


51

Generally,itispossibletomakeanassumptionovertheloanofaprincipalamountP,whichshouldberepaidannually.Themoneyneededtoberepaidispresentedbytheannualinstallmentpayment,representedbyAandisexpressedbytherepeatingpaymenttype:

A Pr r

r

n

n=

+( )+( ) −1

11

(1)

whererrepresentstheperiodicinterestrateandnrepresentsthenumberofpayments,i.e.,thelengthoftheinstallmentplaninyears.

4.2. Ultra-Dense DeploymentInthissection,weanalyticallypresentthecoststhatbearasubscriberoranoperatorthatchoosestoimplementtheultra-densityinanetworkanditisimportanttopresentthetwocasesofexpendituresofultra-densedeployments.

4.2.1. Capital ExpenditureTheCAPEX isdescribedasexpenses that stemfrom thebase stationand the routersneeded tocontrolthenetwork’straffic.Thereisalsoatypeofcostthatisrelatedwiththecorenetworkofthemobileoperator.Thesecostsarethemostexpensiveones,thisiswhywedonotconsiderothercheaperexpenses,suchas thecost for theEvolvedPacketCore(EPC).Furthermore,weassumethattherealreadyexistsamobilenetworkoperatorthatprovidesabroadbandconnection.Thus,wedonotincludeinouranalysisthecostsforthebroadbandequipmentandthebackhaulequipment.TheCAPEX,basedonthehypothesisin(1)andassoonas,thebasestationcostisrepresentedbyCHeNBandthecostoftheinterfaceneededforthemanagementofthenetworkisrepresentedbyCi/f,thentheannualcostfortheinstallmentofanultradensedeployment,whichconsistsofNHeNBsisdescribedbythefollowingequation:

CNC

id nsCX i f

ne e

i=− +( )

/

1 1 (2)

CcxdensedenotestheannualtotalcostofCAPEXandNisthenumberofHeNBs.

C N C Cr r

rd nsCX

HeNB i f

n

ne e= +( )

+( )+( ) −

/

1

11

(3)

CcxdensedenotestheannualtotalCAPEXandNisthenumberofeNBsconsistingtheultra-dense

deployment.

4.2.2. Operational ExpenditureOPEXdoesnotincludetheexpensespresentedbelow:

• Siteleasingcostisignoredgiventhatthebasestationsareinstalledinthesubscriber’sproperty,soitisoftheuser’spointtopaythecosts.


52

• Powerconsumptionisnegligible,duetosmallcellsizeandenvironmentally-friendlyfeaturesandispaidbythesubscriber.

• Support and maintenance costs bare mainly the broadband service provider as well as thesubscriber.Thesmallcellisacquiredbythesubscriber,soifdamaged,heisobligedtoreplaceit.

Consequently,onlyonecostcategoryisconsideredintheOPEXfortheultra-densedeploymentand is thecost for theequipmentof routingmanagementof thenetwork.MaintenancecostsareconsideredlinearlyproportionaltoCAPEXandarecalculatedasCAPEXmultipliedwithacoefficientfst, that denotes bandwidth and site costs due to maintenance activities. Subsequently, OPEX isrepresentedbythefollowingequation:

C f NCr r

rd ns st i f

n

n

OXe e=

+( )+( ) −

/

1

11

(4)

Consequently,thefollowingequation:

C fNC

id nsTCO

m

i f

ne e

i= +( )

−( )1

1

/ (5)

whereCTCOdenseexpressestheTCOforsmallcelldeploymentthatbearsthemobilenetworkoperator’s

sideonanannualbasis.Thisexpressionisbasedon(2)and(3)anditshouldberemindedthatiistheinterestrateandnisthedurationoftheinstallmentplaninyears.

4.3. Macrocellular DeploymentInthissubsection,wepresentthebasiccoststhatareincludedinamacrocellulardeployment.Inthiscasealso,themacrocellularcostsaresplitinthetwosamesidesaspreviously.

4.3.1. Capital ExpenditureItrepresentsthecoststhataremadeinordertoexpandthecoreEPCnetwork.AssumingthatthesecostsareexpressedbyCeNBandCEPCrespectively,theamountofmoneyneededforonebasestationisgivenbytheexpression:CeNB+CEPC.ItissignificanttoestimatethecostofasingleevolvedNode-B(eNB),namelythemacrocellularbasestation.Itconsistsofthenetworkequipment,soweassumeCAPEXisrepresentedbythenetworkbasestationcosts,becauseitfullycoverstheeNBandtheEvolvedPacketCore(EPC).Forthatreason,thecostisdescribedbythefollowingexpression:CeNB+CEPC.TheamountsCeNBandCEPCarethecostsforeNBandEPC,whichisthetermusedforLongTermEvolution(LTE-A)’scorenetwork,respectively.ItisimportantthattheCeNBapartfromthecostsrelatedtotheeNBequipmentandimplementation,alsoincludesanyadditionalcostsforthesiteacquisition,constructionandeNB’sbackhaul.TheamountCEPCincludesallthecostsrelatedtothecorenetwork,suchascostsoccurforroutingthenetwork’straffic.

Usually, the macrocellular deployment consists of several base stations, the number ofmacrocellularbasestationsexistingisrepresentedbythecoefficientN,thatiscomputedinnumbersofbasestations,thenthetotalcostforallthebasestationsisgivenby:N(CeNB+CEPC).

IfwepresumethattheCAPEXforthemacrocellulardeploymentisaninvestmentamountN(CeNB+CEPC)thathastobemadeinadvance,thenbasedonthebasicassumption(1)wecanformthefollowingequationforthemacrocellularCAPEX:


53

C N C Cr r

rmaCX

eNB

n

nEPCcro= +( )

+( )+( ) −1

11

(6)

whereCcxmacrodenotestheannualtotalcostofCAPEX.

4.3.2. Operational Expenditurecrunisacoefficient,thatrepresentsthetotalannualcostsforrunningauniquesiteprovidingthecostsforpower,in-siteandoff-sitesupport,in-siteandoff-sitemaintenanceandalsointroducesacoefficientcbh,thatexpressesthebackhaulcosts,whateverthematerialofthebackhaulingis.WedescribetheannualOPEXCox

macrobythefollowingequation:C N C CmacroOX

run bh= +( ) (7)

Thecosts formaintaining thesiteare linearlyproportional to theCAPEXmultipliedwithacoefficientfmthatdenotescostsrelatedtotheoperationandalltherestsitecosts,forexampletheoperation,thesupportetc.aresummedbytheamountcst.Therefore,theamountNcrunisexpressedas:fmCCX

macro+Ncst.Whereas,thecoefficientcbhisnotonlyconsideredasthebackhaulcosts,butislinearlyproportionaltotheusedbandwidthBWmultipliedwithacoefficientfBW.Concluding,basedonalltheassumptionsabove,theannualOPEXasdescribedin(Liuetal.,2012)isexpressedas:

C f C Nc f BWmacroOX

m macroCX

st BW= + + (8)

or,bysubstitutingtheCAPEXprovidedby(6),theOPEXisrepresentedbytheequation:

f N C Cr r

rNc f BW

m eNB EPC

n

n st BW( )

( )+

+

+( )+ +

−

1

11

(9)

Reclaimingthe(6)and(11)theTCOformacrocellularforthetelecommunicationoperatorisrepresentedbythefollowingequation:

C f N C Cr r

rNc f BW

macroTCO

m eNB EPC

n

n st BW= + +

+

+( )+ +

−( ) ( )

( )1

1

11

(10)

CTCOmacrorepresentstheTCOforamacrocellularbasestation,iistheinterestrateandnisthe

durationoftheinstallmentplanexpressedinyears.crunrepresentsthemaincostpaidannually,duetorunningasinglesite,includingthecostsfor

energyconsumption,in-siteandoff-sitesupportandmaintenanceandcbhdenotestheexpendituresfortheintroductionofthebackhaulingtechnology.Thus,theannualOPEXCOX

macroisexpressedbythefollowingequation:C N C Cmacro

OXrun bh

= +( )

Wehavealreadyshownthatalltherestsitecosts(operation,support,etc.)areexpressedbytheamountcstandarelinearlyproportionaltotheCAPEX,whichismultipliedwithacoefficientfm.Therefore,theamountNcrunisfurtherexpressedas:fmCCX

macro+Ncst.Moreover,weindicatedthattheamountcbhrepresentsthebackhaulcostsandisconsideredtobelinearlyproportionaltotheusedbandwidthBWmultipliedwithacoefficientfBW.So,theannualOPEXissuedin(6),(10)isexpressedbythefollowingequation:


54

C f N C Cr r

rNc f BW

macroOX

m eNB EPC

n

n st BW= +

+

+( )+ +

−( )

( )1

11

(11)

Basedon(6)and(11)theTCOforthemobilenetworkoperatoronanannualbasisisexpressedbythefollowingequation:

C f N C Cr r

rNc f BW

macroTCO

m eNB EPC

n

n st BW= + +

+

+( )+ +

−1

1

11

( )( ) (12)

whereCTCOmacroistheTCOforamacrocellularbasestation,iistheinterestrateandnistheduration

oftheinstallmentplanexpressedinyears.

4.4. DAS DeploymentInthissubsection,thecostsfortheDASdeploymentisslightlydifferentfromthetwopreviouscases.TheTCOconsistsofthreemainparts:CAPEX,OPEXandIMPEX(ImplementationExpenditure).

4.4.1. Capital ExpenditureCAPEXhasalreadybeenconsideredandresearchedinthepastandincludesthecostsforthefollowingassets(Liuetal.,2012):

• TheDASbasestation,• Thedistributedsystem,suchastheremoteantennas,thepowersplitters,thewide-bandcombiners,

coaxialcableoropticfibercable,cableconnector,etc.• Thebackhaulequipmentwhetherisopticfiberorcoaxialcableandthesoftwarecost• Thesupportingequipment, suchasWallmountingkit, thepowercable, thebatterybackup,

possiblyexistingalarmsystem,etc.

TheDAS includes abase station that is similar to themacrocellularone, this iswhy,DASandmacrocellularbasestationsincludethesametypesofcosts.TheestimationofthecostsisthatCeNBrepresentsthecostforoneDASbasestation,aswellasanyothercoststhatstemfromthesiteacquisitionortheconstructionoranybackhaulcostsfortheeNBnodes.CEPCrepresentstheEPCcostsandaremadeforthenetwork’srouting.TheTCOforthenetworkequipmentisexpressedbythefollowingequation:CeNB+CEPC.

TheestimationoftheCAPEXfortheDASdeploymentshouldbemadeannuallybytakingintoconsiderationtheannualinstallmentpaymentsoftheinvestment.WepayatotalinvestmentplanforCAPEX.IfthereareNbasestations,thenthetotalbasestation’scostisexpressedbythesubsequentequation:N(CeNB+CEPC).Generally,theannualinvestmentplanforthebasestationisbasedonthecoststhataredescribedinsimilarnetworks,suchasthemacrocellularbasestationpresentedbytheCEPC(Bourasetal.,2014).

WeconsiderthattheCAPEXfortheDASbasestationdeploymentaccruesthefollowingbudgetN(CeNB+CEPC)thatneedstobeoverpoweredfromthebeginning,andbyusingthehypothesis(1)wecouldcalculatetheDASbasestationcosts.TheCAPEXestimationonanannualbasisfortheDASbasestationisexpressedbythefollowingequation:


55

C N C Cr r

rBS EPCCX

eNB

n

n= +( )

+( )+( ) −1

11

(13)

whereiistheinterestrateandnisthedurationoftheinstallmentplanexpressedinyears.Itisvaluabletoanalyzethenecessaryexpenditures,becauseoftheadditionalequipmentneeded

inaDASsystemfortheDistributedSystem.ThecoefficientCeqrepresentstheequipmentneededfortheDASstructuresandislinearlyproportionaltoanotherfactord,thatdependsonthetotalnumberoftheDASstructuresthatexistsinthedistributedsystem.Therefore,wedescribetheCAPEXfortheantennasystemannuallybyintroducingthesubsequentequation:

C C dDASEQCX

eq=

r r

r

n

n

1

11

+( )+( ) −

(14)

whereCCXDASEQ,denotestheannualtotalCAPEXfortheDASequipment.

ThecompleteDASCAPEXisthesumofthecostsofalltheDASfeaturesandisdescribedbythefollowingequation:

C N C Cr r

rC d

DAS eq EPCCX

eNB

n

n= +( )

+( )+( )

+−

( )1

11

(15)

whereCCXDASdenotestheannualtotalCAPEXforthewholeDASsystem.

4.4.2. Operational ExpenditureDASOPEXwasdescribedasthesumoftheaboveexpenditures(Liuetal.,2012):

• Costsofbackhauloperationsandmaintenance.Itispossibleforsomepartsofthebackhaultoneedreplacementafteraperiodoftime.

• Thebackhaulrent,ifthesiteisrent,• Theconsiderationofthepowerconsumptioncosts,becauseoftheenergyconsumption.• Theoff-sitesupport,• Thesitevisitfortroubleshootingormaintenance,• Theleasingcosts,incasethesiteisleased.

TheDASbasestationdenotescosts,suchascrunthatrepresentstheannualtotalcostforrunningasinglesite,alsocomputingtheenergyconsumption,in-siteandoff-sitesupportandmaintenanceandcbhdenotesthebackhaulcost.So,theOPEXfortheDASbasestationisdescribedasfollows:C N C CDASOX

run bh= +( ) (16)

Whereas, thecoefficientcbhexpresses thebackhaulcosts,whichare linearlyproportional totheusedbandwidth,thatisdescribedbythecoefficientBWmultipliedwithacoefficientfBW,thatrepresents thebackhaulcosts inrelationwith theavailablebandwidth.Tosimplify theproducedequations,weconsiderthatthemaintenancecostsarelinearlyproportionaltotheCAPEXmultipliedwithacoefficientfst,thatdenotestheoperationalandthesitecostsandwerepresentalltheotherkindsofexpendituresbytheamountcrunthatrepresentsthecostsforrunningaDASsystem.Thus,theOPEXforrunningtheDASbasestationisfurtherexpressedas:


56

NC f Crun st DAS

CX= (17)

whereNisthenumberofDASnodes,andCCXDASistheCAPEXoftheDAS.

Wecomputethecostsforthemaintenanceandoperationofthedistributedsystem.Thisincludesthemaintenanceoftheantennastructures,becauseoftheantennasandfeedersateveryfloorofthebuilding,butalsoincludesanyextraoccurringactivities.ThecoefficientCeqdenotesthecoststhatareincludedfortheDASassets,forexampletheantennasandthefeeders,thataresituatedineveryfloorofthebuilding.Subsequently,theannualOPEXforthedistributedsystemisexpressedbythefollowingequation:

C C dr r

rDASEQOX

eq

n

n=

+( )+( ) −1

11

(18)

The DAS system, such as every other network structure needs to consume power, in ordertooperate.It is therefore,significant, tointroducetheenergyconsumptioncostdescribedbythecoefficientCpwTosummarize,thetotalOPEXperyearfortheDAScellsisexpressedasfollows:

C N C C Nc f BW f C C C dr r

DASOX

run bh st BW st DASCX

pw eq

n

= + + + + + + ++

( ) ( )( )1

111

+( ) −r n (19)

4.4.3. Implementation ExpenditureIMPEXisthebudgetthattheownerofthesystemshouldpayifthecellularsiteismoved.Consequently,itdescribestheamountofmoneythatisspentandisassociatedwithplanningandinstallingthenetworkasreferredinformerresearch.Accordingto(Liuetal.,2012)itissplitinthefollowingcosts:

• Thecostsoftheinstallationofbasestations,• Thecostoftheinstallationofdistributedsystem,• ThecoordinationcostduetodisruptiveDASconstructionwork,etc.

TheinstallationexpenditureshavealreadybeenconsideredaccordingtotheCCXDASanalysis,

becausethemainassumptionusedincludeseveryassetofthedistributedsystem.Ontheotherhand,thereemergecoordinationcosts,becausewheneverweinstallsomenewDASequipment,itispossibletomakeadjustmentstotheexistingnetworkinordertosucceedthebestoperationofthetotalsystem.ThecostofinstallationandcoordinationisdescribedbyacoefficientCinc.So,thetotalIMPEXfortheDASisexpressedbythefollowingequation:

C CDASIX

inc= (20)

Finally,theTCOperyearforDASisdescribedasthesumoftheCAPEX,OPEXandIMPEX,soitisrepresentedbythefollowingequation:


57

C N C C C d f C C C d

r r

r

DASTCO

eNB EPC eq st DASCX

pw eq

n

= + + + + + +( )⋅

+

+( )( )1

1 nnN C C f BW C

run bh BW inc−+ + +

1( )

(21)

5. PRICING MoDELS

In thissection, it iscrucial toanalyze thepricingmodels,with theparametersand thevariablesincludedintheequationsinordertocalculateallcostsandrunseveralexperimentsinordertodeducefundamentalconclusionsfortheadoptionofthemostfavorabletechnology.Beforeconducinganyexperiments,itisofgreatvaluetomakeathoroughpresentationoftheparametersofthemodel.Theselectionoftheparametrizationremainsacontroversialissue.Manyoftheparametersarenotonlytimedependent,(e.g.someexpendituresareaugmentingordiminishingwhentimeelapses),butalsomarketdependent,becauseofthedifferentcostssomeassetsandworksmaypresentinalternativeeconomies.Analytically,theinstallationcostinanAfricanoranAsianeconomyisdefinitelycheaperthantheonespresentedintheEuropeanorAmericanmarkets.

Byconductingadetailedresearchactivity,wewerefinallyleadtotheparameters’andcoefficients’costsinGreecefortheyear2016forthecaseofanultra-densedeploymentbasedonfemtocellsandacorrespondingDASdeployment,thatarepresentedinTables1and2respectively.Inthetwotables,notonlywepresentthevaluesfound,butalsothepapersthattheoccurringexpendituresareincluded.WeoptedforthefollowingparametersbasedontheassumptionsmadeforthenetworkmarketforthenextyearsinEuropeancountries.Inpapers(Bourasetal.,2014;Correiaetal.,2010;Markendahletal.,2010)therearemanypricingdatawhenitcomestofemtocellsandsmallcells.(Liu,2013;Liuetal.,2012)presentathoroughinvestigationonDAScostsandparameters.

6. EXPERIMENTAL RESULTS

Inthissection,weconductedexperimentsforthedeployments’costs.Weanalyzethemostfundamentalsuggestionsthatarecombinedwiththecorrespondingtechnologiesandweendupreachingseveralvitalresults.Weconsiderasafundamentalfacttoshowhowthecostsfluctuateifthereisaneedincreatinganewbasestationfromscratch.Weapplythepricesfoundfromthethoroughresearchconducted and we tested our mathematical models. We consider, that the most important casesaretheCAPEX,theOPEXandtheTCO.Inparticular,weanalyticallypresentthefollowingthreetechnologicalsuggestions:

• Femtocells(FEMTO).• DASincludingthedeploymentofabrandnewmacrocellbasestation(DASNB).• DASwithoutincludingthedeploymentofthemacrocellbasestation(DASW/ONB).

Figure 4 depicted the CAPEX of the upper simple case experiments. It presents the maincomparisonofthethreeuppercasesforCAPEX.Unlike,whatweexpectedtheCAPEXforbothDASdeploymentsaremuchlowerthantheonespresentedbyfemtocells.Moreover,thecostsoftheDASarestableandtheaugmentationoftheantennasdoesnotaffecttheinvestmentexpenditure.Themacrocellbasestationcontributesslightlyinthecosts,becauseDASwithdeployinganewmacrocellbasestationisnotmoreexpensivethantheonewithoutconsideringsuchadeployment.Ontheotherhand,femtocells’costsarelinearlyproportionaltothenumberoftheantennasaddedandwhenthenumberofantennasisincreasingtheexpendituresareaugmentingtoo.


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TheoperationalexpendituresforpreviouscasesarepresentedinFigure5.TheexactoppositefactfromtheonepresentedinthecaseofCAPEXishappeningforthisanalysis.Alltheexpendituresarestable,whenthenumberofantennasaugments,butinthiscase,femtocellspresentlowercosts.Ontheotherhand,DAS’operationalexpendituresareveryhighandasamatteroffactcontributealottoitsTCO.Also,intheDAScasesthedeploymentofthemacrocellbasestationcontributestosomemoreexpensesandassiststothefactthatitisthehigherofallthepresentedcosts.DASTCO

Table 1. Cost Parameters and System Variables of DAS

Parameter Description Value

CeNB CapitalcostforEnb 1000€(Bourasetal.,2014)

CEPC Corenetwork’scapitalcostforthedeploymentofasingleeNB 110€(Markendahletal.,2010)

Ν ThetotalnumberofeNB’sandEPC’sneeded 1(Bourasetal.,2014)

i Annualinterestrate 6%(Bourasetal.,2014)

n Durationofinstallmentplanofasiteinyears 10yrs(Bourasetal.,2014)

r Periodicinterestrate 6%(Bourasetal.,2014)

Ceq CostofDASequipment 11900€(Liu,2013)

d FactorrelatedtothenumberofDASstructures 0.002

fst Linearcoefficientcorrelatingsitemaintenancecostswithcapitalexpenditure

0.8(Johanssonetal.,2005)

cst Sitecostsapartfrommaintenancecostswithcapitalexpenditure

3100€(Correiaetal.,2010)

Crun Runningcosts,suchassinglesite,in-site,off-site 892.5€(Liuetal.,2012)

Cbh Backhaulcostsformicrowave/opticfiber 3800€/4800€(Liu,2013)

BW Backhaulbandwidthforasite’sinterconnection 10Gbps(Bourasetal.,2014)

fBW Linearcoefficientcorrelatingsiteannualbackhaulcostswithprovidedbandwidthexpressedin€/Gbps

1170(Bourasetal.,2014)

Cpw OperationalcostsfortheenergyconsumptionoffemtocellOPEXcosts

157.68€(Liu,2013)

Cinc Implementationcostsfortheinstallationandthecoordinationofthesystem

2800€(Liu,2013)

Table 2. Cost Parameters and System Variables of femtocells

Parameter Description Value

CeNB CapitalcostforEnb 1000€(Bourasetal.,2014)

CEPC Corenetwork’scapitalcostforthedeploymentofasingleHeNB

110€(Markendahletal.,2010)

Ν ThetotalnumberofHeNB’sandEPC’sneeded 1(Bourasetal.,2014)

i Annualinterestrate 6%(Bourasetal.,2014)

n Durationofinstallmentplanofasiteinyears 10yrs(Bourasetal.,2014)

r Periodicinterestrate 6%(Bourasetal.,2014)

fm Linearcoefficientcorrelatingsitemaintenancecostswithcapitalexpenditure

0.8(Johanssonetal.,2005)


59

isveryexpensive,becauseofitshighOPEXanditisstable,whilefemtocells’TCOissmaller,butaugmentslinearlyproportionaltotheantennas’augmentation(Figure6).

Inaddition,examiningtheTCOFigure7fordifferentbackhaultechnologies,whenthenumberofantennasaugments,theTCOsofbothDASdeploymentsarehigher,butarefixedamounts.TheDASdeploymentswithamacrocellularbasestationarehigher,thantheotherswithoutimplementingthebasestation.Thebackhaultechnologydoesnotaffectmuchthecosts,althoughthehighercostisnotedfortheDAScasewithformingamacrobasestationandusingfiberasbackhaultechnology.So,itenablesnetworkoperatorstoaddopticfibers.Femtocells’expendituresaugmentlinearly,whilethenumberofantennasisincreasing.IntherespectivecaseofCAPEXpresentedinFigure8,theDASwithoutabasestationdeploymentformicrowaveorfiberislowertotheotherones.DASCAPEXislow,whilefemtocells’islinearlyaugmentingwhileaddingseveralantennas.

Figure 4. The comparison of the CAPEX for DAS and Femtocells

Figure 5. The comparison of the OPEX for DAS and Femtocells

Figure 6. The comparison of the TCO for DAS and femtocells


60

Itiscrucialtopointouttheneedofstudyingthecaseofaverylargeinfrastructure.Supposingseveral decades or a hundred of antennas needed Figure 9, we conclude that the DAS’ TCOexpendituresarestableandhigh.TheDASwithdeployingamacrocellularstationareonceagainhigherthantheotherswithoutthedeploymentofthemacrocellbasestation.Ontheotherhand,thefemtocells’costsarelinearlyproportionaltothenumberofantennasaddedinthesystem.Foronehundredantennas,thefemtocells’expendituresequaltheDAScosts.ThesameexperimentalprocedurefortheCAPEXisdepictedinFigure10,whileincreasingthenumberofantennasthefemtocells’CAPEXisthehighestoneasitislinearlyproportionaltothenumberofantennasadded.ForbothcasesofDAS,theCAPEXareextremelylowerandstablecomparedtothefemtocells’andtheonewiththedeploymentofabasestationremainshigherthantheonewithoutimplementingit.

Figure 7. The comparison of the TCO for DAS and femtocells for different backhaul solutions

Figure 8. The comparison of the CAPEX for DAS and femtocells for different backhaul solutions

Figure 9. The comparison of the DAS and femtocells for very large buildings


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WedepicttheTCOinFigure11consideringtheinstallmentplanovertheyears.TheTCOisextremelyhigh,inbothDASdeploymentswhilethefemtocells’costsseemtodecrease,whileyearselapse.Forexample,fromtwotofouryearstheexpendituresarehigherthantheyareinthenextyears.Fromsixtotwentyyearstheexpensesstabilize.TheDAS’costsarehighercomparedtothefemtocells’.TheCAPEXforalldeploymentsfollowaparabolicorbit.Analytically,thetwocasesofDASandtheoneoffemtocellsdecreasewhiletimeelapses,butfemtocells’CAPEXishigherthanthoseoftheDAS’.TheCAPEXcostsaredepictedinFigure12.CAPEXisdecreasingwiththeelapsingofyearsforallcases.ThefluctuationislargerforthefemtocellcaseandsmallerfortheDAScases.

FromthepreviousexperimentsweconcludethatDASisslightlydifferentcomparedtofemtocells,afactalsodepictedintheircosts.DAScontributestoanoperatormuchOPEXandasaresult,itis

Figure 10. The comparison of the CAPEX for DAS and femtocells for very large buildings

Figure 11. The comparison of the TCO for the investment plan for DAS and femtocells over the years

Figure 12. The comparison of the CAPEX for the investment plan for DAS and Femtocell over the years


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fundamentaltoreduceOPEXviadiminishingpowerconsumptionandintelligentnetworkmanagementpractices.Ontheotherhand,femtocell’sCAPEXislarger,butmostlyburdensasubscriberthatoptsforobtainingit.Accordingtotheapplication,onecouldoptforthemoreconvenientdeployment.DAScoversalargerarea,butcostsmoreandfemtocellscoveracoupleofusers.

Finally,wepointoutthattheexperimentalproceduresandtheresultsdescribethesituationoftheGreekmarketin2016andtherefore,Tables1and2presenttheparametersandcoefficients,thatappearintheGreekmarket.Itispossibletoparameterizetheproblemwithdifferentcostvaluesforothermarkets for futureexperimentalcases.Theparametersareobtainedvia thorough literatureactivityinthefieldoftelecommunications.Thisstudyisdifferentfromothersimilarones,becauseitgathersmanycasesoffemtocellsandDAS.Itcontributeselaboratingonthesubjectandconcludesaboutalltheimportantmattersraisedbefore.

7. CoNCLUSIoN

In this paper,wepresented several experiments for the cost calculationof femtocells andDAS.TCOforfemtocellsislowerthanthecostsofDASformostcases.WeexaminedTCO,CAPEXandOPEXforthetwosuggestions,experimentingwiththenumberofantennasinaccordancewiththebackhaulingtechnology,theyearsofinvestmentforthedeploymentoftechnologiesandtheverylargebuildingsthatincludemanyantennas.

Inmostcases,femtocellscostlessthanDAS.Forverylargeplaces,femtocellsarenotafavorablesolution,becausetheexponentiallyaugmenttheirTCOandfinally,costmorethanDAS.Ontheotherhand,DASiscosteffectivewhenitcoversalargeareawithoutahighaugmentationofcosts.Forlittleareas,thecoverageprovidedbyfemtocellsishelpfulandthecoststheyinducearelowandaffordablebyasinglesubscriber.DASimpartslargerOPEX,soitwouldbevitaltechniquestobedevelopedtodecreasethesetypesofcosts.FemtocellsinducelowOPEX,becauseevenanotexpertuserisabletofixsomeproblemsraisedandplacementandmaintenancecostsaretheminimumpossible.CAPEXislargerforfemtocells,butauserquicklydepreciateshisinvestmentwhenusesthem,especiallyreclaimingpossibilities,theyoffersuchasaccessibilitytootherusers.

8. FUTURE WoRK

Inthefuture,alargeamountofscientistswillbeinterestedinthemobilenetwork’scostcalculationandwilluseourstudy,inordertoconductseveralexperimentsandinduceawiderangeofimportantconclusionsintheexpenditurecases.Thisstudypresentsaflexibility,thatisrelatedtothefactthatitmathematicallydescribesthemodel,soitiseasyforascientisttoapplynewpricesinthefutureorpricesofadifferentmarket,notnecessarilyEuropeanorGreek.Inthenextyears,wesuggestthatscientistsshoulddealwithothersignificantissuesaswell,suchastheexpendituresrelatedtothebandwidth,thedepreciationforeachtechnology,thepowerconsumption,thetechnology’slife-cycle,theusage,thebasestationcostsoreventhedensityofthedeployments,improvingthesuggestedmodelanddiminishingtheOPEXcostsofDAS.

Scientistswoulddealwithahugevarietyofselectionsforfemtocells,suchasusergroupselection,femtocellsafety,reductionofpowerconsumption,reductionofbasestationcosts.Marketingandmanagementforwardingconvincingusersaboutthebenefitsoffemtocellsshouldalsobeconsidered.Thereisalsoaneedindelineatingthefutureoffemtocellscombinedwithotherdifferenttechnologicalsuggestions, such as Software Defined Networking in Wireless Networks and the way of theirmanagementbytheSDNsoftware.DASshouldbeinvestigatedinordertodiminishitsbasiccostsforboththeindoorandoutdoorcasesandalternativestoreducetheirhighOPEXshouldbeproposed.Thereshouldalsobeaninvestigationforhealthconcernsalongsidewithimposingexactlegislationconsideringthesetechnologies.


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Christos Bouras is Professor in the University of Patras, Department of Computer Engineering and Informatics. Also he is a scientific advisor of Research Unit 6 in Computer Technology Institute and Press - Diophantus, Patras, Greece. His research interests include Analysis of Performance of Networking and Computer Systems, Computer Networks and Protocols, Mobile and Wireless Communications, Telematics and New Services, QoS and Pricing for Networks and Services, e-learning, Networked Virtual Environments and WWW Issues. He has extended professional experience in Design and Analysis of Networks, Protocols, Telematics and New Services. He has published more than 400 papers in various well-known refereed books, conferences and journals. He is a co-author of 9 books in Greek and editor of 1 in English. He has been member of editorial board for international journals and PC member and referee in various international journals and conferences. He has participated in R&D projects.

Vasileios Kokkinos obtained his diploma from the Physics Department of the University of Patras on October 2003. Next, he was accepted in the postgraduate program “Electronics and Information Processing” in the same department and on March 2006 he obtained his Master Degree. In 2010 he received his PhD on Power Control in Mobile Telecommunication Networks from the Computer Engineering and Informatics Department. He works in the Research Unit 6 of Computer Technology Institute and Press “Diophantus” since September 2006. His research interests include data networks, third and fourth generation mobile telecommunications networks, multicast routing and group management and radio resource management. He has published several research papers in various well-known refereed conferences and articles in scientific journals.

Anastasia Kollia obtained the Proficiency in English of Michigan University in 2007. She obtained the “Diplome Approfondi de la langue francaise C2” de l’ “Institut francais” in 2007. She entered the Computer Engineering and Informatics Department in 2010 and obtained her diploma in 2015. She joined the ru6 of the Computer Engineering and Informatics Department at the University of Patras in 2014 and she has been a member ever since. She is currently a master student in the same department in the Computer Science and Technology. She is a member of the IEEE student branch at Patras since 2015. Her research interests include future mobile and wireless networks, Ultra-dense deployments and Software Defined Networking.

Andreas Papazois is a post-doctoral researcher at Computer Engineering and Informatics Department, University of Patras and an R&D engineer at GRNET S.A. In the past, he worked as telecommunications engineer in Intracom Telecom S.A. His research interests include future mobile networks, ultra-dense deployments and software defined networking. He has published several research papers in various well-known refereed conferences, books and journals. He has been technical committee member for several conferences and a reviewer for various scientific journals.

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