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1 Femtocell/Small-cell Networks: A survey and challenges Prof. Rami Langar LIGM/UPEM [email protected] http://perso.u-pem.fr/~langar
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Femtocell/Small-cell Networks: A survey and challenges
Prof. Rami Langar
LIGM/UPEM
[email protected] http://perso.u-pem.fr/~langar
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Mobile data growth…
The pope elections in 2005 and 2013 Source: Cisco VNI Mobile, 2016
Weneedinnovativenetworkdesignstohandleallofthis!
Wirelessdatagrowthleadstospectrumdeficit!
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• Operatorsdilemma– Meetthedemandandmaintainlowcosts(i.e.,revenuesanissue)– Increasingtheindoorcoverageanddownloadcapacity– improvingcustomersatisfaction
• Solutionsthathavebeenexploredinthepastfewyears– MultipleantennasystemsandMIMO
ü Cannotprovideorderofmagnitudegainsü Scalabilityandpracticalityissues
– Cognitiveradioü Availabilityofwhitespacesinmajorareasatpeakhoursisquestionableü Complexityissue
• MIMOandCognitiveradiowillstaybutmustco-existalongwithbetter,morescalable,andsmarteralternatives.
• Isthereanybetter,cost-effectivesolution?
Main Implications
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• 0-G– Veryfirstmobilecommunicationsystems– Alsocalledas“Pre-Cellularsystems”or“MobileRadioTelephony”– MostworkedonAM,FMmodulationschemes– Poorcapacity,lowefficiency,fewercustomers
• 1-G– CalledasFirstGenerationsystems(e.g.,AMPS)– Bornafterintroductionofcellularconceptin1970– Stillpoorcapacity,lowefficiencyandanalogsystems
• 2-G– Firstpopularcellularmobilecommunicationsystems– CalledasSecondGenerationsystems– FirstDigitalCellularCommunicationSystems– Duetodigitalization:efficiencyincreased,higherperformance,higher
capacity,roamingabilitiesandincreasedbatterylife.– GSM,D-AMPS,IS-95were2-G
Cellular Generations
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• 3-G– CalledasThirdGenerationsystems– 2.5G(GPRS),2.75G(EDGE)haddatacapabilitiesandformedthebasisof3G– Bettermodulationtechniquesandimprovementinelectronicshelpedin
gaininghigherspeeds,betterinterference,videoabilitiesandlowerpowerrequirements
– W-CDMA,cdma2000,andUMTSwere3G
• 4-G– CalledasFourGenerationsystems– UsesomeofadvancedfeatureslikeMIMO,AMC(AdaptiveModulationand
Coding),UWB(Ultra-wideband).– Broadbandspeeds,bettercoverage,highcapacity,lowinterferencearesome
aspectsof4G– WiMAX,LTEare4G
• 5-G– Nextgenerationofcellularcommunications,expectedin2020.– SomeoftheadvancedfeaturesincommunicationlikeSoftware-defined
Radio,NetworkSlicing,etc.
Cellular Generations
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• Wecanseethatonelargecellisdividedinto7smallercells.
• Eachcellwithadifferentnumberusesdifferentbandoffrequencies
• Eachsmallercellisplacedataminimumre-usedistancefromitsinterferingcell.
• Thispatternisa7-cellReusepattern
Cellular concept
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• Becauseofintroductionofcellularconcept,capacityincreasedasshownbelow.
Cellular concept
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• Withinventionofeverynewtechnology,comesitsproblems.
• Problemswithcellulararrangementwasthat:
- Lowerreusedistance:smallercells,highinterferenceduetocloseinterferingcells,complexhand-overabilities
- Higherreusedistance:largercells,lowercapacity
Cellular concept: Problems
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• Introducenewchannelsuntilsaturation• Cellsplitting• Cellsectoring• Cellularhierarchy
Cellular concept: Solutions
Cell splitting
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Cell sectoring
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• Soontheotherthreesolutionscametosaturationandengineershadtocomeupwithanewsolution.
• Engineersbroughtincellularhierarchyintheexistingcellstoreduceloadoncellularbasestationandincreasecoverage.
• Thismeantreducingthesizeofthecellintostillsmallercellscreatingacellularpatternintothepresentpattern.
Cellular hierarchy
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Cellular hierarchy
• Asthroughputdemandandusageincrease,cellsizedecreases.
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Small Cell Networks
Ultimately,theonlyviablewayofreaching“thepromisedland”ismakingcellssmaller,denser,andsmarter
• Operatorsfaceanunprecedentedincreasingdemandformobiledatatraffic.• 70–80%volumefromindoor&hotspotsalreadynow.• Mobiledatatrafficexpectedtogrow500–1000xby2020.• IncreasednetworkdensityintroducesLocalareaandsmallcells• 2013,AT&TandSprintalreadydeployed1millionoffemtocellseach,andthisisexpectedtoreachnearly70millionworldwideby2017.
Facts
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• Femtocellnetworksoperateonlicensedspectrumownedbythemobileoperator.• Fundamentallydifferentfromthemacrocellintheirneedtobeautonomousandself-organizingandself-adaptivesoastomaintainlowcosts.• FemtocellsareshortrangeaccesspointsandareconnectedtotheoperatorthroughDSL/cable/Ethernetconnection.
- offloadingthemacrocells,increasingtheindoordownloadcapacity• Heterogeneous(wired,wireless,andmix)backhaulsareenvisioned.
In a nutshell…
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• In2002,agroupofMotorolaengineerintroducedaHomeBaseStationtechnology.
• In2007,vendorsformedtheFemtoForumtopromotefemtocelluse
• In2008,SprintNextelreleasedhome-based2GfemtocellbuiltbySamsungElectronicsthatworkswithanySprinthandset
• In2009,VerizonandVodafonerolledouttheirfemtocellnetworkservicewith3Gstandard.
• InFrance,SFRisthefirstoperatortointroduceFemtocellin2009(calledSFRHome3G).
• In2010,FreeincludedthefemtocellofferintheirFreebox• In2012and2013,BouyguesTelecomandOrange,respectively,
rolledouttheirfemtocellnetworkservicewith3Gstandard.
Femtocell Development
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Standardization Efforts
• NextGenerationMobileNetworks(NGMN)Alliance
• Createdin2006bygroupofoperators• Businessrequirementdriven• Oftenbasedonuse-casesofdailynetworkingroutines• HeavilyrelatedtoSelf-OrganizingNetworks(SON)activities
• SmallCellForum(formerlyFemto-Forum)isagoverningbodywitharguablymostimpactontostandardization
• Non-profitmembershiporganizationfoundedtoenableandpromotesmallcellsworldwide.
• SmallCellForumisactiveintwomainareas:
- Standardization,regulation,andinteroperability;- Marketingandpromotionofsmallcellsolutions.
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• Lowcostsolution• Improvereliability• Increasesbothcoverageandcapacity• Reducecoverageholesandcreatenewconvergedservices
• Reducemacro-cellbackhaulcapacityrequirements(offloading)
• Workswithallexistinghandsets• Increase3Gadoption
Benefits of Femtocell Networks: for Operators
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Benefits of Femtocell Networks: for Operators
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• Reducecost(freecallsathome!)• Noneedforexpensivenewdevice• Superiorindoorcoverageandqualitywithoutchangeinphones
• Simplicity:- Onephone- Onemode- Onenumber- Locationspecificpricing
• Seamlessservicesacrossallenvironments.
Benefits of Femtocell Networks: for Consumers
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• Threeaccesspolicies- Closedaccess:
ü Onlyregisteredusersbelongingtoaclosedsubscribergroup(CSG)canconnect
ü Non-authorizedsubscribersaredeniedaccesstothefemto(redirectedbacktothepublicmacrocellnetwork)
ü Homeorenterpriseenvironments- Openaccess:
ü Norestrictiononsubscribertousethefemtocellü Allusersconnecttothesmallcellsü Hotspottypescenario:coffeeshoporairportü Thefemtocellbecomesanotherpartofthepublicmobilenetwork
- Hybridaccess:ü Allusers+prioritytoafixednumberoffemtousersü Subjecttocostconstraintsandbackhaulconditions
• Femtocellsaregenerallyclosed,openorhybridaccess• Picocellsareusuallyopenaccessbynatureandusedforoffloadingmacrocelltrafficandachievingcellsplittinggains
Small Cell Access Policies
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Network architecture - ASN(AccessService
Network):anall-IPnetworkstructureisapplied
- CSN(Connectivity
ServiceNetwork):composingofservices,suchasauthentication,authorization,andaccounting(AAA)server,MobileIP,HA,andpolicyserver.
- ASNGateway:interfacebetweenASNandCSN
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• Microcells- Operatorinstalledmicrocelltowers- Improvesignalinurbancoverage- Capitalexpenditure:
ü Installingnewcelltowers- Operatingexpenditure:
ü Electricity,sitelease,andbackhaul.- Benefits:
ü Systemcapacitygainfromsmallcellsizethanamacrocell
ü Completeoperatorcontrol- Shortcoming:
ü Installationandmaintenanceofcelltowersisexpensive
ü Doesnotcompletelysolveindoorcoverageproblem
Comparisons of Femtocells, Distributed Antennas, and Microcells
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• DistributedAntennasSystem(DAS)- Operatorinstalledspatially
separatedantennaelements(AEs)connectedtoamacroBSviaadedicatedfiber/microwavebackhaullink.
- Capitalexpenditure:ü AEandbackhaul
installation
- Operatingexpenditure:ü AEmaintenanceand
backhaulconnection
Comparisons of Femtocells, Distributed Antennas, and Microcells
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• DistributedAntennas- Benefits:
ü BettercoveragesinceusercommunicatewithnearbyAE
ü Capacitygainbyexploitingbothmacro-andmicro-diversity(usingmultipleAEspermacrocelluser)
- Shortcomings:
ü Doesnotsolvetheindoorcoverageproblem
ü RFinterferencefromnearbyAEsdiminishescapacity
ü BackhaulcostsbetweenBSandAEs
Comparisons of Femtocells, Distributed Antennas, and Microcells
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Small Cells vs. WiFi • RecenttrialsusingaconvergedgatewayWi-Fi/3Garchitectureshowedhowthetechnologiescouldbecombinedandexploited.
• Severalcompaniesarelikelytosimultaneouslyintroducebothtechnologiesforoffloading.
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• Physique- Physicallysmallforlimitedspaceinsomehouseholds/offices- Silentinoperationwhilegeneratinglowlevelsofheatoutput
• RFpower- TxRFpowerisbetween10–100mW(lowerthan1WbyWiFi)- 3Ghandsetisabletotransmitatlowerpowerlevelswhenbeingclosetothe
femtocell• Coverage
- Dedicated3Gcoveragewithinahousehold(10–200m)- Designedforacapacityof2to8end-users.
• Backhaul- UtilizeIPwithaflatBSarchitecture- Linktooperatornetworksviawiredbroadbandconnections
• Interference- MacrocellsvsFemtocells- FemtocellsvsFemtocells
Femto Characteristics
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• Security- SecurityrisksduetobroadbandInternet(openaccess)- NetworksecurityismanagedbytheIPSecprotocol
• Operation- Compatiblewithexisting2G/3Ghandsetsanddevices- Operatesinlicensedspectrumownedbyoperators- Remotedevicemanagement(updatesoftware/firmware,monitorstaus/
performance,anddodiagnostictests(Allfromaconsoleintheoperator’snetwork)
- Ideally,supportSelfOrganizingNetwork(SON)aspect
• WorldwideStandardSupport- Developedtosupportboth3GPP(UMTS)and3GPP2(CDMA)- AlsosupportsemergingtechnologiessuchasWiMAXandLTE
Femto Characteristics
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• InterferenceManagement- FAPcaninterferebothmacro-cellnetworksandeachother- PowercontrolisrequiredinFAPtoavoidinterferenceforoutdoorusers
• QualityofService- SharedIPaccesslink(voice,data,video,P2P,etc.)- Trafficprioritizationisessential(ensuresconsumersatisfaction)
• Time/NetworkSynchronization- 3GPPspecifiesthatBSTxfrequenciesbecloselysynchronized- Candidatecalibrationstrategies
ü IEEE1588² Self-adaptivetimingrecoveryprotocol² 100nstimingaccuracy
ü GPS² Popularandlowcostsolutionforlocalization² Receptionproblemforindoorenvironment
Femto Challenges
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• SecurityandPerformance- Moresophisticatedregistrationandauthenticationprocessandencryption
ofIPpacketsarenecessaryü FAPsutilizelocalISPnetworks,whichmaybedifferentfromthe
operator’snetwork- Collaborationandservicelevelagreement(SLA)betweencellularandISP
operatorsarerequired
• Mobilitymanagement- 3typesofhandovers:Hand-in,hand-out,andhandoff- Seamlesshandoversupport
• Self-Organizationandautonomousoperation- FAPsshallbeaplug-and-playdevicethatcanintegrateitselfintothe
networkwithoutuserintervention
Femto Challenges
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Summary of Challenges
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Resource and Interference Management
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Challenges: Interference (case 1)
• DLinterferencefromthefemtoBStonearbyMacroUE• AmacroUEfarfromitsMacro-BSwillbeaffectedthemost
• ULinterferencefromnearbymacroUEtofemtoBS• AmacroUEfarfromitsMacro-BScausesinterferencetowardsthefemtocell.
MacroUEinside/nearfemtocoverage!
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Challenges: Interference (case 2)
• DLinterferencefromnearbyMacro-BStofemtoUE• InterferencefromnearbyMacro-BScanlowerSINRoffemtoUE.
• ULinterferencefromfemtoUEtonearbyMacro-BS• ManyactivefemtoUEscancausesevereinterferencetotheMacro-BS.
SmallcellveryclosetomacroBS!
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Challenges: Interference (case 3)
• DLinterferenceamongnearbysmallcellnetworks • ULinterferenceamongnearbysmallcellnetworks
(co-tier)interferenceamongsmallcellnetworks!
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Co-tier Interference Management • Indensenetworkdeployments,femto-to-femtointerferencecanbesevere
– Especiallyforcelledgeusers
• AssigningorthogonalresourcesamongneighboringfemtocellsprotectscelledgeUEsbutlowspectralefficiency!
• Key:Assignresourcesdependingoninterferencemap,dynamicinterferencemitigationthroughpowermanagement.
• Centralizedvs.Distributedapproaches
J Resourcesareassignedautonomouslybyfemto-BSsJ LesscomplexityL RequireslongtimeperiodtoreachastableresourceallocationL Lowresourceefficiency
J ResourcesareassignedbyacentralcontrollerJ MoreefficientresourceutilizationthanthedistributedapproachL Needsextrasignalingbetweenthefemto-BSsandthecontrollerL Highlycomputational
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Cluster-based approach
• Hybridsolution:– Distributedalgorithmto
constructclusters– Centralizedoptimizationwithin
thecluster.
• Threephasesalgorithm:– Clusterformation– Intra-clusterResourceallocation– Inter-clusterResourcecontentionresolution
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Cluster Formation
F1
F2 F3
F4
Cluster-Head Cluster-Member Is attached to cluster
1)Eachfemtocellsensesthesurroundingsandobtainitsinterferencedegree2)Itsendsittoonehopneighborsandbuildsinterferencelist3)TheonewithhighestinterferencedegreewillbeClusterHead
2 4 3
2 4 2
4 2 3 2 2
3 4 2 3 2 5 3 2
5 3 3 3 3 2
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Intra-cluster resource allocation
Minimize gap between allocated and requested resources
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Inter-cluster resource contention resolution
F1
F2
F3
F4
F6
F7
F8
Cluster 1 Cluster 2
1 2 3 4 5 6 7 81 2 3 4 5 6 7 8 1 2 3 4 5 6 7 81 2 3 4 5 6 7 8
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Solving LP/IP/MILP with CPLEX/AMPL
• CPLEX is the best LP/IP/MIP optimization engine out there.
• AMPL is a standard programming interface for many optimization engines.
• Student version windows/unix/linux – 300 variables limit
• Full version on LIGM-TP platform
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Introduction to AMPL
• Each optimization program has 2-3 files – optprog.mod: the model file
• Defines a class of problems (variables, costs, constraints)
– optprog.dat: the data file • Defines an instance of the class of problems
– optprog.run: optional script file • Defines what variables should be saved/displayed,
passes options to the solver and issues the solve command
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Running AMPL-CPLEX • Start AMPL by typing ampl at the prompt • Load the model file
– ampl: model optprog.mod; (note semi-colon) • Load the data file
– ampl: data optprog.dat; • Issue solve and display commands
– ampl: solve; – ampl: display variable_of_interest;
• OR, run the run file with all of the above in it – ampl: quit; – prompt:~> ampl example.run
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AMPL Example
• minimizing maximal users’ non-satisfaction (i.e., gap between allocated and requested resources)
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AMPL: the model
parameters
Decision variables
Objective
Constraints
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AMPL: the data
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Thanks for your attention
Questions ?
