5G Networks: Planning, Design and Optimization

405 Pages·2018·12.877 MB·English

by  Christofer Larsson

5G Networks

5G Networks
Planning, Design and Optimization
Christofer Larsson
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To the memory of my father
Preface
ThisbookisinsomesenseasequeltoDesignofModernCommunicationNetworks(2014)
havingtheaimofdescribingsomeofthemostimportantconceptsandcapabilitiesof5Gfrom
amathematicalpointofview.Iwouldliketoseethisasanideabook;itscontentisinfluenced
bymyownunderstandingof5Gandchallengesthatoperatorsandsolutionvendorsarefac-
ing.
5Gnetworksareinherentlycomplexandtheirplanningrequiresawiderscientificscopethan
traditionalnetworkdesign.Thus,someattentionispaidtobigdataandmachinelearning
techniquesaswell.Indeed,optimizationandmachinelearningcanbeseenasdualdisciplines,
andbigdataoccurasanaturalpartofnetworkmanagement.
Thecontentfocusesondesignandoptimizationtasksindesignandoperationsthatcanbe
formulatedastractableoptimizationproblems.Manyoftheseproblemsmayseemover-
whelminglycomplex,butappropriateproblemformulationsandnoveloptimizationmethods
havebeenusedtoshowamazingresultsandprovidenewinsightintonetworkplanningmat-
ters.
Theoverallemphasisisonresourceefficiency,whethertheprimaryobjectiveiscapacity,cov-
erage,latencyorenergyconsumption.Itcanbeshownthatproperplanninganddesignleadto
substantialgainsinseveralperformanceparameters.Theachievableimprovementwithproper
optimizationisoftensubstantial,possibly10–30%comparedwith“traditional”methods,and
thegaincanoftenbenoticedinseveralaspectssimultaneously.
Ithasbeentheaimtopresenttechnology-independentcontentasfaraspossible.Thatisthe
reasonwhytherearefewdetailsonactualnetworktechnologies,protocols,andfunctional-
ity.Thereisplentyofliteratureavailableonthesetopics,andthealgorithmsdescribedinthis
bookcanrathereasilybetranslatedintotechnology-specificsituations.
Themainideapermeatingthemethodsdescribedinthisbookisrandomization.Insteadoftry-
ingtosolveproblemsexactly,weaimatfindingagoodsolutionwithhighprobability.Most
designtasksarecombinatorialintheirnature.Inaddition,thenumberofpotentialoptimiza-
tionparametersincreasesasnewfunctionalityisintroducedandcomplexdependenciesmust
xv
Preface
beresolved.Mostproblemsdiscussedthroughoutthetextcanthereforebecharacterizedas
“hard”.
Ingeneral,combinatorialoptimizationisdifficult,anddiverseproblemsneeddifferentap-
proaches,thoughtheideasunderpinningmanysolutionmethodsarestillfairlysimple.It
shouldbepossibletoimplementthedescribedalgorithmsinanyprogramminglanguageof
choicewithreasonableeffort.
Alargepartofthecontentofthebookpresentsmethods,findingsandconclusionsdrawn
fromindustrialoracademicprojectsIhavetakenpartin.Asmathematicalprerequisites,the
readerisprobablyfamiliarwithsomecombinatorics,optimization,fundamentalprobability
theory,queueingtheory,statisticsandanalysis,thatis,alittlebitofeverything,andanopen
mind.
Iamgratefultothemanyresearchersandscientistswhohavemadetheirinterestingpapers
freelyavailableontheInternet.
ChristoferLarsson
Bratislava
June2018
xvi
CHAPTER 1
Concepts and Architectures in 5G
5Gnetworksareoftendescribedbyasetofstrictperformancecriteria.Tocaterforvastlydi-
versetrafficandqualityofservicerequirementsofvarioususecases,thegeneraldemandson
thenetworksare
• Massivesystemcapacity,
• Veryhighdatarates,
• Minimallatency,
• Extremelyhighreliabilityandavailability,
• Energy-efficientandsecureoperation.
Toachievethis,notonlyneednetworksbeupgradedwithhigh-performanceelements,but
planning,designandmanagementhavetobecarriedoutaccordingtooptimalengineering
methodstomaintainperformanceandcostefficiency.
Afairlynewparadigmincommunicationnetworkingisnetworkelasticity,whichcanbeinter-
pretedasadynamicandoptimalutilizationofresourcesand–asfaraspossible–ademand-
drivenallocationofcapacity.Thejustificationsforflexibleresourceallocationareatleast
twofold:fromacapacitypointofview,resourcepoolingisalwaysmoreefficientthandis-
tributedresourcesintermsofutilization;secondly,dynamicfunctionalallocationsthrough
networkfunctionvirtualization(NFV)improvestheresilienceapproachingthatofadis-
tributedlogic.Toachievethesegoalscost-effectively,planningforhighresourceutilization
andresilienceareimperative.
Aconsequenceofvirtualizedarchitecturesistheneedforanovelapproachtotrafficengineer-
ing,whichmustbeabletocaterforawiderangeofdiversetrafficsourcesfromapplications
suchasmassivesensornetworks,telemedicine,andvirtualreality.
Itiswellknownthataggregationofmanytypesoftrafficleadstoself-similarbehavior,of-
tenleadingtostarvationofsometraffictypesbyothers.Furthermore,usermobilityhasbeen
compensatedforbyresourceoverprovisioningintraditionalnetworks,whichbecomeswaste-
fulwhentrafficdemandsandmobilityincreasefurther.
1.1 Software-Defined Networking (SDN)
Theconceptofsoftware-definednetworking(SDN),whichoriginatedinthemid-1990s,isa
frameworktomanagenetworkbehaviordynamicallyviaprogrammableapplicationsusing
5GNetworks.https://doi.org/10.1016/B978-0-12-812707-0.00006-1
Copyright©2018ElsevierLtd.Allrightsreserved. 1
2 Chapter1
openinterfacestothenetwork.Thisallowsforaflexibleutilizationofnetworkresources,in
contrasttothestaticallocationofresourcesinconventionalnetworks.
Traditionally,thecontrolofpacketflowsisrealizedbynodesforwardingpacketstothebest
destinationaccordingtothepacketheaderinformationandasetofstaticrules.Ineffect,
routerstrytoaccommodatethequalityofserviceonaper-flowbasis,mostlyagnosticofthe
statesinotherpartsofthenetwork.Thecontrolofthesinglepacketflowandtheinteraction
betweenflowsareintrinsicallylinkedtogether.Asaresult,somepartsofthenetworkmaybe
overloadedwhereasothersmaybeunderutilized.
SDNallowsdecouplingofthecontrolfromtheflow,resultingintwoseparatedomainsre-
ferredtoasthecontrolplaneandthedataplane,respectively.Aconsequenceofthisdecou-
plingisthepossibilitytocreateresourceandflowcontrollogicthatisbasedonmoreinforma-
tionthaniscontainedinindividualflows.Thelogiccanthenbebasedonthestateofdifferent
partsofanetwork,thecharacteristicsandinteractionofvariousflows,orexternalfactors,
suchasdynamicreservationofresources.
Asamatteroffact,thelogicalseparationintocontrolplaneanddataplanewasimplemented
forsynchronousdigitalhierarchy(SDH),thatis,connection-orientednetworks,alreadyinthe
mid-1990s.Theimplementationwasfacilitatedbythefactthattheroutesinsuchnetworks
alreadyweresemistatic,andnetworksconsistedofrelativelyfewnodes[1].
ThereareseveralincentivesforanSDN-basedimplementation.Firstly,trafficcharacteristics
changemuchmorerapidlytodaythaninthepastthroughthefastdeploymentofnewservices.
Secondly,trafficflowsdependonanincreasinglycloud-basedservicedistribution.Thirdly,
withrapidlyincreasingtrafficvolumesandbigdata,resourcesneedtobemanagedmorecost-
efficiently.
Centralized and Distributed Control
Inprinciple,networkcontrolfunctionscanbeeithercentralizedordistributed.Theadvantage
ofacentralizedcontrolistheabilitytoapplyacontrolpolicytakingintoaccountthestate
oftheentirenetwork.Themaindisadvantagesaredelaysinreceivinginformationupdates
andapplyingcontrolactionsandtheriskofoverloadorfailureofasinglecentralizedcontrol
function.
Atpresent,networkcontrolistypicallydecentralizedandresidingintheroutersduetoits
fastreactiontimeandresilienceagainstfailure.Thecontrolactions,however,areonlybased
onnetworkstateinformationinasmallneighborhoodofthenodeitself.Distributedcontrol
functionsarealsobasedonrathersimplelogic,whichmaynotleadtoflowcontrolwhichis
optimalfortheentirenetwork.