With Contributions of the following partners (in order of ap(4)

1.4Transportprotocolsforwirelessnetworks

Finally,itisworthnotingthattransportprotocolssuchasTCPfordatatraf cwereoriginallydesignedforwirelinenetworksandarenotwell-suitedtotheradiomediumwhichisinherentlyslowandlossy.SomerecentproposalsthataddressthisissuearepresentedinSection22.Butthereaderwill ndanextensivestateoftheartofthistopicindeliverablesrelatedtoworkpackageJRA2.1.

A state of the art

2.AdmissionControlinUMTS-StateoftheArt

2AdmissionControlinUMTS-StateoftheArt

S-E.Elayoubi,T.Chahed

GET/InstitutNationaldesTelecommunications,France

SeveralCACalgorithmshavebeendevelopedforcellularnetworksduringthepastdecade.However,fewofthesealgorithmswereadaptedtothedynamicnatureofthirdgenerationwirelessnetworks.Infact,theradiointerfaceofthesenetworksisbasedonWideband-CDMAandthecapacityisdetermined,notonlybythenumberofusersandtheirbitrates,butalsobytheirpositioninthecellwhichinturnchangeswithmobility.WewillanalyzeinthisdocumentthemostimportantCACalgorithmspresentedintheliterature,withrespecttothevariousconstraintstheyconsider,aswellastheircomplexityandtheirabilityornottohandledifferentclassesofmultimediatraf c.

2.1CACalgorithmsbasedonamaximalnumberofusers

The rstCACalgorithmsweredesignedfor2Gsystems,especiallyGSM,andwerebasedonamaximalpredeterminednumberofusersinthesystem,orequivalentlyona xedcapacity.Infact,forsystemsbasedonTimeDivisionMultipleAccess(TDMA)orFrequencyDivisionMultipleAccess(FDMA),userscanbeacceptedaslongastherearechannels(timeslotsorfrequenies)available.ThisiscalledNCACandcorre-spondstoahardcapacityallocation,whichisnotthecasein3Gsystems,whosecapacityvariesdynamicallywiththequalityoftheairchannelandmobilityofusers,asshallbeseennext.

Nevertheless,thissimplisticassumptionmakesitpossibletointroduceseveralclassesoftraf c(Leongetal.in[277]andBartolinietal.in[41]),basedontheLimitedFractionalGuardChannel(LFGC)policy, rstproposedbyRamjeeetal.[353]for2Gsystems.Theythusobtainimportantperformancemeasuressuchthattheblockingprobability,i.e.theprobabilitythatacallisblockedduetothelackofresources,orthehandoffblockingprobability,i.e.theprobabilitythatamobile,acceptedinagivencellandmovingtowardsanadjacentone,failstocontinueitsconnectioninthenewcell.

2.2CDMA-orientedCACalgorithms

The rstCDMA-orientedalgorithmsweredesignedfor2GsystemsusingCDMAasaccessprotocolontheradiointerface,i.e.IS95system.TheseearlieralgorithmsconsideredinterferenceasthelimitingfactorwhenmakingaCACdecision.Infact,incontrastwiththehardcapacityallocation,CDMAsystemsarecharacterizedbyasoftcapacitywherethereisnohardtheoreticallimitonthenumberofusers.Ausercanthenbeacceptedifitsadmissiondoesnotcauseanexcessivedegradationforalreadyconnectedusersduetoahighlevelofinterference[31].

TherearethreeclassesofCDMA-orientedCACintheliterature,namelytheInterference-CAC,thePower-CACandtheSIR-CAC.

2.2.1Interference-CAC

InInterference-CAC(ICAC)algorithms,thedecisionisbasedonapredeterminedinterferencethresholdatthebasestation[213][82]:acallisacceptediftheresultinginterferenceremainsacceptable.Letusnotethat,

A state of the art

2.2CDMA-orientedCACalgorithms

byde nition,ICACalgorithmsaredesignedforthereverselink(uplink)astheyconsidertheinterferenceatthebasestationandnotatthemobile.Furthermore,ICACalgorithmsdevelopedintheliteraturedonottakeintoconsiderationmultipleclassesoftraf c.

2.2.1.1ModelingthesystemA rstenhancementtoICACwaspresentedbyHoetal.in[204]whereseveralCACschemeshavebeenbuiltbasedonananalyticalmodelofaDirectSequenceCDMA(DS/CDMA)cellularuplinksystem.TheaimoftheproposedCACschemesistomaximizethecell’sErlangcapacity,de nedastheratiooftheaveragenumberofcallsinthecelltothesystembandwidth,whilesatisfyingtwosystemconstraints:the rstisonblockingprobabilityandisgivenby(PBL≤θ)andthesecondisonoutageprobability,i.e.probabilitythatanongoingcallseesitsQoSdegraded(withouttakingintoaccountthehandoffblocking)(Pout≤ ).The rstandsecondmomentsoftheother-cellinterferencehavebeencalculatedusingatwo-slopepathlosspropagationmodelandanequivalentnumberofactiveusersZisderived,inthesensethattheeffectoftheother-cellinterferenceonthecapacityisequivalenttotheeffectofZlocalusers.Theoutageconditionisthenobtainedas

K+Z+noise>max.Interference

whereKisthenumberofusersinthecell.

Theimportanceofthisequation(1)isthatitde nesanICACalgorithmwiththesimplicityofNCAC.

ThesystemismodeledasaMarkovchainwitheachstaterepresentingthenumberofongoingcalls.TheblockinganddroppingprobabilitiesarethencalculatedusingaGaussianapproximationofK,forfourdif-ferentCACschemes:

Complete-SharingCallAdmissionControlScheme:thenumberofacceptedcallsislimitedtoGmax,Th.ThisnumberandthearrivalrateλarecalculatediterativelytomaximizetheErlangcapacitywhilesat-isfyingthesystemconstraints.ThisisequivalenttoanNCAC,withthedifferencethatthethresholdisvariablewiththeother-cellinterference.

Check-Interference-Upon-Call-ArrivalCallAdmissionControlScheme:Gmax,Th=∞,butacallisacceptedifandonlyiftheinterferencedoesnotexceedathresholdTTh.Again,TThandλarecalculatedbyiterationstosatisfythesystemconstraints.

Position-BasedCallAdmissionControlScheme:eachcellisdividedintotwozones:theinnercellandtheoutercell,andtwodifferentthresholdsTinandToutarede nedfortheacceptanceofthenewcallsinthetwozones.

However,thesealgorithmsremainlimitedtothecaseofasingleclassofvoicecalls,andnodistinctionismadebetweennewandhandoffcalls.

2.2.1.2IntroducingthewiredcapacityAnotherimportantenhancementtoICACwasintroducedbyKaseraetal.[236]whereadmissioncontrolisstudiedasacongestioncontrolpolicyintheIP-basedRadioAccessNetwork(RAN).Thisisbasedontheideathatthecurrentpoint-to-pointlinksusedinconnectingbasestationstonetworkcontrollerswillevolvetoanIP-basedRANforreasonsoflowercostduetostatisticalmultiplexinggains,betterscalabilityandreliability,andtheprojectedgrowthindataapplications.(1)

A state of the art

2.2CDMA-orientedCACalgorithms

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