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4G/5G RAN architecture: how a split can make the difference
As 5G evolves, the architecture of radio access networks (RAN) is transforming for enhanced deployment flexibility and dynamic performance to meet increasing service demands while controlling costs. This involves a proposed software-configurable split architecture to optimize scalability, energy efficiency, and support for new services, addressing the needs of extreme mobile broadband and massive machine-type communications. Key strategies include seamless radio resource management, functional splitting, and dynamic software-defined RAN to adapt to changing traffic and service requirements.
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4G/5G RAN architecture: how a split can make the difference
- 1. VIRTUALIZE, SPLIT, ANDREORGANIZE ✱ JULY 22, 2016 ✱ ERICSSON TECHNOLOGY REVIEW 1 ERICSSON TECHNOLOGY RF RF BPF RCF PPF C H A R T I N G T H E F U T U R E O F I N N O V A T I O N V O L U M E 9 3 | # 6 ∙ 2 0 1 6 4G/5GRANARCHITECTURE: HOWASPLITCANMAKE THEDIFFERENCE
- 2. ✱ VIRTUALIZE, SPLIT,AND REORGANIZE 2 ERICSSON TECHNOLOGY REVIEW ✱ JULY 22, 2016 ERIK WESTERBERG As 5g evolves, many innovative services like extreme mobile broadband and long-range massive mtc will come into play. In line with the evolution of 4g and the introduction of 5g, ran architecture is undergoing a transformation: to increase deployment flexibility and network dynamicity, enabling networks to meet increasing performance requirements, while at the same time keeping a lid on the total cost of ownership. The proposed future-proof software- configurable split architecture will be able to support new services, deployed on general-purpose and specialized hardware, with functions ideally placed to maximize scalability, spectrum, and energy efficiency, all while supporting the concept of network slicing. t h e r e q u i r e m e n t s created by extreme mbb, the IoT, and massive mtc call for an alternative to today’s deployment architectures. The changes to architecture include the capability to place selected functions closer to the network edge, for example, and the ability to increase ran resilience. Cost is naturally a factor, as spectrum availability and site infrastructure continue to dominate operator expenditure for wide-area systems. The evolution of ran architecture therefore needs to include measures for enhanced spectrum efficiency that are harmonized with other improvements in the areas of hardware performance and energy efficiency. 4G/5GRAN HOW A SPLIT CAN MAKE THE DIFFERENCE architecture
- 3. VIRTUALIZE, SPLIT, ANDREORGANIZE ✱ JULY 22, 2016 ✱ ERICSSON TECHNOLOGY REVIEW 3 In light of these cost and performance requirements, a number of capabilities are shaping the evolution path of ran architecture: SeamlessRadioResourceManagement Thebestcombinationofanyradiobeamwithin reachofausershouldbeusedforconnectivityacross allaccessnetworktechnologies,antennapoints,and sites.Thiscapabilitywillbeachievedbyapplying carrieraggregation,dualconnectivity,comp,anda numberofmimo andbeamformingschemes. Functionalsplit Some5g requirements—suchasultra-lowlatency andultra-highthroughput—requirehighlyflexible ran architectureandtopology.Thiswillbeenabled bysplittingran functions,includingtheseparation oftheuserplane(up)andthecontrolplane(cp)in higherlayers. Dynamicandsoftware-definedran Thecapabilitytoconfigure,scale,andreconfigure logicalnodesthroughsoftwarecommandsenables theran todynamicallyadjusttochangingtraffic conditions,hardwarefaults,aswellasnewservice requirements.Thiscapabilitywillbeachieved byseparatingoutlogicalnodessuitablefor virtualization(onagpp)anddesigningfunctions thatrequirespecializedhardwaretobedynamically (re)configurableonanspp. Deploymentflexibility Deploymentflexibilityenablesanoperatortodeploy andconfiguretheran withmaximumspectrum efficiencyandserviceperformanceregardlessofthe sitetopology,transportnetworkcharacteristics,and spectrumscenario. Thisisachievedthroughacorrectsplitoftheran architectureintologicalnodes,combinedwiththe future-prooffreedomtodeployeachnodetypein thesitesthataremostappropriategiventhephysical topologyandservicerequirements. Theprocesstoreachthetargetarchitecturewiththe correctsplitinvolvesanumberofsteps: 〉〉 determining the logical functions that comprise 5g ran on a level below 3gpp 〉〉 identifying the latency-critical functions that need to be placed within a few ttis to antenna elements 〉〉 identifying which functions have more relaxed latency requirements Terms and abbreviations bpf — baseband processing function | co — central office | comp — coordinated multipoint | cp — control plane | cpri — Common Public Radio Interface | c-ran — cloud RAN | dl — downlink | epc — Evolved Packet Core | e2e — end-to-end | gpp — general purpose processor | harq — hybrid automatic repeat request | iot — Internet of Things | mac — media access controller | mbb — mobile broadband | mimo — multiple-input, multiple-output | mtc — machine-type communications | nfv — Network Functions Virtualization | nr — next generation rat | oss — operations support systems | pdcp — packet data convergence protocol | pdu — protocol data unit | pgw — packet data network gateway | phy — physical interface transceiver | ppf — packet processing function | rat — radio-access technology | rcf — radio control function | rdc — regional data center | rf — radio function | rlc — Radio Link Control | rrm — Radio Resource Management | son — self-organizing networks | spp — special purpose processor | s-rrm — server rrm | tti — time transmit interval | ue — user equipment | ul — uplink | up — user plane | u-rrm — user rrm | vnf — Virtualized Network Function THE CAPABILITY TO CONFIGURE, SCALE, AND RECONFIGURE LOGICAL NODES THROUGH SOFTWARE COMMANDS ENABLES THE RAN TO DYNAMICALLY ADJUST TO CHANGING TRAFFIC
- 4. ✱ VIRTUALIZE, SPLIT,AND REORGANIZE 4 ERICSSON TECHNOLOGY REVIEW ✱ JULY 22, 2016 RAN domain Device functions OSS MME SGW Radioand antennas PHY control PHY control PHY control L1/ PHY MAC RLC SysArea handling UE handling Frame handling Multipath handling PDCP S1-U S1- MME Radioand antennas Mgmtand analytics Mgmtand analytics Mgmtand analytics Mgmt andSON Figure 1: The logical 4g/5g ran architecture — one level below 3gpp 〉〉 determining where to place anchor points for soft combining, carrier aggregation, and dual connectivity — among the user-plane functions 〉〉 identifying which nodes can be implemented as vnfs ThisprocessisillustratedinFigures 1,2,and3. Figure 1showsthe4g/5g logicalarchitectureata levelbelow3gpp;Figure 2showstoday’s4g split intoan ru andadu;andFigure 3showsthetarget splitarchitecture.Throughouttheprocess,andas aresultofthefunctionaldecomposition,newinter- nodeinterfacesemerge,whosecharacteristics needtobetakenintoconsiderationtoensurethat theunderlyingtransportnetworkcansupportthe variousdeploymentscenarios. Thelogical4g/5g ran architecture Theexternalinterfacesoftheran domain(except totheoss)arestandardizedunder3gpp,asisthe functionalbehavioroftheran domainasawhole. Belowthehigh-levelspecification,3gpp leaves roomforinnovationtoenhancethenetworkwith ran-internalvalue-addfeatures—aflexibilitythat hasoveranumberofyearsresultedincontinuous improvementinmanyareas,includingspectrum efficiency(intheformofschedulingalgorithms, powercontrolalgorithms,andvariousrrm features),energyefficiency,andenhancementsto servicecharacteristicssuchaslowerlatencies.To determinetheoptimalarchitecturalsplit,however, theran architectureneedstobeexaminedwitha finerlevelofgranularitythanthatofferedby3gpp. ran anchorpoints Figure1illustratesthelogicalran architecture, whichforthepurposesofsimplificationshowsthe ul and dl instancesofeachfunctioncombined, andthesolidlinesindicateuserplanefunctions. Inthedownlink,pdus entertheran domain overthes1-u interface(right)andaredeliveredto devices(ontheleft)overtheradiointerface.The multipath-handlingfunctionistheanchorpointfor
- 5. VIRTUALIZE, SPLIT, ANDREORGANIZE ✱ JULY 22, 2016 ✱ ERICSSON TECHNOLOGY REVIEW 5 Baseband processing function Radio function Radio control function RF RCF Device functions OSS MME SGW Radioand antennas PHY control PHY control PHY control L1/ PHY MAC RLC SysArea handling UE handling Frame handling Multipath handling PDCP S1-U S1- MME Mgmtand analytics Mgmtand analytics Mgmtand analytics Mgmt andSON Radioand antennas Packet processing functionPPF BPF Fast S-RRM Fasy U-RRM Device functions OSS MME SGW Radioand antennas PHY control L1/ PHY MAC RLC SysArea handling UE handling Frame handling Multipath handling PDCP S1-U S1- MME Mgmtand analytics Mgmtand analytics Mgmtand analytics Mgmt andSON Radioand antennas DU functionRU function RF BPF Figure 2: Logical ran architecture — present split into an ru function and a du function Figure 3: Logical ran architecture — target split into the functions rf, bpf, ppf, and rcft
- 6. ✱ VIRTUALIZE, SPLIT,AND REORGANIZE 6 ERICSSON TECHNOLOGY REVIEW ✱ JULY 22, 2016 dualconnectivity,whichschedulesindividualpdcp pdus inthesameuser-datastreamtodifferentrlc instances,possiblyondifferentrats.Inthisway, asingle ue cansimultaneouslyreceiveandsend dataoverdifferentradiochannels—forexample, one nr andonelte channel—thatareconnected todifferentsites.Themac functionistheanchor pointforcarrieraggregation,whichschedules mac pdus toeachuseroveramultitudeof4g or 5g carriers.Themac functionhandlescomp and multi-beamtransmissions.Intheuplink,thel1/phy functionperformssoftcombining,themac function aggregates ul dataincarrieraggregation,and multipathhandlingaggregatesdatareceivedfrom dualconnectivity ul datastreams. Theharq loop 3gpp specifiesretransmissionperiodsandresponse timesattheradiolevelbetweenthe ue andthe networkastheharq loop,whichincludes:theair- interfacetransmissiontime,completiontimesfor rf-l1/phy-mac functions,andrf-l1/phy-mac functionsintheue. Theloopresultsinastandardizedround-trip latencybudgetof3msforlte,anddownto200µs fornr.Theran functionsparticipatingintheloop worksynchronouslywiththeair-interfacetti,while thepdcp andmultipathhandlingfunctionfeedand receivepacketstravelingtoandfromtherlc layer asynchronously—whichhasimplicationsforthe splitarchitecture. Controlplanefunctions Runtimecontrolfunctionscangenerallybedivided intothreecategories,dependingonwhetherthey: actonaper-userbasis(u-rrm),controlspectrum onasystemlevel(s-rrm),ormanageinfrastructure andothercommonresources. Theu-rrm functionsincludemeasurement reporting,selectionofmodulationandcoding schemes,per-ue bearerhandling,andhandover execution.Thefunctionsinfastu-rrm actwithin theharq loopandservetheschedulerwith processedreal-timeper-ue information.Incontrast, theu-rrm function(ue-handling)worksonatime scaleof10msandabove,includingbearerhandling, per-ue policyhandling,handoffcontrol,andmore. Functionsthatcontrolspectrumonthesystem levelincluderadioscheduling,distributionof thepowerbudgetacrossactiveues,andsystem- initiatedload-sharinghandovers.Thefasts-rrm operatingwithintheharq loopisresponsiblefor radioschedulingandfunctionsintightcoordination withthemac andrlc.System-areahandlers—such asloadsharing,systeminformationcontrol,and dual-connectivitycontrol—controlspectrumona 10mstimescale,orslower. Functionsthatcontrolinfrastructureand commonresources—otherthanspectrum— includehandlingoftransport,connectivity, hardware,andenergy.Byallowingthecontrol functionsforspectrum,transport,infrastructure, andconnectivitytointeract,aholisticcontrolsystem forran resourcescanbebuilt. Interfacecharacteristics Theran harq looptimebudgetofthreettisis dividedintotimeforprocessing,andtimeforsignals anddatatotraversethevariousinter-function interfaces.Thelesstimespentoninterfacesignaling, themoretimeisavailableforprocessing,which translatesintolowercostforhardwareandfor energyconsumption.Tominimizesignalinglatency, andthusmaximizehardwareefficiency,themac, rlc,andfast-u/s-rrm functionsshouldrunonthe samehardwareinstance.Astrafficmovestotheright inFigure 4,therequirementoninterfacelatency graduallyrelaxes. Thecpri scaleswitheffectivecarrierbandwidth andthenumberofantennaelements.Aninter-site cpri interfacewithjointcombiningatthecentral office(co)can,inmanydeployments,resultinagain inuplinkspectrum.Forlte,thecpri canbeinter- site(afewgbps),butin nr —withwidercarriersand moreantennaelements—aninter-sitecpri would bechallengingfrombothalatencyandbandwidth perspective. Theinterfacebetweentherlc andthemultipath handlerscaleswithuserdataandhasalatency toleranceintheorderofseveralmilliseconds.This interfaceislimitedbytheperformanceofthedual connectivityfeature,whichdegradesgracefullyas
- 7. VIRTUALIZE, SPLIT, ANDREORGANIZE ✱ JULY 22, 2016 ✱ ERICSSON TECHNOLOGY REVIEW 7 RAN domain Device functions CPRI Control interfaces, RTT 10-100ms, moderate data volumes Interfaces contributing to the RAN HARQ loop latency budget User-plane interfaces, latency tolerance 3–5ms Mobile backhaul, delay tolerant up to service requirements OSS MME SGW Radioand antennas PHY control PHY control PHY control L1/ PHY MAC RLC SysArea handling UE handling Frame handling Multipath handling PDCP S1-U S1- MME Mgmtand analytics Mgmtand analytics Mgmtand analytics Mgmt andSON Radioand antennas Figure 4: The logical interfaces in the ran architecture and their characteristics requirements theinterfacelatencyincreases.Thisinterfacecan, therefore,eitherbenodeinternaloranetworked interfacebetweennodesandevenbetweensitesthat arenotmorethan3-5msapart. TheremaininginterfacesinFigure4carryeither slowcontroldata(indicatedbythebluelines)oruser databetweentheran andtheepc (s1-u interface). Atover10ms,thelatencyrequirementsonthese interfacesarequiterelaxed. Hardwarerequirements Controlfunctionsthatareasynchronoustotheradio interfacetendtobesuitableforvirtualizationand vnf deployments,astheyaretransactionbasedand donotinvolveheavypacketprocessing. Ontheotherhand,functionslikemultipath handling,pdcp,ands1-u terminationinvolvepacket processing(encapsulation,headerreading/creation, encryption/decryption,androuting)andcanbe challengingtovirtualize.However,iftheunderlying hardwarecontainscipheringoffloadandpacket- processingaccelerators,virtualizationispossible withoutperformancedegradation,andsothese functionscanbevirtualizedanddeployedinannfv environment. Mostran processingcyclesoccurintheharq synchronousfunctions.Taskslikeuplinkradio decodingandschedulingare,forexample,highly processingintense.Andso,themoreprocessingthat canbecarriedoutintheuplinkdecoding,thebetter theuplinksensitivity,andthemoreprocessingthat canbeallocatedtothescheduler,thebettertheuse ofspectruminboththeuplinkandthedownlink. Reducingprocessingintheharq synchronous
- 8. ✱ VIRTUALIZE, SPLIT,AND REORGANIZE 8 ERICSSON TECHNOLOGY REVIEW ✱ JULY 22, 2016 RUHW SPP GPP Device functions Radioand antennas PHY control Fast S-RRM Fast U-RRM L1/ PHY MAC RLC OSS MME SGW SysArea handling UE handling Frame handling Multipath handling PDCP S1-U S1- MME Mgmtand analytics Mgmtand analytics Mgmt andSON Radioand antennas Mgmtand analytics Figure 5: Preferred execution environments for the various ran functions Figure 6: Hierarchy, instantiation, and inter-node interfaces in the ran split architecture Sys area 4Sys area 3Sys area 2 OSS RCF MME RF RF RF RF RF RF Sys area 1 S1-MME S1-U CC-IBB-CI BB-II BB-UI C1 RF RF RF RF BPF1 BPF2 BPF3 BPF4 PPF1 PPF2 SGW
- 9. VIRTUALIZE, SPLIT, ANDREORGANIZE ✱ JULY 22, 2016 ✱ ERICSSON TECHNOLOGY REVIEW 9 functionsisnotagoodideaifspectrumefficiency istobemaintainedorimproved.Special-purpose multi-corehardwareisbestsuitedtothistype ofprocessing,asitsprice-performanceratiois presentlyfivetimesthatofsingle-corehardware. Andso,harq synchronousfunctionsarelikelyto continuetorunonspecialpurposeprocessor(spp) hardwareforatleastoneortwomoregenerationsof ran hardware. Toavoidflowcontrolissuesbetweenthemac and therlc —andgiventhelevelofinteractionbetween theschedulerandrlc —themac,rlc,andthefast rrm shouldrunonthesamehardwareinstance. Theresultinghardwareenvironmentisshownin Figure 5. Thefunctionsontherightintheillustration(blue area)runongeneralpurposeprocessors(gpps)that includehardwareacceleratorsandcipheringoffload formultipathhandlingandpdcp.Thefunctions inthemiddle(greenarea)runonsppswithmulti- corehardwaresuitableforsupportingfunctionsin theharq loop,andtheradiohardwareisontheleft (yellowarea). Resultingsplitarchitecture Basedonfunctionandinterfacecharacteristics, preferredexecutionenvironment,andspectrum efficiency,thetargetfunctionalcomposition,which isshowninFigure 6,includesthefollowinglogical ran nodes: Packetprocessingfunction—ppf Theppf,whichissuitableforvirtualization,contains user-planefunctionsthatareasynchronoustothe harq loop,andincludesthepdcp layer—suchas encryption—andthemultipathhandlingfunction forthedualconnectivityanchorpointanddata scheduling. Basebandprocessingfunction—bpf Giventhestringentrequirementsforspectrum efficiency,thebpf benefitsfrombeingplacedonan spp.Thebpf includesuser-planefunctionsthatare synchronoustotheharq loop,includingtherlc, mac,andl1/phy,anditisalsotheanchorpointfor carrieraggregation(mac)andsoftcombining(l1/ phy).Thebpf containstheper-tti rrm (fastradio scheduler),andisalsoresponsibleforthecomp,for theselectionofthemimo scheme,andforbeamand antennaelements. Radiofunction—rf The rf requiresspecialradiohardwareand includesfunctionssuchasmodulation,d/a conversion,filtering,andsignalamplification. Radiocontrolfunction—rcf Thercf handlesloadsharingamongsystemareas anddifferentradiotechnologies,aswellastheuse ofpoliciestocontroltheschedulersinthebpfsand ppfs.Attheuserandbearerlevel,thercf negotiates qos andotherpolicieswithotherdomains,andis responsiblefortheassociatedsla enforcement intheran.Thercf controlstheoverallran performancerelativetotheservicerequirement, createsandmanagesanalyticsdata,andis responsiblefortheran son functions.Liketheppf, thercf issuitableforvirtualization. Thelogicalinterfacesare: 〉〉 c1—anevolutionofthecpri interface,thisinterface scaleswitheffectivecarrierbandwidth(carrier bandwidth×numberofantennastreams)withalatency requirementofaroundonetti (1msforlte anddownto 67µsfornr). 〉〉 bb-ui —theuser-planeinterfacebetweentheppf and thebpf,itcarriespdcp pdus,whichscaleaccordingto theamountofuserdatasentbythebpf instancetothe systemarea. 〉〉 bb-ii—theinterfacebetweentwobpf instances,it carriesuserdataforscenariosthatuseinter-bpf carrier aggregation(carrieraggregationovertwocarriers controlledbytwodifferentbpf instances).Thisinterface alsocarriescontroldatafortheinter-bpf comp,scales inlinewiththeamountofuserdatatransmitted,andthe latencyrequirementisthesameasforc1. 〉〉 bb-ci —thecontrol-planeinterfaceforthebpfs,which carriescontrolandanalyticsdatafromthebpf tothe rcf.Thisinterfaceprimarilyscaleswiththevolume ofanalyticsdata,andat10msormore,thelatency requirementsarequiterelaxed. 〉〉 cc-i —thecontrol-planeinterfacefortheppfs,which
- 10. ✱ VIRTUALIZE, SPLIT,AND REORGANIZE 10 ERICSSON TECHNOLOGY REVIEW ✱ JULY 22, 2016 RCF RUHW SPP GPP GPP Antenna location RBS site Functions/ software configuration Hardware deployment across site types 1 st level CO 2nd level CO RDC RF RF BPF PPF MME SGW PGW Figures 7a and 7b: Deployment of hardware and nodes across site types in a classic main-remote deployment — valid for both lte and nr RCF RUHW SPP GPP GPP Antenna location RBS site Functions/ software configuration 1st level CO 2nd level CO RDC RF RF BPF PPF MME SGW PGW
- 11. VIRTUALIZE, SPLIT, ANDREORGANIZE ✱ JULY 22, 2016 ✱ ERICSSON TECHNOLOGY REVIEW 11 carriescontrolandanalyticsdatafromtheppf to thercf.Likebb-ci,thisinterfacescalesprimarily accordingtothevolumeofanalyticsdatatransmitted, andhasrelaxedlatencyrequirementsof10msormore. Inadeployment,eachfunction(rf,bpf,ppf, andrfc)isinstantiated.Aninstanceoftheradio functionswillbeassociatedwithanumberof antennaelementsatanantennasite,andasetofn rf instancesareconnectedtooneinstanceofthebpf. Eachantennaelement(rf)isassociatedwith onebpf.Hence,abpf instancehandlesthecells correspondingtothe rf antennaelementsitis associatedwith.Thesetofcellsunderthecontrol ofabpf instanceisreferredtoasasystemarea. Bydefinition,onebpf instancehandlestheradio transmissionandreceptionoftrafficinitssystem area.Withinitssystemarea,abpf instance alsocontrolsbeamforming,power,spectrum, scheduling,loadsharing,andfastu/s-rrm. Mobilitywithinasystemareaishiddenunder thebpf andnotvisibletotheppf ortheepc.A multitudeofbpf instancesareconnectedtoone instanceoftheppf.Oneppf instanceistherefore associatedwithalargenumberofbpfs,aswellas thetrafficsenttoandbyusersinalargesetofsystem areas.Asthes1-u terminatesintheppf,ausercan movearoundwithinthissetofsystemareasorcells withoutcausingans1orx2handover.Eachinstance ofthercf canhandleasmalloralargesetofppfs— andalltheassociatedbpfs.Inthisway,thercf can keepaholisticviewofanareathatisjustasinglecell, uptoanareaconsistingofthousandsofcells.With thisarchitecture,rrm coordinationandspectrum efficiencywithinasystemareacanbemaximized, usingthefullsuiteofrrm featuresavailable,which laysthefoundationfortheapplicationoffuture innovationsandrrm technologies. Deploymentalternativesandexamples Havingdefinedthesplitran architecture,it ispossibletodescribesomeofthedeployment alternativesitsupportsandtheassociateddynamics ofthesoftware-definedradionetwork.Figures 7a and7bshowadistributedmain-remotemacrosite. Thehardwaredeployedateachsiteisshownin thebottomhalfofeachfigure,whilethetoppart showstheconfigurationofnetworkfunctionsacross thathardware.Thehardwaredeploymentissemi- static,butthenetworkfunctionsare(re)configured usingcommandsormachineinstructions,andare thereforesoftwaredefined. Theantennalocationcontainsradiounit hardwarethathoststherfs.Inthedistributed main-remotedeployment,afiberlinkconnectsthe antennalocationtotherbs mainsiteoveracpri (c1interface).Therbs siteisconfiguredwithan spp forthebpf,andagpp fortheppf andrcf,and isconnectedovers1mobilebackhaultransportto epc gatewaysresidinginamorecentrallylocated regionaldatacenter(rdc).Inadditiontoproviding anexecutionenvironmentfortheppf andrcf,the gpp hardwareoffersavirtualizationenvironment forvnfsandapplications. Thisdeploymentenablescomputingatthe mobileedgeforselectedapplications,users,ordata streamstobemovedtotherbs sitebymeansofa systemreconfiguration—orevenautomatically basedonpoliciesandtraffictriggers.InFigure7b, avirtualpacketgateway—deployedasavnf —is locatedattherbs siterunninginthevirtualization environmentofthegpp.WhileFigures7aand 7bdescribethesamehardwareinstallations,the configurationof7bsupportscomputingatthe mobileedgeintherbs site—duetotheabilityto breakouttrafficinthelocalpacketgatewayfunction. In7a,allthetrafficisbackhauledtothegatewayin therdc.Asthehardwaredeploymentsin7aand 7barethesame,theradio-networkarchitecture differenceiscreatedthroughdynamicsoftware commands.Inthisway,thenetworkarchitecture canadaptaccordingtopoliciesandvaryingtraffic conditions,eitherthroughsoftwareconfigurationor automatically(automationandson)—whichisthe basisforsoftware-definedran. Asecondexample,illustratedinFigure 8,shows atypicallte c-ran deploymentextendedwith main-remotenr.AsFigure 8aillustrates,theradio unithardwareislocatedattheantennalocation, whilethespp andgpp aredeployedinthecentral officesites.Thespp hardwarerunsoneorseveral instancesofthebpf,andthegpp providesthenfv
- 12. ✱ VIRTUALIZE, SPLIT,AND REORGANIZE 12 ERICSSON TECHNOLOGY REVIEW ✱ JULY 22, 2016 Figure 8a and 8b: c-ran deployment with (instance a) a centralized packet gateway and (instance b) a second instance of the pgw distributed to the co site for local breakout of selected traffic NR RUHW LTE RUHW SPP SPP GPP GPP Antenna location RBS site 1st level CO 2nd level CO RDC NR RF NR RF LTE RF LTE RF NR BPF LTE BPF PPF RCF MME SGW PGW Functions/ software configuration Hardware deployment across site types NR RUHW LTE RUHW SPP SPP GPP GPP Antenna location RBS site Functions/ software configuration 1stlevel CO 2nd level CO RDC NR RF NR RF LTE RF LTE RF NR BPF LTE BPF PPF RCF MME SGW PGW 1 PGW 2 Hardware deployment across site types
- 13. VIRTUALIZE, SPLIT, ANDREORGANIZE ✱ JULY 22, 2016 ✱ ERICSSON TECHNOLOGY REVIEW 13 environmentfortheppf andthercf.Compared withthedistributedmacrodeploymentshownin Figure 7a,thelte bpf inthec-ran deployment holdsamorecentralizedposition.Eachinstance ofthebpf coversmoreantennalocations,which resultsinhighspectrumefficiency,asthebpf can usethecompletesetoffastrrm features—including jointcombining,multipointtransmission,and coordinatedscheduling—acrossalltheantenna pointsinthesystemareacoveredbythefirst-level centralofficesite. Thec-ran deploymentrequireshigh-bandwidth fiberforthec1interfacebetweenthebpf andthe rf (cpri fronthaul).Likethedistributedmacro architectureof7b,thec-ran deploymentoffersa gpp environmentforvnfsandapplicationsinthe centraloffice.Thegpp maybepartofadistributed datacenter,inwhichcase,theppf andrcf are deployedasvnfs,whilethespp isdeployedas standalonehardware.Alternatively,thespp can bepartofthedistributeddatacenter,providing specializedhardwareforthebpf —similartothe wayothertypesofdata-centerspecializedhardware canbeusedbyapplicationswithspecialneeds, suchaspacketprocessingorfirewalling.Inthisway, nextgenerationcentralofficescanbeturnedinto acombinationofmobile-edgesitesandbaseband hotels. Theflexiblec-ran architectureillustratedin Figure 9supportsmorecentralizeddeployments comparedwiththec-ran configurationshownin Figure8.Thegpp intheflexiblec-ran architecture isprovisionedatthenextlevelinthehierarchy, movingtheppf andhencethedual-connectivity anchorpointtoamorecentralposition,which enablessmoothdualconnectivitymobility. Spectrumefficiencyisthesameorslightlyimproved, thenumberofdistributeddatacentersdrops, andthemobileedgeisslightlymorecentralized. Thetransportrequirementsofbothc-ran configurationsaresimilar. Figure 10showsanon-premisesarchitecturethat isfullyself-containedusingpicobasestationsandan on-premisesdatacenterhubthatstorescontentand carriesoutprocessinglocally.Inthiscase,allfour ran nodes(rf,bpf,ppf,andrcf)areintegrated ontothesamechip. Theidealsplitarchitecturecontainspoolsof NR RUHW LTE RUHW SPP SPP GPP GPP Antenna location RBS site Functions/ software configuration 1st level CO 2nd level CO RDC NR RF NR RF LTE RF LTE RF NR BPF LTE BPF PPF RCF MME SGW PGW1 PGW2 Hardware deployment across site types Figure 9: Flexible c-ran architecture second- level co for better dual connectivity performance
- 14. ✱ VIRTUALIZE, SPLIT,AND REORGANIZE 14 ERICSSON TECHNOLOGY REVIEW ✱ JULY 22, 2016 hardware(anspp andgpp)strategicallydeployed inselectedrbs and co sites.Instancesofthethree functiontypesbpf,ppf,andrcf —andanyvnfs inthemobilenetwork—aredynamicallycreated, modified,scaled,andterminatedbasedonneedand operatorpolicies.Buildingmobilenetworksinthis software-definedwayresultsinanarchitecturethat: 〉〉 isreliableandresilient—asitenablesfunctionsto relocatefollowingahardware,site,orlinkfailure 〉〉 isflexibleandenergyefficient—asitautomatically adaptstopeaksandtroughsintrafficpatternsand serviceusage 〉〉 reducestimetomarketfornewservicesandnetwork features 〉〉 canmaximizespectrumefficiency(minimizecost forspectrumandsites)giventhegeographyand sitetopologyofthenetwork,throughitsflexibility todynamicallydistributethehubpointsforjoint combining,multipointtransmission,comp,carrier aggregation,anddualconnectivity Conclusions Thedesignofthe4g/5g splitran architecture focusesonincreasedspectrumefficiency,full deploymentflexibility,andelasticity;processing iscarriedoutwhereresourcesareavailableand needed.Thesplitran architectureconsistsof thetwouser-planenetworkfunctions:apacket processingfunction(ppf)andabaseband processingfunction(bpf),togetherwiththe antenna-nearradiofunction(rf),andthecontrol- planeradiocontrolfunction(rcf). Theppfsandrcfscaneachbedeployedeitherin classicalpre-integratednodesorinfullyvirtualized environmentsasvnfsoranycombinationthereof. Bothfunctionsaresuitableforvirtualizationwith existingtechnology,withbenefitstotheppf brought bypacketacceleratorsandcipheringsupportinthe underlyinghardware. Inprinciple,thebpf canalsobevirtualized. However,special-purposehardwareisstillabout fivetoseventimesmoreefficientthangeneral- purposehardwareforthetypeofprocessingthebpf performs,andsoitisexpectedthatthebpf willbe deployedonanspp foroneortwomoregenerations ofhardware. Thercf takesholisticresponsibilityforRadio ResourceManagement,ran analyticsandson, itmaintainspolicyandbearerinformation,and interworkswithnon-ran domainssuchastheepc Pico site Functions/ software deployment On-premises hub 2nd level CO RDC RF RF BPF SGW PGW Local cloud RCF MME PPF PGW Hardware deployment across site types Figure 10: Factory deployment examples using pico 4g/5g base stations (green) and with on- premises breakout possibility
- 15. VIRTUALIZE, SPLIT, ANDREORGANIZE ✱ JULY 22, 2016 ✱ ERICSSON TECHNOLOGY REVIEW 15 Erik Westerberg ◆ joined Ericsson from mit, Massachusetts, the us, in 1996 and is a senior expert in system and network architecture. During his first 10 years at Ericsson, he worked with development of the mobile broadband systems before broadening his field to include the full network architecture. He presently holds the position of chief network architect in Ericsson's Business Unit Network Products. He holds a Ph.D. in quantum physics from Stockholm University, Sweden. author andresourceorchestrationlayers.Thercf canbe centralizedordistributedinaclosedon-premises factorynetwork,forexample.Deployingtheuser- planebpf (processingsynchronoustothetti) andppf (asynchronouspacketprocessing)canbe achievedinavarietyofways,aslongasthebpf is withinonetotwottis fromtheantennapoints.The ppf,ontheotherhand,canbemorecentralized,with adistanceofupto5-7msfromtheradiofunctions. Andsouser-planefunctionscanbedeployedto matchservicerequirements,andmaximizespectrum efficiencyaccordingtothespectrum,transport, andsiteavailability,aswellastheparticularlocal geography. Thesplitarchitectureresultsinthenecessary scalingdimensionstosupport5g usecasesand trafficstructuresinacost-efficientway.Itsflexibility anddecouplingofhardwarefromsoftwareenables asoftware-definedelasticresilientran.Italso guaranteesthatran architectureisfuture-proof. Asanevolutionof 4g ran,thesplitcanbegradually introducedinlinewithbusinessneeds.
- 16. ✱ VIRTUALIZE, SPLIT,AND REORGANIZE 16 ERICSSON TECHNOLOGY REVIEW ✱ JULY 22, 2016 ISSN 0014-0171 284 23-3283 | Uen © Ericsson AB 2016 Ericsson SE-164 83 Stockholm, Sweden Phone: +46 10 719 0000