5G C-RAN Architectures: A Comparison of Multiple Optical ... · 5G C-RAN Architectures: A...

5G C-RAN Architectures: A Comparison of Multiple Optical FronthaulNetworksChathurika Ranaweera 1, Elaine Wong 1, Thas A Nirmalathas 1,2, Chamil Jayasundara 1, and Christina Lim 1

1Department of Electrical and Electronic Engineering, The University of Melbourne, Australia2 Melbourne Networked Society Institute, The University of Melbourne, Australia

@nirmalathas

Why 5G?• The development of the fifth generation (5G) wireless

technology is in progress to address– The increasing demands for high capacity,– Low latency, – Ubiquitous mobile access

• 5G expedited to attain – 1000x higher data volume per unit area– 100x higher connecting devices, – 10x longer battery life and – 5x reduced latency

• Demands will be instigated by next-generation mobile and machine-centric applications.

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Central Office

Macro cell

Key Feature of 5G :Small cells

Small Cells

Capacity Coverage

small cells create an enormous weight in the transport network as it

needs to carry a significant amount of data with a

minimal delay from thousands of cells.

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Why C-RAN ? • Observation: the evolution of radio access network needs to be

complimented by an evolution of the transport network. • One architectural evolutionary solution: Centralised/Cloud Radio

Access Network (C-RAN) architecture.– significantly lower cost– greener communication– supporting advanced

wireless technologiesEg. Cooperative Multi-Point

(CoMP)

Base-BandUnit(BBU)RemoteRadioHead(RRH)

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Challenges in C-RAN• In the current C-RAN

architecture (use in LTE-A): the fronthaul network uses common public radio interface (CPRI) [13] over fiber links.

• Ex: supports 150 Mbps of downlink bandwidth in LTE-A, more than 2 Gbps of optical bandwidth When using CPRI.

• If 5G fronthaul networks use CPRI à

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Architecture Comparison• Three Fronthaul Network Architectures

– CPRI– Physical Layer Split (PLS)– Analogue Radio over Fibre (ARoF)

CPRIandPLS

ARoF

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Bandwidth Calculations - CPRI

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Ns isthenumberofsectorsperRRHNa isthenumberofantennasSf isthesamplingfrequency

Sbw isthesamplingbit-width(I/Q)Be istheratioforthecontrollingoverheadLc isthecodinginducedcapacityincrease

Bandwidth Calculations -PLS

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T T I the transmission time interval (=1mS)M modulation order (=8 i.e. 64QAM)Nsy number of symbol within a TTI (=12) Nsc number of subcarriers (=12)Nrb number of resource blocks (=500)Nmimo number of MIMO streams (=8)

5ResourceBlocksperusersomaximumof100usersconsidered

Comparison of Bandwidth Requirements

• ARoF: required fronthaul bandwidth depends on the wireless carrier frequency and the bandwidth in use, a typical low-cost transceiver can be used to achieve the 5G targeted data rates when 5G uses the frequency range below 6GHz (IF conversion can be used with very low cost component for higher frequencies).

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Comparison: Delay, Advanced Wireless Functions and RRH complexityDelay AdvancedWirelessFunctions Complexityof RRH

CPRI Afewhundredsofμsincludingthepropagationdelay,roundtripCPRIprocessingdelay,andtheotherfronthaulequipment

processingdelays.

Facilitateadvancewirelesscooperationtechnologies

Simple.However, forhighertransmissiondatarates,Fronthaul

needshighdatarateopticaltransceivers.

PLS AnadditionalprocessingdelayattheRRHcomparedtotheCPRI: symbollevel

processingimplementedinRRH(however,additionaldelayislessthanfewμs).

WirelesscodingfunctionsandMAClayerfunctionsarecentralizedinthe

BBU:canfacilitateadvancewirelesscooperationtechnologies

RRHrelatedequipmentandsoftwareneedtobeupgraded.Networkfunctionvirtualization(NVF)

paradigmcanbeusedtoovercomethedifficultyinupgrading

ARoF RRHwillbemoredelayefficientcomparedtotheCPRI.

Fronthaul linkrange willbe lowcomparedtootherarchitectures(howeverstillfacilitate

fewkmthatconfirmwith5GBBU-RRHrange).

Facilitateadvancewirelesscooperationtechnologies

allthewirelesssignalsareprocessedcentrallyatthe

BBU

Simplearchitecture

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Optimization framework finds the cost-optimal deployment of

Fibre Fronthaul + RRHs + BBUs

Deployment Cost comparison

Macro cell

Central Office

BBUs

• Optimal Deployment Cost : ILP-based optimization framework

• The total cost consists of the cost of BBU placement, fronthaul and Deploying RRHs.

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Optimization FrameworkMinimizethetotaldeploymentcostofCRANdeployment

Subject to a range of constraints imposedbyrequirementsofthenetwork such as,• Population coverage• The maximum number of BBUs in one

central office • The maximum distance from a RRH to its

BBU• Fibre connectivity

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Equipment&installationcostsofRRHsandFronthaul

Newfibreroutes,andfibrebundles

installationcosts

Fibrepreparation

Fibreconnectionsatthecentralofficeforusingexistingfibrefacility.

CostofBBUsandtheirinstallation

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Costparameter DescriptionȠs Equipment costofRRHandfronthaulȠri CostofRRHInstallationȠt Fibretrenchingcost/mȠfb Cost ofaFibrebundle/mȠfs CostoffibrepreparationȠe Costofconnectingafibreatexistingfibrefacility

Ƞb Cost ofaBBUȠbi InstallationcostoftheBBUatthefibrefacility

Data Set for Cost Comparison

• 18km2suburbanareainstateofVictoria,Australia

• Population:30,000

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Cost – Summary of Optimal Solutions

Contributionoffronthaul,RRH,andBBUcostwhenthepopulationcoverageis50%and90%

• ThecostvaluesarenormalizedWRTthetotaldeploymentcostofCPRI-basedC-RANunder90%populationcoveragerequirement.

• Conservativeapproach:CPRIusesa1/2compressiontechniquewithoutanyadditionalcost:CPRIrequire40Gbps transceiversinsteadof100Gbps

• PLSandARoF architecturesuses10Gbps transceivers

NormalizedCostValues*

CPRI:Fronthaul 2912

PLS: Fronthaul 200

ARoF:Fronthaul 200

CPRI:RRH 220

PLS:RRH 300

ARoF:RRH 200

BBU 10000

Fibrebundlecost 1

*Normilized tocostoffiberbundles/m

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Summary• We investigated the applicability of different optical fronthaul technologies for

CRAN– CPRI, PLS and ARoF

• Comparatively analysed their ability to fulfil requirements of delay, bandwidth,and cost-effectiveness of 5G CRAN, ability to support advanced wirelesscooperation technologies, and complexity of RRH.

• Comparative cost analyses carried out using developed optimization frameworkshowed that cost-effective fronthaul for 5G could be achieved using PLS andARoF architectures

• Overall, our analyses provide insight into how a future proof fronthaul networkcan be realized for 5G C-RAN.

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Foranymoredetailscsr@unimelb.edu.au

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Variables

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Variable Values DescriptionXi 1 Ifith locationisselectedforthe deploymentofaRRH

0 otherwiseZi 1 Ifith fibrefacilityisselectedforthe deploymentofBBU

0 otherwiseCi,j 1 Ifthere isafibreroutefromith nodetojth node

0 otherwiseYi,j integer Numberoffibresinthepathfromith nodetojth nodeBi 1 Ifith householdiscovered

0 otherwise

Antenna Base-Stations• Multiple Sectors, MIMO, Multiple Bands, Carrier Aggregation – leads

to complexities or complex requirements for backhaul/front-haul

CoreNetwork

Interfa

ce

BaseStatio

nCo

ntrol,

Clockand

Managem

ent

Baseband

Processin

gFunctio

ns

DownlinkDigitalIF

TxInterface

RxInterface

UplinkDigitalIF

…

…

GainBlocks

GainBlocks Du

plex/Switch

…AntennaSystem

…

…

…

…

Inter-basestationInterface

Base-bandUnit(BBU) RemoteRadioUnit(RRU)

Backhaul Fronthaul

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NetworkingofBase-Stations(BSs)Evolutionbasestationarchitectures

Base-Station

SwitchingCentre/

MobileCore

WirelessBack-haul

WirelessFront-haul(RF)

Base-BandProcessing

Unit

RemoteRadioUnit(RRU)

DistributedAntennaSystems

DigitalFiber Links/NetworksFeedingBase-stations

IndustryApproachhasbeenCommonPublicRadioInterface(CPRI)andOpenBase-StationArchitectureInterface

Smallcellsand/orRemoteAntennaTerminals

CloudofBBUs

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Optical-WirelessIntegrationIncreaseinBase-

stationdensitiesduetomoresmallerCells

>85/25km2

Increasingshareofpowerconsumptionof

cellularnetworks~60%

Rapidlyrisingbandwidth

requirementsforbackhaul/fronthaul

Increasedfootprintofinstalledfiberand

planneddeployment(>>180Mkm )

MaturingofopticalTransceiver

(10Gbpsandbeyond)

Pathwaysforloweringthecostof

deployment

Whyoptical– wirelessnetworkintegration

makessense

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Cloud/Virtualisation/Software Defined

FullyCentralisedandVirtualPoolofBBUs PartiallyCentralised

ChinaMobile’sC-RANVirtualNetworkFunction

VirtualisationContainer

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4G-5G:ChallengesandOpportunities

CellDensity10x

RFBandwidth10x

SpectralEfficiency20x

Latency1/10

• AntennaArraysinMassiveMIMO?

• Millimeter-wavesorSpectralfarming

• Virtualisable andSoftwaredefined

• Cloudaccessnetwork• Storageinthenetwork• Secure• Criticalservices

• PhotonicSystemsforMassiveMIMOs

• Microwave/Millimeter-wave/Photonicintegration

• JointNetworkPlanningandOptimisation

• SoftwareDefinedOpticalNetworking

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5G – Early Demonstrations• Use of 1GHz is useful for coverage (rural and indoor) • above 6GHz is useful for very high data rates and

shorter-range connectivity (15GHz, 28GHz, 60GHz, 70-85GHz)

• Samsung: 1.2Gbps transmission at 110km/h speed using 28GHz frequency. The stationary transmission test is up to 7.5Gbps

• Ericsson: 5 Gbps throughput at 15 GHz

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Optical Interfaces - CPRICo

reNetwork

Interfa

ce

BaseStatio

nCo

ntrol,

Clockand

Managem

ent

Baseband

Processin

gFunctio

ns

DownlinkDigitalIF

TxInterface

RxInterface

UplinkDigitalIF

…

…

GainBlocks

GainBlocks Du

plex/Switch

…AntennaSystem

…

…

…

…

Inter-basestationInterface

Base-bandUnit(BBU) RemoteRadioUnit(RRU)

Backhaul Fronthaul

Base-BandProcessing

Unit

RemoteRadioUnit(RRU)

CPRI/OBSAIDigitisedIFoverFiber

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Digital Interface – CPRI/OBSAI

Totalflow=Data+ControlManagement+SYNC

OBSAI/CPRI

DUC

DDC

CFR/DPD

D_Filter

DAC

ADC

ADC

FilterDUC

DDCD_Filter

Filter

LO_1 LO_2

SampleRateConversion Filter

Filter

FilterFilter

FilterFilter

I/Q

I/Q

I/Q

I/Q

RF_1

RF_2

RF_1

RF_2

SFP+

Base-band

AnalogRFunit

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OBSAI Vs CPRIOBSAI CPRI

8B/10Blinecoding 8B/10Blinecoding

upto6.144/3.072Gbps upto3.072Gbps

FixedIQsampleenvelopesizeat16 Programmable8-20indownlink4-20inuplink

Includetransportandapplicationlayers OnlyPhysicalanddatalinklayers

OBSAI CPRI

UserData(IQ) 80% 93.75%

ControlData(O&M) 4% 6.225%

Synchronization(K-char) 0.25% 0.025%

FixedOverheads 15.75% 0%

OBSAI CPRI

LTE10MHz@12bits 4 6

LTE20MHz@12bits 2 3

LTE10MHz@16bits 4 4

LTE20MHz@16bits 2 2

• OBSAI - higher overheads (+15.75%) for enabling flexibility

• CPRI- capacity advantage (+13.75%) for optimized bandwidth allocation

• OBSAI capacity - independent of sample envelope size;

• CPRI - optimized sample envelope size => more carrier space

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