RoF

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UCL DEPARTMENT OF ELECTRONIC AND ELECTRICAL ENGINEERINGWireless Over Fibre NetworksJ.E. Mitchell

Department of Electronic and Electrical Engineering

University College London, London, UK

Support From:OverviewRadio Over Fibre

Generation Techniques Research MAC Layer Research NetworksWhy do things differently?For current radio access(here GSM), large amounts of equipment is located at the antenna siteDataCentral Office

Network

Framing,Channelisation, Modulation, Upconversion, AmplificationWhy do things differently?Data

With fibre-radiotechniques most of the radio processing is moved back to the central office, resulting in a simplified and compact RAUFraming,Channelisation, Modulation, Upconversion, AmplificationCentral Office

FibreNetwork

Simplified Radio Access Unit (RAU)Fibre Radio ArchitectureBase unitData/ optical interface

Optical network

RAU RAU

MobileEntityMERadioCentral OfficeOptical Network

RAU

AirInterfaceOptical RFgeneration and modulation imposition

Optical network andlink impairments

Remote Antenna UnitWhat Services?GSM900MHz1800MHz

UMTS2GHzWLAN

HiperAccess18GHz

MVDS40GHz2.4GHz5.1GHz

WIMAX3.5GHz10GHz26GHz

42GHz LMDS28GHz

MBS60GHz

110Frequency (GHz)RoF uses optical fibre links for distribution of RF signals from a main unit to Radio

Antenna Units (RAU)Britecell: One step ahead technologyBRITECELL: A PROPRIETARY RADIO-OVER-FIBRE TECHNOLOGY WHICH ENABLES A COMPLETE RANGE OF ACTIVE SOLUTIONS TO MEET ANY DISTRIBUTION NEEDS, FROM ENTRY LEVEL TO COMPLEX APPLICATIONS.Plug&play, effortless installation,

environmentally friendly solution formedium-small coverage areasIdeal for complexenvironments, supporting multi-service &

multi-operators networks, enables demanding coverage and capacity solutions

Street level shared applications

improve QoS and reduce environmental impact at a fraction of cost.

RoF @ Sydney 2000 Olympics: the worldlargest system

THE SCENARIO1.8 km by 0,8 km, 500,000 daily attendance

THE TARGET:Extremely high traffic capacity & flexible routing

THE PROJECT All GSM operators in Australia sharing the wireless system

Multi-standard in building and pico-cell wireless cellular infrastructure capable of handling millions of calls during the Olympic events

Installation of multiple layers of wireless in- building and external pico-cell coverage systems (900MHz &1800MHz)

More than 500 remote units installed

Impact of Chromatic Dispersion Intensity Modulationcreates a 3 term optical spectrum Chromatic dispersion changes the phase relationship between the optical carrier and upperand lower sidebands.60 The result is a length dependent fluctuation in the detected signal.Direct Modulation is only applicable for frequencies up to

10GHz

50

40

30

20

10

0

0 5 10

Fiber Length (km)

Power

Penalty

0 dB

-5 dB

-10 dB

-15 dB

-20 dB

Radio over Multimode Fibre

0

A: manufacturer 1, 62.5/125-2

-4

-6

Fibre length = 1 km

(B) (C)

(A)

B: manufacturer 1, 50/125

C: manufacturer 2, 62.5/125

-8

-10

Specified bandwidth = 500MHz

0123456

frequency, GHzSimultaneous distribution of cellular and broadba

at frequencies up to 6 GHz using modified low-cost technologies, including VCSEL, ethernet TX/RXs and multi-

mode fibre.32-QAM radio transmission over multimode fibre beyond the fibre bandwidthWake, D.; Dupont, S.; Vilcot, J.-P.; Seeds, A.J.;

2001 International Topical Meeting on Microwave Photonics, 2001. MWP '01.

Generation TechniquesSingle stage

2-term

Dual stage

Other3-termDirect mod.via a MZI

2-term

Optical

Single

Double Sideband Suppressed Carrier

1 laser

Mode Locked Laser

Optical freq. multiplying

Two

Optical Phase Locked Loop

2 lasers

Optical Feed Forward Modulation

Remote

Up-conv

Optical

Non linearor EAM

sideband

2f or 4f

Diode& Gain Switching

Modelaser

Optical

Freq. Locked Loop

Optical Injection Locking

Effect

utilisation

Spectrum

Sliced 2f

Modulated RFOptical Injection Phase-Lock LoopDetected spectra around 36 GHz, res. B/w: 1 MHz

MasterDFB Laser

36 GHz modulated optical output

-30

-40

-50

-70

-80

-90

-400 -200 0 200 400

SlaveDFB Laser

PIN

Frequency offset from carrier (MHz)

Loop filter

Subharmonicallypumped double balanced mixerElectrical

-7 0

-8 0

-9 0

-1 0 0

OIPLL Reference

12 GHz reference source

Optical

10 0 0 1 0 4

10 5

10 6

10 7

10 8Freq. offset from the 36 GHz carrier (Hz)

Johansson, L.A.; Wake, D.; Seeds, A.J.OFC 2001, Vol. 3, WV3/1-WV3/3, 2001RF Down RF UpRF IN1mm source

1,2

BPFLaser22RF

WDM

EAT

Circ.AntennaOUT

BPF

Photo diode

LNA2Central SiteMicro-Cell Site

Electrical

OpticalKitayama K. et al., Microwave Theory and Techniques, 2000, Vol. 48, No. 12, pp. 2588-2595RF Down IF UpIF1 INIF2 IN

LaserLaser

Photo- diode

BPFIFN IN

Laser

RF IN

WDM

AntennaCirc.IF

BPF

Photo- diodeEOM

LaserMicro-Cell Site

Electrical

OpticalKitayama K., Fiber and Integrated Optics, 2000, 19, 167-186.Optical mm-wave/DWDM OverlayWDM techniques will deliver data to

each antenna sector independently,

maximizing radio efficiency.f1 Separation of IF and mm-wave1modulation allows2 standard WDM sourcesy multiplexing of baseband signalsynfn sharing of high speed modulatorand local oscillator

frequency allocation controlled by

fIF Key is suppressed optical carrierupconversion.

mm-wave up- conversion1n

BTSBTSy yBTS

EDFA

f mm f1f mm f n

10 kmRadio-over-fiber distribution using an optical millimeter-wave/DWDM overlayGriffin, R.A.; Lane, P.M.; O'Reilly, J.J., OFC99

4-f carrier generation

SSB Filter rejection

DSB-SC Filter rejection

180 0

18 GHzfmm/4P.M. Lane, J.J. OReilly,Electronics Letters Vol 30, 16, Aug. 1994 pp. 1329 - 1330

36 GHz

Biasing at maximum transmission can create the spectrum

shown above

Appropriate filtering can then be used to give either a

18GHz or 36GHz signalSEOUC - Dual Channel ExperimentESG DataSource

LaserDiode

LaserDiode

EO Modulator

PA

FBGPDFBGEDFA FSQ40

PDBias9 GHz

Both Channels

Ch 1 Data (18GHz)

Ch2 CW

15Carrier to Noise Ratio (50kHz away)5102100-5

9896IF Down IF UpRF INLaserIF IN

IF OUT

LaserWDM PINPhoto-diode

WDM

PIN Photo- diodeLaser

PIN Photo- diode

PALNA

Circ.

AntennaCentral Site

Electrical

OpticalDRO temp. coeff. 10-6/K 7.5 MHz drift at 60 GHz over -40C to +85 C

Disadvantage: Limited frequency agility.40 GHzLO sourceLO 0IF 1IF 3

MUX 12.8 kmSMFBi-directionalSOA

OADM 1

2.2 kmSMF

01BaseStation 120 , 2, 3IF 2IF 4

DE- MUX

OADM 2

03BaseStation 24Central StationIF Down IF Up Ring ExampleT. Ismail, C-P. Liu, J.E. Mitchell, A.J. Seeds, X. Qian, A. Wonfor, R.V. Penty, I.H. White IEEE Photonics Technology Letters, Vol 17(9) Sept 2005pp.1989- 1991LO DistributionReflected Power at 36GHz1011km19km40km0-5-10-15-20-25-30

7 8 9 1011 1213 1415 16Launch Power (dB)IF Down IF Up, Gbit/s Example0-6 GHz

1570 nm

HubDataSource5 GHz

DifferentialEncoder1 Gbit/ssourceDC PowerSupplyUp-conversion

2.2-km SMF

AUReceived Eye

Wireless Path

40 GHz

LO source40 GHz

LO source

1 bit delay

MS0-2.25 GHzAnalyserDown-conversionTransmission of WiMAX using Optical Up-conversion to K BandOptically generated LO

CWLaserRF Source

fLO/2= 8 GHz

Mach

Zehnder

EDFA

0M U

X12.8 km

SOAPD

FSQ26Vector SignalSMU200A Vector Signal Generator (3.5 GHz)OFDM 16QAM OFDM 64QAM

RF Amplifier

1Laser 1

SMF

AnalyserWDM Network ConceptUMTS cell plan

Operator 2

LMDS cell plan

Operator n

MBS cell plan

Operator n

Operator

1

Operator

2

Operator

nDifferent plans for individual operators

Protocol Independent

Hybrid Fibre Radio access network

Hybrid Fibre Radio Infrastructure

1:N Static Wavelength mapping Single shared by nRAUs Facilitates simulcast operation

PON overlay

Requires optical and

electrical filters

Limited reconfiguration available

Complex upstream

Spectrum Planning within Enhancement band Assuming an EAT similar to the one developed

in [*] which had an optimum photodetection band between 1530-1560nm, and a modulation band within the 1560-1600nm region Exact location of the bands are dependent onthe device manufacture and biasing

(*) Kitayama K. et al., Microwave Photonics 2001 (MWP2001), pp. 73-76.ATM PON

Upstream

Reserved

by ITU-T

ATM PON

Downstr.

~15channels of100GHz

Video

distrib.

~ 4channels of100GHZ12601360 1380

~1460 14801500153915 5015 601565 nmEAT

absorption band

DOWNSTREAM CHANNELS

EAT modulation band

UPSTREAM CHANNELS & Loopback sources

1:1 Static Wavelength mapping Simple mapping of to RAU

No filtering required at RAU

Support RAU capacity increase

Inefficient use of head end resources and increased resources (lasers) required

Careful routing planningrequired1:1 Dynamic Wavelength mapping Simple head-end

mapping with increased efficiency.

No filtering required

blocking possible

Limited routing combinations

1:( 1 or n) Dynamic Wavelength mapping Full, dynamic reconfiguration

possible

Includes all previous schemes

Complex equipment at the

distribution point

Complex control required

Tunable electrical filters at RAU

increase efficiency

Tight vertical integration

Simulcast operationCreation of a Super-Sized Cell

Static: Interesting for Broadcast Networks (MVDS, DVB-T)

Dynamic: Allows low traffic cells to be grouped together to increase the efficiency of the head-end resource use. Control to re-increase capacity difficult.

1:1 Sub-carrierRAU mappingUnique sub-carrier per RAU

Provides traditional cell coverage, with capacity increased by adding extra sub-carriers to a

particular RAUs Inefficient at the head-end

Power control at the RAU required

Hybrid Simulcast/1:1RAU mappingDistribution network allows cells to be either individually address with n sub-carriers, or group together to for a super cell

Optimum use of head-end resources with wide reconfigurability

Protocol Investigations 802.11The Basic Access Method:

The RTS-CTS Method:

Experimental Set-upTCP transmission using the Basic Access method>

Fiber length (m)Insignificant performance loss for first

2km.

Max 13.2 km fibre used in Basic mode.

Max throughput 5.20 Mbps (Downlink)

and 5.11 Mbps (Uplink).

Fiber length (m)050001000066

050001000066

Uplink55

44

33

1 MS, uplink5Downlink

2Basic Access, 802.11b (11, 1)Mbps 25Experimental - Med err. 5% Simulation - Med err 0%1Simulation - Med err 5% 1Simulation - Med err 10%44

331 MS, downlinkBasic Access, 802.11b (11, 1)Mbps

00010203040506070Fiber delay (us)Gradual & steady drop in performance due to additional

2Experimental - Med err 5%Simulation - Med err 0% Simulation - Med err 5%1Simulation - Med err 10%

2fibre delay.

1Sharpdecline(cut-off)in throughput due to expiry of

00010203040506070Fiber delay (us)

ACK_Timeout.

TCP transmission using the RTS-CTS method >

Fiber length (m)020004000600080004Downlink433

Max 8.2 km fibre used in RTS-

CTS mode.

Max Downlink throughput 3.64Mbps and 3.55 Mbps (Uplink).221 MS, downlinkRTS/CTS, 802.11b (11, 1)MbpsExperimental - Med err 5%

Fiber length (m)0200040006000800044Uplink1Simulation - Med err 0% 1Simulation - Med err 5%Simulation - Med err 10% 3300010203040Fiber delay (us)Downlink performance follows a similar trend to Uplink due to having

221 MS, uplinkRTS/CTS, 802.11b (11, 1)MbpsExperimental - Med err. 5%1only one Mobile Station.

Sharp decline (cut-off) in throughput

Simulation - Med err 0% 1Simulation - Med err 5% Simulation - Med err 10%due to expiry of CTS_Timeout.

00010203040Fiber delay (us)TCP, UDP and MAC maximum achievable throughput > Basic Mode >

Simulation >

Insignificant performance loss over 13.2 km of fibre (in case of employing UDP

and MAC Max throughput).

The MAC Max achievable throughput is 6.1 Mbps (Downlink) which is very close to the case where UDP protocol is used (5.9 Mbps).

Fiber length (m)The TCP throughput is 5.2 Mbps(Downlink).

Sharpdecline(cut-off)in

5000 10000 15000

Downlink6 6

ACK_Timeout.4 4

3 Basic Access, downlink 3802.11b, (11, 1)MbpsTCP2 UDP2MAC maximum achivable throughput1 1

0 20 40 60

Fiber delay (us)Vertical IntegrationRADIO CAPACITY PLANNING ISSUESDIFFERENT RADIO PROTOCOL COVERAGE ISSUESWAVELENGTH AGILE OPTICAL NETWORKSSCMA

WDMA

CDMA

TDMA

OPTICAL MULTIPLE ACCESS TECHNIQUESNT RF

mm-WaveOoptical sourceECLASSICAL FIBRE RADIOMETROPOLITAN AREA AND ACCESS NETWORK PHYSICAL TOPOLOGIESConclusionPrior to the widespread deployment of fibre radio over a wide area important architectural issues must be resolved namely, The need for fibre radio to coexist on the same fibre infrastructure with other fibre radio systems or with other services; i.e. the development of suitable WDM operation and wavelength sharing schemes;

The need for WDM fibre radio to inherently support and facilitate the flexible reconfiguration of capacity in the radio network;

The need for future wireless networks and systems to be fibre radio network capability aware

The need for the design of a vertically and horizontally integrated network.

Fixed Network

Carrier Frequency (GHz)

relative response, dBe

nd services

Signal power (dBm)

Phase noise (dBc/Hz)

RF IN

mm source

LNA

Central Site

Router

Air

Interface

y

Router

90

36GHz

18GHz

Power (dBm)

1552.5

-15

94-2592

90

-35

88

-4586

0102030401549.51550.51551.5Length (km)Wavelength (nm)

CNR (dBc/Hz)

LO

Micro-Cell Site

RefelctedPower (dBm)

MUX

DMUX

Throughput (Mbps)

Throughput (Mbps)

Throughput (Mbps)

Throughput (Mbps)

7 7

5 5

Throughput (Mbps)

BB