Recent Trends in Radio over Fibre for Wireless Access

David Wake

Outline

• Introduction• Microwave Photonics Inc.• Radio over fibre

• Applications

• Technologies• Current• Emerging

• Summary & conclusions

Microwave Photonics

• MP• Headquarters located in

Santa Monica, CA• Product portfolio based on

radio over fibre

• ADG• Advanced Development

Group located in Suffolk, UK• Responsible for R&D within

MP • future products• IPR generation

Radio over Fibre

• What?• transmission of radio signal over optical fibre link• semiconductor lasers and photodiodes

• Why?• extended reach compared to coax

• typically 15km over single mode fibre• secure transmission• simplification of remote antenna unit

• small, light, low power units• easier maintenance and installation

• centralisation of complex electronics• simpler management, higher security • equipment in controlled environment• trunking efficiency gains• dynamic capacity allocation

5

Radio Systems

• Private Mobile Radio• TETRA

• Cordless• DECT

• Cellular• 2G (GSM); 3G (UMTS)

• Wireless LAN• IEEE802.11b/g/a

TETR

A

GSM

900

GSM

1800

DEC

TU

MTS

IEEE

802.

11b/

g

IEEE

802.

11a

0.1 1 10

frequency, GHz

Analogue Fibre Optics

electrical-opticalconverter

(e.g. laser diode)

optical - electricalconverter

(e.g. PIN photodiode)

L

I

I

L

• Analogue or Digital modulation of radio carrier

• FM, FSK, PSK, QAM• Protocol agnostic

• Radio carrier is analogue waveform

• Optical transmission of radio signals is therefore analogue

Link Design

PD

L

L

PDBTS

Tx

Rx

Tx

Rx

REMOTE ANTENNA UNITCENTRAL UNIT20km

LNAG1= 30 dBNF1= 2 dB

TOTAL LINKGtot= 5 dB

NFtot= 10 dB

FIBRE LINKG2= -25 dBNF2= 40 dB +

Silica Fibre Attenuation

0

0.5

1

1.5

2

800 1000 1200 1400 1600 1800

wavelength, nm

fibre

att

enua

tion,

dB/

km

0

0.5

1

1.5

2

800 1000 1200 1400 1600 1800

wavelength, nm

fibre

att

enua

tion,

dB/

km

1550nm1310nm

Primary coated fiber (1mm)

Weight: 2 kg/km

Bend radius: 3cm

Loss: <0.5dB/km @ 6GHz

Coaxial Cable Attenuation

0

200

400

600

800

1000

1200

1400

0 1000 2000 3000 4000 5000 6000 7000

frequency, MHz

atte

nuat

ion,

dB/

km

RG-142

RG-214

RG-214 (1/2 inch)

Weight: 200kg/km

Loss: 730dB/km @ 6GHz

Outline

• Introduction• Microwave Photonics Inc.• Radio over fibre

• Applications

• Technologies• Current• Emerging

• Summary & conclusions

Applications

• In-building voice & data• Office buildings• Airports, Shopping Malls• Campus

• Base-station hotels• Shared infrastructure• Dense urban• Difficult deployments

• Fixed wireless access• LMDS deployments• FTTA (Radio DP)

• Secure communications• Military installations

• Temporary networks• Emergency services / military

In-building Voice & Data

• Unreliable coverage from outdoor cells

• Dedicated indoor capacity

• Fewer RF transceivers needed compared to distributed radios

• Protocol agnostic• Multiple protocol

remoteantenna

unit

fibreopticcable

opticaltransceiver

hub

centralbase

station

Base Station Hotels

BTS 1

BTS 2

BTS 3

BTS n

E/O

E/O

E/O

E/O

O/E

O/E

O/E

O/E

< 10 milesRF C

OM

BIN

ER

POW

ER S

PLIT

TER < 500ft

Low visual footprintSimple maintenanceTrunking efficiency gainsDynamic capacity allocationMultiple servicesSimple upgrading

Dark fibre!

Fixed Wireless Access

• Local Multipoint Distribution System (LMDS)• a broadband wireless point-to-multipoint system operating above 20 GHz

that can be used to provide voice, data, Internet, and video services

• Radio over Fibre• for connecting the base-

station unit to multiple remote microwave transmission and reception systems

• consolidation of digital equipment, resource sharing, reduced service costs, rapid deployment …

• in early stages of design process for vendors and standards bodies

Outline

• Introduction• Microwave Photonics Inc.• Radio over fibre

• Applications

• Technologies• Current• Emerging

• Summary & conclusions

Current Technologies

Added complexity (cost) at remote unit. Can use pre-installed fibre.

ADCDigivanceDigital over MMF

Simple remote unit but relatively expensive optics. Uses specially installed fibre.

AndrewBriteCellRF over SMF

Added complexity (cost) at remote unit. Can use pre-installed fibre.

LGC Wireless

LGCellIF over MMF

CommentsCompanyExampleType

Emerging Technologies

• Passive remote antenna units

• RoF using multimode fibre

• RoF using WDM

• RoF using VCSELs

• Millimetre wave RoF

• Switched RoF

passive RAUs RoF using MMF

RoF using WDMRoF using VCSELs

mm-wave RoFswitched RoF

Passive Remote Antenna Units

• Electroabsorption transceiver• acts as photodiode for downlink• acts as modulator for uplink

• Low power applications• Applications where remote

power provision is difficult or impractical

10-1-2-3-4-50.0

0.1

0.2

0.3

0.0

0.3

0.6

0.9

Bias (V)

Tran

smis

sion

Res

pons

ivity

(A/W

)

downlink fibre

uplink fibre

CENTRAL UNITPASSIVE REMOTE

ANTENNA UNIT

EAT

laser

photodiode

Passive RAU Demonstration

dual fibre link

Ethernet

PSTN

WLANaccess point m

ultip

lexe

r+

circ

ulat

orDECTbase unit

opticalreceiver

opticalsource

Passive EAT Radio Range

• Forward link is power limited• output power typically -20dBm

• optical source power = 10mW• OMI = 0.5• fibre loss = 3dB• EAT responsivity = 0.5A/W

• Reverse link is noise limited (SNR)• noise figure typically 50dB

• laser RIN = -150dB/Hz• EAT efficiency = 3dB/V

• Radio range (reverse link limited) of around 7m• indoor, single floor with obstructions (Motley-Keenan model)• IEEE802.11b wireless LAN system @ 11Mb/s

Radio Range Enhancement

• Device optimisation• e.g. EAT saturation power, insertion loss,

modulation efficiency• Circuit optimisation

• e.g. better impedance matching between antenna and EAT

• System optimisation• e.g. twin optical source configuration

10 - 20dB improvement in transmit power and noise figure

radio range increase to 20m

Example Deployment Scenario

Wireless Home Broadband Distribution System

• protocol independent• new services easily introduced

• no remote power provisioning• simple installation, emergency function

• low power• mitigates interference and health concerns

• low maintenance• user replaceable

• high security• no expensive hardware in customers premises

passive EAT unit

oe

access unit

optical transceiver

optical fibre pair hometelephone exchange

Resilient Links and Networks

• Single mode fibre is difficult to connect repeatably

• Multimode fibre is easier to connect and reconnect but has low bandwidth

• Recent developments at MP to extend bandwidth of multimode fibre

• Simple and repeatable high performance deployments refractive

index

n2n1

single mode fiber

graded-indexmultimode fiber

n2n1

Enhanced MMF Transmission

coaxial cable reference Fibre: 1km 50/125Specified

bandwidthis 500MHz!

Modulation: 32QAMFrequency: 2 GHzSymbol rate: 2 Msym/s

First radio frequency transmission over multimode fibre

RoF using WDM

• Efficient usage of metropolitan fibre base for BTS hotel concept

• Neutral host, multi-operator

• Typically 8 x 200GHz

• Full RF bandwidth per wavelength

• Flexible service provision

BTS 1

BTS 2

BTS 3

BTS n

E/O

E/O

E/O

E/O

O/E

O/E

O/E

O/E

RF

COM

BIN

ER

POW

ER S

PLIT

TER

BTS 1

BTS 2

BTS 3

BTS n

E/O

E/O

E/O

E/O

O/E

O/E

O/E

O/E

RF

SWIT

CH

OPT

ICAL

MU

X

RoF using VCSELs

1 m

100 m

300 m

97dB.Hz2/3 at 2GHz

Source: C. Carlsson, Chalmers University, Sweden

millimetre-wave RoF

• dispersion problems at high frequencies• standard fibre: 17 ps/nm/km at 1550nm• causes time lag between carrier and

sidebands• beat components interfere at regular

intervals along fibre• 3 dB rf signal degradation for double

sideband modulation • 6 km at 20 GHz• 0.7 km at 60 GHz

single sideband modulation

SSB using dual-electrode MZM

Optical SSB Generator

MZM

ElectricalOptical

Optical Input

RF Input

Optical Output

DC Bias

measuredoptical spectrum

f = 36.86 GHzθ = π/2

Wavelength (nm)

Opt

ical

Pow

er (d

Bm

)

-55

-15

1552.7 1553.7G.H. Smith, et al., Electronics Letters, Vol. 33, pp.74-75, Jan. 1997.G.H. Smith, et al., IEEE Trans. Microwave Theory Tech., Vol. 45, pp. 1410-1415, Aug. 1997.

Overcoming Fibre Dispersion

-40

-30

-20

-10

0

10

0 2 4 6 8 10 12 14 16 18 20

RF

Pow

er L

oss

(dB

)

Frequency (GHz)

Measured SSBMeasured DSBPredicted DSB

L = 80 km

G.H. Smith, et al., Electronics Letters, Vol. 33, pp.74-75, Jan. 1997.G.H. Smith, et al., IEEE Trans. Microwave Theory Tech., Vol. 45, pp. 1410-1415, Aug. 1997.

Radio Switching

• Switching provides:

• Real-time• software controlled• Protocol

independent• Service provisioning• Time of day

scheduling• Congestion mgt• Neutral host• Basestation

resilience• Fault recovery

BTS13G

BTS23G

BTS3GSM

WirelessLAN

BTS4

GSM

Area 1 Area 2 Area 3

CAPACITY SWITCH

Summary & Conclusions

• Radio over Fibre has compelling benefits for current applications

• Emerging Radio over Fibre technologies• Passive remote antenna units for short range wireless apps• Multimode fibre deployments for link and network resilience• VCSELs for low cost deployments• RoF using WDM for efficient use of metro fibre• mm-wave systems for future broadband wireless• Radio Switching for ease of use (O&M savings)

• Radio over Fiber has enormous potential for future broadband wireless applications

Questions ?