MTM’99 Workshop

Heidelberg, 25 February 1999

How big is a passive picocell ?

David Wake

BT Laboratories

UK

MTM’99 Workshop

Heidelberg, 25 February 1999

introduction

• work is based on results of EURESCOM Project P816

– evaluation of technology for hybrid optical - radio networks

• passive picocell is one potential technology identified in this project

– novel concept using unpowered remote optical - radio transceiver

• important question: what is the radio range without amplifiers ?

– i.e. how big is a passive picocell ?

MTM’99 Workshop

Heidelberg, 25 February 1999

outline

• what is a passive picocell ?

• how does it work ?

• what are the benefits ?

• what are the potential applications ?

• how big is a passive picocell ?

– second generation cellular (DCS1800)– third generation cellular (UMTS)

MTM’99 Workshop

Heidelberg, 25 February 1999

what is a passive picocell ?

• a small radio cell formed using a fibre-supported antenna unit that is :

– small, light and unpowered

– multiband capable– upgradable and

reconfigurable from central location

MTM’99 Workshop

Heidelberg, 25 February 1999

how does it work ?

• electroabsorption modulator transceiver

– acts as photodiode for downlink

– acts as modulator for uplink

– connected directly to antenna

– can operate without bias voltage

laserdownlink fibre

photodiode

EAM

uplink fibre

CENTRAL SITE REMOTE SITE

MTM’99 Workshop

Heidelberg, 25 February 1999

demonstration system

central site

dual fibre link

Ethernet

PSTNpicocell

passive optical transceiver passive base station

radio LANaccess point

opticalreceiver

opticalsource

mul

tiple

xer

+ c

ircu

lato

rDECTbase unit

MTM’99 Workshop

Heidelberg, 25 February 1999

what are the benefits ?

• simple installation

• low maintenance

• multiband, multisystem

• easily reconfigured and upgraded

• simple dynamic radio resource control

• low total network cost ?

MTM’99 Workshop

Heidelberg, 25 February 1999

what are the potential applications ?

• indoor and outdoor

• public and private

• cellular, cordless, fixed radio access, wireless LAN

• picocells, microcells

• urban, in-building

• offices, factories, warehouses, railway stations, airports, sports stadia, ...

MTM’99 Workshop

Heidelberg, 25 February 1999

how big is a passive picocell ?

• relies only on rf power available after photodetector

– optical system parameters used to compute power

• cell size depends on propagation environment and sensitivity of terminal

• two systems analysed (DCS1800 and UMTS)

• two propagation environments considered

– open, line-of-sight (power reduces with square of distance)

– cluttered, non line-of-sight (power reduces with cube of distance)

MTM’99 Workshop

Heidelberg, 25 February 1999

important optical parameters

• EAM responsivity 0.3 A/W

• EAM efficiency 0.5 /V

• EAM insertion loss 7 dB

• photodiode responsivity 1 A/W

• fibre insertion loss 3 dB

• source optical power main variable

MTM’99 Workshop

Heidelberg, 25 February 1999

important radio parameters

DCS1800 UMTS

• terminal transmit power +20 dBm +20 dBm

• terminal sensitivity -100 dBm -110 dBm

• optical modulation depth 20% pc 50% pc

• antenna gain 8.5 dB 8.5 dB

• fade margin 10 dB 10 dB

• path loss exponent secondary variable

MTM’99 Workshop

Heidelberg, 25 February 1999

cell size equations

n

mr

amdmfod

fp

cgZMRgpr

/1

22

22222

....32

......

n

br

pmpmmfoamtu

fp

ZZRggpgcpr

/1

22

222422

....16

.........

MTM’99 Workshop

Heidelberg, 25 February 1999

results - DCS1800

10.0

100.0

1000.0

0 10 20

optical power, mW

range,

m

NLOS

LOS

MTM’99 Workshop

Heidelberg, 25 February 1999

results - UMTS

10.0

100.0

1000.0

0 10 20

optical power, mW

range,

m

NLOS

LOS

MTM’99 Workshop

Heidelberg, 25 February 1999

conclusions

• emerging new technology for picocells

• important benefits

– installation, maintenance, upgrading, reconfiguring, dynamic resource allocation

• how big is the picocell ?

– DCS1800: 52m LOS 14m NLOS– UMTS: 374m LOS 52m NLOS

• powered version for larger range ?

• next major question - cost