WIRELESS ACCESS USING MICROWAVE
PHOTONICS
Alwyn Seeds
Dept. of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, U. K., Tel. +44 20 7679 7928, Fax. +44 20 7388 9325, [email protected]
Outline
• Introduction; commercial systems.• Broadband access.• Millimetre-wave systems; architecture options.• Local oscillator signal generation; Optical Injection Phase Lock
Loop (OIPLL).• Future systems; Wavelength Division Multiplex (WDM).
Commercial Fibre-Radio Systems
Circ.
AntennaLNA
PAPIN
Photo-diode
PINPhoto-diode
1.3µmLaser
1.3µmLaser
16 ChannelsTransmit/Receive
CENTRAL SITE BASE STATION
ElectricalOptical
Sydney Olympic Games• Tekmar BriteCell™• In-building and external pico-cell• Multi-operator system (3 GSM operators)• Multi-standard radio (900/1800 MHz GSM)• > 500 Remote Antenna Units• 0.8 x 1.8 km• Low RF power distributed antenna system• Dynamic allocation of network capacity• 500 000 wireless calls on the opening day
Application ExampleApplication Example
• Unreliable coverage from outdoor cells
• Dedicated indoor capacity• Fewer access points (APs)
needed compared to distributed radios
• Centralised managementand hand-over
remoteantenna
unit
fibreopticcable
opticaltransceiver
hub
APs andswitch
Distributed Antenna Systems
Evolution to Broadband Traffic
1.4
2.3
216
8
1080
650
0.064
0.01 0.1 1 10 100 1000 10000
Voice
CD Quality Stereo Audio
Professional Quality Stereo Audio
Compressed Digital Video (MPEG)
Studio Quality Digital Video
Medical Imaging Quality Digital Video
Studio Quality Digital HDTV
Data Rate (Mb/s)
Future Broadband Access
• Connections to mobile and portable terminals.
• Reduced cost final drop in areas of medium population density.
• Date rates evolving from 64 kb/s to 100 Mb/s+.
• Carrier frequencies evolving from UHF to millimetre-wave —UK allocations in 5.3, 28, 42, 48 and 60 GHz bands.
MillimetreMillimetre--Wave over Wave over FibreFibre: Systems Concept: Systems Concept
Remote Base Station,Video distribution
Remote Base Station,Mobile communication
(Optic/RF and RF/Optic converter)
Central Station(Optical transmitter
and receiver)
OPTICAL FIBRE
•Millimetre-wave radio provides high bandwidth capacity.•Limited propagation distance allows well defined microcells and frequency re-use.•Inexpensive mm-wave equipment is essential.•Base stations and central station are connected by low-loss optical fibre.•Possible applications are:
High resolution mobile multimedia servicesWireless Video Distribution SystemsWireless Local Area Networks (WLANs)
Modulation Frequency LimitsModulation Frequency Limits
• Direct Modulation (1,550 nm): > 25 GHz [Morton et al, Electron Lett., 1994, 30, pp. 2,044-2,046]
• External Modulation: > 75 GHz[Noguchi et al, J. Lightwave Technol., 1998, 16, pp. 615-619]
• Detectors: > 300 GHz[Ito et al, Electron Lett., 2000, 36, pp. 1,809-1,810]
Cell Site Transceiver mm-wave Fibre-Radio System
Electrical
OpticalCentral SiteCentral Site Micro-Cell SiteMicro-Cell Site
Antenna
Multi-channelMod.and TX
PINPhoto-diode
1.3µmLaser
Circ.
PINPhoto-diode
1.5µmLaser
WDMWDM
Bas
eban
dIN
/OU
T
Disadvantage: Cell Site Complexity.
Multi-channelRX and Demod.
Cell Site LO mm-wave Fibre-Radio System
Electrical
OpticalCentral SiteCentral Site Micro-Cell SiteMicro-Cell Site
AntennaLNA
PAPIN
Photo-diode
1.3µmLaser
Circ.LO
PINPhoto-diode
1.5µmLaser
WDMWDM
IF IN
/OU
T
DRO temp. coeff. 10-6/K ⇒ 7.5 MHz drift at 60 GHz over -40°C to +85 °C Disadvantage: Limited frequency agility.
Central Site LO mm-wave Fibre-Radio System
Electrical
OpticalCentral SiteCentral Site Micro-Cell SiteMicro-Cell Site
AntennaLNA
PAPIN
Photo-diode
1.3µmLaser
Circ.
PINPhoto-diode
1.5µmLaser
WDMWDM
IF IN
/OU
T
Diplexer
RFLO
LO
Optical HeterodyningOptical Heterodyning vsvs. Modulators. Modulators
Advantages:• High generated frequency possible,
limited only by photodetector bandwidth.• High detected power, all optical power
contributes to generated mm-wave carrier. • Single sideband modulation, low
sensitivity to chromatic dispersion.
Disadvantage:• Need for control for phase noise
reduction, can result in a complex system
λ1 λ2
Photo-detector
ƒmm=ƒλ1-ƒλ2
OIL OIL -- OOPTICAL PTICAL IINJECTION NJECTION LLOCKINGOCKING
Advantages:•Wide linewidth lasers usable.
•Good phase noise suppression.
Disadvantages:•Limited locking range. •Optimum phase noise
suppression at only one point of slave laser detuning relative to the free-running frequency.
Master Laser Optical
output
Sub-harmonicReference
Optical Frequency
fmm-wavefref
Slave Laser
ML SL
Optical Phase Lock Loop (OPLL)
Master Laser
Photo/ Phase det.
Loop filter
Optical output
Reference
Advantages: Wide locking rangeGood tracking capabilities
Disadvantages: Narrow linewidth lasers or low delay electronics andshort optical path needed.
Slave Laser
Lase
r lin
ewid
th (M
Hz)
Loop delay (ns)
Requirement for 0.01 rad phase error variance
2
0 .0 1
0 .1
1
1 0
0 .1 1 1 0 1 0 0
ElectricalOptical
LO Generation by Optical Injection Phase Lock Loop (OIPLL)
PIN
Loop filter
36 GHz modulated
optical output
Master DFB Laser
Slave DFB Laser
12 GHz reference source
Subharmonically pumped double balanced mixer Electrical
Optical
Spectral Purity of Generated CarrierSpectral Purity of Generated CarrierL. Johansson (UCL)
Sign
al p
ower
(dB
m)
Frequency offset from carrier (kHz)
Detected spectra around 36 GHz,res. B/w: 300 Hz
Sign
al p
ower
(dB
m)
Frequency offset fromcarrier (MHz)
Detected spectra around 36 GHz, res. B/w: 1 MHz
Spectral Purity of GeneratedSpectral Purity of Generated CarrierCarrier[L. Johansson (UCL)]
-110
-100
-90
-80
-70
1000 104 105 106 107 108
Frequency offset from the 36 GHz carrier (Hz)
Phas
e no
ise
(dB
c/H
z)Phase noise of generated carrier,
relative to reference source
OIPLLReference
68 Mb/s DPSK Transmission Experiment
36 GHz, 68 Mbit/s 3π/2-DPSK modulated optical output
65.0 km SSM fibre
PIN
37.8 GHz
36 GHz 1.8 GHz
BERdetector
Spectrumanalyser
Oscillo-scope
68 Mbit/s223-1 PRBS 12 GHz
OIPLL
RX
τd
DifferentialEncoding
TX
[L. Johansson (UCL)]
Detected Eye and Spectra
1m of fibre, BER < 10-10.
65 km of fibre, BER ~10-9
-70-60-50-40-30-20-10
-204-136-68 0 68 136 204
0 km25 km40 km65 km
Frequency offset (MHz)0 8 16 24 32 40 48 50
0 8 16 24 32 40 48 50
Time (ns)
Time (ns)
Det
ecte
d po
wer
(dB
m)
BER Versus Received Optical Power
• Transmission over up to65 km of fibre.
• No optical amplification required.
• No fibre dispersion compensation required -10
-8
-6
-4
-2
0
-24 -22 -20 -18 -16
0 km25 km65 km
Received optical power (dBm)
Log
(BER
)
[L. Johansson (UCL)]
• 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• Dual ring architecture using
OADM being trialled by Tekmar Sistemi
Emerging Technologies: WDMEmerging Technologies: WDM
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/ER
F SW
ITCH
OPT
ICAL
MU
X
Remote Up- and Down-Conversion
1.8 GHz transceiver
1.8 GHz transceiver
Up and down-
conversion
mm-wave Optical receiver
Control station
Antenna unit
155 Mbit/s data
WDM DEMUX
WDMMUX
mm-wave-modulated
optical source
ElectricalOptical
WDM mm-Wave Fibre-Radio DistributionSystem
MU
X / D
EM
UX
HeterodyneOptical Source
(OIPLL)
LIN. LASER
LIN. LASER
RX
RX
BIDIRECTIONALOPTICAL
AMPLIFIEROADM
ANTENNASITE
λλλλ0 λλλλ1 λλλλ3
IF1T
IF2T
IF1R
IF2R
λλλλ0
λλλλ1
λλλλ2
λλλλ3
λλλλ4
ElectricalOptical
CII Wireless over Fibre: Objectives
• Study technologies for achieving Gb/s transfer rates using millimetre-wave over fibre infrastructure.
• Investigate low-cost wavelength division multiplex (WDM) technology to place wireless overlay on single mode fibre infrastructure.
• Study seamless wireless hand-over in multiple antenna systems.
• Study implications of wireless over fibre networks for wireless protocols.
Conclusion• Fibre-radio is established as a technique for improving cellular radio
coverage, particularly for in-building and multi-operator applications.• Expanding demand for broadband services such as IEEE 802.11x
requires microwave and millimetre-wave radio systems, with consequent small cell sizes. Fibre-radio simplifies antenna units, with most equipment remoted to the central site, allowing centralised management, security and resource sharing.
• Fibre-radio distribution networks are signal format transparent enabling future-proof multi-operator and multi-service usage. The wide transmission bandwidth is attractive for UWB and other future wireless systems.
• The main future challenges are to provide high volume, low-cost opto-electronics technology and to develop wireless protocols which allow optimally for hand-over and antenna remoting.
Acknowledgements
• EPSRC OSI Broadband Radio Over Fibre project: (Leif Johansson), University of Kent (Dr. N. J. Gomes), Nortel, BT.
• EPSRC OSI Passive Integrated Picocells project: (Chin-Pang Liu); Imperial College (Professor G. Parry), Bookham, Corning.
• EPSRC OSI Wavelength Multiplexed Bilateral Linearised Optically Fed Wireless Systems project: (Chin-Pang Liu); University of Cambridge (Professor R. V. Penty/Professor I. H. White), Agilent.
• EPSRC/DTI LINK Fibre Radio for In-Building Distributed Antenna Systems project: (Chin-Pang Liu); University of Cambridge (Professor R. V. Penty/Professor I. H. White), Agilent, Remec, ZinWave.
• EU FP6 GANDALF project.
