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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 ?
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