Transcript Signal Processing - Micro/Nano

Thursday, January 10, 2008
Microwave Photonics Applications:
Radio-over-Fiber
Christina Lim
ARC Special Research Centre for Ultra-Broadband Information
Networks (CUBIN)
Department of Electrical and Electronic Engineering,
The University of Melbourne, Victoria 3010, Australia
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Outline
• Motivation
• Wireless communications
• Cellular wireless networks
• Wireless LANs
• Broadband fixed wireless access operating at higher frequencies
• Fiber-feed backbone networks
• Merging of wireless and wired network infrastructures
• Network architectures
• Wavelength division multiplexing
• Optical signal transport schemes and required hardware
• Techniques for improving optical spectral efficiency
• Antenna base-station technologies
• Signal impairments
• Challenges
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Bandwidth and Frequency Allocation
Mobility
3G
Phase 1
Cellular
phone
- GSM
- PDC
3G (3GLTE/4G/??)
Phase 2
mobile
up to 144 kb/s
Pedestrian
up to 384 kb/s
P
H
S
Cordless
mobile
up to ? Mb/s
Indoor
up to 2Mbit/s
Wireless Wireless
LANS
Pedestrianportable
> 20Mb/s
LAN
FWA (Fixed Wireless Access)
0.1
1
Broadband
Wireless
Access
(BWA)
10
100
1000
Information Rate (Mbit/s)
110 MHz
3G
1.8-2.1GHz
1100 MHz
> 2GHz
> 2GHz
LMDS
28-32GHz
ECE282 “Microwave Photonics” 2008
37- 42 GHz
55-66 GHz
University of California, San Diego
Frequencies for Wireless
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Wireless Trend
• Convergence of cellular network and fixed
wireless access
• High bit-rate + mobility
• Frequency spectrum congestion
• Improve coding – more efficient spectral usage by
increasing no. of bits per hertz
• Reduce cell size – increase capacity by limiting
number of users per cell
• Moving up in frequency band
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Radio Signal Propagation
Propagation loss is high
100.00
at mm-wave frequencies
5565GHz
 Smaller coverage radius
 Micro-cellular
 Pico-cellular
 Adjacent cell Interference
is minimum
ATTENUATION (dB/km)
10.000
1.000
2540GHz
0.100
O2+1%H2O
0.010
 Can have high degree of
frequency re-use
O2+3%H2O
0.001
1GHz
10GHz
100GHz
RF FREQUENCY
Source: Carson et al, Microwave
Journal, Nov. 1968
ECE282 “Microwave Photonics” 2008
University of California, San Diego
1000GHz
Narrowband Wireless Access Backbone
Microwave
links as
backbone
network
Customer
Units
Central
Office
Base-Station
Switching
center
call
processing
Access pointmulti-user
access
• Microwave links – insufficient capacity to support increased radio traffic
• Needs high capacity backbone!
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Wired Environment – Optical Fiber Networks
• Rapid deployment of fiber for metro and access
networks – FTTx
• Infrastructure readily available
• Optical Ethernet standardization efforts
• Gigabit Ethernet (1 GbE) and 10 Gigabit Ethernet (10 GbE)
• Customer access networks using passive optical
networks (PON)
• Ethernet/ATM technologies
• Sufficient fiber capacity, WDM channel resources near
customer premises
Merging of wired and wireless infrastructure
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Integrated Wired and Wireless Scenario
METRO
NETWORK
EDGE ROUTER
li
Mini
switching
center
(CO)
OPTICAL
ACCESS
NETWORK
PON Ring
ln
•
•
•
•
lk
lw2
lw1
l-services through metro and access networks
Deploy “as you grow”
Network management advantages (protection/routing)
Overlay wireless services on existing infrastructure
ECE282 “Microwave Photonics” 2008
University of California, San Diego
“Radio-over-Fiber” (RoF)
Base-Station
Wireless
Link
Trunk
Network
Central
Office
•••
Fiber-Feed
Networks
Customer
Units
• Radio links – microwave or millimeter-wave signals
• Backbone networks – optical fiber feed networks
• interconnection between base-stations and the central office
• “wavelength division multiplexing (WDM)
• Antenna base-stations
• radio-to-optical and optical-to-radio signal conversion
• functionally simple and compact
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Example of Indoor Wireless Signal Distribution
• Fed by a central office
which interfaces to an
external network
• Central office distributes
the wireless signals to
remote units on each
floor
• Antenna base-stations
located throughout the
building
• MMF or SMF from the
central office to each
floor
Central
Office
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Challenges in Implementing RoF
Wireless
Link
Trunk
Network
Central
Office
•••
Fiber-Feed
Networks
Base-Station
•
•
•
•
•
•
•
How radio signals are converted into optical signals?
How these signals are transported over fiber?
What signal impairments do the signals experience?
Will optical fiber affect the performance of the radio signals?
What is the overall efficiency?
What are the trade-offs?
Compatibility issues with existing WDM infrastructure?
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Signal Transport Schemes
Central Office
(CO)
Optical
Interface
RF
Interface
Base-Station (BS)
fRF
Baseband Over Fiber
RF Over Fiber
fIF
Digital
photonic link
Analog photonic link
IF Over Fiber
Analog photonic link
• Analog photonic links
• higher carrier-to-noise ratio (CNR) requirements
• limited by noise+intermodulation
ECE282 “Microwave Photonics” 2008
University of California, San Diego
RF-over-Fiber Transport
Base-Station
Trunk
Network
Central
Office
•••
Fiber-Feed
Networks
fRF
IF1
Optical spectrum
fRF
IFm
IF1
O/E
fRF
Y
Node
E/O
LO
RF spectrum
O/E
fc-fRF
fc
fc+fRF
E/O
IFm
straightforward – wireless signals transported at radio
carrier transmission frequency
• Most
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Pros/Cons – RF-over-Fiber Scheme
 Simpler base-stations as no frequency conversion
required
 Centralized channel frequency management
 CO equipment sharing among users
 Air-interface independent
 Multi-band operation possible
Issues:


high-speed opto-electronic interfaces
signal transport issues:

effect of fiber chromatic dispersion on received RF
power and phase-noise



upstream transmission technology
optical spectral wastage
dynamic range performance
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Commercial Product
• Commercial RoF systems based on RF-over-fiber transport
scheme have been developed – only for wireless networks <
3GHz
• Typically uses:
– Direct modulation of low-cost lasers – FP or DFB –
depending on applications
ECE282 “Microwave Photonics” 2008
University of California, San Diego
IF-over-Fiber Transport
Base-Station
Trunk
Network
Central
Office
Fiber-Feed
Networks
•••
fRF
IF1
Node
E/O
IFm
IF1
fIF
O/E
LO
O/E
fc-fIF fc fc+fIF
Y
Optical spectrum
fRF
RF spectrum
E/O
IFm
• Wireless
signals optically transported at a frequency <
wireless transmission frequency
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Pros/Cons – IF-over-Fiber Scheme
 Reduced dispersion effects as low frequencies are used
 Lower cost opto-electronic interfaces
 Centralized channel frequency management still possible
 Air-interface independent
 Low cost upstream transport possible
Issues:
 LO for frequency conversion required at the base-station
• may limit ability for future upgrade – especially changes
in RF frequency
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Baseband-over-Fiber Transport
Base-Station
Trunk
Network
Central
Office
Fiber-Feed
Networks
•••
fRF
O/E
Node
IFm
LO
IF1
O/E
fc
fRF
Y
E/O
Optical
spectrum
IF1
RF spectrum
E/O
IFm
• Wireless
signals transported digitally over fiber
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Pros/Cons – Baseband-over-Fiber
 Mature digital hardware
 Negligible dispersion effects
 Low speed opto-electronic interfaces
 Digital fiber transmission and improved intermodulation
characteristics
Issues:



Air interface dependent base-station architecture
Multi-user access complicates the base-station design
LO signal required however:
• remote delivery of LO possible
ECE282 “Microwave Photonics” 2008
University of California, San Diego
Optical Impairments in Analog Photonics RoF Links
Wireless
Link
Central
Office
Fiber-Feed
Networks
•••
Base-Station
O/E
Conversion
• Conversion efficiency
- Link gain
• Nonlinear transfer function
- Intermodulation
E/O
Conversion
• Dispersion
- RF power penalty
- Phase noise
- Crosstalk
ECE282 “Microwave Photonics” 2008
• Conversion efficiency
- Link gain
• Nonlinear transfer function
- Intermodulation
University of California, San Diego
RF-over-Fiber – Dispersion I
A2, q2
A1, q1
fRF
fRF
Central
Office
RF Over Fiber
Photo
detector
RF spectrum
• Optical signals with double sideband modulation
– detected RF power will vary as a function of dispersion
parameter, RF frequency and fiber length
– RF power dependent on relative phase shifts between two
beat components
– Worse for mm-wave frequency signals transport
ECE282 “Microwave Photonics” 2008
University of California, San Diego
RF-over-Fiber – Dispersion II
Normalized RF Power
fRF = 36.8 GHz
0
-5
-10
-15
-20
0
20
10
30
40
50
Fiber Length (km)
• Dispersion tolerant transport schemes for higher frequencies
– optical single side-band with carrier modulation (OSSB+C)
– modulation of dual-mode or multimode optical signals
fRF
RF Over Fiber
ECE282 “Microwave Photonics” 2008
University of California, San Diego
RF-Over-Fiber –
Optical Single Sideband with Carrier Modulation
optical spectrum, f = 36.86 GHz
Optical Power (dBm)
DC bias
MZM
optical
input
optical
output
RF input
MZM = Mach-Zehnder Modulator
electrical
optical
Normalized RF Power (dB)
q=
90o
-15
-55
1552.7
Wavelength (nm)
1553.7
10
Fiber Link Distance = 80 km
0
-10
-20
Measured OSSB
Measured DSB
Predicted DSB
-30
-40
0
2
4
6
8
10 12 14 16
Modulation Frequency (GHz)
18
G.H. Smith et al, Elec Lett, vol. 33, pp. 74-75, 1997
ECE282 “Microwave Photonics” 2008
University of California, San Diego
20
RF-over-Fiber –
Uplink Transmission Technology
Base-Station
Central
Office
•••
Fiber-Feed
Networks
fRF
Y
O/E
Optical
Modulator
WDM
Laser
E/O
• Requires optical source in BS for uplink
• Techniques to reduce optical hardware in BS
• Wavelength re-use scheme with external modulator
• Electro-absorption transceiver
• CO provides uplink carrier
• Direct modulation of multi-section laser
ECE282 “Microwave Photonics” 2008
University of California, San Diego
RF-over-Fibre – Wavelength Reuse
Downstream
RF signal
Photo detector
Downlink
optical fiber
Optical
Carrier
Recovery
Central
Office
Upstream
RF signal
DC
RF
BS RF Interface
RF
Uplink
optical fiber
Dual-Electrode
MZM
Base Station
Base Station Optical Interface
Optical Carrier Recovery
Downlink
signal
50% reflectivity
FBG
fc
Uplink
carrier
ECE282 “Microwave Photonics” 2008
Downlink
signal
Nirmalathas et.al,
IEEE Trans. MTT,
vol. 49, pp. 2030-5, 2001
University of California, San Diego
RF-over-Fibre –
Electroabsorption Transceiver in BS
Two-Section EAT
LD2
SMF
LD1
EAM
EDFA-1
59.6GHz
59.6GHz
PRBS
(156 Mb/s)
DPSK
(mod.)
(2.6 GHz)
SMF
PD
LO
BERT
LO
60GHz
EDFA-2
57GHz
BERT
DPSK
(mod.)
(3.0 GHz)
PRBS
(156 Mb/s)
57GHz
Att.
(BS)
amplifier
DPSK
(demod.)
(3.0 GHz)
E
A
T
DPSK
(demod.)
(2.6 GHz)
(CU)
60GHz
(CO)
courtesy of
Prof. K. Kitayama
R. Heinzelmann, T. Kuri, K. Kitayama, A. Stöhr, and D. Jäger, “OADM of 60 GHz-millimeter-wave
signal in WDM radio-on-fiber ring”, Proc. Optical Fiber Conference, FH4, Baltimore, USA, 2000.
ECE282 “Microwave Photonics” 2008
University of California, San Diego
RF-over-Fibre –
CO Provides Optical Carrier for Uplink
EDFA
L. Chen et. al., IEEE Photon. Technol.
Lett., vol. 18, pp. 2056-2058, 2006
• Use interleaver to separate carrier and sidebands in BS
ECE282 “Microwave Photonics” 2008
University of California, San Diego
RF-over-Fiber –
Direct Modulation of Multi-Section Laser
5m
MPA
Costas Loop
fc=2.5GHz
IF=2.5GHz
LNA
34.3GHz
40km SMF
LNA
Baseband
Data
MPA
EDFA
PD
Multi-section
Semiconductor
Laser
BPF
Central Office
36.8 GHz
Customer Unit
Base Station
Frequency Response
Optical Spectrum
Optical Power 10 dB/div
RF power (dBm)
C. Lim et. al.,
Proc. OFC, pp.
16-17, 1998
51.8 Mb/s
PRBS
BERT
MPA
RL 1.04 dBm
Center 1545.3nm Span 5nm
5 GHz
36.8 GHz
• Simple technique
• Multiple modes – how does fiber chromatic dispersion affect the performance?
ECE282 “Microwave Photonics” 2008
University of California, San Diego
multi-section laser
multi-section laser
Normalized rf power (dBm)
Conventional DSB
modulation
Normalized rf power (dBm)
optical spectrum
Normalized rf power (dBm)
Direct modulation of multi-section laser with multiple
modes: Effect of fiber dispersion
0
phasor diagram
-5
-10
ripple
depth
-15
-20
0
30
40
20
10
Fiber Length (km)
50
0
ripple
depth
-5
-10
-15
-20
0
30
40
20
10
Fiber Length (km)
50
0
ripple
depth
-5
-10
-15
-20
0
ECE282 “Microwave Photonics” 2008
10
30
40
20
Fiber Length (km)
50
University of California, San Diego
Optimizing System Performance
•
RF-over-Fiber
– Direct advantage – simpler base station architectures
– Needs optical components with good analog performance over
bandwidth/freq band of wireless networks
• More challenging for millimeter-wave based RoF
– Suitable high-speed optical modulation techniques
» Easiest – via external modulator
» Low drive voltage
» Good linearity
» High bias stability
» Low optical insertion loss
– High-speed photodetection techniques
» High saturation power
» Large electrical output power
– Resonantly enhanced modulator or photodetector??
ECE282 “Microwave Photonics” 2008
University of California, San Diego