Microwave Photonics Applications: Radio-over-Fiber

1
Microwave Photonics Applications Radio-over-Fiber
Thursday, January 10, 2008

• 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
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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
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Bandwidth and Frequency Allocation
ECE282 Microwave Photonics 2008 University of
California, San Diego
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Frequencies for Wireless
ECE282 Microwave Photonics 2008 University of
California, San Diego
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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
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Radio Signal Propagation

• Propagation loss is high at mm-wave frequencies
• Smaller coverage radius
• Micro-cellular
• Pico-cellular
• Adjacent cell Interference is minimum
• Can have high degree offrequency re-use

55-65GHz
100.00
10.000
25-40GHz
ATTENUATION (dB/km)
1.000
0.100
O21H2O
0.010
O23H2O
0.001
1GHz
10GHz
100GHz
1000GHz
RF FREQUENCY
Source Carson et al, Microwave Journal, Nov.
1968
ECE282 Microwave Photonics 2008 University of
California, San Diego
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Narrowband Wireless Access Backbone
Microwave links as backbone network
Access point- multi-user access
Switching center call processing

• Microwave links insufficient capacity to
  support increased radio traffic
• Needs high capacity backbone!

ECE282 Microwave Photonics 2008 University of
California, San Diego
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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
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Integrated Wired and Wireless Scenario
METRO NETWORK
EDGE ROUTER
OPTICAL ACCESS NETWORK
li
lk
PON Ring
ln

• 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
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Radio-over-Fiber (RoF)
Base-Station
Wireless Link
Fiber-Feed Networks
Central Office
Trunk Network
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
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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

ECE282 Microwave Photonics 2008 University of
California, San Diego
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Challenges in Implementing RoF
Wireless Link
Fiber-Feed Networks
Central Office
Trunk Network
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
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Signal Transport Schemes

• Analog photonic links
• higher carrier-to-noise ratio (CNR) requirements
• limited by noiseintermodulation

ECE282 Microwave Photonics 2008 University of
California, San Diego
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RF-over-Fiber Transport
Base-Station
Fiber-Feed Networks
Trunk Network
Central Office

• Most straightforward wireless signals
  transported at radio carrier transmission
  frequency

ECE282 Microwave Photonics 2008 University of
California, San Diego
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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
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Commercial Product

• Commercial RoF systems based on RF-over-fiber
  transport scheme have been developed only for
  wireless networks lt 3GHz
• Typically uses
• Direct modulation of low-cost lasers FP or DFB
  depending on applications

ECE282 Microwave Photonics 2008 University of
California, San Diego
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IF-over-Fiber Transport
Base-Station
Fiber-Feed Networks
Trunk Network
Central Office

• Wireless signals optically transported at a
  frequency lt wireless transmission frequency

ECE282 Microwave Photonics 2008 University of
California, San Diego
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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
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Baseband-over-Fiber Transport
Base-Station
Fiber-Feed Networks
Trunk Network
Central Office

• Wireless signals transported digitally over fiber

ECE282 Microwave Photonics 2008 University of
California, San Diego
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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
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Optical Impairments in Analog Photonics RoF Links

• Conversion efficiency
• - Link gain
• Nonlinear transfer function
• - Intermodulation

• Conversion efficiency
• - Link gain
• Nonlinear transfer function
• - Intermodulation

• Dispersion
• - RF power penalty
• - Phase noise
• - Crosstalk

ECE282 Microwave Photonics 2008 University of
California, San Diego
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RF-over-Fiber Dispersion I
fRF
Photo detector

• 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
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RF-over-Fiber Dispersion II

• Dispersion tolerant transport schemes for higher
  frequencies
• optical single side-band with carrier modulation
  (OSSBC)
• modulation of dual-mode or multimode optical
  signals

fRF
RF Over Fiber
ECE282 Microwave Photonics 2008 University of
California, San Diego
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RF-Over-Fiber Optical Single Sideband with
Carrier Modulation
optical spectrum, f 36.86 GHz
-15
DC bias
MZM
Optical Power (dBm)
optical input
optical output
-55
q 90o
1552.7
1553.7
Wavelength (nm)
RF input
MZM Mach-Zehnder Modulator
G.H. Smith et al, Elec Lett, vol. 33, pp. 74-75,
1997
ECE282 Microwave Photonics 2008 University of
California, San Diego
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RF-over-Fiber Uplink Transmission Technology
Base-Station
Fiber-Feed Networks
Central Office

• 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
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RF-over-Fibre Wavelength Reuse
Downstream RF signal
Photo detector
Downlink optical fiber
Optical Carrier Recovery
Upstream RF signal
Central Office
DC
RF
RF
Uplink optical fiber
Dual-Electrode
MZM
Base Station
Base Station Optical Interface
Optical Carrier Recovery
50 reflectivity
Nirmalathas et.al, IEEE Trans. MTT, vol. 49, pp.
2030-5, 2001
ECE282 Microwave Photonics 2008 University of
California, San Diego
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RF-over-Fibre Electroabsorption Transceiver in
BS
Two-Section EAT
LD
2
SMF
DPSK
(demod.)
BERT
LD
EAM
EDFA-1
1
(2.6 GHz)
59.6GHz
E
59.6GHz
A
DPSK
LO
57GHz
SMF
PRBS
T
(mod.)
(156 Mb/s)
(2.6 GHz)
DPSK
PRBS
60GHz
(mod.)
PD
Att.
EDFA-2
(156 Mb/s)
(3.0 GHz)
LO
57GHz
(BS)
amplifier
(CU)
DPSK
60GHz
(demod.)
BERT
(3.0 GHz)
(CO)
The EAT is the only optical component at the BS!
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
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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
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RF-over-Fiber Direct Modulation of
Multi-Section Laser
5 m
MPA
IF2.5GHz
LNA
MPA
34.3GHz
40km SMF
LNA
Baseband Data
EDFA
BPF
Central Office
Base Station
C. Lim et. al., Proc. OFC, pp. 16-17, 1998
Frequency Response
Optical Spectrum

• Simple technique
• Multiple modes how does fiber chromatic
  dispersion affect the performance?

ECE282 Microwave Photonics 2008 University of
California, San Diego
30
Direct modulation of multi-section laser with
multiple modes Effect of fiber dispersion
optical spectrum
phasor diagram
0
-5
-10
Normalized rf power (dBm)
ripple depth
-15
-20
Conventional DSB modulation
20
30
40
50
0
10
Fiber Length (km)
0
-5
ripple depth
-10
Normalized rf power (dBm)
-15
multi-section laser
-20
30
40
50
0
10
20
Fiber Length (km)
0
ripple depth
-5
-10
Normalized rf power (dBm)
-15
-20
multi-section laser
10
0
ECE282 Microwave Photonics 2008 University of
California, San Diego
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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