OFDM for Next Generation Optical Access NetworksOFDM for Next Generation Optical Access Networks...
Transcript of OFDM for Next Generation Optical Access NetworksOFDM for Next Generation Optical Access Networks...
OFDM for Next Generation Optical
Access Networks
Neda Cvijetic
NEC Laboratories America
ECOC 2010 Access Workshop
September 19, 2010
Orthogonal Frequency Division Multiplexing (OFDM)
▐ Key idea: use many narrow-band orthogonal subcarriers to transmit
symbols in parallel
▐ By orthogonality spectra may partially overlap for high spectral
efficiency
High resistance to linear dispersion; efficient DSP implementation
Advance modulation can be exploited in high-speed fiber transmission
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OFDM Sub-carriers
in frequency domainOFDM Sub-carriers
in time domain
……
.
The Rise of Optical OFDM
▐ 2006— present: exponential growth of optical OFDM
publications
▐ OFDM shown superior physical layer performance for next-
generation fiber systems
Linear dispersion tolerance, spectral efficiency, efficient channel
estimation/equalization
▐ However, for 100 Gb/s long-haul transmission
OFDM requires digital transmitter, QPSK does not
Blind equalization simple + sufficiently good (for now…)
Single-carrier QPSK leading candidate for 100 Gb/s long-haul
Why Optical OFDM in Access?
▐ Fiber-to-the-home emerging as future-proof access solution
▐ Bandwidth driver: digital video
▐ Point-to-multipoint passive optical network (PON) expected to play
leading role in next-generation access
▐ Global deployment of Gigabit/Gigabit Ethernet PON (G/GE PON)
▐ Ratification of 10G/GE PON standards
▐ Bandwidth flexibility between users/applications of premium value in
future access
▐ Services include mix of digital, analog, circuit and packet-switched,
legacy and emerging applications
▐ Orthogonal Frequency Division Multiple Access (OFDMA)
OFDMA-PON Technology
▐ Several candidates for future passive optical network (PON)
OFDMA, TDM, WDM, hybrid TDM/WDM…
▐ OFDMA-PON differentiator: tackle key challenges in electronic domain
through digital signal processing (DSP)
▐ Leverage advanced DSP to achieve superior performance, rapid and
robust network re-configurability, cost reduction
▐ OFDMA-PON: novel DSP-based platform for speed, flexibility and cost-
efficiency in future high-speed PON access systems
▐ Critical that future PON technologies be highly cost-efficient to remain
attractive and practical
Re-use existing optical distribution network (ODN)
Upgrade with advanced modulation and digital signal processing (DSP)
OFDM-Based PON for Next Generation Optical Access
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System is transparent, flexible and extensible to any emerging applications
OFDM sub-carriers become transparent pipes for delivery of arbitrary signals
(e.g. T1/E1, Ethernet, RF mobile backhaul, IPTV, VPN, etc..)
OLT
Business area
Mobile station
Residential area
Splitter ONU 1
ONU 2
ONU 3
OFDMA frame
Fre
qu
en
cy
Time
ONU-3
ONU-2
ONU-1
1
2
3 f
f
11 1
Analog baseband T1/E1 signal
Ethernet packets
Analog wireless RF signal
Ethernet packets3 3 3
11
ONU-1
f
3 3 3
11 1 1 1 1
11 1
t
f
f
Integrated DSP-based transmission and control planes
Bandwidth dynamically assigned to different services in different time slots
OFDM-based PON Flavors for Multi-User Access
▐ OFDMA-PON: Different users assigned different OFDM
subcarriers within one OFDM band of total N subcarriers
▐ OFDMA + TDMA PON: Different users assigned
different OFDM subcarriers and TDM slots within one OFDM
band; 2-dimensional dynamic bandwidth allocation
▐ OFDMA + TDMA + WDMA PON: Different users assigned
different OFDM subcarriers, and TDM slots and WDM
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Frequency (sub-carriers)
Packet service TDM service
Frequency (sub-carriers)
Packet service TDM service
Frequency (sub-carriers)
Packet service TDM service
Frequency (sub-carriers)
Packet service TDM service
1 2 M…
…
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Practical OFDM-PON Implementation
▐ Mathematically, each data carrier can be
described as a complex wave
▐ However, through advanced digital
signal processing (DSP), practical
implementation is simple and efficient
through Fast Fourier Transform (FFT)knNj
N
k
pp ekXN
nx )/2(1
0
][1
][
Constellation
mapperIFFT
P/S
& D/A
DC
offsetMZM… .
… .….
DSP OFDM MODULATOR
Laser
OPTICAL
MOD.
data inTo fiber & ODN
Transmitter
Architecture
PD A/Dfrom fiber
DSP OFDM DEMODULATOR data out
Receiver
Architecture
Advanced DSP enables practical, cost-efficient, multi-user implementation
)]([)()(
ttwj
ccccetAts
amplitude
phase
Key Benefits of OFDM-PON Transmission
▐ SPEED & DISTANCE
Up to 100 Gb/s/ downstream transmission
Up to 100 Gb/s/ upstream transmission
Up to 100km reach for PON, 1000km for metro
▐ FLEXIBILITY
Adaptive modulation and FEC on subcarrier basis
Dynamic bandwidth allocation in time and frequency
Transparency to arbitrary services
Optically-transparent ONUs
▐ COST-EFFICIENCY
Colorless architecture
Stable, accurate DSP-based operation
Non-disruptive to legacy ODN
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Summary of Experimental Demonstrations
▐ (NEC Labs, ECOC 2007): 10 Gb/s Bi-Directional OFDMA-PON
▐ (NEC Labs, OFC 2008): Heterogeneous OFDMA-PON
▐ (NEC Labs, Paper OMV3, OFC 2009): 40 Gb/s OFDMA-PON
▐ (NEC Labs, Paper OTuO7, OFC 2009): 1000km OFDM-DD
Transmission
▐ (NEC Labs, Paper PDPD5, OFC 2009):108 Gb/s OFDMA-PON
▐ (NEC Labs, ECOC 2009): 36 Gb/s/ OFDMA-PON over 100km
▐ (NEC Labs, ECOC 2009 PD 3.3): 108 Gb/s/ Upstream OFDMA-
PON
▐ (NEC Labs, OFC 2010): 44 Gb/s/ Polarization Insensitive
Upstream OFDMA-PON
▐ (NEC Labs, OFC 2010 PDPD9): 41.25 Gb/s Real-Time, Variable-
Rate WDM-OFDMA-PON
“OFDM is a great technology…”
Orthogonal Frequency Division Multiplexing (OFDM) PON
very well-suited for future PON systems
Transparent to emerging heterogeneous applications
Highly-flexible, dynamic bandwidth allocation
Non-disruptive to legacy ODN
Recent demonstrations of ultra high-speed OFDMA PON
Speed: 108 Gb/s/ downstream and upstream
Feasible on class C+ ODN (30+ dB power budget)
Highly dispersion tolerant (60km-100km transmission)
“But it requires advanced Digital
Signal Processing (DSP)”
DSP Component Characteristics
▐ Silicon platform
ADC/DAC + DSP integration, mass production, cost-
efficiency
▐ Low power consumption
65nm, 40nm, 28nm CMOS processes
▐ Cost-efficient packaging options
Component cost profile driven by volume
▐ DSP complexity: IFFT/FFT dominates, ~log(N) scaling
Optimized, readily available algorithms
Technology Trends and Next Steps
▐ DSP-based system cost can be significantly and rapidly reduced
by component integration and mass production
▐ Optimized OFDM algorithms re-used from wireless and
wireline building blocks
▐ Next generation 100 Gb/s long-haul fiber transmission will be
heavily DSP-based
50+ GS/s, 2 channel ADC chips commercially available
10-30GS/s, 2 channel DAC chips commercially available
Intensive on-going effort in parallelized, real-time DSP
architectures
▐ Aggressive 100 Gb/s DSP development for fiber transmission
expected to have favorable effect on ultra high-speed OFDM-
PON
Summary and Conclusions
OFDMA PON very well-suited for high-speed future PON
Transparent to emerging heterogeneous applications
Highly-flexible, dynamic bandwidth allocation
DSP-based for stable, cost-efficient implementation
Key challenges tackled in DSP
2 channel ADC/DAC, DSP processor key components
Favorable technology trends in terms of cost profile
41.25 Gb/s real-time, variable-rate receiver for WDM-OFDMA-PON
demonstrated
Key OFDMA-PON advantages : high flexibility and cost-efficiency
with record transmission rates/distances