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L N T
-1-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Advanced Electronic Equalization for High-Speed Data Transmission over Multi-Mode as Well as Single-Mode Optical Fiber
Werner Rosenkranz and Chunmin Xia
University of Kiel, Germany
Chair for CommunicationsKaiserstr. 2, 24143 Kiel, Germany
Email: wr@tf.uni-kiel.de, Tel: 0431-8806300
L N T
-2-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
MotivationMMF short haul links: Differential mode delay (DMD) limits bandwidth-distance product of installed MMF: 500MHz-km. for 10Gb/s data rate, transmission distance is less than 100m. 10GE: 300m transmission distance over installed MMF at 10Gb/s.
- Mode selective launch & Mode selective detection
- Wavelength division multiplexing (CWDM)
- Multilevel modulation & Subcarrier multiplexing
- Electrical equalization: FFE, DFE, MLSE, DDFSE
SMF Long haul links: Chromatic dispersion (CD), Polarization mode dispersion (PMD), non-linear fibre properties limit the signal integrity in 10/40G optical system.
- Advanced modulation formats: Duobinary, M-DPSK,…
- Wavelength division multiplexing: CWDM & DWDM
- Dispersion compensation: DCF
- Error correction with channel coding: FEC
- Optical and electrical dispersion compensation: ODC & EDC
L N T
-3-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
OutlineDMD mitigation in MMF short links
- MMF link model and link characteristics (DMD, Launch conditions)
- Statistical analysis of FFE/DFE on DMD mitigation
- Comparison of various Equalizers (FFE, DFE, MLSE, DDFSE) on DMD mitigation
- Equalizers combined with multilevel signalling
- Conclusions
EDC on CD/PMD mitigation in SMF long haul links
- Introduction of different EDC setups
- EDC on CD mitigation for OOK and advanced modulation formats
• Optical duobinary modulation (ODB)
• Differential-phase-shift-keyed (DPSK)
• Optical single side band modulation (OSSB)
- EDC on PMD mitigation for OOK and advanced modulation formats
- Conclusions
L N T
-4-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
MMF Channel Model
•Refr. index profile
•Beam spot size
•Launch Offset
•Radial wave equation
•Solutions (Modes) in core and cladding
•Solve overlap integral
0( ) ( )
M
mm
mh t tP δ τ=
= +∑0
( ) exp( )M
mm mPH jϖ τϖ
== ∑
•Refr. index profile
•Length of fibre
L N T
-5-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
MMF Channel Model
1( ) ( )
M
m mm
h t P tδ τ=
= +∑1
( ) exp( )M
m mm
H P jϖ ϖτ=
= ∑m mP
M mτ
Mode number
Max mode numberPower carried by each mode
Delay of each mode
Differential Mode Delay (DMD)
DMD can be described by a linear systemsimilar to multipath reception
L N T
-6-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
DMD of Installed MMF
MMF #1 #2 #3 #4 #5 #6
Index Profile
g=2.03 with dip
g=2.03 with peak
g=1.88 with dip
g=1.88 with peak
g1=1.96, g2=2,with dip
g1=1.96, g2=2,
• Installed MMF Great variety of parameters of channel model Statistical analysis
• 6 typical worst case profiles of various index exponents (g) with dip or peak are examined.
#1
#4
LP0n
LP0n
L N T
-7-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Launch Conditions
Overfilled Launch (OFL)
LED MMF
core
Restricted Mode Launch (RML)
LASER
MMF
coreoffset
L N T
-8-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Example 1: MMF #4: 300m,FWHM of Gaussian beam spot=10µm
Different impulse responses and frequency responses
Channel Characteristics vs. Launch ConditionsVarious MMF profilesVarious launch spot sizesVarious launch positions
Example 2: MMF #5: 300m,FWHM of Gaussian beam spot=10µm
L N T
-9-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
MMF #5: L=130m, Spot size=10µm (FWHM)
Offset 5µm Offset 10µm
Offset 20µm Offset 25µm
[PS]
[PS]
[PS] [PS]
[PS]
OFLOffset Launch
Offset 15µm[PS]
[PS]
Offset 0µm
Offset 30µm
[PS]
L N T
-10-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
MMF Bandwidth vs. Launch ConditionsChannel: 11 MMF (including #1~#6) with various imperfections.FWHM of incident Gaussian beam spot: 4µm …14µm.Offset launch:0µm…30µmTransmission distance:130m.
Preferred launch range
L N T
-11-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Demonstration of EDC on DMD MitigationSimulation (OFL,MMF #4,300m,10Gb/s)
FFE [6]
[PS] [PS]
Experiment (300-m Legacy MMF; 1310 nm @10.3 Gb/s)
SCN3142EDCE™
IN OUT
Source: Courtesy of Scintera Networks
L N T
-12-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
FFE FFE-DFE
Maximum Likelihood Sequence Estimator or Viterbi equalizer (VE):
0 0
1
1
1
0
{0, 0}
{0, 1}
{1, 0}
{1, 1}
Reduced complexity Viterbi equalizer:
Various EDC Techniques
FFE
FFE
DFE
2-1MLSE 0 =0
=min ( ) - ( ) ( )k N l L
k lL y k h l d k l= =
=−∑ ∑
-1DDFSE 0 0
21
=min | ( )- ( ) ( - )-
ˆ( ) ( - ) |
Kk N l
k ll L
l K
L y k h l d k l
h l d k l
= =
= =
=
= +
∑ ∑∑
1 or 2 samples per Bit
delayed decision feedback sequence estimation:
The complexity of this algorithm is controlled by the parameter K, which can be varied from 0 to L. K = 0 DFE; K = L MLSE.
L N T
-13-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Statistical Analysis of EDC (FFE+DFE)
Total: 1674 different impulse responses
Transmission distance:300m
FFE+DFE:
Order of FFE: 12
Order of DFE: 0,1,…,6
Target: EOP<2dB required!
Which parameters (spot size, launch offset) require lowest DFE order
The required order of DFE
4~14 µm 17~28 µm
6 MMF profiles (MMF #1~#6)9 beam spot sizes (FWHM): 4µm ~20µm31 launch positions: 0µm ~30µm
L N T
-14-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Statistical Analysis Based on Worst Case Samples of MMF Channels
11 MMF profiles (MMF #1~#11)Beam spot size: FWHM= 12µmOffset launch 20 µm
L N T
-15-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Various EDC Techniques: Comparison4 different equalizer setups:
- FFE- FFE+DFE- VE (Viterbi equalizer)- Reduced state VE
Mean value over MMF samplesMonto-Carlo simulation
2 Samples/bit1 Sample/bit
L N T
-16-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC on DMD mitigation for 4-ASK signalling
Sampling: 1sample/bitOptimum sampling positionFFE with 6-delay tap
11 MMF profiles (MMF #1~#11)Beam spot size: FWHM= 12µmOffset launch 20 µm
Benefit from reduced bandwidth of 4-ASK
L N T
-17-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
ConclusionsEDC on DMD Mitigation in MMF Short Links
MMF channel characteristics vary greatly from one link to another due to different launch conditions as well as different index profiles. Statistical analysis is required.
Various EDC techniques on DMD mitigation in MMF links based on representative MMF samples are demonstrated.
- FFE alone can not guarantee the EDC performance for 10GE in MMF links for 2-ASK signalling.
- DFE with 2-delay tap feedback filter is enough to mitigate post-cursor ISI with appropriate offset launch.
- MLSE (=VE) and reduced state MLSE can achieve optimum performance on DMD mitigation.
- FFE alone can guarantee the EDC performance for 10GE with 4-ASK signalling.
L N T
-18-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
OutlineEDC on DMD mitigation in MMF short links
- MMF links model
- MMF links characteristics(DMD,Launch conditions)
- Statistical analysis of EDC performance
- Performance comparison of various EDC techniques
- EDC used for multilevel signalling
- Conclusions
EDC on CD/PMD mitigation in SMF long haul links
- Introduction of different EDC setups
- EDC on CD mitigation for OOK
- EDC on CD mitigation for advanced modulation formats
• Optical duobinary modulation (ODB)
• Differential-phase-shift-keyed (DPSK)
• Optical single side band modulation (OSSB)
- EDC on PMD mitigation for different modulation formats
- Conclusions
L N T
-19-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Nonlinear ISI in Optical Fiber System
E/O O/E
2 Kerr-effectof Fiber
Nonlinear ISI
L N T
-20-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC setups (1)
FFE-DFE
FFEFFE
DFE
FFE
Delay tap spacing: T (synchronous) or T/2 (fractionally spaced)
Equalization coefficients are adaptively optimized, based on MMSE rule.
L N T
-21-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC setups (2)
Nonlinear-FFE-DFE
NL[2,2]-FFE[1]-DFE[2]
Nonlinear order of FFE
Nonlinear order of DFE
Order of FFE
Order of DFE
Extended from FFE-DFE including nonlinear ISI mitigation.
Based on Voterra theory.
L N T
-22-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Implementation of the Adaptive LMS-Algorithm
f0(ki)∆−m
se
f1(ki)
ki
0
weightingerrorfactor
ˆ ˆ( 1) ( ) ( 1) ( ) ( )eq. state
db k b k d k d k y t kµ ⎡ ⎤+ = + − − +⎣ ⎦
( )dy k
ˆ( )d k
[ ]{ }2( ) ( )dmse E d k y k= −
mse as a function of theequalizer coefficientsreceived signal
f0(ki)T
Tb
f1(ki)
µ
-ε(ki )
T
+ -
Tb
b(ki)T
slicer
Minimumerror-signal(MSE)
L N T
-23-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC setups (3)
MLSE0 0
1
1
1
0
{0, 0}
{0, 1}
{1, 0}
{1, 1}
Optimum receiver based on Viterbi algortihm
Channel estimation (based on Lookup table method where PDF is estimated) first with training symbols.
High speed A/D Converter required
Memory: 2 or 3 (ISI from 2 or 3 previous bits)
L N T
-24-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC on CD mitigation for OOK (1)
1 sample/bit, 10 Gb/s
FFE[4]-DFE[2] exhibits obvious advantage over FFE[6] at longer distance
NL[2,2]-FFE[4]-DFE[2] outperforms MLSE[2] at longer distance (>160km)
L N T
-25-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC on CD mitigation for OOK (2)
2 samples/bit, 10Gb/s
Improvement through oversampling
FFE[4]-DFE[2] exhibits obvious advantage over FFE[6] at longer distance (>120km)
MLSE[2] outperforms FFE[4]-DFE[2]
MLSE[3] outperforms MLSE[2] starting from distance 160km
L N T
-26-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC on CD mitigation for Optical Duobinary
ODB: larger dispersion tolerance, B2B penalty
FFE and FFE-DFE very little performance improvement
NL-FFE-DFE (1S/T) can achieve sub-optimum performance
MLSE[2] with 2 sample/T required for better performance
L N T
-27-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC on CD mitigation for NRZ-DPSK
NL-FFE-DFE outperforms MLSE[2] with 1sample/Bit
MLSE[2] with 2samples/bit required for better performance
All the EDC are limited at short distance due to the balanced detection
L N T
-28-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC on CD mitigation for OSSB
CD results in Linear distortion in OSSB systems
FFE[6] can achieve the similar performance to MLSE[2] up to 400km
FFE alone can achieve very good compensation, DFE &MLSE are unnecessary
L N T
-29-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
EDC on PMD mitigation for different modulation formats
NRZ-OOK NRZ-Duobinary
NRZ-DPSK RZ-DPSK
L N T
-30-Faculty of EngineeringChristian-Albrechts-Universität zu Kiel
Chair forCommunications
Conclusions (2)EDC on CD/PMD mitigation in SMF links
EDC exhibits good performance on CD mitigation for conventional OOK but limited performance for advanced modulation formats suchas ODB and DPSK.
EDC with 2-fold oversampling can achieve much better performance than with 1 sample per bit, especially for ODB.
Nonlinear FFE-DFE shows nearly as good performance as MLSE.
CD results in linear distortion in OSSB systems and thus FFE alone can achieve good compensation.
Performance difference of EDC on PMD mitigation is less than that on CD mitigation for different modulation formats, because firstorder PMD causes linear ISI in electrical domain.
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