advanced electronic equalization for high-speed data transmission over multi-mode … · 2014. 11....

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-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: [email protected], Tel: 0431-8806300

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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

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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

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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

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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

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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

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Launch Conditions

Overfilled Launch (OFL)

LED MMF

core

Restricted Mode Launch (RML)

LASER

MMF

coreoffset

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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

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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]

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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

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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

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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.

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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

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Statistical Analysis Based on Worst Case Samples of MMF Channels

11 MMF profiles (MMF #1~#11)Beam spot size: FWHM= 12µmOffset launch 20 µm

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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

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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

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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.

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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

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Nonlinear ISI in Optical Fiber System

E/O O/E

2 Kerr-effectof Fiber

Nonlinear ISI

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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.

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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.

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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)

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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)

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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)

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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

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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

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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

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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

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EDC on PMD mitigation for different modulation formats

NRZ-OOK NRZ-Duobinary

NRZ-DPSK RZ-DPSK

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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.

advanced electronic equalization for high-speed data transmission over multi-mode … · 2014. 11....

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