PMD and PMD compensation NOBEL WP5 results NOBEL_WP5_PMD_summary_draft_4_extended.ppt Henning...

PMD and PMD compensationNOBEL WP5 results

NOBEL_WP5_PMD_summary_draft_4_extended.ppt

Henning Bülow Yu Rong Zhou

Alfons Schinabeck Stefano Santoni

Andrew Lord Bernd Bollenz

Thomas Fischer

PMD / PMDC models Overview

PMD / Q dependency

•Equaliser S (FFE + DFE)

•Receiver (AT)•In-line compensator S E

•Receiver•1stage/2stage PMDC

•Receiver (NRZ, CS-RZ, DB)•Equalisers (NRZ, CS-RZ, DB) (FFE+DFE, MLSE=VE)

Independent rules:PMD > thresholdOSNR> threshold

Table: Q-penalty vs PMD / Q

Curve: Q-penalty vs PMD

Representationin model

PM

D o

rders

S: NW simulationE: Experiment

PMD: 1st order

1st+2nd

multi-order

PMD/Receiver models

PMD / Q dependency

•Equaliser (FFE + DFE)

•Receiver (AT)•In-line compensator


•Receiver (NRZ, CS-RZ, DB) see mitigation•Equalisers (NRZ, CS-RZ, DB) (FFE+DFE, MLSE=VE)





PM

D o

rders

PMD: 1st order

1st+2nd

multi-order

PMD penalties (all-orders) evaluation

EOP evaluation modelling the fiber with the wave plates approach (all-orders PMD) and numerical simulation (Split-Step Fourier method) EOP vs. instantaneous DGD (100,000 realisations) for RZ and

NRZ EOP pdf for NRZ and RZ

NRZ 10Gb/s

NRZ 10Gb/s

outage probabiltiy

PMD penalties (all-orders) evaluationResult (table representation)

0123456789

10 15 20 25

Baseline Q (dB)

Q p

en

alt

y (

dB

)

5ps

10ps

15ps

17.5ps20ps

22.5ps25ps

Q penalty vs. baseline Q for different mean DGD (OP = 10-5 , 10Gb/s NRZ signal)

PMD penalties (all-orders) evaluation Impact of fiber non-linearity

Comparison with simulations including non linear (Kerr) effects (0dBm) G.652 (top) and G.655

(bottom) cases NRZ (left) and RZ 30 ps

FWHM (right) Comparing EOP due to

non linear effects and to PMD (blue line) with EOP due to PMD only (red line):

EOP due to non linear effects and to PMD can be linearly added for NRZ signals

Cumulative EOP due to non linear effects and to PMD is less than the linear sum of the two independent components, for RZ signals

NRZ RZ

NRZ RZ

Comparison of different PMD modelling approaches

Analytical model for 1st order PMD: Q-factor penalty as a function of PMD and outage probability (OP):

A: pulse factor, B: bit rate, : mean DGD Comparison of approaches:

Wave plate approach (all order PMD) Analytical (1st order PMD) split-step (1st order PMD)

Good agreement of all different approaches for 10Gb/s NRZ signal

Analytic model giving efficient calculation with sufficient accuracy for baseline Q value relevant to system applications

0

1

2

3

4

5

6

7

8

9

0 10 20 30

mean DGD (ps)Q

pen

alt

y (

dB

)

10 (̂-5), statistical10 (̂-3), statistical10 (̂-5), analytic10 (̂-3), analytic1st order P MD, numerical

)log(201610

10ln

log20)(

22

OPBA

Q

QdBQP baseline

PMD

< >

PMD mitigation

PMD / Q dependency









PM

D o

rders

PMD: 1st order

1st+2nd

multi-order

PMD mitigationInvestigated approaches

eopmdc_axes

PMD / Tbit 0.0 0.1 0.2 0.3 0.4 0.5

rel.

OSNR p

enal

ty (

dB)

-2

0

2

4

6

8

multi-stage

Rx2stage

OPMDC1stage

Q-p

enalty [d

B]

PMF1PC1

feedback signal2 PMFs

(c)(c)11x44PMF2

PC2

PMF:variable DGDPC

feedback signal

(b)(b)11x33

SC with variable DGD: VarDGD

.....

Cn-1

Tc

Cn

C0

Tc

C1

CUref

TB

-+

B1

FFE

DFE

low passfilter

ADC Viterbiequal.

low passfilter

ADC Viterbiequal.

-1

0

1

2

3

4

5

6

0 20 40 60 80 100

DGD [ps]

Q-f

ac

tor

pe

na

lty

[d

B]

@ 1

*10

-3

DB(ATC,model 1) NRZ (ATC,model 1) DB(VE,model 1)

NRZ (VE,model 1) NRZ(FFE+DFE,model 2) NRZ(VE,model 2)

CSRZ (ATC,model 1) CSRZ (VE,model 1)

duobinaryNRZ

VE1

FFE+DFE

CSRZ

ATCVE

ATC

VE

Q-penalty vs. DGD (=3xPMD)

VE2

-1

0

1

2

3

4

5

6

0 20 40 60 80 100

DGD [ps]

Q-f

ac

tor

pe

na

lty

[d

B]

@ 1

*10

-3

DB(ATC,model 1) NRZ (ATC,model 1) DB(VE,model 1)

NRZ (VE,model 1) NRZ(FFE+DFE,model 2) NRZ(VE,model 2)

CSRZ (ATC,model 1) CSRZ (VE,model 1)

duobinaryNRZ

VE1

FFE+DFE

CSRZ

ATCVE

ATC

VE


VE2

optical PMDC

1stage

2stage

in-line(distributed

el. Equalizer

FFE+DFE

MLSE (=VE)

PMD-, Q-thresholds from literatur

details on next pages

Q-penalty vs. PMD curves andQ-p. vs. (Q,PMD) for FFE+DFE

details on next pages

0

1

2

3

4

5

6

7

8

12 17 22Baseline Q (dB)

Resid

ual Q

pen

alt

y a

fter

PM

D

eq

ualizati

on

(d

B)

5ps

10ps

15ps

20ps

25ps

PMD rules with optical compensators (1stage, 2stage)

PMD thresholds are based on literature values (10-5 outage) (multi-order PMD simulations) Near-optimum feedback signal (eye monitor) for 2 stage device

Q threshold referenced to ATC receiver (w/o. PMD)

eopmdc_axes

PMD / Tbit 0.0 0.1 0.2 0.3 0.4 0.5

rel. O

SN

R p

enalty

(dB

)

-2

0

2

4

6

8

multi-stage

Rx2stage

OPMDC1stage

Q-p

enal

ty [d

B]

PMD threshold

Q threshold (referenced to ATC receiver)

PMD in-line mitigation /1

In-line PMD mitigation (optical, bit-rate independent approach)

Simulation on EOP and DOP correlation DOP < 0.9 is a condition to limit the penalty below around 2 dB

EOP [dB]

PMD

PMD + CD + NL

DOP

ECP [dB]EOP [dB]DOP [dB]


EOP – DOP correlation Possible behaviour of DOP

along the link

Pulses depolarisation can be caused by both first and second order PMD (in this cases, first order is dominant)

PMD

PMD + CD + NL


Compensation at receiver DOP degrades along the link. The energy causing ISI can be no longer discriminated from the

energy within the bit slot based on the polarisation. As a consequence, the performance improvement is limited.

In-line compensation DOP is maintained high (> 0.9) along the link and pulses are confined in the bit slot

5 x 100 Km

5 x 100 Km

EOP [dB]

EOP [dB]

Physical terminal designElectronic equalisation / Receiver

Dynamic electronic signal processing in receiver for PMD / distortion mitigation ensures maximum length optical paths

under dynamically changing path conditions in dynamic optical networks

Most-likely equalisation schemes identified Feed-forward + decision feedback equal. (FFE+DFE) analog

processing Viterbi equaliser (VE, also referred to as MLSE) digital

processing

.....

Cn-1

Tc

Cn

C0

Tc

C1

CUref

TB

-+

B1

FFE

DFE

low passfilter

ADCViterbiequal.

FFE + DFEViterbi equaliser (MLSD)

PMD rules without and with mitigation by electronic equalisers

Performance analysed: Q-penalty vs. DGD equalisers: FFE+DFE, VE

as reference: Receiver w. adaptive threshold control (ATC) modulation formats: NRZ, duobinary, CSRZ

-1

0

1

2

3

4

5

6

0 20 40 60 80 100

DGD [ps]

Q-f

ac

tor

pe

na

lty

[d

B]

@ 1

*10

-3

duobinaryNRZ

VE1

FFE+DFE

CSRZ

ATCVE

ATC

VE


VE2

PMD rules with mitigation by MLSE

MLSE model for network simulation VE with 4 states and 3 ADC bits for 10.7 Gb/s Assumption: PMD 1st order is the dominant effect for NRZ, ODB, CM-DML Figures show PMD penalty after MLSE related to b-t-b with equaliser for each modulation format Parameter DGD; Chromatic dispersion: 0 ps/nm

10 11 12 13 14 15 16 170

0.5

1

1.5

2

2.5

3

3.5

4ODB

Baseline Q [dB]

Q p

enal

ty [

dB

]

16ps32ps48ps64ps80ps

10 12 14 16 180

0.5

1

1.5

2

2.5

3

3.5

4

4.5NRZ

Baseline Q [dB]

Q p

enal

ty [

dB

]


10 11 12 13 14 15-1

-0.5

0

0.5

1

1.5

2

2.5

3CM-DML

Baseline Q [dB] Q

pe

na

lty

[d

B]


NRZ ODB CM-DML

PMD rules of FFE+DFE equaliserbased on refined PMD model

In detail: FFE+DFE equaliser model for 10Gb/s NRZ BER limit trace in 1st and 2nd order PMD plane; given PMD, OSNR Integration of outage probability OP; Iteration: OP=10-5 by OSNR variation Table quantifies: PMD improvement by equaliser / margin

Mlogtab

DGD/PMD

SO

PM

D/P

MD

2

0 4

4.5

BER=limit

CP (BER>limit)

pdf of 1st + 2nd order PMDpdf of 1st + 2nd order PMD PMD rules for FFE+DFE PMD equaliserPMD rules for FFE+DFE PMD equaliser

0

1

2

3

4

5

6

7

8

12 17 22Baseline Q (dB)

Resid

ual Q

pen

alt

y a

fter

PM

D

eq

ualizati

on

(d

B)

5ps

10ps

15ps

20ps

25ps

Experimental evaluation of PMDC

PMD / Q dependency









PM

D o

rders

PMD: 1st order

1st+2nd

multi-order

PMD-C Measurement results

Polarization Scrambler

Tx10G DGD OSNR

Rx10G

BER

Polarization Scrambler

Pol. Contr. OA

Polarization Controller

PMD Emulator (1st order)

OPMOpt. Power

meter

Polarizer

Measurement setup:

Measurement results:OSNR penalty vs. DGD @ BER 1e-6

(10.7 Gb/s NRZ)

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80

DGD (ps)

OS

NR

pe

na

lty

[d

B]

uncompensated

compensated

• Compensation possible with the polarizer approach at 10 Gbit

• Can compensate 4.7 ps mean PMD (2 dB OSNR penalty)

Conclusion:

System parameters:

• Modulation format NRZ• Bitrate 10.7 Gbit• BER w/o FEC 1e-6

Network simulations w. PMD

PMD / Q dependency









PM

D o

rders

PMD: 1st order

1st+2nd

multi-order

Q penalty vs. mean DGD

0123456789

10,0

13,5

15,5

18,0

19,6

20,7

21,7

22,4

23,1

23,6

24,1

Q factor (baseline)

Q p

enal

ty

5 ps

7,5 ps

10 ps

12,5 ps

15 ps

17,5 ps

20 ps

22,5 ps

25 ps

27,5 ps

30 ps

32,5 ps

35 ps

Network simulation (RWA)

Q-factor distribution

0%

5%

10%

15%

20%

25%

30%

35%

12 14 16 18 20 22 24 26 28 30 32

Q-factor

Equaliser Rx

Standard RX

Modeled for standard receivers and for equalisers FFE5+DFE1

Static dimensioning simulations on DT-17nodes network, with random fiber PMD coefficient distribution:Avg. links load with standard Rx:

72%Avg. links load with equaliser FFE5+DFE1:79%And consequently the network dimensioning with equaliser results in less node relationsEqualiser provides more flexibility in the route selection (more routing options with Q-factor higher than the accepted threshold) thus enabling a more efficient network optimisation.

Network simulations with scaled PMD and with different PMD distribution (and other some pessimistic assumptions) on DT-17 network show blocking due to impairments (no transparent routing possible)

Possible approach for impairments-aware RWA including PMDC, Equalisers and 3R

Possible extension of RWA to overcome blocking events due to physical

impairments

Modified Dijkstra algorithm including information on different mitigation methods, together with a strategy to properly assign resources (regenerators, equalisers, PMDCs), trying to maintain transparent routing in a cost-effective way

Algorithm description

• In its iterative process the Dijkstra routing algorithm starts from a node that is reachable and tries to move to adjacent nodes: in the impairments-aware routing, to consider a node reachable the Q factor shall remain over the selected threshold. Comparison between Q and Q-threshold refers to the total Q-factor of the lightpath segment or to a single component of the Q factor, e.g. Q-penalty due to PMD greater than few dBs).

• If Q is below the threshold a blocking occurs and, in this case, instead of discarding the path routing under analysis (as in D26 simulations), a possible solution can be selected, among:

Putting an equaliser (or any other compensation technique) at the receiver Inserting an in-line PMDC Inserting a Regenerator (no transparent routing, last choice)

• It should be noted that all the rest of the network is unknown at this point (from the algorithm point of view) and decisions on how to solve possible Q-related blocking is not optimal, since cannot be based on the knowledge of the whole path/network

• In case all of the listed solutions can solve the blocking, the iterative Dijkstra process can continue. In order not to select just one solution (that in few next steps can become apparently the ‘worst’ one) all the three possible solutions are kept and independently ‘propagated’ with proper ‘labelling’ in order to keep trace of them

• For each kind of label (Regen, PMDC, EQUAL), in case a certain node is reached with different paths the path with the best Q-factor is selected. Since this procedure applies independently for each label, a certain node can be reached from a subpath ‘x’ adopting Regen and with subpath ‘y’ adopting PMDC

• The multiple labelling is kept and propagated till another blocking event occurs: in this case a single solution to solve the previous blocking has to be selected (otherwise the alternatives can grow exponentially), according to a predefined rule (e.g. minimum cost) and the same process applies.

• As a final result a single lightpath can be routed, for instance, with a regenerator and a couple of in-line PMDCs, or with any other combination. At this point a post-analysis can be performed in order to optimise Regenerators/PMDCs placement

Network example /1

A Z

lightpathQ > Qthreshold Q < Qthreshold

Comparison between Q and Qthreshold could refer to the total Qfactor of the lightpath segment or to a single component of the Q factor (e.g. Qpenalty due to PMD greater than few dBs)

A Z

A Z

A Z

Equaliser at RX

In-line PMDC

Regenerator

To overcome the blocking, one among the three approaches below can be chosen

i j

i j

i j

i j

Label type

Q < Qthreshold

Q > Qthreshold

Node not yet reached

Network example /2

A Z

A Z

A Z

Equaliser at RX

In-line PMDC

Regenerator

In case some solutions experience a further block while others are still valid, they are no longer considered. When only one solution remains, it is ‘promoted’ to permanent

Q < Qthreshold

Q < Qthreshold

‘promoted’ to permanent solution

i

i

i j

j

j k

k

k

Network example /4

in case more than one subpath with the same label reach a node, the subpath associated to the best Q will be selected and further propagated

x

iy

w

Label type

Q-facto

r

Other Info on subpath

26 Predecessor,…

22 Predecessor,…

21 Predecessor,…

Label type

Q-facto

r


24 Predecessor,…

25 Predecessor,…

22 Predecessor,…

Label type

Q-facto

r


23 Predecessor,…

24 Predecessor,…

24 Predecessor,…

Label

type

Q-factor


26 Predecessor x,…

25 Predecessor y,…

24 Predecessor w,…

Preliminary considerations

Possible approach for impairments-aware RWA including PMDC, Equalisers and 3R

• This procedure only applies to static network dimensioning. Extension to dynamic dimensioning requires further evaluations

• This method fits with heuristic approaches as the multi-layer graph RWA adopted in D26

• The method does not reach an optimum solution, but a post-elaboration with optimisation is possible (once the preferred path has been chosen, actual placement of PMDC/Regenerator can be optimised and some over-dimensioning removed)

• Mixing up different mitigation techniques, some configurations resulting form the algorithm could need further analysis

• Modelling of some components (e.g. PMDC) not yet available for implementation of the RWA algorithm. Moreover the computation of Qpenalty due to PMD in the different configurations should take into account other mitigation techniques possibly applied on the path

• In principle more solutions can be included (different mitigation solution at receiver can be computed, provided that a proper modelling in term of Q-factor is available)

PMD and PMD compensation NOBEL WP5 results NOBEL_WP5_PMD_summary_draft_4_extended.ppt Henning...

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