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
Page 2
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
Page 3
PMD/Receiver models
PMD / Q dependency
•Equaliser (FFE + DFE)
•Receiver (AT)•In-line compensator
•Receiver•1stage/2stage PMDC
•Receiver (NRZ, CS-RZ, DB) see mitigation•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
PMD: 1st order
1st+2nd
multi-order
Page 4
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
Page 5
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)
Page 6
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
Page 7
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
< >
Page 8
PMD mitigation
PMD / Q dependency
•Equaliser (FFE + DFE)
•Receiver (AT)•In-line compensator
•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
PMD: 1st order
1st+2nd
multi-order
Page 9
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
Q-penalty vs. DGD (=3xPMD)
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
Page 10
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)
Page 11
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]
Page 12
PMD in-line mitigation /2
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
Page 13
PMD in-line mitigation /3
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]
Page 14
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)
Page 15
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
Q-penalty vs. DGD (=3xPMD)
VE2
Page 16
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
]
16ps32ps48ps64ps80ps
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]
16ps32ps48ps64ps80ps
NRZ ODB CM-DML
Page 17
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
Page 18
Experimental evaluation of PMDC
PMD / Q dependency
•Equaliser (FFE + DFE)
•Receiver (AT)•In-line compensator
•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
PMD: 1st order
1st+2nd
multi-order
Page 19
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
Page 20
Network simulations w. PMD
PMD / Q dependency
•Equaliser (FFE + DFE)
•Receiver (AT)•In-line compensator
•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
PMD: 1st order
1st+2nd
multi-order
Page 21
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.
Page 22
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
Page 23
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
Page 24
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
Page 25
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
Page 26
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
Other Info on subpath
24 Predecessor,…
25 Predecessor,…
22 Predecessor,…
Label type
Q-facto
r
Other Info on subpath
23 Predecessor,…
24 Predecessor,…
24 Predecessor,…
Label
type
Q-factor
Other Info on subpath
26 Predecessor x,…
25 Predecessor y,…
24 Predecessor w,…
Page 27
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)