Inter
national
J
our
nal
of
Electrical
and
Computer
Engineering
(IJECE)
V
ol.
7,
No.
5,
October
2017,
pp.
2627
–
2634
ISSN:
2088-8708
2627
I
ns
t
it
u
t
e
o
f
A
d
v
a
nce
d
Eng
ine
e
r
i
ng
a
nd
S
cie
nce
w
w
w
.
i
a
e
s
j
o
u
r
n
a
l
.
c
o
m
Raman
Pumping
as
an
Ener
gy
Efficient
Solution
f
or
NyWDM
Flexible-grid
Elastic
Optical
Netw
orks
Arsalan
Ahmad
1
,
Andr
ea
Bianco
2
,
V
ittorio
Curri
3
,
Guido
Mar
chetto
4
,
and
Sar
osh
T
ahir
5
1
School
of
Electrical
Engineering
and
Computer
Science
(SEECS),
National
Uni
v
ersity
of
Sciences
and
T
echnology
(NUS
T),
Islamabad,
P
akistan
2,3
Department
of
Electronics
and
T
elecommunications
(DET),
Politecnico
di
T
orino,
T
urin,
Italy
4,5
Department
of
Control
and
Computer
Engineering
(D
A
UIN),
Politecnico
di
T
orino,
T
urin,
Italy
Article
Inf
o
Article
history:
Recei
v
ed:
Feb
23,
2017
Re
vised:
Jun
7,
2017
Accepted:
Jun
26,
2017
K
eyw
ord:
Fix
ed-grid
Fle
xible-grid
WDM
TDHMF
GN-Model
HF
A
ABSTRA
CT
This
paper
in
v
estig
ates
transparent
w
a
v
elength
rout
ed
optical
netw
orks
using
three
dif-
ferent
fiber
types
NZDSF
,
SMF
and
PSCF
-
and
v
alidates
the
ef
fecti
v
eness
of
Hybrid
Raman/EDF
A
Fiber
Amplification
(HF
A)
with
dif
ferent
pumping
le
v
els,
up
to
the
mod-
erate
60%
pumping
re
gime.
Nodes
operate
on
the
basis
of
fle
xible-grid
elastic
NyWDM
transponders
able
to
adapt
the
modulation
format
to
the
quality-of-transmission
of
the
a
v
ailable
lightpath,
e
xploiting
up
to
fi
v
e
12.5
GHz
spectral
slots.
Results
consider
a
37-
node
P
an-European
netw
ork
for
v
ariable
Raman
pumping
le
v
el,
span
length
and
a
v
erage
traf
fic
per
node.
W
e
sho
w
that
HF
A
in
moderate
pumping
re
gime
reduces
the
po
wer
con-
sumption
and
enhances
spectral
ef
ficienc
y
for
all
three
fiber
types
with
particular
e
vidence
in
NZDSF
.
In
essence
to
that,
introduction
of
HF
A
is
also
beneficial
to
a
v
oid
blocking
for
higher
traf
fic
loads.
Copyright
c
2017
Institute
of
Advanced
Engineering
and
Science
.
All
rights
r
eserved.
Corresponding
A
uthor:
Name:
Sarosh
T
ahir
Af
filiation:
D
A
UIN,
Politecnico
di
T
orino
Address:
Corso
Duca
de
gli
Abruzzi,
24,
10129
T
orino,
Italy
Email:
sarosh.tahir@polito.it
1.
INTR
ODUCTION
W
orldwide
IP
traf
fic
will
under
go
a
significant
incre
ase
of
up
to
23%
i
n
the
years
to
come,
as
estimated
in
[1].
Therefore,
operators
are
k
een
to
impro
v
e
the
capacity
of
currently
deplo
yed
Dense
W
a
v
elength
Di
vision
Multiple
xing
(D
WDM)
infrastructure.
A
cos
t
ef
fecti
v
e
solution
is
to
enhance
the
capacity
without
replacing
the
installed
equipment
[2].
Numerous
in
v
estig
ations
re
v
eal
three
promising
solutions
for
capacity
impro
v
ement:
the
achie
v
ement
of
elasticity
at
the
grid
le
v
el
[3],
the
use
of
adv
anced
modulation
formats
[4]
and
the
introduction
of
h
ybrid
Ra-
man/EDF
A
fiber
amplification
(HF
A)
[5]
to
lo
wer
ASE
noise
figure
[6]
[7].
W
e
in
v
estig
ate
the
merits
of
incorporat-
ing
aforementioned
tec
h
ni
ques
in
the
netw
ork
des
ign
problem.
Approaching
the
problem
from
a
transmission-le
v
el
point-of-vie
w
[8],
multile
v
el
modulation
formats
with
DSP-based
Tx/Rx
permit
to
maximize
the
spectral
ef
ficienc
y
(SE)
enabling
Nyquist-WDM
(NyWDM)
transmission
[9].
Moreo
v
er
,
the
y
enable
the
use
of
fle
xible
transponders
to
trade-of
f
the
bit-rate
(
R
b
)
with
the
lightpath
quality-of-transmission
(QoT).
A
major
current
focus
for
transmiss
ion
le
v
el
is
the
impro
v
ement
of
the
amplification
quality
.
The
seamless
solution
in
currently
deplo
yed
netw
orks
turns
out
to
be
the
use
of
HF
A,
i.e.
adding
Raman
pumping
to
EDF
As.
In-
deed,
it
has
been
sho
wn
in
[5]
that
HF
As
operated
in
modera
te
pumping
re
gime
are
a
feasible
solut
ion
for
upgrading
re-configurable
point-to-point
opti
cal
links.
Using
multile
v
el
modulation
formats,
linear
propag
ation
impairments
such
as
chromatic
dispersion
and
polarization
mode
dispersion
(PMD)
are
fully
reco
v
ered
by
the
Rx
DSP
imple-
menting
a
blind
equalizer
compensating
for
lightpath
de
gradations.
Therefore,
links
are
not
tailored
for
a
specific
transmission
technique,
and
transponders
may
adapt
the
deli
v
ered
(
R
b
)
to
the
lightpath
QoT
,
while
nodes
may
per
-
form
transparent
w
a
v
elength
routing.
As
a
consequence,
the
entire
netw
ork
can
be
configured
on
the
basis
of
a
J
ournal
Homepage:
http://iaesjournal.com/online/inde
x.php/IJECE
I
ns
t
it
u
t
e
o
f
A
d
v
a
nce
d
Eng
ine
e
r
i
ng
a
nd
S
cie
nce
w
w
w
.
i
a
e
s
j
o
u
r
n
a
l
.
c
o
m
,
DOI:
10.11591/ijece.v7i5.pp2627-2634
Evaluation Warning : The document was created with Spire.PDF for Python.
2628
ISSN:
2088-8708
T
able
1.
P
arameters
for
the
fiber
types
Fiber
T
ype
Loss
Dispersion
Ef
fecti
v
e
Area
dB
D
A
ef
f
[dB/km]
[ps/(nm
km)]
[
m
2
]
NZDSF
0.222
3.8
70
SMF
0.200
16.7
80
PSCF
0.167
21.0
135
T
able
2.
P
an-Eu
T
opology
P
arameters
P
an-Eu
mean
min
max
Fiber
Distance
(km)
648
218
1977
Node
De
gree
3.08
2
5
unique
QoT
parameter
for
ph
ysical
le
v
el
lightpath:
the
generalized
optical
signal-to-noise
ratio
(OSNR),
includ-
ing
both
the
ASE
noise
introduced
by
amplifiers
and
the
non-linear
interference
(NLI)
[10]
generated
by
the
K
err
ef
fect
in
fiber
propag
ation.
It
has
been
sho
wn
that
a
netw
ork
control
plane,
named
LOGO
(Local-Optimization
Global-Optimization),
based
on
local
OSNR
maximization
enhances
lightpath
QoT
[11].
Much
research
in
recent
years
has
focused
on
approaching
the
netw
ork
design
problem
with
the
intro-
duction
of
detailed
ph
ysical
layer
modelling
for
both
fix
ed
and
fle
xible-Grid
Netw
orks
[12]
[13]
[14].
In
[15],
we
sho
wed
the
adv
antages
of
using
HF
As
in
fix
ed-
g
r
id
netw
orks.
W
e
e
xtend
such
analysi
s
to
the
fle
xible-grid
scenario
in
[16]
to
sho
w
ho
w
HF
A
in
moderate
pumping
re
gime
reduces
the
spectral
occupanc
y
.
In
this
w
ork
we
perform
a
sensiti
vity
study
by
changing
i)
ph
ysical
layer
characteristics
lik
e
fiber
type,
Raman
pumping
le
v
el
(RPL)
and
span
length,
and
ii)
netw
ork
parameters
such
as
a
v
erage
traf
fic
per
node
(
R
b;N
).
Results
are
analysed
in
terms
of
performance
matrices
lik
e
spectral
ef
ficienc
y
,
po
wer
consumption
and
number
of
block
ed
requests.
The
remainder
of
this
paper
is
or
g
anized
as
follo
ws:
Sec.
2.,
introduces
the
transmissi
on
layer
model.
Sec.
3.,
pro
vides
details
on
netw
ork
layer
model
used.
Sec.
4.,
sho
ws
the
simulation
scenarios
and
results
obtained.
Finally
,
sec.
5.
gi
v
es
a
conclusion
and
highlights
the
possible
future
w
ork.
2.
TRANSMISSION
LA
YER
MODEL
W
e
consider
a
uniform,
uncompensated
and
amplified
netw
ork
topology
,
and
suppose
the
distance
between
the
amplifiers
-
the
fiber
span
L
s
-
is
the
same
for
all
netw
ork
links
as
well
as
the
amplifiers
g
ain
G
dB
=
dB
.
L
s
and
noise
figure
F
dB
.
W
e
assume
the
netw
ork
is
operating
in
C-Band
e
xploiting
fle
x-grid
t
ransponders
based
on
v
ariable
symbol
rate
R
S
G
.
On
this
transmission
scenario
we
may
apply
a
detailed
model
for
the
e
v
aluation
of
the
lighpaths
QoT
.
It
uses
the
incoherent
Gaussian
noise
model
(IGN)
[10]
to
e
v
aluate
the
amount
of
NLI
on
each
lighpath
that
together
with
the
ASE
noise
determines
the
related
OSNR.
Consequently
,
the
generalized
OSNR
for
a
lightpath
directly
connecting
no
intermediate
nodes
node
i
to
node
j
,
with
N
s
amplified
spans
is:
S
N
R
i;j
=
P
ch
N
s
[
P
AS
E
+
N
LI
P
3
ch
]
(1)
where
N
LI
and
P
ch
are
the
NLI
ef
ficienc
y
and
optimal
LOGO-defined
po
wer
per
channel
[11],
respecti
v
ely
.
Both
v
alues
refer
to
the
w
orst-case
s
cenario
represented
by
the
full
spectral
load,
that
in
general
is
close
to
be
realistic
in
an
y
case
thanks
to
the
weak
dependence
of
NLI
generation
on
the
spectral
occupation
[17].
F
or
the
optimal
po
wer
,
we
considered
a
hard-limit
of
20
dBm
gi
v
en
by
the
maximum
po
wer
that
the
amplifier
may
deli
v
er
on
the
entire
C-band,
b
ut
the
LOGO
v
alue
ne
v
er
induced
to
e
xce
ed
such
a
limit.
P
AS
E
is
the
ASE
noise
generated
by
a
single
amplifier
EDF
A
or
HF
A
whose
e
xpression
is:
P
AS
E
=
h
f
0
F
(
G
1)
R
S
G
(2)
where
h
is
the
Planks
constant,
f
0
is
the
C-band
center
frequenc
y
.
G
and
F
are
the
g
ain
and
noise
figure
in
linear
units.
F
or
pure
EDF
A
amplification
we
suppose
F
dB
=
5
dB,
while
introducing
some
Raman
pumping
F
dB
decreases
as
sho
wn
in
[5].
As
we
are
focusing
on
a
dynamic
netw
ork
scenario,
we
limit
Raman
amplification
to
the
moderate
pumping
scenario,
roughly
corresponding
to
up
to
60%
of
fiber
loss
reco
v
ered
by
Raman
g
ain.
Hence,
according
to
[5],
the
related
HF
A
beha
viour
is
practically
independent
of
the
channel
add/drop
and
does
not
modify
the
NLI
impairments
with
respect
to
the
ones
gi
v
en
by
the
use
of
pure
EDF
A,
and
the
only
ef
fect
of
Raman
is
the
beneficial
noise
figure
reduction.
W
e
analyze
the
possible
use
of
three
typical
fiber
types:
Single
Mode
Fiber
(SMF),
Pure-Silica
Core
Fiber
(PSCF)
and
Non-zero
Dispersion-Shifted
Fiber
(NZDSF).
The
main
fiber
parameters
are
sho
wn
in
table
1.W
e
IJECE
V
ol.
7,
No.
5,
October
2017:
2627
–
2634
Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE
ISSN:
2088-8708
2629
T
able
3.
Ph
ysical
layer
details
for
fle
xible-grid
Modulation
F
ormat
O
S
N
R
min;m
(dB)
R
b
(GBpS)
BpS
#
No.
of
Slots
!
1
2
3
4
5
PM-BPSK
4.323
2
20
40
60
80
100
PM-QPSK
7.334
4
40
80
120
160
200
PM-16QAM
13.887
8
80
160
240
320
400
PM-64QAM
19.709
12
120
240
360
480
600
assume
to
operate
with
Nyquist-WDM
(NyWDM)
transponders,
implementing
a
spectrally
sliceable
technology
,
attainable
using
v
ariable
symbol-rate
(
R
s
)
DSP
.
According
to
[
1
8]
,
B
sl
ot
=12.5
GHz
and
laser
sources
must
be
tunable
on
a
B
sl
ot
/2
grid.
T
ransponders
are
assumed
to
be
able
to
occup
y
up
to
5
slots.
Thus,
the
R
S
G
,
the
lightpath
spec
tral
occupation,
may
v
ary
from
12.5
up
to
62.5
Gbaud.
Assuming
a
typical
25%
protocol
and
coding
o
v
erhead
(OH),
the
net
symbol
rate
R
s
is
tunable
from
10
to
50
Gbaud,
step
10
Gbaud.
The
full
optical
C-band
(
B
opt
=
4
THz)
is
assumed
to
be
a
v
ailable.
Therefore,
each
point-to-point
link
has
320
spectral
slots
a
v
ailable.
W
e
assume
transponders
are
able
to
tune
the
deli
v
ered
bit-per
-symbol
(BpS)
switching
modulation
formats
as
sho
wn
in
T
a
b
l
e
3.
In
particular
,
we
assume
to
use
polarization-
di
vision
multiple
x
ed
(PM)
multile
v
el
modulation
formats
in
the
follo
wing
set
of
square
constellations
with
coherent
recei
v
ers:
Binary
Phase-Shift
K
e
ying
(PM-
BPSK),
Quadrature
Phase-
Shift
K
e
ying
(P
M-QPSK),
16
Quadrature
Amplitude
Modulation
(PM-16QAM)
and
64-Quadrature
Amplitude
Modulation
(PM-64QAM).
Hence,
the
net
bit-rate
R
b
per
lightpath
may
v
ary
from
20
to
600
Gbps.
The
parameter
enabling
the
use
of
a
specific
modulation
format
is
the
lightpath
OSNR
that
must
e
xceeds
the
v
alue
required
by
each
format,
as
display
in
T
able
3,
second
column.Considering
possible
transparent
w
a
v
elength
routing
in
nodes,
the
OSNR
for
a
gi
v
en
lightpath
crossing
N
N
odes
is:
S
N
R
=
1
P
N
nodes
1
i
=1
1
O
S
N
R
i;i
+1
(3)
Furthermore,
table
3
depicts
information
a
b
out
multile
v
el
modulation
formats
used
with
their
minimum
required
SNR
S
N
R
min;m
,
the
number
of
Bits-per
-Symbol
(BpS)
and
the
bit
rate
C
m
.
The
O
S
N
R
min;m
is
deri
v
ed
from
the
tar
get
BER
defined
by
the
forw
ard
error
correction
(FEC)
code
as
follo
ws:
S
N
R
min;m
=
1
m
(
B
E
R
tar
g
et
)
(4)
where
m
is
the
function
gi
ving
the
BER
for
modulation
format
m
.
In
the
paper
,
we
assume
B
E
R
=
10
2
.
3.
NETW
ORK
LA
YER
MODEL
W
e
consider
an
IP
netw
ork
o
v
er
an
optical
WDM
infrastructure
with
a
fle
xible
distrib
ution
of
the
spectrum
grid
[19].
The
ph
ysical
topology
of
the
netw
ork
can
be
represented
as
a
directed
graph
in
which
v
ertices
representing
nodes
are
connected
with
edges
representing
ph
ysical
links
e
xisting
in
the
netw
ork.
W
e
assumed
to
ha
v
e
an
IP
router
and
an
Optical
Cross
Connect
(O
XC)
installed
at
each
node
in
the
netw
ork.
Each
ph
ysical
link
from
i
to
j
is
characterized
by
a
ph
ysical
length
D
ij
,
e
xpressed
in
km
and
such
that
D
ij
=
D
j
i
.
The
traf
fic
demands
are
transmitted
from
the
source
to
the
destination
node
using
lightpaths,
which
are
optical
logical
channels
that
can
span
o
v
er
one
or
more
ph
ysical
links.
A
traf
fic
demand
can
use
one
or
more
consecuti
v
e
lightpaths
to
reach
the
final
destination.
In
this
case,
the
IP
router
electronically
switches
the
demand
between
tw
o
consecuti
v
e
lightpaths.
The
set
of
all
the
established
lightpaths
forms
the
logical
topology
(L
T).
Each
lightpath
is
generated
at
the
source
node
and
terminated
at
the
destination
node
by
dedicated
fle
xible
transponders.
A
fle
xible
transponder
can
use
an
y
modulation
format
among
the
a
v
ailable
ones
and
it
is
characterized
by
a
maximum
transmitting
capacity
C
M
ax
equal
to
300
Gbps.
At
intermediate
nodes
the
lightpath
is
transparently
switched
by
the
fle
xible-grid
O
XC.
Since
optical
switching
de
vices
w
orking
in
a
gridless
f
ashion
are
not
yet
a
v
ailable,
the
spectrum
is
usually
di
vided
in
spectrum
slots
with
a
much
finer
granularity
than
the
coarse
ITU
grid.
The
optical
spectrum
on
each
link
is
di
vided
in
slot
of
size
12.5
GHz
[18],
which
results
in
320
slots
per
link
by
di
viding
the
C-band
(4
THz)
by
the
slot
HF
A:
an
Ener
gy
Ef
ficient
Solution
for
Fle
xible
Optical
Networks
(Sar
osh
T
ahir)
Evaluation Warning : The document was created with Spire.PDF for Python.
2630
ISSN:
2088-8708
size.
It
is
also
assumed
that
tw
o
empty
slots
are
left
as
guard-band
between
tw
o
lightpaths
so
that
the
O
XC
can
correctly
switch
the
lightpaths.
A
gi
v
en
modulati
on
format
and
a
gi
v
en
number
of
spectrum
slots
are
associated
to
each
lightpath.
Each
modulation
format
m
is
characterized
by
a
maximum
bandwidth
capacity
C
m
of
a
single
spectrum
slot
and
by
a
maximum
optical
reach
in
km.
The
modulation
formats
considered
in
this
w
ork,
their
transmission
rate
and
their
optical
reach
are
listed
in
T
able
3.
Depending
on
the
modulation
chosen,
it
is
thus
possible
to
create
either
lightpaths
for
long
distances
operating
at
lo
w
bit
rate
or
lightpaths
for
short
distances
charact
erized
by
v
ery
high
bit
rate.
The
maximum
among
the
optical
reach
distances
of
the
a
v
ailable
modulation
formats
corresponds
to
the
maximum
reach
of
the
fle
xible
transponder
.
The
maximum
number
of
slots
that
can
be
associated
to
a
lightpath
with
modulation
format
m
is
equal
to
b
C
M
ax
=C
m
c
.
The
netw
ork
design
initially
defines
the
set
of
lightpaths
that
can
satisfy
the
traf
fic
demands,
i.e.,
the
design
of
the
L
T
,
whi
le
optimizing
a
gi
v
en
design
tar
get.
When
deciding
which
lightpaths
ha
v
e
to
be
es
tablished,
it
is
required
to
choose
for
each
lightpath
the
most
suitable
modulation
and
the
correct
number
of
slots
according
to
the
distance
that
the
lightpath
has
to
co
v
er
and
the
amount
of
traf
fic
that
it
has
to
carry
.
Finally
,
slots
in
the
spectrum
are
assigned
to
each
lightpath,
with
the
constraints
that
the
same
set
of
consecuti
v
e
slots
is
assigned
to
a
lightpath
o
v
er
all
the
ph
ysical
links
that
the
lightpath
is
flo
wing
on.
Ob
viously
,
each
slot
on
a
ph
ysical
link
can
be
assigned
only
to
one
lightpath.
3.1.
Design
of
Flexible-Grid
Netw
orks
Under
a
Detailed
T
ransmission
Lay
er
Model
W
e
f
ace
the
problem
of
designing
a
logical
topology
and
mapping
it
to
a
ph
ysical
infrastructure,
the
classical
Logical
T
opology
Design-Routi
ng
and
Spectrum
Assignment
(L
TD-RSA).
This
f
amily
of
problems
is
defined
by
an
inte
ger
linear
program
(ILP),
which
is
NP
complete.
Because
of
the
comple
xity
of
the
problem
the
use
of
heuristic
algorithms
is
justified
and
it
is
a
comm
on
approach
to
solv
e
it.
Thus,
we
use
a
v
ery
simple
greedy
heuristic,
named
Direct
Lightpath
Heuristic
(DLH),
to
define
a
set
of
lightpaths
satisfying
the
traf
fic
matrix
[19].
W
e
choose
a
simple
heuristic
because
the
focus
of
the
w
ork
is
to
discuss
the
influence
of
ph
ysica
l
layer
parameters
lik
e
the
use
of
HF
A
and
dif
ferent
fiber
types
on
netw
ork
perform
ance
metrics,
with
no
major
emphasis
on
resource
allocation
policies.
A
brief
summary
of
the
DLH
heuristic
is
pro
vided,
whereas
a
more
detailed
description
can
be
found
in
[19].
DLH
satisfies
node-to-node
traf
fic
requests
be
ginning
from
the
lar
gest
one.
Each
node-to-node
traf
fic
request
is
transported
on
the
number
of
lightpaths
depending
on
the
ratio
between
traf
fic
reques
t
and
lightpath
capacity
.
Dif
ferently
from
[19],
we
include
a
detailed
ph
ysical
layer
model
performing
the
computation
of
the
SNR
v
alues
to
better
define
the
transmission
reach
for
dif
ferent
modulation
formats
for
each
lightpath.
The
algorithm
w
orks
as
follo
w
on
each
traf
fic
request.
Initially
,
the
shortest
path
from
source
to
destination
is
analysed.
The
path
is
feasible
if
its
ph
ysical
length
is
less
than
the
maximum
admissible
optical
reach
of
the
transmitter
using
the
lo
west
modulation
format,
i.e.
BPSK,
based
on
the
OSNR.
If
feasible,
the
heuristic
selects
the
highest
m
od
ul
ation
format
am
ong
the
a
v
ailable
ones
that
can
be
supported
on
the
path,
to
use
as
fe
w
as
possible
spectrum
slots.
The
a
v
ailability
of
the
spectrum
slots
on
the
selected
path
is
v
erified.
If
suf
ficient
slots
are
a
v
ailable,
the
lightpath
is
established
and
the
traf
fic
request
is
allocated
to
the
lightpath.
Otherwise,
the
same
operations
are
repeated
for
the
ne
xt
feasible
shortest
path
from
source
to
destination,
until
the
request
is
satisfied.
When
the
request
is
satisfied,
the
heuristic
mo
v
es
to
the
ne
xt
traf
fic
request
repeating
the
same
procedure,
until
all
requests
are
satisfied,
pro
viding
a
set
of
lightpaths
and
spectrum
slot
allocation.
When
all
traf
fic
demands
ha
v
e
been
assigned,
spectrum
slots
are
associated
with
each
lightpath.
If
a
slot
assignment
is
possible,
the
solution
is
v
alidated,
otherwise
it
is
rejected.
4.
RESUL
TS
4.1.
Netw
ork
Simulation
Scenarios
In
this
section,
we
present
the
results
of
using
HF
A
with
dif
ferent
fiber
types.
In
a
pre
vious
contrib
ution
[16]
only
one
performance
metric
w
as
considered
for
simplicity:
the
spectral
occupanc
y
(SO)
defined
as
the
total
number
of
used
spectral
slots
di
vided
by
the
total
number
of
a
v
ailable
slots.
Ob
viously
,
a
decrease
in
SO
reflects
a
better
ef
ficienc
y
in
spectrum
utilization.
Dif
fe
rently
from
[16],
here
we
analysed
the
performance
ag
ainst
the
ma-
trices
lik
e
po
wer
consumption,
number
of
block
ed
requests
and
spectral
ef
ficienc
y
.
W
e
use
the
follo
wing
e
xpression
IJECE
V
ol.
7,
No.
5,
October
2017:
2627
–
2634
Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE
ISSN:
2088-8708
2631
Figure
1.
[P
an-EU
T
opology]
0.4
0.5
0.6
0.7
0.8
0.9
0
10
20
30
40
50
60
Spectral Efficiency
Raman Pumping [%]
NZDSF
PSCF
SMF
Figure
2.
Spectral
ef
ficienc
y
vs.
Raman
pumping
le
v
el
for
dif
ferent
fiber
types
(traf
fic
=
1500
Gbps,
number
of
nodes
=
37,
span
length
=
100km
and
a
v
erage
connecti
vity
=
3.08)
for
the
spectral
ef
ficienc
y
SE
:
S
E
=
B
pS
R
s
B
ch
[
bit=s
H
z
]
(5)
Se
v
eral
traf
fic
matrices
are
generated,
for
v
ariable
a
v
erage
generated
traf
fic
per
node.
T
raf
fic
loads
are
analysed
into
tw
o
re
gimes:
lo
w
load
re
gime
and
high
load
re
gime.
In
the
lo
w
load
re
gime
we
mainly
use
the
SE
along
with
po
wer
consumption
as
a
performance
inde
x,
in
the
high
load
re
gime
we
focus
on
the
number
of
block
ed
requests
along
with
SE.
W
e
consider
real
topology
of
the
P
an-European
(P
an-Eu)
netw
ork
sho
wn
in
Fig.
1,
with
the
distance
between
nodes,calculated
using
Eq.
1
in
[20],
ranging
from
218km
to
1977km.
The
a
v
erage
node
de
gree
is
3.08.
Detailed
netw
ork
characteristics
are
reported
in
T
ab
.2.
W
e
consider
the
non-linear
interference
(NLI)transmission
model,
introduced
in
Sec.
2.
The
design
heuristic
is
in
v
esti
g
at
ed
o
v
er
:
the
fiber
type,
among
SMF
,
PSCF
and
NZDSF
,
as
in
[15],
Raman
pumping
le
v
el
(
R
P
L
),
span
length
L
s
and
traf
fic
load
R
b;N
.
4.2.
Effect
due
to
change
in
Raman
Pumping
Le
v
el
R
P
L
Fig.
2
sho
ws
the
spectral
ef
ficienc
y
respecti
v
ely
vs.
RPL,
for
traf
fic
load
R
b;N
=
1500
Gbps,
L
s
=
100
km,
N
num
=
37
nodes
and
N
C
onn:
=
3.08
and
three
dif
ferent
fiber
types.
It
is
e
vident
that
SE
increases
with
the
increase
in
RPL.
This
is
because
the
amplifier
noise
figure
decreases
with
the
increase
in
RPL.
PSCF
sho
ws
the
highest
SE
due
to
its
ph
ysical
properties
which
help
it
to
cater
the
non-linearities
more
ef
ficiently
.
while
increasing
RPL
from
0-6
(i.e.
from
pure
EDF
A
upto
60%
Raman
pumping)
NZDSF
sho
ws
an
SE
impro
v
ement
of
upto
12%.
This
impro
v
ement
is
9%
and
7%
for
SMF
and
PSCF
respecti
v
ely
.
Fig.
3a
sho
ws
the
po
wer
consumption
vs.
RPL,
for
traf
fic
load
R
b;N
=
,
1500
Gbps,
L
s
=
100
km,
N
num
=
37
nodes
and
N
C
onn:
=
3.08
and
three
dif
ferent
fiber
types.
The
po
wer
consumption
decreases
as
the
RPL
increases
due
to
the
lo
w
po
wer
consumption
of
IP
routers
the
Ram
an
impro
v
ement
v
aries
fiber
by
fiber
.
Out
of
three
finer
types,
here
NZDSF
enjo
ys
the
maximum
benefit
due
to
the
used
of
HF
A
with
respect
to
other
tw
o
fiber
types.
PSCF
,
already
being
ener
gy
ef
ficient,
tak
es
the
least
adv
antage
of
the
phenomena.
F
or
the
remaining
in
v
estig
ations,
tw
o
RPLs
are
used:
EDF
A
only
,
RPL=0%
(RA0)
and
RPL=60%
(RA60).
4.3.
Effect
due
to
change
in
the
span
length
L
s
Fig.
3b
sho
ws
the
spectral
ef
ficienc
y
vs.
the
L
s
at
R
b;N
=
1000
Gbps,
N
num
=
37
nodes
N
C
onn:
=
3.08
and
three
dif
ferent
fiber
types.
As
the
the
span
length
increas
es
from
80km
to
120
km,
we
notice
a
decrease
in
the
spectral
ef
fici
enc
y
.
This
is
because
of
the
increase
in
ph
ysical
distance
between
the
amplifiers
which
adds
more
linear
and
non
linear
impurities
to
the
system.
Since
higher
order
modulation
formats
are
used
for
shorter
distances
which
transforms
into
the
use
of
lo
wer
order
modulation
formats
by
increasing
the
distance.
Therefore
as
the
HF
A:
an
Ener
gy
Ef
ficient
Solution
for
Fle
xible
Optical
Networks
(Sar
osh
T
ahir)
Evaluation Warning : The document was created with Spire.PDF for Python.
2632
ISSN:
2088-8708
91.6
91.8
92
92.2
92.4
0
10
20
30
40
50
60
Power [MW]
Raman Pumping Level
NZDSF
PSCF
SMF
(a)
Po
wer
consumption
vs.
Raman
pumping
le
v
el
for
dif
fer
-
ent
fiber
types
(traf
fic
=
1500
Gbps,
number
of
nodes
=
37,
span
length
=
100km
and
a
v
erage
connecti
vity
=
3.08)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
80
90
100
110
120
Spectral Efficiency
Span Lenght [km]
NZDSF EDFA
PSCF EDFA
SMF EDFA
NZDSF Raman
PSCF Raman
SMF Raman
(b)
Spectral
ef
ficienc
y
vs.
Span
Length
for
dif
ferent
fiber
types
(traf
fic
=
1000
Gbps,
number
of
nodes
=
37
and
a
v
erage
connecti
vity
=
3.08)
89.9
90
90.1
90.2
90.3
90.4
90.5
90.6
80
90
100
110
120
Power [MW]
Span Lenght [km]
NZDSF EDFA
PSCF EDFA
SMF EDFA
NZDSF Raman
PSCF Raman
SMF Raman
(c)
Po
wer
Consumption
vs.
Span
Length
for
dif
ferent
fiber
types
(traf
fic
=
1000
Gbps,
number
of
nodes
=
37
and
a
v
erage
connecti
vity
=
3.08)
0
100
200
300
400
500
600
500
1000
1500
2000
2500
3000
3500
4000
Number of Blocked Requests
Traffic [Gb/s]
NZDSF EDFA
PSCF EDFA
SMF EDFA
NZDSF Raman
PSCF Raman
SMF Raman
(d)
Number
of
block
ed
requests
vs.
T
raf
fic
for
di
f
ferent
fiber
types
(number
of
nodes
=
37,
span
length
=
100km
and
a
v
er
-
age
connecti
vity
=
3)
Figure
3
distance
increases
OSNR
decreases
due
to
the
use
of
l
o
wer
order
modulation
formats.
Resul
ting
in
the
decrease
of
spectral
ef
ficienc
y
.This
decrease
in
SE
is
well
addressed
by
increasing
RPL
especially
for
NZDSF
.
The
e
xplanation
for
this
beha
viour
is
related
to
the
comments
to
results
of
Fig.
2.
W
e
are
observing
impro
v
ement
in
SE
enabled
by
RPL,
the
fiber
hierarch
y
already
observ
ed
in
Fig.
2.
Fig.
3c
reports
the
po
wer
consumption
vs.the
L
s
at
R
b;N
=
1000
Gbps,
N
num
=
37
nodes
N
C
onn:
=
3.08
and
three
dif
ferent
fiber
types
to
discuss
the
ef
fect
due
to
ph
ysical
distance
L
s
between
in-line
amplifiers.
Except
for
NZDSF
,
it
is
e
vident
that
po
wer
consumption
reduces
with
the
increase
in
span
length.
Which
is
due
to
in
v
olv
ement
of
lesser
electronic
equipment,
especially
in-line
amplifiers.
The
v
ariation
sho
wn
by
each
fiber
is
dif
ferent
as
the
L
s
increases
from
80
km
to
120
km.
In
particular
,
NZDSF
displays
a
much
lar
ger
adv
antage
as
compared
other
tw
o
fibers.
Since
we
notice
an
o
v
er
all
decrease
in
the
po
wer
consumption
of
a
system
e
v
en
for
the
longer
spans.
Therefore
introduction
of
HF
A
is
also
beneficial
in
reducing
the
ener
gy
requirements
of
a
netw
ork.
4.4.
Effect
due
to
change
in
Load
Le
v
el
Number
of
block
ed
requests
depicted
in
Figs.
3d
e
xplains
the
netw
ork
performance
under
hea
vy
traf
fic
loads
for
L
s
=
100
km,
N
num
=
37
nodes
and
N
C
onn:
=
3.08
and
three
dif
ferent
fiber
types.
In
the
p
r
o
vided
static
solution,
spectrum
resources
can
not
allocated
due
to
to
una
v
ailability
slots
in
one
or
more
than
one
fiber
in
a
link.
Which
results
in
blocking
of
traf
fic
requests.
It
is
e
vident
that
the
the
number
increases
with
the
increase
in
traf
fic
load.
In
case
of
NZDSF
for
pure
EDF
A,
we
f
ace
blocking
starting
from
2000
Gbps
that
increases
upto
the
count
of
548
i.e
41%
of
total
requests
generated.
(T
otal
number
of
requests
=
N
num
*
N
num
-
N
num
).
This
implies
that
IJECE
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October
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IJECE
ISSN:
2088-8708
2633
netw
ork
with
pure
EDF
A
may
not
carry
hea
vy
traf
fic
loads
using
NZDSF
.
But
the
same
netw
ork
with
the
same
fiber
can
be
impro
v
ed
upto
the
one
using
SMF
by
introducing
HF
A.
This
is
an
impro
v
ement
of
almost
20%.
in
case
of
SMF
and
PSCF
the
reduction
in
the
number
of
block
ed
requests
is
8%
and
2%
respecti
v
ely
.
5.
CONCLUSIONS
Prior
w
ork
has
documented
the
ef
fecti
v
eness
of
detailed
ph
ysical
layer
modelling
for
both
fix
ed
and
fle
xible-Grid
Netw
ork.
Ho
we
v
er
a
proposed
solution
to
reduce
spectral
occupanc
y
has
to
be
the
use
of
Hybrid
Raman/EDF
A
Fiber
Amplification.
In
this
study
we
tested
the
impact
of
dif
ferent
fiber
types
and
moderate
Ra-
man
pumping
as
a
complement
to
EDF
A
in
fle
xible
grid
optical
netw
orks.
W
e
considered
t
hree
typical
fiber
types
NZDSF
,
SMF
and
PSCF
and
e
v
aluated
the
benefit
of
Raman
pumping
ag
ai
nst
traf
fic
load
and
span
length.
we
found
that
the
maximum
considered
percentage
of
Raman
amplification
-
60%
of
the
span
loss
in
dB
-
permits
to
increase
SE
and
reduces
po
wer
consumption.
In
addition,
the
impro
v
ement
noted
in
our
study
is
a
significant
decrease
in
number
of
block
ed
request
as
a
result
of
HF
A
introduction.
Furthermore,as
observ
ed
for
fix
ed-grid
netw
orks
[15],
the
fiber
e
xperiencing
the
lar
gest
benefit
from
Raman
pumping
is
t
he
one
e
xperiencing
the
lar
gest
transmission
impairments,
i.e.,
the
NZDSF
in
our
case.
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IJECE
V
ol.
7,
No.
5,
October
2017:
2627
–
2634
Evaluation Warning : The document was created with Spire.PDF for Python.