
266 Optical Fiber Communication Systems with MATLAB
®
and Simulink
®
Models
6.9 Duobinary modulation format
D
esign
a
b
lock
d
iagram
o
f
a
p
recoder
t
hat
w
ould
g
enerate
t
ri-level
m
odied
d
uo-
binary
f
ormat
s
ignals.
Ma
ke
s
ure
t
hat
t
he
c
oefcients
o
f
t
he
lters
a
re
s
pecied.
H
int:
y
ou
m
ay
r
efer
t
o
p
ages
8
–11
o
f
t
he
l
ectures
n
otes.
H
ence,
d
erive
t
he
s
pectrum
o
f
t
he
s
ignals after the precoder of the modied duobinary.
I
f
po
ssible
ob
tain
t
he
p
recoders
f
or
A
MI
a
nd
d
uobinary
a
nd
t
heir
f
requency
r
esponses. Compare the frequency responses of the three modulation schemes.
S
ketch
t
he
s
tructure
o
f
t
he
t
ri-level
d
uobinary
p
recoder
w
ith
i
ts
o
utput
o
f
−1
,
0
, ...