<s>
In	O
telecommunication	O
,	O
equalization	B-Algorithm
is	O
the	O
reversal	O
of	O
distortion	O
incurred	O
by	O
a	O
signal	O
transmitted	O
through	O
a	O
channel	O
.	O
</s>
<s>
Equalizers	B-Algorithm
are	O
used	O
to	O
render	O
the	O
frequency	O
response	O
—	O
for	O
instance	O
of	O
a	O
telephone	O
line	O
—	O
flat	O
from	O
end-to-end	O
.	O
</s>
<s>
Telephones	O
,	O
DSL	O
lines	O
and	O
television	O
cables	O
use	O
equalizers	B-Algorithm
to	O
prepare	O
data	O
signals	O
for	O
transmission	O
.	O
</s>
<s>
Equalizers	B-Algorithm
are	O
critical	O
to	O
the	O
successful	O
operation	O
of	O
electronic	O
systems	O
such	O
as	O
analog	O
broadcast	O
television	O
.	O
</s>
<s>
Early	O
telephone	O
systems	O
used	O
equalization	B-Algorithm
to	O
correct	O
for	O
the	O
reduced	O
level	O
of	O
high	O
frequencies	O
in	O
long	O
cables	O
,	O
typically	O
using	O
Zobel	O
networks	O
.	O
</s>
<s>
These	O
kinds	O
of	O
equalizers	B-Algorithm
can	O
also	O
be	O
used	O
to	O
produce	O
a	O
circuit	O
with	O
a	O
wider	O
bandwidth	O
than	O
the	O
standard	O
telephone	O
band	O
of	O
300Hz	O
to	O
3.4kHz	O
.	O
</s>
<s>
It	O
is	O
necessary	O
to	O
remove	O
or	O
cancel	O
any	O
loading	O
coils	O
in	O
the	O
line	O
before	O
equalization	B-Algorithm
can	O
be	O
successful	O
.	O
</s>
<s>
Equalization	B-Algorithm
was	O
also	O
applied	O
to	O
correct	O
the	O
response	O
of	O
the	O
transducers	O
,	O
for	O
example	O
,	O
a	O
particular	O
microphone	B-Application
might	O
be	O
more	O
sensitive	O
to	O
low	O
frequency	O
sounds	O
than	O
to	O
high	O
frequency	O
sounds	O
,	O
so	O
an	O
equalizer	B-Algorithm
would	O
be	O
used	O
to	O
increase	O
the	O
volume	O
of	O
the	O
higher	O
frequencies	O
(	O
boost	O
)	O
,	O
and	O
reduce	O
the	O
volume	O
of	O
the	O
low	O
frequency	O
sounds	O
(	O
cut	O
)	O
.	O
</s>
<s>
A	O
television	O
equalizer	B-Algorithm
consequently	O
typically	O
requires	O
more	O
filter	O
sections	O
than	O
an	O
audio	O
equalizer	B-Algorithm
.	O
</s>
<s>
To	O
keep	O
this	O
manageable	O
,	O
television	O
equalizer	B-Algorithm
sections	O
were	O
often	O
combined	O
into	O
a	O
single	O
network	O
using	O
ladder	O
topology	O
to	O
form	O
a	O
Cauer	O
equalizer	B-Algorithm
.	O
</s>
<s>
The	O
second	O
issue	O
is	O
that	O
phase	O
equalization	B-Algorithm
is	O
essential	O
for	O
an	O
analog	O
television	O
signal	O
.	O
</s>
<s>
Modern	O
digital	O
telephone	O
systems	O
have	O
less	O
trouble	O
in	O
the	O
voice	O
frequency	O
range	O
as	O
only	O
the	O
local	O
line	O
to	O
the	O
subscriber	O
now	O
remains	O
in	O
analog	O
format	O
,	O
but	O
DSL	O
circuits	O
operating	O
in	O
the	O
MHz	O
range	O
on	O
those	O
same	O
wires	O
may	O
suffer	O
severe	O
attenuation	O
distortion	O
,	O
which	O
is	O
dealt	O
with	O
by	O
automatic	O
equalization	B-Algorithm
or	O
by	O
abandoning	O
the	O
worst	O
frequencies	O
.	O
</s>
<s>
Picturephone	B-Application
circuits	O
also	O
had	O
equalizers	B-Algorithm
.	O
</s>
<s>
In	O
digital	O
communications	O
,	O
the	O
equalizer	B-Algorithm
's	O
purpose	O
is	O
to	O
reduce	O
intersymbol	O
interference	O
to	O
allow	O
recovery	O
of	O
the	O
transmit	O
symbols	O
.	O
</s>
<s>
MMSE	B-General_Concept
equalizer	B-Algorithm
:	O
designs	O
the	O
filter	O
to	O
minimize	O
E[|e|2],	O
where	O
e	O
is	O
the	O
error	O
signal	O
,	O
which	O
is	O
the	O
filter	O
output	O
minus	O
the	O
transmitted	O
signal	O
.	O
</s>
<s>
Zero-forcing	O
equalizer	B-Algorithm
:	O
approximates	O
the	O
inverse	O
of	O
the	O
channel	O
with	O
a	O
linear	O
filter	O
.	O
</s>
<s>
Decision	O
feedback	O
equalizer	B-Algorithm
:	O
augments	O
a	O
linear	O
equalizer	B-Algorithm
by	O
adding	O
a	O
filtered	O
version	O
of	O
previous	O
symbol	O
estimates	O
to	O
the	O
original	O
filter	O
output	O
.	O
</s>
<s>
Blind	B-Algorithm
equalizer	I-Algorithm
:	O
estimates	O
the	O
transmitted	O
signal	O
without	O
knowledge	O
of	O
the	O
channel	O
statistics	O
,	O
using	O
only	O
knowledge	O
of	O
the	O
transmitted	O
signal	O
's	O
statistics	O
.	O
</s>
<s>
Adaptive	O
equalizer	B-Algorithm
:	O
is	O
typically	O
a	O
linear	O
equalizer	B-Algorithm
or	O
a	O
DFE	O
.	O
</s>
<s>
It	O
updates	O
the	O
equalizer	B-Algorithm
parameters	O
(	O
such	O
as	O
the	O
filter	O
coefficients	O
)	O
as	O
it	O
processes	O
the	O
data	O
.	O
</s>
<s>
Viterbi	B-Algorithm
equalizer	I-Algorithm
:	O
Finds	O
the	O
maximum	O
likelihood	O
(	O
ML	O
)	O
optimal	O
solution	O
to	O
the	O
equalization	B-Algorithm
problem	O
.	O
</s>
<s>
BCJR	B-Error_Name
equalizer	I-Error_Name
:	O
uses	O
the	O
BCJR	B-Error_Name
algorithm	I-Error_Name
(	O
also	O
called	O
the	O
Forward-backward	B-Algorithm
algorithm	I-Algorithm
)	O
to	O
find	O
the	O
maximum	B-General_Concept
a	I-General_Concept
posteriori	I-General_Concept
(	O
MAP	O
)	O
solution	O
.	O
</s>
<s>
Turbo	B-Algorithm
equalizer	I-Algorithm
:	O
applies	O
turbo	O
decoding	O
while	O
treating	O
the	O
channel	O
as	O
a	O
convolutional	O
code	O
.	O
</s>
