<s>
Complementary	B-Device
code	I-Device
keying	I-Device
(	O
CCK	O
)	O
is	O
a	O
modulation	B-Application
scheme	O
used	O
with	O
wireless	B-General_Concept
networks	I-General_Concept
(	O
WLANs	O
)	O
that	O
employ	O
the	O
IEEE	O
802.11b	O
specification	O
.	O
</s>
<s>
In	O
1999	O
,	O
CCK	O
was	O
adopted	O
to	O
supplement	O
the	O
Barker	B-Protocol
code	I-Protocol
in	O
wireless	O
digital	O
networks	O
to	O
achieve	O
data	O
rate	O
higher	O
than	O
2Mbit/s	O
at	O
the	O
expense	O
of	O
shorter	O
distance	O
.	O
</s>
<s>
This	O
is	O
due	O
to	O
the	O
shorter	O
chipping	O
sequence	O
in	O
CCK	O
(	O
8	O
bits	O
versus	O
11	O
bits	O
in	O
Barker	B-Protocol
code	I-Protocol
)	O
that	O
means	O
less	O
spreading	O
to	O
obtain	O
higher	O
data	O
rate	O
but	O
more	O
susceptible	O
to	O
narrowband	O
interference	O
resulting	O
in	O
shorter	O
radio	O
transmission	O
range	O
.	O
</s>
<s>
The	O
Barker	B-Protocol
code	I-Protocol
,	O
however	O
,	O
only	O
has	O
a	O
single	O
chipping	O
sequence	O
.	O
</s>
<s>
CCK	O
is	O
the	O
form	O
of	O
modulation	B-Application
used	O
when	O
802.11b	O
operates	O
at	O
either	O
5.5	O
or	O
11	O
Mbit/s	O
.	O
</s>
<s>
CCK	O
was	O
selected	O
over	O
competing	O
modulation	B-Application
techniques	O
as	O
it	O
used	O
approximately	O
the	O
same	O
bandwidth	O
and	O
could	O
use	O
the	O
same	O
preamble	O
and	O
header	O
as	O
pre-existing	O
1	O
and	O
2	O
Mbit/s	O
wireless	B-General_Concept
networks	I-General_Concept
and	O
thus	O
facilitated	O
interoperability	O
.	O
</s>
<s>
The	O
CCK	O
modulation	B-Application
used	O
by	O
802.11b	O
transmits	O
data	O
in	O
symbols	O
of	O
eight	O
chips	B-Device
,	O
where	O
each	O
chip	O
is	O
a	O
complex	O
QPSK	O
bit-pair	O
at	O
a	O
chip	O
rate	O
of	O
11Mchip/s	O
.	O
</s>
<s>
and	O
are	O
determined	O
by	O
the	O
bits	O
being	O
modulated	B-Application
.	O
</s>
<s>
In	O
other	O
words	O
,	O
the	O
phase	O
change	O
is	O
applied	O
to	O
every	O
chip	O
,	O
is	O
applied	O
to	O
all	O
even	O
code	O
chips	B-Device
(	O
starting	O
with	O
)	O
,	O
is	O
applied	O
to	O
the	O
first	O
two	O
of	O
every	O
four	O
chips	B-Device
,	O
and	O
is	O
applied	O
to	O
the	O
first	O
four	O
of	O
the	O
eight	O
chips	B-Device
.	O
</s>
<s>
Therefore	O
,	O
it	O
can	O
also	O
be	O
viewed	O
as	O
a	O
form	O
of	O
generalized	O
Hadamard	B-Algorithm
transform	I-Algorithm
encoding	O
.	O
</s>
