<s>
In	O
telecommunications	O
,	O
direct-sequence	B-Device
spread	I-Device
spectrum	I-Device
(	O
DSSS	B-Device
)	O
is	O
a	O
spread-spectrum	B-Architecture
modulation	B-Application
technique	O
primarily	O
used	O
to	O
reduce	O
overall	O
signal	O
interference	O
.	O
</s>
<s>
The	O
direct-sequence	B-Device
modulation	B-Application
makes	O
the	O
transmitted	O
signal	O
wider	O
in	O
bandwidth	O
than	O
the	O
information	O
bandwidth	O
.	O
</s>
<s>
After	O
the	O
despreading	O
or	O
removal	O
of	O
the	O
direct-sequence	B-Device
modulation	B-Application
in	O
the	O
receiver	O
,	O
the	O
information	O
bandwidth	O
is	O
restored	O
,	O
while	O
the	O
unintentional	O
and	O
intentional	O
interference	O
is	O
substantially	O
reduced	O
.	O
</s>
<s>
With	O
DSSS	B-Device
,	O
the	O
message	O
bits	O
are	O
modulated	B-Application
by	O
a	O
pseudorandom	B-Error_Name
bit	O
sequence	O
known	O
as	O
a	O
spreading	O
sequence	O
.	O
</s>
<s>
The	O
modulation	B-Application
of	O
the	O
message	O
bits	O
scrambles	O
and	O
spreads	O
the	O
pieces	O
of	O
data	O
,	O
and	O
thereby	O
results	O
in	O
a	O
bandwidth	O
size	O
nearly	O
identical	O
to	O
that	O
of	O
the	O
spreading	O
sequence	O
.	O
</s>
<s>
The	O
smaller	O
the	O
chip	O
duration	O
,	O
the	O
larger	O
the	O
bandwidth	O
of	O
the	O
resulting	O
DSSS	B-Device
signal	O
;	O
more	O
bandwidth	O
multiplexed	O
to	O
the	O
message	O
signal	O
results	O
in	O
better	O
resistance	O
against	O
interference	O
.	O
</s>
<s>
Some	O
practical	O
and	O
effective	O
uses	O
of	O
DSSS	B-Device
include	O
the	O
code-division	B-Protocol
multiple	I-Protocol
access	I-Protocol
(	O
CDMA	B-Protocol
)	O
method	O
,	O
the	O
IEEE	O
802.11b	O
specification	O
used	O
in	O
Wi-Fi	O
networks	O
,	O
and	O
the	O
Global	O
Positioning	O
System	O
.	O
</s>
<s>
DSSS	B-Device
phase-shifts	B-General_Concept
a	O
sine	O
wave	O
pseudorandomly	O
with	O
a	O
continuous	O
string	O
of	O
chips	O
,	O
each	O
of	O
which	O
has	O
a	O
much	O
shorter	O
duration	O
than	O
an	O
information	O
bit	O
.	O
</s>
<s>
That	O
is	O
,	O
each	O
information	O
bit	O
is	O
modulated	B-Application
by	O
a	O
sequence	O
of	O
much	O
faster	O
chips	O
.	O
</s>
<s>
DSSS	B-Device
uses	O
a	O
signal	O
structure	O
in	O
which	O
the	O
spreading	O
sequence	O
produced	O
by	O
the	O
transmitter	O
is	O
already	O
known	O
by	O
the	O
receiver	O
.	O
</s>
<s>
Direct-sequence	B-Device
spread-spectrum	B-Architecture
transmissions	O
multiply	O
the	O
data	O
being	O
transmitted	O
by	O
a	O
pseudorandom	B-Error_Name
spreading	O
sequence	O
that	O
has	O
a	O
much	O
higher	O
bit	O
rate	O
than	O
the	O
original	O
data	O
rate	O
.	O
</s>
<s>
While	O
a	O
transmitted	O
DSSS	B-Device
signal	O
occupies	O
a	O
much	O
wider	O
bandwidth	O
than	O
a	O
simple	O
modulation	B-Application
of	O
the	O
original	O
signal	O
would	O
require	O
,	O
its	O
frequency	O
spectrum	O
can	O
be	O
somewhat	O
restricted	O
for	O
spectrum	O
economy	O
by	O
a	O
conventional	O
analog	O
bandpass	O
filter	O
to	O
give	O
a	O
roughly	O
bell-shaped	O
envelope	O
centered	O
on	O
the	O
carrier	O
frequency	O
.	O
</s>
<s>
In	O
contrast	O
,	O
frequency-hopping	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
pseudorandomly	O
retunes	O
the	O
carrier	O
and	O
requires	O
a	O
uniform	O
frequency	O
response	O
since	O
any	O
bandwidth	O
shaping	O
would	O
cause	O
amplitude	O
modulation	B-Application
of	O
the	O
signal	O
by	O
the	O
hopping	O
code	O
.	O
</s>
<s>
This	O
effect	O
is	O
the	O
basis	O
for	O
the	O
code-division	B-Protocol
multiple	I-Protocol
access	I-Protocol
(	O
CDMA	B-Protocol
)	O
property	O
of	O
DSSS	B-Device
,	O
which	O
allows	O
multiple	O
transmitters	O
to	O
share	O
the	O
same	O
channel	O
within	O
the	O
limits	O
of	O
the	O
cross-correlation	O
properties	O
of	O
their	O
spreading	O
sequences	O
.	O
</s>
<s>
The	O
United	O
States	O
GPS	O
,	O
European	O
Galileo	O
and	O
Russian	O
GLONASS	O
satellite	O
navigation	O
systems	O
;	O
earlier	O
GLONASS	O
used	O
DSSS	B-Device
with	O
a	O
single	O
spreading	O
sequence	O
in	O
conjunction	O
with	O
FDMA	O
,	O
while	O
later	O
GLONASS	O
used	O
DSSS	B-Device
to	O
achieve	O
CDMA	B-Protocol
with	O
multiple	O
spreading	O
sequences	O
.	O
</s>
<s>
DS-CDMA	O
(	O
Direct-Sequence	B-Device
Code	B-Protocol
Division	I-Protocol
Multiple	I-Protocol
Access	I-Protocol
)	O
is	O
a	O
multiple	O
access	O
scheme	O
based	O
on	O
DSSS	B-Device
,	O
by	O
spreading	O
the	O
signals	O
from/to	O
different	O
users	O
with	O
different	O
codes	O
.	O
</s>
<s>
It	O
is	O
the	O
most	O
widely	O
used	O
type	O
of	O
CDMA	B-Protocol
.	O
</s>
