<s>
In	O
telecommunications	O
and	O
signal	O
processing	O
,	O
baseband	B-Algorithm
is	O
the	O
range	O
of	O
frequencies	O
occupied	O
by	O
a	O
signal	O
that	O
has	O
not	O
been	O
modulated	B-Application
to	O
higher	O
frequencies	O
.	O
</s>
<s>
Baseband	B-Algorithm
signals	I-Algorithm
typically	O
originate	O
from	O
transducers	B-Algorithm
,	O
converting	O
some	O
other	O
variable	O
into	O
an	O
electrical	O
signal	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
electronic	O
output	O
of	O
a	O
microphone	O
is	O
a	O
baseband	B-Algorithm
signal	I-Algorithm
that	O
is	O
analogous	O
to	O
the	O
applied	O
voice	O
audio	O
.	O
</s>
<s>
In	O
conventional	O
analog	O
radio	O
broadcasting	O
,	O
the	O
baseband	B-Algorithm
audio	O
signal	O
is	O
used	O
to	O
modulate	B-Application
an	O
RF	O
carrier	O
signal	O
of	O
a	O
much	O
higher	O
frequency	O
.	O
</s>
<s>
A	O
baseband	B-Algorithm
signal	I-Algorithm
may	O
have	O
frequency	O
components	O
going	O
all	O
the	O
way	O
down	O
to	O
DC	O
,	O
or	O
at	O
least	O
it	O
will	O
have	O
a	O
high	O
ratio	O
bandwidth	B-Algorithm
.	O
</s>
<s>
A	O
modulated	B-Application
baseband	B-Algorithm
signal	I-Algorithm
is	O
called	O
a	O
passband	B-Algorithm
signal	I-Algorithm
.	O
</s>
<s>
This	O
occupies	O
a	O
higher	O
range	O
of	O
frequencies	O
and	O
has	O
a	O
lower	O
ratio	O
and	O
fractional	O
bandwidth	B-Algorithm
.	O
</s>
<s>
A	O
baseband	B-Algorithm
signal	I-Algorithm
or	O
lowpass	B-Algorithm
signal	O
is	O
a	O
signal	O
that	O
can	O
include	O
frequencies	O
that	O
are	O
very	O
near	O
zero	O
,	O
by	O
comparison	O
with	O
its	O
highest	O
frequency	O
(	O
for	O
example	O
,	O
a	O
sound	O
waveform	O
can	O
be	O
considered	O
as	O
a	O
baseband	B-Algorithm
signal	I-Algorithm
,	O
whereas	O
a	O
radio	O
signal	O
or	O
any	O
other	O
modulated	B-Application
signal	O
is	O
not	O
)	O
.	O
</s>
<s>
A	O
baseband	B-Algorithm
bandwidth	B-Algorithm
is	O
equal	O
to	O
the	O
highest	O
frequency	O
of	O
a	O
signal	O
or	O
system	O
,	O
or	O
an	O
upper	O
bound	O
on	O
such	O
frequencies	O
,	O
for	O
example	O
the	O
upper	O
cut-off	O
frequency	O
of	O
a	O
low-pass	B-Algorithm
filter	I-Algorithm
.	O
</s>
<s>
By	O
contrast	O
,	O
passband	B-Algorithm
bandwidth	B-Algorithm
is	O
the	O
difference	O
between	O
a	O
highest	O
frequency	O
and	O
a	O
nonzero	O
lowest	O
frequency	O
.	O
</s>
<s>
A	O
baseband	B-Algorithm
channel	I-Algorithm
or	O
lowpass	B-Algorithm
channel	O
(	O
or	O
system	O
,	O
or	O
network	O
)	O
is	O
a	O
communication	O
channel	O
that	O
can	O
transfer	O
frequencies	O
that	O
are	O
very	O
near	O
zero	O
.	O
</s>
<s>
Examples	O
are	O
serial	O
cables	O
and	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LANs	B-General_Concept
)	O
,	O
as	O
opposed	O
to	O
passband	B-Algorithm
channels	I-Algorithm
such	O
as	O
radio	O
frequency	O
channels	O
and	O
passband	B-Algorithm
filtered	O
wires	O
of	O
the	O
analog	O
telephone	O
network	O
.	O
</s>
<s>
Frequency	B-Protocol
division	I-Protocol
multiplexing	I-Protocol
(	O
FDM	O
)	O
allows	O
an	O
analog	O
telephone	O
wire	O
to	O
carry	O
a	O
baseband	B-Algorithm
telephone	O
call	O
,	O
concurrently	O
as	O
one	O
or	O
several	O
carrier-modulated	O
telephone	O
calls	O
.	O
</s>
<s>
Digital	O
baseband	B-Algorithm
transmission	I-Algorithm
,	O
also	O
known	O
as	O
line	B-Protocol
coding	I-Protocol
,	O
aims	O
at	O
transferring	O
a	O
digital	O
bit	O
stream	O
over	O
baseband	B-Algorithm
channel	I-Algorithm
,	O
typically	O
an	O
unfiltered	O
wire	O
,	O
contrary	O
to	O
passband	B-Algorithm
transmission	O
,	O
also	O
known	O
as	O
carrier-modulated	O
transmission	O
.	O
</s>
<s>
Passband	B-Algorithm
transmission	O
makes	O
communication	O
possible	O
over	O
a	O
bandpass	O
filtered	O
channel	O
,	O
such	O
as	O
the	O
telephone	O
network	O
local-loop	O
or	O
a	O
band-limited	O
wireless	O
channel	O
.	O
</s>
<s>
The	O
word	O
"	O
BASE	O
"	O
in	O
Ethernet	B-Protocol
physical	I-Protocol
layer	I-Protocol
standards	O
,	O
for	O
example	O
10BASE5	O
,	O
100BASE-TX	B-Protocol
and	O
1000BASE-SX	O
,	O
implies	O
baseband	B-Algorithm
digital	O
transmission	O
(	O
i.e.	O
</s>
<s>
that	O
a	O
line	B-Protocol
code	I-Protocol
and	O
an	O
unfiltered	O
wire	O
are	O
used	O
)	O
.	O
</s>
<s>
A	O
baseband	B-Algorithm
processor	O
also	O
known	O
as	O
BP	O
or	O
BBP	O
is	O
used	O
to	O
process	O
the	O
down-converted	O
digital	O
signal	O
to	O
retrieve	O
essential	O
data	O
for	O
a	O
wireless	O
digital	O
system	O
.	O
</s>
<s>
The	O
baseband	B-Algorithm
processing	O
block	O
in	O
GNSS	O
receivers	O
is	O
responsible	O
for	O
providing	O
observable	O
data	O
:	O
that	O
is	O
,	O
code	O
pseudo-ranges	O
and	O
carrier	O
phase	O
measurements	O
,	O
as	O
well	O
as	O
navigation	O
data	O
.	O
</s>
<s>
An	O
equivalent	B-Algorithm
baseband	I-Algorithm
signal	I-Algorithm
or	O
equivalent	B-Algorithm
lowpass	I-Algorithm
signal	I-Algorithm
is	O
—	O
in	O
analog	O
and	O
digital	O
modulation	B-Application
methods	O
for	O
(	O
passband	B-Algorithm
)	O
signals	O
with	O
constant	O
or	O
varying	O
carrier	O
frequency	O
(	O
for	O
example	O
ASK	O
,	O
PSK	B-General_Concept
QAM	B-Device
,	O
and	O
FSK	O
)	O
—	O
a	O
complex	O
valued	O
representation	O
of	O
the	O
modulated	B-Application
physical	O
signal	O
(	O
the	O
so-called	O
passband	B-Algorithm
signal	I-Algorithm
or	O
RF	O
signal	O
)	O
.	O
</s>
<s>
The	O
equivalent	B-Algorithm
baseband	I-Algorithm
signal	I-Algorithm
is	O
where	O
is	O
the	O
inphase	O
signal	O
,	O
the	O
quadrature	O
phase	O
signal	O
,	O
and	O
the	O
imaginary	O
unit	O
.	O
</s>
<s>
In	O
a	O
digital	O
modulation	B-Application
method	O
,	O
the	O
and	O
signals	O
of	O
each	O
modulation	B-Application
symbol	O
are	O
evident	O
from	O
the	O
constellation	B-Application
diagram	I-Application
.	O
</s>
<s>
A	O
signal	O
at	O
baseband	B-Algorithm
is	O
often	O
used	O
to	O
modulate	B-Application
a	O
higher	O
frequency	O
carrier	O
signal	O
in	O
order	O
that	O
it	O
may	O
be	O
transmitted	O
via	O
radio	O
.	O
</s>
<s>
Modulation	B-Application
results	O
in	O
shifting	O
the	O
signal	O
up	O
to	O
much	O
higher	O
frequencies	O
(	O
radio	O
frequencies	O
,	O
or	O
RF	O
)	O
than	O
it	O
originally	O
spanned	O
.	O
</s>
<s>
A	O
key	O
consequence	O
of	O
the	O
usual	O
double-sideband	O
amplitude	B-Device
modulation	I-Device
(	O
AM	O
)	O
is	O
that	O
the	O
range	O
of	O
frequencies	O
the	O
signal	O
spans	O
(	O
its	O
spectral	B-Algorithm
bandwidth	I-Algorithm
)	O
is	O
doubled	O
.	O
</s>
<s>
Thus	O
,	O
the	O
RF	B-Algorithm
bandwidth	I-Algorithm
of	O
a	O
signal	O
(	O
measured	O
from	O
the	O
lowest	O
frequency	O
as	O
opposed	O
to	O
0Hz	O
)	O
is	O
twice	O
its	O
baseband	B-Algorithm
bandwidth	B-Algorithm
.	O
</s>
<s>
Steps	O
may	O
be	O
taken	O
to	O
reduce	O
this	O
effect	O
,	O
such	O
as	O
single-sideband	B-Device
modulation	I-Device
.	O
</s>
<s>
Conversely	O
,	O
some	O
transmission	O
schemes	O
such	O
as	O
frequency	B-Application
modulation	I-Application
use	O
even	O
more	O
bandwidth	B-Algorithm
.	O
</s>
<s>
The	O
figure	O
below	O
shows	O
AM	O
modulation	B-Application
:	O
</s>
