<s>
A	O
sinusoid	O
with	O
modulation	B-Application
can	O
be	O
decomposed	O
into	O
,	O
or	O
synthesized	O
from	O
,	O
two	O
amplitude-modulated	B-Device
sinusoids	O
that	O
are	O
offset	O
in	O
phase	O
by	O
one-quarter	O
cycle	O
(	O
90	O
degrees	O
or	O
/2	O
radians	O
)	O
.	O
</s>
<s>
The	O
two	O
amplitude-modulated	B-Device
sinusoids	O
are	O
known	O
as	O
the	O
in-phase	O
(	O
I	O
)	O
and	O
quadrature	O
(	O
Q	O
)	O
components	O
,	O
which	O
describes	O
their	O
relationships	O
with	O
the	O
amplitude	O
-	O
and	O
phase-modulated	O
carrier	O
.	O
</s>
<s>
The	O
implication	O
is	O
that	O
the	O
modulations	B-Application
in	O
some	O
signal	O
can	O
be	O
treated	O
separately	O
from	O
the	O
carrier	O
wave	O
of	O
the	O
signal	O
.	O
</s>
<s>
I/Q	O
data	O
is	O
used	O
to	O
represent	O
the	O
modulations	B-Application
of	O
some	O
carrier	O
,	O
independent	O
of	O
that	O
carrier	O
's	O
frequency	O
.	O
</s>
<s>
And	O
in	O
functional	O
analysis	O
,	O
when	O
is	O
a	O
linear	O
function	O
of	O
some	O
variable	O
,	O
such	O
as	O
time	O
,	O
these	O
components	O
are	O
sinusoids	O
,	O
and	O
they	O
are	O
orthogonal	B-Algorithm
functions	I-Algorithm
.	O
</s>
<s>
In	O
both	O
conventions	O
is	O
the	O
in-phase	O
amplitude	B-Device
modulation	I-Device
,	O
which	O
explains	O
why	O
some	O
authors	O
refer	O
to	O
it	O
as	O
the	O
actual	O
in-phase	O
component	O
.	O
</s>
<s>
In	O
an	O
angle	O
modulation	B-Application
application	O
,	O
with	O
carrier	O
frequency	O
φ	O
is	O
also	O
a	O
time-variant	O
function	O
,	O
giving	O
:	O
</s>
<s>
Because	O
of	O
the	O
modulation	B-Application
,	O
the	O
components	O
are	O
no	O
longer	O
completely	O
orthogonal	B-Algorithm
functions	I-Algorithm
.	O
</s>
<s>
A	O
stream	O
of	O
information	O
about	O
how	O
to	O
amplitude-modulate	O
the	O
I	B-Algorithm
and	I-Algorithm
Q	I-Algorithm
phases	O
of	O
a	O
sine	O
wave	O
is	O
known	O
as	O
the	O
I/Q	O
data	O
.	O
</s>
<s>
a	O
phasor	B-Application
)	O
then	O
the	O
carrier	O
also	O
can	O
be	O
frequency	O
modulated	B-Application
.	O
</s>
<s>
So	O
I/Q	O
data	O
is	O
a	O
complete	O
representation	O
of	O
how	O
a	O
carrier	O
is	O
modulated	B-Application
:	O
amplitude	O
,	O
phase	O
and	O
frequency	O
.	O
</s>
<s>
For	O
received	O
signals	O
,	O
by	O
determining	O
how	O
much	O
in-phase	O
carrier	O
and	O
how	O
much	O
quadrature	O
carrier	O
is	O
present	O
in	O
the	O
signal	O
it	O
is	O
possible	O
represent	O
that	O
signal	O
using	O
in-phase	B-Algorithm
and	I-Algorithm
quadrature	I-Algorithm
components	I-Algorithm
,	O
so	O
IQ	O
data	O
can	O
get	O
generated	O
from	O
a	O
signal	O
with	O
reference	O
to	O
a	O
carrier	O
sine	O
wave	O
.	O
</s>
<s>
IQ	O
data	O
has	O
extensive	O
use	O
in	O
many	O
signal	O
processing	O
contexts	O
,	O
including	O
for	O
radio	O
modulation	B-Application
,	O
software-defined	B-Architecture
radio	I-Architecture
,	O
audio	B-Algorithm
signal	I-Algorithm
processing	I-Algorithm
and	O
electrical	O
engineering	O
.	O
</s>
<s>
Some	O
sources	O
treat	O
I/Q	O
as	O
a	O
complex	O
number	O
;	O
with	O
the	O
I	B-Algorithm
and	I-Algorithm
Q	I-Algorithm
components	I-Algorithm
corresponding	O
to	O
the	O
real	O
and	O
imaginary	O
parts	O
.	O
</s>
<s>
This	O
technique	O
of	O
using	O
I/Q	O
data	O
to	O
represent	O
the	O
modulations	B-Application
of	O
a	O
signal	O
separate	O
to	O
the	O
signal	O
's	O
frequency	O
is	O
known	O
as	O
equivalent	O
baseband	O
signal	O
,	O
supported	O
by	O
the	O
.	O
</s>
<s>
The	O
data	O
rate	O
of	O
I/Q	O
is	O
largely	O
independent	O
to	O
the	O
frequency	O
of	O
the	O
signal	O
being	O
modulated	B-Application
.	O
</s>
<s>
millions	O
of	O
bits	O
per	O
second	O
)	O
,	O
perhaps	O
generated	O
by	O
software	O
in	O
part	O
of	O
the	O
physical	B-Application
layer	I-Application
of	O
a	O
protocol	O
stack	O
.	O
</s>
<s>
Designs	O
such	O
as	O
the	O
Digital	B-Algorithm
down	I-Algorithm
converter	I-Algorithm
allow	O
the	O
input	O
signal	O
to	O
be	O
represented	O
as	O
streams	O
of	O
IQ	O
data	O
,	O
likely	O
for	O
further	O
processing	O
and	O
symbol	O
extraction	O
in	O
a	O
DSP	B-Architecture
.	O
</s>
<s>
Since	O
I/Q	O
allows	O
the	O
representation	O
of	O
the	O
modulation	B-Application
separate	O
to	O
the	O
actual	O
carrier	O
frequency	O
,	O
it	O
is	O
possible	O
to	O
represent	O
a	O
capture	O
of	O
all	O
the	O
radio	O
traffic	O
in	O
some	O
RF	O
band	O
or	O
section	O
thereof	O
,	O
with	O
a	O
reasonable	O
amount	O
of	O
data	O
,	O
irrespective	O
of	O
the	O
frequency	O
being	O
monitored	O
.	O
</s>
<s>
if	O
there	O
is	O
a	O
capture	O
of	O
100	O
MHz	O
of	O
Wi-Fi	O
channels	O
within	O
the	O
5	B-Algorithm
GHz	I-Algorithm
U-NII	I-Algorithm
band	I-Algorithm
,	O
that	O
IQ	O
capture	O
can	O
be	O
sampled	B-Algorithm
at	O
200	O
million	O
samples	O
per	O
second	O
(	O
according	O
to	O
Nyquist	O
)	O
as	O
opposed	O
to	O
the	O
10,000	O
million	O
samples	O
per	O
second	O
required	O
to	O
sample	O
directly	O
at	O
5	O
GHz	O
.	O
</s>
<s>
Many	O
modulation	B-Application
schemes	O
,	O
e.g.	O
</s>
<s>
quadrature	B-Device
amplitude	I-Device
modulation	I-Device
rely	O
heavily	O
on	O
I/Q	O
.	O
</s>
