<s>
Polar	B-Protocol
modulation	I-Protocol
is	O
analogous	O
to	O
quadrature	B-Device
modulation	I-Device
in	O
the	O
same	O
way	O
that	O
polar	O
coordinates	O
are	O
analogous	O
to	O
Cartesian	O
coordinates	O
.	O
</s>
<s>
Quadrature	B-Device
modulation	I-Device
makes	O
use	O
of	O
Cartesian	O
coordinates	O
,	O
x	O
and	O
y	O
.	O
</s>
<s>
When	O
considering	O
quadrature	B-Device
modulation	I-Device
,	O
the	O
x	O
axis	O
is	O
called	O
the	O
I	O
(	O
in-phase	O
)	O
axis	O
,	O
and	O
the	O
y	O
axis	O
is	O
called	O
the	O
Q	O
(	O
quadrature	O
)	O
axis	O
.	O
</s>
<s>
Polar	B-Protocol
modulation	I-Protocol
makes	O
use	O
of	O
polar	O
coordinates	O
,	O
r	O
(	O
amplitude	O
)	O
and	O
Θ	O
(	O
phase	O
)	O
.	O
</s>
<s>
In	O
a	O
polar	B-Protocol
modulation	I-Protocol
system	O
,	O
the	O
power	O
amplifier	O
input	O
signal	O
may	O
vary	O
only	O
in	O
phase	O
.	O
</s>
<s>
Thus	O
a	O
polar	B-Protocol
modulation	I-Protocol
system	O
allows	O
the	O
use	O
of	O
highly	O
non-linear	O
power	O
amplifier	O
architectures	O
such	O
as	O
Class	O
E	O
and	O
Class	O
F	O
.	O
</s>
<s>
Polar	B-Protocol
modulation	I-Protocol
was	O
originally	O
developed	O
by	O
Thomas	O
Edison	O
in	O
his	O
1874	O
quadruplex	O
telegraph	O
–	O
this	O
allowed	O
4	O
signals	O
to	O
be	O
sent	O
along	O
a	O
pair	O
of	O
lines	O
,	O
2	O
in	O
each	O
direction	O
.	O
</s>
<s>
Sending	O
a	O
signal	O
in	O
each	O
direction	O
had	O
already	O
been	O
accomplished	O
earlier	O
,	O
and	O
Edison	O
found	O
that	O
by	O
combining	O
amplitude	O
and	O
phase	B-Device
modulation	I-Device
(	O
i.e.	O
,	O
by	O
polar	B-Protocol
modulation	I-Protocol
)	O
,	O
he	O
could	O
double	O
this	O
to	O
4	O
signals	O
–	O
hence	O
,	O
quadruplex	O
.	O
</s>
