<s>
Phase	B-Device
modulation	I-Device
(	O
PM	O
)	O
is	O
a	O
modulation	B-Application
pattern	O
for	O
conditioning	O
communication	O
signals	O
for	O
transmission	O
.	O
</s>
<s>
Phase	B-Device
modulation	I-Device
is	O
one	O
of	O
the	O
two	O
principal	O
forms	O
of	O
angle	B-Device
modulation	I-Device
,	O
together	O
with	O
frequency	B-Application
modulation	I-Application
.	O
</s>
<s>
In	O
phase	B-Device
modulation	I-Device
,	O
the	O
instantaneous	O
amplitude	B-Application
of	O
the	O
baseband	B-Algorithm
signal	I-Algorithm
modifies	O
the	O
phase	O
of	O
the	O
carrier	O
signal	O
keeping	O
its	O
amplitude	B-Application
and	O
frequency	O
constant	O
.	O
</s>
<s>
The	O
phase	O
of	O
a	O
carrier	O
signal	O
is	O
modulated	B-Application
to	O
follow	O
the	O
changing	O
signal	O
level	O
(	O
amplitude	B-Application
)	O
of	O
the	O
message	O
signal	O
.	O
</s>
<s>
The	O
peak	O
amplitude	B-Application
and	O
the	O
frequency	O
of	O
the	O
carrier	O
signal	O
are	O
maintained	O
constant	O
,	O
but	O
as	O
the	O
amplitude	B-Application
of	O
the	O
message	O
signal	O
changes	O
,	O
the	O
phase	O
of	O
the	O
carrier	O
changes	O
correspondingly	O
.	O
</s>
<s>
Phase	B-Device
modulation	I-Device
is	O
widely	O
used	O
for	O
transmitting	O
radio	O
waves	O
and	O
is	O
an	O
integral	O
part	O
of	O
many	O
digital	O
transmission	O
coding	O
schemes	O
that	O
underlie	O
a	O
wide	O
range	O
of	O
technologies	O
like	O
Wi-Fi	O
,	O
GSM	O
and	O
satellite	O
television	O
.	O
</s>
<s>
It	O
is	O
also	O
used	O
for	O
signal	O
and	O
waveform	O
generation	O
in	O
digital	O
synthesizers	O
,	O
such	O
as	O
the	O
Yamaha	O
DX7	O
,	O
to	O
implement	O
FM	B-Application
synthesis	O
.	O
</s>
<s>
Phase	B-Device
modulation	I-Device
changes	O
the	O
phase	O
angle	O
of	O
the	O
complex	O
envelope	O
in	O
proportion	O
to	O
the	O
message	O
signal	O
.	O
</s>
<s>
This	O
shows	O
how	O
modulates	O
the	O
phase	O
–	O
the	O
greater	O
is	O
at	O
a	O
point	O
in	O
time	O
,	O
the	O
greater	O
the	O
phase	O
shift	O
of	O
the	O
modulated	B-Application
signal	O
at	O
that	O
point	O
.	O
</s>
<s>
It	O
can	O
also	O
be	O
viewed	O
as	O
a	O
change	O
of	O
the	O
frequency	O
of	O
the	O
carrier	O
signal	O
,	O
and	O
phase	B-Device
modulation	I-Device
can	O
thus	O
be	O
considered	O
a	O
special	O
case	O
of	O
FM	B-Application
in	O
which	O
the	O
carrier	O
frequency	B-Application
modulation	I-Application
is	O
given	O
by	O
the	O
time	O
derivative	B-Algorithm
of	O
the	O
phase	B-Device
modulation	I-Device
.	O
</s>
<s>
The	O
mathematics	O
of	O
the	O
spectral	B-Algorithm
behaviour	O
reveals	O
that	O
there	O
are	O
two	O
regions	O
of	O
particular	O
interest	O
:	O
</s>
<s>
As	O
with	O
other	O
modulation	B-Application
indices	O
,	O
this	O
quantity	O
indicates	O
by	O
how	O
much	O
the	O
modulated	B-Application
variable	O
varies	O
around	O
its	O
unmodulated	O
level	O
.	O
</s>
<s>
Compare	O
to	O
the	O
modulation	B-Application
index	O
for	O
frequency	B-Application
modulation	I-Application
.	O
</s>
