<s>
Constellation	B-Device
shaping	I-Device
is	O
an	O
energy	O
efficiency	O
enhancement	O
method	O
for	O
digital	B-General_Concept
signal	O
modulation	B-Application
that	O
improves	O
upon	O
amplitude	B-Device
and	I-Device
phase-shift	I-Device
keying	I-Device
(	O
APSK	B-Device
)	O
and	O
conventional	O
quadrature	B-Device
amplitude	I-Device
modulation	I-Device
(	O
QAM	B-Device
)	O
by	O
modifying	O
the	O
uniform	O
distribution	O
of	O
the	O
data	O
symbols	O
to	O
match	O
the	O
channel	O
.	O
</s>
<s>
In	O
digital	B-General_Concept
signal	O
modulation	B-Application
,	O
information	O
bits	O
modulate	O
the	O
carrier	O
electromagnetic	O
wave	O
signal	O
to	O
a	O
set	O
of	O
desired	O
phase	O
,	O
frequency	O
and	O
amplitude	O
states	O
.	O
</s>
<s>
Probabilistic	B-Device
constellation	I-Device
shaping	I-Device
attempts	O
to	O
directly	O
modify	O
the	O
Probability	O
mass	O
function	O
by	O
applying	O
a	O
distribution	O
matcher	O
between	O
the	O
user	O
data	O
and	O
the	O
mapper	O
to	O
constellation	O
symbols	O
.	O
</s>
<s>
Geometric	O
constellation	B-Device
shaping	I-Device
attempts	O
to	O
modify	O
the	O
distribution	O
of	O
transmission	O
power	O
by	O
optimizing	O
the	O
constellation	O
states	O
themselves	O
.	O
</s>
<s>
A	O
notable	O
examples	O
are	O
satellite	O
links	O
,	O
where	O
an	O
APSK	B-Device
constellation	O
is	O
preferred	O
to	O
QAM	B-Device
.	O
</s>
<s>
The	O
benefits	O
of	O
geometric	O
constellation	B-Device
shaping	I-Device
is	O
that	O
no	O
distribution	O
matcher	O
is	O
required	O
,	O
which	O
simplifies	O
the	O
digital	B-General_Concept
signal	O
processing	O
at	O
the	O
transmitter	O
and	O
receiver	O
.	O
</s>
<s>
However	O
,	O
geometric	O
constellation	B-Device
shaping	I-Device
does	O
not	O
typically	O
allow	O
Gray	B-Device
code	I-Device
labeling	O
of	O
the	O
constellation	O
points	O
,	O
leading	O
to	O
a	O
performance	O
degradation	O
.	O
</s>
