<s>
Hierarchical	B-Protocol
modulation	I-Protocol
,	O
also	O
called	O
layered	O
modulation	B-Application
,	O
is	O
one	O
of	O
the	O
signal	O
processing	O
techniques	O
for	O
multiplexing	B-Architecture
and	O
modulating	B-Application
multiple	O
data	O
streams	O
into	O
one	O
single	O
symbol	O
stream	O
,	O
where	O
base-layer	O
symbols	O
and	O
enhancement-layer	O
symbols	O
are	O
synchronously	O
overplayed	O
before	O
transmission	O
.	O
</s>
<s>
Hierarchical	B-Protocol
modulation	I-Protocol
is	O
particularly	O
used	O
to	O
mitigate	O
the	O
cliff	O
effect	O
in	O
digital	B-Application
television	I-Application
broadcast	O
,	O
particularly	O
mobile	B-Application
TV	I-Application
,	O
by	O
providing	O
a	O
(	O
lower	O
quality	O
)	O
fallback	O
signal	O
in	O
case	O
of	O
weak	O
signals	O
,	O
allowing	O
graceful	B-General_Concept
degradation	I-General_Concept
instead	O
of	O
complete	O
signal	O
loss	O
.	O
</s>
<s>
It	O
has	O
been	O
widely	O
proven	O
and	O
included	O
in	O
various	O
standards	O
,	O
such	O
as	O
DVB-T	O
,	O
MediaFLO	B-Device
,	O
UMB	O
(	O
Ultra	O
Mobile	O
Broadband	O
,	O
a	O
new	O
3.5th	O
generation	O
mobile	O
network	O
standard	O
developed	O
by	O
3GPP2	O
)	O
,	O
and	O
is	O
under	O
study	O
for	O
DVB-H	B-Protocol
.	O
</s>
<s>
Hierarchical	B-Protocol
modulation	I-Protocol
is	O
also	O
taken	O
as	O
one	O
of	O
the	O
practical	O
implementations	O
of	O
superposition	O
precoding	O
,	O
which	O
can	O
help	O
achieve	O
the	O
maximum	O
sum	O
rate	O
of	O
broadcast	O
channels	O
.	O
</s>
<s>
When	O
hierarchical-modulated	O
signals	O
are	O
transmitted	O
,	O
users	O
with	O
good	O
reception	O
and	O
advanced	O
receivers	O
can	O
demodulate	O
multiple	O
layers	O
.	O
</s>
<s>
With	O
hierarchical	B-Protocol
modulation	I-Protocol
,	O
a	O
network	O
operator	O
can	O
target	O
users	O
of	O
different	O
types	O
with	O
different	O
services	O
or	O
QoS	O
.	O
</s>
<s>
However	O
,	O
traditional	O
hierarchical	B-Protocol
modulation	I-Protocol
suffers	O
from	O
serious	O
inter-layer	O
interference	O
(	O
ILI	O
)	O
with	O
impact	O
on	O
the	O
achievable	O
symbol	O
rate	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
figure	O
depicts	O
a	O
layering	O
scheme	O
with	O
QPSK	B-General_Concept
base	O
layer	O
,	O
and	O
a	O
64QAM	B-Device
enhancement	O
layer	O
.	O
</s>
<s>
For	O
a	O
hierarchically-modulated	O
symbol	O
with	O
QPSK	B-General_Concept
base	O
layer	O
and	O
16QAM	B-Device
enhancement	O
layer	O
,	O
the	O
base-layer	O
throughput	O
loss	O
is	O
up	O
to	O
about	O
1.5bits/symbol	O
with	O
the	O
total	O
receive	O
signal-to-noise	O
ratio	O
(	O
SNR	O
)	O
at	O
about	O
23	O
dB	O
,	O
about	O
the	O
minimum	O
needed	O
for	O
the	O
comparable	O
non-hierarchical	O
modulation	O
,	O
64QAM	B-Device
.	O
</s>
<s>
But	O
unlayered	O
16QAM	B-Device
with	O
the	O
same	O
SNR	O
would	O
approach	O
full	O
throughput	O
.	O
</s>
