CDM-750 Advanced High-Speed Trunking Modem
Revision 2
Appendix C
MN-CDM750
C–10
Table C-4. Modulation Type Impairment
Additional Impairment
Variable Name
dB (Factory Default Shown)
Adjustable 0.0 to 9.9 dB
QPSK Degradation
QPSK_DEG
0.0
8PSK Degradation
8PSK_DEG
0.0
16APSK Degradation
16APSK_DEG
0.0
32APSK Degradation
32APSK_DEG
0.0
Note:
Impairment Setting – QPSK
≤
8PSK
≤
16APSK
≤
32APSK
C.4.3 Pilots
DVB
‐
S2
originally
introduced
Pilots
as
a
means
to
combat
phase
noise.
An
additional
concern
arose
because
the
very
powerful
Low
Density
Parity
‐
Check
Forward
Error
Correction
(LDPC
FEC)
reduced
the
conventional
operating
point
of
a
demodulator
much
closer
to
the
noise
floor
than
was
done
historically,
increasing
the
risk
of
cycle
slips.
There
are
several
ModCods
where
DVB
‐
S2
advised
using
Pilots
to
avoid
cycle
slips:
•
8PSK
3/5
and
2/3
•
16APSK
3/4
•
32APSK
3/5
The
use
of
Pilots
was
also
recommended
by
DVB
‐
S2
for
ACM
operation
to
guarantee
continuous
receiver
synchronization.
Here,
the
DVB
advises
that
there
are
ModCod
cases
that
are
simply
more
reliable
with
Pilots
on
,
even
in
the
case
of
reasonable
phase
noise.
For
the
purpose
of
data
integrity
and
maximum
ModCod
selection,
the
CDM
‐
750
modem
always
enables
Pilots
ON
for
all
ModCods
whenever
ACM
mode
is
selected
.
C.4.4 Long and Short Frames
It
is
possible
to
process
a
mix
of
Normal
and
short
frames,
although
is
not
believed
to
be
very
valuable
for
high
speed
point
to
point
trunking
applications.
In
addition,
9/10
ModCod
is
not
allowed
for
short
frames,
and
it
is
not
selectable
in
short
frame
mode.
The
CDM
‐
750
can
be
configured
for
either
Normal
or
short
frames,
and
does
not
support
mixing
frame
types.
When
operating
in
ACM
mode,
ALWAYS
use
Normal
frames
at
both
ends
of
the
link.
C.4.5 Monotonic Operation
shows
the
ideal
Es/No
at
QEF
for
each
DVB
‐
S2
ModCod
along
with
spectral
efficiency
and
ModCod
#.
The
QEF
or
Quasi
Error
Free
point
corresponds
to
a
Packet
Error
Rate
(PER)
=
10
‐
7
,
based
on
188
byte
packets.
Scanning
down
the
table,
there
are
two
entries,
ModCods
#12
and
#18,
where
the
Spectral
Efficiency
does
not
change
monotonically.
In
ACM
mode,
the
table
is
resorted
by
Spectral
Efficiency
to
assure
monotonic
behavior
and
system
stability.
Summary of Contents for CDM-750
Page 76: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Updating Firmware MN CDM750 4 12 Notes...
Page 224: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix A MN CDM750 A 4 Notes...
Page 234: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix B MN CDM750 B 10 Notes...
Page 256: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix C MN CDM750 C 22 Notes...
Page 280: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix D MN CDM750 D 24 Notes...
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