CDM-750 Advanced High-Speed Trunking Modem
Revision 2
Appendix C
MN-CDM750
C–12
C.4.6 ModCod Selection
shows
considerable
overlap
of
ModCod
combinations.
The
overlap
depicted
in
this
figure
implies
omitting
some
of
the
ModCods;
therefore,
without
dropping
some
of
the
ModCods,
there
is
a
non
‐
monotonic
change
of
Bits/Hz
with
changing
Es/No.
As
this
would
result
in
an
unstable
system,
re
‐
sorting
the
DVB
‐
S2
table
resolves
this.
Also,
a
practical
system
needs
some
hysteresis
to
provide
orderly
transition
to
adjacent
ModCods
and
avoid
dithering.
The
minimum
distance
between
adjacent
ModCods
must
be
at
least
the
amount
of
hysteresis
–
the
figure
used
for
hysteresis
is
fixed
in
the
CDM
‐
750
at
0.5
dB.
The
actual
Es/No
values
used
are
based
on
the
guaranteed
Es/No
values
+
Target
Es/No
Margin
+
modulation
type
impairment,
not
the
DVB
‐
S2
ideal
Es/No
figures.
Taking
into
account
the
ModCod
spacing,
hysteresis,
Target
Es/No
Margin,
modulation
type
impairment
and
monotonic
behavior
suggests
a
practical
way
to
select
the
Es/No
thresholds
for
switching
ModCods,
and
a
way
to
prune
ModCods
from
the
list.
During
parameter
configuration,
the
modem
selects
the
usable
ModCods.
Figure C-5. Spectral Efficiency vs. Ideal Es/No @ QEF
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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