CDM-750 Advanced High-Speed Trunking Modem
Revision 2
Appendix D
MN-CDM750
D–13
The
link
budget
summary
for
the
different
ModCod
combinations
is
as
follows:
S. No.
Modulation & FEC
Allocated
BW (MHz)
PEB (MHz) Leased BW
(MHz)
Savings Compared
to Original
PSD
Ratio
(dB)
1
S2 8PSK 5/6
18.2
26.9
26.9
25%
0.0
2
S2 8PSK 8/9
17.9
34.9
34.9
4%
0.0
3
S2 16APSK 2/3
17.35
25.1
25.1
31%
0.0
4
S2 16APSK 5/6
13.9
38.3
38.3
-9.7%
0.0
Based
on
this
analysis,
S2
16APSK
2/3
with
CnC
provides
the
maximum
savings
of
31%.
D.4.6.1 Asymmetric Data Rate Link
As
occupied
(or
allocated)
bandwidth
of
a
CnC
circuit
is
dictated
by
the
larger
of
the
two
carriers,
it
is
strongly
recommended
that
the
smaller
carrier
be
spread
as
much
as
possible
using
a
lower
order
modulation
and/or
FEC,
while
meeting
the
CnC
ratio
spec.
Spreading
the
smaller
carrier
using
a
lower
order
modulation
has
multiple
benefits:
•
Lower
order
modulation
is
always
more
robust;
•
Lower
order
modulation
uses
less
transponder
power
–
this
reduces
total
required
transponder
power,
and
increases
available
link
margin;
•
Lower
order
modulation
uses
less
transmit
power
on
the
ground
–
this
can
significantly
reduce
the
BUC/SSPA
size
not
only
by
reducing
the
transmit
EIRP,
but
also
by
reducing
the
BUC/SSPA
backoff.
Consider
the
following
example:
Satellite & Transponder
IS-901 @ 342º W, 22/22 (EH/EH)
Earth Station 1
Africa – 4.5 m
Earth Station 2
Africa – 3.6 m
Data Rate
30 Mbps / 10 Mbps
While
the
traditional
link
was
based
on
8PSK,
TPC
3/4
and
required
27.8
MHz
of
leased
bandwidth,
the
CnC
link
was
based
on
8PSK
3/4
and
8PSK
3/5
and
required
19.3
MHz
of
leased
bandwidth.
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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