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The link budget summary for the different ModCod combinations is shown in Table F-4.
S. No.
Modulation & FEC
1
8-QAM, LDPC 2/3
2
QPSK, LDPC 3/4
3
QPSK, LDPC 2/3
4
QPSK, LDPC 1/2
Based on this analysis, QPSK, LDPC 2/3 with Carrier-in-Carrier provides the maximum savings of
40%. In addition to 40% reduction in Leased Bandwidth, using Carrier-in-Carrier also reduced the
required HPA Power by almost 40%:
HPA Power
HPA @ 4.6 m
HPA @ 2.4 m
F.2.5.2
Asymmetric Data Rate Link
As occupied (or allocated) bandwidth of a Carrier-in-Carrier 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 PSD 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 transponder,
and increases available link margin;
•
Lower order modulation uses less transmit power on the ground – this can significantly
reduce the BUC/SSPA size by not only reducing the transmit EIRP, but also reducing the
BUC/SSPA backoff
Appendix F
Table F-4. Link Budget Summary for ModCod Combinations
Allocated
BW (MHz)
0.3584
0.47785
0.53735
0.7168
Table F-5. HPA Power Reduction
Traditional Link
(QPSK, TPC 3/4)
0.7 W
1.5 W
CDM-425 Advanced Satellite Modem
Leased BW
PEB (MHz)
(MHz)
1.1468
1.1468
0.6734
0.6734
0.5777
0.5777
0.5184
0.7168
CnC Link
(QPSK, LDPC 2/3)
0.5 W
1.1 W
F–13
Revision 0
PSD
Savings Compared
Ratio
to Original
(dB)
-20%
2.1
30%
2.1
40%
2.1
25%
2.1
HPA Power Reduction
40%
36%
MN-CDM-425
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