Comtech EF Data SLM-5650A Installation And Operation Manual page 479

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
G.3.4.2 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.
Consider this example:
Satellite & Transponder
Earth Station 1
Earth Station 2
Data Rate
Appendix H
Traditional Link
(QPSK, LDPC 2/3)
(QPSK, TPC 3/4)
0.7 W
1.5 W
Africa – 4.5 m
Africa – 3.0 m
3000 Mbps / 1000 Mbps
G–13
SLM-5650A Satellite Modem
CnC Link
HPA Power Reduction
0.5 W
1.1 W
IS-901 @ 342º W, 22/22 (EH/EH)
Revision 10
40%
36%
MN-SLM-5650A