Asymmetric Data Rate Link - Comtech EF Data CDM-570A Installation And Operation Manual

CDM-570A/570AL Satellite Modem with Optional Packet Processor
Appendix G
Total Leased Resource Usage
LST Calculated
(MultiCarrier Transponder Lease)
Total EIRP Utilized
Total EIRP Available
Margin (available-utilized)
The link budget summary for the different ModCod combinations is as follows:
S.No. Modulation & FEC (CnC Carrier)
1 QPSK, VersaFEC 0.533, 10% ROF
2 QPSK, VersaFEC 0.631, 15% ROF
3 QPSK, VersaFEC 0.706, 25% ROF
Based on this analysis, QPSK, VersaFEC 0.533 with Carrier-in-Carrier provides savings of 36%. In
addition to this 36% reduction in Leased Bandwidth, using Carrier-in-Carrier also reduced the
BUC requirement from 10W to 5W:
BUC Size
BUC @ 4.5 m
BUC @ 3.0 m
G.4.5.2 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.
12.8 dBw
13.3 dBw
.5 dBw
Allocated
BW
(MHz)
1.0319 0.9755
0.9113 1.1069
0.8859 1.3223
Traditional Link
(QPSK, TPC 7/8) (QPSK, VersaFEC 0.533)
10 W
10 W
G–12
Total BW Allocated
TotalBW PEB*
Total BW Utilized
Total BW Available
Margin (available-utilized)
*PEB = Power Equivalent Bandwidth
CnC Allocated BW = 1.0319 MHz
CnC PEB = 0.9755 MHz
CnC Leased BW = 1.03196 MHz
Leased
PEB CnC Leased
BW
(MHz) BW Savings
(MHz)
1.0319 36%
1.1069 31%
1.3223 17%
CnC Link
BUC Size Reduction
5 W
5 W
MN-CDM570A
Revision 3
1.0319 MHz
.9755 MHz
1.0319 MHz
1.1000 MHz
0.681 MHz
PSD Ratio
(dB)
2.2
2.2
2.2
50%
50%