Asymmetric Data Rate Link - Comtech EF Data DMD-2050E Installation And Operation Manual

DMD2050E Universal Satellite Modem
The link budget summary for the different MODCOD combinations is as follows:
S.
Modulation & FEC
No.
8-QAM, LDPC
1
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

3.11.9.2 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 the following example:
Satellite & Transponder IS-901 @ 342º W, 22/22 (EH/EH)
Earth Station 1
Earth Station 2
Data Rate
MN-DMD2050E Revision 2
Allocated BW
(MHz)
0.3584
2/3
0.47785
0.53735
0.7168
Traditional Link CnC Link
(QPSK, TPC 3/4) (QPSK, LDPC 2/3)
0.7 W
1.5 W
Africa – 4.5 m
Africa – 3.0 m
3000 Mbps / 1000 Mbps
PEB Leased BW
(MHz) (MHz)
1.1468 1.1468
0.6734 0.6734
0.5777 0.5777
0.5184 0.7168
HPA Power Reduction
0.5 W 40%
1.1 W 36%
Theory of Operation
Savings PSD
Compared Ratio
to Original (dB)
-20% 2.1
30% 2.1
40% 2.1
25% 2.1
3–39