Power Limited Links - Comtech EF Data DMD-2050E Installation And Operation Manual

DMD2050E Universal Satellite Modem

3.11.9.3 Power Limited Links

Carrier-in-Carrier can provide substantial savings even when the original link is power limited.
Spreading the carrier by using a lower modulation and/or FEC along with the latest FEC can
substantially reduce the total power which can then be traded with bandwidth using Carrier-in-
Carrier. The concept is illustrated with the following examples.
The conventional link is using 8-PSK, TPC 3/4:
Switching to an advanced FEC and using a lower order modulation – e.g., QPSK,
STANAG TURBO 7/8 increases the total occupied bandwidth, while reducing the total power
equivalent bandwidth:
Now using DoubleTalk Carrier-in-Carrier, the second QPSK, STANAG TURBO 7/8 carrier can be
moved over the first carrier – thereby significantly reducing the total occupied bandwidth and total
power equivalent bandwidth when compared to the original side-by-side 8PSK, TPC 3/4 carriers:
Consider this example:
Satellite & Transponder IS-901 @ 342º W, 22/22 (EH/EH)
Earth Station 1
Earth Station 2
Data Rate
MN-DMD2050E Revision 2
9.2 m
4.5 m
2.048 Mbps / 2.048 Mbps
Theory of Operation
3–41