Comtech EF Data CDM-570A - Manual (Page 531)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix G Revision 2
G–13
Consider the following example:
Satellite & Transponder IS-901 @ 342º W, 22/22 (EH/EH)
Earth Station 1 Africa – 4.5 m
Earth Station 2 Africa – 3.0 m
Data Rate 3 Mbps / 1 Mbps
While the traditional link was based on QPSK, TPC 3/4 for the Hub to Remote and QPSK TPC 7/8
for Remote to Hub and required 4.0 MHz of leased bandwidth, the Carrier-in-Carrier link was
based on QPSK, VersaFEC 0.631 and QPSK, VersaFEC 0.533 and required 2.9 MHz of leased
bandwidth.
The savings summary is as follows:
Item
Original Link With Carrier-in-Carrier and VersaFEC
Savings /
Reduction
Hub to
Remote
Remote
to Hub
Total
Hub to
Remote
Remote to
Hub
Total
Data Rate (kbps) 3000 1000 3000 1000
Modulation QPSK QPSK QPSK QPSK
FEC TPC 3/4 TPC 7/8
VersaFEC
0.631
VersaFEC
0.533
Occupied BW (MHZ) 2.8 1.2 4.0 2.9 1.4 2.9
Power Eq. BW (MHz) 3.2 0.7 3.9 2.3 0.5 2.8
Leased BW (MHz) 4.0 2.9 28.7%
Hub BUC (W) 30 20 33%
Remote BUC (W) 20 10 33%
G.4.5.3 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 latest FEC such as
VersaFEC 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 VersaFEC and using a lower order modulation – e.g.,
QPSK, VersaFEC 0.803 increases the total occupied bandwidth, while
reducing the total power equivalent bandwidth:
Now using DoubleTalk Carrier-in-Carrier, the second QPSK, VersaFEC
0.803 carrier can be moved over the first carrier – thereby
significantly reducing the total occupied bandwidth and total power