Power Limited Links - Comtech EF Data CDM-570A Installation And Operation Manual

CDM-570A/570AL Satellite Modem with Optional Packet Processor
Appendix G
Consider the following example:
Satellite & Transponder
Earth Station 1
Earth Station 2
Data Rate
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
Data Rate (kbps)
Modulation
FEC
Occupied BW (MHZ)
Power Eq. BW (MHz)
Leased BW (MHz)
Hub BUC (W)
Remote BUC (W)
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
IS-901 @ 342º W, 22/22 (EH/EH)
Africa – 4.5 m
Africa – 3.0 m
3 Mbps / 1 Mbps
Original Link
Hub to Remote
Total
Remote to Hub
3000 1000
QPSK QPSK
TPC 3/4 TPC 7/8
2.8 1.2 4.0
3.2 0.7 3.9
4.0
30
20
G–13
With Carrier-in-Carrier and VersaFEC
Hub to Remote to
Remote Hub
3000 1000
QPSK QPSK
VersaFEC VersaFEC
0.631 0.533
2.9 1.4
2.3 0.5
20
10
MN-CDM570A
Revision 3
Savings /
Reduction
Total
2.9
2.8
2.9 28.7%
33%
33%