Comtech EF Data cdm-570a - Power Limited Links

CDM-570A/570AL Satellite Modem with Optional Packet Processor
Revision 5
DoubleTalk Carrier-in-Carrier Option G–15 MN-CDM570A
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
equivalent bandwidth when compared to the original side-by-side
8PSK, TPC 3/4 carriers: