Comtech EF Data SLM-5650A - Manual (Page 311)

SLM5650A_CDM625 Satellite Modem Revision 8
DoubleTalk Carrier-in-Carrier Option MN-SLM5650A
15–13
The savings summary is as follows:
Item
Original Link With Carrier-in-Carrier and LDPC
Savings 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 3/4 LDPC 3/4 LDPC 1/2
Occupied BW
(MHZ) 2.8 0.9 3.7 2.8 1.4 2.8
Power Eq. BW
(MHz) 3.3 0.6 3.9 2.5 0.3 2.8
Leased BW (MHz) 3.9 2.8 27.5%
Hub HPA (W) 26.0 20.3 22%
Remote HPA (W) 10.6 6.4 40%
If this link was designed using QPSK, LDPC 3/4 in both directions, it would have required:
Occupied BW 2.8 MHz
Power Eq. BW 3.0 MHz 7.2% increase in Power Eq. BW
Leased BW 3.0 MHz 7.2% increase in Leased BW
Hub HPA 20.3 W
Remote HPA 8.3 W 30% increase in Remote power
15.4.5.3 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 CnC, 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: