Power Limited Links - Comtech EF Data SLM-5650A Installation And Operation Manual

SLM5650A_CDM625 Satellite Modem
DoubleTalk Carrier-in-Carrier Option
The savings summary is as follows:
Item
Data Rate (kbps)
Modulation
FEC
Occupied BW
(MHZ)
Power Eq. BW
(MHz)
Leased BW (MHz)
Hub HPA (W)
Remote HPA (W)
If this link was designed using QPSK, LDPC 3/4 in both directions, it would have required:
Occupied BW
Power Eq. BW
Leased BW
Hub HPA
Remote HPA

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:
Original Link
Hub to Remote to
Remote Hub
3000 1000
QPSK QPSK
TPC 3/4 TPC 3/4
2.8 0.9
3.3 0.6
26.0
10.6
2.8 MHz
3.0 MHz 7.2% increase in Power Eq. BW
7.2% increase in Leased BW
3.0 MHz
20.3 W
8.3 W 30% increase in Remote power
15–13
With Carrier-in-Carrier and LDPC
Hub to Remote to
Total
Remote Hub
3000 1000
QPSK QPSK
LDPC 3/4 LDPC 1/2
3.7 2.8
3.9 2.5
3.9
20.3
Revision 8
MN-SLM5650A
Savings
Total
1.4 2.8
0.3 2.8
2.8 27.5%
22%
40%
6.4