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CDM-625 Advanced 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
10.4.5.3 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:
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
3.0 MHz
7.2% increase in Leased BW
20.3 W
30% increase in Remote power
8.3 W
10–13
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 13
MN-CDM625
Savings
Total
1.4
2.8
0.3
2.8
2.8
27.5%
22%
6.4
40%
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