Specifications

DMD20/20LBST Universal Satellite Modem Theory of Operation
MN-DMD20-20LBST Revision 14 3–38
3.15.8.3 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:
To continue, consider this example:
Satellite & Transponder
IS-901 @ 342º W, 22/22 (EH/EH)
Earth Station 1
Africa – 9.2 m
Earth Station 2
Africa – 4.5 m
Data Rate
2.048 Mbps / 2.048 Mbps
Whereas the original link used 8-PSK TPC 3/4, the Carrier-in-Carrier link used QPSK VersaFEC
0.803. The savings summary is as follows:
Item
Original Link
With Carrier-in-Carrier and VersaFEC
Savings
Hub to
Remote
Remote To
Hub
Total
Hub to
Remote
Remote to
Hub
Total
Data Rate (kbps)
2048
2048
2048
2048
Modulation
8-PSK
8-PSK
QPSK
QPSK
FEC
TPC 3/4
TPC 3/4
0.803
0.803
Occupied BW (MHZ)
1.3
1.3
2.6
1.8
1.8
1.8
Power Eq. BW (MHz)
2.2
1.0
3.2
1.1
0.5
1.6
Leased BW (MHz)
3.2
1.8
44%
Hub HPA (W)
5.0
2.0
60%
Remote HPA (W)
11.6
4.7
60%
Note: 1 dB HPA BO for QPSK, 2 dB HPA BO for 8-PSK, 1 dB Feed Loss.
Using Carrier-in-Carrier and VersaFEC reduced the leased bandwidth by almost 44% and HPA
power by 60%