Power Limited Links - Radyne DMD20 Installation And Operation Manual

DMD20/20LBST Universal Satellite Modem
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
Earth Station 1
Earth Station 2
Data Rate
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
Data Rate (kbps)
Modulation
FEC
Occupied BW (MHZ)
Power Eq. BW (MHz)
Leased BW (MHz)
Hub HPA (W)
Remote HPA (W)
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%
MN-DMD20-20LBST Revision 14
IS-901 @ 342º W, 22/22 (EH/EH)
Africa – 9.2 m
Africa – 4.5 m
2.048 Mbps / 2.048 Mbps
Original Link
Hub to Remote To
Total
Remote Hub
2048 2048
8-PSK 8-PSK
TPC 3/4 TPC 3/4
1.3 1.3
2.2 1.0
5.0
11.6
With Carrier-in-Carrier and VersaFEC
Hub to Remote to
Remote Hub
2048 2048
QPSK QPSK
0.803 0.803
2.6 1.8 1.8
3.2 1.1 0.5
3.2
2.0
4.7
Theory of Operation
Savings
Total
1.8
1.6
1.8 44%
60%
60%
3–38