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CDM-750 High Speed Trunking Modem
DoubleTalk Carrier-in-Carrier Option
If the CnC link was designed using S2-8PSK 3/4 in both directions, it would have required:
•
Occupied BW – 19.3 MHz;
•
Power Eq. BW – 17.9 MHz (a 5.9% increase in Power Eq. BW);
•
Leased BW – 19.3 MHz;
•
Hub HPA – 310 W;
•
Remote HPA – 166 W (a 28.7% increase in Remote power).
8.4.6.2
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
DVB-S2 LDPC 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 8PSK, TPC 3/4:
Switching to DVB-S2 8PSK 3/4 slightly increases the total occupied
bandwidth, while substantially reducing the total power equivalent
bandwidth:
Now, using CnC, the second 8PSK 3/4 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 8PSK TPC 3/4, the CnC link used DVB-S2 8PSK 3/4. The
savings summary is as follows – using CnC and DVB-S2 reduced the leased bandwidth by almost
50% and HPA power by almost 60%:
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 8PSK, 1 dB Feed Loss.
IS-901 @ 342º W, 22/22 (EH/EH)
Africa – 9.1 m
Africa – 4.5 m
20.48 Mbps / 20.48 Mbps
Original Link
Hub to
Remote To
Total
Remote
Hub
20.48
20.48
8PSK
8PSK
TPC 3/4
TPC 3/4
13.1
13.1
26.2
10.3
4.9
15.2
-
-
26.2
44
112
8–13
With Carrier-in-Carrier
Hub to
Remote to
Remote
Hub
-
20.48
20.48
-
8PSK
8PSK
-
S2 3/4
S2 3/4
13.2
13.2
6.4
2.0
-
-
27
47
Revision 1
MN-CDM750
Savings
Total
-
-
-
13.2
8.4
13.2
49.6%
38.3%
58.3%
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