J.4.6.2 Power Limited Links - Comtech EF Data CDM-760 Installation And Operation Manual

Appendix J
CDM-760 Advanced High-Speed Trunking Modem
The savings summary is (note TPC 7/8 is 20/23 actual):
Item
Data Rate (kbps)
Modulation
FEC
Occupied BW (MHZ)
Power Eq. BW (MHz)
Leased BW (MHz)
Hub HPA (W)
Remote HPA (W)
If the CnC link was designed using S2-8PSK 3/4 in both directions, it would require:
•
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).
J.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 these 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
Original Link
Hub to Remote To
Total
Remote Hub
30 Mbps 10 Mbps
8PSK 8PSK
TPC 3/4 TPC 7/8
19.1 5.5 24.6
22.0 5.8 27.8
27.8
503
219
IS-901 @ 342º W, 22/22 (EH/EH)
Africa – 9.1 m
Africa – 4.5 m
20.48 Mbps / 20.48 Mbps
J–12
With Carrier-in-Carrier and LDPC
Hub to Remote to
Remote Hub
30 Mbps 10 Mbps
8PSK 8PSK
S2 3/4 S2 3/5
19.3 8.0
13.5 3.4
310
129
Revision 4
MN-CDM760
Savings
Total
19.3
16.9
19.3 30.5%
38.3%
41.1%