Comtech EF Data CDM-750 Installation And Operation Manual page 270

CDM-750 Advanced High-Speed Trunking Modem
Appendix D
The savings summary is as follows (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 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).
D.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:
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
D–14
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 2
MN-CDM750
Savings
Total
19.3
16.9
19.3 30.5%
38.3%
41.1%