Comtech EF Data CDM-750 - Manual (Page 272)

CDM-750 Advanced High-Speed Trunking Modem Revision 2
Appendix D MN-CDM750
D–14
The savings summary is as follows (note TPC 7/8 is 20/23 actual):
Item
Original Link With Carrier-in-Carrier and LDPC
Savings
Hub to
Remote
Remote To
Hub
Total
Hub to
Remote
Remote to
Hub
Total
Data Rate (kbps)
30 Mbps 10 Mbps 30 Mbps 10 Mbps
Modulation 8PSK 8PSK 8PSK 8PSK
FEC
TPC 3/4 TPC 7/8 S2 3/4 S2 3/5
Occupied BW (MHZ)
19.1 5.5 24.6 19.3 8.0 19.3
Power Eq. BW (MHz) 22.0 5.8 27.8 13.5 3.4 16.9
Leased BW (MHz)
27.8 19.3 30.5%
Hub HPA (W) 503 310 38.3%
Remote HPA (W) 219 129 41.1%
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: