Comtech EF Data CDM-425, Installation And Operation Manual

Page: 616 / 744

CDM-425 Advanced Satellite Modem
Revision 0
Appendix F F–14 MN-CDM-425
Consider the example shown in Table F-6.
Table F-6. Asymmetric Data Rate Link Example
Satellite & Transponder IS-901 @ 342º W, 22/22 (EH/EH)
Earth Station 1 Africa – 4.5 m
Earth Station 2 Africa – 3.0 m
Data Rate 3000 Mbps / 1000 Mbps
While the traditional link was based on QPSK, TPC 3/4 and required 3.9 MHz of leased
bandwidth, the Carrier-in-Carrier link was based on QPSK, LDPC 3/4 and QPSK, LDPC 1/2 and
required 2.8 MHz of leased bandwidth.
The savings summary is shown in Table F-7.
Table F-7. Asymmetric Data Rate Link Savings Summary
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) 3000 1000 3000 1000
Modulation QPSK QPSK QPSK QPSK
FEC TPC 3/4 TPC 3/4 LDPC 3/4 LDPC 1/2
Occupied BW (MHZ) 2.8 0.9 3.7 2.8 1.4 2.8
Power Eq. BW (MHz) 3.3 0.6 3.9 2.5 0.3 2.8
Leased BW (MHz) 3.9 2.8 27.5%
Hub HPA (W) 26.0 20.3 22%
Remote HPA (W) 10.6 6.4 40%
If this link was designed using QPSK, LDPC 3/4 in both directions, it would have required:
Table F-8. QPSK and LDPC ¾ Link Requirements
Occupied BW 2.8 MHz
Power Eq. BW 3.0 MHz 7.2% increase in Power Eq. BW
Leased BW 3.0 MHz 7.2% increase in Leased BW
Hub HPA 20.3 W
Remote HPA 8.3 W 30% increase in Remote power