Comtech EF Data CDM-570A - Manual (Page 602)

CDM-570A/570A Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix P Revision 2
P–12
• The value of Max ModCod may be limited by other FAST codes installed in the CDM-
570A/570AL. For example, suppose the 3000 ksps FAST option is installed, and the symbol
rate set to 3000 ksps, the theoretical maximum data rate would be 10.239 Mbps at ModCod
11. However, if CnC is being used with a 5 Mbps FAST limit, then ACM Max ModCod will be
limited to ModCod 4, or 4.83 Mbps. Therefore, if it is not possible to set the Maximum
ModCod to the desired value for a given symbol rate, you should check to determine what
other FAST codes may be limiting it.
• The BER versus Eb/No performance of the ModCods is identical to the VersaFEC CCM modes
described in the FEC Options Chapter.
• SNR is the preferred metric for driving the adaptation – this is the value displayed on the
monitor screens. If you want to convert this to Eb/No then remember that the relationship is
simply Eb/No = SNR - 10
log
(Spectral Efficiency).
• ACM and AUPC are supported at the same time.
• All IP features that are available in the CDM-570A/570AL-IP (VLAN, QoS, etc) are available
when in IP-ACM mode.
• VersaFEC ACM is 100% compatible with Carrier-in-Carrier (CnC)
• ACM maximizes throughput not only when Eb/No varies due to atmospheric conditions, but
will also mitigate the effects of other impairments, such as antenna pointing error, excessive
phase noise and certain types of interference. However, rapidly fluctuating impairments (~
less than 1 second) such as scintillation at low antenna look-angles at C-band will generally not
be improved by ACM.
• VersaFEC ACM modes are not compatible with VersaFEC CCM modes, due to differences in
frame preambles.