M–1
Appendix M. VERSAFEC /
VERSAFEC-2 ACM (ADAPTIVE
CODING AND MODULATION)
OPTION
M.1 Overview
VersaFEC® and VersaFEC-2 are technologies that are wholly owned and developed by
Comtech EF Data and Comtech AHA Enterprise Products Group. VersaFEC is a
registered trademark of Comtech AHA Enterprise Products Group.
ACM (Adaptive Coding and Modulation) is a significant feature in the CDM-625A. It may be used
with either VersaFEC or, for modems running Firmware Version 1.3.1 or later, with a VersaFEC-2
plug-in Option Card (see Sect. M.13), and activated with the appropriate FAST codes.
• ACM turns fade margin into increased link capacity – gains of 100% or more are possible,
compared to traditional Constant Coding and Modulation (CCM). This is accomplished by
automatically adapting the modulation type and FEC code rate to give highest possible
throughput.
• ACM maximizes throughput regardless of link conditions (noise or other impairments, clear
sky, rain fade, etc). Initial setup is easy, and then requires no further user intervention.
• With CCM systems, severe rain fading can cause the total loss of the link, and zero
throughput. ACM keeps the link up (with lower throughput) – and can yield much higher
system availability.
• ACM in the CDM-625A is used in conjunction with VersaFEC and is currently for IP traffic
only.
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