Versafec-2 - Comtech EF Data CDM-570A Installation And Operation Manual

B.7

VersaFEC-2

Comtech EF Data's second generation VersaFEC-2 comprises 38 new ModCods, with a family of
constellations. This new functionality requiresthe plug-in VersaFEC-2 Option Card, Firmware
Version 1.5.2 or higher, and activation of the appropriate FAST codes.
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VersaFEC-2 has two modes:
Long Block – Maximum coding gain with higher latency.
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Short Block – Slightly lower coding gain with much more latency.
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CCM and point-to-point ACM are supported in both modes.
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In CCM, links can be run with VersaFEC-2 in one direction, and any other supported FEC
type in the other.
Example: Rx = VersaFEC-2, Tx = TPC
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In ACM, the range of rate bit rate adaption is approximately 9:1.
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In ACM, both sides need to be VersaFEC-2, but Tx and Rx can be Short or Long – no
restrictions (but NOT compatible in any way with 1
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If VersaFEC-2 is used on both sides of the link, even in CCM operation, the remote
modem's Eb/No can be seen on the front panel display/web pages, etc., of the local
modem.
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VersaFEC-2 provides five modulation types – BPSK, QPSK, 8-ARY, 16-ARY, and 32-
ARY.
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VersaFEC-2 adds new circular or quasi-circular constellations for higher-order
modulations (above QPSK) to replace the square VersaFEC constellations.
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Es/No span from -1.3 dB (ModCod 0) to 16.7 dB (ModCod 37), giving an average of
approximately 0.45 dB per ModCod, and a 17.6 dB total span.
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The overhead associated with AUPC is eliminated. (A framed mode such as EDMAC is
normally required.)
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Combined AUPC and ACM operation is possible – VersaFEC-2 permits up to 10 dB of
AUPC power increase, followed by 17.6 dB of ACM range, for a total of 27.6 dB of fade
protection.
FEC (Forward Error Correction) Options
CDM-570A/570AL Satellite Modem with Optional Packet Processor
38 ModCods – BPSK to 32-ARY modulation, 9600 symbol block size.
Spectral efficiency up to 4.4 bps/Hz for Long Block Versa FEC-2.
36 Mod Cods – BPSK to 32-ARY modulation, 1600 symbol block size.
Short Block performance is overall considerably better than 1
VersaFEC with similary latency performance.
Short Block deliberately limits throughput to 2 Mbps in CCM and 1 Msps in ACM.
Above these limits, latency is no longer an issue, and Long Block is preferred.
Spectral efficiency up to 4.15 bps/Hz for Short Block VersaFEC-2.
Appendix P.7. ADAPTIVE CODING MODULATION OPTION
AND
st
generation VersaFEC).
B–10
Revision 5
st
generation
MN-CDM570A