Comtech EF Data CDM-570AL - Versafec-2

CDM-570A/570AL Satellite Modem with Optional Packet Processor
Revision 5
FEC (Forward Error Correction) Options B–10 MN-CDM570A
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.
• VersaFEC-2 has two modes:
o Long Block – Maximum coding gain with higher latency.
 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.
o Short Block – Slightly lower coding gain with much more latency.
 36 Mod Cods – BPSK to 32-ARY modulation, 1600 symbol block size.
 Short Block performance is overall considerably better than 1
st
generation
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.
• CCM and point-to-point ACM are supported in both modes.
Appendix P.7. ADAPTIVE CODING AND MODULATION OPTION
• 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
• In ACM, the range of rate bit rate adaption is approximately 9:1.
• 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
st
generation VersaFEC).
• 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.
• VersaFEC-2 provides five modulation types – BPSK, QPSK, 8-ARY, 16-ARY, and 32-
ARY.
• VersaFEC-2 adds new circular or quasi-circular constellations for higher-order
modulations (above QPSK) to replace the square VersaFEC constellations.
• 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.
• The overhead associated with AUPC is eliminated. (A framed mode such as EDMAC is
normally required.)
• 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.