Mocomtech CDM-570 - Manual (Page 191)

Chapter 7. FORWARD ERROR
CORRECTION OPTIONS
7.1 Introduction
As standard, the CDM-570/570L Modem is equipped with an industry-standard Viterbi
Forward Error Correction (FEC) encoder/decoder. The constraint lengths and encoding
polynomials are compatible with the vast majority of existing modems from other
manufacturers. Comtech EF Data has performed compatibility testing to ensure
interoperability. In addition, there are two plug-in daughter cards (SIMM modules), both
field upgradeable, for adding other FEC functionality.
The first of these is a Concatenated Reed-Solomon Codec, which is combined with
Viterbi coding, to significantly improve BER versus Eb/No performance. It is required
for running 8-PSK/TCM, and for the 16-QAM Viterbi modes.
The second optional plug-in card is the Turbo Product Codec. Turbo Coding represents a
very significant development in the area of FEC, and Comtech EF Data’s Turbo Product
Codec offers Rate 5/16 and Rate 21/44 for BPSK, Rate 21/44 QPSK, Rate 3/4 and Rate
7/8 for QPSK, OQPSK, 8-QAM, 8-PSK and 16-QAM, and Rate 0.95 for QPSK, 8-QAM
and 8-PSK. Turbo Product Coding provides the best Forward Error Correction
technology currently available, and is now offered with a sufficiently broad range of code
rates and modulation types that link performance can be optimized under any conditions.
At the time of writing, Comtech EF Data is planning to release a new codec, which is a
combination of Turbo Product Coding and Low Density Parity Check (LDPC) coding.
Please consult the factory for details of availabilty on this new TPC/LDPC Codec.
7–1