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6–1
Chapter 6. FORWARD ERROR
CORRECTION OPTIONS
6.1 Introduction
As standard, the Modem is equipped with three Forward Error Correction
encoders/decoders – Viterbi, concatenated Reed-Solomon and Trellis (which is available
with the 8-PSK FAST option). The constraint lengths and encoding polynomials are not
only Open Network compatible (IESS-315), but are also Closed Network compatible
with the vast majority of existing modems from other manufacturers. Comtech EF Data
has performed compatibility testing to ensure inter-operability.
Turbo Coding represents a very significant development in the area of FEC, and
optionally, the modem may be fitted with a Turbo Product Codec. They are plug-in
daughter cards (SIMM modules) that are field upgradeable. The codec provides data rate
capability up to 20 Mbps, and code rates of:
• Rate 5/16 (BPSK
• Rate 21/44 (BPSK, QPSK)
• Rate 3/4, and 7/8 (QPSK, 8-PSK, and 16-QAM)
• Rate 17/18 (QPSK and 8-PSK)
Turbo Product Coding provides one of the best Forward Error Correction technologies
currently available, and is now offered with a sufficient range of code rates and
modulation types that link performance can be optimized under any conditions.