Product specifications

5–1
Chapter 5. FORWARD ERROR
CORRECTION
5.1 Introduction
As standard, the CDD-56X Satellite Demodulator is equipped with an integral 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 3/4 and 0.95 for QPSK and 8-PSK
• Rate 3/4 for 16-QAM
• Rate 7/8 for QPSK, 8-PSK, and 16-QAM
Turbo Product Coding provides the best of class Forward Error Correction technology currently
available, along with modulation types that optimize link performance under any conditions.
5.2 Turbo Product Codec
5.2.1 Description
Turbo coding is an FEC technique developed within the last few years that delivers significant
performance improvements, when compared to more traditional techniques.
Two general classes of Turbo Codes have been developed: Turbo Convolutional Codes (TCC),
and Turbo Product Codes (TPC, a block coding technique). Comtech EF Data has chosen to
implement an FEC codec based on TPC.
A Turbo Product Code is a 2 or 3 dimensional array of block codes. Encoding is relatively
straightforward, but decoding is a very complex process requiring multiple iterations of
processing for maximum performance to be achieved.
Unlike the popular method of concatenating a Reed-Solomon codec with a primary FEC codec,
Turbo Product Coding is an entirely standalone method. It does not require the complex
interleaving/de-interleaving of the RS approach and, consequently, decoding delays are
significantly reduced.
Furthermore, the traditional concatenated RS schemes exhibit a very pronounced threshold effect:
A small reduction in Eb/No can result in total loss of demod and decoder synchronization. TPC