Mocomtech CIM-550 Manuel D’Utilisation

 

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TURBO Product Codec 

Uncoded Operation 

 

As standard, the CiM-550 Modem is equipped with two Forward Error Correction 
Decoders, Viterbi and Sequential. The constraint lengths and encoding polynomials are 
compatible with the vast majority of existing modems from other manufacturers, and 
Comtech EF Data has performed compatibility testing to ensure inter-operability. 

As an option, the CiM-550 may be fitted with two additional Forward Error Correction 
(FEC) devices. The first is a concatenated Reed-Solomon Codec. This is always used in 
conjunction with, rather than instead of, the main FEC method (Viterbi or Sequential). 
The second option is Comtech EF Data’s Turbo Product Codec, which is an entirely 
stand-alone method of FEC. These options are small daughter cards, and may be fitted at 
the factory at the time of order, or may be added by the user at a later date. 

The combination of convolutional coding and Viterbi decoding has become an almost 
universal standard for satellite communications. The CiM-550 complies with the Intelsat 
IESS 308/309 standards for Viterbi decoding with a constraint length of seven. This is a 
de facto standard, even in a closed network environment, which means almost guaranteed 
inter-operability with other manufacturer’s equipment.  It provides very useful levels of 
coding gain, and its short decoding delay and error-burst characteristics make it 
particularly suitable for low data rate coded voice applications. It has a short constraint 
length, fixed at 7, for all code rates. (The constraint length is defined as the number of 
output symbols from the encoder which are affected by a single input bit.)