Comtech EF Data CDM-570A - Manual (Page 434)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix B Revision 2
B–6
concatenation of a Viterbi decoder with Reed-Solomon hard-decision block codes. It remained
clear, however, that the Shannon Limit was still an elusive target.
Berrou’s work on Turbo Codes showed, through the use of an ingeniously simple approach
(multiple, or iterative decoding passes) that it is possible to achieve performance close to the
Shannon Limit. Berrou’s early work dealt exclusively with iteratively-decoded convolutional
codes (Turbo Convolutional Coding, or TCC), but in time the iterative approach was applied to a
particular class of block codes called Product Codes – hence Turbo Product Coding (TPC). TPC
exhibits inherently low decoding latency compared with TCC, and so is considered much more
desirable for 2-way, interactive satellite communications applications.
In August 1999, Comtech became the first company in the world to offer satellite modems that
incorporate TPC. Since its inception, Comtech has continued to develop and refine its
implementation of TPC in its products, and now offers a comprehensive range of code rates
(from Rate 5/16 to Rate 0.95) and modulations (from BPSK to 16-QAM).