  Iterative decoding techniques have gain popularity due to their performance
and their application in most communications systems. In this paper, we present
a new application of our iterative decoder on the GPCB (Generalized Parallel
Concatenated Block codes) which uses cyclic permutations. We introduce a new
variant of the component decoder. After extensive simulation; the obtained
result is very promising compared with several existing methods. We evaluate
the effects of various parameters component codes, interleaver size, block
size, and the number of iterations. Three interesting results are obtained; the
first one is that the performances in terms of BER (Bit Error Rate) of the new
constituent decoder are relatively similar to that of original one. Secondly
our turbo decoding outperforms another turbo decoder for some linear block
codes. Thirdly the proposed iterative decoding of GPCB-BCH (75, 51) is about
2.1dB from its Shannon limit.
