On the application of approximate APP decoding to digital videotransmission

For transmitting compressed digital video, the authors propose using threshold decodable block codes with large block length, and a posteriori probability (APP) soft decision decoding. A new approximation of the weight function associated with APP soft decision decoding of threshold decodable codes is presented. When the number of components in the parity equations is large, the new method gives excellent error performance, whereas there is a substantial degradation in the performance of the least reliable symbol approximation presented by Tanaka et al. (1980) and others. The effect of feedback on the performance of the APP decoder is also analyzed. It is shown that if the performance criterion is word error rate rather than bit error rate, feedback of previously decoded bits is essential to obtain all possible coding gain from the soft decision decoder. Finally, the performance of the proposed coding scheme is compared to the performance of a concatenated coding system with the same rate