Different iterative decoding algorithms for combined concatenated coding and multiresolution modulation

In this article a three hierarchy level source coding scheme providing three image qualities, HDTV, EDTV and SDTV, respectively, is taken into account. The proposed system maintains graceful degradation. It is based on a concatenated coding scheme. The inner convolutional code is combined with 64-multiresolution QAM. The outer code is a RS code. The simulation results with perfect channel estimation showed that one can obtain a very high performance in independent Rayleigh/Rician fading channels. However, in a realistic correlative fading channel, the loss due to the non-perfect channel estimation and non-perfect interleaving is about 2-3 dB. In order to improve the system performance, one may apply iterative decoding, where its use for the future receivers may be just an option: this allows one to build higher-quality receivers. Three different iterative decoding algorithms with different complexities are analyzed. They are based on iterative-multistage and -concatenated multistage decoding algorithms calling upon soft output decoding techniques. The simulation results in a Rayleigh fading channel, for the last algorithm showed, that one can obtain up to 2.5 dB gain after only one iteration, and 3 dB after a higher number of iterations, which is quite significant