Concatenated coded modulation schemes for the Rayleigh fading channel

The purpose of the paper is to present a performance analysis of concatenated coded modulation schemes for the Rayleigh fading channel. This structure consists of concatenated codes using Reed-Solomon and Hamming codes respectively as outer and inner codes, incorporated into a multilevel code. In order to provide a large coding gain with a minimum complexity, the authors propose a new algorithm, with reduced complexity, for soft decoding the inner code. This algorithm is named DSCR (decodage souple a complexite reduite). The advantage of the proposed suboptimal algorithm lies in the significant reduction computation complexity compared to the classical Viterbi algorithm. This is obtained by associating reliability information to each received signal. In this algorithm which is based on the Chase algorithm (Chase, 1972), the authors have developed a reliability measurement method which uses four thresholds for the decision reliability. The proposed schemes coding 8-QAM and 16-QAM, provide in average a coding gain of 12 dB over uncoded 4-QAM at bit error rate of 10^-3. The overall code rate of coded 8-QAM is not the same as the uncoded 4-QAM spectral efficiency which can be easily obtained by coding 16-QAM instead. The ratio of the average complexities of the DSCR algorithm versus the hard decoding Hamming code is in the range of 2 to 3