Coded modulation schemes based on partial Gray mapping and unpunctured high rate turbo codes

The paper deals with coding for the band-limited AWGN channel. Coded modulation schemes based on high rate unpunctured turbo codes are proposed. It is shown that, owing to efficient decoding based on the trellis of the dual code and to the optimised code design, coded modulations based on this class of turbo codes allow excellent performance with moderate complexity for practical values of block size and redundancy. A mapping rule already envisaged in previously published papers, based on the partition Z/2lZ with Gray mapping of l bits is exploited. Schemes based on the partition chain Z/2Z/4Z are also presented in a comparative way. From this comparison it is concluded that, when constraints are imposed on the number of dimensions and on the redundancy of the coded modulation, partial Gray mapping based on Z/4Z should be preferred to pure mapping by set partitioning and, with QAM constellations with more than 16 points, it should also be preferred to pure Gray mapping.