Combined multilevel Turbo-code with MR-modulation

Different concepts of iterative decoding algorithms for multi-dimensional coding, serial or parallel concatenated coding (called Turbo-code) as well as for the case of generalized concatenated coding schemes have previously been introduced. In order to achieve high performance expected by Turbo-codes and to assume a great flexibility, the present authors combine multilevel Turbo-code with a high order of modulation. This allows examination of the performance of this combination compared with different coding and decoding approaches: Turbo-code with Gray mapping and iterative multistage decoding using Turbo codes or convolutional coding. The authors consider a super-concatenated coding scheme, where the outer code is based on Reed-Solomon code. As modulation they use multi-resolution (MR) modulation (a potential candidate for hierarchical digital TV/HDTV for terrestrial broadcasting). The performance of these three approaches are presented for the three hierarchy layers (SDTV, EDTV and HDTV). All these coding scheme have the same average coding rates. The number of iterations for Turbo code of memory 4 with interleaver size 2048, is 3. However, for convolutional code of memory 6 the number of iterations considered is 1. The results showed that the coding gain at BER of 4×10^-4 for the three approaches are the same compared to a convolutional coding with Gray mapping. However, the small gain of Turbo-multilevel code with respect to the Turbo-Gray mapping case is due to the “error propagation” after re-encoding for multistage detection