Combined multilevel turbo-code with 8PSK modulation

Different concepts of iterative decoding algorithms for serial or parallel concatenated coding (called turbo-code) as well as for the special case of the generalized concatenated coding schemes have been introduced. These algorithms being very efficient, are based on soft output decoding, where, the soft decisions are used as feed-forward information for the next steps of iterations. In order to achieve the high performance expected by turbo-codes and to assume a great flexibility for the system, we combine a multilevel turbo-code with 8PSK modulation. This allow us to examine in detail the performance of this combination compared with different coding and decoding approaches: turbo-code with Gray mapping and iterative multistage decoding using convolutional codes or a combination of turbo codes, convolutional and single parity check codes. In all of our studies we consider a super-concatenated coding scheme, where the outer code is based on Reed-Solomon code. The results showed that the coding gain at a BER of 10^-4 (since we employ a powerful outer RS decoder) for the iterative convolutional coding and for the combination of convolutional/turbo coding is quite the same compared to turbo coding with Gray mapping, which is 0.5 dB. However, compared to uncoded QPSK, the coding gain is 4 dB (at a BER of 10^-4), which is quite significant