Improved Iterative Decoders for Turbo-Coded Decode-and-Forward Relay Channels

An Improved Maximum A Posteriori (IMAP) decoder for turbo-coded decode-and-forward (DF) relay channels which takes into account the decoding errors at the relay is analyzed. This decoder is implemented in an iterative manner similar to the traditional iterative decoder (TID) used for turbo codes. The performance of this IMAP decoder is compared with the performance of an iterative decoder normally used in the literature which does not take into account the decoding errors at the relay, by simulation. The comparison shows that although the proposed IMAP decoder provides a better performance, especially when many decoding errors occur at the relay, the improvement is not significant. Then, another heuristic modification for the iterative decoder is proposed. In spite of the lack of theoretical analysis, the numerical results show that the proposed heuristically modified iterative decoder (HMID) gives significantly better performance than the traditional one.