Code characteristic matching for iterative decoding of serially concatenated codes

The design of serially concatenated codes has yet been dominated by optimizing asymptotic slopes of error probability curves. We propose mutual information transfer characteristics for soft in/soft out decoders to design serially concatenated codes based on the convergence behavior of iterative decoding. The exchange of extrinsic information is visualized as a decoding trajectory in the Extrinsic Information Transfer Chart (exit chart). By finding matching pairs of inner and outer decoder transfer characteristics we are able to construct serially concatenated codes whose iterative decoder converges towards low bit error rate at signal- to- noise ratios close to the theoretical limits.