Designing Iterative Decoding Schemes with the Extrinsic Information Transfer Chart

Since the discovery of parallel concatenated (turbo) codes, iterative decoding has become a vital field of research in digital communications. Applications of the “turbo principle” to many detection and decoding problems have been found. While most studies have focused on designing code concatenations with respect to maximum likelihood decoding performance, the convergence properties of iterative decoding schemes have gained a considerable amount of interest just recently. In this paper we use the extrinsic information transfer chart (EXIT chart) to illuminate the convergence properties of bit– interleaved coded modulation, equalization, and serially concatenated binary codes. The EXIT chart leads to new design ideas like inner and outer doping, facilitating the construction of code concatenations with iterative decoders operating close to the capacity limit.