Design of serially concatenated systems depending on the block length

Based on extrinsic information transfer (EXIT) charts, the convergence behavior of iterative decoding is studied for a number of serially concatenated systems, such as a serially concatenated code, coded data transmission over an intersymbol interference channel, bit-interleaved coded modulation, or trellis-coded modulation. Efficient optimization algorithms based on simplified EXIT chart construction are devised to find irregular codes improving the convergence of iterative decoding. One optimization criterion is to find concatenated systems exhibiting thresholds of successful decoding convergence, which are close to information-theoretic limits. However, these thresholds are approached only for very long block lengths. To overcome this problem, the decoding convergence after a fixed, finite number of iterations is optimized, which yields systems performing very well for short block lengths, too. As an example, optimal system configurations for communication over an additive white Gaussian noise channel are presented.