Design of serially concatenated systems for long or short block lengths

We study the convergence behavior of iterative decoding of various serially concatenated systems such as a concatenated code, coded transmission over a channel introducing inter-symbol interference, bit-interleaved coded modulation, trellis coded modulation, a.s.o. We use EXIT charts to construct simple irregular codes, which can significantly improve the convergence behavior of iterative decoding. An efficient optimization algorithm is presented yielding system which approach information theoretic limits very closely. However, these systems exhibit a satisfactory performance only for very long block lengths. To overcome this problem, we also show how to optimize a concatenated system such that the decoding performance is optimal after a certain fixed number of iterations. It turns out that these systems perform very well for short block lengths, too. As an example, optimal system configurations for data transmission over an AWGN channel are presented.