Coding theorems for turbo code ensembles

This paper is devoted to a Shannon-theoretic study of turbo codes. We prove that ensembles of parallel and serial turbo codes are "good" in the following sense. For a turbo code ensemble defined by a fixed set of component codes (subject only to mild necessary restrictions), there exists a positive number /spl gamma//sub 0/ such that for any binary-input memoryless channel whose Bhattacharyya noise parameter is less than /spl gamma//sub 0/, the average maximum-likelihood (ML) decoder block error probability approaches zero, at least as fast as n/sup -/spl beta//, where /spl beta/ is the "interleaver gain" exponent defined by Benedetto et al. in 1996.