Serial Concatenation of Interleaved Codes: Performance Analysis, Design, and Iterative Decoding

A serially concatenated code with an interleaver consists of the cascade of an outer code, an interleaver permuting the outer codewords’ bits, and an inner code whose input words are the permuted outer codewords. The construction can be generalized to h cascaded codes separated by h − 1 interleavers. We obtain upper bounds to the average maximum-likelihood bit-error probability of serially concatenated block and convolutional coding schemes. Then, we derive some design guidelines for the outer and inner codes that maximize the interleaver gain and the asymptotic slope of the error probability curves. Finally, we propose a new, lowcomplexity iterative decoding algorithm that yields performance close to maximumlikelihood decoding. Throughout the article, extensive comparisons with parallel concatenated convolutional codes, known as “turbo codes,” are performed, showing that the new schemes offer superior performance.