Non-binary decoding of structured LDPC codes: Density evolution

A class of serial turbo codes admitting low-density parity-check (LDPC) representation is considered. Their parity matrix has a random and a structured part. Thanks to their turbo structure, these codes are linear-time encodable, while they can be decoded as LDPC codes. Previous works enlightened the role of the inner encoder in the error floor region and suggested the use of a non-binary iterative decoding algorithm. In this paper, a density-evolution analysis is developed giving insight into the performance of these codes in the waterfall region. The inner encoder is optimized in order to guarantee the best tradeoff between error floor and threshold.