Erasing gains for concatenated codes

The optimal strategy for erasing symbols in a concatenated coding system, in which the outer code is decoded once, is considered. In general, the strategy involves comparison of a posteriori symbol likelihoods to nonuniform thresholds. The performance of a greedy version of such a rule is evaluated for a number of specific short inner codes, over both memoryless and bursty channels, with hard and soft decisions. It is shown that the gains achievable via erasing can be substantial when hard decision inner decoders are used and when short inner codes are used, but are less so otherwise. It is shown that erasing gains can be very large when applied over channels with memory, with interleaving at the symbol level