Concatenated multilevel coding

The authors study different strategies for decoding the concatenated inner code, applied in the case of multilevel coding with a multistage decoding procedure. The first strategy recapitulates the classical method of decoding the concatenated code. The second strategy is based on an erasing technique using hard detection. Maximum likelihood (ML) detection is applied in a third strategy. A fourth strategy is the combination of the second and the third strategies using an ML decoding and the erasing technique. For each decoding strategy, the overall performance of the system is derived analytically and the criterion of erasing is defined. The analytical results show that significant coding gain can be achieved by using the erasing technique with an ML Viterbi decoder