Reverse concatenated watermark codes

In this paper, we introduce an error correction coding scheme, known as reverse concatenated watermark codes for substitution, insertion and deletion channel. This code is obtained by concatenating a distribution transformer with an LDPC code. If the distribution transformer is implemented using a sparsify code then this code is the reverse concatenation of inner and outer codes of the watermark scheme introduced by Davey and Mackay [1]. We show that reverse concatenation significantly decreases decoder complexity and enables an increase in the overall code rate without a prohibitive increase in complexity, although it incurs a loss in performance.