Abstract: Apparatus for decoding digital signals, such as digital television signals, which have been transmitted by concatenated coded modulation using partitioning levels of a constellation of points representing different code values. The apparatus includes successive decoding stages which respectively operate on the successive partitioning levels of the constellation. Each decoding stage includes a detector for detecting received points in the relevant partitioning level. At least one stage includes an internal decoder for generating estimated bit sequences in accordance with an inner code and erasures of bit sequences for which the estimation is found to be ambiguous, an external decoder decoding in accordance with an outer code and correcting bit sequence erasures, and an encoder for encoding the output of the external decoder and supplying the resulting re-encoded bit sequences to the succeeding stages of the decoding apparatus to validate detection thereby of points in their partitioning levels.