A multi-carrier transmitter apparatus is disclosed. The apparatus includes an outer encoder, a shell mapper and an inner encoder. The outer encoder is configured to receive a signal, perform error correction using an outer code on the received signal and generate an outer encoder signal. The shell mapper is configured to perform constellation shaping on a subset of bits from the outer encoder signal and generate one or more constellation shaping bits. The inner encoder is configured to perform inner error correction/encoding using an inner code on a second subset of bits from the outer encoder signal and generate an inner correction signal.