A digital television (DTV) transmitter and a method of processing data in the DTV transmitter are disclosed. A pre-processor pre-processes the enhanced data by coding the enhanced data for forward error correction (FEC) and expanding the FEC-coded enhanced data. A data formatter generates enhanced data packets including the pre-processed enhanced data and for inserting known data to at least one of the enhanced data packets. A first multiplexer multiplexes the enhanced data packets with main data packets including the main data. An RS encoder RS-codes the multiplexed main and enhanced data packets, the RS encoder adding systematic parity data to each main data packet and adding RS parity place holders to each enhanced data packet. And, a data interleaver interleaves the RS-coded main and enhanced data packets, wherein a known data sequence is included in every Nth enhanced data segment outputted from the data interleaver.