Channel equalizer and method of processing broadcast signal in DTV receiving system

A broadcast transmitting system comprising:

• a first randomizer configured to randomize enhanced data;
• a Reed-Solomon (RS) frame encoder configured to RS encode and Cyclic Redundancy Check (CRC) encode the randomized enhanced data to build an RS frame;
• a block processor configured to encode the enhanced data in the built RS frame at a coding rate of at least ½ or ¼ and to first interleave the encoded enhanced data;
• a deinterleaver configured to deinterleave the first interleaved enhanced data;
• a first multiplexer configured to first multiplex enhanced data packets including the deinterleaved enhanced data with main data packets including main data;
• a second randomizer configured to randomize the main data in the multiplexed enhanced and main data packets;
• an interleaver configured to second interleave the enhanced data in the multiplexed enhanced and main data packets and the randomized main data to output a data group having the interleaved enhanced data and the interleaved main data;
• a trellis encoding unit configured to trellis encode data in the data group;
• and
• a second multiplexer configured to second multiplex the trellis-encoded data with field synchronization data and segment synchronization data,
• wherein the data group includes first segments, second segments and third segments, the second segments being positioned between the first and third segments, the first segments having enhanced data and main data, the second segments having enhanced data and a plurality of known data sequences, and the third segments having enhanced data and main data, and
• wherein the enhanced data in the first, second and third segments are encoded by a non-systematic RS encoding scheme, the main data in the first and third segments are encoded by a systematic RS encoding scheme, and at least two of the plurality of known data sequences have different patterns.