A digital television (DTV) transmitter and a method of processing known data in the DTV transmitter are disclosed. The method of processing known data in a digital television (DTV) transmitter includes generating a known data sequence, trellis-encoding the known data sequence, the trellis-encoded known data sequence having upper, middle, and lower bits, wherein at least one of the upper, middle, and lower bits has an m-sequence property, and mapping the trellis-encoded known data sequence into one of 2-level, 4-level, and 8-level data sequences, wherein the mapped data sequence has substantially an m-sequence property, wherein a data sequence has an m-sequence property when a peak value among auto-correlation values of the data sequence having a length of N is 1 and all the off-peak auto-correlation values are −1/N.