Digital broadcasting system and method of processing data

A receiving system, comprising:

• a tuner configured to receive a broadcast signal comprising a data group that includes mobile service data, main service data and known data sequences, wherein the data group comprises regions A, B and C, wherein the region A is central, the region B is concentric about the region A, and the region C is concentric about the regions A and B, wherein the region A includes mobile service data encoded at a 1/X coding rate and the known data sequences, and wherein the regions B and C include mobile service data encoded at a 1/Y coding rate, but no known data sequences, wherein X≠Y, wherein at least two of the regions A, B or C include the main service data, and wherein at least two of the known data sequences differ from each other in length;
• an equalizer configured to compensate for channel distortion of the received broadcast signal using channel impulse responses (CIRs) estimated based on at least one of the known data sequences;
• a block decoder configured to:
• perform trellis decoding and additional decoding by a block unit on the mobile service data in the channel distortion compensated broadcast signal;
• and
• perform trellis decoding on the main service data in the channel compensated broadcast signal;
• and
• an error correction unit configured to estimate a number of errors by performing Cyclic Redundancy Check (CRC) decoding on each row of a Reed Solomon (RS) frame including the trellis and additional decoded mobile service data by the block unit, and generate a reliability map representing reliability information of each mobile service data byte within the RS frame, wherein the error correction unit performs general RS decoding or RS erasure decoding on each column of the RS frame based upon the reliability map and the number of errors.