Digital broadcasting system and method of processing data

A broadcast transmitting system comprising:

• a first encoder for performing Reed-Solomon (RS) encoding and Cyclic Redundancy Check (CRC) encoding on mobile service data bytes in order to build an RS frame including the mobile service data bytes, dividing the RS frame into a plurality of RS frame portions and adding K bytes of dummy data to one of the plurality of RS frame portions, wherein K is greater than or equal to 0;
• a byte to bit converter for converting the mobile service data bytes of the plurality of RS frame portions into data bits;
• a second encoder for encoding each of the data bits at a coding rate of 1/H in order to output data symbols, wherein H is greater than or equal to 2;
• a first interleaver for interleaving the data symbols;
• a symbol to byte converter for converting the interleaved data symbols into data bytes;
• a group formatting unit for forming data groups including mobile service data corresponding to the data bytes and inserting a plurality of known data sequences in each of the data groups;
• a deinterleaver for deinterleaving data of the data groups;
• a third encoder for RS encoding mobile service data packets including the deinterleaved data and inserting first RS parity data in the mobile service data packets;
• a second interleaver for interleaving data of the RS-encoded mobile service data packets;
• a fourth encoder for trellis encoding the interleaved data of the RS-encoded mobile service data packets, wherein at least one memory included in the fourth encoder is initialized by initialization data at a start of each of the plurality of known data sequences;
• a backward compatible processor for recalculating second RS parity data based on the initialization data, replacing the first RS parity data with the second RS parity data and outputting the second RS parity data to the fourth encoder;
• and
• a modulator for modulating a broadcast signal including the trellis-encoded data, wherein at least two of the plurality of known data sequences in the broadcast signal differ from each other in length,
• wherein at least two of the plurality of known data sequences in the broadcast signal are spaced 16 segments apart,
• wherein one of the plurality of known data sequences in the broadcast signal includes a first M-symbol sequence and a second M-symbol sequence that have a first pattern,
• wherein the other of the plurality of known data sequences in the broadcast signal include an N-symbol sequence that has a second pattern other than the first pattern, and
• wherein N is greater than M.