Transmitting/receiving system and broadcast signal processing method

A receiving system, comprising:

• a tuner configured to receive a broadcast signal including first mobile service data and second mobile service data through a slot, wherein the slot is configured of M1 number of packets, wherein, among the M1 number of packets included in the slot, M2 number of packets include the first mobile service data and a plurality of known data sequences, wherein, among remaining M3 number of packets, at least one packet includes the second mobile service data and wherein M1=M2+M3, M2>M3;
• a demodulator configured to demodulate the broadcast signal;
• a block decoder configured to perform turbo-decoding on the first and second mobile service data included in the demodulated broadcast signal;
• and
• a Reed-Solomon (RS) frame decoder configured to build a primary RS frame by collecting the turbo-decoded first mobile service data, to perform error correction decoding on the primary RS frame, to build a secondary RS frame by collecting the second mobile service data and to perform error correction decoding on the secondary RS frame.