A receiving system and a data processing method are disclosed. The receiving system includes: a receiving unit receiving a broadcast signal including a first group comprising mobile service data, known data and signaling data; a signaling decoder decoding the signaling data from the received broadcast signal; a demodulator demodulating the received broadcast signal based upon the known data; an equalizer channel-equalizing the demodulated broadcast signal based upon the known data; a turbo decoder performing turbo decoding on the mobile service data of the channel-equalized broadcast signal by applying a Serial Concatenated Convolutional Coding (SCCC) mode based upon the signaling data; and an error correction unit performing error correction decoding on the turbo-decoded mobile service data based upon the signaling data.