A method of processing data in a receiving system, the method includes receiving a broadcast signal including a plurality of data groups that include broadcast data and first parity data; demodulating the received broadcast signal; performing first decoding on the broadcast data in a frame based on the first parity data for error correction, wherein the frame is formed based on the plurality of data groups in the demodulated broadcast signal and wherein the plurality of groups have a same size; and de-randomizing the first decoded broadcast data, wherein second decoding on the broadcast data in the frame is selectively performed, wherein the broadcast signal further includes signaling information that contains a transmission parameter to indicate whether second encoding was performed on the broadcast data in a transmitting system, wherein, when the transmission parameter indicates that the second encoding was performed on the broadcast data.