A receiving system and data processing method therein are disclosed, by which mobile service data is received and processed. The present invention includes a demodulator receiving a broadcast signal including mobile service data and main service data, the demodulator converting the received broadcast signal to a baseband signal, the mobile service data configuring a data group, the data group including a plurality of know data sequences, a known data detector detecting a location of at least one of the known data sequence within the data group, the known data detector outputting detected known data location information, an equalizer channel-equalizing the demodulated mobile service data using the detected known data location information, and a signaling decoder reconstructing transmission parameter channel (TPC) data and fast information channel (FIC) data received by being included in a signaling information area allocated between a first known data sequence and a second known data sequence among a plurality of the known data sequences.