A receiving system and a method of processing broadcast signals in the receiving system are disclosed. The receiving system includes a tuner, a known sequence detector, a carrier recovery unit, and a channel equalizer. The tuner receives a broadcast signal including a data group. Herein, the data group comprises mobile service data, a plurality of known data sequences, and signaling data. One of the plurality of known data sequences comprises a first M symbol sequence and a second M symbol sequence each having a first data pattern. The known sequence detector estimates an initial frequency offset and detects position information of each known data sequence based on the known data sequence having the first data pattern. The carrier recovery unit acquires initial frequency synchronization and performs carrier recovery from the broadcast signal based on the initial frequency offset estimated by the known sequence detector. The channel equalizer performs channel equalization on the broadcast signal based upon the position information of each known data sequence.