Apparatus for transmitting broadcast signals, apparatus for receiving broadcast signals, method for transmitting broadcast signals and method for receiving broadcast signals

An apparatus for transmitting broadcast signals, the apparatus comprising:

• an encoder for encoding service data bits;
• a mapper for mapping the encoded service data bits into symbols;
• a frequency interleaver for frequency-interleaving data of the symbols in a signal frame,
• wherein an interleaving sequence for the signal frame is generated based on a main sequence and a symbol offset, and wherein the interleaving sequence is used for every OFDM (Orthogonal Frequency Division Multiplex) symbol pair,
• wherein the frequency interleaving is reset when a first signal frame is changed to a second signal frame;
• a modulator for modulating the frequency-interleaved data by an OFDM (Orthogonal Frequency Division Multiplex) scheme;
• and
• a transmitter for transmitting the broadcast signals carrying modulated data,
• wherein the OFDM symbol pair comprises two consecutive OFDM symbols.