Provided are a transmitter and a method for transmitting a data block in a wireless communication system. The method comprises the following steps: deciding the number of bits (s) and encoders (NES) to allocate to one axis of a signal constellation; encoding an information bit based on the s and the NES and generating a coded block; parsing the coded block based on the s and the NES and generating a plurality of frequency sub-blocks; and transmitting the plurality of frequency sub-blocks to a receiver.