The present invention relates to a wireless communication system. In more detail, a method for performing HARQ (hybrid automatic repeat request) retransmission by a communication device in a wireless communication system, the method comprising: initially transmitting a data block to a Base Station (BS); attempting PDCCH (physical downlink control channel detection) in a predetermined time interval including a plurality of subframes after transmission of an uplink channel signal; and retransmitting the data block when a PDCCH signal indicating retransmission of the data block is detected in the predetermined time interval, wherein reception of a PHICH (physical hybrid ARQ indicator channel) corresponding to initial transmission of the data block is skipped.