The present invention relates to a wireless communication system. More particularly, the present invention relates to a method including receiving only one downlink signal in a set of slots; generating an acknowledgement/negative acknowledgement (A/N) codebook for the one or more downlink signals; and transmitting the A/N codebook, wherein if a specific condition is satisfied, the A/N codebook includes only A/N information for the one downlink signal, and an apparatus therefor.