The present invention relates to a wireless communication system, and specifically, to a method and a device for the method which comprises the steps of: aggregating a LCell and a UCell in order to communicate with a base station; and transmitting a slotted uplink physical channel via only one slot among a plurality of slots of a subframe #m of the UCell, wherein the transmission of the slotted uplink physical channel includes performing a first CCA procedure X-time prior to a reference time point of the first slot of the subframe #m, and if the first CCA procedure fails, performing a second CCA procedure Y-time (Y>X) prior to a reference time point of the second slot of the subframe #m.