A method performed by a wireless device in a wireless communication system, the method including detecting a first subframe, wherein the first subframe includes a first slot and a second slot, and wherein orthogonal frequency division multiplexing (OFDM) symbols in the first slot are not occupied, detecting a second subframe, wherein the second subframe a next subframe of the first subframe, and wherein all OFDM symbols in the second subframe are occupied and receiving a downlink signal from a network on an unlicensed carrier via at least one of the first subframe and the second subframe.