According to one embodiment of the present invention, a method by which a wireless communication device including a plurality of antennas transmits and receives a wireless signal in an unlicensed band in a wireless communication system comprises the steps of: performing a clear channel assessment (CCA) by using the plurality of antennas for a predetermined time interval in the unlicensed band; and transmitting the wireless signal through the unlicensed band when it is determined that the unlicensed band is in an idle state in which the unlicensed band is not occupied by other wireless communication devices, wherein the step of performing the CCA can comprise the steps of: acquiring one reference value by using energy sensing indicators (ESIs) measured through the plurality of antennas; and comparing the reference value with a CCA threshold value so as to determine whether the unlicensed band is in an idle state.