A method for performing clear channel assessment, CCA, by a station, STA, in an IEEE 802.11 based wireless LAN system, the method comprising: receiving, by a physical layer, PHY, of the STA, a PHYCONFIG.request primitive including a parameter indicating a CCA level type from a higher layer; and determining (S2920, S2930) whether a medium is busy based on whether a signal equal to or greater than a CCA threshold is sensed, when the STA intends to transmit a Physical layer Protocol Data Unit, PPDU, wherein the CCA threshold is determined based on one of a plurality of CCA threshold sets each having a plurality of CCA thresholds, and the CCA level type indicating the one of the plurality of CCA threshold sets, wherein when the parameter is set to a first CCA level type, a first CCA threshold of a first CCA threshold set is determined to be the CCA threshold, wherein when the parameter is set to a second CCA level type, a second CCA threshold of a second CCA threshold set is determined to be the CCA threshold, wherein the first CCA threshold set supports a smaller channel width than the second CCA threshold set, wherein the second CCA threshold of the second CCA threshold set for the second CCA level type is higher than the first CCA threshold of the first CCA threshold set for the first CCA level type, wherein, in a first case, the PPDU uses a first channel width and the higher layer configures the parameter of the PHY-CONFIG.request primitive to the first CCA level type, wherein, in a second case, the PPDU uses a second channel width, and the higher layer configures the parameter of the PHY-CONFIG.request primitive to the second CCA level type, and wherein the second channel width is greater than the first channel width. receiving, by a physical layer, PHY, of the STA, a PHYCONFIG.request primitive including a parameter indicating a CCA level type from a higher layer; and determining (S2920, S2930) whether a medium is busy based on whether a signal equal to or greater than a CCA threshold is sensed, when the STA intends to transmit a Physical layer Protocol Data Unit, PPDU, wherein the CCA threshold is determined based on one of a plurality of CCA threshold sets each having a plurality of CCA thresholds, and the CCA level type indicating the one of the plurality of CCA threshold sets, wherein when the parameter is set to a first CCA level type, a first CCA threshold of a first CCA threshold set is determined to be the CCA threshold, wherein when the parameter is set to a second CCA level type, a second CCA threshold of a second CCA threshold set is determined to be the CCA threshold, wherein the first CCA threshold set supports a smaller channel width than the second CCA threshold set, wherein the second CCA threshold of the second CCA threshold set for the second CCA level type is higher than the first CCA threshold of the first CCA threshold set for the first CCA level type, wherein, in a first case, the PPDU uses a first channel width and the higher layer configures the parameter of the PHY-CONFIG.request primitive to the first CCA level type, wherein, in a second case, the PPDU uses a second channel width, and the higher layer configures the parameter of the PHY-CONFIG.request primitive to the second CCA level type, and wherein the second channel width is greater than the first channel width.