Method for supporting carrier sensing in wireless access system supporting unlicensed band, and device supporting same

A base station performing carrier sensing in a wireless access system supporting an unlicensed band, the base station comprising:

• a transmitter;
• a receiver;
• and
• a processor,
• wherein the processor is configured to:
• select a backoff counter value for performing a carrier sensing procedure, based on a contention window size;
• decrease the backoff counter value based on a determination that the unlicensed band is an idle state while performing the carrier sensing procedure in the unlicensed band;
• control the transmitter to transmit downlink data based on the backoff counter value being equal to 0;
• obtain a hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback for the downlink data from;
• and
• adjust the contention window size based on the plurality of HARQ-ACK feedback,
• wherein the processor is further configured to:
• initialize the contention window size or decreasing the contention window size when the HARQ-ACK feedback includes an acknowledgement (ACK) signal for the downlink data;
• increase the contention window size when the HARQ-ACK feedback includes a negative acknowledgement (NACK) signal for the downlink data;
• and
• maintain the contention window size and change a modulation and coding scheme (MCS) level when the HARQ-ACK feedback includes neither the ACK signal nor the NACK signal.