Abstract: The present invention relates to a wireless communication system, and specifically to a method and a device therefor, the method comprising: a step for receiving group common DCI on a first cell, wherein the group common DCI includes availability information about one or more RB sets configured for the first cell; a step for, on the basis of all of the RB set(s) being indicated as unavailable, performing first PDCCH monitoring, but skipping channel measurement on the RB set(s) during a certain duration; and a step for, on the basis of at least one of the RB set(s) being indicated as available, performing second PDCCH monitoring and the channel measurement on the at least one available RB set.

Abstract: Provided are a method of performing a channel access procedure by an apparatus in an unlicensed band, and an apparatus using same method. The apparatus determines a contention window size (CWS) and performs a channel access procedure with respect to a first channel on the basis of the determined contention window size. The contention window size may be adjusted on the basis of feedback information relating to a second channel. When a transmission history of the second channel, which is to be reflected in determining the contention window size, does not exist, the contention window size may be determined to be a minimum CWS value in a specific channel access priority class.