Disclosed are wireless communication system base stations. Each wireless communication base station comprises a communication module and a processor. When the base stations carry out DRS- and nonunicast data-multiplexed transmission, the processors select one channel access type among two channel access types according to whether both of two conditions are satisfied, the two conditions being that the duration of the DRS- and nonunicast data-multiplexed transmission is 1 ms or less, and the duty cycle of DRS transmission is 1/20 or less. Among the two channel access types, the first type is channel access in which random backoff is carried out using a variable-size contention window (CW), the size of the CW being determined according to channel access priority class; and the second type is channel access in which only single time interval-based LBT is carried out.