Techniques for defining a reference duration and one or more reference transmissions that are utilized for contention window update are provided to address these new features. An apparatus, such as a wireless device, determines a reference duration of a channel occupancy time (COT), the reference duration based at least in part on a subcarrier spacing (SCS) and based on reception of a physical downlink shared channel (PDSCH) transmission. The apparatus updates a contention window (CW) based at least in part on reception of the PDSCH transmission during the reference duration. For example, the apparatus may increase the CW when a negative acknowledgement (NACK) is received for the determined PDSCH in the COT and may assign CW with a predetermined minimum value (CW_min) when a positive acknowledgement (ACK) is received for the determined PDSCH.