An access point to transmit a first message that instructs stations (STAs) to bypass uplink transmissions for a first time interval indicated in the first message. The access point is to transmit one or more first messages at a transmission power sufficient for a first portion of the STAs to decode the one or more first messages and insufficient for a second portion of the STAs to decode the one or more first messages. The transmission power can be determined based on minimum transmit powers associated with the STAs. Subsequent second time intervals can be determined based on uplink transmissions received from the STAs during the first time interval.