Methods, systems, and devices for wireless communications are described. A transmitter may identify a contention window for a no-energy-detection protocol for determining a channel availability for a data transmission. After the contention window expires, the transmitter may send a request message to a receiver. The receiver may measure a quality of the request message against a request threshold and transmit a response message if the measured quality exceeds the request threshold. The transmitter may then measure a quality of the response message against a response threshold. If the measured quality exceeds the response threshold, the transmitter may initiate a data transmission with the receiver. If the quality falls below the response threshold or the response message is not received, the transmitter may adjust the contention window and reattempt the no-energy-detection protocol. The contention window may also be adjusted based on an acknowledgement message received after the data transmission.