Methods, systems, and devices for wireless communications are described. A contending wireless device may transmit a reservation request signal on the channel during a gap period associated with the channel. The contending wireless device may monitor for a reservation challenge signal resource associated with the gap period for a reservation challenge signal. A challenging wireless device may receive the reservation request signal and determine an interference risk based at least in part on the reservation request signal. The challenging wireless device may transmit a reservation challenge signal over a reservation challenge signal resource associated with the gap period based at least in part on the determination. The contending wireless device may selectively perform a transmission on the channel based at least in part on a result of the monitoring.