Methods, systems, and devices for wireless communication are described for a channel reservation signal that may be transmitted upon gaining contention-based access to a channel in a shared radio frequency spectrum. The channel reservation signal may include a channel reservation preamble and a channel reservation payload. The channel reservation payload may be formatted with other control channel information transmitted by the transmitter, such as downlink control information (DCI), and aligned with a transmission boundary of the other control channel information. When deployed on a shared medium, a downlink control channel may carry an extra trigger field that may schedule a receiving UE to transmit its own channel reservation signal within an uplink transmission burst.