Methods, systems, and devices are described for wireless communication. In one method, a first transmission may be transmitted on a contention-based channel, and a scheduling request for the first transmission may be transmitted on a scheduled channel. The scheduling request may be transmitted prior to determining that an acknowledgment (ACK) message has been received for the first transmission. In another method, a scheduling request for a first transmission may be received on a scheduled channel from a wireless device. Upon decoding a reception of the first transmission on a contention-based channel, transmission of a transmission grant to the wireless device may be withheld. Upon failing to decode the reception of the first transmission on the contention-based channel, the transmission grant may be transmitted to the wireless device.