A user equipment (UE) may transmit a UE-generated uplink message to a base station to request resources for an uplink transmission. The UE may be configured to send the message (e.g., a scheduling request (SR)) using different transmission modes. For example, the UE may transmit the SR using a scheduled mode where the UE conveys the SR along with another uplink message (e.g., a control message). In some examples, the UE may transmit the SR using an autonomous mode where the UE transmits the SR in resources reserved for SR transmissions. The UE may determine which transmission mode to use based on certain characteristics of the SR or the data associated with the SR.