Apparatuses, methods, and systems are disclosed for carrier determination. One apparatus includes a processor that determines a first carrier of multiple carriers for a first device to transmit control information. The apparatus also includes a transmitter that transmits, to the first device, a first physical control signal indicating the first carrier, wherein the first physical control signal further indicates an interlace index for transmitting control information. The apparatus includes a receiver that receives control information from the first device on the first carrier.