A base station configured to communicate over a plurality of carriers. The plurality of carriers comprise at least one backward compatible carrier and at least one non-backward compatible carrier. The base station transmits a control message to a wireless device. The control message comprises an identifier for a carrier and information identifying a carrier type. The carrier type is either a backward compatible type or a non-backward compatible type. The base station configured to transmit a plurality of packets to a wireless device on non-backward compatible carrier(s) and backward compatible carrier(s).