A wireless device receives a control message configuring cell groups comprising a primary cell group and a secondary cell group. The wireless device receives a control command causing the wireless device to transmit a random access preamble on random access resources of a secondary cell in the secondary cell group. The wireless device transmits the random access preamble on the random access resources to the base station. Transmission timing of the random access preamble is determined, at least in part, employing uplink subframe transmission timing of the primary cell or a stored timing advance value.