COMMUNICATION SYSTEM, MOBILE STATION DEVICE, BASE STATION DEVICE, RANDOM ACCESS PROCESSING METHOD, AND INTEGRATED CIRCUIT

摘要

A base station device uses a downlink control channel and instructs a mobile station device to perform a random access procedure. The mobile station device switches, according to whether or not random access parameters are included in parameters of a secondary cell that has been allocated to the mobile station device, between a first random access procedure in which information in a carrier indicator field included in the downlink control channel is not used for selection of a cell in which a random access procedure is performed, and a second random access procedure in which information in the carrier indicator field included in the downlink control channel is used for selection of a cell in which a random access procedure is performed.