Patent ID: 8462712

Claim:
A mobile station device included in a mobile communication system, the mobile station device comprising: a receiver configured to receive, on a physical downlink control channel (PDCCH) from a base station device, control information including a sub-region for radio resource assignment information; a detector configured to detect, based on a predetermined first region in the control information, an indication to order a random access and to detect, based on a second region in the control information, that does not overlap with the first region, an identification number specifying a random access preamble and information specifying a region on a radio frame available for the random access; and a transmitter configured to transmit, to the base station device, the random access preamble specified by the identification number in the region specified by the information detected, in a case that the indication to order a random access is detected, wherein the first region includes the sub-region.