Mobile communication system, base station apparatus, mobile station apparatus, and communication method

A mobile station apparatus which is configured to communicate with a base station apparatus, the mobile station apparatus comprising:

• a transceiver configured to receive on a plurality of downlink component carriers, wherein
• the transceiver is configured to receive, from the base station apparatus, a radio resource control message including first information, the first information being used to indicate whether a carrier indicator field is present or not in second information, and
• the transceiver is configured to receive on a physical downlink control channel, from the base station apparatus, the second information including information for requesting a transmission of channel state information, the second information being used for scheduling of a physical uplink shared channel in an uplink component carrier;
• and
• the transceiver is configured to transmit on the physical uplink shared channel in the uplink component carrier, channel state information of a first downlink component carrier of the plurality of downlink component carriers, wherein
• the transmission of the channel state information on the physical uplink shared channel in the uplink component carrier is scheduled by using the second information that is received on the physical downlink control channel in the first downlink component carrier in a case that the carrier indicator field is not present in the second information, wherein
• for the second information that is mapped onto a first search space different from a second search space given by C-RNTI (Cell-Radio Network Temporal Identifier), a size of the information for requesting a transmission of channel state information is 1 bit.