A base station comprising: a transmitter configured to transmit control information in a Physical Downlink Control Channel, PDCCH, to a terminal apparatus, the control information including a transmission request for an aperiodic sounding reference signal, A-SRS, and a transmission power control command, TPC command, a receiver configured to receive the A-SRS from the terminal apparatus, and control circuitry configured to measure channel state information, CSI, based on the received A-SRS, wherein, the receiver is configured to receive a first A-SRS at a first transmission power value, and, in response to the transmitter transmitting a request for a second A-SRS, receive the second A-SRS at a second transmission power value; the first transmission power value is controlled at the terminal apparatus using a first TPC command transmitted within a first time; and the second transmission power value is controlled at the terminal apparatus using a second TPC command transmitted within a second time which is other than the first time, follows the first time, and has a different time length than the first time, and the relationship between transmission time of the first TPC command and the first A-SRS signal to which the first TPC command is applied is predetermined. a transmitter configured to transmit control information in a Physical Downlink Control Channel, PDCCH, to a terminal apparatus, the control information including a transmission request for an aperiodic sounding reference signal, A-SRS, and a transmission power control command, TPC command, a receiver configured to receive the A-SRS from the terminal apparatus, and control circuitry configured to measure channel state information, CSI, based on the received A-SRS, wherein, the receiver is configured to receive a first A-SRS at a first transmission power value, and, in response to the transmitter transmitting a request for a second A-SRS, receive the second A-SRS at a second transmission power value; the first transmission power value is controlled at the terminal apparatus using a first TPC command transmitted within a first time; and the second transmission power value is controlled at the terminal apparatus using a second TPC command transmitted within a second time which is other than the first time, follows the first time, and has a different time length than the first time, and the relationship between transmission time of the first TPC command and the first A-SRS signal to which the first TPC command is applied is predetermined. wherein, the receiver is configured to receive a first A-SRS at a first transmission power value, and, in response to the transmitter transmitting a request for a second A-SRS, receive the second A-SRS at a second transmission power value; the first transmission power value is controlled at the terminal apparatus using a first TPC command transmitted within a first time; and the second transmission power value is controlled at the terminal apparatus using a second TPC command transmitted within a second time which is other than the first time, follows the first time, and has a different time length than the first time, and the relationship between transmission time of the first TPC command and the first A-SRS signal to which the first TPC command is applied is predetermined.