User apparatus, base station, and communication method

There is provided a user apparatus of a radio communication system provided with a base station and the user apparatus, the user apparatus including a determination unit configured to determine a size of a soft buffer to be secured within the user apparatus based on a total soft buffer size corresponding to a UE category of the user apparatus, a modulation scheme configured for a downlink by the base station, and a MIMO-layer number configured for the downlink by the base station; and a receiving unit configured to store data received from the base station in the soft buffer with the size determined by the determination unit, wherein the UE category includes 2 layers, 4 layers, and 8 layers as maximum MIMO-layer numbers to be supported, and the UE category includes 64 QAM and 256 QAM as the modulation schemes to be supported.