A communication apparatus comprising: a receiver configured to receive downlink control information including uplink resource block assignment information that indicates resource blocks of which one allocated cluster or a plurality of allocated clusters are comprised, the plurality of allocated clusters being inconsecutive in a frequency domain, and each cluster being comprised of resource blocks that are consecutive in the frequency domain; and a transmitter configured to map uplink data to the resource blocks indicated by the uplink resource block assignment information and to transmit the mapped uplink data; wherein the downlink control information is transmitted, from a base station, with a downlink control information, DCI, format that is used for uplink scheduling; characterized in that the DCI format has a same size according to a maximum value of the number of clusters for each number of codewords, each number of layers, or each number of streams; wherein the maximum value of the number of clusters is reduced as the number of codewords increases; wherein a number of bits used to transmit the uplink resource block assignment information indicating the resource blocks of which the plurality of clusters are comprised is larger than a number of bits used to transmit the uplink resource block assignment information indicating the resource blocks of which the one cluster is comprised; wherein a size of the DCI format depends on the number of codewords, the number of layers, or the number of streams; and wherein the size of the DCI format is unified regardless of the number of clusters actually allocated to the communication apparatus for each number of codewords, each number of layers, or each number of streams; wherein the maximum value of the number of clusters according to each number of codewords is set such that an amount of the uplink resource block assignment information does not exceed a reference number of bits but is closest to the reference number of bits. a receiver configured to receive downlink control information including uplink resource block assignment information that indicates resource blocks of which one allocated cluster or a plurality of allocated clusters are comprised, the plurality of allocated clusters being inconsecutive in a frequency domain, and each cluster being comprised of resource blocks that are consecutive in the frequency domain; and a transmitter configured to map uplink data to the resource blocks indicated by the uplink resource block assignment information and to transmit the mapped uplink data; wherein the downlink control information is transmitted, from a base station, with a downlink control information, DCI, format that is used for uplink scheduling; characterized in that the DCI format has a same size according to a maximum value of the number of clusters for each number of codewords, each number of layers, or each number of streams; wherein the maximum value of the number of clusters is reduced as the number of codewords increases; wherein a number of bits used to transmit the uplink resource block assignment information indicating the resource blocks of which the plurality of clusters are comprised is larger than a number of bits used to transmit the uplink resource block assignment information indicating the resource blocks of which the one cluster is comprised; wherein a size of the DCI format depends on the number of codewords, the number of layers, or the number of streams; and wherein the size of the DCI format is unified regardless of the number of clusters actually allocated to the communication apparatus for each number of codewords, each number of layers, or each number of streams; wherein the maximum value of the number of clusters according to each number of codewords is set such that an amount of the uplink resource block assignment information does not exceed a reference number of bits but is closest to the reference number of bits.