A mobile station apparatus supporting base station configurations of up to eight antenna ports, the mobile station apparatus comprising: a receiving section configured to receive first reference signals on a plurality of first resource elements, and second reference signals different from the first reference signals on a plurality of second resource elements, the first reference signals and the second reference signals being transmitted from a base station via a plurality of antenna ports; and a estimating section configured to estimate a channel per antenna port using one or both of the first reference signals and the second reference signals, characterized in that a number of the plurality of second resource elements in a resource block is less than a number of the plurality of first resource elements in the resource block, the first reference signals being associated with mobile stations supporting base station configurations of up to four antenna ports, and the second reference signals being associated with mobile stations supporting base station configurations of up to eight antenna ports, the antenna ports, via which the second reference signals are transmitted, are divided in pairs, and, for each pair, the receiving section is configured to receive on one of the plurality of second resource elements: a first one of the second reference signals, which is multiplied by "1" and transmitted via a first one of the pair of antenna ports; and a second one of the second reference signals, which is multiplied by "-1" and transmitted via a second one of the pair of antenna ports, and prior to multiplication, the first one of the second reference signals and the second one of the second reference signals are identical. a receiving section configured to receive first reference signals on a plurality of first resource elements, and second reference signals different from the first reference signals on a plurality of second resource elements, the first reference signals and the second reference signals being transmitted from a base station via a plurality of antenna ports; and a estimating section configured to estimate a channel per antenna port using one or both of the first reference signals and the second reference signals, characterized in that a number of the plurality of second resource elements in a resource block is less than a number of the plurality of first resource elements in the resource block, the first reference signals being associated with mobile stations supporting base station configurations of up to four antenna ports, and the second reference signals being associated with mobile stations supporting base station configurations of up to eight antenna ports, the antenna ports, via which the second reference signals are transmitted, are divided in pairs, and, for each pair, the receiving section is configured to receive on one of the plurality of second resource elements: a first one of the second reference signals, which is multiplied by "1" and transmitted via a first one of the pair of antenna ports; and a second one of the second reference signals, which is multiplied by "-1" and transmitted via a second one of the pair of antenna ports, and prior to multiplication, the first one of the second reference signals and the second one of the second reference signals are identical. a first one of the second reference signals, which is multiplied by "1" and transmitted via a first one of the pair of antenna ports; and a second one of the second reference signals, which is multiplied by "-1" and transmitted via a second one of the pair of antenna ports, and prior to multiplication, the first one of the second reference signals and the second one of the second reference signals are identical.