A base station apparatus comprising: a plurality of antenna ports; and a transmitter (306, 310, 313, 317, 320, 324, 327, 331) configured to transmit, via the plurality of antenna ports, 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, 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 the transmitter is configured to transmit on one of the plurality of second resource elements and via each of the pairs: a first one of the second reference signals, which is multiplied by "1", via a first one of the pair of antenna ports; and a second one of the second reference signals, which is multiplied by "-1", 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 plurality of antenna ports; and a transmitter (306, 310, 313, 317, 320, 324, 327, 331) configured to transmit, via the plurality of antenna ports, 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, 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 the transmitter is configured to transmit on one of the plurality of second resource elements and via each of the pairs: a first one of the second reference signals, which is multiplied by "1", via a first one of the pair of antenna ports; and a second one of the second reference signals, which is multiplied by "-1", 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", via a first one of the pair of antenna ports; and a second one of the second reference signals, which is multiplied by "-1", 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.