Patent ID: 8542770

Claim:
A base station apparatus comprising: a plurality of antenna ports; and a transmitter 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, a number of which 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, wherein the transmitter is configured to transmit on one of the plurality of second resource elements and via a pair of the plurality of antenna ports: a first reference signal of the second reference signals, which is multiplied by “1”, via a first one of the pair of antenna ports; and a second reference signal of the second reference signals, which is multiplied by “−1”, via a second one of the pair of antenna ports.