A base station apparatus comprising: a first antenna group corresponding to a first reference signal group; a second antenna group corresponding to a second reference signal group; a reference signal multiplexing unit configured to multiplex two or more reference signals of the first reference signal group on each of resource blocks of a downlink signal at a same pattern for a first-type user equipment and a second-type user equipment, and multiplex two or more reference signals of the second reference signal group on a certain resource block allocated to the second-type user equipment among said resource blocks such that the reference signals of the second reference signal group are arranged in same sub-carriers on which the reference signals of the first reference signal group are multiplexed and at different OFDM symbols on which the reference signals of the first reference signal group are not multiplexed; and a transmitting unit configured to transmit the downlink signal using the first antenna group and the second antenna group, the downlink signal including a resource block in which the first reference signal group is multiplexed but the second reference signal group is not multiplexed, and a resource block in which both the first reference signal group and the second reference signal group are multiplexed, wherein the second-type user equipment is capable of communicating using antennas greater than the number of antennas of the first antenna group, and wherein which resource block is allocated as said certain resource block to the second-type user equipment is determined on a subframe-by-subframe basis. a first antenna group corresponding to a first reference signal group; a second antenna group corresponding to a second reference signal group; a reference signal multiplexing unit configured to multiplex two or more reference signals of the first reference signal group on each of resource blocks of a downlink signal at a same pattern for a first-type user equipment and a second-type user equipment, and multiplex two or more reference signals of the second reference signal group on a certain resource block allocated to the second-type user equipment among said resource blocks such that the reference signals of the second reference signal group are arranged in same sub-carriers on which the reference signals of the first reference signal group are multiplexed and at different OFDM symbols on which the reference signals of the first reference signal group are not multiplexed; and a transmitting unit configured to transmit the downlink signal using the first antenna group and the second antenna group, the downlink signal including a resource block in which the first reference signal group is multiplexed but the second reference signal group is not multiplexed, and a resource block in which both the first reference signal group and the second reference signal group are multiplexed, wherein the second-type user equipment is capable of communicating using antennas greater than the number of antennas of the first antenna group, and wherein which resource block is allocated as said certain resource block to the second-type user equipment is determined on a subframe-by-subframe basis.