Techniques are disclosed for determining transmitter antenna weights at a base station (12) having more available transmit antennas (150) than the available number of reference signals. An exemplary method includes transmitting (530) a plurality of reference signals and receiving (540) channel feedback data derived by a mobile terminal (14) from the reference signals. The reference signals are each assigned to a corresponding one of two or more antenna groupings, wherein at least a first one of the antenna groupings comprises two or more transmit antennas (150), and transmitted using at least one transmit antenna (150) from the corresponding antenna grouping. The method further includes determining (550) a first beam-forming vector for the first one of the antenna grouping and mapping (570) the one or more data streams to the transmit antennas (150) according to a final precoding matrix that depends on the channel feedback data and the first beam-forming vector, to obtain a weighted transmit signal for each of the antennas (150).