A method for transmitting payload data from a base station (BS) to a user equipment (UE) via a MIMO channel is provided. Channel estimation is performed first and the channel-estimation result is used for optimizing data transmission. Instead of reporting CQI, RI and PMI to the BS, the UE reports a first channel transfer function characterizing an end-to-end process of obtaining received CSI-RS symbols from originally-sent CSI-RS symbols. Computation burden at the UE is reduced as computation of the CQI, RI and PMI is eliminated. At the BS, an effect caused by the antenna port-to-transceiver unit (AP-to-TXRU) virtualization operation is removed from the first channel transfer function to yield a second channel transfer function. With the second channel transfer function closer to the MIMO channel transfer function than the first one, the “content” of the MIMO channel is better utilized in optimizing data-transmission performance.