Method for transmitting plurality of beamformed reference signals for open-loop MIMO transmission in wireless communication system and apparatus therefor

A User Equipment (UE) in a wireless communication system, the UE comprising:

• a wireless transceiver;
• and
• a processor connected to the wireless transceiver,
• wherein the processor is configured to:
• receive, from a base station, N reference signals including a first reference signal and a second reference signal, N being equal to or greater than 2, the N reference signals either (a) being beamformed in horizontal transmission directions and not in vertical transmission directions or (b) being beamformed in vertical transmission directions and not in horizontal transmission directions, the N reference signals being cyclically beamformed in different horizontal transmission directions or in different vertical transmission directions, and the N reference signals being cycled on a first resource unit (RU) basis based on that a reference signal having an index of R is mapped to an RU having an index of r, wherein R=(r modulo N);
• and
• report a single set of channel state information to the base station at least based on both the first reference signal and the second reference signal, and
• wherein the single set of channel state information includes both a first precoder set related to the first reference signal and a second precoder set related to the second reference signal,
• wherein the single set of channel state information includes a common rank indicator and a common channel quality indicator calculated on an assumption that both the first precoder set and the second precoder set are applied, and
• wherein reception directions of the N reference signals are cycled on a second RU basis, and one of the first RU or the second RU is a multiple of the other.