Method of feedback for beamforming in a wireless communication system and apparatus therefor

1. A method of transmitting channel state information (CSI) for hybrid beamforming from a user equipment (UE) in a wireless communication system, the method comprising:

measuring a gain of a directional analog beam formed with reference to a first direction and a gain of an omni-directional beam formed equivalently in all directions; and

transmitting the CSI including a gain difference between the directional analog beam and the omni-directional beam to a base station,

wherein a direction of a digital beamforming in the hybrid beamforming is determined in accordance with a UE direction with respect to the base station, and the UE direction is estimated without using a precoding matrix by utilizing the gain difference between the directional analog beam and the omni-directional beam,

wherein the precoding matrix for the digital beamforming is determined from the determined direction of the digital beamforming, and

wherein a direction of an analog beamforming in the hybrid beamforming is determined in accordance with the first direction.

2. The method of claim 1 , wherein the directional analog beam indicates an angle range where a hybrid beam is formable.

3. The method of claim 1 ,

wherein the directional analog beam is formed using prescribed radio frequency (RF) chains selected from a plurality of RF chains performing the analog beamforming, and

wherein the prescribed RF chains are selected based on a plurality of antenna patterns forming directional analog beams equivalent to each other.

4. The method of claim 1 , wherein the CSI further comprises an indicator indicating whether the user equipment is located in a clockwise direction or a counterclockwise direction from the first direction.

5. The method of claim 1 ,

wherein the directional analog beam is rotated by a prescribed unit angle, and

wherein the CSI further comprises information on a direction having a maximum gain of the directional analog beam and a direction having a second highest gain of the directional analog beam according to the rotation of the directional analog beam.

6. A method of receiving channel state information (CSI) for hybrid beamforming by a base station in a wireless communication system, the method comprising:

transmitting a first signal through a directional analog beam formed with reference to a first direction;

transmitting a second signal through an omni-directional beam formed equivalently in all directions; and

receiving the CSI including a gain difference between the directional analog beam and the omni-directional beam from a user equipment (UE),

wherein a direction of digital beamforming in the hybrid beamforming is determined in accordance with a UE direction with respect to the base station, and the UE direction is estimated without using a precoding matrix by utilizing the gain difference between the directional analog beam and the omni-directional beam,

wherein the precoding matrix for the digital beamforming is determined from the determined direction of the digital beamforming, and

wherein a direction of an analog beamforming in the hybrid beamforming is determined in accordance with the first direction.

7. The method of claim 6 , wherein the directional analog beam indicates an angle range where a hybrid beam is formable.

8. The method of claim 6 ,

wherein the directional analog beam is formed using prescribed radio frequency (RF) chains selected from a plurality of RF chains performing the analog beamforming, and

wherein the prescribed RF chains are selected based on a plurality of antenna patterns forming directional analog beams equivalent to each other.

9. The method of claim 6 , wherein the CSI further comprises an indicator indicating whether the user equipment is located in a clockwise direction or a counterclockwise direction from the first direction.

10. The method of claim 6 ,

wherein the directional analog beam is rotated by a prescribed unit angle, and

wherein the CSI further comprises information on a direction having a maximum gain of the directional analog beam and a direction having a second highest gain of the directional analog beam according to the rotation of the directional analog beam.

11. The method of claim 6 , further comprising:

determining a direction where the user equipment is located from the base station is based on the CSI.

12. A user equipment (UE) of transmitting channel state information (CSI) for hybrid beamforming in a wireless communication system, the user equipment comprising:

a processor for measuring a gain of a directional analog beam formed with reference to a first direction and a gain of an omni-directional beam formed equivalently in all directions; and

a transmitter for transmitting the CSI including a gain difference between the directional analog beam and the omni-directional beam to a base station,

wherein a direction of digital beamforming in the hybrid beamforming is determined in accordance with a UE direction with respect to the base station, and the UE direction is estimated without using a precoding matrix by utilizing the gain difference between the directional analog beam and the omni-directional beam,

wherein the precoding matrix for the digital beamforming is determined from the determined direction of the digital beamforming, and

wherein a direction of an analog beamforming in the hybrid beamforming is determined in accordance with the first direction.

13. A base station of receiving channel state information (CSI) for hybrid beamforming in a wireless communication system, the base station comprising:

a transmitter for transmitting a first signal through a directional analog beam formed with reference to a first direction, and for transmitting a second signal through an omni-directional beam formed equivalently in all directions;

a receiver for receiving the CSI including a gain difference between the directional analog beam and the omni-directional beam from a user equipment (UE); and

a processor for determining a direction of digital beamforming in the hybrid beamforming in accordance with a UE direction with respect to the base station, for estimating the UE direction without using a precoding matrix by utilizing the gain difference between the directional analog beam and the omni-directional beam, for determining the precoding matrix for the digital beamforming from the determined direction of the digital beamforming, and for determining a direction of an analog beamforming in the hybrid beamforming in accordance with the first direction.