Method and apparatus for channel estimation in wireless communication system

1. A method for estimating a channel transmitted through a 2-dimensional (2D) array antenna in a wireless communication system, the method being performed by a user equipment (UE) and comprising:

calculating channel estimation values for each of horizontal and vertical direction antenna arrays of the 2D array antenna in a channel state information-reference signal (CSI-RS) resource using a discrete Fourier transform (DFT) based channel estimation scheme, wherein the channel estimation values are expressed as one or more non-zero channel taps due to multipath fading;

filtering channel taps having a delay value less than a maximum delay value from the channel estimation values for each of the horizontal and vertical direction antenna arrays;

obtaining, at each reference point on time axis, a power sum of the filtered channel taps for all antenna arrays of the 2D array antenna;

determining L significant power sums from among power sums obtained for all reference points, where L is an integer more than one;

deriving channel vectors for each of the horizontal direction antenna arrays and channel vectors for each of the vertical direction antenna arrays for each channel tap corresponding to respective one of the L significant power sums using the L significant power sums;

calculating channel vectors of the 2D array antenna by operating Kronecker product of the channel vectors for each of the horizontal direction antenna arrays and the channel vectors for each of the vertical direction antenna arrays for each channel tap corresponding to respective one of the L significant power sums; and

transmitting CSI feedback based on the channel estimation values.

2. The method according to claim 1 , further comprising receiving a CSI-RS configuration for each of the horizontal and vertical direction antenna arrays of the 2D array antenna.

3. The method according to claim 1 , further comprising receiving a CSI-RS configuration for fallback to be used when the channel estimation is not available.

4. The method according to claim 3 , further comprising reporting wideband CSI feedback for a fixed rank using the CSI-RS configuration for fallback when the channel estimation is not available.

5. The method according to claim 1 , wherein the maximum delay value corresponds to a largest value among delay values of channels for all horizontal and vertical direction antenna arrays of the 2D array antenna.

6. The method according to claim 1 , further comprising reporting a precoding matrix indicator (PMI) for each of the L significant power sums.

7. The method according to claim 6 , further comprising reporting relative sizes and phase differences of the PMIs for the L significant power sums.

8. A user equipment (UE) for estimating a channel transmitted through a 2-dimensional (2D) array antenna in a wireless communication system, the UE comprising:

a radio frequency (RF) unit; and

a processor configured to control the RF unit,

wherein the processor is further configured to:

calculate channel estimation values for each of horizontal and vertical direction antenna arrays of the 2D array antenna in a channel state information-reference signal (CSI-RS) resource using a discrete Fourier transform (DFT) based channel estimation scheme, wherein the channel estimation values are expressed as one or more non-zero channel taps due to multipath fading;

filter channel taps having a delay value less than a maximum delay value from the channel estimation values for each of the horizontal and vertical direction antenna arrays;

obtain, at each reference point on time axis, a power sum of the filtered channel taps for all antenna arrays;

determine L significant power sums from among power sums obtained for all reference points, where L is an integer more than one;

derive channel vectors for each of the horizontal direction antenna arrays and channel vectors for each of the vertical direction antenna arrays for each channel tap corresponding to respective one of the L significant power sums using the L significant power sums;

calculate channel vectors of the 2D array antenna by operating Kronecker product of the channel vectors for each of the horizontal direction antenna arrays and the channel vectors for each of the vertical direction antenna arrays for each channel tap corresponding to respective one of the L significant power sums; and

transmit CS feedback based on the channel estimation values.