Apparatus and method for channel sounding

1 . An operating method of a first device communicating with a second device in a wireless local area network (WLAN) system, the WLAN system including the first device and the second device, and the method comprising:

estimating channels corresponding to a plurality of subcarriers using a null data packet (NDP) received from the second device to obtain estimated channels;

generating beam steering matrices corresponding to the plurality of subcarriers by performing singular value decomposition on the estimated channels;

generating overridden angle information based on the beam steering matrices, the overridden angle information corresponding to target subcarriers among the plurality of subcarriers; and

transmitting beamforming feedback to the second device, the beamforming feedback including the overridden angle information.

2 . The method of claim 1 , further comprising:

determining the target subcarriers to include all of the plurality of subcarriers.

3 . The method of claim 1 , further comprising:

determining the target subcarriers to include a subset of the plurality of subcarriers.

4 . The method of claim 3 , wherein the subset of the plurality of subcarriers comprises subcarriers sequentially arranged by index between a start subcarrier and an end subcarrier among the plurality of subcarriers, the start subcarrier corresponding to a start index, and the end subcarrier corresponding to an end index.

5 . The method of claim 3 , wherein the generating of the overridden angle information comprises: generating angle information corresponding to subcarriers other than the target subcarriers among the plurality of subcarriers, the beamforming feedback including the overridden angle information.

6 . The method of claim 1 , wherein the plurality of subcarriers match subcarriers indicated in a ‘Partial BW Info’ field of an NDP announcement (NDPA) frame received from the second device.

7 . The method of claim 1 , further comprising:

determining whether each respective subcarrier among the plurality of subcarriers is among the target subcarriers.

8 . The method of claim 7 , wherein

the plurality of subcarriers comprise a first subcarrier; and

the determining comprises:

generating singular values corresponding to a plurality of streams of the first subcarrier,

comparing a maximum value among at least one difference with a threshold to obtain a comparing result, the at least one difference being between the singular values; and

determining whether the first subcarrier is among the target subcarriers based on the comparing result.

9 . The method of claim 7 , wherein

the plurality of subcarriers comprise a first subcarrier; and

the determining comprises:

measuring signal to noise ratios (SNRs) corresponding to a plurality of streams of the first subcarrier,

comparing a maximum value among at least one difference with a threshold to obtain a comparing result, the at least one difference being between the SNRs, and

determining whether the first subcarrier is among the target subcarriers based on the comparing result.

10 . The method of claim 7 , wherein the target subcarriers comprise first and second subcarriers spaced apart from each other based on an index.

11 . The method of claim 1 , wherein

the beam steering matrices comprise first beam steering matrices corresponding to the target subcarriers; and

the generating of the overridden angle information comprises:

generating first angle information corresponding to the target subcarriers based on the first beam steering matrices, and

generating the overridden angle information by replacing values of the first angle information with values corresponding to a unitary matrix.

12 . The method of claim 1 , wherein

the beam steering matrices comprise first beam steering matrices corresponding to the target subcarriers; and

the generating of the overridden angle information comprises:

replacing the first beam steering matrices with unitary matrices, and

generating the overridden angle information from the unitary matrices.

13 . The method of claim 1 , further comprising:

monitoring a communication state with the second device; and

determining whether the communication state satisfies an overriding condition,

wherein the generating of the overridden angle information is performed in response to determining that the communication state satisfies the overriding condition.

14 . The method of claim 13 , wherein the overriding condition comprises: a condition in which a number of negative acknowledgments (NACKs) transmitted to the second device during a period of time exceeds a threshold number.

15 . The method of claim 13 , wherein the overriding condition comprises: a condition in which data throughput due to beamforming between the first device and the second device is below a threshold.

16 . The method of claim 1 , wherein the first device communicates with the second device in the WLAN system based on an extremely high throughput (EHT) protocol standard.

17 . A first device communicating with a second device in a wireless local area network (WLAN) system, the first device comprising:

processing circuitry configured to:

estimate channels corresponding to a plurality of subcarriers using a null data packet (NDP) received from the second device to obtain estimated channels, and

generate overridden angle information based on beam steering matrices and unitary matrices, the overridden angle information corresponding to target subcarriers among the plurality of subcarriers, the beam steering matrices and the unitary matrices corresponding to the plurality of subcarriers, and the beam steering matrices and the unitary matrices being generated based on the estimated channels.

18 . The first device of claim 17 , wherein the processing circuitry is configured to: generate the overridden angle information in response to determining that a communication state with the second device meets an overriding condition.

19 . The first device of claim 17 , wherein the processing circuitry is configured to; determine that the target subcarriers include some or all of the plurality of subcarriers.

20 . The first device of claim 17 , wherein the processing circuitry is configured to; transmit beamforming feedback to the second device, the beamforming feedback including the overridden angle information.