Channel sounding method in wireless LAN system and device for supporting same

1. A method for channel sounding in a wireless local area network (WLAN) system performed by an access point (AP), the method comprising:

broadcasting a beacon comprising information on a sub-channel selective transmission (SST) sounding restricted access window (RAW) for channel sounding;

transmitting a plurality of null data packet (NDP) frames for a plurality of channels in the SST sounding RAW for the channel sounding to a station (STA); and

receiving, from the STA, a report frame including information on at least one channel selected by the STA based on the NDP frames,

wherein the SST sounding RAW is allocated to the STA only for the channel sounding,

wherein the AP controls the data transmission by the STA to be prohibited over the SST sounding RAW duration for the channel sounding,

wherein the NDP frames for the plurality of channels are used in sub-channel selective transmission (SST) in the SST sounding RAW duration for the channel sounding, and

wherein each of the NDP frames indicates channel allocated to each of the NDP frames.

2. The method of claim 1 , wherein the AP controls transmission of the channel information to the AP to be allowed, and other transmission to be prohibited, subsequent to the transmission of the NDP frames in the SST sounding RAW duration for the channel sounding.

3. The method of claim 1 , wherein the beacon comprises at least one of:

a bit value indicating whether the channel sounding is performed through the SST sounding RAW, a bit value to control the transmission by the STA in the SST sounding RAW duration, and a bit value indicating a communication type to be performed by the AP.

4. The method of claim 1 , wherein the transmitting comprises:

transmitting the NDP frames for a plurality of sectors set by the AP in the SST sounding RAW duration for the channel sounding.

5. The method of claim 1 , wherein the transmitting comprises:

transmitting the NDP frames successively at predetermined time intervals.

6. The method of claim 1 , wherein channel information is estimated based on the NDP frames.

7. The method of claim 6 , wherein the receiving comprises:

receiving the report frame through an additional RAW for a feedback report,

wherein the additional RAW for the feedback report is allocated subsequent to the SST sounding RAW for the channel sounding.

8. The method of claim 1 , wherein the transmitting comprises:

transmitting the NDP frames at predetermined time intervals of a short inter-frame space (SIFS) or a point inter-frame space (PIFS).

9. The method of claim 1 , wherein the STA wakes up at a beginning of the SST sounding RAW for the channel sounding, and remains awake until the SST sounding RAW for the channel sounding terminates or the transmission of the NDP frames ends.

10. A method for channel sounding in a wireless local area network (WLAN) system performed by a station (STA), the method comprising:

receiving, from an access point (AP), a beacon comprising information on a sub-channel selective transmission (SST) sounding restricted access window (RAW) for channel sounding;

receiving, from the AP, a plurality of null data packet (NDP) frame for a plurality of channels in the SST sounding RAW for the channel sounding;

estimating channel information based on the NDP frames received from the AP;

selecting at least one channel based on the estimated channel information; and

transmitting a report frame including information on the at least one channel to the AP,

wherein the NDP frames are transmitted to the STA in the SST sounding RAW,

wherein the SST sounding RAW is allocated to the STA only for the channel sounding,

wherein the AP controls the data transmission by the STA to be prohibited over the SST sounding RAW duration for the channel sounding,

wherein the NDP frames for the plurality of channels are used in sub-channel selective transmission (SST) in the SST sounding RAW duration for the channel sounding, and

wherein each of the NDP frames indicates channel allocated to each of the NDP frames.

11. The method of claim 10 , wherein the STA is prohibited from transmitting data over a duration of the SST sounding RAW for the channel sounding.

12. The method of claim 10 , wherein the STA is allowed to transmit the channel information to the AP, and prohibited from performing other transmissions, subsequent to the transmission of the NDP frames over the SST sounding RAW duration for the channel sounding.

13. The method of claim 10 , wherein the estimating comprises:

identifying a communication type to be performed by the AP based on the received beacon;

receiving the NDP frames from the AP in the SST sounding RAW when the STA supports the communication type; and

estimating channel information based on the received NDP frames and the identified communication type.

14. The method of claim 10 , wherein the estimating comprises:

searching for a frequency channel that satisfies a predetermined reference from among frequency channels used in communication with the AP, and

determining information on the found frequency channel to be channel information.

15. The method of claim 10 , wherein the estimating comprises:

searching for a sector to which the STA belongs from among a plurality of sectors set by the AP, and

determining identification information on the found sector to be channel information.

16. The method of claim 10 , wherein when the report frame is transmitted to the AP, transmission by other STAs aside from the STA that transmits the channel information is prohibited.

17. The method of claim 10 , wherein the estimating comprises:

determining a frequency channel that satisfies a predetermined reference from among a plurality of frequency channels based on the NDP frame, and

wherein information included in the report frame includes the determined frequency channel.

18. A wireless apparatus comprising:

a transceiver to transmit and receive a frame; and

a processor functionally associated with the transceiver,

wherein the processor is configured to:

control the transceiver to receive a beacon comprising information on a sub-channel selective transmission (SST) sounding restricted access window (RAW) for channel sounding from an access point (AP),

control the transceiver to receive a plurality of null data packet (NDP) frames for a plurality of channels in the SST sounding RAW for the channel sounding from the AP,

estimate channel information based on the NDP frames received from the AP,

select at least one channel based on the estimated channel information, and

transmit a report frame including information on the at least one channel to the AP,

wherein the NDP frames are transmitted to a station (STA) in the SST sounding RAW,

wherein the SST sounding RAW is allocated to the STA only for the channel sounding, and

wherein the AP controls the data transmission by the STA to be prohibited over the SST sounding RAW duration for the channel sounding,

wherein the NDP frames for the plurality of channels are used in sub-channel selective transmission (SST) in the SST sounding RAW duration for the channel sounding, and

wherein each of the NDP frames indicates channel allocated to each of the NDP frames.