Method and device for receiving feedback frame in wireless LAN system

A beamformer in a wireless local area network (WLAN) system, the beamformer comprising:

• a memory;
• a transceiver;
• and
• a processor being operatively connected to the memory and the transceiver, wherein the processor is configured to:
• receive a feedback frame for multi input multi output (MIMO) beamforming from a beamformee;
• and
• decode the feedback frame,
• wherein the feedback frame includes information on first feedback tones for a preset frequency band,
• wherein a tone index of the first feedback tones is set based on Ng which is a parameter related to a tone index interval,
• wherein based on the preset frequency band being a 20 MHz band, the tone index of the first feedback tones is set to [−122, −116:8:−4, −2, 2, 4:8:116, 122] when the Ng is 8, and is set to [−122, −116, −108:32:−12, −4, −2, 2, 4, 12:32:108, 116, 122] when the Ng is 32,
• wherein based on the preset frequency band being a 40 MHz band, the tone index of the first feedback tones is set to [−244:8:−4, 4:8:244] when the Ng is 8, and is set to [−244, −236:32:−12, −4, 4, 12:32:236, 244] when the Ng is 32,
• wherein the Ng is determined based on a tone plan for the preset frequency band,
• wherein based on the preset frequency band being an 80 MHz band, the tone plan for the 80 MHz band is composed of first to 36th 26-tone RUs in case of only 26-tone RUs, first to 16th 52-tone RUs in case of only 52-tone RUs, first to 8th 106-tone RUs in case of only 106-tone RUs, first to 4th 242-tone RUs in case of 242-tone RUs, first and second 484-tone RUs in case of 484-tone RUs, or one 996-tone RU, and
• wherein in the first feedback tones, A:B:C indicates tone indices disposed at intervals of B between A having the lowest tone index and C having the highest tone index.

A method in a wireless local area network (WLAN) system, the method comprising:

• configuring, by a beamformee, a feedback frame for multi input multi output (MIMO) beamforming;
• and
• transmitting, by the beamformee, the feedback frame to a beamformer,
• wherein the feedback frame includes information on first feedback tones for a preset frequency band,
• wherein a tone index of the first feedback tones is set based on Ng which is a parameter related to a tone index interval,
• wherein based on the preset frequency band being a 20 MHz band, the tone index of the first feedback tones is set to [−122, −116:8:−4, −2, 2, 4:8:116, 122] when the Ng is 8, and is set to [−122, −116, −108:32:−12, −4, −2, 2, 4, 12:32:108, 116, 122] when the Ng is 32,
• wherein based on the preset frequency band being a 40 MHz band, the tone index of the first feedback tones is set to [−244:8:−4, 4:8:244] when the Ng is 8, and is set to [−244, −236:32:−12, −4, 4, 12:32:236, 244] when the Ng is 32, and
• wherein the Ng is determined based on a tone plan for the preset frequency band,
• wherein based on the preset frequency band being an 80 MHz band, the tone plan for the 80 MHz band is composed of first to 36th 26-tone RUs in case of only 26-tone RUs, first to 16th 52-tone RUs in case of only 52-tone RUs, first to 8th 106-tone RUs in case of only 106-tone RUs, first to 4th 242-tone RUs in case of 242-tone RUs, first and second 484-tone RUs in case of 484-tone RUs, or one 996-tone RU, and
• wherein in the first feedback tones, A:B:C indicates tone indices disposed at intervals of B between A having the lowest tone index and C having the highest tone index.