Method for operating sounding in wireless lan system, and apparatus therefor

A method for a station (STA) to transmit a frame for uplink channel quality information in a wireless local area network (WLAN) system, the method comprising:

• receiving, from at least one access point (AP), a null data packet announcement (NDP-A) frame including information on null data packet (NDP) sounding;
• and
• receiving an NDP frame from the AP following the NDP-A frame,
• wherein the NDP frame includes an L-part for a legacy STA and a HE -part for an HE (High Efficiency) STA, and
• wherein the HE-part consists of an HE-signaling A (HE-SIG A) field, an HE-short training field (HE-STF), and an HE-long training field (HE-LTF).

An access point (AP) apparatus operating in a wireless local area network (WLAN) system, the AP apparatus comprising:

• a transceiver transmitting, to at least one station (STA), a null data packet announcement (NDP-A) frame including information on null data packet (NDP) sounding, transmitting an NDP frame to the at least one station following the NDP-A frame, and receiving, from the at least one STA, a feedback frame including downlink channel quality information;
• and
• a processor generating the NDP-A frame and the NDP frame, delivering the generated NDP-A frame and the NDP frame to the transceiver and receiving the feedback frame from the transceiver,
• wherein the processor is configured to generate the NDP frame to include an L-part for a legacy STA and a HE-part for a HE (High Efficiency) STA, and
• wherein the processor generates the HE-part consisting of an HE-signaling A (HE-SIG A) field, an HE-short training field (HE-STF), and an HE-long training field (HE-LTF).

A station (STA) apparatus operating in a wireless local area network (WLAN) system, the station apparatus comprising:

• a transceiver receiving, from at least one access point (AP), a null data packet announcement (NDP-A) frame including information on null data packet (NDP) sounding, and receiving an NDP frame from the AP and
• a processor processing at least one of the NDP-A frame and the NDP frame received from the transceiver,
• wherein the NDP frame includes an L-part for a legacy STA and a HE-part for a HE (High Efficiency) STA, and
• wherein the HE-part consists of an HE-signaling A (HE-SIG A) field, an HE-short training field (HE-STF), and an HE-long training field (HE-LTF).