A method performed in a wireless local area network (LAN) system is presented. Particularly, a first type access point (AP) #1 can receive a trigger frame from a second type AP. The first type AP #1 can transmit a null data packet (NDP) request frame to a first station (STA). The first type AP #1 can receive a first NDP frame from the first STA, and receive a second NDP frame from a second STA. The first type AP #1 can receive a feedback request frame from the second type AP. The first type AP #1 can transmit an NDP feedback frame to the second type AP on the basis of the first and second NDP frames.