Signal transmission using plurality of APs in wireless LAN system

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

receiving, by a first serving access point (AP), a trigger frame from a served AP;

transmitting, by the first serving AP, a Null Data Packet (NDP) request frame to a first station STA;

receiving, by the first serving AP, a first NDP frame from the first STA and a second NDP frame from a second STA;

receiving, by the first serving AP, a feedback request frame from the served AP; and

transmitting, by the first serving AP, an NDP feedback frame to the served AP based on the first and second NDP frames.

2. The method of claim 1 , further comprising:

receiving, by the first serving AP, a selection frame from the served AP; and

transmitting, by the first serving AP, first data to the first STA and second data to the second STA.

3. The method of claim 2 , wherein the selection frame includes at least one of information related to an antenna, information related to a stream, information related to a Modulation and Coding Scheme (MCS), and information related to a physical service data unit (PSDU) length.

4. The method of claim 2 , further comprising:

receiving, by the first serving AP, the first data and the second data together with the selection frame from the served AP.

5. The method of claim 1 , wherein the first STA is associated with the first serving AP, and the second STA is associated with a second serving AP.

6. The method of claim 5 , wherein the trigger frame includes information related to addresses of the first and second STAs, information related to a basic service set (BSS) to which the first and second STAs belong, and information related to an address of a serving AP to which the first and second STAs are associated.

7. The method of claim 5 , wherein the NDP request frame includes information related to the first serving AP and the second serving AP that will receive the first and second NDP frames.

8. The method of claim 1 , wherein the NDP feedback frame includes information related to a channel estimation value between the first serving AP and the first STA and information related to a channel estimation value between the first serving AP and the second STA.

9. A first serving AP in a Wireless Local Area Network system, the first serving AP comprising:

a memory;

a transceiver; and

a processor operatively connected to the memory and the transceiver,

wherein the processor is configured to:

receive a trigger frame from a served AP;

transmit a Null Data Packet (NDP) request frame to a first station STA;

receive a first NDP frame from the first STA;

receive a second NDP frame from a second STA;

receive a feedback request frame from the served AP; and

transmit an NDP feedback frame to the served AP based on the first and second NDP frames.

10. The first serving AP of claim 9 , wherein the processor is further configured to:

receive a selection frame from the served AP; and

transmit first data to the first STA and second data to the second STA.

11. The first serving AP of claim 10 , wherein the selection frame includes at least one of information related to an antenna, information related to a stream, information related to a Modulation and Coding Scheme (MCS), and information related to a physical service data unit (PSDU) length.

12. The first serving AP of claim 10 , wherein the processor is further configured to:

receive the first data and the second data together with the selection frame from the served AP.

13. The first serving AP of claim 9 , wherein the first STA is associated with the first serving AP, and the second STA is associated with a second serving AP.

14. The first serving AP of claim 13 , wherein the trigger frame includes information related to addresses of the first and second STAs, information related to a basic service set (BSS) to which the first and second STAs belong, and information related to an address of a serving AP to which the first and second STAs are associated.

15. The first serving AP of claim 13 , wherein the NDP request frame includes information related to the first serving AP and the second serving AP that will receive the first and second NDP frames.

16. The first serving AP of claim 9 , wherein the NDP feedback frame includes information related to a channel estimation value between the first serving AP and the first STA and information related to a channel estimation value between the first serving AP and the second STA.