Space division multiple access for wireless lan, and channel estimation for the same

A method of transmitting data in a wireless local access network, the method comprising:

• transmitting, by an access point (AP), a request-to-send (RTS) frame to a plurality of receiving stations, the RTS frame including recipient information and channel information, the recipient information indicating the plurality of receiving stations, the channel information indicating a plurality of subchannels allocated to the plurality of receiving stations;
• receiving, by the AP, a plurality of clear-to-send (CTS) frames from the plurality of receiving stations as a response to the RTS frame, each CTS frame being received through at least one subchannel allocated to a corresponding one of the plurality of receiving stations;
• and
• transmitting, by the AP, a physical layer protocol data unit (PPDU) to the plurality of receiving stations, the PPDU including address information indicating the plurality of receiving stations and a plurality of Aggregate-Medium Access Control (MAC) Protocol Data Units (A-MPDUs) for the plurality of receiving stations,
• wherein each of the plurality of A-MPDUs includes at least one MPDU for a corresponding one of the plurality of receiving stations, and
• wherein each of the plurality of A-MPDUs further includes zero or more padding bits so that all of the plurality of A-MPDUs have the same transmission time corresponding to a transmission time of a longest A-MPDU among the plurality of A-MPDUs.