A method of transmitting data in a wireless local access network, the method comprising: transmitting, by an access point, a downlink management frame to a plurality of recipients, the downlink management frame including information about a group address indicating a station group to which the plurality of recipients belongs; transmitting, by the access point, a data frame to the plurality of recipients, the data frame including the group address and a plurality of Aggregate-Medium Access Control (MAC) Protocol Data Units (A-MPDUs) for the plurality of recipients, wherein each of the plurality of A-MPDUs includes at least one MPDU for a corresponding one of the plurality of recipients, 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.