Patent ID: 9564999
Date: 2017-02-07
CPC Classifications: H04B,H04L,H04W

Claim:
1. A method of transmitting data for multiple input multiple output (MIMO) in a wireless local access network, the method comprising: broadcasting, by an access point, a channel request frame to request a channel feedback for a plurality of recipients over a bandwidth in which a downlink channel estimation is to be performed, the channel request frame including an initiator field and a recipient set field, the initiator field indicating an address of the access point, the recipient set field including a plurality of subfields indicating the plurality of recipients, each of the plurality of subfields including a recipient field indicating an identifier for a corresponding one of the plurality of recipients; transmitting, by the access point, to the plurality of recipients, a null data packet frame commonly used for the downlink channel estimation after broadcasting the channel request frame; sequentially receiving, by the access point, from each of the plurality of recipients, a channel response frame including a channel state for a MIMO channel that is estimated by a corresponding recipient based on the null data packet frame; and transmitting, by the access point, to the plurality of recipients, a data frame by using a MIMO transmission after receiving the channel response frame, the data frame including a group address and a plurality of aggregate-medium access control (MAC) protocol data units (A-MPDUs) for the plurality of recipients, wherein the group address indicates a station group to which the plurality of recipients belongs, 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 a same transmission time corresponding to a transmission time of a longest A-MPDU among the plurality of A-MPDUs.