Patent ID: 8867394

Claim:
An interference avoidance method performed by an access point (AP) in a wireless local area network (WLAN) system, the method comprising: transmitting a training request (TRQ) message for requesting transmission of a sounding frame to a first station which is a target of multi-user multiple input multiple output (MU-MIMO) transmission, a second station which receives data through a direct link during the MU-MIMO transmission, and a third station which transmits data through a direct link; receiving first and second sounding frames respectively transmitted by the first and second stations in response to the TRQ message; receiving from the third station a sounding frame and a multi-user direct link setup (MU DLS) frame including a station identifier (STA ID) field indicating a transmitting station which transmits data by the third station to the second station through the direct link; estimating a channel by using the first sound frame to determine a beam-forming vector to be used for the MU-MIMO transmission; and performing the MU-MIMO transmission for MU-MIMO transmission target stations, wherein the beam-forming vector is determined such that the MU-MIMO transmission has a minimum effect on the second station by considering channel information between the AP and the second station and acquired on the basis of the second sounding frame received from the second station, and wherein the MU DLS frame further includes at least one of a multi-TID field indicating quality of service (QoS) information of data transmitted by the third station to the second station, a start offset field indicating a time at which the third station starts to transmit the data to the second station through the direct link, and a duration field indicating a duration in which the third station transmits the data to the second station through the direct link.