Methods and apparatus are provided for burst OFDMA support MU-MIMO in the WLAN network. In one novel aspect, pluralities of user channels are configured for a downlink wideband channel, wherein each user channel is associated with a user group selecting from a SU-SISO, or a SU-MIMO or a MU-MIMO. In one embodiment, the SIG1 and SIG2 signaling fields are independent for each user channel. In another embodiment, the SIG1 fields are duplicates for all user channels carrying common information. The SIG2 fields for each user group are different from each other carrying user group specific information. In another novel aspect, an uplink OFDMA frames contains ACK packets from multiple STAs concurrently using an uplink wideband channel. In one embodiment, one ACK packet is sent for a MU-MIMO user group. In another embodiment, the uplink ACK packet assignment is based on indications in the downlink PHY SIG field.