Figure 4
From: User scheduling for MU-MIMO transmission with active CSI feedback
Operation example of 802.11ac+. Both AP and users participate in scheduling decisions. Except for the first scheduled user, all users should send a feedback report through a contention. If the AP fails in reception of any CSI reports, then it does not go to the next contention round and finishes the feedback procedure. Therefore, there could be maximum (M−1) contention rounds in the case of M AP antennas.