Design and Analysis of a Downlink Multi-User MIMO MAC Protocol in WLANs

Equipped with multiple antennas, Access Point (AP) can simultaneously communicate with multiple nodes in WLANs, which is called Multi-User Multi-Input Multi-Output (MU MIMO). The traditional IEEE 802.11 Distributed Coordination Function (DCF) protocol cannot take benefit of the multiple simultaneous downlink transmission. Instead, it may be the bottleneck of improving the system performance. Therefore, we propose a Downlink (DL) MU MIMO MAC protocol which extends DCF to the downlink MU MIMO scenario. A Markov chain model is utilized to analyze the performance of the proposed protocol under saturated conditions. By modeling the channel access actions of AP and each node respectively, we can obtain the access delay of AP. We also simulate the proposed protocol in MATLAB. Both the theoretical analysis results and simulation results confirm that the proposed protocol outperforms DCF in terms of the delay and throughput.