Performance Analysis of Random Access Multi-user MIMO Wireless LANs

A multi-antenna access point (AP) can transmit or receive data simultaneously from multiple clients, however, this multi-user MIMO (MU-MIMO) capability is underutilized in conventional 802.11 wireless LANs (WLANs). To address this problem, researchers have recently developed a CSMA/CA-based MAC protocol that supports concurrent transmissions from different transmitters. In this paper we propose an analytical model to investigate the throughput performance of this CSMA/CA-based MAC protocol operating in a MU-MIMO WLAN. Comparisons with simulation results show that our analytical model provides a close estimation of the network throughput. Based on this model, we analyze the throughput performance with respect to different network parameters. Specifically, we show that: 1) the optimal backoff window sizes can be designed to achieve the maximum throughput; 2) there exists a threshold for the number of antennas at the AP, above which the network throughput will no longer increase even if we add more antennas at the AP.