Enhancement of the TXOP Sharing designed for DL-MU-MIMO IEEE 802.11ac WLANs

IEEE 802.11ac is one of the ongoing Wireless Local Area Network (WLAN) standard aiming to support Very High Throughput (VHT) with data rate up to 7 Gbps below the 6 GHz band. This new generation of 802.11 WLANs is expected to support Down-Link Multi-User Multiple-Input Multiple-Output (DL-MU-MIMO) transmission, which is a promising technique to greatly increase the spectral efficiency by simultaneously transmitting to multiple users. In this paper, we propose to enhance the TXOP Sharing mechanism, introduced in the 802.11ac amendment, to achieve efficient DL-MU-MIMO transmission. At first, we give new definitions about both events of successful and failed DL-MU-MIMO transmission. Then, we devise a revised Backoff procedure for the primary Access Category (AC) in order to improve the DL-MU-MIMO. Simulation results demonstrate the benefits of the enhanced TXOP Sharing Mechanism in terms of channel utilization and achieved throughput.