DL MU-MIMO with TXOP Sharing and Suppressed Acknowledgments in IEEE 802.11ac WLANs

Abstract

Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contribution of the IEEE 802.11ac amendment. It is essentially an enhanced version of the standard TXOP mechanism initially introduced by the IEEE 802.11e amendment, specifically engineered to improve performance of the Downlink Multi-User Multiple-Input-Multiple-Output (DL MU-MIMO) technology. DL MU-MIMO transmissions with TXOP sharing are performed only by the Access Point (AP) allowing multiple frames from multiple traffic classes to be transmitted simultaneously towards multiple users in the downlink. However, in the reverse path, acknowledgments must be transmitted sequentially. The default acknowledgment scheme selected by the IEEE 802.11ac is the Block Acknowledgments (BlockACK) which is a poll-based approach. In this paper, we investigate the application of an acknowledgment-free scheme, known as No Acknowledgment (NoACK), during DL MU-MIMO transmissions in IEEE 802.11ac Wireless Local Area Networks (WLANs). Its impact on the overall achieved throughput is evaluated through an analytical study.