Uni-MUMAC: A Unified Down/Up-link MU-MIMO MAC Protocol for IEEE 802.11ac WLANs

Due to the dominance of the downlink traffic in Wireless Local Area Networks (WLANs), a large number of previous research efforts have been put to enhance the transmission from the Access Point (AP) to stations (STAs). IEEE 802.11ac, the amendment for next generation WLANs, will support MultiUser Multiple-Input Multiple-Output (MU-MIMO) in the downlink, which is considered as one of the key techniques leading WLANs to the Gigabit era. However, as cloud-based uploading services, Peer-to-Peer (P2P) and telepresence applications get popular, the need for a higher uplink capacity has also become inevitable. In this paper, a unified down/up-link Medium Access Control (MAC) protocol called Uni-MUMAC is proposed to enhance the performance of IEEE 802.11ac WLANs by exploring the multi-user spatial multiplexing. Specifically, in the downlink, we implement an IEEE 802.11ac-compliant MU-MIMO transmission scheme to allow the AP to simultaneously send frames to a group of STAs. In the uplink, we extend the traditional one round channel access contention to two rounds, which enable multiple STAs to transmit frames towards the AP in parallel. 2-nd round Contention Window (CW2nd), a parameter that makes the length of the 2-nd contention round elastic according to the traffic condition, is introduced. Uni-MUMAC is evaluated through simulations in saturated and non-saturated conditions when both downlink and uplink traffic are present in the system. By properly setting CW2nd and other parameters, a WLAN implementing Uni-MUMAC exhibits that the system not only performs well in the downlink traffic dominated scenario, R. Liao · B. Bellalta · T.C. Minh · J. Barcelo · M. Oliver Department of Information and Communication Technologies Universitat Pompeu Fabra, Barcelona, 08018, Spain E-mail: {ruizhi.liao, boris.bellalta, trang.cao, jaume.barcelo, miquel.oliver}@upf.edu ar X iv :1 30 9. 50 49 v2 [ cs .N I] 1 2 D ec 2 01 3 but it is also able to balance both the downlink and uplink throughput in the emerging uplink bandwidthhungry scenario.