Multi-user downlink with single-user uplink can starve TCP

In this paper we present the first cross-layer analysis of wireless LANs operating under downlink multi-user MIMO (MU-MIMO), considering the fundamental role played by closed-loop (TCP) traffic. In particular, we consider an 802.11ac scenario in which the access point transmits on the downlink via MU-MIMO, whereas stations must employ single-user transmissions on the uplink. With the help of analytical models built for the different regimes that can occur in the considered system, we identify and explain crucial performance anomalies that can result in very low throughput in some scenarios, completely offsetting the theoretical gains achievable by MU-MIMO. We discuss solutions to mitigate the risk of this performance degradation and alternative uplink strategies allowing WLANs to approach their maximum theoretical capacity under MU-MIMO.

[1]  Lena Schwartz.  Next Generation Wireless Lans 802 11n And 802 11ac , 2016 .

[2]  Eitan Altman,et al.  New Insights From a Fixed-Point Analysis of Single Cell IEEE 802.11 WLANs , 2007, IEEE/ACM Transactions on Networking.

[3]  Chiung-Jang Chen,et al.  Performance Analysis of Scheduling in Multiuser MIMO Systems with Zero-Forcing Receivers , 2007, IEEE Journal on Selected Areas in Communications.

[4]  Sung-Ju Lee,et al.  Mode and user selection for multi-user MIMO WLANs without CSI , 2015, 2015 IEEE Conference on Computer Communications (INFOCOM).

[5]  Edward W. Knightly,et al.  MUTE: Sounding inhibition for MU-MIMO WLANs , 2014, 2014 Eleventh Annual IEEE International Conference on Sensing, Communication, and Networking (SECON).

[6]  Andrea J. Goldsmith,et al.  On the optimality of multiantenna broadcast scheduling using zero-forcing beamforming , 2006, IEEE Journal on Selected Areas in Communications.

[7]  Eitan Altman,et al.  A queueing model for HTTP traffic over IEEE 802.11 WLANs , 2006, Comput. Networks.

[8]  David Murray,et al.  The state of enterprise network traffic in 2012 , 2012, 2012 18th Asia-Pacific Conference on Communications (APCC).

[9]  Giuseppe Caire,et al.  Multiuser MIMO Achievable Rates With Downlink Training and Channel State Feedback , 2007, IEEE Transactions on Information Theory.

[10]  Edward W. Knightly,et al.  A Scalable Multi-User Uplink for Wi-Fi , 2016, NSDI.

[11]  A. Girotra,et al.  Performance Analysis of the IEEE 802 . 11 Distributed Coordination Function , 2005 .

[12]  Wei Wang,et al.  SAM: enabling practical spatial multiple access in wireless LAN , 2009, MobiCom '09.

[13]  Edward W. Knightly,et al.  IEEE 802.11ac: from channelization to multi-user MIMO , 2013, IEEE Communications Magazine.

[14]  Boris Bellalta,et al.  An Approximate Queueing Model for Multi-Rate Multi-User MIMO Systems , 2011, IEEE Communications Letters.

[15]  Robert A. Scholtz,et al.  Performance Analysis of , 1998 .