IEEE 802.11ax: On Time Synchronization in Asynchronous OFDM Uplink Multi-User MIMO Physical Layer

The High Efficiency WLANs (HEW) Task Group (TG) has been developing since 2014 the IEEE 802.11ax amendment, the 6th generation of wireless local area networks (WLANs). One major novel feature of IEEE 802.11ax standard is the specification of uplink multi-user multiple-input multiple-output (UL MUMIMO) techniques to cope with the increase of UL data/video traffic from small-form devices in ultra-dense networks. In this paper, we first show that the UL MU-MIMO physical layer performance can be dramatically impaired due to the asynchronous reception over the uplink channel. Next, we propose and evaluate the performance of a time advance mechanism designed for IEEE 802.11ax WLANs that mitigates adequately the performance loss due to asynchronous UL MU-MIMO channels