Recovering CSI and Data in Dense Network Environments Using IEEE 802.11ax Midamble.

There has been considerable amount of research to improve performance for a dense wireless local area network (WLAN) environment. While some studies focus on aggressive channel access, others highlight frequent channel state information (CSI) corruption by excessive transmissions. We pay attention to midamble, adopted in the IEEE 802.11ax standard specification, to overcome CSI corruption. If the transmitter inserts midamble symbols, the receiver can acquire new CSI periodically during a physical layer convergence protocol (PLCP) protocol data unit (PPDU) frame. In this paper, we propose a precise receiver performance model to describe the impact of CSI, and design a standard-compliant algorithm called REMEDY that works with conventional channel access schemes by handling CSI corruption and time-varying channels in high-density WLAN networks. REMEDY determines whether to use midamble considering overhead, estimates on-frame signal-to-interference and noise ratio (SINR) to notice channel environments, and cancels the effects of scrambling and incorrect descrambling. We evaluate the performance of the conventional schemes with and without REMEDY in 11ax task group (TGax) indoor simulation scenarios using the ns-3 simulator, considering time-varying channels and CSI corruption. REMEDY helps the existing channel access schemes to achieve up to $2.20\times $ higher throughput while improving the throughput of the lowest performing group, compared to the existing schemes without REMEDY.