REFRAIN: promoting valid transmission in high-density modern wi-fi networks

For emerging high-density Wi-Fi networks, there have been plenty of studies that claim the need for more aggressive channel access to enhance spatial reuse. Against those previous ideas, this paper presents a different perspective that existing Wi-Fi devices already have excessive transmission opportunities, even without protecting each other in certain scenarios. We shed light on an anomaly within actual carrier sensing (CS) behaviors, which makes some neighboring devices become blind to each other and transmit simultaneously, due to undetected preambles. Through experimental study and analysis, we reveal both sides of the anomaly heavily affecting the overall network performance. Based on the observations, we design REFRAIN, a standard-compliant PHY/MAC framework, which copes with and further exploits the anomaly for better spatial reuse. Our prototype using NI USRP and commercial Wi-Fi devices shows the feasibility and effectiveness of our approach, while extensive simulation results demonstrate that REFRAIN achieves up to 1.57× higher average throughput by promoting valid transmissions, without modifying the 802.11 CS specification at all.