Towards Understanding and Enhancing Association and Long Sleep in Low-Power WiFi IoT Systems

Enhancing the energy efficiency of WiFi IoT stations introduces unique challenges compared to 802.15.4 and BLE. The four essential operations performed to ensure connectivity between stations and the access point in a WiFi network are association, periodic beacon reception, maintaining association, and station wake up. Understanding and enhancing these operations are essential for building energy-efficient and dependable IoT systems. However, it is unclear how the software and hardware configuration of station and access point, concurrent traffic, power management, and security protocols affect the reliability and energy efficiency of these operations. In this paper, first, we present a thorough analysis of the association cost of WPA2 and WPA3 and mitigate the effect of key computation on association overhead. Second, we prove that increasing listen interval to reduce beacon reception wake-up duration may negatively impact energy efficiency. We identify the primary causes of this problem subject to link quality estimation algorithm and beacon delay. Third, we show that maintaining association by relying on access-point-based polling is not reliable. In particular, we confirm the wake-up delay of low-power stations is highly affected by factors such as channel utilization and beacon listen interval. We also confirm that key renewal aggravates the chance of disassociation.