Energy Efficient Window Control Scheme for IEEE 802.11ah (Wi-Fi HaLow) Based Networks

IEEE 802.11ah brings in Restricted Access Window (RAW) to decrease contention, which is the grouping-based MAC protocol. The way to group a large number of devices and application of RAW size would have influence on the energy efficiency in the process of medium access and communications. In this paper, we study an efficient window control algorithm to improve the uplink energy efficiency with a novel retransmission scheme that utilises the next empty slot for retransmission in the uplink. The grouping scheme is based on the college admission game. The problem is formulated based on energy efficiency by probability theory and Markov chain. To optimise energy efficiency, a window control scheme is proposed to group the devices and set the adaptive window size (number of slots per RAW and internal slot interval) based on the number of groups, applications and the distance between devices and Access Point (AP). The optimal solution is derived by Gradient Descent approach. Simulation results show that our proposed algorithm outperforms existing one on uplink energy efficiency and fairness.