A Target Wake Time Scheduling Scheme for Uplink Multiuser Transmission in IEEE 802.11ax-Based Next Generation WLANs

IEEE 802.11ax Wireless Local Area Networks (WLANs) introduce Orthogonal Frequency Division Multiple Access (OFDMA) physical layer technology to improve throughput in dense scenarios. In order to save power of battery operated stations (STAs), a novel broadcast Target Wake Time (TWT) operation for negotiating wake time between an access point (AP) and a group of STAs is also proposed by making full use of the new capability of uplink OFDMA-based multiuser transmissions. However, if the wake time of each STA which is determined by the offset and wake interval (listen interval) is not properly scheduled, deteriorated throughput and high power consumption occur because of collisions. In this paper, we take the advantage of uplink multiuser transmission with the novel TWT scheduling to maximize throughput. We first investigate the fundamental relationship between throughput and energy efficiency with several key aspects, such as the number of simultaneously active STAs, the number of eligible random access resource units, and the contention window size. We further derive the formulations of throughput and energy efficiency on the listen interval of each STA. Based on the relationship, a TWT-based sleep/wake-up scheduling scheme (TSS) is proposed to improve the throughput by reducing or even cancelling collisions. Simulation results demonstrate the effectiveness in terms of average throughput and energy efficiency. The TSS also makes a practical step towards a collision-free and deterministic access in future WLANs when cooperating with TWT service period scheduling.