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

Abstract

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. INDEX TERMS IEEE 802.11ax, WLAN, power conservation, target wake time (TWT), orthogonal frequency division multiple access (OFDMA).

Joint optimization of target wake time mechanism and scheduling for IEEE 802.11ax

“…to both sides of ( 15) and rearranging the resulting terms, we have the bound in (12). This completes the proof.…”

“…The Lyapunov optimization framework now helps to solve our primary problem by finding an algorithm that minimizes the right hand side (R.H.S) of the bound (12). Clearly, the solution of following problem minimizes the R.H.S of (12).…”

“…The "clock drift" problem which is the misalignment of the scheduling times of STAs within TWT mechanism and its effect on the power consumption is investigated in [11]. The most relevant studies to our work are found in [6,12,13].…”

“…no consideration of dynamic network conditions). In [12], the optimization of broadcast TWT mechanism is performed for energy saving and the authors in [13] aims at reducing energy for uplink multiuser transmission. The works in [12,13] do not attempt to optimize TWT interval of STAs (e.g., wake-up period) and also do not consider a scenario where different STA may have different traffic conditions.…”

“…Also in [12,13], a full-buffer scenario is assumed, in which the traffic conditions of users is same and they have always data, and the authors try to address the problem of reducing congestion. It is still an open problem that how TWT mechanism of 802.11ax should be optimized according to time-varying network conditions to save more power and to control the users' traffic.…”