Target Wake Time Scheduling Strategies for Uplink Transmission in IEEE 802.11ax Networks

Target wake time (TWT) has been introduced to provide the low power consumption mode for stations (STAs) with low traffic and periodic data transmissions in IEEE 802.11ax networks. The TWT operation starts with negotiating wake and doze periods between an access point (AP) and STAs. Thanks to the nature of wake and doze period negotiation, TWT operation enables time scheduled access, like time-division multiple access (TDMA) without modification overhead. In this paper, we demonstrate TWT scheduling issues that include scheduling requirements and results notifications from the AP to STAs, using standard-compliant methods. Then we establish TWT scheduling strategies by exemplifying two well-known schedulers, max-rate and proportional fairness schedulers. Through ns-3 simulation, we evaluate the performance of TWT scheduling and highlight the benefits of TWT for a large number of STAs from the fairness and power consumption perspective.

I. Introduction

Low energy consumption is an important issue for Internet of things (IoT) devices, considering their low battery capacity and long lifetime requirement. However, conventional schemes for power saving, such as power save mode in IEEE 802.11 or automatic power save delivery (APSD) [1], still have limitations because they require Beacon frames or they are STA-driven. They suffer from collisions and work disorderly when many devices are involved.