Target Wake Time: Scheduled Access in IEEE 802.11ax WLANs

Abstract

The increasing interest for ubiquitous networking, and the tremendous popularity gained by IEEE 802.11 Wireless Local Area Networks (WLANs) in recent years, is leading to very dense deployments where high levels of channel contention may prevent to meet the increasing users' demands. To mitigate the negative effects of channel contention, the Target Wake Time (TWT) mechanism included in the IEEE 802.11ax amendment can have a significant role, as it provides an extremely simple but effective mechanism to schedule transmissions in time. Moreover, in addition to reduce the contention between stations, the use of TWT may also contribute to take full advantage of other novel mechanisms in the IEEE 802.11 universe, such as multiuser transmissions, multi-AP cooperation, spatial reuse and coexistence in high-density WLAN scenarios. Overall, we believe TWT may be a first step towards a practical collision-free and deterministic access in future WLANs.1 It is expected that the IEEE 802.11ax amendment will be published in 2019.

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

“…In [8], Nurchis and Bellalta gave the throughput analysis of the TWT operation in 802.11ax WLANs which shew that the TWT operation results in 10 times throughput increase than the scenario in which MU capability is not supported. The TWT mechanism alleviates WLAN power consumption problem [5], [6] and improve throughput.…”

“…The setup phase of a TWT session requires the exchange of several messages. In [8], Nurchis and Bellatra evaluated the management overheads of both individual and broadcast TWT agreements. TWT management overhead only implies a small fraction of channel airtime even if management packets are transmitted at the lowest available transmission rate, roughly represent about 6 percent of the airtime.…”

“…inference, a new IEEE 802.11ax [4] amendment is approved as the next generation WLAN, which employs many new technologies [5]- [7] like Orthogonal Frequency Division Multiple Access (OFDMA) based multiuser (MU) transmission, spacial reuse (SR), and Target Wake Time (TWT) [8] to improve performance.…”

“…Furthermore, the scheme for scheduling a proper TWT is out of scope in the IEEE 802.11ax draft 3.0 [4] and is implementation-specific [8]. In order to achieve higher throughput and efficient power consumption in infrastructure basic service sets (IBSSs), we propose a TWT based sleep/wake-up scheduling scheme (TSS) which takes the OFDMA based MU transmission capability into consideration by minimizing contention between STAs in each beacon slot.…”

Interference-Aware Adaptive Beam Alignment for Hyper-Dense IEEE 802.11ax Internet-of-Things Networks

“…Furthermore, the TWT enables STAs to operate energy efficiently with the doze mode. For example, the authors of [ 16 ] proposed a scheduling scheme in IEEE 802.11ax with TWT to efficiently handle MU transmissions and multi-AP cooperation. The authors in [ 17 ] explored several new IEEE 802.11ax UL scheduling mechanisms and compared them among the maximum throughput of MU.…”