IEEE 802.11ax


IEEE 802.11ax, marketed as Wi-Fi 6 by Wi-Fi Alliance, is a draft Wi-Fi specification standard, and the proposed successor to Wi-Fi 5.
The 802.11ax standard is expected to become an official IEEE specification in September 2020. It is designed to operate in license exempt bands between 1 and 6 GHz when they become available for 802.11 use. All Wi-Fi 6 devices work over the previously allocated 2.4 and 5 GHz bands. The Wi-Fi 6E designation is for products that also support the standard over 6 GHz.
Devices presented at CES 2018 claimed a combined 11 Gbit/s of theoretical data rates. For dense deployments, throughput speeds are 4× higher than IEEE 802.11ac, even though the nominal data rate is just 37% faster at most. Latency is also down 75%.
To improve spectrum efficient utilization, the new version introduces better power-control methods to avoid interference with neighboring networks, orthogonal frequency-division multiple access, higher order 1024-QAM, and up-link direction added with the down-link of MIMO and MU-MIMO to further increase throughput, as well as dependability improvements of power consumption and security protocols such as Target Wake Time and WPA3.

Rate set

Notes

Technical improvements

The 802.11ax amendment will bring several key improvements over 802.11ac. 802.11ax addresses frequency bands between 1 GHz and 6 GHz. Therefore, unlike 802.11ac, 802.11ax will also operate in the unlicensed 2.4 GHz band. To meet the goal of supporting dense 802.11 deployments, the following features have been approved.
Feature802.11ac802.11axComment
OFDMANot availableCentrally controlled medium access with dynamic assignment of 26, 52, 106, 242, 484, or 996 tones per station. Each tone consists of a single subcarrier of 78.125 kHz bandwidth. Therefore, bandwidth occupied by a single OFDMA transmission is between 2.03125 MHz and ca. 80 MHz bandwidth.OFDMA segregates the spectrum in time-frequency resource units. A central coordinating entity assigns RUs for reception or transmission to associated stations. Through the central scheduling of the RUs contention overhead can be avoided, which increases efficiency in scenarios of dense deployments.
Multi-user MIMO Available in Downlink directionAvailable in Downlink and Uplink directionWith Downlink MU MIMO an AP may transmit concurrently to multiple stations and with Uplink MU MIMO an AP may simultaneously receive from multiple stations. Whereas OFDMA separates receivers to different RUs, with MU MIMO the devices are separated to different spatial streams. In 802.11ax, MU MIMO and OFDMA technologies can be used simultaneously. To enable uplink MU transmissions, the AP transmits a new control frame which contains scheduling information. Furthermore, Trigger also provides synchronization for an uplink transmission, since the transmission starts SIFS after the end of Trigger.
Trigger-based Random AccessNot availableAllows performing UL OFDMA transmissions by stations which are not allocated RUs directly.In Trigger frame, the AP specifies scheduling information about subsequent UL MU transmission. However, several RUs can be assigned for random access. Stations which are not assigned RUs directly can perform transmissions within RUs assigned for random access. To reduce collision probability, the 802.11ax amendment specifies special OFDMA back-off procedure. Random access is favorable for transmitting buffer status reports when the AP has no information about pending UL traffic at a station.
Spatial frequency reuseNot availableColoring enables devices to differentiate transmissions in their own network from transmissions in neighboring networks.
Adaptive Power and Sensitivity Thresholds allows dynamically adjusting transmit power and signal detection threshold to increase spatial reuse.		Without spatial reuse capabilities devices refuse transmitting concurrently to transmissions ongoing in other, neighboring networks. With coloring, a wireless transmission is marked at its very beginning helping surrounding devices to decide if a simultaneous use of the wireless medium is permissible or not. A station is allowed to consider the wireless medium as idle and start a new transmission even if the detected signal level from a neighboring network exceeds legacy signal detection threshold, provided that the transmit power for the new transmission is appropriately decreased.
NAVSingle NAVTwo NAVsIn dense deployment scenarios, NAV value set by a frame originated from one network may be easily reset by a frame originated from another network, which leads to misbehavior and collisions. To avoid this, each 802.11ax station will maintain two separate NAVs — one NAV is modified by frames originated from a network the station is associated with, the other NAV is modified by frames originated from overlapped networks.
Target Wake Time Not availableTWT reduces power consumption and medium access contention.TWT is a concept developed in 802.11ah. It allows devices to wake up at other periods than the beacon transmission period. Furthermore, the AP may group device to different TWT period thereby reducing the number of devices contending simultaneously for the wireless medium.
FragmentationStatic fragmentationDynamic fragmentationWith static fragmentation all fragments of a data packet are of equal size except for the last fragment. With dynamic fragmentation a device may fill available RUs of other opportunities to transmit up to the available maximum duration. Thus, dynamic fragmentation helps reduce overhead.
Guard interval duration0.4 µs or 0.8 µs0.8 µs, 1.6 µs or 3.2 µsExtended guard interval durations allow for better protection against signal delay spread as it occurs in outdoor environments.
Symbol duration3.2 µs12.8 µsSince the subcarrier spacing is reduced by a factor of 4, the OFDM symbol duration is increased by a factor of 4 as well. Extended symbol durations allow for increased efficiency.

Products

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