IEEE 802.11ax-2021 or 802.11ax, is an IEEE standard from the Wi-Fi Alliance, for wireless networks (WLANs). The standard is marketed as Wi-Fi 6. It operates in the 2.4 GHz and 5 GHz bands, with an extended version, Wi-Fi 6E, that adds the 6 GHz band; these are license-exempt ISM bands. It is an upgrade from Wi-Fi 5 (IEEE 802.11ac), with improvements for better performance in crowded places.
This standard aims to boost throughput in crowded places like offices and malls. Though the nominal data rate is only 37% higher than that of Wi-Fi 5, the throughput increases by at least four times, making it more efficient and reducing latency by 75%. The quintupling of overall throughput is made possible by higher spectral efficiency.
Wi-Fi 6 has a main feature called OFDMA, similar to how cellular common-carrier networks work. This brings better spectrum use, improved power control to avoid interference, and enhancements like 1024QAM, MIMO and MU-MIMO for faster speeds. There are also reliability improvements such as lower power consumption and security protocols like Target Wake Time and WPA3.
The 802.11ax standard was approved on September 1, 2020, with Draft 8 getting 95% approval. Subsequently, on February 1, 2021, the standard received official endorsement from the IEEE Standards Board.
Rate set
+ Modulation and coding schemesMCSindexModulationtypeCodingrateData rate (Mbit/s) Channel width (MHz)204080160 Guard Interval (μs) 1.6 0.8 1.6 0.8 1.6 0.8 1.6 0.80 BPSK 1/2 8 8.6 16 17.2 34 36.0 68 721 QPSK 1/2 16 17.2 33 34.4 68 72.1 136 1442 QPSK 3/4 24 25.8 49 51.6 102 108.1 204 2163 16-QAM 1/2 33 34.4 65 68.8 136 144.1 272 2884 16-QAM 3/4 49 51.6 98 103.2 204 216.2 408 4325 64-QAM 2/3 65 68.8 130 137.6 272 288.2 544 5766 64-QAM 3/4 73 77.4 146 154.9 306 324.4 613 6497 64-QAM 5/6 81 86.0 163 172.1 340 360.3 681 7218 256-QAM 3/4 98 103.2 195 206.5 408 432.4 817 8659 256-QAM 5/6 108 114.7 217 229.4 453 480.4 907 96110 1024-QAM 3/4 122 129.0 244 258.1 510 540.4 1021 108111 1024-QAM 5/6 135 143.4 271 286.8 567 600.5 1134 1201
Notes
MU-MIMO and OFDMA With the previous generation Wi-Fi 5, multi-user MIMO was introduced, which is a spatial multiplexing technique. MU-MIMO allows the access point to form beams towards each client, while transmitting information simultaneously. By doing so, the interference between clients is reduced, and the overall throughput is increased, since multiple clients can receive data simultaneously.
With Wi-Fi 6, a similar multiplexing is introduced in the frequency-division multiplexing: OFDMA. With OFDMA, multiple clients are assigned to different Resource Units in the available spectrum. By doing so, an 80 MHz channel can be split into multiple Resource Units, so that multiple clients receive different types of data over the same spectrum, simultaneously.
To support OFDMA, Wi-Fi 6 needs four times as many subcarriers as Wi-Fi 5. Specifically, for 20, 40, 80, and 160 MHz channels, the 802.11ac standard has, respectively, 64, 128, 256 and 512 subcarriers while the 802.11ax standard has 256, 512, 1024, and 2048 subcarriers. Since the available bandwidths have not changed and the number of subcarriers increases by a factor of four, the subcarrier spacing is reduced by the same factor. This introduces OFDM symbols that are four times longer: with Wi-Fi 5, an OFDM symbol takes 3.2 microseconds to transmit. With Wi-Fi 6, it takes 12.8 microseconds (both without guard intervals).
Technical improvements The 802.11ax amendment brings several key improvements over 802.11ac. While 802.11ac only uses the 5GHz band, which is a bit over 700 MHz wide, 802.11ax also allows the use of the 2.4GHz band of some earlier protocols, less than 100MHz wide, and the larger 6GHz band, about 1200MHz wide. adds to the use of the 6GHz band and, thereby, channels that are wide without the restrictions of Dynamic Frequency Selection that apply to all channels in the band. The number and selection of channels available depends on the country a given Wi-Fi 6 network operates in. To meet the goal of supporting dense 802.11 deployments, the following features have been approved.
Feature Wi-Fi 5 Wi-Fi 6 CommentOFDMAnot 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, a single transmission is between 2.03125 MHz and ca. 80 MHz wide. segregates the spectrum in time-frequency resource units (RUs). A central coordinating entity (the AP in 802.11ax) 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- an AP may transmit concurrently with multiple stations, and with uplink MU-MIMO an AP may simultaneously receive from multiple stations. Whereas separates receivers to different , with MU-MIMO the devices are separated into different spatial streams. In 802.11ax, MU-MIMO and OFDMA can be used simultaneously. To enable uplink MU transmissions, the AP transmits a new control frame (Trigger) which contains scheduling information (RU allocations for stations, and the modulation and coding scheme (MCS) that shall be used for each station). Furthermore, a Trigger also provides synchronization for an uplink transmission, since the transmission starts SIFS after the end of a Trigger. Trigger-based Random Accessnot availableAllows performing UL OFDMA transmissions by stations which are not allocated RUs directlyIn a 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 (i.e. situation when two or more stations select the same RU for transmission), the 802.11ax amendment specifies a 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 allow dynamically adjusting transmit power and signal detection threshold to increase spatial reuse. Without spatial reuse capabilities devices refuse transmitting concurrently with transmissions in neighboring networks. With basic service set coloring (BSS 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. A station is allowed to consider the wireless medium idle and start a new transmission even if the detected signal level from a neighboring network exceeds the legacy signal detection threshold, provided that the transmit power for the new transmission is appropriately decreased. NAVSingle NAVDual NAVs In dense deployment scenarios, the NAV (network allocation vector) value set by a frame from one network may be easily reset by a frame 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 from a network the station is associated with, while the other NAV is modified by frames from overlapping networks.Target Wake Time (TWT)not availableTWT reduces power consumption and medium access contention.TWT is a concept developed in 802.11ah. It allows devices to wake up at times other than the periodic beacon transmission time. Furthermore, the AP may group devices with various TWT periods, thereby reducing the number of devices contending simultaneously for the wireless medium.FragmentationStaticDynamicWith 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 or 0.8 μs0.8, 1.6 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 four, the OFDM symbol duration is increased by a factor of four as well. Extended symbol durations allow for increased efficiency.Frequency bands5 GHz only2.4 and 5 GHz802.11ac falls back to 802.11n for the 2.4 GHz band.
Adoption Following the ratification of the IEEE 802.11ax standard in February 2021, Wi-Fi 6 saw rapid adoption across consumer and enterprise devices. The Wi-Fi Alliance began certifying Wi-Fi 6 devices under its Wi-Fi CERTIFIED 6 program in September 2019, ahead of the standard's formal approval. Major smartphone, laptop, and router manufacturers incorporated Wi-Fi 6 support into their product lines beginning in 2020.
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References
External links Evgeny Khorov, Anton Kiryanov, Andrey Lyakhov, Giuseppe Bianchi. 'A Tutorial on IEEE 802.11ax High Efficiency WLANs', IEEE Communications Surveys & Tutorials, vol. 21, no. 1, pp. 197–216, First quarter 2019.