Wi-Fi 6

IEEE 802.11ax, officially marketed by the Wi-Fi Alliance as Wi-Fi 6 (2.4 GHz and 5 GHz)[5] and Wi-Fi 6E (6 GHz),[6] is an IEEE standard for wireless local-area networks (WLANs) and the successor of Wi-Fi 5 (802.11ac). It is also known as High Efficiency Wi-Fi, for the overall improvements to Wi-Fi 6 clients in dense environments.[7] It is designed to operate in license-exempt bands between 1 and 7.125 GHz, including the 2.4 and 5 GHz bands already in common use as well as the much wider 6 GHz band (e.g. 5.925–7.125 GHz in the US, a band 1.200 GHz wide).[8]

Wi-Fi generations
Generation IEEE
standard		 Adopted Maximum
link rate
(Mbit/s)		 Radio
frequency
(GHz)
Wi-Fi 7 802.11be (2024) 1376 to 46120 2.4/5/6
Wi-Fi 6E 802.11ax 2020 574 to 9608[1] 6[lower-alpha 1]
Wi-Fi 6 2019 2.4/5
Wi-Fi 5 802.11ac 2014 433 to 6933 5[lower-alpha 2]
Wi-Fi 4 802.11n 2008 72 to 600 2.4/5
(Wi-Fi 3)* 802.11g 2003 6 to 54 2.4
(Wi-Fi 2)* 802.11a 1999 5
(Wi-Fi 1)* 802.11b 1999 1 to 11 2.4
(Wi-Fi 0)* 802.11 1997 1 to 2 2.4
*Wi-Fi 0, 1, 2, and 3 are by retroactive inference [2][3][4]

The main goal of this standard is enhancing throughput-per-area[lower-alpha 3] in high-density scenarios, such as corporate offices, shopping malls and dense residential apartments. While the nominal data rate improvement against 802.11ac is only 37%,[7]: qt  the overall throughput increase (over an entire network) is 300% (hence High Efficiency).[9]: qt  This also translates to 75% lower latency.[10]

The quadrupling of overall throughput is made possible by a higher spectral efficiency. The key feature underpinning 802.11ax is orthogonal frequency-division multiple access (OFDMA), which is equivalent to cellular technology applied into Wi-Fi.[7]: qt  Other improvements on spectrum utilization are better power-control methods to avoid interference with neighboring networks, higher order 1024‑QAM, 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.

The IEEE 802.11ax standard was finalised on September 1, 2020 when Draft 8 received 95% approval in the sponsor ballot and received final approval from the IEEE Standards Board on February 1, 2021.[11]

Rate set
Modulation and coding schemes
MCS
index[lower-roman 1]		 Modulation
type		 Coding
rate		 Data rate (Mbit/s)[lower-roman 2]
20 MHz channels40 MHz channels80 MHz channels160 MHz channels
1600 ns GI[lower-roman 3]800 ns GI1600 ns GI800 ns GI1600 ns GI800 ns GI1600 ns GI800 ns GI
0BPSK1/288.61617.23436.06872
1QPSK1/21617.23334.46872.1136144
2QPSK3/42425.84951.6102108.1204216
316-QAM1/23334.46568.8136144.1272282
416-QAM3/44951.698103.2204216.2408432
564-QAM2/36568.8130137.6272288.2544576
664-QAM3/47377.4146154.9306324.4613649
764-QAM5/68186.0163172.1340360.3681721
8256-QAM3/498103.2195206.5408432.4817865
9256-QAM5/6108114.7217229.4453480.4907961
101024-QAM3/4122129.0244258.1510540.410211081
111024-QAM5/6135143.4271286.8567600.511341201

Notes

  1. MCS 9 is not applicable to all combinations of channel width and spatial stream count.
  2. Per spatial stream.
  3. GI stands for guard interval.

OFDMA

In 802.11ac (802.11's previous amendment), 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 802.11ax, a similar multiplexing is introduced in the frequency domain: 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, 802.11ax needs four times as many subcarriers as 802.11ac. 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, 1,024, and 2,048 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: in 802.11ac, an OFDM symbol takes 3.2 microseconds to transmit. In 802.11ax, it takes 12.8 microseconds (both without guard intervals).

Technical improvements

The 802.11ax amendment brings several key improvements over 802.11ac. 802.11ax addresses frequency bands between 1 GHz and 6 GHz.[12] Therefore, unlike 802.11ac, 802.11ax also operates in the unlicensed 2.4 GHz band. To meet the goal of supporting dense 802.11 deployments, the following features have been approved.

Feature 802.11ac 802.11ax Comment
OFDMA Not available Centrally 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 (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 (MU-MIMO) Available in Downlink direction Available in Downlink and Uplink direction With 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 (Trigger) which contains scheduling information (RUs allocations for stations, modulation and coding scheme (MCS) that shall be used for each station). Furthermore, Trigger also provides synchronization for an uplink transmission, since the transmission starts SIFS after the end of Trigger.
Trigger-based Random Access Not available Allows 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 (i.e. situation when two or more stations select the same RU for transmission), 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 reuse Not available Coloring 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 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 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.
NAV Single NAV Two NAVs In 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 (TWT) Not available TWT 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 devices to different TWT periods, thereby reducing the number of devices contending simultaneously for the wireless medium.
Fragmentation Static fragmentation Dynamic fragmentation With 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 duration 0.4 µs or 0.8 µs 0.8 µs, 1.6 µs or 3.2 µs Extended guard interval durations allow for better protection against signal delay spread as it occurs in outdoor environments.
Symbol duration 3.2 µs 12.8 µs Since 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.[13]
Frequency bands 5 GHz only 2.4 GHz and 5 GHz 802.11ac falls back to 802.11n for the 2.4 GHz band.

Notes
  1. Wi-Fi 6E is the industry name that identifies Wi-Fi devices that operate in 6 GHz. Wi-Fi 6E offers the features and capabilities of Wi-Fi 6 extended into the 6 GHz band.
  2. 802.11ac only specifies operation in the 5 GHz band. Operation in the 2.4 GHz band is specified by 802.11n.
  3. Throughput-per-area, as defined by IEEE, is the ratio of the total network throughput to the network area.[7]

Comparison
802.11 network standards
Frequency
range,
or type		 PHY Protocol Release
date [14]		 Frequency Bandwidth Stream
data rate [15]		 Allowable
MIMO streams		 Modulation Approximate
range
Indoor Outdoor
(GHz) (MHz) (Mbit/s)
1–7⅛ GHz DSSS[16], FHSS[upper-alpha 1] 802.11-1997 June 1997 2.4 22 1, 2 — DSSS, FHSS[upper-alpha 1] 20 m (66 ft) 100 m (330 ft)
HR/DSSS [16] 802.11b September 1999 2.4 22 1, 2, 5.5, 11 — CCK, DSSS 35 m (115 ft) 140 m (460 ft)
OFDM 802.11a September 1999 5 5/10/20 6, 9, 12, 18, 24, 36, 48, 54
(for 20 MHz bandwidth,
divide by 2 and 4 for 10 and 5 MHz)		 — OFDM 35 m (115 ft) 120 m (390 ft)
802.11j November 2004 4.9/5.0
[upper-alpha 2][17]		 ? ?
802.11y November 2008 3.7 [upper-alpha 3] ? 5,000 m (16,000 ft)[upper-alpha 3]
802.11p July 2010 5.9 200 m 1,000 m (3,300 ft)[18]
802.11bd December 2022 5.9/60 500 m 1,000 m (3,300 ft)
ERP-OFDM 802.11g June 2003 2.4 38 m (125 ft) 140 m (460 ft)
HT-OFDM [19] 802.11n
(Wi-Fi 4)		 October 2009 2.4/5 20 Up to 288.8[upper-alpha 4] 4 MIMO-OFDM
(64-QAM)		 70 m (230 ft) 250 m (820 ft)[20]
40 Up to 600[upper-alpha 4]
VHT-OFDM [19] 802.11ac
(Wi-Fi 5)		 December 2013 5 20 Up to 693[upper-alpha 4] 8 DL
MU-MIMO OFDM
(256-QAM)		 35 m (115 ft)[21] ?
40 Up to 1600[upper-alpha 4]
80 Up to 3467[upper-alpha 4]
160 Up to 6933[upper-alpha 4]
HE-OFDMA 802.11ax
(Wi-Fi 6,
Wi-Fi 6E)		 May 2021 2.4/5/6 20 Up to 1147[upper-alpha 5] 8 UL/DL
MU-MIMO OFDMA
(1024-QAM)		 30 m (98 ft) 120 m (390 ft) [upper-alpha 6]
40 Up to 2294[upper-alpha 5]
80 Up to 4804[upper-alpha 5]
80+80 Up to 9608[upper-alpha 5]
EHT-OFDMA 802.11be
(Wi-Fi 7)		 May 2024
(est.)		 2.4/5/6 80 Up to 11.5 Gbit/s[upper-alpha 5] 16 UL/DL
MU-MIMO OFDMA
(4096-QAM)		 30 m (98 ft) 120 m (390 ft) [upper-alpha 6]
160
(80+80)		 Up to 23 Gbit/s[upper-alpha 5]
240
(160+80)		 Up to 35 Gbit/s[upper-alpha 5]
320
(160+160)		 Up to 46.1 Gbit/s[upper-alpha 5]
WUR [upper-alpha 7] 802.11ba October 2021 2.4/5 4/20 0.0625, 0.25
(62.5 kbit/s, 250 kbit/s)		 — OOK (multi-carrier OOK) ? ?
mmWave
(WiGig)		 DMG [22] 802.11ad December 2012 60 2160
(2.16 GHz)		 Up to 8085[23]
(8 Gbit/s)		 — OFDM[upper-alpha 1], single carrier, low-power single carrier[upper-alpha 1] 3.3 m (11 ft)[24] ?
802.11aj April 2018 60 [upper-alpha 8] 1080[25] Up to 3754
(3.75 Gbit/s)		 — single carrier, low-power single carrier[upper-alpha 1] ? ?
CMMG 802.11aj April 2018 45 [upper-alpha 8] 540/
1080		 Up to 15015[26]
(15 Gbit/s)		 4[27] OFDM, single carrier ? ?
EDMG [28] 802.11ay July 2021 60 Up to 8640
(8.64 GHz)		 Up to 303336[29]
(303 Gbit/s)		 8 OFDM, single carrier 10 m (33 ft) 100 m (328 ft)
Sub 1 GHz (IoT) TVHT [30] 802.11af February 2014 0.054
-0.79		 6, 7, 8 Up to 568.9[31] 4 MIMO-OFDM ? ?
S1G [30] 802.11ah May 2017 0.7/0.8
/0.9		 1–16 Up to 8.67[32]
(@2 MHz)		 4 ? ?
Light
(Li-Fi)		 LC
(VLC/OWC)		 802.11bb December 2023
(est.)		 800–1000 nm 20 Up to 9.6 Gbit/s — O-OFDM ? ?
IR[upper-alpha 1]
(IrDA)		 802.11-1997 June 1997 850–900 nm ? 1, 2 — PPM[upper-alpha 1] ? ?
802.11 Standard rollups
  802.11-2007 (802.11ma) March 2007 2.4, 5 Up to 54 DSSS, OFDM
802.11-2012 (802.11mb) March 2012 2.4, 5 Up to 150[upper-alpha 4] DSSS, OFDM
802.11-2016 (802.11mc) December 2016 2.4, 5, 60 Up to 866.7 or 6757[upper-alpha 4] DSSS, OFDM
802.11-2020 (802.11md) December 2020 2.4, 5, 60 Up to 866.7 or 6757[upper-alpha 4] DSSS, OFDM
802.11me September 2024
(est.)		 2.4, 5, 6, 60 Up to 9608 or 303336 DSSS, OFDM
  1. This is obsolete, and support for this might be subject to removal in a future revision of the standard
  2. For Japanese regulation.
  3. IEEE 802.11y-2008 extended operation of 802.11a to the licensed 3.7 GHz band. Increased power limits allow a range up to 5,000 m. As of 2009, it is only being licensed in the United States by the FCC.
  4. Based on short guard interval; standard guard interval is ~10% slower. Rates vary widely based on distance, obstructions, and interference.
  5. For single-user cases only, based on default guard interval which is 0.8 micro seconds. Since multi-user via OFDMA has become available for 802.11ax, these may decrease. Also, these theoretical values depend on the link distance, whether the link is line-of-sight or not, interferences and the multi-path components in the environment.
  6. The default guard interval is 0.8 micro seconds. However, 802.11ax extended the maximum available guard interval to 3.2 micro seconds, in order to support Outdoor communications, where the maximum possible propagation delay is larger compared to Indoor environments.
  7. Wake-up Radio (WUR) Operation.
  8. For Chinese regulation.

References
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