# Wi-Fi 6

Wi-Fi generationsvte :
| Generation | Visual | IEEE standard | Adopted | Maximum link rate (Mbit/s) | Radio frequency (GHz) |
| — | — | 802.11 | 1997 | 1–2 | 2.4 |
| — | — | 802.11b | 1999 | 1–11 | 2.4 |
| — | — | 802.11a | 1999 | 6–54 | 5 |
| — | — | 802.11g | 2003 | 6–54 | 2.4 |
| Wi-Fi 4 | | 802.11n | 2009 | 6.5–600 | 2.4, 5 |
| Wi-Fi 5 | | 802.11ac | 2013 | 6.5–6933 | 5 |
| Wi-Fi 6 | | 802.11ax | 2021 | 0.4–9608 | 2.4, 5 |
| Wi-Fi 6E | | 802.11ax | 2021 | 0.4–9608 | 6 |
| Wi-Fi 7 | | 802.11be | 2024 | 0.4–23,059 | 2.4, 5, 6 |
| Wi-Fi 8 | — | 802.11bn | 2028 | 100,000 | 2.4, 5, 6 |
Wi-Fi 6, or IEEE 802.11ax, is an IEEE standard from the Wi-Fi Alliance, for wireless networks (WLANs). It operates in the 2.4 GHz and 5 GHz bands, with an extended version, Wi-Fi 6E, that adds the 6 GHz band. It is an upgrade from Wi-Fi 5 (802.11ac), with improvements for better performance in crowded places. Wi-Fi 6 covers frequencies in license-exempt bands between 1 and 7.125 GHz, including the commonly used 2.4 GHz and 5 GHz, as well as the broader 6 GHz band.
This standard aims to boost data speed (throughput-per-area) in crowded places like offices and malls. Though the nominal data rate is only 37% better than 802.11ac, the total network speed increases by 300%, making it more efficient and reducing latency by 75%. The quadrupling of overall throughput is made possible by a higher spectral efficiency.
802.11ax Wi-Fi has a main feature called OFDMA, similar to how cell technology works with Wi-Fi. This brings better spectrum use, improved power control to avoid interference, and enhancements like 1024‑QAM, 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

Notes
* ↑ MCS 9 is not applicable to all combinations of channel width and spatial stream count.
* ↑ Per spatial stream.

## 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-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, 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, 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: 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. Therefore, unlike 802.11ac, 802.11ax also operates in the unlicensed 2.4 GHz band. Wi-Fi 6E introduces operation at frequencies of or near 6 GHz, and superwide channels that are 160 MHz wide, the frequency ranges these channels can occupy and the number of these channels depends on the country the Wi-Fi 6 network operates in. 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 | Dual 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 | Dynamic | 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 or 0.8 μs | 0.8, 1.6 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. |
| Frequency bands | 5 GHz only | 2.4 and 5 GHz | 802.11ac falls back to 802.11n for the 2.4 GHz band. |