TopTechnical DictionaryWi-Fi 6 (802.11ax) - wireless network standard

Wi-Fi 6 (802.11ax) - wireless network standard

Wi-Fi 6 or IEEE 802.11ax is an IEEE standard developed by the Wi-Fi Alliance for wireless networks (WLANs). It operates in the 2.4 GHz and 5 GHz bands, with an enhanced version Wi-Fi 6E that adds the 6 GHz band. It is an update to the Wi-Fi 5 (802.11ac) standard with enhancements for better performance in crowded areas. Wi-Fi 6 covers frequencies in licence-exempt bands from 1 to 7.125 GHz, including the commonly used 2.4 GHz and 5 GHz bands, as well as the wider 6 GHz band.

 

The aim of this standard is to increase data transmission speed in crowded areas such as offices and shopping centers. With 1024-QAM modulation, the symbol carries 10 bits instead of 8, enabling speeds as much as 37% higher than those achieved with 256-QAM modulation in the 802.11ac standard, while the overall network speed increases by 300%, increasing efficiency and reducing latency by 75%. The fourfold increase in total throughput is made possible by higher spectral efficiency.

 

The main feature in Wi-Fi 6 (802.11ax) is a digital modulation technology called OFDMA (Orthogonal Frequency Division Multiple Access), which works similarly to the combination of cellular and Wi-Fi technology. It provides better spectrum utilization, better power control to avoid interference and enhancements such as 1024-QAM, MIMO and MU-MIMO for faster speeds. There are also reliability improvements such as lower power consumption and security protocols such as target wake-up time and WPA3.

 

Fig. 1. The concept of Wi-Fi 5 and Wi-Fi 6 transmission

 

With OFDMA, multiple clients are assigned to different individual resources in the available spectrum. In this way, the 80 MHz channel can be divided into multiple resource units, so that multiple clients simultaneously receive different types of data in the same spectrum.

 

To support OFDMA, the 802.11ax standard needs four times more subcarriers than the 802.11ac standard. Specifically, for channels 20, 40, 80 and 160 MHz, the 802.11ax standard has 256, 512, 1024 and 2048 subcarriers respectively. Since the available bandwidths have not changed and the number of subcarriers has quadrupled, the subcarrier spacing decreases by the same factor. This introduces OFDM symbols, which are four times longer. In the 802.11ac standard, the transmission of an OFDM symbol takes 3.2 microseconds. In 802.11ax, it takes 12.8 microseconds (times given in both cases without guard breaks - OFDMA guard break times can be dynamically adjusted depending on radio conditions).

 

Wi-Fi 6 (802.11ax) introduces several key improvements over 802.11ac. It supports frequency bands from 1 GHz to 6 GHz. Therefore, unlike 802.11ac, 802.11ax also operates in the unlicensed 2.4 GHz band. Wi-Fi 6E introduces operation at or near 6 GHz and super-wide 160 MHz channels. The frequency ranges that these channels can occupy and the number of channels depends on the country in which Wi-Fi 6 operates.

 

Transmission speeds for individual bands:

 

Protocol Frequency [GHz] Bandwidth [MHz] Streaming speed [Mbps] MIMO streams allowed Modulation type Indoor range [m] Outdoor range [m]
802.11ax
(Wi-Fi 6,
Wi-Fi 6E) 		2.4, 5, 6 20
40
80
80 + 80 		Up to 1147
Up to 2294
Up to 4804
Up to 9608 		8 UL/DL
MU-MIMO
OFDMA
(1024-QAM) 		~30 ~120

Key features that distinguish the 802.11ax standard from 802.11ac:

 

Feature 802.11ac 802.11ax Description
OFDMA Not available Centrally controlled medium access with dynamic allocation. The bandwidth occupied by a single OFDMA transmission is in the range from 2.03125 MHz. Bandwidth 80 MHz. OFDMA segregates spectrum in time and frequency resource units (RUs. A central coordinating unit (802.11ax access point) allocates RU for reception or transmission to associated stations. By centrally scheduling RUs, contention overhead can be avoided, improving performance in dense deployment scenarios.
Multi-user MIMO (MU-MIMO) Available in downlink direction Available in downlink and uplink directions OFDMA splits receivers into different resource units (RUs) in the case of MU-MIMO, devices are split into different spatial streams. In 802.11ax, MU-MIMO and OFDMA can be used simultaneously. To enable MU uplink transmissions, the AP transmits a new control frame (Trigger), which contains scheduling information (RU allocations for stations, modulation and coding scheme (MCS) to be used for each station). In addition, the Trigger also ensures that the uplink transmission is synchronized, as the transmission starts SIFS after the Trigger has finished.
Trigger-based random access Not available It enables UL OFDMA transmission to be carried out by stations that have not been directly assigned RUs (resource units). In the trigger frame, the AP specifies the scheduling information for the next UL MU transmission. However, several RUs may be assigned to random access. Stations not directly assigned RUs may make transmissions within the RUs assigned to random access. In order to reduce the probability of collisions (i.e. situations where two or more stations choose the same RU for transmission), an amendment to the 802.11ax standard specifies a special OFDMA withdrawal procedure. Random access is beneficial for sending buffer status reports when the AP has no information about pending UL traffic at the station.
Reuse of spatial frequency Not available Coloring enables devices to distinguish transmissions in their own network from those in neighboring networks. Adaptive power and sensitivity thresholds allow dynamic adjustment of transmit power and signal detection threshold to increase space reuse. Without the possibility to reuse space, devices refuse to transmit simultaneously with transmissions in progress in other, neighboring networks. With basic service set coloring (BSS coloring), the transmission helps surrounding devices to decide whether simultaneous use of the wireless medium is allowed. A station can declare the wireless medium free and start a new transmission even if the detected signal level from the neighboring network exceeds the detection threshold of the existing signal, provided that the transmission power of the new transmission is reduced accordingly.
NAV (band sampling) Single NAV Two NAVs In dense deployment scenarios, the NAV set by a frame originating from one network can easily be reset by a frame originating from another network, leading to abnormal behaviour and collisions. To avoid this, each 802.11ax station will maintain two separate NAVs - one NAV is modified by frames originating from the network with which the station is associated, the other NAV is modified by frames originating from overlapping networks.
Target Wake Time (TWT) Not available TWT reduces energy consumption and competition for access to the medium. TWT is a concept developed from the 802.11ah standard. It allows devices to be woken up during periods other than the beacon transmission period. In addition, the access point can group devices into different TWT periods, thus reducing the number of devices competing simultaneously for the wireless medium.
Fragmentation Static fragmentation Dynamic fragmentation In the case of static fragmentation, all fragments of the data packet are of equal size except for the last fragment. In the case of dynamic fragmentation, the device can fill the available RUs with other transmission possibilities up to the available maximum duration. Thus, dynamic fragmentation helps to reduce the load.
Guard interval duration 0.4, 0.8 µs 0.8, 1.6, 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.