What is WiFi 6 (802.11ax)?

WiFi 6 (Wi-Fi 6), also known as 802.11ax, is the latest generation of the Wi-Fi industry standard following Wi-Fi 5 (802.11ac). Prior to the release of Wi-Fi 6, Wi-Fi standards were identified by version numbers, from 802.11b to 802.11ac. As Wi-Fi standards evolve, the Wi-Fi Alliance has chosen to rename Wi-Fi using numerical numbers to make it easier for Wi-Fi users and device manufacturers to understand Wi-Fi standards.
Wi-Fi 6 introduces new technologies such as OFDMA, uplink/downlink MU-MIMO, BSS Coloring, and TWT, resulting in a significant performance improvement. The bandwidth and number of concurrent users are increased by four times compared to Wi-Fi 5, while also offering lower latency and greater energy efficiency.

What problems does Wi-Fi 6 solve?

Wi-Fi 6 was designed from the outset to address high-density wireless access and high-capacity wireless services, such as those found in large outdoor public venues, high-density stadiums, high-density indoor wireless offices, and e-classrooms.

In these scenarios, the number of client devices connecting to Wi-Fi networks will increase dramatically. Furthermore, the ever-increasing volume of voice and video traffic will also place demands on Wi-Fi networks. It's well known that 4K video streaming (requiring 50 Mbps per user), voice streaming (latency less than 30ms), and VR streaming (requiring 75 Mbps per user and latency less than 15ms) are highly sensitive to bandwidth and latency. If network congestion or retransmissions cause transmission delays, the user experience will be significantly impacted.

While existing Wi-Fi 5 (802.11ac) also offers high bandwidth capabilities, its throughput performance is reaching a bottleneck as access density continues to increase. Wi-Fi 6, by introducing new technologies like OFDMA and uplink/downlink MU-MIMO, delivers a significant performance boost, quadrupling bandwidth and concurrent users compared to Wi-Fi 5, while also reducing latency. For example, in an electronic classroom, large lectures with over 100 students previously presented significant challenges in transmitting video and ensuring uplink and downlink interactions. Wi-Fi 6 networks can easily handle these scenarios.

Wi-Fi 6 vs Wi-Fi 5

Wi-Fi 6 Core Technologies

The following are the core technologies of Wi-Fi 6.

1. OFDMA Frequency Division Multiplexing Technology
Prior to Wi-Fi 6, data transmission used the OFDM mode, in which users were distinguished by time segments. In each time segment, a user fully occupied all channel resources and sent a complete data packet.

Wi-Fi 6 introduces a more efficient data transmission mode called OFDMA (also known as MU-OFDMA because Wi-Fi 6 supports uplink and downlink multi-user mode). This mode multiplexes channel resources by allocating subcarriers to different users and adding multiple access to the OFDM system. This mode has been adopted by many wireless technologies, such as 3GPP LTE. In this mode, a single user no longer monopolizes a full subcarrier; instead, multiple users share channel resources, improving spectrum efficiency.

2. Uplink/Downlink MU-MIMO Technology
MU-MIMO leverages spatial diversity in the channel to transmit independent data streams within the same bandwidth. Unlike OFDMA, all users use the full bandwidth, resulting in multiplexing gains. Due to the size limitations of the number of antennas, terminals typically have only one or two spatial streams (antennas), which is fewer than the number of spatial streams (antennas) available on an AP. Therefore, the introduction of MU-MIMO technology in APs allows simultaneous data transmission between the AP and multiple terminals, significantly improving throughput.

MU-MIMO was introduced in Wi-Fi 5, but only supported 4x4 MU-MIMO in the downlink. Wi-Fi 6 further increases the number of MU-MIMO channels, supporting 8x8 MU-MIMO in both uplink and downlink.

3. Spatial Division Multiplexing (SR) and BSS Coloring
802.11ax introduces a new mechanism for identifying co-channel transmissions, called BSS Coloring. This mechanism adds a BSS color field to the PHY header to "color" data from different BSSs. Each channel is assigned a color, which identifies a Basic Service Set (BSS) that should not interfere. This allows the receiver to identify co-channel interference signals early and stop receiving, avoiding wasted transceiver time. If the colors are the same, they are considered interference signals within the same BSS, and transmission will be delayed. If the colors are different, there is no interference, and the two Wi-Fi devices can transmit concurrently on the same channel and frequency. In a network designed this way, channels with the same color are far apart, making these signals insensitive, thus achieving spatial reuse.

4. Target Wake Time (TWT)
Target Wake Time (TWT) is another important resource scheduling feature supported by 802.11ax, borrowed from the 802.11ah standard. It allows devices to negotiate when and how often they will wake up to send or receive data. Furthermore, Wi-Fi APs can group client devices into different TWT cycles, reducing the number of devices competing for the wireless medium simultaneously after waking up. TWT also increases device sleep time, significantly improving battery life for battery-powered devices.

5. Higher-order modulation technology (1024-QAM)
The primary goals of the Wi-Fi 6 standard are to increase system capacity, reduce latency, and improve efficiency in high-density multi-user scenarios. However, greater efficiency and faster speeds are not mutually exclusive. Wi-Fi 5 uses 256-QAM quadrature amplitude modulation, transmitting 8 bits of data per symbol. Wi-Fi 6 will use 1024-QAM quadrature amplitude modulation, transmitting 10 bits of data per symbol. This improvement from 8 to 10 is 25%, meaning that Wi-Fi 6's single spatial stream data throughput is increased by another 25% compared to Wi-Fi 5.

6. Support for the 2.4 GHz Band
We all know that the 2.4 GHz band has a narrow bandwidth and only three 20 MHz non-interfering channels (1, 6, and 11). It has been abandoned in the Wi-Fi 5 standard. However, it is undeniable that 2.4 GHz remains a viable Wi-Fi band and is still widely used in many scenarios. Therefore, the Wi-Fi 6 standard continues to support 2.4 GHz to fully utilize the unique advantages of this frequency band. 7. Improved Coverage
Because the Wi-Fi 6 standard utilizes the Long OFDM Symbol transmission mechanism, the duration of each data transmission is increased from 3.2μs to 12.8μs. This longer transmission time reduces the packet loss rate for terminals. Furthermore, Wi-Fi 6 can utilize a minimum bandwidth of only 2MHz for narrowband transmission, effectively reducing frequency band noise interference, improving terminal reception sensitivity, and increasing coverage distance.