What is 802.11ax (Wi-Fi 6)?

802.11ax is an IEEE draft amendment that defines modifications to the 802.11physical layer (PHY) and the medium access control (MAC) sublayer for high-efficiency operation in frequency bands between 1 GHz and 6 GHz. The technical term for an 802.11ax is High Efficiency (HE).

Past amendments defined 802.11 higher data rates and wider channels but did not address efficiency. The bulk of 802.11 data frames (75-80%) are small and under 256 bytes. The result is excessive overhead at the MAC sublayer and medium contention overhead for each small frame. Higher data rates and wider channels are not the goals of 802.11ax. The goal is better and more efficient 802.11 traffic management. Another goal is to increase the average throughput of 4X per user in high-density WLAN environments.

The IEEE is currently scheduled to ratify the 802.11ax amendment in Q1 2021. However, WLAN vendors have already released 802.11ax products before the ratification of the amendment. Extreme Networks has an entire family of 802.11ax APs, with more on the way in 2021. The Wi-Fi Alliance began certifying 802.11ax technology in August 2019 with a new certification called Wi-Fi CERTIFIED 6.

Recently the Wi-Fi Alliance adopted a new generational naming convention for Wi-Fi technologies. The goal is that the new naming convention will be easier to understand for the average consumer than the alphabet-soup naming used by the IEEE. Because 802.11ax technology is such a significant paradigm shift from previous versions of 802.11 technology, it has been bestowed with the generational name of Wi-Fi 6. 802.11ax and Wi-Fi 6 mean the same thing. Still, the term Wi-Fi 6 will be more prevalent with the general population. The Wi-Fi Alliance’s Wi-Fi CERTIFIED 6 certification for the technology is also called Wi-Fi 6.

Unlike 802.11ac, which operates in 5 GHz only, 802.11ax radios can transmit and receive either the 2.4 GHz or 5 GHz frequency bands. In the future, 802.11ax technology will also be available in the 6 GHz band as part of Wi-Fi 6E.

Yes, 802.11ax radios are able to communicate will legacy 802.11a/b/g/n/ac radios. 802.11ax radios communicate with other 802.11ax radios using OFDMA and/or OFDMA. 802.11ax radios communicate with legacy radios using OFDM or HR-DSSS. When 802.11ax-only OFDMA conversations are occurring, RTS/CTS mechanisms are used to defer legacy transmissions.

Although Wi-Fi is a resilient technology, it has not necessarily been efficient. Wi-Fi operates at both layer one and layer two of the OSI model, and the inefficiency exists at both layers.

Historically, previous 802.11 amendments defined technologies that gave us higher data rates and wider channels but did not address efficiency. An often-used analogy is that faster cars and bigger highways have been built, but traffic jams still exist. Despite the higher data rates and 40/80/160 MHz channels used by 802.11n/ac radios, multiple factors contribute to the Wi-Fi traffic congestion, which does not provide efficient use of the medium.

That leads us to a Wi-Fi traffic jam. 802.11 data rates are not TCP throughput. Always remember that radio frequency (RF) is a half-duplex medium and that the 802.11 medium contention protocol of CSMA/CA consumes much of the available bandwidth. In laboratory conditions, TCP throughput of 60 to 70 percent of the operational data rate can be achieved using 802.11n/ac communication between one access point (AP) and one client. The aggregate throughput numbers are considerably less in real-world environments with the active participation of multiple Wi-Fi clients communicating through an AP. As more clients contend for the medium, the medium contention overhead increases significantly, and efficiency drops. Therefore, the aggregate throughput is usually at best 50 percent of the advertised 802.11 data rate.

Wi-Fi 6 (802.11ax) technology is all about better and more efficient use of the existing radio frequency medium. Higher data rates and wider channels are not the goals of Wi-Fi 6. The goal is better and more efficient 802.11 traffic management. Most of the Wi-Fi 6 enhancements are at the PHY layer and involve a new multi-user version of OFDM technology instead of the single-user OFDM technology already used by 802.11a/g/n/ac radios. Another significant Wi-Fi 6 change is that an access point (AP) can supervise both downlink and uplink transmissions to multiple client radios while the AP controls the medium. In addition to these multi-user efficiency enhancements, Wi-Fi 6 (802.11ax) radios will be backward compatible with 802.11/a/b/g/n/ac radios. Please note that unlike 802.11ac radios, which can transmit only on the 5 GHz frequency band, 802.11ax radios can operate on both the 2.4 GHz and 5 GHz frequency bands.

802.11ax APs do not improve the performance or range of any legacy Wi-Fi clients (802.11a/b/g/n/ac). 802.11ax clients are needed to take full advantage of 802.11ax high-efficiency capabilities such as multi-user OFDMA. While there are no PHY improvements with legacy clients, performance improvements can be improved due to newer hardware capabilities of the new 802.11ax access points, such as stronger CPUs, better memory handling, and other standard hardware advancements. However, as we see more 802.11ax clients mixed into the client population, the efficiency improvements gained by 802.11ax client devices will free valuable airtime for those older clients, therefore improving the system’s overall efficiency.

Broadcom manufactures 70% of client radios. Wi-Fi 6 clients have already entered the marketplace, and with Wi-Fi 6 as the new default client population explosion is coming soon. All the major chipset vendors such as Broadcom, Qualcomm, and Intel are manufacturing 2×2:2 Wi-Fi 6 radios that will find their way into smartphones, tablets, and laptops. Samsung released the Galaxy S10, the first Wi-Fi 6 smartphone, into the market in February of 2019, but the iPhone 11 and lower contain Wi-Fi 6. All iPads but the lowest-end iPad (7th generation) and iPad mini also support Wi-Fi 6. At the end of 2020, Apple’s newest laptops and desktop with Apple Silicon also include Wi-Fi 6 on the Mac for the first time.

Intel has announced 100s of new Wi-Fi products Industry analysts all agree that the Wi-Fi 6 technology growth will be fast and furious. Several analysts already are predicting 1 billion Wi-Fi 6 chipsets will ship annually by 2022.

802.11ax APs have faster processors and provide future-proofing as 802.11ax clients find their way into the marketplace. If you are choosing between buying a new 802.11ax or 802.11ac, there is no reason to deploy the older technology. Even if your devices don’t include Wi-Fi 6 today, your next purchase will include it.

The term multi-user (MU) simply means that transmissions between an AP and multiple clients can occur simultaneously depending on the supported technology. However, MU terminology can be very confusing when discussing 802.11ax. MU capabilities exist for both OFDMA and MU-MIMO.

Orthogonal Frequency Division Multiple Access (OFDMA) a multi-user version of the OFDM digital modulation technology. 802.11a/g/n/ac radios currently OFDM for single-user transmissions on an 802.11 frequency. OFDMA subdivides a channel into smaller frequency allocations called resource units (RUs). By subdividing the channel, parallel transmissions of small frames to multiple users happen simultaneously. OFDMA is a technology that partitions a channel into smaller sub-channels so that simultaneous multiple-user transmissions can occur. For example, a traditional 20 MHz channel might be partitioned into many as nine smaller channels. Using OFDMA, an 802.11ax AP could simultaneously transmit small frames to nine 802.11ax clients. Initially, the Wi-Fi Alliance will be testing for simultaneous transmissions of four RUs using OFDMA on both the downlink and the uplink. OFDMA is a much more efficient use of the medium for smaller frames. The simultaneous transmission cuts down on excessive overhead at the MAC sublayer as well as medium contention overhead.

When subdividing a 20 MHz channel, The AP can designate 26, 52, 106, and 242 subcarrier Resource Units(RUs), which equates roughly to 2 MHz, 4 MHz, 8 MHz, and 20 MHz channels. The 802.11ax AP dictates how many RUs are used within a 20 MHz channel, and different combinations can be used. For example, a Wi-Fi 6 access point could simultaneously communicate with one 802.11ax client using 8 MHz of frequency space while communicating with two other 802.11ax clients using 4 MHz sub-channels.

Both! The AP coordinates OFDMA transmissions both downstream and upstream using a trigger frame mechanism. For the first time in 802.11 technology, an access point can coordinate upstream client transmissions. The AP uses a trigger frame to allocate client resource units (RUs) and set transmit timing for each client.

No! Do not confuse OFDMA with MU-MIMO. OFDMA allows for multiple-user access by subdividing a channel. MU-MIMO allows for multiple-user access by using different spatial streams. Access points send unique steams of data to multiple clients simultaneously. The 802.11ax standard also provides for the combined use of MU-MIMO and OFDMA, but it is not expected to be widely implemented.

Wi-Fi 6 radios also support a secondary multi-user technology called multiple-input multiple-output (MU-MIMO). Much like OFDMA, MU-MIMO allows multiple user communications downlink from an access point (AP) to numerous clients during the same transmission opportunity (TXOP). However, instead of partitioning the frequency space, MU-MIMO instead takes advantage of the fact that APs have multiple radios and antennas. A MU-MIMO access point transmits unique modulated data streams to multiple clients simultaneously. The goal is to improve efficiency by using less airtime.

Downlink MU-MIMO was first introduced in the second generation of 802.11ac radios. However, very few MU-MIMO-capable 802.11ac (Wi-Fi 5) clients currently exist in the marketplace, and the technology has rarely been used in the enterprise.

A critical difference between Wi-Fi 5 (802.11ac) MU-MIMO and Wi-Fi 6 MU-MIMO is how many MU-MIMO clients communicate with an AP at the same time. Wi-Fi 5 is limited to a MU-MIMO group of only four clients. Wi-Fi 6 is designed to support up to 8×8:8 MU-MIMO in both downlink and uplink, which allows it to serve up to eight users simultaneously and provide significantly higher data throughput.

Downlink MU-MIMO will be available in Wi-Fi 6 radios. Support for uplink MU-MIMO is not supported in the first generation of Wi-Fi 6 radios.

Most industry experts believe that OFDMA is the most relevant technology that 802.11ax offers. Downlink MU-MIMO was introduced with Wave-2 802.11ac access points. However, real-world implementation of MU-MIMO for indoor environments is rare:

• Hardly any MU-MIMO capable 802.11ac clients exist in the current marketplace, and the technology is rarely used in the enterprise. However, 802.11ax clients will support downlink MU-MIMO.
• MU-MIMO requires spatial diversity. Therefore the physical distance between the clients is necessary. Most modern-day enterprise deployments of Wi-Fi involve a high density of users that is not conducive for MU-MIMO conditions.
• Because MU-MIMO requires spatial diversity, a sizable distance between the clients and the AP is necessary. Most modern-day enterprise deployments of Wi-Fi involve a high density of users that is not conducive for MU-MIMO conditions.
• MU-MIMO requires transmit beamforming (TXBF), which requires sounding frames. The sounding frames add excessive overhead, especially when the bulk of data frames are small.
• MU-MIMO would only be a favorable option in very low density, high bandwidth environments.

If all things were equal, a quick comparison of potential benefits from each technology:

A very good use case for MU-MIMO is a point-to-multipoint (PtMP) bridge links between buildings. The spatial diversity that is required for MU-MIMO exists in this type of outdoor deployment.

In theory, BSS color can provide the capability to take advantage of 80 MHz channels. However, this is assuming no legacy devices exist. In reality, designing for 20 MHz channels is still the best practice. If deploying 40 MHz channels in the 5 GHz frequency band, design best practices remain the same:

• Only use if DFS channels are available.
• Thick walls
• Low transmit power

Okay, there is always an exception. 802.11ax radios support 1024-QAM modulation, which will also mean some new Modulation and code schemes (MCS) that define some higher data rates. Much like 256-QAM, very high SNR thresholds (~ 35 dB) will be needed for 802.11ax radios to use 1024-QAM modulation. Pristine RF environments with a low noise floor and close proximity between an 802.11ax AP and 802.11ax client are required.

802.11ax also includes Target Wake Time (TWT) that can be very useful for IoT devices. The TWT has first proposed under 802.11h. TWT uses negotiated policies based on expected traffic activity between 802.11ax clients and an 802.11ax AP to specify a scheduled wake time for each client. 802.11ax IoT clients could potentially sleep for hours and conserve battery life.

BSS Color (also referred to as BSS Coloring) is a method for addressing medium contention overhead due to overlapping basic service set (OBSS). BSS color aims to uniquely identify different BSSs even though they are transmitting on the same channel. 802.11ax radios can differentiate between BSSs by adding a number (color) to the PHY and MAC headers. The same color bit indicates an intra-BSS. Different color bits indicate inter-BSS. Inter-BSS detection means that a listening radio may not necessarily have to defer. Adaptive CCA implementation could raise the signal detect (SD) threshold for inter-BSS frames while maintaining a lower threshold for intra-BSS traffic. BSS Color potentially decreases the channel contention problem resulting from existing 4 dB signal detect (SD) thresholds.

Some WLAN vendors offer an 8×8:8 access point using a non-Broadcom chipset. It supports eight 5 GHz streams and four 2.4 GHz streams. Some key points should be understood about 8×8:8 APs versus 4×4:4 802.11ax APs:

• 8×8:8 APs are more expensive and require more power. The main advantage of 8×8:8 AP is to take advantage of MU-MIMO capabilities, which 802.11ax clients will need to support. Regardless of stream count, all APs will support the same number of 802.11ax OFDMA clients. There is no real advantage with an 8×8:8 AP over a 4×4:4 when using the OFDMA technology.
• Extreme APs use a Broadcom chipset. The chipset provides for a 4×4:4 2.4 GHz radio and a 4×4:4 5 GHz radio. However, one of the radios is an adaptive software-selectable radio (SSR), meaning you can have two dual-5 GHz 4×4:4 802.11ax radios in a single AP. Almost all of the Extreme 802.11ax APs have software-selectable radios (SSRs) that allows for dual 5 GHz functionality.
• Extreme has been a leader in dual 5 GHz technology. Two dual-5 GHz 4×4:4 802.11ax radios transmitting on two separate 5 GHz, 20 MHz channels will provide better performance and efficiency. The competitor’s AP 8X8:8 radio transmits on a single 5 GHz/20 MHz channel and a single 2.4 GHz/20MHz channel.

Let’s look at this historically:

• 802.11n: Claims were made in 2009 that we were going to need aggregate GbE ports with two cables when 802.11n debuted. Did not happen.
• 802.11ac: Claims were made in 2013 that we were going to need aggregate GbE ports with two cables when 802.11ac Did not happen.
• 802.11ac – Wave 2: When the second generation of 802.11ac chipsets debuted in 2016, several enterprise switch vendors made claims that everyone needed to upgrade their switches to support 2.5 GbE uplinks with 802.3bz MultiGig technology. That Did not happen.

Will we need 2.5 GbE or 5 GbE ports for 802.11ax? The whole point of Wi-Fi 6 (802.11ax) is better spectrum efficiency and a reduction in airtime consumption. Logic dictates that if Wi-Fi becomes more efficient, the user traffic generated by a dual-frequency Wi-Fi 6 AP could exceed 1 Gbps. The fear is that a standard Gigabit Ethernet wired uplink port could be a bottleneck, and therefore 2.5 Gbps uplink ports will be needed. As a precaution, WLAN vendors’ Wi-Fi 6 APs will include at least one 802.3bz Multi-Gig Ethernet port capable of a 2.5 or 5 Gbps wired uplink. Think of this as future-proofing.

Before Wi-Fi 6 (802.11ax), the only time a 1 Gbps uplink has not been sufficient is in laboratory test environments or unique corner cases. Bandwidth bottlenecks rarely occur at the access layer. However, bandwidth bottlenecks can certainly happen on the wired network due to poor wired network design. The number one bandwidth bottleneck is usually the WAN uplink at any remote site.

Although past gloom and doom predictions of access-layer bottlenecks have not come true, as Wi-Fi 6 client populations grow and as WLAN vendors add tri-band radios into their APs, 1 GbE uplinks may no longer be sufficient, although historically, 1 Gbps uplinks have been more than enough, eventually, at least 2.5 Gbps uplinks and maybe 5 Gbps uplinks may be needed. Any vendor claims that 10 Gbps uplinks will be required are fantasy.

Wi-Fi 6 brings several crucial wireless enhancements for IT administrators when compared to Wi-Fi 5. The first significant change is using 2.4 GHz. Wi-Fi 5 was limited to only using 5 GHz. While 5 GHz is a ‘cleaner’ band of RF, it doesn’t penetrate walls and 2.4 GHz and requires more battery life. For Wi-Fi driven IoT devices, 2.4 GHz will likely continue to be the band of choice for the foreseeable future.

Another critical difference between the two standards is the use of OFDMA and MU-MIMO. Wi-Fi 5 was limited to downlink only on MU-MIMO, where Wi-Fi 6 includes downlink and uplink. OFDMA, as referenced above, is also only available in Wi-Fi 6.

Extreme 802.11ax APs use the Broadcom chipset.

• Support for four streams of 802.11ax
• 4.8 Gbps PHY rate
• 160 MHz channel bandwidth
• 1024 QAM modulation
• Uplink & downlink OFDMA
• MU-MIMO
• BSS Color
• Target Wake Time
• ZeroWait DFS
• AirIQ interference identification
• Full compliance with IEEE 802.11ax specifications
• Wi-Fi CERTIFIED 6 by the Wi-Fi Alliance

5G is an exciting technology, and it will take its place as the next evolution of licensed technology and not as an all-encompassing technology to replace other wireless solutions. 5G, LTE, P-LTE, CBRS, Wi-Fi, BLE, and even the evolving ultra-wideband (UWB) will have a seat at the table supporting multiple wireless use cases.

It’s not a replacement for Wi-Fi, though. When advocates for 5G discuss it becoming the replacement of Wi-Fi, the focus is always on comparing speeds. They neglect to consider all the existing devices, the cost of replacement, and common sense. At best, 5G will only augment existing Wi-Fi networks.