Wi-Fi 101 — Wi-Fi 6E In-Depth
Originally Posted: October 17th, 2020
Last Edited: February 14th, 2021
Wi-Fi 101 — Wi-Fi 6E In Depth
What is Wi-Fi 6E?
Wi-Fi 6E is Wi-Fi 6 extended into the newly unlocked 6 GHz spectrum.
On April 23, 2020 the United States FCC voted to allow the unlicensed use of the 6 GHz band. This added 1200 MHz of spectrum (5.925 to 7.125 GHz) for devices like Wi-Fi access points. Previously, devices operating in this band had to be licensed, which prevented use by the general public. This added spectrum is arguably the biggest change in wireless networking since the original 802.11 standard came out in 1997, or the original allocation of the ISM bands in 1985.
For perspective, there is only 260 MHz of unrestricted spectrum available in other bands. The exact channels available vary by region, but without getting bogged down in specifics:
- 80 MHz unrestricted in the 2.4 GHz ISM band.
- 180 MHz unrestricted in the 5 GHz band.
- 500 MHz requiring Dynamic Frequency Selection (DFS) in the 5 GHz band.
- DFS channels require an access point to continuously monitor for the presence of weather or military radar signals. Wi-Fi access points using DFS channels are required to back off to avoid interference. Due to this, DFS channels are often either not supported or not used.
This limited amount of contiguous spectrum makes it difficult to enable wider 80 MHz or 160 MHz channels, and can cause channel re-use and interference. The 6 GHz spectrum allows for any combination of the following:
- 59 additional 20 MHz channels.
- 29 additional 40 MHz channels.
- 14 additional 80 MHz channels.
- 7 additional 160 MHz channels.
- 3 potential 320 MHz channels, due to be included in the 802.11be (Wi-Fi 7) standard.
What Is 6 GHz Used For Currently?
Wi-Fi 101 — Wi-Fi 6E In-Depth
The 6 GHz band is in use by many licensed services. In the US, there are 47,695 unique uses between 5.925 and 7.125 GHz. Namely fixed point-to-point radios, fixed satellite service (FSS), broadcast auxiliary service (BAS), and cable television relay services (CARS).
An incomplete list of services using 6 GHz:
- Communication to geostationary satellites.
- Police and fire dispatch services.
- Management of electric grids.
- Control of natural gas and oil pipelines.
- Coordination of railroad train movements.
- Fixed wireless backhaul by service providers like AT&T and Verizon.
- Mobile TV stations and video relay from remote locations.
- Radio Astronomy.
- Portable cameras and wireless microphones.
- Long-distance telephone service.
- Ultra-wideband systems.
Automated Frequency Coordination (AFC) is the New DFS
In the US, the 6 GHz band is broken down into the U-NII-5, U-NII-6, U-NII-7 and U-NII-8 sub bands, with different rules for each.
Indoors, the full 1200 MHz is unrestricted and can be used by normal Wi-Fi networks without concern for those existing services. This is due to the nature of radio transmissions in the 6 GHz rapidly attenuating. In the vast majority of situations, indoor 6 GHz devices won’t be able to detect outdoor radio transmissions. Low-power indoor 6 GHz devices will use the existing CSMA/CA protocol to provide medium access fairness and coordinate wireless transmissions.
Outdoor use of 6 GHz is a little more complicated. Only the U-NII-5 and U-NII-7 sub bands can be used. Due to the large amount of critical infrastructure running in the 6 GHz band, Wi-Fi 6E devices operating outdoors will need to implement Automated Frequency Coordination (AFC). This is similar to how 5 GHz devices using DFS channels need to monitor for radar, and defer to their use of the channel. AFC works by having 6 GHz wireless networking equipment connect to a cloud-based AFC database to report their position. The AFC database would determine the risks of interference with incumbent services and assign a specific channel to the AP.
What Does Wi-Fi 6E Give Us?
TL;DR: Higher capacity, higher speeds, and lower latency.
The only devices that will be able to operate in the 6 GHz spectrum are devices that are based on the Wi-Fi (802.11ax) standard. Unlike every other Wi-Fi standard, there is no backwards compatibility for the 6 GHz band.
To be clear:
- Wi-Fi 6E client devices will be able to join and use legacy 2.4 GHz and 5 GHz networks.
- Devices supporting Wi-Fi 6 and older standards will not be able to operate in the 6 GHz band.
- Most Wi-Fi 6E networks will be dual or tri-band, allowing older clients to connect using the old spectrum, while exclusively allowing 6E clients to operate over 6 GHz.
The lack of backward compatibility is a feature, not a bug. This will limit usage of 6 GHz until Wi-Fi 6E devices are more common, but it provides a lot of benefits. Every Wi-Fi 6E device will support Wi-Fi 6 technologies like OFDMA and Target Wake Time, making transmissions more efficient. OFDMA requires all devices participating in the transmission to be synchronized. Time, frequency, and power must all be synchronized between the AP and client. OFDMA only becomes fully effective when all client devices and access points use it.
Older Wi-Fi generations like 802.11n and 802.11ac were based on OFDM modulation, where each channel was fully reserved to a single user for each transmission. In contrast, OFDMA divides the channel into sub-channels, also known as Resource Units (RU). This allows multiple users to communicate simultaneously, rather than waiting for their turn. Each time a Wi-Fi 5 or older device transmits in a Wi-Fi 6 network, the transmission reverts back to standard OFDM with a single transmission occupying the entire spectrum. Flipping back and forth between OFDM and OFDMA degrades the network for everyone, especially Wi-Fi 6 devices. Things get even slower when older, low data rate devices supporting 802.11b or 802.11g are in the mix.
Going forward, Wi-Fi 6E devices will be a lot less of a drag on 6 GHz networks than legacy devices are on current 2.4 and 5 GHz networks. Until now, Wi-Fi standards have always been backward compatible with previous standards. This allows older and newer devices to interoperate, but restricts overall data throughput to the rates supported by the slowest devices. Legacy devices such as 802.11b/g/n require more airtime to transmit data, increasing latency and reducing throughput for all users. This policy towards always supporting old standards is a great benefit and strength of Wi-Fi. Unfortunately it can also impair the performance of even the highest-end Wi-Fi 6 devices using the 2.4 GHz and 5 GHz bands.
Taken as a whole, the 6 GHz band will allow for more ubiquitous usage of the required aspects of high performance wireless transmissions. All 6 GHz transmitters and receivers will include all the advances in Wi-Fi 6, including wide channels, 1024-QAM modulation, and OFDMA. 6 GHz will provide a cleaner RF environment with less interference, with less issues caused by adjacent or overlapping channel interference. The same policies that guide Wi-Fi network design will still apply, but this big chunk of new spectrum will allow for more design flexibility, better performance, and a better experience for everyone.
Potential Problems with Wi-Fi 6E
If the rollout of Wi-Fi 6E is anything like Wi-Fi 6, early devices will likely skip optional features, or have non-working implementations of key technologies like OFDMA. Small Net Builder has a few great articles about the current state of Wi-Fi 6 OFDMA. That same dynamic will likely apply to early Wi-Fi 6E devices. The earliest Wi-Fi 6E devices may not fully comply with the standard, may not implement every feature, and may not perform as expected.
Another potential issue is all the design, testing, and validation that will be required. Wi-Fi 6E brings a lot of new engineering challenges for network operators and device manufacturers. Existing Wi-Fi components and equipment used for design and manufacturing are optimized for frequencies below 6 GHz. Retooling for support up to 7.125 GHz will require changes to antenna design, manufacturing, and validation. Devices will need to be calibrated and tested up to the highest frequencies to ensure that they can generate the expected power levels.
Wi-Fi 6E devices will likely be dual or tri-band, complicating heat dissipation and power management for the multiple bands and MIMO streams to coexist. Proper band isolation will need to be developed and tested to avoid interference within the device. More coexistence testing will need to be done, and multiple bands need to be tested simultaneously. All of these things increase complexity. Even well-engineered Wi-Fi 6E devices are likely going to be power hungry, increasing PoE requirements for access points and limiting battery life on mobile devices.
Another potential issue relates to the scanning and probing that Wi-Fi devices perform when looking for an access point to join. With 1200 MHz to cover and 59 potential 20 MHz channels to scan, a client would require around 6 seconds to complete a passive scan of the entire band. This would cause many roaming and association issues, so the IEEE proposed a fast passive scanning method using a reduced set of channels called Preferred Scanning Channels (PSC). PSCs are a set of fifteen 20 MHz channel spaced every four channels (80 MHz) apart. Passive scanning of these fifteen PSCs reduces the total scan time to the more manageable 1.5 seconds. This is yet another feature of Wi-Fi 6E that will need to be developed, tested, and perfected.
A lot of Wi-Fi 6 and Wi-Fi 6E features sound great on paper, but come with compromises. For example, wider channel widths cause network design challenges, and often run into physical limits. A wider channel requires more OFDMA data carriers being transmitted and received simultaneously. An 80 MHz channel has 996 sub-carriers, while 160 MHz channel has twice that. In a wide channel, the SNR per carrier is reduced, and requires higher signal strength for a successful transmission. Saturating a wide channel with Wi-Fi 6E devices will be hard to do in practice, especially since a lot of this complexity is being pushed onto device manufacturers. Just like with current devices, it will only take one poorly designed Wi-Fi 6E device or one bad actor to limit everyone’s performance. That’s the unavoidable nature of using a shared medium like Wi-Fi.
When Can We Expect Wi-Fi 6E? Should I Wait?
At first, Wi-Fi 6E was a US-only affair. In July 2020, Ofcom voted to allow 500 MHz of the 6 GHz band in the UK. In October 2020, MSIT voted to allow 6 GHz use in South Korea.
There’s no official timeline for when regulators around the world will make the spectrum available for unlicensed use. Wi-Fi 6E has no definitive release date in most countries. In the US, Wi-Fi 6E devices will probably start appearing in 2021 and become more common heading into 2022.
During CES 2020, Broadcom announced several system-on-a-chip products that router manufacturers can purchase to create Wi-Fi 6E devices. Qualcomm also has Wi-Fi 6E chipsets available. Intel announced that it will have WI-Fi 6E chips available in January 2021. The Wi-Fi Alliance plans to have their Wi-Fi 6E certification ready by early 2021, but devices using a draft Wi-Fi 6E certification may be out before then.
Wi-Fi 6E should be a big improvement for high-density and high-speed networks, but it is unlikely to make a large difference in most people’s homes. Think about dense Wi-Fi networks in a convention center, or a stadium — that’s where I think the extra spectrum from Wi-Fi 6E will be most relevant. It should also have a big impact on wireless mesh networks, but time will tell. Keep in mind that only Wi-Fi 6E devices will be able to use the new spectrum, meaning none of the devices you have now will see any benefit.
I've seen many people say that they wouldn't consider buying any networking equipment that doesn't support Wi-Fi 6E. I can't tell you what to buy or what to do, but I don't think that holding out for Wi-Fi 6E is necessary, especially for a home network. Getting use of a Wi-Fi 6E network will require all new devices, and we don't have any of those yet. Even after you can buy Wi-Fi 6E-enabled devices, it will take time until the benefits are relevant to most people. If you have an older network, it might make more sense to upgrade to Wi-Fi 6 now, and wait for mature Wi-Fi 6E products or Wi-Fi 7 which is due in 2023 or 2024. By then, clients supporting 6 GHz should be more common, and the upgrade cost will make more sense.
If you want to chase high channel widths and high data rates, Wi-Fi 6E has plenty to offer. It’s an exciting time for Wi-Fi, but it helps to have patience. Wi-Fi 6E may be right around the corner, but it isn’t here yet.
