Wi-Fi 7 - The future of Wi-Fi
Known as 802.11be Extremely High Throughput or simply Wi-Fi 7, building upon the previous iteration of Wi-Fi 6/ 802.11ax adopted back in 2020. Wi-Fi 7 is available for the 2.4Ghz, 5Ghz and 6Ghz frequency bands and is looking to bring in additional changes to try and bump up throughput, interference mitigation and better use of the medium.
I'll be going over a few of the notable changes below from documents provided to us by the IEEE. Pre-warning you, the standard itself is subject to change as they work through the motions with a potential for full approval in 2024. IEEE however are quite good at keeping documentation up to date and I shall provide links to the relevant documents below for future use.
 |
| https://ieeexplore.ieee.org/document/9090146 |
320Mhz Channels and 240Mhz
We start with a simple change, channel bonding. The standard is looking increase overall channel bonding to 320Mhz, doubling the size from Wi-Fi 6 and its 160Mhz maximum. This comes in the form of a single 320Mhz channel or two 160Mhz channels.
On top of that, they've more recently announced the use of 240Mhz bandwidth availability. Allowing the bonding of a 160Mhz and 80Mhz, allowing a greater level of control when it comes to the larger channel sizes.
QAM Increase (4096-QAM)
Good old QAM getting an uplift to 4096-QAM, although at this point it seems to be decreasing in its provided improvements and I quote...
"Each additional increase in the order of constellation gives a smaller and smaller gain. While introducing 256-QAM in 802.11ac provides a 33% gain with respect to 64-QAM of 802.11n, 1024-QAM of 802.11ax increases nominal data rates by only 25%. 4096-QAM gives only 20%."
https://ieeexplore.ieee.org/document/9090146 - Section 3, EHT PHY, 1) 4K-QAM
An improvement is an improvement you might say but, think of the requirement when it comes to Signal To Noise (SNR). Greater complexity of modulation requires better SNR. The IEEE mention the receiver requiring 40db SNR to achieve said modulation, which isn't a small feet and I can't imagine in the real world environment being widely achievable. As a result however they are going to optionally support 4K-QAM in Wi-Fi 7.
Spatial Streams
Increasing max Spatial Streams (SSs) from 8 to 16, again another standard addition that isn't out of the ordinary. Looking at the specifics, a Single User-MIMO can be assigned the max 16 SSs while if a shared Multi User-MIMO, a max of 4 SSs can be assigned per device. Given the benefits of Upload MU-MIMO being introduced in Wi-Fi 6, we can expect to see an even greater use of the medium when it comes to concurrent devices receiving and transmitting.
Non-Contiguous Channels
The use non-contiguous bandwidth, previously any use of channel bonding required for example channel 36 to 64 in a Wi-Fi 6 to be available for a 160Mhz combination. However with non-contiguous, you can select two non-adjacent networks allowing them to be bonded instead. This will allow the network to avoid any particularly heavily burdened channels.
The Dynamic Frequency Selection (DFS) requirements being removed between 5725 and 5850 MHz and the use of the 6Ghz band (5925-6425) in the UK, we may see an increase in channel bonding if it suits the environment.
 |
| https://www.commscope.com/insights/the-enterprise-source/wi-fi-6-the-fact-file/ |
Preamble Puncturing
Building upon the feature implemented in Wi-Fi 6 OFDMA which is was not as heavily talked about. Preamble Puncturing allows a device when connected and using a channel bond to circumnavigate a channel that is busy through interference.
One of the issues when it came to using larger channel widths like 80Mhz was that if the immediate secondary channel was busy for whatever reason, even if the remaining two 20Mhz is free you will still be restricted to solely the primary 20Mhz. This makes the probability of using the full 80Mhz in a populated environment hard.
Multi-Link Architecture
Most devices are able to comfortably use either the 2.4Ghz, 5Ghz and as time goes by 6Ghz ready. However you are not able to establish more then one link to a single band and switching is not the quickest process. Wi-Fi 7 is looking to implement a solution to allow multiple connections known as Multi Link Devices. This allows stations to transmit concurrently on multiple channels at the same time hopefully improving throughput either using a different or the same band. An example being connecting to 5Ghz and also 6Ghz at the same time or being connected to 5Ghz twice.
There is two modes being discussed to enact multi-link operation, restricted and dynamic link switch, Restricted mode and dynamic link switch. Restricted allows data flows solely for a single link, and management frames are sent over both but are are again limited to their particular link. Dynamic allows data flows to be passed over the separate links and for management traffic to be applied for either links allowing avoidance and congestion avoidance and increased throughput.
Multi-Link Power Saving
Given a potential increase in links available and to alleviate any power supply issues especially for portable devices, Target Wake Time (TWT) will be able to act independently on both of the links. This stopping both links being forced to remain awake if one of them is not receiving any traffic. In addition if one link for example in power save mode while the other is active, the active link is able to pass on an power related messaging to the AP but the AP is also able to tell the active link to wake the currently asleep link up as well.
Multi-AP Cooperation
In the current Wi-Fi networks, APs are very much isolated from one another other and are mostly concerned with trying to reduce their interference from an individual perspective. An interesting concept the standard is looking to implement is to allow APs to form a multi-AP system. The idea being that if the APs work together they can benefit those devices connected to the Wireless network.
When it comes to this type of multi-AP systems they're is two overall approached being considered and they are Coordinated and Joint. Each has their own ways of achieving this which I will cover below.
Coordinated Spatial Reuse (CSR)
Simplest of the bunch and one of the contenders to be implemented. Improves upon Wi-Fi 6s Spatial Reuse (RS)/BSS Colouring and utilises similar protocols to that of beamforming.
APs coordinate their TX Power with each other, limiting their cell size along with their surrounding APs. This is done by measuring the receiving Overlapping Basic Service Set / Preamble Detection (OBSS/PD) found in the preamble (similar to BSS Colouring) and manging their Tx Power accordingly. This is done in an attempt to provide as strong as signal as possible to their connection station while allowing them to continue transmitting.
Example, groups of people in the same room talking. You are able to hear them but not too the point where it's too loud for you to continue your conversation without not being heard by others within your group. So why would you stop talking? The same applies here with CSR.
A good approach given the lack of Channel State Information that would be needed between the APs and stations and the overall benefits that have been noted during testing.
 |
| https://ieeexplore.ieee.org/document/9090146 - Figure 15 11ax SR vs. CSR |
Coordinated OFDMA
Another one of the potential solutions that we may be seeing due to its limited complexity and the benefits it provides.
Coordinated OFDMA allows multiple APs to coordinate between each other, assigning specific Resource Units (RUs) to different stations devices limiting interference and allowing APs to effectively split a channel between themselves.
Each AP defines that RUs that would be preferable for their connected stations and those that are not, again looking for a high level of Overlapping Basic Service Set (OBSS) causing interference. From then on the APs exchange the information of the preferred/non-preferred RUs prior to coordinated transmissions.
During the coordinated OFDMA transmissions the APs involved use the gathered by themselves and provided by their neighbouring APs to effectively allocate sub-channels.
This does require more conversation between the APs prior to communicating than CSR does. It's also been mentioned that some stations may benefit more then others specifically those in range of multiple APs but this is to be expect.
Coordinated Null Steering
While forming its beams to its stations devices, AP also works to effectively stop its interference to neighbouring stations through its use of beamforming.
This solution allows an AP when transmitting and receiving to place spatial radiation nulls towards non-connect stations to try and prohibit any interference. Similar to that of beamforming
The effectively coordinate null steering the APs will require Channel State Information from their non-served stations (i.e. those not directly connected to themselves). Other then how do you go about getting said info from non-connected stations, sending and receiving this information will require additional overheard which overall may reduce the overall benefits that can be gained.
Joint Transmission and Reception
Probably one of the most complex solutions that have been proposed. Multiple APs serving the same station, the next improvement upon MU-MIMO. It has been noted in experiments that when it comes to downloads to a station by far the best solution when it comes to multi-AP Cooperation.
Unfortunately with this level of cooperation the complexity is already off putting and I imagine one of the reasons why we won't be seeing this included in a Wi-Fi standard for a good few years to come. Having to coordinate numerous APs would be extremely difficult and to allow high throughput for a single station you would most likely end up under utilising the shared medium especially in medium to large scale deployments.
 Joint Transmission and Reception (Left), Coordinated OFDMA (Middle), Coordinated Null Steering (Right) |
https://ieeexplore.ieee.org/document/9090146 - Figure 16 Joint transmission and reception (left), Co-OFDMA (centre), Coordinated null steering (right) |
Sources:
Wi-Fi 6 - Features and Capabilities
https://wi-fight-it.blogspot.com/2021/12/wi-fi-6-re-introduction.html
Statement: Improving spectrum access for wifi – spectrum use in the 5 and 6 GHz bands
IEEE 802.11be Extremely High Throughput: The Next Generation of Wi-Fi Technology Beyond 802.11ax
https://ieeexplore.ieee.org/document/8847238
Current Status and Directions of IEEE 802.11be, the Future Wi-Fi 7
https://ieeexplore.ieee.org/document/9090146
Status of Project IEEE P802.11be
https://www.ieee802.org/11/Reports/tgbe_update.htm
Coordinated Spatial Reuse with TPC (CSR) Power Point:
https://mentor.ieee.org/802.11/dcn/20/11-20-0073-00-00be-on-coordinated-spatial-reuse-in-11be.pptx#:~:text=Coordinated%20Spatial%20Reuse%20(CSR)&text=Note%20that%20the%20fundamental%20difference,in%20the%20network%20including%20itself.
Preparations for Coordinated OFDMA Power Point:
https://mentor.ieee.org/802.11/dcn/20/11-20-0056-00-00be-preparations-for-coordinated-ofdma.pptx
Comments
Post a Comment