Understanding IEEE 802.11be Wi-Fi 7

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IEEE 802.11be which is also given the designation Wi-Fi 7 by the Wi-Fi Alliance is the next major advance for Wi-Fi wireless communications technology.

The new standard provides a significant advance in performance over the previous 802.11ax or Wi-Fi 6 technology and it focusses in Extremely High Throughput, EHT and it is aimed at improving all aspects of WLAN, Wireless Local Area Network performance.

Wi-Fi 7 paves the way for a new generation of applications to utilise Wi-Fi in Wireless LANs with the confidence that the standard can provide the required performance over a wireless communications link.

The development of the new standard has been driven by the increase in use of 4k and 8k video as well as real time apps and the use virtual reality, augmented reality remote working and other Wireless LAN applications that need very high data speeds and capabilities.

These all require much higher throughput rates as well as lower latency, especially if multiple units are connected to the same Wi-Fi node.

802.11be Wi-Fi-7 timelines

Once the previous version of the Wi-Fi standard in the form of 802.11ax was adopted - Wi-Fi6 in 2019 and Wi-Fi6E with the additional 6 GHz bands in 2020, the focus soon turned to Wi-Fi 7.

Although significant amounts of work had already been undertaken on the standard to follow 802.11ax, its adoption enabled the new 802.11be work to surge ahead.

The initial draft of the specification w as available in March 2021, and the final version and adoption of the Wi-Fi 7 standard is expected by early 2024.

New product should be available shortly after this because many manufacturers will ahve been working on product using draft versions of the standard.

IEEE 802.11be Wi-Fi 7 specifications & capabilities

The 802.11be Wi-Fi 7 standard provides a significant leap in performance over the previous 802.11ax standard used in WLANs .

In essence, Wi-Fi 7, 802.11be utilises increased number of spatial streams along with doubled bandwidth, the 802.11be standard provides an impressive performance. It enables a wireless communications standard to provide significantly better performance than even many wired solutions.

There are some highlight parameters associated with the standard and these are summarised below, comparing the figures with those of IEEE 802.11ax, Wi-Fi 6.

It can be seen from the headline specifications that the new standard offers a significant enhancement over previous versions of the 802.11 WLAN specifications.

802.11be bands, channels & frequencies

With the huge speeds that are offered by Wi-Fi 7, 802.11be, the bands used along with the bandwidths available and the required transmission bandwidths have been carefully defined to enable them to fit within the available bands.

As Wi-Fi uses unlicensed spectrum known as the ISM or Industrial Scientific and Medical band. The main two bands used for this are the 2.4 GHz band and the 5 GHz band. More is being made available around 6 GHz, but this is not all available in all countries yet. Nevertheless 802.11be will still be able to operate within the existing allocations, but without being able to utilise the full speeds.

The 2.4 GHz was once thought of as being a wide space for all forms of wireless communications now seems relatively narrow. The wider spectrum allocation within the 5GHz band is also not sufficiently wide, so the new 6GHz band will be able to provide the full bandwidth required for the top speeds.

The maximum obtainable transmission bandwidth within the 2.4 GHz band is 40 MHz comprising two continuous 20 MHz channels. Then on 5 GHz it is 160 MHz consisting of two continuous/discontinuous 80 MHz channels.

These may not meet the requirements for high throughput and low-latency applications including the 4k/8k video, AR or VR and online gaming.

To achieve the top performance the additional bandwidth provided by the new 6 GHz band spectrum allocations which extends from 5.925 GHz to 7.125 GHz, in U.S.

This new spectrum allocation has an available bandwidth of 1.2 GHz is now under regulatory discussion for opening up to Wireless LANs.

The much large bandwidth available at 6 GHz enables 802.11be to utilise transmission bandwidth levels up to 320 MHz. This will enable the specification parameters for extra high throughput, EHT of at least 30 Gbps to be achieved.

802.11be supports the 320 MHz bandwidth being contiguous and located in the same 6 GHz band or noncontiguous and located in different bands. This may be partly in the 5 GHz band and partly at 6 GHz band.

Orthogonal Frequency Division Multiple Access, OFDMA

IEEE 802.11be, Wi-Fi 7 uses OFDMA, a technology which has been widely used in both the 4G and 5G mobile telecommunications systems as well as previous Wi-Fi Wireless LAN standards.

In fact OFDMA is the modulation waveform format of choice for very many wireless communication systems these days as it offers link resilience while also providing a high data capability.

The basic technology is based upon OFDM, orthogonal frequency division multiplex, where the data speed is slowed down to overcome reflections and multi-path propagation by spreading it over a number of very close spaced low data rate channels. This makes very good use of the available spectrum.

QAM modulation

Like many other wireless LAN and mobile communications systems, 802.11be uses a form of modulation called quadrature amplitude modulation or QAM.

QAM transmits data through symbols containing a specific number of bits. So higher the number, more data is conveyed in a given cycle. The new 4K-QAM, 4096-QAM, is able to transmit 12-bits per symbol as compared to 10 bits of 1024-QAM.

The increased capability of 4096-QAM is very useful carrying increased levels of data more quickly, but is does come with the penalty that it requires a strong signal to provide a sufficiently low bit error rate.

Accordingly it will need to fall back to lower orders of QAM when the link signal strength is not so high, or when interference levels are high. This is achieved dynamically within the system as it monitors strength, bit error rate, etc.

In the diagrams below it can be seen that the distance between the different positions on the constellation diagram reduces between 32-QAM and 64QAM. The same is true between the higher levels of QAM used for 1024-QAM and 4096QAM.

The distance on the constellation diagram between the different positions is much less for 64-QAM.

In view of the reduction in distance between the different points on the constellation diagram, it is necessary to only operate the higher order modulation formats when the link quality is good - signal strength levels are high and noise levels are low.

It is for this reason that dynamic link adaptation is required in wireless communications systems using high order QAM modulation formats.

In reality the use of 4096-QAM to give the highest throughput rates over the wireless LAN would only be used where multiple antennas and beamforming technology are available as well as the signal giving the required signal to noise performance in terms of the error vector magnitude, EVM.

802.11be MU-MIMO techniques

IEEE 802.11be, Wi-Fi 7 has improved the MIMO performance over previous 802.11 versions. It has increased the number of spatial streams from 8x8 to 16x16.

MIMO utilises the reflections and different signal paths to enhance the signal performance either in terms of the data rate performance, and or the signal performance.

The increase in the number of MIMO spatial streams available with IEEE 802.11be brings advantages in terms of the data speeds available, and dependent upon the circumstances the performance in low noise conditions.

Increasing the MIMO performance to 16x16 comes with some disadvantages. In particular the number of antennas required. Accordingly Wi-Fi 7 routers may be seen with an increased number of antennas sprouting from the box, making them a little less aesthetically pleasing. However the performance will be better. It is likely though that many routers will utilise internal antennas, so this problem may not arise on all units.

Multi-link techniques

The IEEE 802.11be standard supports multi-link techniques that enable it to reduce wireless LAN congestion and improve the overall performance of the specific link as well as the overall network.

Wi-Fi 7 uses alternative multi-link techniques that scans for the best band to complete a data transfer, and can switch between the various bands intelligently.

Multi-Link Operation, MLO enables the devices known as Multi-Link Devices, or MLDs to use multiple channels at one. The technique also uses load balancing so that each channel can accommodate the levels of data that it can handle.

This technique reduces reliance on one channel which may have varying levels of interference, and as a result the overall technique results in higher speeds and lower congestion levels on the wireless LAN.

A second technique is to aggregate the links that can be set up on multiple bands and use them simultaneously.

To complete the suite of techniques, 802.11be, Wi-Fi 7 uses a technique called preamble puncturing which enables devices to use wider channels.

The new wireless LAN standard has provision to use 320MHz channels but the protocol allows devices to combine up two 160MHz channels or one 80MHz channel and one 160MHz channel to create a wider one. The wider bandwidth available enables much higher data rates to be accommodated on the WLAN.

Apart from just enabling higher data rates, multi-link operation also reduces the latency because the network does not need to wait the additional time when channels are busy or congested. The multi-link operation means that data can be transmitted as required and without the same levels of waiting, thereby reducing the latency on the whole of the wireless LAN.

IEEE 802.11be, Wi-Fi 7 will provide a significant leap in performance over the previous 802.11ax, Wi-Fi 6 standard. Aimed at providing a significant step up in performance to accommodate the much higher usage of applications like 4K and 8K streaming as well as virtual and augmented reality as well as a host of other data hungry applications, Wi-Fi 7 will enable wireless communications to be the technology of choice where other options may have needed to be considered if the new standard was not available.

  Written by Ian Poole .
  Experienced electronics engineer and author.

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