Wi-Fi 7 the new kid on the block

Rail Engineer 175 (June 2019) ran a feature explaining how and why the future of Wi-Fi technology would be Wi-Fi 6 (IEEE 6802.11ax). But things move fast in telecoms development and, just four years later, the new kid on the block is Wi-Fi 7 (IEEE 802.11be). So why is Wi-Fi 7 needed, how does it work, and what will the benefits be?

Wi-Fi has been a huge success and is now the established technology for providing the final telecoms link to devices in the home, offices, stations, shops, schools, and just about anywhere in the world requiring connectivity. UK-based telecom consultancy Analysys Mason, says Wi-Fi now carries the majority of all wireless network data traffic, and the International Data Corporation (IDC) Wi Fi Technology Forecast says there are 19.5 billion Wi-Fi devices in use around the world. The Wi Fi Alliance, based in the USA, says the global economic value of Wi-Fi is some £2.73 trillion ($3.5 trillion).

Wi-Fi 6 provides a relatively fast 9.6Gbps data download rate, but Wi-Fi 7 will provide an incredible theoretical data download rate of 48Gbps. Wi-Fi 7 will also reduce latency and improve overall network capacity, distance, and reliability.

There is a saying in telecoms engineering that there can never be too much bandwidth in a network. As Wi-Fi network speeds have improved (see table 1) application designers have been quick to design systems that provided even greater benefits, but using the ‘spare’ data rate available. The Covid-19 pandemic changed many things, including the way people work, communicate, socialise, shop, learn, and entertain themselves. Wi-Fi is expected by many to be available at railway stations and its use for monitoring railway equipment is significant.

All aspects of life and industry are more reliant on communications than ever and there has a been a huge increase in the use of such things as video conferencing, video streaming, and online gaming. For example, Microsoft says the use of its remote-meeting software Teams increased by 252% from 2020 to 2022.

Fibre to the home and places of work is also fast becoming a reality with Gbps connections, and Wi-Fi must not become a ‘bottleneck’. Wi-Fi 7 is designed to accommodate modern, data-hungry applications, and will support the inevitable arrival of 8K video streaming, and such things as immersive, low-latency extended reality (XR) applications for social, industrial, and gaming purposes.

2.4 GHz interference

The first three generations of Wi-Fi used a carrier frequency of 2.4GHz, however Wi-Fi interference can be caused by other devices which also use this frequency. This can include devices such as microwave ovens, security cameras, door alarms, Bluetooth devices, cordless phones, baby monitors, and, in some countries, amateur radio.

A solution from Wi-Fi 4 onwards introduced another carrier frequency of 5GHz. This allowed higher data speeds with less interference, although the higher the frequency of the carrier signal, the shorter the range. This can be an advantage though, allowing the frequency to be reused for another connection not too far away. Wi-Fi 6E (Extended) introduced yet another carrier frequency of 6GHz and Wi-Fi 7 will also use 6GHz, but in a new clever way along with the use of the 2.4GHz and 5GHz carrier frequencies.

Each generation of Wi-Fi after Wi-Fi 4 required the user to select which carrier they wished to use when the system was configured. However, Wi-Fi 7 introduces Multi Link Operation (MLO). With MLO, all three carrier link frequencies are used at the same time. By connecting simultaneously using the 2.4 GHz, 5 GHz, and 6 GHz frequencies, the data throughput is increased, latency in reduced, and reliability improved by duplicating packets across the multiple links. Some suppliers say the real time latency in Wi-Fi 7 can be reduced by 75% compared to Wi-Fi 6.

Wi-Fi 7 also uses improved dynamic mesh technology to increase and vary the range, so, for example the 2.4 GHz frequency could be used to connect further away from the Wi-Fi point with less data carrying capability, or the higher carrier frequencies could be used for shorter range with greater data carrying capability, leaving the 2.4 GHz frequency for other applications such as Bluetooth.

The other factor for Wi-Fi data carrying capacity is the number and size (bandwidth) of the channels on each carrier. Although some channels overlap, they have increased both in number and size of the channels in each generation of Wi-Fi and this varies around the world. Wi-Fi 7 will provide a total of 1200MHz bandwidth of the 6GHz spectrum, which is more than double that of 2.4GHz and 5GHz combined. Wi-Fi 6 provides channels of 20MHz, 40MHz, 80MHz, and 160MHz, but Wi-Fi 7 will add 320MHz channels.

MU-MIMO and QAM

Wi-Fi 5 saw the introduction of Multi-User, Multiple Input, Multiple Output (MU-MIMO) downlinks to better support multiple connections simultaneously accessing a wireless access point. Wi-Fi 6/6E also introduced MU-MIMO uplink and Wi-Fi 7 now doubles both the MU-MIMO downlink and uplink streams from eight to 16.

Quadrature Amplitude Modulation (QAM) is a method to translate data packets to analogue signals transmitted wirelessly. Wi-Fi 6E supports 1024 QAM, but Wi-Fi 7 increases this to 4K QAM, resulting in a 20% data throughput increase.

Like previous Wi-Fi standards, Wi-Fi 7 will be backward compatible. But taking advantage of the new features and improved performance will require new devices capable of Wi-Fi 7. That means new routers and access points, smartphones, laptops, TVs, and so on, will be required.

6 GHz for Wi-Fi and mobile

Nothing is easy with the radio spectrum which is a limited, finite resource. Radio spectrum is managed internationally by the World Radiocommunication Conferences (WRC), held every three to four years, and in the UK by Ofcom. Some countries have released 6GHz for Wi-Fi and Ofcom has permitted the use of the lower 6GHz band (5925- 6425MHz) for Wi-Fi 6E, but it has not yet released the upper 6GHz band for Wi-Fi 7.

Ofcom says 6GHz could be used for either licensed mobile communications (5G) or unlicensed Wi-Fi 7. However, rather than choosing between the two, Ofcom is exploring options for that which would enable the use of both Wi-Fi and mobile 5G in the 6GHz band. It is calling this ‘hybrid sharing’ and says this could be achieved by enabling the indoor use of Wi-Fi whilst also enabling licensed mobile use outdoors. This is because Wi-Fi routers generally tend to be indoors for broadband traffic, with mobile radio transmitters located outdoors for wider area coverage.

Ofcom also says it may be possible to enable licensed mobile use in specific high-traffic locations while allowing Wi-Fi use elsewhere. Ofcom is also pressing for international harmonisation of hybrid sharing 6GHz, to enable economies of scale for equipment production.
As well as problems with 6GHz, the Wi-Fi 7 standard is still in development and is not expected to be released until sometime in 2024. However, some pre-certified equipment is already being released, so manufacturers must be confident in Wi-Fi 7 and the use of unlicensed 6 GHz, as any early-release products may not offer all of the features that will be available once fully-certified Wi-Fi 7 devices are released.

It is early days for Wi-Fi 7, as Wi-Fi 6 and 6E have not yet been widely deployed. However, in a few years’ time, will Wi-Fi 7 with or without 6GHz be fast enough in Britain? Or will Rail Engineer be reporting on the release of Wi-Fi 8, with even faster data rates and features we can only dream of?

Only time will tell.