What's cool about WiFi 7

Crazy QAM, wide bandwidths, parallel links, spectral efficiency, and more

WiFi 7 is the latest iteration of WiFi technology labeled as IEEE 802.11be. Before we go into any technical details, it begs the question: Do we really care about better WiFi?

The short answer is yes. Emerging technologies require better connectivity. The long answer is the rest of this article.

In this article, you will learn the following:

1. Where WiFi 7 will be useful

2. Specific improvements in WiFi 7:

   1. Frequency bands and data rates

   2. Modulation schemes

   3. Multilink operation

   4. Preamble puncturing

   5. Spatial streams and MIMO

Let’s dive in!

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Before you buy the latest WiFi 7 gear for your home, here's the thing. It is not sufficient to have a WiFi 7 enabled router. All your client devices have to support WiFi 7 and the advanced features it provides. At the time of this writing, there are not a whole lot of client devices that support it, but eventually more hardware will roll out.

Even with available hardware support between router and client, the software still needs to support advanced protocols used by WiFi 7. Microsoft, Apple and Google need to have the necessary drivers available to use in their operating systems to make the best of WiFi 7.

For most common applications, WiFi 4 or 5 is probably sufficient. We have access to both 2.4 GHz and 5 GHz bands and sufficient bandwidth to perform most day to day tasks in a home environment.

The need for performant WiFi emerges in dense enterprise networks when a large number of clients are present, or in situations that require demanding performance.

Here are some examples:

• Wireless backhaul: In a mesh router system, the connections between the wireless mesh units are connected by a high speed data link called the backhaul. This typically requires to be a high speed, high reliability connection. The faster speeds and improved reliability offered by WiFi 7 provides enhancements in backhaul capability.

• AR/VR headsets: With the rise of Augmented/Virtual Reality (AR/VR) headsets in the market, there is a need for very low latency in the wireless connection between the headset and its peripherals. Users have reported feeling nausea while using AR/VR headsets if this delay is high, and nobody cares for an ethernet cable running to their headset.

• Enhanced video and audio: Current WiFi technology can easily stream 4K video but with the rise of 8K devices in the future, we could always use more wireless data rates. With the arrival of WiFi connected headphones, we can expect more client devices on the network demanding low latency and low power operation.

Let’s dig in to the engineering.

Frequency Bands and Data Rates

WiFi 7 allows for the use of three different frequency bands - 2.4 GHz, 5 GHz, and 6 GHz. The 6 GHz frequency band with 1200 MHz of spectrum was added on for WiFi 6E in April 2020 by the US Federal Communications Commission (FCC).

WiFi 7 provides higher channel bandwidths that allow for faster data rates. Here are the channel bandwidth allocations in each of the three frequency bands. You can see the detailed channel allocations here.

• 2.4 GHz: 11 channels at 20 MHz each

• 5 GHz: 45 channels of 20 MHz each. It also allows the aggregation of channels into 40 MHz and 80 MHz channels.

• 6 GHz: 60 channels with up to 160 MHz bandwidth in WiFi 6E, and up to 320 MHz in WiFi 7. Higher bandwidth channels are creating by aggregating multiple 40 MHz channels.

With the addition of these higher frequency channels and wider bandwidths, WiFi 7 is expected to provide a theoretical maximum data rate of 46 Gbps. In comparison, WiFi 6 has a theoretical maximum of 9.6 Gbps. Such data rates are rarely achieved in practice due to software and hardware limitations.

Source: Spectrum needs of WiFi 7, Intel white paper (link).

Modulation Scheme

Modulation scheme used in a WiFi standard represents how many bits of information are packaged into a symbol that is then transmitted. Higher the number of bits bundled, the more the data rate. It is also correspondingly harder for the receiver to discern which bundle of bits or symbol was received if there are too many of them to distinguish between. If the received symbol is wrongly interpreted, then the error rate of the wireless connection increases.

In WiFi 6, 10-bits of data were bundled together and a modulation scheme called Quadrature Amplitude Modulation (QAM) was used. The result was the use of 1024-QAM. The receiver needs to accurately distinguish between 1024 different received symbols to interpret the received data without error.

In WiFi 7, 12 bits were packaged up together in a symbol resulting in the use of 4096-QAM. This 4x increase in the number of symbols received makes it quite a work of engineering to correctly interpret the received symbols. The result of using higher number of bits is a 20% increase in data rate due to choice of modulation scheme.

The use of a high order modulation scheme poses a strict –38 dB requirement on the constellation error vector magnitude (EVM) at the transmitter. Due to its inherent complexity, the modulation scheme is most effective only in the 6 GHz band over short distances and requires the use of antenna beamforming to mitigate path loss.

Multi Link Operation

This is one of the most prominent features in WiFi 7. MultiLink Operation (MLO) allows for the use of multiple simultaneous connections between access points over different channels, and even different frequency bands.

Earlier WiFi generations made connections only over a single channel at a single frequency band. Even a triband WiFi 6E router connects devices on a single band over a fixed channel. If the connection quality was poor, the router had to manually switch over to a more reliable one.

With MLO, there is significant improvement in reliability of the connection due to multiple redundant links being made simultaneously in addition to speed and latency improvements.

Preamable Puncturing

In WiFi communication, the preamble is a part of the data packet transmitted over the WiFi channel. It helps in synchronizing the receiver by providing a pattern that tells the receiver what to expect in terms of data that will be transmitted over the channel.

Consider the following problem scenario. Let's say there is a 40 MHz subchannel being occupied in a 160 MHz bandwidth channel. In earlier WiFi generations, this renders the rest of the 120 MHz of bandwidth useless within that channel.

Since WiFi 7 implements even wider 320 MHz channels, there needs to be a way to avoid wasted spectrum when a smaller bandwidth signal occupies a wideband channel. This is essential to implement in countries where there is a crowded spectrum around 6 GHz, where it is almost guaranteed that there will be a signal present over a wide 320 MHz spectrum at all times.

This is what preamble puncturing implements. If a 40 MHz signal is occupying a 320 MHz channel, the rest of the 280 MHz is still usable. By puncturing, or selectively omitting parts of the preamble in certain subchannels where there is already a signal present, the receiver is effectively told via the preamble that the rest of the channel still contains usable data. This was optional in WiFi 6 but WiFi 7 makes it mandatory.

As a result, spectrum utilization is far more efficient in WiFi 7.

Increased spatial streams and MIMO

Multiple Input Multiple Output (MIMO) refers to the use of multiple transmit and receive antennas to increase the throughput of a wireless connection. Different antennas receive signals at different times depending on how the transmitted signal bounces around its environment. The final received signal is reconstructed from the inputs of each receive antenna using signal processing algorithms.

The multi-antenna system is also used to transmit data in parallel using a combination of transmit and receive antennas. The higher the data transmission in parallel, the more the data rate over the wireless link. Each parallel data stream is called a spatial stream.

Early WiFi generations only supported 2 or 4 spatial streams, while WiFi 6 supported 8 spatial streams. In WiFi 7, this limit has been increased to 16 spatial streams resulting in a doubling of data rate over WiFi 6. To realize the full benefit of 16 spatial streams, the client devices need to let the access point know what the state of the wireless channel is, at any given point in time because the state of the channel is always continuously varying due to its surrounding environment.

To do this, the client performs "Channel Sounding" to evaluate the state of the channel and provides the access point with Channel State Information (CSI). The overhead to do this is pretty high especially given the large channel bandwidths used in WiFi 7. The 802.11be standard however implements some fairly sophisticated channel sounding mechanisms to reduce this overhead which is too detailed to get into here.

⭐️ Key Takeaways

• WiFi 7 is a significant leap forward in technology and it implements many improvements over WiFi 6/6E.

  • Wider channel bandwidths (up to 320 MHz)

  • High order modulations (4K QAM)

  • Improved Quality of Service (with Multilink operation)

  • Better spectral efficiency (with preamble puncturing)

  • Improved MIMO (with 16 spatial streams)

• As WiFi technology improves, applications will grow to effectively utilize all the features that it offers. Widespread adoption requires hardware and software upgrades that takes a while to catch on.

📚Further Reading

• WiFi Unleashed, by Carlos Cordeiro: This detailed slide set describes the evolution from WiFi 6 to 7 is great detail and has lots of pretty pictures.

• WiFi 7: A Leap Towards Time-Sensitive Networking: This white paper has some nice graphs that show data rates, channel widths, modulations, etc., have evolved over several generations.

• What is WiFi 7: Everything you need to know: This tomsguide.com article is a nicely written, layman’s overview of WiFi 7. It even tells you some routers out there you can buy, should you be so inspired.

• Future Directions for WiFi 8 and beyond: If you’ve had enough of WiFi 7, you can read about WiFi 8.

The views, thoughts, and opinions expressed in this newsletter are solely mine; they do not reflect the views or positions of my employer or any entities I am affiliated with. The content provided is for informational purposes only and does not constitute professional or investment advice.