Wi-Fi 7 Moves Forward, Adding Yet Another Protocol

The latest generation Wi-Fi protocol brings better speeds and data handling, but it does little to bridge various communications technologies. That, in turn, makes it more difficult and more expensive to design chips because they must integrate and support multiple wireless technologies, including different versions of the same technology.

Wireless communications technologies are often victims of their own success, with each new generation promising to solve the congestion problems caused by the fervent adoption of the last generation. This is unavoidable in a world where every day there are new use cases for wireless connectivity, from autonomous vehicles to robots on hospital rounds to further dependence on the cloud, including Microsoft’s interest in making Windows a cloud-based service for consumers. The proliferation of needs has spawned a menagerie of communications protocols, each with its own niche, and even novel protocols, like Matter, to interconnect older protocols.

Wi-Fi, once considered “the poor cousin to cellular,” is now the most commonly used wireless communication technology, with more than 3.8 billion devices shipping annually and nearly 20 billion devices in use, according to the Wi-Fi Alliance, the trade group that coined the term and registered it as a trademark in 2000.

Technically, Wi-Fi is the IEEE 802.11 protocol, the wireless local area network (WLAN) subset of the 802 protocols, which cover local area networks (LANs), personal area networks (PANs), and metropolitan area networks (MANs) packet-based networks. 802.11 has acquired various suffixes, as the protocol has been amended in the years since it was first released in 1997. An entire generation has already grown up with no idea what an Ethernet cable is.

Fig. 1: Wi-Fi by the numbers 2023. Source: Wi-Fi Alliance

The services and protocols specified in IEEE 802 map to the lowest layers (Layer 2, data link and Layer 1, physical) of the seven-layer Open Systems Interconnection (OSI) networking reference model. IEEE 802 further divides Layer 2 into two sub-layers — logical link control (LLC) and medium access control (MAC) — which controls the hardware responsible for interaction with the transmission medium.

Conventional Wi-Fi is primarily an indoor technology, with a range of approximately 150 feet, depending on the frequency. Its reach can be increased by a wired signal extender or wireless repeater, but at higher frequencies there’s still a risk, due to attenuation and absorption, of the signal being blocked by a wall or other solid object. Outdoors, with a clear path, a signal may range 300 feet or more. Low-powered HaLow Wi-Fi (802.11ah), which operates at lower frequencies, can travel up to a kilometer.

“At lower frequencies, everything looks like glass to a radio wave,” said Marc Swinnen, director of product marketing at Ansys. “But as you get to higher and higher frequencies, things get much more opaque and even small barriers will block the signal. Additionally, long wavelengths go round corners more easily than shorter wavelengths. So at shorter wavelengths, you need more line-of-sight. With both 6G cellular and Wi-Fi 7, you’re going to have to put in many more base stations that are much more local.”

Wi-Fi underpins most IoT applications, whether consumer or enterprise, and therein lies the problem. If every home appliance needs spectrum, from the smart lightbulb to the EV pulling into the garage, and every office device needs spectrum from the wireless printer to the 4D display in the conference room, then interference and network slowdowns seem inevitable.

“There is significant consumer demand for improved Wi-Fi performance,” said Gabriel Desjardins, director of product marketing for Broadcom’s Wireless Communication and Connectivity Division. “We get endless requests from our customers. This isn’t something that consumers know about per se, but given that a lot of operators are rolling out 10 gigabit fiber or 10 gigabit cable in the next couple of years, consumers will demand that when they pay X number of dollars a month to get upgraded fiber, they want wireless that matches it.”

In addition, said Andy Davidson, senior director of technology planning at Qualcomm, Extended Reality (ER) is making the jump from recreational uses, like immersive games, to enterprise uses, like sales demonstrations and virtual hands-on training. They all require a latency standard beyond the limits of a Bluetooth-connected headset.

Spectrum allocation
At the heart of the challenge is spectrum allocation. The electromagnetic spectrum is narrow and crowded territory, which has been regulated for more than a century into licensed and unlicensed bands. If the EM spectrum is raw land, then designated frequency bands are the boundaries parceled out as land grants.

The FCC split of the spectrum into licensed and unlicensed bands created one of the major distinctions between Wi-Fi and cellular networks. Licensed spectrum is the domain of cellular companies, where spectrum is legally protected from being poached. Unlicensed spectrum, used by Wi-Fi networks, is an open highway. The good news is there are no tolls. But there are also no traffic cops, and the limited lanes available can become overcrowded. That said, unlicensed doesn’t mean unregulated. Operators need to be aware of specific usage rules for their areas.

Originally, Wi-Fi was only allowed to operate at 2.4 GHz (3 channels) and 5GHz (24 channels). A “channel” in this sense is a section of frequency that has been further divided, similar to television and radio channels, not channel in the Shannon information theory sense. As devices multiplied, so did competition for those channels, especially because many older devices were factory-set to specific channels. Even today, without the ability to switch channels, customers can experience delays from competing devices.

In a welcome decision in April 2020, the FCC allowed the use of the 6 GHz frequency band, which made 1,200 MHz of spectrum available in the United States (59 channels) and much of the rest of the world, as well as nearly 500 MHz of clean spectrum in the EU. Notably, the channels within that spectrum could be divided into both narrower and wider segments, so that 59 channels could be, for example, 59 channels at 20 MHz or 7 channels at 160 MHz.

Fig. 2: Channels up through Wi-Fi 6. Wi-Fi 7, which is native at 6 GHz, introduces a 320 MHz channel. Source: HPE Aruba

Wi-Fi 6, Wi-Fi 6E
Here the nomenclature can get confusing. At the time, there was already a standard called Wi-Fi 6 (IEEE 802.11ax), which referred only to generation, not spectrum. Wi-Fi 6, initiated in 2014 and officially published in 2021, introduced innovations (discussed below) that also set the stage for the upcoming standard, Wi-Fi 7 (802.11be). When the spectrum opened up, the consumer-facing name was redubbed Wi-Fi 6E, for extended. Wi-Fi 6E has all the same capabilities as Wi-Fi 6, while also being able to operate in the 6 GHz band. (It doesn’t help clarity that the newest cellular standard is called 6G.)

Fig. 3: Wi-Fi generations and IEEE standards. According to the Wi-Fi Alliance’s Kevin Robinson, “There’s a four- to six-year cadence between generations.” Source: Wi-Fi Alliance

Wi-Fi 6’s updates aimed to achieve the industry’s universal goal of reduced latency. “We always are looking for faster interconnects with lower latencies to improve network capacity and performance, that would include our wireless interconnects,” Rita Horner, director of product marketing and strategic programs for Synopsys’ System Solutions Group.

In essence, Wi-Fi 6 reduces latency through two different techniques, which both contribute to easing network congestion.

Orthogonal frequency division multiple access (OFDMA) is a multi-user version of orthogonal frequency-division multiplexing (OFDM), which in turn was an advance on classic frequency division multiplexing (FDM). These techniques allow a channel to be split into subcarriers, with the splitting getting more fine-grained and flexible in every generation.

“OFDM sends the signal across multiple different carriers,” said Qualcomm’s Davidson. “If any of those specific carriers has an issue, you get the backup of the other ones, which means a higher quality signal can feed into the device. OFDMA send some carriers to one device and some carriers to another. In essence, you communicate to multiple devices at the same time by splitting up the available bandwidth.”

Multi-user, multiple-input, multiple output (MU-MIMO) controls how many data streams come from an antenna. Prior to its introduction in Wi-Fi 5 (802.11ac), while a router could communicate with multiple devices, it could only do so one at a time. With WiFi 5 MU-MIMO, that was upped to four, and then in Wi-Fi 6, it was doubled to eight.

Combined with the Wi-Fi 7 version of OFDMA, which gives even more control over different traffic flows to different devices, MU-MIMO will substantially decrease congestion. Also helping is an increase in quadrature amplitude modulation (QAM), which controls the amplitude and phase of the signal. At 4k QAM, Wi-Fi 7 should offer a 20% increase in the highest data rate, according to Davidson.

The advantages for consumers are obvious, but the signal complexities underscore why there are so many open positions for RF engineers. “These higher and higher order modulation schemes turn what is a nice digital signal, zeros and ones, into a multi-level signal with overlaps and phase shifts,” said Ansys’ Swinnen. “It becomes a very complex electromagnetic signal that’s very analog and requires careful modeling over long distances. All your traditional digital tools don’t work for that. You need to do a complete analog suite for analysis, including electromagnetics and the full resistance/inductance/capacitance modeling rather than just resistance/capacity.”

Along with the signal attenuation challenges, “It’s a multi-physics bonanza,” said Swinnen.

There will also be many more considerations for test engineers, according to Chen Chang, senior director for semiconductor and electronics at National Instruments. “Wi-Fi 7 introduces a lot more complexity in test and in the number of test cases due to the increased bandwidth, higher-order modulation, increased number of spatial streams, and multi-link devices. One of the key goals for Wi-Fi 7 is higher throughput. With a maximum data rate of 48 Gbps, many users won’t be able to tell the difference between a wired or wireless connection. Online gaming, 4K/8K video, and live streaming will all be seamless with Wi-Fi 7. This is achieved through a variety of techniques, all of which will add complexity to the testing needs for these new products. The new 320 MHz-wide signal will require a corresponding increase in the measurement instrument instantaneous bandwidth to support SEM tests, even more if DPD is to be introduced. Also, the higher order QAM means that the linearity of both the signal generator and signal analyzer are critical for PA/FEM modulation accuracy testing.”

Wi-Fi  7
Unlike Wi-Fi 6E, in which the additional spectrum is merely available, Wi-Fi 7 incorporates 6 GHz access as part of its fundamental design. For example, for the first time, subchannels can be further combined to give an extra-wide 320 MHz channel, which gives much higher bandwidth.

“Wi-Fi 7 becomes the first standard that could take advantage of that extra spectrum,” said Davidson. “If you want to deliver more capacity to users, you tend to split up into a larger number of devices with narrower bandwidth that you repeat throughout your building. Quite often for enterprise applications, they’re still at 40 MHz and 5 GHz, because they can have more access points (APs). And when they have more APs, it gives more people access to a higher speed back-end. So you can deliver more capacity to more users by splitting it up. However, in those enterprises, you also want to get the advantage of the higher speeds. With the advantages of 6 GHz you could, for example, step up your base level to 80 MHz channels. So you could have 20 MHz channels in 2.4 for your IoT devices, 40 MHz channels in 5 for your high speed devices, and for applications such as ER, you could do 160 MHz at 6 GHz.”

From an end-user IT department perspective, Wi-Fi 7 provides a new level of control over allocation. Yet in some ways, from a design engineering perspective, it’s just further optimization of the previous generation.

“You have to re-design the chip, but not necessarily from the ground up,” said Desjardins. “It’s basically just a modification in the protocol and it’s not terribly different from Wi-Fi 6E. There’s PHY changes, wider channel bandwidths, a higher modulation format, but that stuff is relatively simple. We’ve gone from 40 MHz channels in 2011 to 320 MHz channels 12 years later. Those are just incremental chip complexity modifications.”

But there is one major, novel addition that is key to Wi-Fi 7’s value—the incorporation of Multi-Link Operation (MLO).

“Even though there were multiple different radios on the AP, the client always connected to one of those bands and had to choose which one to connect. The big change with Wi-Fi 7 is the client can now connect to the AP on multiple bands at the same time,” said Davidson. “And it can use them either one at a time, or it can use them in combinations dependent on the capability of the device.”

Desjardins also emphasized MLO’s significance. “Wi-Fi 7 switches so quickly between different bands, it essentially can switch at a packet level. At the MAC layer in Layer 2, the way that Wi-Fi 7 works is just different from the way prior technologies work. There was never a mechanism to do fast switching between multiple channels. There was never a way to hop around interference or hop around congestion in the way that there now is. It’s a modification and improvement of the MAC, the timing within the chip.”

All of this can open up further use cases for Wi-Fi.

“Wi-Fi 7 capabilities such as multilink operation, which give you a high probability of low latency, become important with something like a backup camera, where obviously the designer needs to feel confident that the video signal that the driver is getting up on the dash is coming to that driver in real time,” said Kevin Robinson, president and CEO of Wi-Fi Alliance. “Today when you have a multi-band device, it really only has an active link in one of those bands or channels at a time. With multi-link operation, you could have two GHz channels, you could have a 5 GHz and a 6 GHz channel and both links can be active, which means a device can choose to send the same packet across both links simultaneously, adding redundancy and improving reliability. The device also could look at both links and make a decision in its scheduler as to which link it can access first and send the packet over whichever link becomes available first, improving latency. In addition to those features, you also have 4k QAM, higher-order modulation that improves data rates and transmission efficiency when you’re at shorter ranges.”

Because of all this, Wi-Fi 7 also can provide a point of differentiation for vendors, said Wi-Fi Alliance’s Robinson. “These capabilities require an incredible amount of intelligence in the chip, either in the firmware or the software stack, to decide which bits of data get queued, which of those multiple links do I actually want to use? For a lot of vendors, they are going to differentiate themselves not just in having the protocol implemented, but in the sophistication and performance of things like schedulers that ultimately are going to deliver the full benefits of those capabilities.”

Fig. 4: New capabilities in each standard. Source: Qualcomm

Wi-Fi 7 timeline
Wi-Fi 7 is still in committee, but that hasn’t stopped companies from producing Wi-Fi 7 based-devices, in part because the membership of the Wi-Fi Alliance covers enough of the industry that companies are confidently setting to work. Broadcom, for example, recently announced sample availability of its second generation of wireless connectivity chipset solutions for Wi-Fi 7. This selection builds on the company’s first-generation Wi-Fi 7 chips—all before the Wi-Fi 7 standards have been officially ratified.

“The .11 BE standard is likely to be ratified sometime late next year, yet the industry is going to be shipping interoperable Wi-Fi 7 gear well before that time,” said Robinson. “The work that goes on within the Wi-Fi Alliance enables products to get to market even ahead of ratification because the features that are included in our program are sufficiently mature and tested that it still allows the IEEE to put the finishing touches on some other capabilities that might come out a little bit later.”

However, waiting for standards to be fully complete and published may be a bit of naïve idea, in light of market pressures and excellent engineering staff, noted Broadcom’s Desjardins. “What our standards engineers have been able to do over the last two-plus decades—and every company that’s involved in this is doing the same thing—is make sure that the standard spec is clear enough years in advance of ratification, so that you can design a chip that’s forward compatible or may need some level of very minor tunability in the chip,” he said. “There’s a lot of inter-op that goes on between the different players in all these spaces well in advance of the actual standard’s release. I have never seen anybody have a meaningful miss on forward compatibility for Wi-Fi.”

Security
There’s a comfort level with security in Wi-Fi 7, because it’s based on WPA3, already successfully implemented in Wi-Fi 6. Nevertheless, Bart Stevens, senior director of product marketing for Security IP at Rambus, sounded a cautionary note for vendors. “The implementation of the WPA3 transforms needs to focus much more on high throughput and low latency than used to be for older Wi-Fi standards, due to the larger bandwidth.”

In essence, the faster the native protocol, the faster the crypto needs to be to keep up with the link speed. Wi-Fi security employs the Advanced Encryption Standard (AES) cipher algorithm, which uses either 128-, 192-, or 256-bit keys, and can take 10 to 14 clock cycles for encryption, depending on the size of the key. “The protocol and implementations in older Wi-Fi standards had a disadvantage of only processing 128-bit each 10 to 14 clock cycles, typically maxing out at a couple of gigabit per second, still fast enough for Wi-Fi 6,” said Stevens. “With Wi-Fi 7, this scheme cannot keep up anymore.”

Will we always live in a multiprotocol world?

Now that the “poor cousin” has grown up to be entrenched and wealthy, it’s tempting to ask if any of the alphabet soup of protocols might eventually merge or supersede each other. Most sources find that scenario doubtful, for a variety of reasons.

“People will be living in a multi-protocol world. That’s just the reality of it,” said Robinson. “It’s hard to imagine any scenario where only one technology is going to is going to meet every single use case. Wi-Fi and cellular are complements to one another. Wi-Fi is going to be the predominant connectivity technology indoors, particularly residential and enterprise, and that includes IoT use cases. The Matter stack sits on top of Thread and Wi-Fi. Wi-Fi represents a very sizeable number of matter devices, and that’s not going to change.”

Davidson agreed. “I believe it’s going to be multi-protocol because each of them is targeted at specific use cases with real value. For example, Bluetooth continues to thrive. Even as other technologies are being added, such as UWB for measuring distance, it’s in combination with Bluetooth, because Bluetooth already does that low power discovery better than anything else can. Wi-Fi has that that sweet spot of very high speed with good power, low costs within a building connection. And then cellular gets you the connection everywhere. Over time, each of these technologies may borrow ideas from the other, or they reach a point where they implement the same theoretical ideas, such as OFDMA [originally a cellular scheme] getting added into Wi-Fi. But there’s a definite place for each of the technologies over time. Each will continue to be optimized for specific applications.”

Desjardins believes there’s more likely to be a divergence in the future, than a convergence. As for cellular vs. Wi-Fi, he said that’s already been asked and answered.

“Regardless of how much effort there was in the 5G cellular launch era to make the case that this is a single technology, it just hasn’t happened,” he said. “There was an attempt by a lot of people to make the case for convergence between Wi-Fi and cellular or between unlicensed and licensed technologies. It just didn’t work. The way the technologies have been architected, they have certain strengths and certain weaknesses. Cellular obviously is very good for outdoor coverage, very good for high-speed movement. But it’s an expensive technology to install. Wi-Fi is much more of an indoor technology, though it does work outdoors. It’s not something that’s going to work when you’re driving your car down the highway. It’s really a stationary or slow-moving technology, but it’s incredibly cheap to roll out.”

Still, there is a lot to support. “You have two different quite essential technologies that have such divergent advantages and disadvantages that it would be impossible to integrate them into a single technology,” Desjardins said. “And then in parallel with that, there are other technologies that have their own spaces that work really well. Bluetooth, obviously, is great for audio. It’s very low cost. There are 30 billion devices out there — way more than there are Wi-Fi — so it has it has its own advantages. And then we see these technologies like ZigBee and Thread coming into their own where they’re very cheap, and they just don’t need to move that much data. So you have a number of different requirements throughout the communication space, from sending 1 byte once a month but not burning up your battery and not costing very much, all the way up to 5 or 10 gigabits per second of constant throughput with low latency. And those are diametrically different, so multiple technologies are going to continue to exist. The industries are too large and too entrenched for any customer to really knock any of them over.”

While the general consensus is that separate communications protocols will continue to serve distinct niches, Daren McClearnon, product manager at Keysight, pointed out that spectrum usage has already blended for practical reasons.

“Apple started that a generation ago with the iPhone, and being able to roll over to make calls over Wi-Fi,” McClearnon said. “That multi-mode radio architecture will continue to expand. For example, in 5G there are 28 GHz and frequency range two (FR2) bands, where they’re doing clever beamforming for urban canyons. Between fiber, DOCSIS through cable networks, mobility networks, and then satellite, you’ve had this data revolution at every stage of altitude, buried in the ground as well as overhead, providing this increasingly ubiquitous coverage. So long as there’s money to be made, there will be a drive toward innovation at the technical level to fill those gaps.”

References

The History of Wi-Fi

History and importance of Wi-Fi

Wi-Fi Evolves for the Internet of Things

Official IEEE 802.11 Working Group Project Timelines

Wi-Fi 7 Multi-Link Operation (MLO) white paper