6G is looking to achieve a broad range of goals in turn, requiring an extensive array of technologies. Like 5G, no single technology will define 6G. The groundwork laid out in the previous generation will serve as a starting point for the new one. As a distinct new generation though, 6G will also break free from previous ones, including 5G, by introducing new concepts. Among them, new spectrum technologies will help the industry achieve complete coverage for 6G.
Tapping into new spectrum
Looking back, every generation of cellular technology looks to leverage new spectrum. 6G won’t be an exception, with the emergence of new use cases and more demand for high-speed data. As a result, 6G needs to deliver much higher data throughputs than 5G, making millimeter-wave (mmWave) bands extremely attractive.
This spectrum presents regulatory challenges though and is used by various entities including governments and satellite service providers. However, some bands could work for mobile communications with the implementation of more advanced spectrum sharing techniques. Figure 1 provides an overview of the frequencies allocated for mobile and wireless access in this spectrum.
Figure 1 An overview of frequency allocation for mobile and fixed wireless access in the upper mid-band. Source: Radio Regulations, International Telecommunication Union, 2020
While these frequencies have been used for a variety of applications outside of cellular, channel sounding is needed to characterize the use of this spectrum in 6G to ensure it provides the benefits for the targeted 6G application.
The 7 to 24 GHz spectrum is key area of focus for RAN Working Group 1 (RAN1) within the Third Generation Partnership Project (3GPP) for the purpose of Release 19, which will be finalized in late 2025 and facilitate the transition from 5G to 6G.
Scaling with ultra-massive MIMO
Over time, wireless standards have continued to evolve to maximize the bandwidth available in various frequency bands. Multiple-input multiple-output (MIMO) and massive MIMO technologies were major enhancements for radio systems with a significant impact for 5G. By combining multiple transmitters and receivers and using constructive and destructive interference to beamform information toward users, MIMO significantly enhanced performance.
6G can improve on this further. MIMO is expected to scale to thousands of antennas to provide greater data rates to users. Data rates are expected to grow from single gigabits per second to hundreds of gigabits per second. Ultra-massive MIMO will also enable hyper-localized coverage in dynamic environments. The target for localization precision in 6G is of 1 centimeter, a significant leap over 5G’s 1 meter.
Interacting with signals for better range and security
Reconfigurable intelligent surfaces (RIS) also represents a significant development for 6G. Currently, this technology is the focus of discussions at the 3GPP and the European Telecommunications Standard Institute (ETSI).
Using high-frequency spectrum is essential to achieve greater data throughputs but this spectrum is prone to interference. RIS technology will play a key role in addressing this challenge helping mmWave and sub-THz signals to overcome the high free space path loss and blockage of high-frequency spectrum.
RISs are flat, two-dimensional structures that consist of three or more layers. The top layer comprises multiple passive elements that reflect and refract incoming signals, enabling data packets to go around large physical obstacles like buildings, as illustrated in Figure 2.
Figure 2 RISs are two-dimensional multi-layer structures where the top layer consists of an array of passive elements that reflect/refract incoming signals, allowing the sub-THz signals used in 6G to successfully go around large objects. These elements can be programmed to control the phase-shift the signal to into a narrow beam directed at a specific location. Source: RIS TECH Alliance, March 2023
Engineers can program the elements in real time to control the phase shift enabling the RIS to reflect signals in a narrow beam to a specific location. With the ability to interact with the source signal, RISs can increase signal strength and reduce interference in dense multi-user environments or multi-cell networks, extending signal range and enhancing security.
Going full duplex
Wireless engineers have tried to enable simultaneous signal transmission and reception for years to drive a step-function increase in capacity for radio channels. Typically, radio systems employ just one antenna to transmit and receive signals, which requires the local transmitter to deactivate during reception or transmit on a different frequency to be able to receive a weak signal from a distant transmitter.
Duplex communication requires either two separate radio channels or splitting up the capacity of a single channel, but this is changing with the advent of in-band full duplex (IBFD) technology, which is currently under investigation in 3GPP Release 18. IBFD uses an array of techniques to avoid self-interference enabling the receiver to maintain a high level of sensitivity while the transmitter operates simultaneously on the same channel.
Introducing AI/ML-driven waveforms
New waveforms are another exciting development for 6G. Despite widespread use in cellular communications, the signal flatness of orthogonal frequency division multiplexing (OFDM) creates challenges with wider bandwidth signals in radio frequency amplifiers. Moreover, the integration of communication and sensing into a single system, known as joint communications and sensing (JCAS), also requires a waveform that can accommodate both types of signals effectively.
Recent developments in AI and machine learning (ML) offer the opportunity to reinvent the physical-layer (PHY) waveform that will be used for 6G. Integrating AI and ML into the physical layer could give rise to adaptive modulation, enhancing the power efficiency of communications systems while increasing security. Figure 3 shows how the physical layer could evolve to include ML for 6G.
Figure 3 The proposed migration to an ML-based physical layer for 6G to enhance both the power efficiency and security of the transmitter and receiver. Source: IEEE Communications Magazine, May 2021.
Towards complete coverage
6G is poised to reshape the communications landscape pushing cellular technology to make a meaningful societal impact. Today, the 6G standard is in its infancy with the first release expected to be Release 20, but research on various fronts is in full swing. These efforts will drive the standard’s development.
Predicting the demands of future networks and which applications will prevail is a significant challenge, but the key areas the industry needs to focus on for 6G have emerged, new spectrum technologies being one of them. New spectrum bands, ultra-massive MIMO, reconfigurable intelligent surfaces, full duplex communication, and AI/ML-driven waveforms will help 6G deliver complete coverage to users.
It’s been years in the making, but 5G — the next big chapter in wireless technology — is finally approaching the mainstream. While we haven’t yet reached the point where it’s available everywhere, nearly all of the best smartphones are 5G-capable these days, and you’re far more likely to see a 5G icon lit up on your phone than not.
There’s more to 5G than just a fancy new number, though. The technology has been considerably more complicated for carriers to roll out since it covers a much wider range of frequencies than older 4G/LTE technology, with different trade-offs for each. It’s also a much farther-reaching wireless technology, promising the kind of global connectivity that was once merely a dream found in futuristic sci-fi novels.
SOPA Images/LightRocket/Getty Image
All of this hype around 5G may leave you wondering exactly what to make of it, but the good news is that it’s not as complicated for consumers as you may think. It ultimately comes down to knowing what 5G service is like where you live and work, deciding on the best 5G phone, and picking the best 5G cell phone plan.
Still, with the powerful new capabilities offered by 5G networks, a deeper understanding of how it works can help you make the right decisions. Here’s everything you need to know about 5G.
What is 5G?
Mavenir
Simply put, 5G is the fifth generation of mobile networking that is slowly replacing 4G/LTE networks. And 5G offers the potential for dramatically faster download and upload speeds than 4G networks, plus considerably lower latency — the time it takes devices to communicate with wireless networks.
Also, 5G networks are inherently more efficient, handling more connections per tower and at faster speeds per device. It is also designed to work across a wider range of radio frequencies (aka spectrum), opening up new possibilities in the midrange and extremely high frequency (EHF) mmWave (millimeter-wave) bands for carriers to expand their network offerings. Because 5G is an entirely new technology that operates on new frequencies and systems, 4G-only phones are incompatible with the new 5G networks.
The first 5G networks commenced deployment in 2019, but the groundwork for the next-generation network was laid years earlier. The 5G standard architecture was created in 2016, at which point every company and person involved from both the network and consumer sides could start making devices that were compliant with the new 5G standard.
Joe Maring/Digital Trends
At this point, 5G hasn’t hit total market saturation quite yet — but it’s getting close. It takes a considerable amount of investment to build an entirely new network. For example, 4G/LTE took about three years to reach mainstream status following its initial 2010 deployment in the U.S. However, 4G/LTE didn’t have to suffer through the same growing pains as the newer 5G technology since it was easier to deploy by comparison. All major U.S. carriers used the same basic 4G/LTE technology.
With 5G, carriers have had to take unique approaches in working around existing 4G/LTE deployments while also working to acquire licenses for the higher frequencies that are necessary to deliver on the biggest promise of 5G: ultrafast gigabit speeds. That’s taken more time, and there have been a few roadblocks along the way.
It will likely still be a year or two before 5G becomes the dominant network worldwide, but we’re definitely getting closer, particularly in the U.S. T-Mobile already boasts that its fastest 5G coverage is available to 260 million people, and it expects that to grow to over 300 million — or 90% of the U.S. population — by the end of 2023. While T-Mobile had a big head start over its rivals, the other companies are catching up quickly: earlier this month, Verizon announced it had surpassed the 200 million mark.
Those numbers also only refer to the carriers’ enhanced 5G networks. Depending on the carrier, standard low-band 5G already reaches 85% to 95% of the U.S. population. While these lower-band frequencies don’t deliver the same impressive speeds, they offer other benefits — and the ability to replace 4G/LTE.
How does 5G network technology work?
O-RAN Alliance
Like 4G, 5G technology operates on a wide range of radio spectrum allotments, but is capable of running on a wider range than current networks. With 5G, there are three distinct frequency ranges that work in different ways. The most common form of 5G has traditionally been referred to as Sub-6, but that’s more recently been divided into two subcategories. Beyond that is mmWave, which operates on significantly higher frequencies — with some important tradeoffs.
Sub-6 (Low-Band): Short for Sub-6GHz, the term Sub-6 technically includes all 5G frequencies that operate below that 6GHz threshold. However, in the early days of 5G, that was almost entirely made up of low-band frequencies below 2GHz — the same spectrum that had been used for years by 2G, 3G, and 4G/LTE networks. Most carriers began their 5G deployments using these frequencies as it was the easiest and most affordable way to start; 5G hardware could share the same towers and airwaves used by 4G/LTE service, and since low-band frequencies travel much farther and more effortlessly penetrate walls, trees, and other obstacles, carriers also didn’t have to put up a huge number of new towers to blanket areas with 5G coverage. However, there was a downside to using this low-band spectrum: 5G performance wasn’t significantly faster than the 4G/LTE services that came before. In fact, it could actually be slower in some cases, as 5G traffic had to yield the digital right-of-way to older 4G/LTE signals using the same frequencies.
mmWave: At the other end of the 5G spectrum is millimeter wave, a swath of EHF spectrum where 5G currently operates at frequencies between 24GHz and 39GHz, although it’s likely to expand even higher in the future. As the name suggests, these frequencies have a very short wavelength, which means they don’t travel very far at all — a couple of city blocks at best. The upside is that 5G can deliver staggering performance over mmWave — easily reaching 4Gbps download speeds under ideal conditions. More significantly, this higher capacity also allows for better coverage in densely packed areas like stadiums, concert venues, and airports. However, to blanket an area with this incredibly fast coverage requires thousands of small network cells — covering 95% of New York City would require nearly 60,000 individual mmWave towers. This is why Verizon’s early 5G coverage, which relied solely on mmWave, was available only in the downtown cores of a few major cities.
Sub-6 (midband/C-band): To deliver on the promise of 5G, carriers and regulators needed to find a happy medium between the ultrafast but extremely short-range mmWave and the lower-band frequencies that offered expansive range but no meaningful improvement in speed over the 4G/LTE networks that 5G is supposed to replace. The answer was found in a (mostly) new range of midband frequencies, ranging from T-Mobile’s 2.5GHz network to the 3.7GHz to 3.98GHz C-band spectrum licensed by Verizon and AT&T. This spectrum has become the sweet spot for 5G, offering substantially better range than mmWave while delivering near-gigabit performance levels that leave 4G/LTE networks in the dust.
Today, the major U.S. carriers have deployed 5G in all three of these spectrums, although they’ve taken slightly different approaches. Verizon began with mmWave in a handful of cities before launching its nationwide low-band 5G network in late 2020 and then rolling out its C-band frequencies in early 2022. T-Mobile started with a very low-band 600MHz network that allowed it to be first to offer nationwide 5G in all 50 U.S. states, and then used the 2.5GHz midband spectrum it acquired from its 2020 merger with Sprint to get a head start on building out its faster 5G network. It deployed faster mmWave only in places like stadiums, where the higher capacity was absolutely necessary. AT&T has trailed slightly behind both its rivals; it has a large low-band 5G network, and like T-Mobile, it uses mmWave transceivers to cover denser areas, but its C-band deployments have only reached about a dozen cities so far. How fast is 5G?
Peak data rate: 5G offers significantly faster data speeds. Peak data rates can hit 20Gbps downlink and 10Gbps uplink per mobile base station. That’s not the speed you’d experience with 5G (unless you have a dedicated connection) — it’s the speed shared by all users on the cell. Even then, it’s a theoretical maximum that represents the upper limits of the 5G standard.
Real-world 5G speed: While the peak data rates sound impressive, actual speeds will be considerably lower, and vary widely based on many factors, including what spectrum your signal is traveling on and how far away you are from the nearest tower. Typical 5G speeds can range from 50Mbps to more than 3Gbps for downloads. Recent reports have pegged median nationwide download speeds between 100Mbps and 200Mbps.
Latency: Latency refers to the time it takes to establish a network connection before you can begin transmitting data. This has a big impact on activities like surfing and gaming, where smaller amounts of data are regularly sent back and forth. Under ideal circumstances, latency should be under 4 milliseconds (ms), but lower is always better. The best wired fiber-optic networks can offer a latency of 1ms to 2ms.
Efficiency: Radio interfaces should be energy efficient when in use and drop down to low-energy mode when not in use. Ideally, a radio should be able to switch into a low-energy state within 10 milliseconds when not in use.
Spectral efficiency:Spectral efficiency is “the optimized use of spectrum or bandwidth so that the maximum amount of data can be transmitted with the fewest transmission errors.” For example, 5G should improve spectral efficiency over LTE at 30 bits/Hz downlink and 15 bits/Hz uplink.
Mobility: With 5G, base stations should support movement from 0 to 310 mph. This means the base station should function despite antenna movements. Low-band and midband 5G frequencies are much better at handling this than those in the mmWave spectrum. However, that’s not likely to be a practical concern, as you’re more likely to leave mmWave coverage once you start moving at faster speeds.
Connection density: 5G can support many more connected devices than 4G/LTE. The standard states that 5G should be able to support 1 million connected devices per square kilometer. That huge number takes into account the slew of connected devices that will power the Internet of Things (IoT). What kind of performance you’ll get with that many devices connected is another matter, but that’s where mmWave provides a significant advantage.
In the real world, actual 5G speeds vary widely. Eventually, midband networks will be able to deliver speeds of multiple gigabits per second (Gbps) through technologies such as Carrier Aggregation, but for now, you can expect to see speeds of around 200Mbps to 400Mbps if you’re on a midband/C-band network and under 100Mbps on low-band 5G services. Those numbers may go higher under ideal conditions — we’ve measured gigabit speeds on C-band frequencies, but that’s far from typical. Normally, you’ll need to be relatively alone near a mmWave transceiver to get those kinds of speeds. Remember that you’re also sharing whatever bandwidth is available with everyone else using that same tower, so your performance will drop during peak times of the day in a busy area.
If you’re on low-band 5G, you’ll likely find that your connection is no faster than 4G/LTE. In some cases, it may even be slower. This is largely due to 4G/LTE traffic still using those frequencies. Early low-band 5G deployments were “piggybacked” onto 4G/LTE towers using a technology known as Dynamic Spectrum Sharing (DSS). This allows 5G and 4G/LTE traffic to coexist on the same airwaves, but since DSS is a 5G feature, it’s the 5G traffic that has to make room for the 4G/LTE signals. The good news is that low-band 5G performance will improve as more folks move to 5G smartphones, and there’s less 4G/LTE traffic to contend with.5G UW vs. 5G UC vs. 5GE
T-Mobile 5G at the Leaning Tower of Pisa in ItalyAdam Doud/Digital Trends
Since midband 5G offers much better performance than the lower-band 5G frequencies, each carrier has worked hard to promote these enhanced 5G services with unique brand names and special status bar icons on your phone. This lets customers know when they’re using the best 5G, while also setting them apart from their rivals.
AT&T was actually the first to introduce a special 5G brand, but unfortunately, that initial attempt just muddied the waters as it didn’t even represent a real 5G network. AT&T’s so-called 5G Evolution (5GE) network was little more than a marketing stunt; the carrier rebranded its newly upgraded 4G/LTE Advanced network, claiming it was the first step in the “evolution toward 5G.” In reality, it was the same 4G/LTE network technology that Verizon and T-Mobile already offered, falsely labeled to make people think that AT&T had beaten the others to the punch at rolling out 5G.
AT&T
After getting rightfully pilloried for that silly move, AT&T got a bit more conservative with its 5G plans. However, it was still the first to introduce a unique name in early 2020 to distinguish its mmWave service from its broader low-band network. AT&T called this “5G Plus” (5G+), and it was initially available in the downtown cores of about 35 cities. In early 2022, AT&T added its new C-band spectrum to the 5G+ network, increasing coverage in about a dozen U.S. cities over the course of that year.
Verizon followed in late 2020 with 5G Ultra Wideband (5G UW). Unlike AT&T, this was a rebranding of what had been its entire 5G network up to that point since Verizon began 5G solely with mmWave. The 5G UW name became necessary safter Verizon’s CEO took the opportunity to get on stage at Apple’s iPhone 12 launch event and announce the carrier’s new 5G Nationwide service — a low-band 5G network that would bring 5G to the rest of the country. As with AT&T, Verizon expanded its 5G Ultra Wideband service to encompass the new C-band frequencies in early 2022, increasing 5G UW coverage to more than 100 million customers practically overnight.
So, when should you expect to have 5G available in your neighborhood? If you live in a relatively populated area, at least one — and probably all — of the major carriers already offer 5G. T-Mobile, AT&T, and Verizon have all long since rolled out their “nationwide” networks using low-band 5G. Today these networks collectively cover over 90% of the U.S. population.
All three major U.S. carriers are continuing to build out their midband 5G networks, and while Verizon and T-Mobile now cover a majority of the U.S. population, it’s likely to take several years before we reach ubiquitous 5G coverage. Each 5G carrier also has a slightly different 5G rollout strategy, so your experience will vary greatly depending on your carrier. Here are all the details we currently have concerning each carrier’s deployment plans.
Verizon
Verizon’s 5G nationwide low-band network is technically smaller than AT&T and T-Mobile’s, as it launched much later. Verizon spent years building out mmWave before it started work on its low-band 5G Nationwide deployment, which only arrived in late 2020. Since it began with mmWave, Verizon offers a much greater number of smaller mmWave cells, covering the downtown cores of over 80 cities. That’s still not enough to provide a meaningful, reliable, and widespread mmWave network, but Verizon has expanded that significantly over the last year with its new C-band coverage. As of March 2023, Verizon’s 5G Ultra Wideband network reaches 200 million people. As the carrier continues to expand to more rural areas, its smaller low-band network will become considerably less relevant.
AT&T has a widespread low-band 5G network, with nationwide coverage of around 285 million people. However, the type of 5G connectivity that you get depends on where you live. Like Verizon, it relied heavily on mmWave in the early days, but it also saw the writing on the wall and transitioned to a low-band 5G rollout much sooner. This means less mmWave coverage than Verizon — the core areas of about 39 cities — but a much more expansive low-band network. AT&T’s 5G+ service began with this handful of mmWave cells, rolling in the C-band spectrum in early 2022. Nevertheless, AT&T is still playing catch-up with its rivals, and so far, it’s only deployed full C-band coverage to about a dozen cities, bringing the total number of cities where 5G+ is offered to around 50.
T-Mobile 5G has been leaving its rivals in the dust with robust nationwide coverage and a midband 5G network that covers over 75% of the U.S. population. This has allowed T-Mobile to boast the fastest median download speeds by a huge margin since far more of its customers are able to access its 5G Ultra Capacity network. T-Mobile was also the first carrier to deploy a nationwide 5G network to all 50 states, although that initial network — now known as 5G Extended Range (5G XR)— relies on the lowest of the low-band frequencies, so it’s not particularly fast. However, with 5G Ultra Capacity already covering 260 million people, and T-Mobile promising to extend that to 300 million by the end of 2023, most customers will rarely encounter the carrier’s low-band 5G XR network.
It’s tough to find a phone nowadays that doesn’t have 5G, thanks to the carriers’ aggressive network rollouts and development of more affordable mobile chipsets that include 5G radios. So when you’re looking for the best 5G phone, you’re really just asking for the best phone overall.
Right now, that means the iPhone 14 and iPhone 14 Pro, the Samsung Galaxy S23 and S23 Ultra, the Google Pixel 7, and less expensive phones from OnePlus and Motorola. Each of these phones has 5G — though in some cases, on the cheaper end, you may only get Sub-6 and not mmWave. However, that’s nothing to worry about; as we’ve already mentioned, mmWave is more of a “nice to have” than a requirement, and you’re unlikely to even encounter a mmWave signal most of the time, much less need one.
Can you use 5G for home internet?
T-Mobile
With incredible speeds and low latency, 5G has good potential as a replacement for home wireless networks. That’s particularly true in rural areas, where fast wired internet is tough to come by and the only other alternative is satellite internet. While the capability is certainly there, 5G home internet is taking a while to roll out in real numbers.
We’re still a few years away from the promise of 5G to bring direct connectivity to every device in our homes, so today’s 5G home internet solutions, also known as Fixed Wireless Access (FWA), merely replace your wired broadband router with a 5G device; Wi-Fi and wired Ethernet connections are still used to link everything up within your home.
Verizon 5G home internet
Verizon offers 5G home internet starting at $25 per month, and the recent addition of C-band spectrum to its 5G Ultra Wideband service means it’s now available in 1,700 cities. Sadly, this still limits access to the service in rural areas where it could be more helpful. Speeds will vary depending on where you live; Verizon has a lookup tool you can use to get an estimate, but don’t expect these to rival broadband services unless you live in an area with mmWave coverage.
AT&T 5G home internet
AT&T doesn’t yet offer 5G home internet to consumers, although its 4G-based fixed wireless access plans are still available for rural areas. This will likely get upgraded to 5G eventually, but there’s not much point in doing so right now as AT&T’s low-band 5G network doesn’t offer any performance improvements, and its 5G Plus (5G+) network doesn’t reach enough places yet.
T-Mobile 5G home internet
T-Mobile launched in-home 5G internet service in 2021 to augment its nationwide service. For as little as $30 per month (if you’re already a T-Mobile Magenta Max subscriber), you can get unlimited internet with speeds that range from 33Mbps to 182 Mbps, depending on where you’re located. Unlike its competitors, though, T-Mobile’s 5G home internet is available on both its 5G Ultra Capacity and 5G Extended Range networks, making it a great choice for customers in rural areas. It’s also the most popular 5G home internet service; since its introduction, T-Mobile is now celebrating 1 million home internet customers.
Potential benefits of 5G
Christine Romero-Chan / Digital Trends
There are many reasons to be excited about 5G beyond mobile communication. While the extra bandwidth and lower latency mean faster performance for downloading, streaming, and gaming, the most promising part of 5G is its ability to deliver wireless connectivity to a much wider range of devices and applications. We’re already seeing private 5G networks that are replacing or supplementing traditional Wi-Fi on university campuses, at resorts, and even in retail operations. The lower latency, higher capacity, and greater range offered by 5G make it ideal for offering expansive “always-on” connectivity in areas where Wi-Fi won’t cut it.
Improved home broadband
While 5G is commonly perceived as mobile technology, it’s also poised to have a significant impact on home broadband and wireless connectivity. As mentioned in the preceding section, carriers are now offering home internet services that rely on 5G connections instead of cable or fiber. While it doesn’t yet provide the speed of fiber or cable, it’s more than adequate for everyday surfing, streaming, and browsing, and better than the wired options available in many rural areas.
More significantly, 5G connectivity could someday replace your home router entirely, with all of the devices in your home connecting directly to the 5G network. There are security and performance issues that will need to be worked out before this happens, but work on it is already underway.
Autonomous vehicles
The low latency of 5G makes it ideal for autonomous vehicles, allowing real-time communications with other vehicles on the road, up-to-the-second information about road conditions, and performance feedback to drivers and automakers. For instance, your vehicle can be informed immediately if another car brakes quickly ahead of you and preemptively apply your brakes as well, preventing a collision. This kind of vehicle-to-vehicle communication could ultimately save lives and improve road efficiency.
Public safety and infrastructure
Eventually, 5G will become the backbone of the smart cities of the future, allowing municipalities to operate more efficiently. Utility companies will be able to easily track usage remotely, sensors can notify public works departments when drains flood or streetlights go out, and municipalities will be able to quickly and inexpensively install surveillance cameras.
Remote device control
Since 5G has remarkably low latency, remote control of heavy machinery will become a reality. While the primary aim is to reduce risks in hazardous environments, it will also allow technicians with specialized skills to control machinery from anywhere in the world.
Health care
The ultrareliable and low-latency communications (URLLC) component of 5G could fundamentally change health care. Since URLLC reduces 5G latency even more than 4G, a world of new possibilities opens up. Expect to see improvements in telemedicine, remote recovery, physical therapy via augmented reality, precision surgery, and even remote surgery in the coming years. Hospitals can create massive sensor networks to monitor patients, physicians can prescribe smart pills to track compliance, and insurers can even monitor subscribers to determine appropriate treatments and processes.
IoT
One of the most exciting and crucial aspects of 5G is its effect on the Internet of Things. While we currently have sensors that can communicate with each other, they tend to require a lot of resources and are quickly depleting 4G data capacity. With 5G speeds and dramatically higher capacity limits, the IoT will be powered by communications among sensors and smart devices. What do 5G towers look like?
You might be wondering where the 5G towers in your town are located. For the most part, 5G towers look just like 4G towers — largely because they are 4G towers. The nationwide coverage that T-Mobile, Verizon, and AT&T all offer now is built on slightly tweaked 4G towers, so if you see a traditional cell tower and have 5G coverage in your area, chances are that same tower also supports your area’s 5G network. The fact that they were able to reuse these 4G cell towers is partly how all three carriers were able to roll out nationwide 5G networks on such a short timeline.
Julian Chokkattu/Digital Trends
As carriers start to roll out midband and high-band (mmWave) spectrum, however, this may change. As mentioned, mmWave frequencies can’t travel as far as the Sub-6 frequencies that nationwide networks rely on, and as such, to get mmWave coverage in a city, there must be hundreds, or even thousands, of small cells around the city. These are small white nodes that hang on the side of a building or sometimes on their own little pole. Sometimes they’ll be painted a different color to blend in with their environment, but usually, they’ll remain white.
More of these small cell towers and nodes are likely to pop up in cities in the near future, although they’ll likely be limited to heavily populated areas. However, most areas are likely to rely on midband transceivers; these may require new towers for better coverage, but they won’t look that different from the cellular towers you’ve seen before. Rural areas are likely to continue using existing 4G towers with upgraded low-band 5G equipment installed on them.
Is 5G safe?
Julian Chokkattu/Digital Trends
Yes, 5G is safe — 5G is not dangerous to your health. Concerns about the safety of radio waves have been around for years, but we have yet to find any evidence suggesting that they’re actually bad for human health despite the 5G conspiracy theories.
There are two kinds of radio waves: Ionizing, and non-ionizing. Ionizing waves — the types of radio waves that are used in radiotherapy and X-ray machines — can definitely be dangerous for human health. However, these waves are typically measured in terahertz (THz) and petahertz (PHz), where the infrared and ultraviolet ranges begin. That’s an order of magnitude beyond even the top of the extremely high frequency 39GHz range used by mmWave 5G.
The radio waves used by 5G are not substantially different from those we’ve already been living with for decades, and almost all of them run on the same frequencies that have been long used for 2G, 3G, 4G, and even TV broadcasts, weather radar, and aircraft communications. Even higher-frequency mmWave signals share spectrum that’s long been used for microwave towers, satellite communications, airport security scanners, and weather and military radar systems — and mmWave operates at substantially lower power levels than any of these other devices.
As 5G continues to roll out, work is already well underway on its successor. 6G wireless technology brings with it a promise for a better future. Among other goals, 6G technology intends to merge the human, physical, and digital worlds. In doing so, there is a hope that 6G can significantly aid in achieving the UN Sustainable Development Goals.
This article answers some of the most common questions surrounding 6G and provides more insight into the vision for 6G and how it will achieve these critical goals.
1. What is 6G?
In a nutshell, 6G is the sixth generation of the wireless communications standard for cellular networks that will succeed today’s 5G (fifth generation). The research community does not expect 6G technology to replace the previous generations, though. Instead, they will work together to provide solutions that enhance our lives.
While 5G will act as a building block for some aspects of 6G, other aspects need to be new for it to meet the technical demands required to revolutionize the way we connect to the world in a fashion.
The first area of improvement is speed. In theory, 5G can achieve a peak data rate of 20 Gbps even though the highest speeds recorded in tests so far are around 8 Gbps. In 6G, as we move to higher frequencies – above 100 GHz – the goal peak data rate will be 1,000 Gbps (1 Tbps), enabling use cases like volumetric video and enhanced virtual reality experiences.
In addition to speed, 6G technology will add another crucial advantage: extremely low latency. That means a minimal delay in communications, which will play a pivotal role in unleashing the internet of things (IoT) and industrial applications.
6G technology will enable tomorrow’s IoT through enhanced connectivity. Today’s 5G can handle one million devices connected simultaneously per square kilometer (or 0.38 square miles), but 6G will make that figure jump up to 10 million.
But 6G will be much more than just faster data rates and lower latency. Below we discuss some of the new technologies that will shape the next generation of wireless communications.
2. Who will use 6G technology and what are the use cases?
We began to see the shift to more machine-to-machine communication in 5G, and 6G looks to take this to the next level. While people will be end users for 6G, so will more and more of our devices. This shift will affect daily life as well as businesses and entire industries in a transformational way.
Beyond faster browsing for the end user, we can expect immersive and haptic experiences to enhance human communications. Ericsson, for example, foresees the emergence of the “internet of senses,” the possibility to feel sensations like a scent or a flavor digitally. According to one Next Generation Mobile Networks Alliance (NGMN) report, holographic telepresence and volumetric video – think of it as video in 3D – will also be a use case. This is all so that virtual, mixed, and augmented reality could be part of our everyday lives.
However, 6G technology will likely have a bigger impact on business and industry – benefiting us, the end users, as a result. With the ability to handle millions of connections simultaneously, machines will have the power to perform tasks they cannot do today.
The NGMN report anticipates that 6G networks will enable hyper-accurate localization and tracking. This could bring advancements like allowing drones and robots to deliver goods and manage manufacturing plants, improving digital health care and remote health monitoring, and enhancing the use of digital twins.
Digital twin development will be an interesting use case to keep an eye on. It is an important tool that certain industries can use to find the best ways to fix a problem in plants or specific machines – but that is just the tip of the iceberg. Imagine if you could create a digital twin of an entire city and perform tests on the replica to assess which solutions would work best for problems like traffic management. Already in Singapore, the government is working to build a 3D city model that will enable a smart city in the future.
3. What do we need to achieve 6G?
New horizons ask for new technology. It is true that 6G will greatly benefit from 5G in areas such as edge computing, artificial intelligence (AI), machine learning (ML), network slicing, and others. At the same time, we need changes to match new technical requirements.
The most sensible demand is understanding how to work in the sub terahertz frequency. While 5G needs to operate in the millimeter wave (mmWave) bands of 24.25 GHz to 52.6 GHz to achieve its full potential, the next generation of mobile connectivity will likely move to frequencies above 100 GHz in the ranges called sub-terahertz and possibly as high as true terahertz.
Why does this matter? Because as we go up in frequency, the wave behaves in a different way. Before 5G, cellular communications used only spectrum below 6GHz, and these signals can travel up to 10 miles. As we go up into the mmWave frequency band, the range is dramatically reduced to around 1,000 feet. With sub THz signals like those being proposed for 6G, the distance the waves can travel tends to be smaller – think 10s to 100s of feet not 1000s.
That said, we can maximize the signal propagation and range by using new types of antennas. An antenna’s size is proportional to the signal wavelength, so as the frequency gets higher and the wavelength gets shorter, antennas are small enough to be deployed in a large number. In addition, this equipment uses a technique known as beamforming – directing the signal toward one specific receiver instead of radiating out in all directions like the omnidirectional antennas commonly used prior to LTE.
Another area of interest is designing 6G networks for AI and ML. 5G networks are starting to look at adding AI and ML to existing networks, but with 6G we have the opportunity to build networks from the ground up that are designed to work natively with these technologies.
According to one International Telecommunication Union (ITU) report, the world will generate over 5,000 exabytes of data per month by 2030. Or 5 billion terabytes a month. With so many people and devices connected, we will have to rely on AI and ML to perform tasks such as managing data traffic, allowing smart industrial machines to make real-time decisions and use resources efficiently, among other things.
Another challenge 6G aims to tackle is security – how to ensure the data is safe and that only authorized people can have access to it – and solutions to make systems foresee complex attacks automatically.
One last technical demand is virtualization. As 5G evolves, we will start to move to the virtual environment. Open RAN (O-RAN) architectures are moving more processing and functionality into the cloud today. Solutions like edge computing will be more and more common in the future.
4. Will 6G technology be sustainable?
Sustainability is at the core of every conversation in the telecommunications sector today. It is true that as we advance 5G and come closer to 6G, humans and machines will consume increasing data. Just to give you an idea of our carbon footprint in the digital world, one simple email is responsible for 4 grams of carbon dioxide in the atmosphere.
However, 6G technology is expected to help humans improve sustainability in a wide array of applications. One example is by optimizing the use of natural resources in farms. Using real-time data, 6G will also enable smart vehicle routing, which will cut carbon emissions, and better energy distribution, which will increase efficiency.
Also, researchers are putting sustainability at the center of their 6G projects. Components like semiconductors using new materials should decrease power consumption. Ultimately, we expect the next generation of mobile connectivity to help achieve the United Nations’ Sustainable Development Goals.
5. When will 6G be available?
The industry consensus is that the first 3rd Generation Partnership Project (3GPP) standards release to include 6G will be completed in 2030. Early versions of 6G technologies could be demonstrated in trials as early as 2028, repeating the 10-year cycle we saw in previous generations. That is the vision made public by the Next G Alliance, a North American initiative of which Keysight is a founding member, to foster 6G development in the United States and Canada.
Before launching the next generation of mobile connectivity into the market, international bodies discuss technical specifications to allow for interoperability. This means, for example, making sure that your phone will work everywhere in the world.
The ITU and the 3GPP are among the most well-known standardization bodies and hold working groups to assess research on 6G globally. Federal agencies also play a significant role, regulating and granting spectrum for research and deployment.
Amid all this, technology development is another aspect to keep in mind. Many 6G capabilities demand new solutions that often use nontraditional materials and approaches. The process of getting these solutions in place will take time.
The good news? The telecommunications sector is making fast progress toward the next G.
Here at Keysight, for instance, we are leveraging our proven track record of collaboration in 5G and Open RAN to pioneer solutions needed to create the foundation of 6G. We partner with market leaders to advance testing and measurement for emerging 6G technologies. Every week, we come across a piece of news informing that a company or a university has made a groundbreaking discovery.
The most exciting thing is that we get an inch closer to 6G every day. Tomorrow’s internet is being built today. Join us in this journey; it is just the beginning.
Learn more about the latest advancements in 6G research.
In the 6G Vision White Paper of MediaTek, which detailed how 6G standardization will accelerate digital transformation globally. This white paper alongside 6G standardization, reveals timeline for 6G rollouts, the key drivers of 6G innovation and practical considerations for the implementation of 6G. The white paper also articulates the opportunities and challenges with 6G mobile performance enhancement, network architecture design, spectrum resource usage efficiency, communication and computing integration and energy efficiency.
6G Vision Whitepaper | Credit – Mediatek
In a statement by MingXi Fan, MediaTek’s deputy general manager of Communication System Design, said, “MediaTek’s vision is that 6G will enable intelligent connectivity with ubiquitous and transformational user experiences globally. With an AI-driven, wireless-compute cross-domain integrated and hyper-optimized communication system, 6G will provide truly user(demand)-centered, immersive and energy-efficient connectivity from dense urban areas to enterprises to even very remote regions. By focusing on the SOC design principles – simplexity, optimization and convergence – MediaTek will work with industry partners to make this vision for 6G a reality.”
Observed 6G trends relative to previous cellular generations
MediaTek white paper lists the following new-generation mobile communication features:
New killer applications that require new performance. These include extreme holographic and haptic interactions, digital avatars, and advanced long-distance engagement communications for consumer and industrial grades.
10 to 100 times the data transfer rate of 5G networks, supporting low latency, QoS.
In the additional frequency bands of 7-24GHz and Sub-TGHz, the total available bandwidth of more than 50GHz is provided. The new RF will help applications with extremely high bandwidth requirements, but will also place extremely high demands on RF penetration and coverage.
The network density deployment ushered in innovative technologies to increase the capacity of the medium and low-frequency bands to make up for the shortcomings of the poor penetration ability of the high-frequency bands. Including indoor-based base station deployment, requires a very different deployment strategy than 5G. 6G hybrid nodes will play an important role in reducing the cost of 6G deployment.
MediaTek 6G strategy: simplicity, optimization and convergence:
Flexible model of data consumption
Simplicity: 6G should find a balance between complexity and simplicity, and improve performance and energy efficiency.
Optimized: Combine AI and machine learning to optimize user experience in high-demand scenarios.
Convergence: This flexibility will open up new opportunities for performance, network coverage and deployment costs.
Cross-layer API concept
MediaTek said that it is currently investing heavily in 6G research and development to ensure its leadership in the next few years. MediaTek expects 3GPP to conduct preliminary standardization in 2024-2025, and the first official standard is expected to be launched in 2027.
This graph shows the progress in mobile cellular frequency ranges – from the first generation (1G) in the 1980s to the sixth generation (6G) that is predicted for the 2030s.
“GSM (TDMA-based), originally from Europe but used in almost all countries on all six inhabited continents (Time Division Multiple Access). Today accounts for over 80% of all subscribers around the world. Over 60 GSM operators are also using CDMA2000 in the 450 MHZ frequency band (CDMA450).” http://www.thefullwiki.org/2G
Discussion of Beyond 5G and 6G topics has started in the academic and research communities, and several research projects are now starting to address the future technology requirements. One part of this is the push to higher frequencies and the talk of “Terahertz Technology”. What is behind this drive towards millimetre wave and now Terahertz technology for beyond 5G, and even 6G mobile networks? In this article, we will turn to our trusted colleague Claude Shannon and consider his work on channel capacity and error coding to see how future cellular technologies will address the fundamental limitations that his work has defined.
The driver behind this technology trend is the ever-increasing need for more capacity and higher data rates in wireless networks. As there are more and more downloads, uploads, streaming services, and inter-active AR/VR type services delivered on mobile networks, then more capacity and higher data rate is needed to handle this ever-increasing number of services (and always increasing the high resolution and high-definition nature of video). So, one of the main drivers for the future 6G technology is to provide more capacity into the networks.
Coverage is usually the other key parameter for wireless network technology. Increase in coverage is generally not seen as a fundamental technology challenge, but more a cost of deployment challenge. Sub 1 GHz networks give good coverage, and now 5G is adding satellite communications (Non-Terrestrial Networks) to provide more cost-effective coverage of hard-to-reach areas. But certainly, the interest in millimetre wave and terahertz technology for 6G is not driven by coverage requirements (quite the opposite really).
Defining channel capacity
The fundamental definition of “Channel Capacity” is laid out in Shannon’s equation, based on the ground breaking paper published in 1948 by Claude Shannon on the principles of information theory and error coding. This defines the theoretical maximum data capacity over a communications medium (a communications channel) in the presence of noise.
Where:
C = Channel Capacity.
B = Channel Bandwidth.
S/N = Signal to Noise Ratio of the received signal.
Clearly then the Channel Capacity is a function of the Channel Bandwidth and of the received Signal to Noise Ratio (SNR). But the important point to note in this equation is that the capacity is a linear function of the bandwidth, but a Logarithmic term of the SNR. We can see that a 10x increase in bandwidth will increase the capacity by 10x, but a 10x increase in SNR will only increase the capacity by 2x. This effect can be seen in figure 1 where we plot capacity versus the linear BW term and the logarithmic SNR term.From this we can quickly see that there appear to be more gains in channel capacity from using more bandwidth, rather than trying to improve SNR. However, there is still considerable interest in optimising the SNR term, so we can maximise the available channel capacity for any given bandwidth that is available for use.
This effect is seen clearly in the development and evolution of 5G networks, and even 4G networks. Much focus has been put into ‘Carrier Aggregation’ as this technique directly increases the channel bandwidth. Especially for the downlink, this requires relatively little increase in the UE performance (generally more processing is needed). There has been only small interest in using higher order modulation schemes such as 256 QAM or 1024 QAM, as the capacity gains are less and the required implementation into the UE is more expensive (higher performance transmitter and receiver is required).
Increasing the Channel Bandwidth term in 6G.
As shown in figure 1, the bandwidth term has a direct linear relationship to the channel capacity. So, network operators are wanting to use ‘new’ bandwidth to expand capacity of their networks. Of course, the radio spectrum is crowded and there is only a limited amount of bandwidth available to be used. This search for new bandwidth was seen in the move to 3G (2100 MHz band), and to 4G (800 MHz, 2600 MHz, and re-farming of old 2G/3G bands), and then in 5G there was the move to the millimetre wave bands (24-29 GHz, 37-43 GHz).
As we are considering the absolute bandwidth (Hz) for the channel capacity, if we search to find 100 MHz of free spectrum to use then at 1 GHz band this is very demanding (10% of the available spectrum) whereas at 100 GHz this is relatively easier (0.1% of the available spectrum). Hence, as we move to higher operating frequency then it becomes increasingly easier to find new bandwidth, as the amount of bandwidth that exists is far wider and the chances to find potentially available bandwidth becomes much higher. However, as we move to higher frequencies then the physics of propagation starts to work against us.
As shown in figure 2, the pathloss of radiation from an isotropic antenna is increased by the square of the frequency (f2). We can see that a 10x increase if the operating frequency leads to a 100x increase in losses (20 dB losses) for an isotropic radiation source if the other related parameter of distance is kept constant. This type of loss is usually overcome by having a physically ‘large’ Rx antenna, so by keeping the physical size of the Rx antenna to the same size when we move to higher frequencies, then this loss can be mostly overcome. By using ‘large’ antennas, we have additional antenna gain due to the narrow beam directivity of the antennas, and this helps to overcome the propagation loses. However, this directivity introduces the need for alignment of Tx and Rx beams to complete a radio link, and the consequent alignment error between Tx and Rx beam that must be controlled.
The second type of loss we incur as we move to higher frequencies is the atmospheric attenuation loss. This occurs due to particles in the atmosphere that absorb, reflect, or scatter the radiated energy from the transmitter and so reduce the amount of signal that arrives at the receiver. This type of loss has a strong link between the wavelength (frequency) of the signal and the physical size of the particles in the atmosphere. So as we move to wavelengths of 1mm or less then moisture content (rain, cloud, fog, mist etc) and dust particles (e.g sand) can significantly increase attenuation. In addition, certain molecular structures (e.g. H2O, CO2, O2) have a resonance at specific wavelengths and this causes sharp increases in the attenuation at these resonant frequencies. If we look at the atmospheric attenuation as we move from 10GHz to 1 THz, we therefore see the gradual increase in attenuation caused by the absorption/scattering, and then we see additional peaks super-imposed that are caused by molecular resonances. In-between these resonant frequencies we can find “atmospheric windows” where propagation is relatively good, and these are seen at 35, 94, 140, 220 & 360 GHz regions.
Current 5G activity is including the window around 35 GHz (5G is looking at 37-43 GHz region), and the O2 absorption region at 65 GHz (to enable dense deployment of cells with little leakage of signal to neighbouring cells due to the very high atmospheric losses). Currently the windows around 94 GHz, 140 GHz, and 220 GHz are used for other purposes (e.g. satellite weather monitoring, military and imaging radars) and so studies for 6G are considering also operation up to the 360 GHz region. As we can see from figure 3, atmospheric losses in these regions are up to 10 times higher than existing 38GHz bands, leading to an extra pathloss of 10 dB per kilometre.
So far we have only considered the ‘real’ physical channel bandwidth. Starting in 3G, and then deployed widely in both 4G and 5G, is the technology called MIMO (Multiple Input Multiple Output). With this technology, we seek to increase the channel bandwidth by creating additional ‘virtual channels’ between transmitter and receiver. This done by having multiple antennas at the transmit side and multiple antennas at the receive side. ‘Spatial multiplexing’ MIMO uses baseband pre- coding of the signals to compensate for the subtle path differences between the sets of Tx and Rx antennas, and these subtle path differences enable separate channels to be created on the different Tx-Rx paths. A 2×2 MIMO system can create 2 orthogonal channels, and hence increase data rate by a factor of 2.
A further step is called ‘Massive MIMO’, where there are significantly more Tx antennas than there are Rx antennas. In this scenario then a single set of Tx antennas can create individual MIMO paths to multiple Rx sides (or vice versa) so that a single Massive MIMO base station may provide MIMO enhanced links to multiple devices simultaneously. This can significantly increase the capacity of the cell (although not increasing the data rate to a single user beyond the normal MIMO rate).
A practical limitation of MIMO is that the orthogonality of the spatial channels must be present, and then must be characterised (by measurements) and then compensated for in the channel coding algorithms (pre-coding matrices). As we move to higher order MIMO with many more channels to measure/code, and if we have more complex channel propagation characteristics at the THz bands, then the computational complexity of MIMO can become extremely high and the effective implementation can limit the MIMO performance gains. For 6G there is great interest in developing new algorithms that can use Artificial Intelligence (AI) and Machine Learning (ML) in the MIMO coding process, so that the computational power of AI/ML can be applied to give higher levels of capacity gain. This should enable more powerful processing to deliver higher MIMO gain in 6G and enable the effective use of MIMO at Terahertz frequencies.
A further proposal that is being considered for future 6G networks is the use of ‘Meta-materials’ to provide a managed/controlled reflection of signals. The channel propagation characteristic, and hence the MIMO capacity gains, are a function of the channel differences (orthogonality) and the ability to measure these differences. This channel characteristic is a function of any reflections that occur along a channel path. Using meta-materials we could actively control the reflections of signals, to create an ‘engineered’ channel path. These engineered channels could then be adjusted to provide optimal reflection of signal for a direct path between Tx and Rx, or to provide an enhanced ‘orthogonality’ to enable high gain MIMO coding to be effective.
The figure 4 shows the difference in a limited BW approach to a wide BW approach for achieving high data rates. The limited BW approach requires very high SNR and high modulation schemes (1024QAM) and high order MIMO (4×4), and even this combination of 1GHz + 1024QAM + 4×4 is not yet realisable in 5G. With the wider BW available in THz regions (e.g. 50GHz) then only a modest SNR level (QPSK) and no MIMO is required to reach much higher data rates. So the clear data rate improvement of wider BW can be easily seen.
Increasing the SNR term in 6G
The detailed operation of the SNR term, and the related modulation coding scheme (MCS), is shown in figure 5. As we increase the SNR in the channel, then it is possible to use a higher order MCS in the channel to enable a higher transmission rate. The use of error correction schemes (e.g. Forward Error Correction, FEC) was established as a means to achieve these theoretical limits when using a digital modulation scheme. As the SNR is reduced, then a particular MCS goes from ‘error free transmission’ to ‘channel limited transmission’ where Shannon’s equation determines the maximum data rate that an error correction process can sustain. This is seen in figure 5, where each MCS type goes from error free to the Shannon limited capacity. In reality, the capacity under channel limited conditions does not meet to the Shannon limit but different error correction schemes attempt to come closer to this theoretical limit (although error correction schemes can have a trade-off between processing power/speed required for the error correction versus the gains in channel capacity). Cellular networks such as 5G normally avoid the channel limited conditions and will switch between different MCS schemes (based on the available SNR) to aim on error free transmission where possible.
The yellow shaded zone, in-between the Shannon Limit line and the actual channel capacity of a specific MCS type, denotes the inefficiency or coding overhead of the Error Correction scheme.
The first aspect of improving the SNR term is to develop new coding schemes and error correction schemes (e.g. beyond current schemes such as Turbo, LDPC, Polar) which attempt to reduce this gap whilst using minimum processing power. This represents the first area of research, to gain improved channel capacity under noise limited conditions without requiring power hungry complex decoding algorithms. As the data rates are dramatically increased, the processing ‘overhead’, the cost/complexity, and the power consumption (battery drain) of implementing the coding scheme must all be kept low. So new coding schemes for more efficient implementation are very important for 6G, with practical implementations that can deliver the 100 Gbps rates being discussed for 6G.
To optimise the channel coding schemes requires more complex channel modelling to include effects of absorption and dispersion in the channel. With more accurate models to predict how the propagation channel affects the signal, then more optimised coding and error correction schemes can be used that are more efficiently matched to the types of errors that are likely to occur.
The second aspect of the SNR term is to improve the Signal level at the receiver (increase the Signal part of the SNR) by increasing the signal strength at the transmitter (increase transmit power, Tx). We normally have an upper limit for this Tx power which is set by health and safety limits (e.g. SAR limits, human exposure risks, or electronic interference issues). But from a technology implementation viewpoint, we also have limitations in available Tx power at millimetre wave and Terahertz frequencies, especially if device size/power consumption is limited. This is due to the relatively low Power Added Efficiency (PAE) of amplifier technology at these frequencies. When we attempt to drive the amplifiers to high power, we eventually reach a saturation limit where further input power does not correspond to useful levels of increased output power (the amplifier goes into saturation). At these saturated power levels, the signal is distorted (reducing range) and the power efficiency of the amplifier is reduced (increasing power consumption).
The chart in figure 6 shows a review of the available saturated (maximum) output power versus frequency for the different semiconductor materials used for electronic circuits. We can see that power output in the range +20 to +40 dBm is commercially available up to 100 GHz. At higher frequencies we can see that available power for traditional semiconductors quickly drops off to the range -10 to +10 dBm, representing a drop of around 30 dB in available output power. The results and trend for InP show promise to provide useful power out to the higher frequencies. Traditional ‘high power’ semiconductors such as GaAs and GaN show high power out to 150 GHz but have not shown commercial scale results yet for higher frequencies. The performance of the alternative technology of Travelling Wave Tubes (TWT) is also shown in figure 6, which provides a technology to generate sufficient power at the higher frequencies. However, the cost, size, power consumption of a TWT does not make it suitable for personal cellular communications today.
For higher frequencies (above 100 GHz) existing semiconductor materials have very low power efficiency (10% PAE for example). This means that generally we have low output powers achievable using conventional techniques, and heating issues as there is a high level (90%) of ‘wasted’ power to be dissipated. This leads to new fundamental research needed in semiconductor materials and compounds for higher efficiency, and new device packaging for lower losses and improved heat management. Transporting the signals within the integrated circuits and to the antenna with low loss also becomes a critical technology issue, as a large amount of power may be lost (turned into heat) from just the transportation of the signal power from the amplifier to the antenna. So, there is a key challenge in packaging of the integrated circuits without significant loss, and in maintaining proper heat dissipation.
In addition to the device/component level packaging discussed above, a commercial product also requires consumer packaging such that the final product can be easily handled by the end user. So, this requires that plastic/composite packaging materials that give sufficient scratch, moisture, dirt, and temperature protection to the internal circuits are available. Moving to the higher frequency bands above 100 GHz, then the properties of the materials must be verified to give low transmission loss and minimal impact on beam shape/forming circuits, so that the required SNR can be maintained.
Moving up to THz range frequency results in large increase in atmospheric path-loss, as discussed earlier in this paper. Very high element count (massive) antenna arrays are a solution to compensate for the path-loss by having higher power directional beams. Designing such arrays that will operate with high efficiency at THz frequency poses many challenges, from designing the feed network and the antenna elements to support GHz-wide bandwidth. The benefit is that an array of multiple transmitters can produce a high output power more easily than having a single high-power output. The challenge is then to focus the combined power of the individual antenna elements into a single beam towards the receiver.
So, we can use beamforming antenna arrays for higher gain (more antennas to give more Tx power arriving at a receiver) to overcome the atmospheric propagation losses and reduced output power. The use of massive arrays to create high antenna gain, and the higher frequency, results in very narrow beams. It is of great importance to optimize the beamforming methods to provide high dynamic-range and high flexibility at a reasonable cost and energy consumption, as beam forming of narrow and high gain beams will be very important. These higher frequency communication links will depend on ‘Line Of Sight’ and direct-reflected paths, not on scattering and diffracting paths, as the loss of signal strength due to diffraction or scattering is likely to make signal levels too low for detection. So, along with the beam forming there needs to be beam management that enables these narrow beams to be effectively aligned and maintained as the users move within the network. Current 5G beam management uses a system of Reference Signals and UE measurements/reports to track the beams and align to be the best beam. This method can incur significant overheads in channel capacity, and for 6G there needs to be research into more advanced techniques for beam management.
The third aspect of the SNR term is to improve the noise in the receiver (to lower the Noise part of the SNR).
The receiver noise becomes an important factor in the move to wider bandwidth (increasing the B term, as discussed above), as the wider bandwidth will increase the receiver noise floor. This can be seen as both the receiver noise power increasing, and also the ‘desired signal’ power density being decreased, as the same power (e.g. +30 dBm of Tx power) of desired signal is spread across a wider bandwidth. Both factors will serve to degrade the Signal to Noise Ratio. So improving the receiver noise power will directly improve the SNR of the received signal.
The receiver noise power is made up of the inherent thermal noise power, and the active device noise power (shot noise)
from semiconductor process. By improving the performance of the semiconductor material, then lower shot noise can be achieved. In addition, a third noise type, transit time noise, occurs in semiconductor materials when they are driven above a certain cut-off frequency (fc). So, there is also interest in improving the cut-off frequency of semiconductor materials to enable them to be used efficiently at the higher frequencies of 100-400 GHz region.
The thermal noise is given by the fundamental equation:
𝑃 = 𝑘𝑇𝐵
Where P is the noise Power, k is the Boltzman constant, and T is the temperature (ºKelvin). So, it is clearly seen that increasing the bandwidth term, B, directly increases the thermal noise power. This noise is independent of the semiconductor material, and assuming a ‘room temperature’ device (i.e. not with a specific ultra-low temperature cooling system) then this noise cannot be avoided and is just increased by having wider bandwidth. So, this represents a fundamental limitation which must be accounted for in any new system design.
OFDM (multi carrier) has challenges due to requirement for low phase noise, versus single carrier systems. This may limit the efficiency of OFDM systems in Terahertz bands, as current available device technology has relatively high phase noise. The phase noise component is normally due to the requirement to have a reference ‘local oscillator’ which provides a fixed reference frequency/phase against which the received signal is compared to extract the I&Q demodulation information.
The reference oscillator is usually built from a resonator circuit and a feedback circuit, to provide a stable high-quality reference. But any noise in the feedback circuit will generate noise in the resonator output, and hence create phase noise in the reference signal that then introduces corresponding phase noise into the demodulated signal. In the Local Oscillator signal of the transmitting and receiving system, the phase noise is increased by the square of the multiplication from the reference signal. Therefore, it is necessary to take measures such as cleaning the phase noise of the reference signal before multiplication.
In Terahertz bands, the phase noise may be solved by advances in device technology and signal processing. In addition, more efficient access schemes (beyond OFDMA) are being considered for 6G. OFDMA has a benefit of flexibility for different bandwidths, and a low cost and power efficient implementation into devices. This is important to ensure it can be deployed into devices that will be affordable and have acceptable battery life (talk time). Moving to very wide bandwidth systems in 6G and expecting higher spectral efficiency (more bits/sec/Hz), then alternative access schemes are being investigated and tested. The impact of phase noise onto the performance of candidate access schemes will need to be verified to ensure feasibility of implementing the access schemes.
Measurement challenges for wireless communications in Terahertz bands.
The move to higher frequency in THz band brings the same RF device technology challenges to the test equipment. The RF performance (e.g. noise floor, sensitivity, phase noise, spurious emissions) of test equipment needs to be ensured at a level that will give reliable measurements to the required uncertainty/accuracy.
As new semiconductor compounds and processes are developed, then the semiconductor wafers need to be characterised so that the device behaviour can be accurately fed into simulations and design tools. The accuracy and reliability of these measurements is essential for good design and modelling of device behaviour when designing terahertz band devices. The principal tool for this characterisation is a Vector Network Analyser (VNA), and new generation VNA’s are now able to characterise 70KHz – 220GHz in a single sweep, using advanced probes and probe station technology to connect to the test wafers. This ‘single sweep’ approach gives the very highest level of measurement confidence and is essential for the high quality characterisation needed for next generation of device design. Figure 7 shows a VNA system configured for ‘single sweep’ 70KHz-220GHz, being used to characterise semiconductor wafer samples on a probe station.Wider bandwidth signals require a wider bandwidth receiver to capture and analyse the signal, and this will have a higher receiver noise floor. This noise floor creates ‘residual EVM’ below which a measurement system cannot measure the EVM of a captured signal. For a 5G NR system (8 x 100 MHz) this is 0.89% EVM, but for a wider bandwidth system (e.g. 10 GHz) this could be 3.2% EVM. So careful attention must be paid to the required performance and measurements for verifying the quality wide bandwidth signals. When analysing a modulated carrier signal, the very wide bandwidth creates a very low power spectral density of the signal. If the power spectral density of the received signal is comparable to the power spectral density of the receiver noise, then accurate measurement will not be possible. The dynamic range and sensitivity of test equipment also becomes a challenge at very wide bandwidths. It is usually not possible to just increase the power level of the measured signal to overcome the receiver noise floor, as the ‘total power’ in the receiver may become excessive and cause saturation/non-linear effects in the receiver.
To overcome the possible performance limitations (e.g. dynamic range, conversion losses) then new architectures are being investigated to give optimal cost/performance in these higher frequency band and higher bandwidth test environments.
This work includes finding new Spectrum Analyser technology, and broadband VNA architectures, to enable fundamental device characterisation. An example of a 300GHz Spectrum measurement system using a new ‘pre-selector’ technology is shown in figure 8.
Radio transmitters and receivers often use frequency multipliers as converters to generate very high frequency signals from a stable reference of a low frequency. One challenge with this method is that any phase noise in the reference frequency is also multiplied by the square of the frequency multiplication factor, which can lead to high noise signals which degrade performance. In a receiver, there may also be a Sub-harmonic mixers to easily down-convert a high frequency into a more manageable lower frequency, but these sub-harmonic mixers give many undesired frequency response windows (images). Both effects represent significant challenges for test equipment, as the tester needs to have very high performance (to measure the signals of interest) and flexibility of configuration to be able to measure a wide range of devices. So new technologies, devices, and architectures to overcome these implementation challenges are being investigated for the realisation of high-performance test equipment. An example of this is the use of photonics and opto-electronic components for implementing a high frequency oscillator with low phase noise and high power, where two laser diode sources are mixed together and a resulting IF frequency is generated in the terahertz band.
During early stages of a new radio access method or new frequency band, then characterisation of the modulation/coding type and the frequency band propagation is a key research activity. This characterisation is used to help develop and verify models for coding and error correction schemes. To support this, often a “Channel Sounding” solution is used to make measurements on the frequency channel and for waveform evaluation. This channel sounder is normally composed of a complex (vector) signal source and vector signal analyser. This enables both the phase and amplitude of the channel response to be measured. Such vector transmission systems can be built from either separate Vector Signal Generator and Vector Signal Analyser, or from a combined Vector Network Analyser. This will require Vector Signal Generators and Vector Signal Analysers capable of operating up into the 300 GHz bands. Figure 9 shows a 300GHz band signal generator and spectrum analyser being used in a laboratory evaluation system.With the expected use of AI/ML in many algorithms that control the radio link (e.g. schedulers for Modulation and Coding Scheme, or MIMO pre-coding), then the ability of a network emulator to implement and reproduce these AI/ML based algorithms may become critical for characterising device performance. Currently in 3GPP these algorithm areas are not standardised and not part of the testing scope, but this is likely to change as AI/ML becomes more fundamental to the operation of the network. So, the test equipment may need the ability to implement/reproduce the AI/ML based behaviour.
The move to millimetre wave (24-43 GHz) in 5G has already introduced many new challenges for ‘Over The Air’ OTA measurements. OTA is required as the antenna and Tx/Rx circuits become integrated together to provide the required low loss transceiver performance. But this integration of antenna and Tx/Rx means that there is no longer an RF test port to make RF measurements, and instead all the measurements must be made through the antenna interface. OTA measurement brings challenges in terms of equipment size (large chambers are required to isolate the test device from external signals), measurement uncertainty (the coupling through the air between test equipment and device is less repeatable), and measurement time (often the measurement must be repeated at many different incident angles to the antenna). When moving to THz band frequencies the chamber size may be reduced, but the measurement uncertainties become more demanding due to the noise floor and power limitations discussed above. So careful attention is now being paid to OTA measurement methods and uncertainties, so that test environments suitable for 6G and THz bands can be implemented.
Summary
The expected requirements for higher data rates (and higher data capacity) in a wireless cell are part of the key drivers for beyond 5G and 6G technology research. These requirements can be met with either a wider channel bandwidth (B), or an improved channel Signal to Noise Ratio (SNR). It is seen from Shannon’s equation that increasing B gives a greater return than increasing SNR, although both are relevant and of interest.
Due to the heavy use of existing frequency bands, there is a strong interest to use higher frequencies to enable more bandwidth. This is generating the interest to move to beyond 100 GHz carrier frequencies and to the Terahertz domain, where higher bandwidths (e.g. 10 GHz or more of bandwidth) can be found and could become available for commercial communications systems. The reason that these bands have not previously been used for commercial wireless systems is mainly due to propagation limits (high attenuation of signals) and cost/complexity/efficiency of semiconductor technology to implement circuits at these higher frequencies.
This requirement, and existing technology/implementation restrictions, is now driving research into the use of higher frequency bands (e.g. in the region of 100-400 GHz) and research activities in the following key topic areas:
Channel sounding and propagation measurements, to characterise and model the propagation of wireless transmission links and to evaluate candidate access schemes such as
Advanced MIMO systems, to additional channel capacity by using multiple spatial
Error coding schemes to improve efficiency and approach closer to Shannon limits of SNR
Advanced beamforming and reflector surfaces (meta-surfaces) to enable narrow beam signals to be used for high gain directional
Device and semiconductor technology to give lower shot noise and high fc, and lower phase noise
Semiconductor and packaging technology to give lower loss transmit modules, higher power efficiency and high output power, at the higher frequency
Technology and packaging for integrated antenna systems suitable for both Cell Site and User equipment
In general, it is seen that there are many implementation challenges in using the frequency range 100-400 GHz. For frequencies below 100 GHz then existing RF semiconductor devices can implement the technology with acceptable size/cost/efficiency. Above 10 THz then there are optical device technologies which can also implement the required functions in an acceptable way. Currently there is this ‘Terahertz gap’, spanning the range 100 GHz to 10 THz, where the cross-over between optical/photonics and RF/electronics technologies occurs and where the new device implementation technology is being developed for commercial solutions.
In parallel, the use of AI/ML is being investigated to enhance the performance of algorithms that are used in many of the communications systems functions. This includes the areas of channel coding and error correction, MIMO, beamforming, and resource scheduling.
All the above technology themes and challenges are now being investigated by research teams and projects across the world. The results will deliver analysis and proposals into the standards making processes and Standards Developing Organisations (SDO’s) such as 3GPP, to enable the selection of technologies and waveforms for the Beyond 5G and 6G networks. Not only the theoretical capability, but the practical implications and available technology for affordable and suitable commercial solutions, are critical points for the selection of technology to be included in the standards for next generation cellular communications systems.
All over the world, scientists, governments, corporations and consumers are collaborating to turn the Earth into a giant computer, fulfilling the warning predictions of the great Swedish physicist and Nobel laureate Hannes Alfvén.
Written under the pen name Olof Johannesson, his 1966 science fiction novel Sagan om den stora datamaskinen (The Tale of the Great Computer) predicted smart phones, the internet, fitbits, artificial intelligence, chip implants enabling direct human-to-computer communication, the colonization of Mars, and ultimately the replacement of humankind entirely by computers, which regarded human beings as just one step on the evolutionary path to themselves.
Some of the national and international groups already working toward 6G are:
6G Flagship, a Finnish research and development program funded by the University of Oulu and the Academy of Finland.
URLLC (Ultra Reliable Low Latency Communications) is a collaboration between the University of Oulu and South Korea’s Electronics and Telecommunications Research Institute (ETRI).
TEMA (Telecom Equipment Manufacturers Association of India), in association with CMAI (Cellular Mobile Association of India), have formed the 6G Council.
CEA-LETI. This is the Laboratoire d’électronique des technologies de l’information (LETI), a subsidiary of the Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA), France’s nuclear and renewable energy commission. LETI employs 1,900 people and is headquartered in Grenoble. Its 6G program is called New-6G.
6GIC (6G Innovation Centre), a project of the University of Surrey, in the UK.
InterDigital, a technology research and development company with offices in the US, Canada, Belgium, England and France.
ATIS, the Alliance for Telecommunications Industry Solutions, which has 150 member companies. ATIS issued a press release on October 13, 2020 proclaiming, “ATIS Launches Next G Alliance to Advance North American Leadership in 6G.”
5G-ACIA, the 5G Alliance for Connected Industries and Automation. This is a working group of Zentralverband Elektrotechnik- und Elektronikindustrie e.V. (ZVEI), the German Electrical and Electronic Manufacturers Association.
5G IA (5G Infrastructure Association), the “Voice of European Industry for the development and evolution of 5G.” In the 5G PPP (5G public private partnership), 5G IA represents the private side and the European Commission the public side. 5G IA is headquartered in Brussels, Belgium.
6G@UT, a new research center launched on July 7, 2021 by the University of Texas at Austin and funded by InterDigital, AT&T, Qualcomm, Samsung, and NVIDIA.
6G will use frequencies from 40 GHz to 330 GHz, called “sub-terahertz” frequencies, in order to support “extreme data rates up to 1 Tbps.” The signal bandwidth will be in tens of GHz to “over 100 GHz.” Among other things, 6G will enable autonomous drones, cars, forklifts, trains, excavators and harvesters.
The first European 6G Symposium, a virtual event with 72 speakers, took place May 4-6, 2021. It was organized jointly by 6GWorld, 6GIC, Interdigital, and 6G Flagship. It featured Andreas Mueller, chairman of ACIA; Colin Willcock, chairman of 5G-IA; BK Syngal, chairman of the 6G Council of TEMA/CMAI; Emilio Calvanese Strinati, program director of New-6G, CEA-LETI; DongKu Kim, professor at Yonsei University, Seoul, South Korea and co-chair of the 6G R&D Strategy Committee of the university.
The 2021 Joint EuCNC & 6G Summit took place June 8-11, 2021. EuCNC is the European Conference on Networks and Communications. This event was a joint program of 6G Flagship and the European Commission. It was a virtual conference based in Porto, Portugal.
On July 13, 2021, at an event called Asia Tech x Singapore, 6G Flagship announced a partnership with the country of Singapore. The Singapore part of the collaboration will be housed at the Singapore University of Technology and Design.
Another 6G Summit will take place on August 31, 2021 at the Colorado Convention Center in Denver, Colorado. There will be speakers from Verizon, AT&T, US Cellular, Rogers Communications, T-Mobile, Northeastern University, the Next G Alliance, the National Science Foundation, Virginia Tech and others. The physical event will be followed by a virtual event on September 2, 2021. This 6G Summit is sponsored by the Big 5G Event in collaboration with the Next G Alliance and ATIS.
A 6G Symposium will take place Sept. 21-22, 2021 in Washington DC at Halcyon House. There will be 50 speakers from industry, universities and governments. It is sponsored by 6GWorld in partnership with InterDigital; the Institute for the Wireless Internet of Things at Northeastern University; and the Next G Alliance.
On September 23, 2021, also at Halcyon House in Washington, the U.S. Department of Defense will hold a symposium called 5G to XG US Defense Symposium. It will feature former FCC Commissioner Robert McDowell as well as speakers from InterDigital, Lockheed Martin, Space Economy Rising, the IEEE, the National Institute of Standards and Technology, the National Spectrum Consortium, DARPA (Defense Advanced Research Projects Agency), and the Department of Defense.
And the Brooklyn 6G Summit, titled “Dawn of 6G” and hosted by the Tandon School of Engineering in Brooklyn, New York, will be held virtually on October 18-19, 2021. It will feature speakers from the U.S., Japan, Europe and China.
The third issue of 6G Waves magazine was published in Spring 2021. In it, we read that “the role of 5G/6G is to cognitively connect every feasible device, process, and human to a global information grid.” Its articles paint a picture of a nightmare world into which scientists and engineers are leading us:
The Hexa-X project promises “seamless unification of the physical, digital and human worlds… Whereas 5G is significantly enhancing our ability to consume digital media anywhere, anytime, 6G should enable us to embed ourselves in entire virtual or digital worlds.” This article talks about “massive twinning,” “telepresence,” “cobots,” “the internet-of-senses,” and “ubiquitous autonomous systems closely interleaved in every aspect of our lives.”“Massive twinning” is “the creation of a digital twin from humans, physical objects, and processes.”“Telepresence” will allow people to “interact with, or experience the physical world remotely with lifelike fidelity.”“Cobots” will be “collaborative robots” in homes and public spaces.
Another article discusses a “tactile internet” enabling “humans wearing wearables and interacting with virtual spaces implemented in the network, where the users feel as if they were present in a real place of interest directly interacting with its surroundings.” It envisions “face-to-face (F2F) conferences where remote attendees feel as if they were in a conference room where they can look at any direction. The ongoing COVID-19 pandemic has highlighted the demand for such applications.”
Another article reviews the development of “extremely fine smart dust” — wireless devices that are so small they are the size of tiny particles.
Dr. Ian Oppermann, a government scientist and professor at the University of Technology in Sydney, Australia, thinks 6G is necessary, and that there is “no alternative path for us, if we are to survive as a species.”
His only concerns are that we protect people’s data and privacy. He imagines “a smart home, where the lights turn on and off as you move from room to room, where the heating is controlled intelligently by the number of people at home.” He envisions “a smart toilet that analyzes your urine chemistry and gives you recommendations for what to eat, based on your phosphate levels. Maybe that information gets shared with your fridge and it suggests you should eat more bananas.”
“Another convenient piece of technology might be a drone hovering above your home, providing you with an ad hoc mobile network (great), but in addition the drone can record your location (dubious, but OK) and perhaps measure your body temperature (definitely not OK). The obvious question is, do you consent to all of this?”
The Northeastern Innovation Zone will be operated jointly by Northeastern University and DARPA. It will cover 0.8 square miles at Northeastern’s main campus in Boston, bordering Carter Playground to the east, Columbus Avenue to the south, and Huntington Avenue to the north; and 0.9 square miles at its satellite campus in Burlington, bordering Mary Cummings Park. These facilities will expose everyone in these test areas to frequencies ranging from 746 MHz all the way up to 1.05 THz (1,050 GHz).
The expanded New York City Innovation Zone, known as COSMOS, will be run jointly by Columbia University, Rutgers University, New York University, and City College of New York, and will cover portions of Columbia University, City College, nearby streets, and parts of Riverside and Morningside Parks. Other partners include Silicon Harlem, the University of Arizona and IBM. The New York City testbed will focus on developing ultra-high bandwidth, low latency wireless communications. It will use frequencies from 2500 MHz to 40 GHz.
The Raleigh Innovation Zone will be split into two areas. One will cover 10.5 square miles, including the North Carolina State University campus, a suburban residential area, and the Lake Wheeler Agricultural Research Station. This zone will house the Aerial Experimentation and Research Platform for Advanced Wireless (AERPAW), which will focus on developing wireless communications from unmanned drones.
An additional 3 square miles, covering a different portion of the university campus and extending into the Town of Cary, will host four fixed towers with wireless transceivers. The Raleigh testbed will be operated by North Carolina State University in partnership with Wireless Research Center of North Carolina, Mississippi State University, the University of North Carolina at Chapel Hill, the Town of Cary, the City of Raleigh, the North Carolina Department of Transportation, Purdue University, and the University of South Carolina.
This testbed will use frequencies from 617 MHz to 40 GHz.
Another Innovation Zone, which was established by the FCC in September 2019, is located in Salt Lake City, Utah. It covers 4 square miles consisting of a portion of the University of Utah campus, a downtown area and a corridor connecting the two. This testbed is a joint project of the University of Utah, Rice University and Salt Lake City. The frequencies used in this testbed range from 698 MHz to 7125 MHz. All of the Innovation Zones are managed by the National Science Foundation’s Platforms for Advanced Wireless Research (PAWR) program.
And on June 22, 2021, PAWR announced the establishment of yet another large testbed, based at Iowa State University in central Iowa. This testbed will be spread across Iowa State University, the City of Ames, and surrounding farms and rural communities. Funded by the National Science Foundation and the U.S. Department of Agriculture, it “will create a multi-modal, high-capacity wireless mesh network including low Earth orbit (LEO) satellite links, a free-space optical (FSOC) platform, and long-distance millimeter wave (mmWave) and microwave point-to-point communications.”
In 1862 Henry Brooks Adams, grandson of the sixth American president, wrote, “I firmly believe that before many centuries more, science will be the master of man. The engines he will have invented will be beyond his strength to control. Some day science may have the existence of mankind in its power, and the human race commit suicide by blowing up the world.”
The nightmares of sages past are coming true at a dizzying pace. Do we have the ability to face them, and the courage to plot a different course? To stop blaming one another, and realize that no one is in charge. To stop fighting fire with fire, to let the flames of technology die out so that the dormant seeds of nature may reemerge through its cinders to rebeautify the world, before it is too late.
6G Communications will become one of the largest technology investments. It is currently in the healthy first stage of promising everything to widely deploy some in 2030. Meanwhile, 5G to “Beyond 5G” awaits.
We upgrade telephony to be more useful every ten years. The new IDTechEx report, “6G Communications Market, Devices, Materials 2021-2041”, predicts 6G communications may be more thing-to-thing than human communication. Once again, frequency increases a magnitude. We may mimic 5G in starting at the easy bottom, then go up another magnitude to grab extra benefits. 5G went from GHz level to tens of GHz. 6G may start at a few hundred GHz, then employ 1THz.
Only 6G can widely serve the exponential growth beyond 500 billion connected machines in 2030, real-time holographic communication, the future of virtual reality and empowerment of the poor in realistic timeframes. Expect cell-less communications and Wireless Information and Energy Transfer. WIET is 26 billion passive-RFID tags yearly (IDTechEx analysis). Some sense at the instant of being interrogated. 6G WIET promises that on steroids, even charging your smartphone.
6G will serve airliners at 10 km using Free Space Optical FSO links and deep underwater with fibre-optic links. Internet of Things nodes real-time monitoring billions of trees and ocean oil spills in 3D, billions in concrete structures? Hold on. This sits awkwardly with the consensus that local 6G has to be at terahertz frequencies to get magnitude-or-more improvements in data-rate, capacity, and latency. Terahertz is the Wild West of physics and electronics: little understood, even less demonstrated. They call it the Terahertz Gap. However, this we know. Beam spreading and attenuation, combined with feeble transmission technologies, currently limits these sad pencil beams to a few meters on earth. They are stopped dead by almost anything. We may need electronic wallpaper to get them round the house and many electronic billboards boosting and redirecting them outside.
Raghu Das, CEO of analysts IDTechEx, advises, “Massively-deployed Reconfigurable Intelligent Surfaces RIS are known by six other names just to confuse you. They will be essential for 6G to boost, redirect, collimate, polarise and otherwise manipulate those feeble THz beams using metamaterials embedding new active devices.”
Even at this early stage, some myths are emerging. They are:
6G will be everywhere. No. It flies in the face of the megatrend of eliminating infrastructure. THz local investment will never be justified to put 6G local infrastructure “everywhere.”
Widest area 6G backhaul/fronthaul is a done deal with thousands of Low Earth Orbit satellites recently flung up there and maybe 60,000 in prospect due to competition? No. They have a growing number of legal, safety, light-pollution, repair, latency and other issues. Solar fixed-wing and airship drones intended to be aloft at only 20km for a similar time of 5-7 years have huge advantages of holding position, far-lower latency and cost, easy repair and heavier payloads. Add them. Smaller numbers suffice.
6G should benefit IoT in locations with long-distance optical links. Serving unpowered devices such as 30-year, multi-sensor IoT nodes with fit-and-forget supercapacitors will be excellent. For more, existing energy harvesting is too weak and intermittent to power 99% of envisioned IoT nodes but add 6G WIET. Nonetheless, affordable 6G IoT everywhere in tens of billions yearly? Unlikely.
6G is essential for autonomous vehicles. No, not even desirable. The Tesla approach is to make a car you can put anywhere and it will navigate safely without being connected to any wireless system. Even the interim stage of LIDAR using ongoing mapping does not need connectivity. Relying on a new form of connectivity that requires exceptionally complex hardware everywhere would be downright dangerous. That is why the telecom operators went quiet about the 6G robot vehicle idea. Vehicles need connectivity and 6G may provide a better form but that is another matter.
License 6G bands near 10THz for even greater 6G performance? Sadly, in air, there is a nasty jump in attenuation beyond 1THz and active components get really challenging. This is not desirable or achievable.
Nevertheless, those arguing B5G means no need for 6G are wrong. Basic physics. IDTechEx report, “5G Technology, Market and Forecasts 2020-2030” explains and the IDTechEx 6G report tracks even more-demanding requirements arriving, making this more of a myth. We need 6G.
From telepresence holograms to machines as the network’s primary users, 6G will be very different from today’s network. But does the hardware for this network even exist?
While 6G networks are a nascent concept in 2021, corporations like Samsung and Nokia are already analyzing the potential hardware and software options required to make 2030 a target year for early commercialization.
Applications of 1G networks from the1980s to the proposed applications of 6G in 2030. Image used courtesy of Arxiv
6G Requires Unprecedented Throughput
The Internet of Things will be a significant driving force to develop the sixth-generation network infrastructure.
For the first time, machines will be the principal users of the network resources in “machine-to-machine (M2M) communication.” Secondary human users may use the expanded bandwidth for virtual/augmented reality, telepresence holography, and tactile control of robotics for high-precision tasks.
Today, 5G technologies rely on disaggregated network functions in the radio access network (RAN), edge computing, and virtualized network hardware to reduce cost and increase performance. These functions exist as trade-offs to each other to deliver the 5G network as it is now: enhanced mobile broadband, ultra-low latency communications, and M2M communications.
Visual of the design requirements for 6G. The 5G trade-offs requiring various RAN configurations are replaced by a heterogeneous online system. Image used courtesy of Samsung
However, for 6G to succeed, the trade-offs will need to be eliminated, allowing for a fully-connected, always-online world. This connectivity represents an exponential increase in RAN throughput and computes capability that isn’t accomplishable with discrete hardware/software functions.
A new spectrum is necessary to overcome these challenges, and engineers will need to develop accommodating hardware and metamaterials. Finally, AI and ML technology for 6G technologies will need to be “taught” and deployed in as few as nine years.
Path loss due to absorption and loss of line-of-sight (LoS)
Electronics hardware dimensions, inducing losses in transmission, reception, and processing
Advanced antenna lens and beamforming requirements to achieve LoS
RF channel optimization, allocation, and the possible development of a replacement for orthogonal frequency-division multiplexing (OFDM)
LoS analysis of the various frequency bands operating today, both in practice and experimental. Image used courtesy of Arxiv
According to the IEEE research group, visible light communications will offer a cost-effective alternative to THz technologies by modulating LEDs and piggybacking on existing RF applications indoors to extend cellular coverage.
6G Requires New Hardware and Materials Research
Printed electronics may be key to the adoption of THz technologies, according to IDTechEx. These printed electronics would take the form of reconfigurable intelligent surfaces (RIS), measure only a few microns thick, and apply to many of the issues surrounding LoS communications.
A future metasurface structure steers the wave from an antenna in a more direct beam. Samsung believes RIS could replace antennas as well. Image used courtesy of Samsung
Metamaterials could address the issue of beamforming the signals for propagation to targets at various elevations on the ground, in the air, or around obstacles.
A high-level depiction of RIS. Developers will need to deploy RIS in high densities to overcome line-of-sight obstacles. This will re-broadcast or redirect signals to their target. Image used courtesy of Samsung
Network Requirements for Disaggregated Compute
Covering the generational shift to 6G, Peter Vetter (head of Nokia Bell Labs access and devices research) notes something of particular interest to hardware designers.
In a webinar, he explains that within the next 10 years, designers may see the advent of specialized hardware performing one function with limited onboard compute, aggregated into one application. This compatibility means that the network itself would be responsible for cloud edge processing and decision-making based on the increased hardware outputs.
Climbing the 6G Mountain Requires All Engineering Disciplines
To overcome the challenges associated with high-reliability, high-throughput 6G networks, engineers from all disciplines will need to work together. Hardware engineers will develop sensor and RF technology, AI/ML experts will develop self-optimizing networks, and computer engineers will create disaggregated compute capability.
Regulatory bodies such as the FCC will also play an essential role in protecting and allocating the spectrum required to facilitate this new digital domain.
5G may be here in 2021, but 6G development is accelerating already, and 2030 doesn’t seem so far away.
The economics of the market will not support widespread deployment of networks at 100 GHz, due to multiple problems.
Two years ago, talking about 6G was a joke. Not anymore. Now that 5G base stations are rolling out in production, the advanced R&D teams of 100 companies are turning their collective attention to “what comes next.”
In every generation so far, the engineers have led the process, driving toward faster data rates and higher spectral efficiency with each step. Extrapolating the trend of the past 30 years, university professors now are testing ever-higher frequency bands, and dreaming about mobile links at speeds in the Tbps range. This is a mistake.
From 1990 to 2020, the speed-driven approach matched up with market requirements pretty well because we had spectrum that was able to propagate well and penetrate indoors. Now things are different.
Terabit links are a great idea, but there’s a problem if you think that this is the next “G.” The economics of the market will not support widespread deployment of networks at 100 GHz, due to multiple problems:
Radio signals above 90 GHz don’t penetrate any barriers, including walls, windows, or the windshield of your car. An access point in one room won’t even work for the adjacent room.
Reflections are not predictable with the small wavelength of signals at 90+ GHz. Operators are trying to use reflections for NLOS 28 GHz and finding that the connection is not stable, because tiny changes due to temperature or moisture can change the angles of a narrow beam’s reflection.
Propagation in the high frequency bands doesn’t allow radio signals to travel very far. The air itself absorbs energy, leaving us with very short range for the envisioned 6G networks.
The above list of problems are not simply engineering challenges to overcome… they’re basic physics. Don’t fight against God.
When you’re confronted by a roadblock, it can be useful to stop and think: What’s my destination anyway? In this case, it’s increasingly clear that pure speed is not the goal anymore. Nobody really needs terabit speed to their mobile phone. We have mobile networks that can run as high as 2 Gbps today, but almost nobody uses an app that requires more than 50 Mbps.
Four years ago, I started to say that speed doesn’t matter anymore. People told me that “apps that use gigabit data will come along.” But hey, here we are with nationwide 5G networks and no app is even close to using the peak speed. When nationwide 4G networks were deployed, Uber and Google Maps had already been on the market for three years or more. Times change.
So, chasing faster speed is not a perfect match with the market need. The unsolved problem in the mobile market is about how to deliver mobile data capacity where the people are, not how to deliver faster data to a few line-of-sight locations.
Instead, I propose a different direction for the thrust of 6G. We should focus our 6G attention on TV white spaces, land-mobile radio bands, radionavigation bands, military bands, and other spectrum below 6 GHz. We have already demonstrated that shared spectrum can work great. Cognitive radios for LAA and CBRS can sense the presence of other radio transmitters and adjust their parameters. Let’s apply these cognitive radio techniques in areas where the spectrum is only lightly utilized, and take advantage of spare channels, coverage holes, and slack time on existing radio services.
Our calculations indicate that below 6 GHz, as much as 3.5 GHz of spectrum is used in ways that leave gaps in either time, frequency, or location. Valuable low-band spectrum is devoted to radio and television broadcasts, which are phasing out in the age of podcasts. As much as 400-500 MHz is devoted to “radionavigation,” which is essentially obsolete in the age of GPS.
I agree, some of these radionavigation aids are important. For example, at 4.2 GHz every aircraft uses a radar to measure its height above the ground. Let’s leave that band alone, okay? But many other navigation aids are no longer necessary, or could be operated at a 10% duty cycle without anybody getting lost.
Even if the industry can only harvest 30% of the available spectrum below 6 GHz, we could extract another 1100 MHz of spectrum for true mobile communications. That’s double the available mobile spectrum today. (This calculation is for the crowded American market. In other markets we believe the available spectrum would be even richer.)
To me, 1100 MHz of low-band mobile spectrum is far more valuable than 100 GHz of spectrum in the high millimeter-wave bands. If we’re going to spend eight years on blue-sky R&D, let’s focus the effort on something really useful.
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