6G might reach 100 Gbit/s, but who will deploy it?

Docomo, NEC, NTT and Fujitsu this week announced new tests of a "wireless device" capable of 100 Gbit/s speeds, running in the 100GHz and 300GHz spectrum bands. The companies said their work represents a precursor to eventual 6G networks.

To be clear, it's still early days for 6G. 3GPP is the primary standards organization for cellular Gs including 4G and 5G. And it's still working on its Release 18 collection of specifications for 5G Advanced systems. Release 20 is expected to contain the group's first 6G specifications, which would put commercial 6G networks (at least those adhering to commonly accepted standards) in the 2030 timeframe.

Regardless, companies like Docomo and Fujitsu continue to play with technologies that might make it into an eventual 6G standard. Their work is somewhat illuminating: "To date, tests of a jointly developed wireless device have achieved ultra-high-speed 100 Gbit/s transmissions in the 100GHz and 300GHz bands at distances of up to 100 meters. By comparison, 100 Gbit/s is approximately 20 times faster than the maximum 4.9 Gbit/s data rate of current 5G networks."

The companies' new tests are taking place in the "sub-terahertz" bands, which is spectrum far above the bands used for 4G and 5G. That's why the companies' tests occurred indoors and at distances up to 100 meters.

Propagation characteristics

In general, transmissions in lower spectrum bands travel farther than transmissions in higher spectrum bands. However, higher spectrum bands – like those in the sub-terahertz range – can generally support much faster data speeds.

None of this comes as a surprise. Some early 5G networks in the US worked in the millimeter wave (mmWave) spectrum bands, which generally sit between 20GHz and 30GHz. As a result, transmissions in those bands only traveled a few thousand feet, and typically could not pass through buildings or other objects.

Not surprisingly, such mmWave 5G networks didn't stretch beyond stadiums and downtown areas. As a result, there are not very many operators around the world that have embarked on their own mmWave network buildouts.

Today, most 5G efforts in the US and internationally are in "midband" spectrum, generally bands between 2GHz and 4GHz. As a result, they can reach much farther than mmWave networks.

What that means from a network-construction standpoint is that midband 5G operators can mostly use the same transmission sites for 5G that they used for 4G. They don't have to invest in building thousands, or millions, of new transmissions sites that would be necessary for widespread mmWave networks.

A fresh look at mmWave

However, it's worth noting that there's some new noise around mmWave. "The past four years have been a difficult time in millimeter-wave technology, but Mobile Experts has been able to identify the bottom-up growth associated with fixed wireless access (FWA), high-density venues (stadiums and airports), private 5G, and transportation applications (metro lines and trains)," wrote the analysts at Mobile Experts in a recent report.

"Mobile operators with widespread outdoor mmWave coverage have failed to achieve effective data offloading for their lowband cellular networks," Dan McNamara, a principal analyst at the firm, said in a release. "As a result, for the past three years the mmWave market has been reset to focus on very specific applications."

Indeed, vendors including Pivotal Commware, PeltBeam, Peraso, Pharrowtech, Movandi and others continue to look for 5G opportunities specifically in the mmWave bands.

And what does all this mean for 6G? First, sub-terahertz bands like 100GHz and 300GHz are not expected to be the primary bands for 6G. Big equipment suppliers like Nokia and Ericsson have begun putting the so-called "centimetric" spectrum bands – those between 7GHz and 20GHz – at the center of their pitches for 6G.

Sensing the future

So why focus on the sub-terahertz bands at all? One reason is because 6G in such bands may give a "sensing" capability to basestations and user devices, enabling radio signals to feel out the size and shape of any unconnected object, and maybe even figure out what it's made of. "Perhaps a 6G radio signal could dip its invisible fingers into an almost-empty pint glass and notify the barman of the need for a refill," wrote my colleague Iain Morris.

A new ETSI report dives into some of the use cases for such technology: "Mobile robots also require high accuracy sensing and localization, which can be provided in the THz [terahertz] spectrum," the association wrote. "The mobile robots not only need to sense and localize themselves in a static environment, but also in relation to other mobile robots, humans and moving objects. ... A group of cooperative robots assembling or jointly carrying an object may require high-precision sensing and localization to complete one or more tasks successfully."

And that is just one of more than a dozen potential examples from ETSI.

However, it's also worth noting that sensing technology isn't restricted to 6G. Already cable company Comcast has been discussing a new motion detection capability for its XB10 in-home Wi-Fi platform. Customers will be able to use the company's app to select devices and create motion detection "zones," all via sensing technology.

Paying for 6G

So is 6G in terahertz spectrum (from 100GHz to 10THz) worth a look? One big player in the mmWave market is not willing to bet on an upswing in demand. Crown Castle – a tower company that invested heavily in the small cells necessary for mmWave transmissions – is now looking to sell its business. Crown Castle has deployed more than 100,000 small cells, mostly outdoors.

However, other companies are reporting growing demand for indoor wireless installations. Such networks promise to allow a building or venue owner to purchase and install its own private 3.5GHz CBRS wireless network and then connect it to a big, public wireless network operator through the Multi Operator Core Network (MOCN) standard. By doing so, the venue can offer indoor cellular coverage – an important stipulation for venues with lots of foot traffic like hotels and hospitals.

Indeed, demand for this kind of installation is high enough that companies like Dense Air are building such indoor networks themselves, and then recouping that investment by renting out the network to the building owner. Jim Estes, CEO of Dense Air, said building owners can pay for their indoor wireless coverage on a monthly basis, just like they already do for electricity, water and heating and air conditioning.

Wireless is "the fourth utility," he said. Estes wouldn't say how long it takes for Dense Air to recoup its investments into building such indoor networks.

Regardless, that kind of trend might help the development of 6G in terahertz networks, at least indoors. After all, most 5G operators have dramatically scaled back their network investments and it's unclear whether they will have the appetite for new 6G investments anytime soon.