Experts Debate Whether 6G Will See the Use of Terahertz

October 6, 2021

Written by Caio Castro
CATEGORY: Exclusives

Several white papers and visions about 6G published in the last two years foresee that the next generation of mobile connectivity will demand a move to the Terahertz spectrum. Universities, private companies and even national governments, such as Japan and South Korea, have started research above 100 GHz. But not everyone believes that’s how things will unfold in a near future.

Speaking at the 6GSymposium, experts showed that some of the telecommunications community hasn’t bought the idea of going to the Terahertz realm so soon, and definitely not in 6G.

“Moving to Terahertz for 6G is premature in my opinion. I think certainly Terahertz [band] is [going to be adopted] in 7G and beyond, it’s not something that’s going to be prevalent at 6G,” Andrew Clegg, Spectrum Lead at Google, said in a panel during the 6GSymposium. “I don’t think we’re going to get to the technology and to the use cases where Terahertz makes sense.”

Part of the concern comes from how much there is to be known about millimetre waves, still an uncharted domain in many aspects, before we need the Terahertz band. Meanwhile, as research and commercial deployments go on, some experts believe today’s frequencies will be enough to meet technological expectations.

“We’re doing actual trials, commercial trials with operators at 600 MHz, 800 MHz, 1.9 GHz. I believe the industry is going to spend another 10, 20 years in the existing frequencies, and during that time we’ll break through the physics issues and the hardware issues on some of these higher frequency bets,” said Raymond Dolan, CEO of Cohere Technologies, also during a panel at the 6GSymposium.

Another challenge is to overcome how much interference signals are subject to in the Terahertz bands. Because a hypothetical 6G technology would operate in such high frequencies, the signal would also be more susceptible to obstruction from elements like raindrops, leaves and other physical obstacles in its way, limiting its use outdoors.

This is a concern researchers also have regarding millimetre waves today.

Monisha Ghosh, Research Professor at the University of Chicago and former FCC CTO, said she’s impressed by how far millimetre technology has come so far, including the dense deployments in Chicago. On the other hand, Ghosh is unsure as to what needs are being truly served.

“That signal does not penetrate [nicely] indoors. We have a location on our campus where there’s a millimetre wave base station right outside a dorm. We went inside the dorm and tried to make some measurements. The window was cracked open just a bit, and you had a line of sight to the panel and the signal came right in and you put your phone right there. Yes, you got your one gigabit per second, but other than that [exact setup] you got nothing,” she said.

Don’t Give Up on Terahertz Just Yet

While there may be some skepticism around how – and when – we will employ Terahertz for telecommunications, experts also say research is fundamental to understand what the best uses for this technology are.

Josep Jornet, Associate Professor at the Northeastern University, believes the Terahertz waves can prove to be efficient in several areas.

“It’s difficult [for an eavesdropper]to understand what you’re saying. Everything that makes this challenging to propagate makes it challenging to intersect,” Jornet mentioned.

“Maybe we can’t yet envision how we’re going to use these higher frequencies in the fronthaul, but clearly in the concept of wireless backhaul, it makes sense.  Backhaul that may not be on the ground but up there in the sky,” the expert finished.

Understanding where Terahertz technology can be useful in the future will take time. But figuring out the best fits for this uncharted realm in telecommunications, be it for 6G or beyond, will definitely come in handy. 

“The use cases of this technology have to be thought out more carefully. Having said that, as a researcher and somebody who has funded a lot of research programs in Terahertz and millimetre wave, I do feel the research on this topic has to continue,” Ghosh said. “It is a frontier. We have to fully understand what the capabilities are and find where it truly fits.”

Featured image by Troy Squillaci

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