As frequencies open up en route to 6G, possible frameworks to best utilise spectrum are becoming increasingly important discussion topics among stakeholders. A few of those key discussions took place at the first annual 6G Symposium.

CBRS as a Basis for 6G Spectrum Sharing?

From the get-go, on a panel entitled “Spectrum Sharing in 6G Systems,” the Citizens Broadband Radio Service (CBRS) in the U.S. served as key reference point. With Spectrum Access Systems (SAS) having been deployed to manage use of the 3.5GHz band and ensure incumbents, like the U.S. Navy and its radar systems, are not interfered with, the CBRS was seen by panelists as a success story.

“CBRS has been under full commercial deployment since January of this year and we are approaching the 100,000 mark for the number of base stations that have been authorized in the CBRS band. So it is working, and despite all of those deployments, we have not had a single reported case of interference to incumbents,” said Andrew Clegg, the Spectrum Engineering Lead at Google, who suggested we may be “overprotecting” spectrum from parties like the commercial sector as a result.

The panelists readily acknowledged the need to build on the CBRS template. Monisha Ghosh, Federal Communications Commission (FCC) CTO, and Tom Rondeau of the Defense Advanced Research Projects Agency (DARPA) each cautioned against looking too much into the success of CBRS, as the radar systems in question are relatively simple and feature protection requirements projected to change. Meanwhile, the need for a new propagation model was another focal point.

Sheryl Genco, Director  of  the Institute  for Telecommunications  Sciences, reported how it’s currently being addressed at the ITS, where they are seeking buy-in from both government and the commercial  sector. She  also  spoke  of the potential for real-time spectrum management.

“That’s a really big  push for  the  whole-of-nation approach  and, with the [Department of Defense], the Defense Spectrum Organization, and [National Telecommunications and Information Administration], we’re discussing a pre­ decisional idea about  incumbent-informing capability,  where federal  users provide data  when  they’re using spectrum and that  data  would grant access  to nearby commercial users when it’s safe and appropriate to do so,” she said.

Masoud Olfat, Senior Director  of Technology  Development  at  Federated Wireless, agreed on the need to inform incumbents as a way to improve the existing CBRS  framework.  Another,  in his view,  is  the  use  of  artificial intelligence (Al) andmachine learning (ML).

“It allows an entity like SAS to  kind of have a better and more efficient  spectrum allocation so that it doesn’t necessarily require a lot of exchange  to  do that,” he said. “By employing those Al-ML systems, we can have a much better and more efficient spectrum-usage prediction and that  allows  us  to make the CBRS model more real-time.”

Moving to Terahertz Frequencies

The preceding panel discussion, “Conquering the Spectrum,”  was  moderated by Josep Jornet, of event co-organiser  Northeastern  University’s  Department of Electrical and Computer Engineering. He spoke of opportunities exploring terahertz frequencies from a technological standpoint.

“We are in the context of 6G, so the first thing  that  comes  to  mind  is  that we’re trying to create faster wireless networks… There are discussions on utilising the THz band  for  wireless  backhaul, maybe to  provide infrastructure  to rural areas…  Maybe  the THz band  is  helpful for inter-satellite communications or even space networks,” he said.

“At these frequencies  different materials, different molecules exhibit some unique electromagnetic signatures and actually those can be leveraged to understand our surroundings. For example, as we speak, there are several satellites orbiting the Earth with THz radios up  top … They  are characterising the atmosphere and also listening to signals from deep space.”

Speaking to 6GWorld in a separate interview, Marco Giordani of the University of Padova discussed the use of THz frequencies in the context of satellite communications. He said even though  they aren’t  suitable  to  provide communications to Earth, intra-satellite communications are a very real use case.

“When you are in free space then you can make satellites communicate with each other at free-space optics and THz,” he said. “So a geo-stationary satellite can communicate with [a Low-Earth-Orbit  satellite]  using  THz  and this actually is very good, because the bandwidth at THz is huge and you don’t have the propagation  issues  that  you experience  when  you  are in the atmosphere.”

6G Questions Still to Be Answered

In addition to macro applications, Jornet pointed out 6G use cases at the “nanoscale” as well.

“We can potentially make very small antennas utilised for wireless networks and achieve device-to-device communications, but also more transformative applications like enabling communication between nanosensors with physical, chemical, and biological capabilities,” he said.

“It is not science-fiction. This more than 20-30 years of  device research  that now finally we may be able to connect to the world… In the Internet of Nano­ Things or the idea that the user, the human is not just a user but actually a part of the network might start to make sense as we move forward.”

Co-panelist Gerhard Schoenthal, COO of Virginia Diodes, relayed several challenges on the manufacturing and testing side. They include indium phosphide as a semiconductor material, which is not completely developed for infrastructure and commercial applications. Another challenge he presented revolves around microelectronic architectures.

“As you move into the THz spectrum, the devices that are in play that have been used and produced today include integrated mmWave, integrated microwave assemblies and chip and wire architecture,” he said. “These are mostly suited for low-volume, high-mix applications.”

Regarding applications from a spectrum-sharing perspective, Rondeau argued there are still a lot of questions that need to be answered as well.

“I think a lot of the talk right now about getting up to  higher  frequencies,  it seems a bit like a land grab versus actually supporting real needs that we can identify,” he said. “I think helping to identify those over the  next few years  in  the SG era will hopefully lead to exactly what we need to share, how much we need to share, in what timelines does that sharing really need to occur.”

Edward Knightly of Rice University’s Department of Electrical and Computer Engineering spoke on the “Conquering  the Spectrum”  panel. He felt predicting a single  “killer”  6G application  wouldn’t  do the developing  technologies justice.

“I think our fallacy is to try to think of one ultra-ridiculously high-speed application and I think the reality, as we’ve seen with the wired internet, has been it’s aggregate,” he said.

“It’s just many, many people watching Netflix that require the high-speed wired infrastructure. I think with wireless it’s the same thing. I don’t think one terabit app is compelling as many, many users, high density, and just wanting

a massive flow of information up and down, and  sensing.  They  want  both those capabilities at the same in a small form factor. I think that together is going to be the key driver.”

The first annual 6G Symposium, co-hosted by lnterDigital and the Institute  for the Wireless Internet  of Things at  Northeastern  University, took place on October 20-21. Recordings of individual sessions, including those mentioned above, will be available to view at www.6GWorld.com.