5G may still be in its infancy, but researchers are already looking ahead to next “G” and a big part of their focus is on Terahertz (THz) spectrum frequencies. It may take some creative engineering, but this spectrum, which is very high on the frequency chart, is thought to be as useful to mobile operators for delivering 6G services as millimeter (mmWave) spectrum is for delivering certain 5G applications.
High on the frequency chart
There are really two components to the THz spectrum band: sub-THz, which is in the range of 100 GHz to 300 GHz, and THz, which is from 300 GHz to 3 THz on the spectrum chart. The sub-THz is also known as D-band spectrum, which falls in the range of 130 GHz to 175 GHz.
The benefits of THz spectrum are that it can deliver data-intensive, high bandwidth applications at super-fast speeds for a short distance.
In March 2019 the FCC saw the potential of the THz bands and issued its Spectrum Horizons Report and Order, which created a new category of experimental licenses for use of frequencies between 95 GHz and 3 THz. These licenses are intended to give researchers the flexibility to conduct experiments lasting up to 10 years, and to more easily market equipment during the experimental period.
Many companies are devoting research and development dollars to exploring THz frequencies. Last summer, Samsung released a white paper detailing its vision for 6G and said that it believes it’s inevitable that the THz spectrum bands will be used in future mobile communications systems.
But Samsung isn’t alone. Apple also is looking for wireless research systems engineers to specifically work on 6G. In a recent advertisement the company said it wanted someone with an understanding of multi-antenna techniques as well as “preferred qualifications” such as familiarity with wireless system design in high frequencies, including GHz and THz.
Mobile or fixed?
According to Andreas Roessler, technology manager at test equipment firm Rhode & Schwarz, a signal can travel in THz spectrum for about 100 to 150 meters. However, similar to mmWave spectrum, that signal may be impacted by environmental conditions, such as heavy rain and snow.
“You can pump a lot of data across a 10 GHz wide channel but your problem is your noise power is so high,” he said, explaining that one way to solve this is to have an antenna array that forms a pencil-thin beam. This helps eliminate interference but it also means that the receiver of that signal must be highly coordinated and be in line of sight, otherwise there may be interference problems.
Because of this challenge, Roessler is uncertain whether THz spectrum will be used for a mobile wireless service. Instead, he believes THz spectrum might work best for a fixed wireless implementation or backhaul or for a specific application such as location sensing.
But not everyone agrees with this. Ted Rappaport, founding director of NYU Wireless, which is currently conducting 6G research, said that it’s a myth to think that THz frequencies have more issues with interference and attenuation than mmWave spectrum.
Instead, he said that many of the lessons learned from mmWave spectrum will work well for THz spectrum. And he believes that THz frequencies will be used for mobile applications as well as fixed wireless and backhaul. “Mobility will happen,” he said. “Mobility requires more sophistication but we will make it work.”
6G in 2030
Roessler said that it’s likely there will be some form of 6G services available in 2030 but he cautions that there are still a lot of steps that have to be accomplished to get to a place where THz spectrum can be used for wireless communications, regardless of whether it’s fixed or mobile.
He also thinks that THz frequencies, similar to mmWave, may end up being used in certain regions of the world but not necessarily all across the globe. “It really depends upon the country and the region,” he said.
And even though mobile operators around the globe are working feverishly to expand their 5G footprints, Rappaport is confident that the 6G standard using THz frequencies will move forward rapidly. He also believes that 2030 is a realistic time frame for 6G services to become a reality.
“It takes a lot of R&D to move to a new standard,” he said. “But it’s too compelling to not do it. When you get that much more bandwidth and 10 times the capacity that means you can bring new capabilities and functionality to consumers.”