Initial 6G work is underway

Martin Rowe

https://www.edn.com/electronics-blogs/5g-waves/4462105/Initial-6G-work-is-underway

At this year's Brooklyn 5G Summit, NYU professor Ted Rappaport gave a presentation about initial research for what could become 6G sometime around 2030 to 2035. Now, you can read the details in "Wireless Communications and Applications Above 100 GHz: Opportunities and Challenges for 6G and Beyond. Published by IEEE, this paper is available for free download. 

In his presentation, Rappaport noted that 5G took fifteen years to reach initial deployment and he assumes the same for 6G. Why go beyond 5G? The paper explains that faster wireless speeds will be needed to keep pace with ever-increasing computing power and will create new opportunities. By 2036, we could have $1000 computers that have the computation power of the human brain. Although wireless networks based on terahertz signals still won’t be fast enough to keep up with that power, it will get us closer. Perhaps 7G will get there. 

Research at NYU Wireless, a program started by Rappaport, is looking at frequencies above 100 GHz with channel data rates of 100 Gbps. Testing is possible in the U.S., given that the FCC has released 21.2 GHz of spectrum above 95 GHz. 

What will it take to get to 6G? A lot of research, both in the electrical and biological domains. In the electrical domain, terahertz signals will present new problems but have the potential for new applications such as sensing that aren’t possible with 5G signals. For example, the ability to "see" around corners and making it possible to sense positions of people in rooms. Even so, much work will be needed to characterize terahertz channels because at such short wavelengths, the roughness of building materials, for example, becomes a factor in absorbing or reflecting the signals. Imagine some building materials acting like the walls of anechoic chambers.

 Figure 1 shows Rappaport's slide depicting signal losses in common building materials.

 
Figure 1. Signal losses created by common building materials could result in future materials developed to minimize signal losses at terahertz frequencies. Image: Martin Rowe. 

We have typically been led to believe that signal attenuation always gets greater as frequencies increase. That's not necessarily the case. Take attenuation in rain. Research has shown that attenuation levels off at about 100 GHz, as seen in this slide presented by Rappaport at the Brooklyn 5G Summit (Figure 2). 

 
Figure 2. Rain attenuation levels off at 100 GHz. As frequencies increase, loss from rain does not.Image: Martin Rowe. 

Another electrical issue that arises at terahertz frequencies that's also wavelength related has to do with antennas and electronics. That is, the antennas get so small that their electronics is the limiting factor in size and thus, electronics may not be integrated into antennas as they are at today's 5G frequencies of 28 GHz and 39 GHz. In fact, heating of components will be more of a problem as engineers try to decrease the size of amplifiers and other components. 

Power amplifiers for terahertz signals will have greater noise issues than those operating below 100 GHz. Compensation for these issues may come from the antennas through a concept called spatially oversampled antennas. Spatially oversampled antennas produce "cones of silence" defined as an antenna array's cone-shaped region of support (ROS). The design goal will be to move noise and other undesirable factors into an area outside of the usable field. Such circuits could be based on sigma-delta ADCs and DACs where feedback loops are used to improve resolution. The paper explains this concept in detail. 

A discussion of mmWave and terahertz signals would not be complete without mention health issues and the need for further study. On the biological front, the paper's authors say that "heating is believed to be the only primary cancer risk" but much work is needed to "understand the biological and molecular impact of THz radiation on human health, even though THz is three orders of magnitude lower in frequency that ionizing radiation," that being X-ray radiation. 

Terahertz Waves Could Push 5G to 6G

At the Brooklyn 5G summit, experts said terahertz waves could fix some of the problems that may arise with millimeter-wave networks

By Michael Koziol

https://spectrum.ieee.org/tech-talk/telecom/wireless/at-the-6th-annual-brooklyn-5g-summit-some-eyes-are-on-6g

It may be the sixth year for the Brooklyn 5G Summit, but in the minds of several speakers, 2019 is also Year Zero for 6G. The annual summit, hosted by Nokia and NYU Wireless, is a four-day event that covers all things 5G, including deployments, lessons learned, and what comes next.

This year, that meant preliminary research into terahertz waves, the frequencies that some researcher believe will make up a key component of the next next generation of wireless. In back-to-back talks, Gerhard Fettweis, a professor at TU Dresden, and Ted Rappaport, the founder and director of NYU Wireless, talked up the potential of terahertz waves.

As a quick primer on the electromagnetic spectrum, terahertz waves (despite what the name implies) occupy the 300 gigahertz to 3 terahertz band of spectrum. This means the frequencies are higher than the highest frequencies that will be used by 5G, which are known as millimeter waves, and fall between 30 and 300 GHz.

In his talk, Fettweis discussed the potential of terahertz waves and 6G to solve some of the problems of 5G. He pointed to the trend established by previous generations of wireless: While 1G provided us with mobile telephony, 2G expanded on that and addressed some of its predecessor’s shortcomings. 3G 

and 4G did the same with mobile data. Now that we’re moving on to 5G, which is expected to support many new applications like the Internet of Things and AR/VR, Fettweis said it was only natural that 6G will function similarly to 2G and 4G to correct the flaws of the previous generation.

As to what, exactly, terahertz waves will correct—that’s still largely unknown. Service providers around the world are only now rolling out their mobile 5G networks, and it will take time to identify the shortcomings. Even so, the physical properties of terahertz waves point to some general ways in which they could help.

Terahertz waves, as mentioned, have shorter wavelengths and higher frequencies than millimeter waves. That suggests terahertz waves should be able to carry more data more quickly, though they will not be able to propagate as far. In general, that means that the introduction of terahertz waves into mobile networks could address any areas in which 5G isn’t able to deliver high enough data throughput or low enough latency. During his talk, Fettweis revealed the results of tests in which terahertz waves were able to transmit 1 terabit per second of data for a grand total of 20 meters (yeah, not very far at all).

But if you think those results are less than impressive, they don’t dissuade Rappaport, who gave a very earnest talk on the future of terahertz waves as they relate to 6G and, dare I say it, 7G. Rappaport, who was one of the pioneering researchers into millimeter waves and played a large role in proving they would be viable for 5G networks, suggested that with these frequencies, as well as additional improvements in cellular technology, we’ll someday see thousand-dollar smartphones that have the computational power of the human brain.

Of course, it’s all highly speculative at this point, but if past trends continue, we can expect to see service providers harnessing terahertz waves for communications in areas with many devices or large amounts of data a decade from now. And that will all be thanks to the fundamental research that’s just getting underway today.