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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

2 min read
Illustration of a base station and waves.
Illustration: iStockphoto/IEEE Spectrum

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.

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Metamaterials Could Solve One of 6G’s Big Problems

There’s plenty of bandwidth available if we use reconfigurable intelligent surfaces

12 min read
An illustration depicting cellphone users at street level in a city, with wireless signals reaching them via reflecting surfaces.

Ground level in a typical urban canyon, shielded by tall buildings, will be inaccessible to some 6G frequencies. Deft placement of reconfigurable intelligent surfaces [yellow] will enable the signals to pervade these areas.

Chris Philpot

For all the tumultuous revolution in wireless technology over the past several decades, there have been a couple of constants. One is the overcrowding of radio bands, and the other is the move to escape that congestion by exploiting higher and higher frequencies. And today, as engineers roll out 5G and plan for 6G wireless, they find themselves at a crossroads: After years of designing superefficient transmitters and receivers, and of compensating for the signal losses at the end points of a radio channel, they’re beginning to realize that they are approaching the practical limits of transmitter and receiver efficiency. From now on, to get high performance as we go to higher frequencies, we will need to engineer the wireless channel itself. But how can we possibly engineer and control a wireless environment, which is determined by a host of factors, many of them random and therefore unpredictable?

Perhaps the most promising solution, right now, is to use reconfigurable intelligent surfaces. These are planar structures typically ranging in size from about 100 square centimeters to about 5 square meters or more, depending on the frequency and other factors. These surfaces use advanced substances called metamaterials to reflect and refract electromagnetic waves. Thin two-dimensional metamaterials, known as metasurfaces, can be designed to sense the local electromagnetic environment and tune the wave’s key properties, such as its amplitude, phase, and polarization, as the wave is reflected or refracted by the surface. So as the waves fall on such a surface, it can alter the incident waves’ direction so as to strengthen the channel. In fact, these metasurfaces can be programmed to make these changes dynamically, reconfiguring the signal in real time in response to changes in the wireless channel. Think of reconfigurable intelligent surfaces as the next evolution of the repeater concept.

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