Where is mmWave research headed?

Millimeter wave spectrum is already in use in 5G networks in the U.S., and is expected to see wider use around the world in the coming years. According to a November 2020 report from the Global mobile Suppliers Association, there are 120 operators around the world which hold spectrum licenses for airwaves above 24 GHz, and only two dozen have thus far used that spectrum to deploy 5G networks. Meanwhile, 19 countries have specific plans to assign spectrum above 24 GHz between now and the end of 2022.

The mmWave device ecosystem is also gaining steam, with 95 announced 5G devices with known support for at least one 5G band above 24 GHz, up from 59 announced devices at this time last year. Nearly 50 of those devices are commercially available.

As the commercialized mmWave ecosystem continues to grow, researchers are devoting time to some of the granular technical work that ultimately impacts or improves such systems and devices. So what aspects of mmWave have come under study this year?

Here are a sampling of published papers and areas of research from 2020. While mmWave research is broad, many of the papers published this year that concern cellular systems fall into three general categories:

Exploring the details of the behavior of mmWave frequencies in various contexts. This can be seen in NIST researchers’ examination of 60 GHz penetration losses for indoor-to-indoor and outdoor-to-indoor mobile scenarios. New York University researchers have also explored the behavior of 60 GHz in an office environment. Others have looked at the impacts of rain and other environmental factors on mmWave links, which could inform network design with an eye toward increased resilience of links. In a 2020 special issue of Electronics devoted to mmWave research, papers touched on mmWave behavior at 26 GHz in an office environment and a comparison of performance of wideband channels at 40 GHz and 60 GHz for indoor radio channels.

Intricacies of massive MIMO systems. Breaking down the specifics of beam-forming, beam selection and beam management in massive MIMO is a popular topic for mmWave research. NYU researchers have looked at optimal multi-user beam alignment in mmWave systems, and massive MIMO and mmWave for fixed wireless access and smart city applications has been conducted as part of the Telecom Infra Project’s work around characterizing mmWave systems in different conditions. One interesting subset of mmWave-related massive MIMO research has been characterizing these systems for drone air-to-ground channels and for vehicle communications. In Electronics, researchers have looked at the potential for multiple back-up beams for instantaneous link recovery.

mmWave and higher frequencies in “6G” systems. While 6G has not yet been standardized, researchers around the world are already exploring what such systems might look like and in what spectrum they could operate — some potentially as high as terahertz spectrum — and what services they will enable that may not be accomplished in 5G. “6G [networks]will incorporate artificial intelligence (AI) based services, edge computing, quantum computing, optical wireless communication, hybrid access, and tactile services,” one paper offers.

“The development of millimeter-wave communication systems has just started,” wrote Manuel García Sánchez of the Signal Theory and Communications Department at Spain’s Universidad de Vigo, in a special issue of Electronics devoted to mmWave research, which was published early in 2020. “Despite the recent developments to cope with the multiple challenges that researchers should solve, there is still a lot of work to be done. … mm-Wave communications will lead us to full development of 5G case studies and beyond.”

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