RF Factors In Play For 5G And Future 6G Systems


By Kelly Hill

When it comes to 5G and spectrum, there are a lot of complicating factors at work. While previous generations of cellular technologies typically brought new spectrum into play, 5G is making use of familiar sub-6 GHz frequencies that have been foundational to cellular networks, but also bringing in higher—sometimes much higher—bands that have never before been used for commercial mobile networks. The shifting radio frequency (RF) landscape was the focus of recent discussion during a session of the virtual Test and Measurement Forum event. So what are some of the factors in play for both 5G and future 6G systems, when it comes to spectrum?

Global variations in spectrum regulation and price

There is a wide range of how 5G spectrum is being put into play around the world, which ultimately impacts how, and how quickly, 5G gets deployed, explains Ceri Howes, head of regulatory at OpenSignal: Different international spectrum assignments for 5G, differences in band prioritization and in spectrum pricing, different models of assigning licenses and the terms of such licenses, as well as how regulators are approaching the sunsetting of legacy 2G or 3G networks and spectrum re-farming. There is, however, some common ground: Howes said that on a global basis, the midband spectrum at 3.5-3.7 GHz is being used to support roughly half of 5G network launches. Meanwhile, 700 MHz has emerged as a key coverage band in around 65 per cent of low-band 5G network launches, Howes said during a recent session at the Test and Measurement Forum virtual event.

Spectrum allocations for private networks

5G spectrum auctions have set records in places like the US, Canada and Australia—but commercial mobile networks aren’t the only focus of spectrum allocations. Director of RF and wireless architecture at Viavi Solutions, . Dr. Ian Wong noted that government regulators are also sometimes making allocations for 5G spectrum specifically aimed at least in part at supporting private industrial/enterprise networks, as in Germany with a midband allocation for industry and in the U.S. in the form of CBRS shared spectrum.

CBRS is a particularly interesting case, as it has a licensed, priority portion of the band which garnered significant interest from traditional mobile network operators while also attracting the largest field of bidders that an FCC auction has ever seen. Mark Watts, associate fellow at Verizon Communications, says that CBRS is a tool that has helped operators provide connectivity where they couldn’t or wouldn’t provide it previously. Howes said that from what OpenSignal has seen, CBRS can boost performance considerably, to the point where customers connected to CBRS spectrum see around 80% faster connections—but because of the low power restrictions on transmission, that experience drops off quickly when customers move out of CBRS range. “In terms of mass-deployed consumer silver bullet, it might not be it, but it might be a tool in a tool box to really get faster speeds in specific areas for certain use cases,” she adds.

Testing and monitoring in a new network paradigm that moves beyond assurance of best-effort, large-scale services. “In a general sense, most of the wireless traffic in the last couple, three decades has been best-effort for the masses,” notes Watts. ” Whereas when we look at slicing, we not only have to continue to support best-effort connectivity for the masses and provide test and measurements based on the connectivity of a couple million users or 100 million users depending, now we have to carve out those tests and those measurements for an individual, customized slice, whether it’s for IoT or even an in-building application.” This, he said, “expands the scope and the volume of tests that a provider like Verizon has to manage and customize.

New, and continuing, challenges for coexistence. So what does the future of RF look like? Well, crowded, for one. And the combination of low/mid/high usage that is emerging with 5G networks is likely to continue. While there’s a lot of talk (and research) around moving into even higher reaches of RF such as sub-terahertz and terahertz frequencies, Wong notes that in 3GPP 5G work, the focus remains on sub-6/7 GHz and higher than 24 GHz. But he also says that he’s most excited about the potential to expand the 7-24 GHz range, sometimes called “upper midband”, for being re-examined to see what additional bands could be freed up for cellular use in 6G—because those frequencies would have a better cost/coverage profile than higher mmWave and terahertz bands. But it will mean treading carefully in how new and existing systems might coexist—both in the band and in terms of potential effects of operating new terrestrial networks that might cause in other bands. No one wants another C-Band/radio altimeter interference situation.

“The methodologies we deploy right now, both regulatory and technological, of being intelligent about monitoring interference, being a lot more deliberate about understanding what the effects of certain decisions in terms of technology with legacy and incumbent users … starting from the lab all the way to the field monitoring. These are very critical and I think the test and measurement industry has a huge role to play in these things,” says Wong.

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