Why mid-band spectrum is the 5G sweet spot

Federal auctions for radio frequency leasing don’t usually generate much excitement or press, but the auction results released this March told a different story.

The Federal Communications Commission was offering 280 megahertz worth of spectrum that purchasers could use to provide 5G cellular service. When the auction was over, bidders had spent a record-shattering $81 billion to charter critical frequencies in a part of the spectrum called the mid-band.

When fully operational, 5G will be the most capable generation of cellular connectivity ever deployed. It will supply download speeds up to 100 times faster than its predecessor, reach into areas that lack service and provide other significant benefits. 5G is able to accomplish all this because it uses a broader range of the radio spectrum than previous generations of cellular networks.

Radio engineers break the radio spectrum range into low, middle and high bands, each with its strengths and weaknesses. For carriers to best their competition and make 5G achieve what it’s capable of, they need to be strategic about the radio frequencies they use.

Catherine Rosenberg, a University of Waterloo electrical and computer engineering professor and 5G systems researcher, said mid-band is the key to those strategies.

“In the past, this part of the spectrum was allocated in a way that didn’t reflect the needs of today,” she said. “And now this band, which has good characteristics in terms of data rate and coverage, has been freed and allocated to 5G.”

Low-band spectrum offers signals that travel very far—on the order of hundreds of square miles. But frequencies in this range can transfer data at rates only a little better than 4G. On the other hand, high-band spectrum lets data fly at unimaginably fast speeds at the expense of distance. High-band signals, also known as millimeter-wave, can travel only a mile or less. And, according to Rosenberg, millimeter-wave signals can be absorbed by raindrops and leaves, quickly diminishing the distance they can cover.

Mid-band spectrum offers an attractive compromise between the two—sending data at broadband speeds to users a few miles away from a tower. This Goldilocks position within the spectrum is what has everyone clamoring for frequencies in that range. But regulators needed to reallocate mid-band frequencies from their previous task of transmitting analog and satellite TV signals before 5G carriers could start using them.

“Figuring out that these frequencies could now be used was like rediscovering a gold mine,” Rosenberg said. “Everybody knew they existed, of course, but nobody had access to this perfect band that offered good speed and coverage at the same time.”

A spectrum gold mine
Radio waves carry voice, text and data between cell towers and users. The LTE networks most of us use are still connected to parts of the radio frequency range that span from 600 megahertz to 2.5 gigahertz, which represents only the low band and the lower part of the mid-band. Mid-band typically refers to frequencies between 1 and 6 GHz.

5G, now rolling out around the world, expands that range dramatically. Using radio spectrum from around 600 MHz to 39 GHz provides a chance for carriers to balance signal distance with faster speeds, but that means they need to cobble together different frequencies to maximize their offering. And because mid-band checks off both boxes, every carrier wants a piece of it.

T-Mobile, for instance, held the 2.5 GHz frequency thanks to its acquisition of Sprint, giving it a leg up against the competition in mid-band spectrum holdings. It also picked up an additional 40 MHz of mid-band in the FCC auction to cement its advantage. All that mid-band, along with its low- and high-band assets, gives T-Mobile a substantial footprint across U.S. urban and suburban markets and puts it on track to cover 200 million people with its Ultra Capacity 5G by the end of 2021.

Of course the spectrum auctions aren’t over yet. Potential bidders are now sharpening their sights on the next block of mid-band licenses the FCC is making available. Bidding will begin in October.

A mid-band powered future
Rosenberg said that while the millimeter-wave high-band aspect of 5G gets all the attention, mid-band frequencies are what’s going to unlock much of 5G’s promise. That signal range will provide users with a far better online experience than 4G afforded and create a sizable and solid foundation for the machine-to-machine communications at the heart of the Internet of Things.

She said the mid-band’s combination of speed, coverage and low latency—the time delay between sending and receiving data—will do incredible things. Companies will use it to improve supply chains, autonomous driving and virtual reality for a much bigger population swath than millimeter-wave will reach.

As just one example, her team is currently working on a 5G-based project that could very much rely on mid-band connectivity. Their goal is for commercial aircraft to automatically download their maintenance data to ground crews during their descent. If successful, that communications advance could significantly speed up turnaround times so that aircraft don’t need to sit idle on the ground for as long as they do today.

“One of the leading technologies for 5G that gets all the attention is millimeter-wave, but the reality is that it’s not obvious we are going to benefit the most with that,” she said. “We might benefit more with mid-band. It’s what’s going to help 5G be so revolutionary.”

Nationwide 5G anchored in mid-band spectrum lays the foundation for businesses to build what’s next. From field operations to supply chain 4.0, see what the 5G future could look like—and why the right network provider matters. Forbes