By Shane Tews

The radio airwaves that power wireless technologies—known as
spectrum—are a finite but critical resource. Tailoring spectrum toward its best
use often entails industry and government sharing airwaves with one another, a
process that has proven complicated as historical use does not always equate to
the best current use of spectrum assets. And, with the advent of 5G wireless,
the stakes are higher than ever.

On the latest episode of Explain
to Shane, I sat down with Peter Rysavy to analyze potential spectrum sharing
solutions and discuss how 5G policy has played out across different industries
and government agencies. Peter is president of Rysavy Research, LLC, a
consulting firm that has specialized in computer networking and wireless
technology since 1993. He recently published a series of articles
and slide decks on the basics of spectrum sharing, along with advanced
concepts that draw on past examples to demonstrate the complexity—and
importance—of the spectrum sharing process.

Below is an edited and abridged transcript of our talk. You can listen to this and other episodes of Explain to Shane on AEI.org and subscribe via your preferred listening platform. You can also read the full transcript of our discussion here. If you enjoyed this episode, leave us a review, and tell your friends and colleagues to tune in.

Shane Tews: What
exactly is spectrum sharing and why are we debating it?

Peter Rysavy: Spectrum sharing is a very broad concept. In
fact, all spectrum is shared. It’s really how you share it that is the topic of
the day. Geographic sharing is simple. You use spectrum in one country; you use
the same spectrum somewhere else. But a much more complex form of sharing is,
for example, 5G and Wi-Fi sharing the same unlicensed spectrum band. That is a
more complicated problem for which the solution is very specific to those
systems. Citizens Broadband Radio Service is another example of spectrum
sharing where cellular networks can share the same spectrum with Department of
Defense radar systems.

So the real question is: How do we take the know-how we have
today and apply it to new scenarios? Are there off-the-shelf solutions that
will allow us to share spectrum between different types of systems in the
future?

What are some lessons
we’ve learned on licensed versus unlicensed spectrum? The theory of unlicensed
is lovely, but I get the sense that it’s hard to plan around.

Both unlicensed and licensed play an extremely important
role. There’s a huge amount of Wi-Fi deployment, but Wi-Fi doesn’t solve
everything. You can’t get ubiquitous coverage like you do with cellular. With a
Wi-Fi approach, what we really need is a balanced amount of spectrum that’s
available for Wi-Fi and a corresponding amount for cellular. In recent years,
we’ve made more spectrum available for Wi-Fi than for cellular. Currently, I
would say that we’re in a bit of an unbalanced situation due to the 6 gigahertz
(GHz) allocation for Wi-Fi.

Both Wi-Fi and cellular play an important role in our lives.
We’re used to our devices being able to seamlessly switch between the two—Wi-Fi
in our homes and cellular outside. It’s this combination that is essential for
people’s day-to-day experience.

What should we be
doing now on spectrum pipeline since the chairwoman of the Federal
Communications Commission (FCC) recently notified Congress that we don’t have
one?

People are innovating and coming up with new applications.
The amount of data that the average person consumes is growing 30–40 percent
per year and will continue to do so. The applications of the future—virtual
reality, the metaverse, cloud gaming, industrial Internet of Things—are going
to consume more data. If we want to use fixed wireless access to address the
digital divide, then we need more spectrum for that.

We can only increase network capacity using three tools. One
is to densify the network with more cell sites, which is happening as quickly
as feasible. We can also increase the spectral efficiency of the technology, which
is happening as quickly as possible with smart antennas, massive input, massive
output (MIMO), and 5G. But ultimately, we need more spectrum. Those three in
combination provide the increases in capacity that allow us to address all the
new use cases that are coming.

MIMO refers to a large array of antennas. Today, 64
transmit/64 receive is a typical configuration at base stations. That allows
the network to dynamically send radio beams to specific users and increases the
efficiency of the network.

There’s been a
challenge in Washington, DC, where the aviation industry somehow did not
realize 5G was coming online while the rest of the world completely knew about
it. What’s going on there?

The aviation situation is very unfortunate. In 2003, the
World Radio Communications Conference identified mid-band frequencies (C-band)
as a future cellular network. So we had 19 years to get ready for this, but we
didn’t heed the warning. In 2016, the EU began a plan to make those frequencies
available for cellular networks. In 2017, the FCC began its C-band process
notifying everybody that these frequencies are going to be used for cellular,
so everybody needs to get ready and share their concerns if they have any.

Then in 2022, the aviation industry basically said, “We
think there’s a problem.” That problem is being addressed and we are making
progress. One of the problems is that some aircraft altimeters are designed
without any filtering. Basically, they can receive radio energy well outside of
the band that the altimeters were designed for (4.2–4.4 GHz).

Yet, it’s a theoretical problem based on worst-case
scenarios and worst-case assumptions. Some 53 countries are using mid-band
frequencies for cellular systems, and so far there hasn’t been a single
reported real-world incident of altimeters adversely failing. Studies addressing
the issue are encouraging. There is a test bed in Colorado where base stations are
installed for the specific test’s purposes. Helicopters fly around with
sensitive measurement equipment, measuring the energy of the base stations at
different altitudes and distances, and the altimeters are likewise being
tested.

While we don’t have any final results yet, the National
Telecommunications and Information Administration indicated that a detailed
report would be available in August. There was some encouraging news that the
base station equipment was performing exactly as it was supposed to. It had great
filtering on its frequencies, meaning that by the time you got to C-band
frequencies, there was virtually no radio energy from the 5G systems.

However, there is at least one altimeter identified that can
receive radio energy all the way down to 3.4 GHz—which is important because
that’s exactly the radio band that other countries are using. So the way I look
at this is: Either this is a problem globally, or it’s not a problem anywhere. And
so far, the US seems to be the only country truly concerned about this.

The post Re-Thinking Spectrum Sharing to Enable a 5G Future: Highlights from My Conversation with Peter Rysavy appeared first on American Enterprise Institute – AEI.