Avionics News June 2022 - 24

IT TAKES TWO TO TANGO ON 5G
Continued from page 23
the area of concern is between 3.7 to 3.98 GHz. This is where
5G frequencies used by Verizon and AT&T may be too close to
radar altimeters in the 4.2 to 4.4 GHz band. The FAA thinks this
may be too close. According to Koziol, " Signals broadcast on
frequencies that are similar (but not exact) to one another can
still cause interference, although not as severe as if they were on
the same frequency. "
Koziol, who has a degree in physics, noted, " This has been
a uniquely U.S. problem. That's because different countries
allocate radio spectrum in different ways for different uses. "
Then he added there isn't much concern about radar altimeters
in Europe because 5G there is using slightly lower frequencies
from 3.4 to 3.8 GHz versus 3.7 to 3.98 in the United States.
Meanwhile, Canada has created buffer zones.
Diamond maintains that radar altimeter antennas can pull in
signals 400 MHz away from the area where they are licensed
to operate. This is because when radar altimeters were designed
there weren't many adjacent bands in use by anyone, and until
5G, only low power signals were using nearby spectrum.
By pulling in more signals, radar altimeter manufacturers
could produce systems with higher performance. " If you
design the antenna to receive signals at 3.8 GHz and your
neighbor is transmitting at 3.8 GHz, you are going to receive
that energy and it's going to become interference, " Diamond
said. " The pulling range is too wide, so they need to narrow it,
and that's easily done with antennas and filters. None of this is
magic; it is well-understood radio technology. Radar altimeter
manufacturers have historically made receivers that can pull in
the energy outside of the band they're intended to operate in so
they can maximize the receiver's performance for customers. "
Diamond said U.S. telecom companies have a notch filter
that prevents them from transmitting outside their authorized
band, as they are tightly regulated. And in Europe, the
restrictions are even tighter than in the U.S. The spectrum
released by the FCC for 5G is broader than it is in Europe, but
the approved 5G band in the U.S. is still 400 MHz below the
lowest authorized band of radar altimeters. So radar altimeters
need to be redesigned and the filters need to be redone. " It is not
the neighbor's (5G providers) fault, " he noted.
There could be other frequencies affected in the future as the
FCC auctions off other portions of the radio spectrum, and if it
gets up to 5 GHz, this could affect weather radar.
Those who assert that 5G frequencies are needed to keep the
United States out in front on this important technology may
be missing a key point. On Feb. 16, former Google CEO Eric
Schmidt co-authored an op-ed article in the Wall Street Journal
that points out America is far from ahead in a global move to
5G. He wrote that America's average internet speed on 5G is a
24 avionics news * june 2022
paltry 75 megabits per second on average, while China's average
is 300 Mbps and Korea is even farther ahead at 400 Mbps.
American 5G Mbps is about 10% to 20% lower than its
4G speed he noted, and while the U.S, government plans to
invest $1.5 billion on 5G networks over the next four years,
China will be boosting its total investment by $50 billion to
$150 billion. The United States has 100,000 5G base stations
versus China's 1 million.
At the General Aviation Manufacturers Association's state
of the industry press conference in February, GAMA President
Pete Bunce said the industry is still working on 5G mitigations
for business aircraft and especially helicopters. When it comes to
solutions, Bunce noted that Dickson has said " this is not going
to be a quick process. " Bunce added, " We've got to be able to
certify our equipment, whether it's with inline filters or whatever
we are going to do, much like we do with ADS-B. And we have
to put a lot of focus on being able to certify that to be able to find
solutions. We are all working toward that. "
" The worst case (for 5G interference) is really for
helicopter operators, since it's easy to limit the interference
around airports with instrument landing systems, not so easy
everywhere a medical helicopter may need to land, " said
Andy Thurling, a former Air Force test pilot instructor and
unit commander. He is chief technology officer at NUAIR, a
nonprofit that conducts unmanned aircraft system flight tests
in a 50-mile corridor between Griffiss Air Force Base and
Syracuse, New York. NUAIR plans to use some parts of the
5G spectrum to control drones in flight tests.
When asked by Avionics News at the state of the industry
press conference how the general aviation industry can avoid
further inroads to aviation bandwidth by the communications
industry, Bunce said, " We sure as heck better learn from this
episode. " It may take legislative action or making sure the
federal government is getting all of its resources together to
talk to one another to avoid a problem because " it for sure will
happen again as spectrum becomes even more precious. "
Phil Straub, who leads Garmin's aviation business, spoke at
the GAMA press conference and agreed with Bunce. " I think
this (the 5G issue) has put a highlight on it, and the industry
will be more proactive going forward, " he said. " Once you
have engineers on each side working together, and there is
trust, there are amazing things that can happen. So we just
need to learn from this experience and then do the right things
going forward. "
Most radar altimeter designs have assumed the adjacent
frequencies were protected. It is not until now that the
protection cannot be assumed and that new designs would be
needed to ensure radar altimeters " stay in their lane " as far as
the use of the assigned frequency, according to Anthony Rios
Continued on page 26
Avionics News June 2022

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