IEEE Spectrum December, 2017 - 46

The network handles traffic based on
priority levels assigned through software. "Software controls just about
everything," Goodyear says.
Unfortunately, that also means faulty
software can knock out a site or disrupt
multiple portions of the network. A few
years ago, while technicians were trying
to upgrade one stretch of towers, a software bug caused the radios to spontaneously reset and pushed GCI nine months
behind schedule.
These problems notwithstanding, software is at the very heart of the TERRA
network's ability to function in the face
of the Arctic's environmental and climatic extremes. Thanks to software, GCI
can remotely route all traffic through
one tower if another one malfunctions.
And software helps the network respond
to weather, altering signals when there's

more fog or rain, in ways that minimize
signal attenuation.
At GCI's office in Anchorage, senior
engineer Goodyear pulls up a photo of
a microwave tower high in the -Askinuk
Mountains on the western coast of
Alaska. The bottom half is buried in
2.5 meters of snow. "This is pretty typ-
ical for this site in the early spring," he
says. He flips to another photo [above,
inset] that shows the top half of the same
tower completely iced over from chilly
coastal winds that whip up moisture
from the Bering Sea.
Snow and ice absorb and reflect radio
waves, impeding an antenna's ability to
receive and transmit signals. Goodyear
estimates GCI poured $2 million into
combating that problem at the Askinuk
Mountains site in its first two years. He
points to the small triangles above each

46 | DEC 2017 | NORTH AMERICAN | SPECTRUM.IEEE.ORG

antenna in the second photo; they're
basically metal hats meant to keep snow
and ice from accumulating.
Crews had also installed long metal
plates to shield the tower's waveguides
from falling ice. Microwaves travel
through waveguides-which are hollow metal tubes-when they are moving between amplifiers and antennas, for
example. But in frigid climates, moisture
can accumulate inside them and cause
them to freeze up, so at particularly vulnerable TERRA sites a special dehydrator pushes air through the waveguides
to keep the moisture out.
Despite all of these effor ts, one
antenna is still missing from the tower in
the photo, and the waveguide that runs
to it sticks out awkwardly into the cold
air. Ice had built up, warmed in the sun,
slid down the tower, and popped the
antenna right off.
Through software, GCI was able to
remotely reroute traffic from the disabled
antenna to go through two antennas
placed higher up on the tower, to keep
the site running. Since then, G
- oodyear's
team has slashed the height of that tower

TOP: GCI; BOTTOM: PATRICK GOODYEAR.

C O L D C A L L : TERRA's 109 -m icro----wave
towers must withstand snow, ice, and
extreme cold. In the Askinuk Mountains
[inset], a black waveguide pokes out
from the right side of the tower, where
an antenna had been mounted before
snow and ice popped it off.

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Table of Contents for the Digital Edition of IEEE Spectrum December, 2017