[Server-sky] A Cure for Urban GPS: a 3-D Antenna

[Eugen Leitl]

http://www.technologyreview.com/news/519811/a-cure-for-urban-gps-a-3-d-antenna/

A Cure for Urban GPS: a 3-D Antenna

GPS readings in cities and indoors can be terrible. One startup has found a
novel solution.

By Tom Simonite on October 9, 2013

WHY IT MATTERS

More and more technology relies on GPS location readings, but the technology
remains unreliable in dense urban areas.

better gps antennae Round receiver: This soccer-ball-size antenna can allow
more accurate GPS readings by distinguishing signals that have come directly
from a positioning satellite from those that have bounced off buildings.

A new antenna design being tested by the U.S. Air Force could make GPS
significantly more reliable and able to function in dense urban areas where
GPS accuracy is weak. It might even allow the technology to work indoors in
some cases.

Good GPS readings are hard to get in cities because of the multipath
phenomenon: signals from positioning satellites bounce off buildings and
other structures. That confuses GPS receivers, which calculate their location
by knowing exactly how long it took for signals to arrive from satellites
overhead.

A signal that has bounced takes longer to arrive than it would if it had
traveled directly, muddying a receiver’s math and sending location readings
off by tens or hundreds of meters. Smartphones and in-car GPS units often
have to work out their true location by analyzing maps and by getting a
series of readings over time.

The Air Force Institute of Technology is now trying to tackle that problem
with an antenna able to recognize and ignore multipath GPS signals. The
project builds on a design invented by Locata, a company based in Canberra,
Australia. The institute is testing the company’s soccer-ball-sized
proof-of-concept prototype, and plans to adapt it into versions that could
conform with the frame of a Humvee or aircraft, or be built into helmets.

As the U.S. military tries to automate aircraft and other vehicles, it must
rely on GPS to know where they are. Nunzio Gambale, cofounder and CEO of
Locata, says that what the Air Force develops stands a good chance of
trickling down to civilians, since most GPS technology in smartphones and
navigational aids originated with the military.

“The requirements of the military are now converging with the requirements of
Apple and Google,” he says. “Everyone wants to use these location
tracking-devices indoors and in urban areas where people say GPS will never
work.”

Locata’s antenna has many different elements that can be activated
individually. In the current prototype there are 80 such elements positioned
around a sphere. Switching on each element individually for about one
millisecond makes it possible for a receiver to sense not only the strength
but also the direction of incoming signals, by comparing what is detected by
the elements on different parts of the antenna.

That makes it possible to ignore GPS signals that have bounced in favor of
pure ones coming directly from a satellite. “It’s like the blinders coming
off,” says Gambale. He believes that in some circumstances the new antenna
design could even allow GPS readings indoors, where multipath effects are
extremely strong and the signals from positioning satellites are extremely
weak.

Constructing antennas from multiple elements isn’t a new idea. But such
designs traditionally had each element controlled by its own radio, causing
different elements to interact with one another in ways that required complex
additional processing to clean up. In Locata’s design, all elements connect
to a single radio. The sequence of signals it produces from different antenna
elements can be processed relatively easily.

Todd Humphreys, a professor at the University of Texas geopositioning lab,
says that Locata’s design shows promise because it can be so much cheaper
than previous attempts to address the multipath problem. However, he cautions
that this approach to antenna design requires a large receiver, so for now it
will be practical only in military applications.

Locata is leaving it up to the Air Force to work out how practical the 3-D
antenna can be. Gambale says his company is instead focused on using the
technology to improve a competing technology to GPS: a system of ground-based
location beacons that allows location readings to within centimeters (see
“Ultra-Fine Location Fixes”). Last year the U.S. Air Force commissioned a
Locata system for the White Sands Missile Range in New Mexico. Locata is also
working to sell systems to companies that operate mines and warehouses.