“SuperGPS” Accurate to 10 Centimeters or Better

New optical-wireless hybrid makes use of existing telecommunications infrastructure

3 min read
illustration of man looking at giant smart phone with map and red "you are here" symbol
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Modern life now often depends on GPS (short for Global Positioning System), but it can err by several meters in cities. Now a new study from a team of Dutch researchers reveals a terrestrial positioning system based on existing telecommunications networks that can deliver geolocation info accurate to within 10 centimeters in metropolitan areas.

The scientists detailed their findings 16 November in the journal Nature.

GPS and other global navigation satellite systems (GNSSs) such as China’s Beidou are capable of reaching centimeter-level precision, notes study senior author Christian Tiberius, a navigation engineer at Delft University of Technology, in the Netherlands.

However, buildings and other obstacles in urban settings can block or reflect the satellite signals on which a GNSS depends, resulting in major errors, Tiberius says. In addition, GNSSs are vulnerable to attacks such as jamming, spoofing, or forging, which have increasingly led scientists to explore possible backup positioning systems.

The atomic clocks onboard GNSS satellites also help keep clocks synchronized worldwide. This results in timing accurate to several nanoseconds, says study lead author Jeroen Koelemeij, who is an optical timing specialist at Vrije Universiteit Amsterdam. The scientists note, however, that emerging technologies such as quantum communication require sub-nanosecond accuracies.

Although researchers have designed a number of alternatives to GNSSs, these often require their own new infrastructure, forming a major barrier to large-scale deployment. Many also rely on two-way communications from the mobile transceiver to a sensor infrastructure. This means anyone using them has to reveal their presence and position, which is less privacy-friendly than a GNSS receiver.

Now scientists have developed a terrestrial positioning system called SuperGPS based on existing telecommunications networks.
Like a GNSS, SuperGPS does not require two-way communications. That’s where they part ways. This prototype is not only independent of any GNSS but can offer superior performance.

The researchers also noted SuperGPS’s compatibility with existing 4G and 5G telecommunications networks.

“Today’s mobile networks may, technically speaking, not be too far from an upgrade with potentially dramatic consequences,” says Koelemeij.

“The mobile infrastructure that now provides only connectivity services may in the future be upgraded to provide an additional crucial service—namely, positioning that is independent from, and more precise than, satellite positioning systems.”

A GNSS depends on satellites that each possess atomic clocks that are tightly synchronized in time. These satellites transmit precisely timed signals broadcasting their positions. A GNSS receiver can then pinpoint its own location by analyzing how long it took signals from each visible satellite to arrive.

Similarly, SuperGPS makes use of precisely timed signals from a mobile telecommunication network’s constellation of radio transmitters. These are connected and synchronized through a fiber-optic Ethernet network linked to an atomic clock.

“There is a global fiber-optic infrastructure and a wireless mobile infrastructure out there that telecom companies worldwide have invested hundreds of billions into,” Koelemeij says. “During the development of the project, we chose signal formats and equipment that are compatible with [those] of existing network infrastructure so that hopefully one day it can be integrated at reasonable additional cost.”

The hybrid optical-wireless system employs a bandwidth of radio signals about 10 times as large as what’s commonly used by GNSS. This helps it detect and deal with reflected signals, enabling higher positioning and timing accuracy.

Bandwidth within the radio spectrum is typically scarce and therefore expensive. The scientists accounted for this by using a number of small-bandwidth radio signals over a large “virtual bandwidth.”

In experiments outdoors with six radio transmitters dispersed over 660 square meters, SuperGPS delivered a positioning accuracy pinpointing objects to within 7.4 to 10.2 cm, as well as sub-nanosecond timing. The researchers could improve the positioning accuracy to within 2.2 cm by taking advantage of information about the phase of the signals—that is, the fraction of a wave that the signal has completed at any given time.

Enabling highly accurate positioning in cities “could advance the general introduction of safe automated driving, in particular if the positioning system is independent of and complementary to GPS positioning,” says Koelemeij.

Future research will examine how to best use the virtual bandwidth on which SuperGPS depends “to implement virtual wideband signals such that available resources are optimally used,” says study coauthor Gerard Janssen, a radio communication engineer at Delft University of Technology.

The Conversation (2)
W George Mckee08 Dec, 2022
LM

In addition top China's Beidou, NASA JPL has been providing a Global Differential GPS System with accuracy better than 10 cm since 2000.

Mauno Aho08 Dec, 2022
M

For the normal user it would be much better if the smartphones equipped with GPS would always have at least the normal accuracy in open terrain. I have a One+ Nord2 that has exceptionally poor GPS.

Last spring I took a photo in an area where the nearest buildings were at several hundreds meters and not higher than 2 floors. Attached location claimed it was about 200 m off.

In September when I had to make an emergency call. The address was 2 km off due false location.

Normally photo locations may claim they are taken another side of buildings.

How Duolingo’s AI Learns What You Need to Learn

The AI that powers the language-learning app today could disrupt education tomorrow

9 min read
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This playful illustration shows Duolingo’s owl mascot, cut away down the midline, showing hidden inside a high-tech skeleton suggestive of some sort of AI robot.
Eddie Guy
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It’s lunchtime when your phone pings you with a green owl who cheerily reminds you to “Keep Duo Happy!” It’s a nudge from Duolingo, the popular language-learning app, whose algorithms know you’re most likely to do your 5 minutes of Spanish practice at this time of day. The app chooses its notification words based on what has worked for you in the past and the specifics of your recent achievements, adding a dash of attention-catching novelty. When you open the app, the lesson that’s queued up is calibrated for your skill level, and it includes a review of some words and concepts you flubbed during your last session.

Duolingo, with its gamelike approach and cast of bright cartoon characters, presents a simple user interface to guide learners through a curriculum that leads to language proficiency, or even fluency. But behind the scenes, sophisticated artificial-intelligence (AI) systems are at work. One system in particular, called Birdbrain, is continuously improving the learner’s experience with algorithms based on decades of research in educational psychology, combined with recent advances in machine learning. But from the learner’s perspective, it simply feels as though the green owl is getting better and better at personalizing lessons.

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