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Tracking Location from the Sole of a Shoe

These days, most of us know how to tell where we are. Advances in Global Navigation Satellite System (GNSS) technology allow us to find our location from anywhere our GPS-enabled smartphones are working.

So, what about when our smartphones are not working? Networks get jammed, infrastructure goes down, or sometimes you’re just inside of a concrete building. If you’ve ever been to a subway station or skyrise building, you know that the coordinates shown on your GPS are approximate at best; it can’t tell you what floor you’re on.

For firefighters, this challenge is especially critical; if there’s an injured firefighter in a building, they need location tracking to be rescued. How else should the incident commander know where to send resources?

Numerous firefighter fatalities can be attributed to the lack of indoor location tracking systems. That’s why, in 2016, a stakeholder group of public safety, government, industry, and academic experts agreed that first responders need indoor positioning systems that are accurate within one meter—not just “approximate.”

NIST’s Public Safety Communications Research (PSCR) Division is accelerating research into indoor tracking measurement systems for first responder operations—and the solution may be under our feet.

The challenge with indoor location

Even if concrete walls and underground settings block outside signals, Internet of Things (IoT) infrastructure such as pre-installed sensors, WiFi access points, or Bluetooth beacons could render a first responder's indoor location. But what happens if IoT data is proprietary, or if power goes out at a scene? First responders need an indoor tracking solution that they can rely on, even when infrastructure-based circumstances are subject to change.

NIST funded the University of California Irvine to research an infrastructure-free localization system as part of its Public Safety Innovation Accelerator Program (PSIAP). Researchers have found a breakthrough in how a microchip with motion sensors and cell signals may determine someone's position with impressive accuracy — something once thought to be a hopeless challenge.

An innovative framework for indoor localization and tracking

UC Irvine's Ultimate Navigation Chip (uNavChip) aims to design, build, and demonstrate a Personal Navigation System (PNS) that works for hours in GPS-denied environments. This novel approach uses three different algorithms—deterministic, probabilistic, and cooperative. These approaches merge them into a single platform with inertial sensors mounted in the sole of a boot. The device can locate the wearer within a meter.

Inertial sensors are designed to sense acceleration and turn rate. Smartphones and pedometers use these sensors to determine how many steps you’ve taken. If you can measure acceleration, you can estimate speed. If you know something’s speed and how long it’s been moving, you can estimate how far it’s traveled. 

However, inertial sensors can only determine where an individual is relative to where they were, not their actual location. The uNavChip project combines inertial sensors with other technologies to achieve location tracking for the first time from the sole of a shoe. Transmitters on the shoes use signals such as cellular, AM/FM radio, WiFi, and lower satellites which are powerful indoors but not intended for navigation. Co-principal investigator (PI) Zak Kassas calls these “signals of opportunity,” which the team can use as a navigation system to track location.

Shoes are unique when it comes to our walking motion. They are reliably stationary during one portion of the walk—at zero velocity. While in motion, the system also uses foot-to-foot ranging to detect the distance from one shoe to another.

When several “agents” outfitted with inertial sensors are moving around within a building, the chip’s ranging-measuring capabilities are used for relative distance measurements between team members to generate an infrastructure-free signal and improve the location accuracy of the foot-mounted sensors. 

UC Irvine, UCI MicroSystems Laboratory

A self-contained, portable solution

The team was able to miniaturize and integrate their components into a single 1 cubic-centimeter system—about the size of a cube of sugar. And the team has also demonstrated the feasibility of using cellular signals of opportunity for location, and it has done so while getting within 1.5-meter accuracy by leveraging a chip-scale PNS.

At the moment, uNavChip mostly stands to benefit the research community, but the chances are good that the technology could be commercialized for biometrics, prosthetics, construction, defense, underground mining, and underwater vehicle industries. For NIST, the critical impact of breakthrough indoor location tracking research is that it may one day help ensure the safety and efficiency of first responders and reduce firefighter fatalities.

UC Irvine, UCI MicroSystems Laboratory

From the lab to first responders’ feet

Recently, the UC Irvine team visited another Department of Commerce agency, the First Responder Network Authority (FirstNet), to validate a high-precision motion-camera system with promising results. Now, they’re working with the Orange County Fire Authority (OCFA) to demonstrate their firefighter tracking and guidance technology in local operations. Once successful in Orange County, the technology will be extending its reach to other counties in California and nationwide. Soon, losing a life due to poor indoor navigation may become a thing of the past. You might even be able to find your way out of a subway tunnel successfully too.

For more information on NIST’s location-based services research and projects, visit PSCR’s website. The First Responder Smart Tracking Challenge launches in early 2022; sign up to receive updates on competition rules, timing, and prizes.