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Bluetooth LE Uses Phase Finding for Affordable RTLS Applications

Aug 20, 2021 - Link Labs' AirFinder OnSite solution provides low-cost indoor location, with Bluetooth LE tags identifying where they are based on phase ranging, and LoRa connectivity forwarding that data to a server.

Maryland-based company Link Labs has developed a real-time location system (RTLS) leveraging Bluetooth Low Energy (LE) and phase-ranging technologies to pinpoint the locations of Bluetooth LE tags in real time. The solution, known as AirFinder OnSite, leverages a series of beacons strung throughout a facility like Christmas lights, and software built into Bluetooth LE tags to calculate location based on timed responses. The system employs low-power wide-area (LoRa) gateways to forward data to a server.

The result, according to the company, is a system that can locate people or things at a lower cost than standard RTLS solutions, with a longer battery life for the tags. The system, released in April of this year, is being tested or deployed by airports, construction sites, warehouses and manufacturing facilities to locate equipment, vehicles, tools and other assets, not only to make it easier to find missing items and track work-in-progress (WIP), but also for analytics purposes, to identify bottlenecks or inefficiencies.

Link Labs was founded in Annapolis, Md., approximately seven years ago with a focus on offering a network layer for LoRa-based systems. "Our goal was to be a purpose-built IoT network provider for large-footprint companies," says Bob Proctor, Link Labs' CEO. The company found that the majority of its customers needed integration support and had a significant pain point around asset management. "We already offered the network layer, so we decided to take it the last mile ourselves to provide a full end-to-end solution."

Since then, there have been several versions of AirFinder OnSite. Previously, Link Labs had leveraged received signal strength indicator (RSSI)-based Bluetooth LE for indoor location, but it found that results were not as accurate as many applications required. "Just using signal strength [to pinpoint a tag's location]," Proctor explains, "is fundamentally not very accurate." Another Bluetooth LE alternative is angle-based location direction, but that has its own limitations since it requires an antenna array to measure a tag's transmission angle, necessitating the meticulous deployment of antennas and heavy processing intensity to determine distance based on the angle of arrival (AoA)—and according to Proctor, AoA provides challenges related to multipath signals from reflections around metal.

AirFinder OnSite uses standard Bluetooth LE 5.1 beaconing devices, Proctor says, while changing the firmware to enable phase ranging—a synchronization system that allows transmissions between locators and tags to hop across channels, and measures the time of response to determine location, similar to how GPS works. The deployment consists of a string of locator antennas that run along a ceiling in rows to create a grid pattern. Phase-ranging systems measure the amount of time it takes for transmissions to be sent and responded to. The tag firmware's "constant tone extension" functionality enables the measurement of time of flight, which he says is fundamentally unique to Link Labs.

In a typical deployment, Bluetooth LE battery-powered tags with a Bluetooth 5.1 chipset are attached to assets; Link Labs loads its own firmware onto the device's internal chip. The locator beacons can be installed quickly, Proctor reports. "As we place those devices in a grid pattern along the ceiling," he says, they can use low-voltage wiring and zip-tie the devices to I-beams along the ceiling. The locator beacons are provisioned to a specific location in the software. The tag receives beacon transmissions and measures the distance from each. As the firmware receives the tag transmissions, the device performs calculations to reduce the amount of data that needs to be sent back to the server.

Once the tag knows its location, it transmits a signal to a second Bluetooth device (known as an access point), which translates the transmission of data to LoRa, enabling a long transmission distance. The LoRa transmission goes to a single gateway that could cover an entire facility, and from there the information is forwarded to a server via an Ethernet cable or a cellular connection. Because the tag accomplishes its location processing within its own firmware, it sends a limited amount of data. Proctor estimates the system extends battery life by a factor of three to five times, and a tag that traditionally might last for nine months could thus continue to transmit for several years.

The technology is being employed by an industrial manufacturer with a production line spanning 100,000 square feet. The tags calculate their location on the assembly line and enable the firm to view WIP status updates, receive alerts, and obtain historical data if bottlenecks or other types of delays occur. Since AirFinder OnSite was released, Proctor reports, "The market interest we're seeing is really exciting." He adds, "The system means a tag the size of a thumbnail can be located within the distance of an arm's length." The technology was built to be affordable enough that tags could be attached to small or low-value tools, such as socket wrenches, enabling missing items to be quickly located rather than manufacturing being delayed.

The location beacons can capture data at a distance of 10 to 30 meters (33 to 98 feet), and can thus capture transmissions even from high ceilings. What's more, they can be suspended from pendants. Typically, with a site measuring 100 meters by 100 meters (328 feet by 328 feet), locator beacons could be installed every 10 to 20 meters (33 to 66 feet). That means about one per 1,000 square feet. Under good conditions, location data can get to within a meter even in a highly metallic environment.

The LoRa technology allows the long-range transmission of data to a server without requiring a facility's existing Wi-Fi or cellular connection. In that way, the technology can be deployed as a standalone Internet of Things network. The system could accommodate hundreds or potentially thousands of tags transmitting at once, Proctor says. "We can drive tremendous scalability as well," he states, with such techniques as configuring tags to sense if any transmissions conflict with those of other tags and thus delay transmission, or by running a second string of location beacons.

In April of this year, the company announced that it had been awarded six U.S. patents for technological innovations with its AirFinder OnSite platform (see  Link Labs Receives Six IoT Asset-Tracking Software Patents).

About Link Labs
Link Labs provides the industry’s most complete, end-to-end IoT platform for tagging, locating and monitoring equipment, supplies and assets. With more than 20 patented technologies, its flagship platform, AirFinder, helps companies in nearly every industry locate, monitor and manage business assets anywhere at any time – indoor, outdoor and everywhere in-between. Through the seamless integration of innovative software and hardware, AirFinder is proven to reduce IoT deployment times from months to days while lowering cost of ownership by 50-90%. Trusted by top global enterprises for their essential IoT solutions, Link Labs is based in Annapolis, Md. and was founded in 2014 by a group of veteran engineers from the Johns Hopkins University Applied Physics Lab, who had worked together on a variety of projects for the U.S. Department of Defense, the U.S. Intelligence Community and the telecommunications industry. For more information, visit https://www.link-labs.com/ and follow on Twitter @LinkLabsInc.

View original press release by Claire Swedberg on the RFID Journal website - click here to read.

Link Labs

Written by Link Labs

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