Precision Positioning


UWB is emerging as a solution for products demanding accurate position information. How does it work and what are the first applications?

Before SARS-CoV-2, the coronavirus behind the COVID-19 pandemic that still grips the world, real time location services (RTLS) were a nascent technology. Engineers were busy developing wireless technologies such as Bluetooth LE Direction Finding to enable devices to determine and report their position in three dimensions.

The market for RTLS is potentially huge—imagine the productivity gains for logistics companies if objects stored in a giant warehouse are able to instantly report their position with centimeter accuracy—but location services were previously proving slow to emerge.

Now the pandemic, like previous crises, has spurred innovation. For example, contact tracing—a key weapon in the battle against the virus which relies on knowing whether a person has been close to another who is later shown to be infectious—is now being supported by a slew of Bluetooth LE wearables.

Most of these solutions currently rely on Bluetooth LE’s Received Signal Strength Indication (RSSI) to measure the distance of one person to another. RSSI estimates the distance between two transceivers by gauging how much the signal power has diminished since it left the transmitter. In perfect conditions the technique works well, but throw in a few walls, ceilings and furniture, and variable effects such as multipath fading, and signal strength becomes a much less precise indicator of distance.

What’s needed is complementary technology that can piggy-back the many advantages of Bluetooth LE—such as its low power capabilities, maturity, wide industry support with SoCs boasting powerful embedded processors and generous memory, and smartphone interoperability—but is less prone to fading and other forms of signal attenuation. One promising candidate is Ultra Wideband (UWB), an RF technology that has traditional applications in radar imaging but has more recently emerged as an option for PC peripherals and contact tracing wearables.

In late 2019, smartphone giant, Apple, gave the technology a significant boost by incorporating UWB in its iPhone 11. According to Computerworld magazine, the idea was to “bring spatial awareness” to the smartphones and encourage new consumer applications, beyond PC peripherals and contact tracing, that would benefit from precision location technology.

Where am I?

The U.S. Defense Advanced Research Projects Agency (DARPA) coined the term ‘ultra wideband’ in the 1990s and defined it as a system with a “fractional bandwidth” greater than 25 percent where fractional bandwidth is the ratio of signal bandwidth over the centre frequency. The U.S. Federal Communication Commission (FCC) defines UWB as “an intentional radiator that has a fractional bandwidth equal to or greater than [20 percent] or has a ... bandwidth equal to or greater than 500 MHz”.

Conventional short range RF technologies use narrowband technology; Bluetooth LE, for example, transmits on a one megahertz channel and carries information using Gaussian frequency shift keying (GFSK) modulation. In contrast, UWB spreads the radio energy across a wide bandwidth. The low power spectral density provides immunity to multipath fading and limits interference. Several modulation techniques are used, but the IEEE802.15.4 standard calls for a Burst Position Modulation - Binary Phase Shift Keying (BPM-BPSK) scheme. 

Information is sent using precisely timed pulses and it’s this timing that makes UWB a good solution for RTLS applications. By timing how long it takes for a pulse to reach the receiver and for a response to come back (and subtracting the processing latency of the receiver), dividing by two and multiplying by the speed of light, the distance between two UWB radios can be accurately measured.

Because the measurement is based on timing rather than signal strength, attenuation due to multipath fading and other forms of signal degradation do not compromise distance measurement accuracy. In addition, UWB supports measurement of Angle of Arrival (AoA) of an incoming signal (by using multiple antennas and a technique also favoured by Bluetooth Direction Finding) to determine the direction of the transmitter. Combining distance and direction data enables the system to determine precisely where, in three dimensions, the transmitter is located.

Combining UWB with Bluetooth LE creates a technology with excellent position-measuring capabilities but with a power consumption close to that of Bluetooth LE alone. By using the ultra low power Bluetooth LE radio to approximate the target object’s position—a process which requires a relatively large amount of RF activity—and then switching from the native radio to the UWB radio for the shorter precision location operation, the on air time for the higher power UWB radio is kept to a minimum. This helps to extend battery life. The Bluetooth LE SoC’s processor is used to control radio switching. Another advantage of the Bluetooth LE/UWB combination is that it allows for RSSI to be used as a fallback position-measuring technique should a non-UWB target device be encountered.

Early to market

Decawave (now part of Qorvo) offers a commercial UWB solution, the DW1000. The chip is targeted at RTLS applications and is compliant with the IEEE802.15.4- 2011 standard. The DW1000 is designed for a distance measurement precision of 10 cm, supports six channels in the 3.5 to 6.5 GHz spectrum allocation and features data throughputs from 110 kbps up to 6.8 Mbps.

In June, Nordic Semiconductor and Qorvo extended their partnership to include dual UWB and Bluetooth LE products. Previous collaboration focused on Nordic’s nRF9160 SiP, which uses an RF front end, advanced packaging and MicroShield technology from Qorvo.

Nordic and Qorvo customers are already taking advantage of a Bluetooth LE/UWB module from Decawave. For example, German developer, PHYTEC, is using the Decawave DWM1001C module—which combines the DW1000 with an nRF52832 SoC—in a UWB and Bluetooth workplace social distancing tracker that was developed specifically to combat COVID-19.

Called the Distancer, the device is worn around the neck like an employee ID card and produces accurate face-to-face separation measurements with what the company claims is greater certainty and accuracy than other COVID-19 wearables - avoiding unnecessary testing.

“The fact that the [Bluetooth LE/UWB module] employs a Nordic SoC was a key deciding factor when developing the Distancer,” explains Jonas Remmert, R&D Engineer at PHYTEC. “Nordic’s chips are by far the best-supported Bluetooth SoCs in Zephyr [an open source, RTOS] and as a result the Distancer was developed from initial concept to working prototype in just four weeks.”

Insight SiP, a French maker of ultra-miniaturized electronic components, has also launched a wearable Bluetooth LE/UWB tag for social distancing monitoring. The product uses the company’s ISP3010 module which is also based on Nordic’s nRF52832 SoC. In addition to the wearable tag format, the device can also be integrated into other products, such as security equipment and hard hats.

Next up for Nordic and Qorvo is a product that combines Nordic’s nRF52833 SoC, a 105°C qualified Bluetooth 5.2 SoC supporting Direction Finding and Bluetooth mesh, with Qorvo’s UWB transceiver for products used in elevated temperature environments such as enterprise lighting.

While the pandemic has wreaked havoc on the global economy, the silver lining could be the mass-introduction of the Bluetooth LE/UWB RTLS solutions currently fighting the virus into new multibillion dollar industry sectors when the world bounces back.

Combining UWB with Bluetooth LE creates a technology with excellent position-measuring capabilities but with a power consumption close to that of Bluetooth LE alone