UWB Explained: What Secure Ranging Means for the IoT and Beyond

IoT 
Aug 4, 2021

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In the time since the IEEE added support for Ultra-Wideband (UWB) communication to the 802.15.4 specification, a number of very big names have moved quickly to adopt the technology. Apple and Samsung now offer UWB as part of their latest smartphones, and a number of automakers, including Volkswagen, are demonstrating cars equipped with UWB features.

Market analysts are talking about UWB, too, predicting it will soon be a standard option in vehicles as well as smartphones. ABI Research, for example, anticipates large-scale adoption, with over 1 billion devices with UWB technology being shipped annually, as soon as 2025.

UWB may be grabbing headlines, but it’s still not as familiar to many as Wi-Fi and Bluetooth have become. With so much rapid growth predicted in the next several years, it’s worth taking a closer look at what UWB is, what it can do, and how it works, with specific reference to secure ranging.

A Unique Structure

UWB is fundamentally different from other communication technologies – including Wi-Fi and Bluetooth – in that it uses extremely narrow RF pulses to communicate between transmitters and receivers. Sending pulses, while operating at a very high frequency and using a wide spectrum (from 500 MHz upwards), makes it possible to determine the relative position of peer devices with a very high degree of accuracy.

Its unique configuration means UWB can perform secure ranging with pinpoint accuracy, while using very little power to send signals. It provides very stable connectivity, with little to no interference, even in dense RF environments.

Figure 1: Power Spectrum of UWB, NXP Semiconductors

A Complementary Technology

UWB delivers more precise readings than any other location technology currently in use. While Wi-Fi and Bluetooth can narrow an item’s location to within an area of around 150 cm (about the size of a dinner table), UWB has a location accuracy of about 10 cm (or the size of a coaster) and needs fewer UWB devices to cover the same area. UWB is also better than satellite signals when it comes to indoor navigation, since UWB’s low-frequency, long-wavelength pulse signals are better at penetrating solid materials like walls and doors.

But UWB isn’t meant to replace Wi-Fi, Bluetooth, or satellite navigation. It can serve instead as a complementary technology that enhances location identification when used in combination with Wi-Fi, Bluetooth, or even satellite navigation. Also, because UWB transmits across a wide channel bandwidth but with low spectral density, it doesn’t interfere with conventional narrowband and carrier-wave transmissions in the same frequency band. Operating below the noise floor of -41 dBm/MHz, UWB is essentially invisible to other wireless formats, so UWB can work alongside Wi-Fi, BLE, satellite navigation, and cellular formats without disrupting their transmission.

Elevating the User Experience

In terms of applications, UWB’s unique signaling and ability to perform secure ranging are particularly relevant to the Internet of Things (IoT). The FiRa Consortium, an industry organization dedicated to the development and widespread adoption of UWB technologies, has identified more than 35 use cases for UWB. Those that have already arrived or are nearing introduction include access control, real-time location services, personal and consumer device tracking, indoor navigation, and point-and-trigger control.

- Access Control

One of the most natural use cases for UWB’s secure ranging capabilities is access, with automatic locking and unlocking of doors. UWB tracks your exact location in relation to the entrance or exit, authenticates your security credentials, and grants access instantly, hands-free, without any further need for your interaction. UWB can detect which side of the door you’re on, as well as your direction of movement, so doors can unlock and lock according to the situation.

UWB also protects against relay attacks, which are an increasingly common form of auto theft, making it well suited for use as a secure car key (and for having your smartphone fill that role, too). Multi-session support prevents tailgating, and credentials can be shared with friends, family, and service people, granting temporary access as needed.

- Real-Time Location Services (RTLS)

UWB is a lot like radar, because it can continuously scan a room and lock onto an object with laser-like precision to calculate its location and transmit data. UWB’s ability to deliver centimeter-level location accuracy, ultra-low latency, and robustness in harsh environments makes it possible to build commercial environments for more stringent asset and vehicle-tracking applications, from high-value tool and equipment tracking to worker safety and even vehicle navigation and collision detection.

In healthcare environments, UWB-based RTLS solutions help streamline operations and keep people safe. UWB can track available beds to maximize utilization, trace valuable equipment to prevent theft or losses, locate patients and personnel to increase safety, monitor hygiene practices, and ensure the right people have access to the right areas and equipment.

UWB can also be used for direct marketing, to send offers to nearby customers who sign up for such a service, and to provide retailers with traffic analytics.

- Personal and Consumer Device Tracking

When easily lost or misplaced items are tagged with UWB, they don’t stay missing for long. All kinds of personal items – keys, wallets, earbuds, remote controls – can be equipped with a UWB tag. A combination system, based on Bluetooth Low Energy (BLE) and UWB, saves power by using BLE to detect general presence, and then using UWB to pinpoint location.

Your smartphone’s camera can visually guide you to your item, making it much easier to find things fast. Location tasks could even be community-sourced. This could lead to new services and new business models for mobile operators and insurance companies and added-value to consumers.

- Indoor Navigation

Bringing satellite-style navigation indoors, with a “blue dot” moving over a map, makes it easier to find a specific store in a shopping center or the right platform in a train station, or to be directed to the correct gate at an airport or your indoor ride pick-up.

UWB can augment Wi-Fi and Bluetooth way-finding applications, by offering much higher accuracy and stronger performance in non-Line of Sight (nLOS) scenarios.

- Point-and-Trigger Control

At home, point your UWB-enabled smartphone at a light bulb, the thermostat, a speaker, your TV, or any other UWB-enabled device, and automatically open a relevant control panel on the smartphone display, so you can direct the device to do things that can be hard to describe with voice-controlled mechanisms. Along with the control panel, your smartphone can engage in other ways, too, by calling up song lyrics, for example, or making recommendations about what to play next.

Precise Measurements

As specified in IEEE 802.15.4a/z, UWB pulse signals are transmitted at a peak rate of 200 to 1000 times per second, making it possible to mark signal timing with a very high degree of certainty. That makes the familiar Time of Flight (ToF) and Angle of Arrival (AoA) calculations, which are the long-standing methods for determining distance and location, produce much more exact results.

The ToF calculation determines the distance between Device 1 and Device 2 by measuring how long it takes for a signal to travel from Device 1 to Device 2 and back. The rapid pulse rate of UWB yields an accuracy of within ±10 cm. ToF diagrams are typically depicted as circles, because ToF calculations determine the radial distance of an object, not its direction. That is, if the ToF calculation reveals that Device 2 is 15 cm away from Device 1, then Device 2 could be anywhere within that 15 cm radius.

Figure 2: UWB Localization based on Time-of-Flight, NXP Semiconductors

The AoA calculation is used to determine where, within that radius calculated by ToF, Device 2 is. A dedicated array of carefully positioned antennas makes it possible to measure the tiny differences in the arrival time and phase of the returned signal at each antenna. The differences are used in a geometric calculation, similar to triangulation, to determine where the signal came from. Not all UWB solutions include the extra antennas used for AoA calculations, but those that do can delivery accuracy to within just a few centimeters.

Stronger Signals

Another feature of the UWB pulse signal is that it resists a common difficulty, known as the multipath effect, which is what happens when radio signals reach the receiver by more than one path, due to reflection or refraction caused by natural or man-made objects close to the main signal path.

The multipath effect is unavoidable in real-world environments, but the short wideband pulses of UWB are better at escaping its effects than the narrowband signals used by Wi-Fi and Bluetooth. The reason is that, since the transmission duration for UWB pulses is less than a nanosecond in most cases, the reflected UWB pulse has an extremely short amount of time in which to collide with the Line of Sight (LoS) pulse, so there’s less chance of signal degradation. The result is higher signal strength in adverse conditions.

Immunity to the multipath effect improves accuracy, especially when compared with alternative technologies that are more susceptible. What’s more, immunity to narrowband fading and jamming also helps make UWB a very robust technology, even when multiple UWB systems are used simultaneously.
UWB can be deployed on a global scale with regionally different frequency channels set aside between 6.490 and 7.987 GHz. The FiRa Consortium recommends the use of UWB bands 5, 6, 8, and 9, using channels 5 and 9 to achieve global acceptance.

Figure 3: UWB Spectrum Availability by Country, Source: FiRaTM Concortium

Uniquely Positioned for the Future

With its ability to provide highly accurate, reliable, robust, and secure positioning information across a wide range of use cases and device types, UWB is poised for widespread adoption. As the UWB installed base continues to expand, we can all look forward to a new generation of device-to-device and device-to-infrastructure applications, with everything from hands-free secure access to vehicles and buildings, indoor localization, asset tracking, hands-free payments, seamless interactions at home, augmented reality, gaming, and a whole range of smart city, industrial, and other IoT applications.

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