The new NXP Trimension SR250 offers advancements in ultra-wideband (UWB) technology by being the first available single-chip solution that incorporates three main functions: 

• Secure UWB ranging
• UWB radar sensing
• On-chip processing

The integration of low-power, short-range UWB radar technology—operating within the 6 to 8.5 GHz frequency band—with secure ranging capabilities, and angle-of-arrival (AoA) computations, facilitates the development of novel applications centered around UWB mapping, human or object detection, and secure positioning. The SR250 expands upon the capabilities of its predecessor, the SR150, which solely integrated the 3D AoA and secure ranging functionalities. An alternative model, the SR040, exclusively leverages the ranging feature and is optimized for battery-operated Internet of Things (IoT) devices such as UWB trackers and tags. A conversation with Sunil Jogi, the Marketing Director at NXP responsible for UWB sensor products in IoT applications described the benefits of the newly released SR250. 

What is UWB radar sensing?

The major benefit of UWB radar sensing lies in its ability to detect and differentiate small to large objects at close range. UWB technology uses very short pulses and thus large bandwidths and low power radio waves from 3.1 GHz to 10.6 GHz  to communicate over short distances (< 50 m). The larger bandwidth allows for an improved range resolution, or the ability to distinguish closely-spaced objects from one another. Millimeter-wave frequencies also have the benefit of larger bandwidth and higher range resolution sensing, however, UWB operates at much lower frequencies, making it more immune to the effects of atmospheric absorption where the signals are able to pass through and diffract around objects much more readily. UWB also utilizes less congested spectrum when compared with alternative wireless protocols that use the popular 2.4 GHz and 5 GHz ISM bands (e.g., Wi-Fi, Bluetooth) making it more resistant to interference.  

What is 3D AoA?

3D AoA calculations allow the sensor to readily discover the general direction of the target from the sensor itself. The 3D AoA measurements are based on phase difference of arrival (PDoA), a technique that uses two antennas to calculate the phase difference of the same received signal. This phase difference is calculated using the carrier signal and not UWB pulses. The AoA can be extrapolated based upon the geometry of the scenario where the difference in path length is related to the distance between the antennas (Rx1 and Rx2). 

What is secure ranging?

The UWB ranging method will be able to obtain the absolute location of the target by measuring the round trip time of life (ToF) of the pulses, or their propagation time. This is done by transmitting a sequence of modulated pulses with a specification pulse repetition frequency (PRF) and calculating the channel impulse response (CIR) from the reflected signal off the target (Figure 1). Large movements of the target, i.e., radial velocity, will be detected via multiple consecutive measurements. 

Figure 1 The round-trip ToF is calculated by obtaining the CIR from the reflected signal off the target. Source: NXP

The SR250’s UWB ranging capabilities occur between two (or more) UWB sensors installed within a space (Figure 2) allowing for a distance accuracy of ±5 cm and an angular displacement accuracy of ±3o in 3D space. This distance measurement is one of the most important features of UWB technology, enabling use cases such as automatic door access, speaker setup, etc. The feature is inherently secure in that it prevents relay attacks in distance measurements. This way, the distance that is measured is accurate and is not subject to, for instance, a man in the middle (MITM) attack. A measurement time of <10 ms allows for near-real-time tracking capabilities and can be especially useful in industrial applications, e.g., tracking personnel, vehicles within a facility. The nanosecond pulses enable a much lower power consumption relative to other radar technologies.

Figure 2 Ranging occurs between two or more UWB sensors to accurately capture the movement of a mobile device within an environment to trigger a speaker system, door lock, vehicle, lights, or laptop. Source: NXP

Radar sensing + AoA + ranging: Tying it all together

As an example, a battery-powered, home-based door lock device could use this technology to carefully enable the lock only when it is sensing the correct mobile device approaching so as to optimize battery life. To avoid continuously logging and sensing for motion, the UWB radar sensing aspect of the chip will “wake up” the lock when the person/mobile device is—for instance, 6 meters from the door lock—via a secure mobile app such as Apple wallet or any other OEM-specific wallet. At this point the secure ranging aspect will detect the approach and calculate the distance from the door lock, e.g., 5m, 4m, 2m, 1m. The door lock might be designed to unlock when the mobile device is within 1 meter from the door; however, it is necessary for the lock to be “aware” that it is an approach from the outside and not the inside. This is where 3D AoA is necessary, to avoid opening the lock on an approach from the inside of the home. 

On- and Off-chip radar processing 

A built-in presence detection algorithm removes the need for an application processor in these specific use cases that require a detection of a change in the environment such as the presence of a human. An off-chip radar processor, e.g., application processor, can be utilized for an application that might require more classification such as differentiating between an adult, a child, and a pet; detecting specific gestures; or detecting vitals such as breathing rate. 

Other applications

By tying UWB sensing, ranging, and 3D AoA measurements with machine learning (ML), new applications are enabled that could effectively replace or augment other sensor technologies. Similar to the smart lock application mentioned above, the integrated solution with ranging can offer automated functionality to many home-based UWB-enabled devices, automating the streaming of music through speakers, opening/closing blinds, turning on thermostats, etc., while consuming minimal power. Many existing smart TVs have cameras that are potentially undesirable for privacy concerns and hardware cost. This could be sidestepped with UWB technology, enabling features like gesture detection, e.g., increasing/decreasing volume via hand motion, without the inhibiting factors associated with cameras.  This can be extended to industrial asset-tracking while offering less susceptibility to interference and much more positional accuracy than alternative Bluetooth beacon technology. 

UWB technology offers a low-power method for object detection with high-range resolution. The Trimension SR250 chip is the first of its kind to incorporate UWB radar sensing, secure ranging, and on-chip processing in a single solution. This integration opens up new possibilities for IoT applications, providing greater capabilities than basic passive infrared (PIR) sensors for motion detection and offering additional advantages in range and cost compared to more advanced millimeter-wave radar systems. The ability to incorporate more complex algorithms allows UWB technology to perform more refined object, gesture, and vital sign classifications, potentially replacing certain well-established vision-based systems.

Aalyia Shaukat, associate editor at EDN, has worked in the design publishing industry for nearly a decade. She holds a Bachelor’s degree in electrical engineering, and has published works in major EE journals.

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