Getting Started with UWB Using NXP Trimension® SR250 - Part 1: UWB Basics and an Overview of the SR250 (Japanese Blog) Introduction
"Doors open with your smartphone still in your pocket," "Lights turn on automatically when you enter a room," "The moment you sit down on the sofa, the soundbar automatically adjusts the sound field to your position"—the NXP Trimension ® SR250 is a device that can make these experiences a reality.
The SR250 is the world's first IC for IoT applications to integrate ultra-high-precision wireless ranging technology " UWB (Ultra-Wideband) " and " UWB radar " that can detect people and objects without an external device, all on a single chip with on-chip processing.
This SR250, which holds so much potential, was finally released to the mass market in March 2026! The evaluation board SR250UWBSHIELD is available for purchase from NXP's e-commerce site .
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If you've been thinking, "That sounds interesting, but it might be difficult," now's your chance to give it a try.
In this first installment, we'll cover everything from the basics of what UWB is to the features of the SR250. Read this article to expand your imagination, and then get your hands on an evaluation board and experience UWB together!
Have you heard of UWB somewhere before?
If you're thinking, "Isn't UWB an old high-speed data transfer technology?", you're very perceptive!
In the early 2000s, UWB attracted considerable attention as a high-speed wireless data transfer technology . The WiMedia Alliance worked to standardize it, but it ultimately failed to gain widespread adoption due to the rapid evolution of Wi-Fi and Bluetooth.
However, in the late 2010s, UWB made a comeback in a completely different form. It was redefined as a precision distance measurement and positioning technology and standardized as IEEE 802.15.4z. Its inclusion in the iPhone 11 in 2019 brought it a surge in popularity.
The fundamental characteristic of UWB—its wide bandwidth—remains unchanged. However, by using this characteristic not as "communication speed" but as "temporal resolution," entirely new applications have emerged.
What is UWB? — Into the world of centimeters
UWB (Ultra-Wideband), as its name suggests, is a wireless technology that uses extremely wide bandwidth in terms of frequency, and conversely, very short pulse signals in terms of time. It has been standardized as the IEEE 802.15.4z standard and is currently rapidly gaining popularity in the field of short-range high-precision positioning.
While Wi-Fi and Bluetooth have a positioning accuracy of ±1-2m, UWB can achieve centimeter-level accuracy of ±5-10cm. This technology can detect "here" rather than "somewhere."
This combination of centimeter-level accuracy and high security enables smart car access and precise indoor positioning. In addition to Android smartphones and AirTag, it has also been announced that it will be integrated into Google Pixel Tag, and further widespread adoption is expected in the future.
*Google Pixel Tag is scheduled for release in November 2026.
Why is UWB so robust against multipath interference and secure? — A comparison with other wireless technologies
What is multipathing?
Radio waves don't just travel in a straight line like light; they also propagate by reflecting off walls, ceilings, furniture, and other objects. The receiver receives a mixture of radio waves that traveled in a straight line and those that have reflected from various points. This is called multipath. Indoors, in particular, there are many reflections, creating a multipath environment.
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RSSI (Radio Speed Indicator) based ranging methods like BLE and Wi-Fi estimate distance using the "strength of mixed radio waves," making them highly susceptible to reflected waves.
Because UWB uses very short pulse signals (a few nanoseconds wide), it can temporally separate and distinguish signals that arrive directly from signals that are reflected and arrive later.
Why is UWB ranging secure?
UWB uses an encrypted signal sequence called STS (Scrambled Timestamp Sequence). The STS is generated each time by an AES-128-based random number generator, producing a different value each time . The receiver calculates the same STS using a pre-shared key and verifies the legitimacy of the sender by comparing it with the received value.
Because a different STS value is generated each time, attacks that involve retransmitting intercepted signals (replay attacks) or relaying/spoofing signals to misinterpret distance are impossible. Furthermore, in secure ranging, the session key used to generate the STS is managed in a secure environment and recalculated periodically. Even if the key information at a specific point in time is leaked, the scope of damage can be limited. As a result, UWB achieves stronger security than BLE or Wi-Fi-based ranging.
Comparison of distance measurement technologies
technology
accuracy
Multipath resistance
security
Main uses
UWB
±5~10 cm
High ( separates waves directly with pulses)
High (STS encryption)
Precision positioning and smart access
BLE Channel Sounding
±0.5 m
Medium (improved by phase measurement)
Medium (Protected by RTT+ phase)
Smart Access IoT
Wi-Fi RTT (FTM)
±1 to 2 m
low to medium
low
Indoor navigation and floor detection
BLE RSSI
±1 to 5 m
Low (intensity-based)
low
Proximity detection and beacons
Other technologies, such as BLE Channel Sounding, offer advantages in terms of cost and power consumption, leading to an increase in their use depending on the application, as well as hybrid configurations with UWB.
UWB ranging principle: ToF and AoA
ToF (Time of Flight)
In TWR (Two-Way Ranging), the Initiator sends a pulse to the Responder, which then returns it. The Initiator measures the round-trip time of the radio waves and calculates the distance. Because radio waves travel at the speed of light, even a small time error directly translates to a distance error. The wider the bandwidth, the higher the time resolution and the better the distance accuracy.
Furthermore, it supports TDOA (Time Difference of Arrival) by combining multiple devices, enabling real-time positioning over a wide area.
AoA (Angle of Arrival)
The angle at which a device is located is calculated from the phase difference of arrival (PDOA) of signals received by multiple antennas. Because the SR250 has three receiving ports, it can perform 3-single-shot 3D AoA , simultaneously calculating horizontal and vertical angles.
What is UWB radar?
While ranging measures distance through communication between two UWB devices, radar takes a completely different approach. By analyzing the signals reflected from pulses that hit people or objects, it can detect distance, direction, and presence even if the other party does not have a UWB device .
UWB radar can detect even the slightest movement of the human body, allowing you to sense whether there is a person present and whether they are moving, while protecting privacy.
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Leave radar processing to the SR250! On-chip radar processing
Radar algorithms are complex and not easy to develop from scratch. The SR250 is designed to handle the detection of a single target's presence, distance, and angle on-chip , allowing you to use radar functionality without developing your own algorithms. For more complex radar processing, reflections can be sent to a host, enabling AI/ML applications.
Applications pioneered by the SR250
The SR250, which integrates ranging and radar into a single chip, is expected to be used in a wide range of fields, from consumer devices such as smart locks and smart speakers to industrial applications such as collision prevention between AGVs (automated guided vehicles) and forklifts and workers in factories and warehouses.
"Knowing location," "Knowing presence," and "Knowing movement"—what kind of devices could be created if these three things were possible without a camera? Please read the series while imagining these possibilities.
Scheduled serialization
This series is planned to consist of four parts.
Part 1 (This article)
Basics of UWB and an overview of the SR250
2nd time
Setting up the SR250 evaluation board (SR250UWBSHIELD)
3rd
Let's try UWB ranging.
4th
Try out UWB radar.
Next time, we'll explain how to obtain an evaluation board and how to set up the hardware and software environment. Let's get ready to run UWB together!
Reference links
Trimension SR250 Product Page (Japanese)
SR250 Evaluation Board (TRIMENSION-SR250)
UWB Radar Fundamentals (AN13989)
UWB Convergence Radar White Paper
Introducing the Trimension SR250 Training (English, 24 minutes)
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We are currently unable to respond to comments left in the "Comment" section of this post. We apologize for the inconvenience, but please refer to " Technical Questions to NXP - How to Contact Us( Japanese Blog) " when making an inquiry. (If you are already an NXP distributor or have a relationship with NXP, you may ask your representative directly.) The NXP Trimension® SR250, which integrates centimeter-precision ranging and a UWB radar that does not require a separate device onto a single chip, was released for the mass market in March 2026. This article explains the basic principles of UWB and the features of the SR250.
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