Ultra-wide band

Ultra wide band (UWB, also written ultra-wide band or ultra-wideband) is radio technology that can be used for 3D tracking. It uses a bandwidth close to or greater than 500 MHz, and in its impulse radio form it sends very short radio pulses whose arrival a receiver can time precisely enough for centimeter-level ranging between devices. In the United States, the Federal Communications Commission (FCC) opened the technology to unlicensed commercial use in 2002.

Apple uses UWB for the Precision Finding feature of its Find My app, which guides an iPhone user to a lost AirTag. Other consumer uses include phone-to-phone sharing and digital car keys. UWB is also used in augmented reality: both Apple's Precision Finding and Samsung's SmartTag+ AR Finder pair UWB ranging with the phone camera to guide the user toward an item, and researchers have attached UWB transceivers to head-mounted displays to locate objects that the headset's cameras cannot see.

Reviewed 27 September 2026. Checked the FCC 2002 rule, the Coppens et al. and Alarifi et al. surveys, FiRa and IEEE 802.15.4ab pages, Apple, Samsung, Android, Qorvo and NXP sources, and the HoloLens UWB and UTrack3D papers against every claim; rewrote the HoloLens paragraph to what its abstract supports. About review dates.

Definition

The FCC defines a UWB transmitter as an intentional radiator that "has a fractional bandwidth equal to or greater than 0.20 or has a UWB bandwidth equal to or greater than 500 MHz", regardless of the fractional bandwidth. UWB's frequency range is between 3.1 GHz and 10.6 GHz. Under the 2002 rules, UWB communications and measurement systems must operate in the 3.1-10.6 GHz band, and indoor and handheld systems in that band are limited to an emission level of -41.3 dBm EIRP per megahertz. UWB transmits at low power so that it does not interfere with narrowband wireless technologies.

A 2022 survey by Coppens and colleagues at Ghent University and imec notes that UWB research has focused on impulse radio UWB (IR-UWB), which transmits radio pulses lasting nanoseconds or picoseconds; the IEEE ranging standards use this form. The authors list three benefits of this approach: high channel capacity at low transmit power, robustness to multipath (reflected copies of a pulse arrive separately and can be filtered out), and very precise timing, because the steep rising edge of each pulse lets the receiver pin down its time of arrival. The FiRa Consortium describes the impulse radio defined in IEEE 802.15.4a as using a 2 ns pulse width.

The IEEE 802.15.4 and 802.15.4z high rate pulse (HRP) physical layers define 16 channels, each a combination of a center frequency and a maximum bandwidth; the narrowest bandwidth is 499.2 MHz. Not every chip supports every channel. Channel 5 is supported by all of the chips Coppens et al. surveyed, and all except Qorvo's older DW1000 also support channel 9.

How UWB positioning works

UWB devices measure position with several techniques:

• Time of flight (ToF) and two-way ranging (TWR): two devices exchange messages and compute the distance from the signal's round-trip time.
• Time difference of arrival (TDoA): fixed, time-synchronized anchors record when a tag's pulse arrives, and the differences between those times give the tag's position.
• Angle of arrival (AoA): a receiver with more than one antenna estimates the direction of the incoming signal. AoA needs no synchronization and fewer measuring units than ToF or TDoA, but the hardware is more complex.

ToF, TDoA and AoA all lose accuracy in non-line-of-sight conditions, when the direct path between devices is blocked. A 2016 survey in Sensors by Alarifi and colleagues notes that UWB keeps high positioning accuracy even with severe multipath and that its signals pass through walls and other obstacles; the main drawback it lists is the high cost of UWB equipment. Because transmit power must stay low to avoid interfering with narrowband systems, UWB links are limited to relatively short distances. FiRa states that UWB can operate with line of sight at up to 200 meters.

UWB ranging is commonly described as centimeter-level. Coppens et al. note that with error-correction techniques the ranging error can be as low as 58 mm. Chip and platform specifications are more conservative: Android's developer documentation describes UWB as providing precise ranging with an accuracy of 10 cm, Qorvo specifies its DW3000 family to within 10 cm for ranging and +/-5 degrees for angle, and NXP rates the time-of-flight readings of its Trimension SR250 at +/-5 cm.

History and standards

UWB was first used mainly in radar and military communications before the 2002 FCC decision moved it into civilian use. The FCC adopted its First Report and Order on 14 February 2002, released it on 22 April 2002, and the rules took effect on 15 July 2002. The order authorized three classes of UWB device: imaging systems (such as ground penetrating radar, wall imaging and medical imaging), vehicular radar, and communications and measurement systems.

Milestones in UWB standardization

Year	Standard or organization	Change
2002	FCC First Report and Order	Unlicensed UWB authorized in the US; 3.1-10.6 GHz band for communications and measurement systems
2007	IEEE 802.15.4a	First IEEE standardization of UWB in its current form: an impulse radio physical layer for low-data-rate communication and precision ranging
2011	IEEE 802.15.4-2011	The 802.15.4a UWB physical layer merged into the main standard
2019	FiRa Consortium	Industry group founded to drive interoperability of UWB devices
2020	IEEE 802.15.4z	Enhancement aimed at the integrity (security) and accuracy of ranging measurements
2021	IEEE P802.15.4ab	Project authorized on 23 September 2021 to further enhance UWB physical and MAC layers; still listed as a draft with an active PAR

IEEE 802.15.4z, published in 2020, added coding and preamble options that improve detection, and chips that support it must implement its scrambled timestamp sequence (STS) security field, which is essential for hands-free, location-aware keyless access. The planned 802.15.4ab amendment covers additional channels, interference mitigation, better ranging accuracy, hybrid narrowband and UWB operation, and sensing for presence detection and environment mapping.

The FiRa ("Fine Ranging") Consortium was announced on 1 August 2019 by the ASSA ABLOY Group (including HID Global), NXP Semiconductors, Samsung Electronics and Bosch; Sony Imaging Products & Solutions, LitePoint and the Telecommunications Technology Association were the first members to join. FiRa builds interoperability profiles on top of the IEEE layers. Apple defined its own Nearby Interaction accessory protocol, which third-party accessories must follow to range with Apple devices, and the Car Connectivity Consortium's Digital Key 3.0 standard uses UWB for keyless car access.

Qorvo is a company that has made UWB tracking components. It entered the market by acquiring Decawave, a Dublin company founded in 2007 whose impulse radio UWB chips had shipped in more than 8 million units; Qorvo announced the completed acquisition on 24 February 2020. Decawave's DW1000 is, according to Coppens et al., the most widely used UWB chip in research and is found in many commercial real-time location systems (RTLS).

Companies that market UWB 3D tracking products include Ciholas. Its CUWB system is a real-time location system that Ciholas says reaches centimeter-level accuracy with tag beacon rates of up to 100 Hz.

Consumer devices

Apple announced the U1 chip with the iPhone 11 Pro on 10 September 2019, describing it as the first use of Ultra Wideband in a smartphone, for "spatial awareness"; iOS 13.1 used it for directionally aware AirDrop suggestions. The AirTag item tracker, announced in April 2021 at US$29 for one or US$99 for a four-pack, also contains a U1 chip. The iPhone 15 and iPhone 15 Plus, announced on 12 September 2023, use a second-generation Ultra Wideband chip that lets two such iPhones connect at three times the previous range, which Apple uses for Precision Finding of friends in Find My, so that users can find each other in crowds.

Samsung added UWB to the Galaxy Note20 Ultra, where it is used for the Nearby Share device-to-device service and as a digital door key. Samsung's Galaxy SmartTag+, available from 16 April 2021, uses UWB with UWB-capable Galaxy phones: the Galaxy Note20 Ultra, Galaxy S21+, Galaxy S21 Ultra and Galaxy Z Fold2. On Android, UWB is available to developers through the Jetpack UWB library on devices running Android 12 or higher that report UWB hardware.

Qorvo announced on 7 June 2021 that its DW3000 family works with Apple's U1 chip and the Nearby Interaction protocol. The DW3000 is compliant with IEEE 802.15.4z, follows the FiRa PHY and MAC specification and supports channel 5 (6.5 GHz) and channel 9 (8 GHz) at data rates up to 6.8 Mbps.

Applications in VR and AR

Camera-assisted finding on phones

Apple's Precision Finding for AirTag "fuses input from the camera, ARKit, accelerometer, and gyroscope" and guides the user with sound, haptics and visual feedback. At WWDC 2022 Apple opened the same approach to developers. In the session "What's new in Nearby Interaction", Apple engineer Jon Schoenberg said that ARKit-enhanced Nearby Interaction "leverages the same underlying technology that powers Precision Finding with AirTag". Setting a single property, isCameraAssistanceEnabled, makes the framework run an ARKit session and use the device trajectory it computes to keep distance and direction estimates available in more situations, "effectively expanding the Ultra Wideband sensor field of view". A helper method returns the nearby object's position as a transform in ARKit's world coordinates so apps can overlay 3D virtual content on it in the camera view.

Samsung's AR Finder, part of the SmartThings Find service, uses augmented reality to guide users visually toward a missing Galaxy SmartTag+ through the smartphone's camera. On a UWB-equipped Galaxy phone it shows how far away the tag is and points in its direction.

Head-mounted displays

In a paper at ION GNSS+ 2018, Francisco Molina Martel, Juri Sidorenko, Christoph Bodensteiner and Michael Arens integrated a UWB transceiver into a Microsoft HoloLens so that the headset could locate and display objects outside the direct line of sight of its cameras, something the authors said no contemporary commercial head-mounted display could do. The transceiver estimated its distance to a second UWB transceiver by time of arrival, using two-way ranging methods from the IEEE 802.15.4a standard; two of the implemented methods used a utility of the Decawave DW1000 chip to estimate clock frequency offset. A static UWB transponder was then located by trilateration from the measured distances and the calculated positions of the headset's UWB antenna in the HoloLens coordinate frame. The authors located and visualized the transponder in the headset with an accuracy of 6 cm when the position dilution of precision (PDOP) was below 10.

Object and hand tracking research

UTrack3D, presented at ACM MobiSys 2024 by Yifeng Cao, Ashutosh Dhekne and Mostafa Ammar of the Georgia Institute of Technology, tracks an object in 3D on a tabletop using commercial UWB chips. It follows changes in the phase of the UWB channel impulse response at dual-antenna receivers and reports a 90th-percentile accuracy of 9 mm in a 1.5 m by 0.8 m by 0.8 m region. The authors list AR/VR among the applications for recording the 3D movements of a user's hand or an object, and argue that camera-based tracking is accurate but expensive, suffers from occlusion and struggles in very dark or very bright rooms.

Examples of chips

Chip	Maker	Notes
U1	Apple	First UWB chip in a smartphone (iPhone 11 Pro, 2019); also in AirTag
DW1000	Qorvo (formerly Decawave)	Supports the IEEE 802.15.4 HRP physical layer only; widely used in research and RTLS products
DW3000 series	Qorvo	IEEE 802.15.4z and FiRa compliant; channels 5 and 9; interoperable with Apple U1
Trimension SR250	NXP	Combines UWB secure ranging, 3D angle of arrival and short-range radar on one chip; 6-8.5 GHz; announced 10 September 2024

The Trimension SR250 performs radar processing on the chip, which lets it detect presence, motion (including breathing and gestures) and the location of people or objects without cameras; NXP aimed it at smart home and industrial uses.

See also

• 3D tracking
• Positional tracking
• Tracking
• Optical tracking
• Sensor fusion
• Time-of-flight
• Inertial measurement unit