Ultra-wideband (UWB) is a short-range radio technology that sends extremely short pulses across a very wide band of frequencies, so that a receiver can time their arrival precisely enough to measure distance to within centimetres.
You may already carry UWB in your pocket: phones use it to point you towards a lost item or to unlock a car as you walk up to it. In factories, warehouses, hospitals and sports arenas, the same radio powers real-time location systems that follow people, vehicles and assets as they move.
What does “ultra-wideband” mean?
Every radio uses a slice of the spectrum, called its bandwidth. A Bluetooth channel is 2 MHz wide and a Wi-Fi channel 20 to 320 MHz. A UWB channel is about 500 MHz wide: some 250 times wider than a Bluetooth channel.
The US Federal Communications Commission (FCC) opened the band from 3.1 to 10.6 GHz to unlicensed UWB devices in 2002. Its definition is still the one most people quote: a transmitter is ultra-wideband if its signal is at least 500 MHz wide, or wider than 20 % of its centre frequency.
To share spectrum with other radios, UWB has to whisper. Its average power is limited to −41.3 dBm per MHz, which is roughly the level of unintentional emissions allowed from any electronic device. Spread across a whole channel, that adds up to about 0.04 milliwatts.
How does UWB measure distance?
UWB measures distance by timing how long a radio pulse takes to travel between two devices. Radio waves move at the speed of light, about 30 cm every nanosecond, so a receiver that can timestamp a pulse to a tenth of a nanosecond can measure distance to a few centimetres.
Because the two devices do not share a clock, they usually exchange messages. A tag sends a short message, the base station (UWB anchor) replies after a delay it knows exactly, and the tag subtracts that delay from the round trip and halves the rest. This is called two-way ranging. Other methods compare arrival times at several receivers or measure the angle a pulse arrives from; TWR vs TDoA vs AoA explains each one.
With distances to three or more fixed base stations, a positioning engine calculates where the tag is. Do that a few times a second and you have a live map.
Why is UWB more accurate than Wi-Fi or Bluetooth?
Most Wi-Fi and Bluetooth positioning estimates distance from signal strength (RSSI). Signal strength changes when a person stands in the way, when a door opens or when a forklift drives past, so the same reading can mean 2 m or 8 m.
UWB measures time instead, and its short pulses help in another way. Indoors, every signal arrives several times: once directly and again from reflections off walls, racks and machines. A 2-nanosecond pulse is short enough that the direct path and a reflection that travelled even a metre further arrive as separate peaks. The receiver takes the first one. A narrowband signal smears these copies together.
| UWB | Bluetooth LE | Wi-Fi | |
|---|---|---|---|
| Channel width | about 500 MHz | 2 MHz | 20 to 320 MHz |
| How position is estimated | Time of flight or time difference | Signal strength, angle, or Channel Sounding | Signal strength or round-trip time |
| Typical indoor accuracy | a few cm to about 30 cm | about 1–5 m with signal strength; under a metre with angle or Channel Sounding | several metres with signal strength; 1–2 m with round-trip time |
| Designed mainly for | Ranging and positioning | Low-power data, audio, beacons | High-speed data |
For the full picture, including RFID, GPS and cameras, see indoor positioning technologies compared.
What is UWB used for?
- Phones and consumer devices: finding items, pointing at a nearby phone to share a file, and hands-free car keys based on the Car Connectivity Consortium’s Digital Key Release 3.0.
- Access control: the Connectivity Standards Alliance’s Aliro 1.0 standard, released in February 2026, uses Bluetooth LE plus UWB for hands-free door access.
- Industrial real-time location systems: forklift and pedestrian proximity warnings, tool and work-in-progress tracking, digital andon calls and evacuation headcounts. See what is RTLS.
- Healthcare: locating equipment, staff and patients.
- Sports: player and ball tracking at high update rates, indoors and outdoors.
- Robots and vehicles: docking, following and navigation where GPS does not reach.
- Sensing: the next amendment of the standard adds radar-style presence detection, for example to notice a child left in a car.
What are the key numbers?
| Item | Value |
|---|---|
| Minimum bandwidth (US definition) | 500 MHz, or 20 % of the centre frequency |
| Allowed band, US | 3.1–10.6 GHz |
| Main band, EU | 6.0–8.5 GHz |
| Channel 5 / channel 9 centre | 6489.6 MHz / 7987.2 MHz, each 499.2 MHz wide |
| Average emission limit | −41.3 dBm/MHz (US and EU) |
| Accuracy | a few cm in line of sight; about 30 cm in harsh factory conditions (FiRa) |
| Range | up to about 100 m in line of sight (FiRa); tens of metres indoors |
How did UWB develop?
| Year | Milestone |
|---|---|
| 2002 | The FCC allows unlicensed UWB devices between 3.1 and 10.6 GHz. |
| 2007 | IEEE 802.15.4a adds an impulse-radio UWB physical layer designed for ranging. |
| 2019 | The iPhone 11 brings UWB to phones; the FiRa Consortium forms to make UWB devices interoperable. |
| 2020 | IEEE 802.15.4z adds secure ranging with a scrambled timestamp sequence (STS). |
| 2023 | FiRa adds downlink time difference of arrival, where a device works out its own position, to its certification. |
| 2024 | IEEE 802.15.4-2024 folds the 802.15.4z features into the base standard. |
| 2025 | FiRa Core 4.0 adds uplink time difference of arrival for tracking tags with fixed infrastructure. |
| 2026 | Aliro 1.0 is released; IEEE P802.15.4ab, the next major amendment, is still a draft in October 2026. |
Does Wi-Fi affect UWB?
Channel 5 sits inside the 6 GHz band that Wi-Fi 6E and Wi-Fi 7 now use. Laboratory measurements have shown heavy UWB packet loss and about 10 cm worse ranging precision on channel 5 next to busy 6 GHz Wi-Fi. Channel 9 lies above that Wi-Fi band, and the FiRa Consortium recommends channels 8 and 9 where UWB and Wi-Fi must run side by side. On channel 5, a radio site survey and Wi-Fi channel planning keep the two apart.
Where to go next
If UWB is new to you, read what is a real-time location system next, then indoor positioning technologies compared. Engineers can continue with TWR vs TDoA vs AoA and UWB accuracy and range. Unfamiliar terms are explained in the glossary.
Frequently asked questions
What does UWB stand for?
Is UWB the same as Bluetooth?
Is UWB safe?
Does UWB need line of sight?
What frequency does UWB use?
Does UWB interfere with Wi-Fi?
Which phones have UWB?
Sources and further reading
- US eCFR, 47 CFR Part 15 Subpart F: Ultra-wideband operation
- IEEE 802.15.4-2024, Standard for Low-Rate Wireless Networks (IEEE SA)
- IEEE P802.15.4ab, Enhanced UWB physical layers and MAC enhancements (IEEE SA project page)
- FiRa Consortium technical FAQ
- Powell, Rolfe, Neirynck and Lansford: IEEE 802.15.4 IR-UWB, a technology precisely positioned for adoption (IEEE OJVT, 2025)
- Brunner et al.: Understanding and mitigating the impact of Wi-Fi 6E interference on UWB (IPSN 2022)
Published . Last reviewed by the Noccela engineering team.