UWB, or ultra wideband, is a short range wireless standard that measures distance very finely, accurate to roughly ten centimetres. It is well suited to precise relative position and secure ranging.
The longer version
Ultra wideband sends very short pulses across a wide slice of spectrum, which lets it time a signal's flight with unusual precision. The practical result is fine ranging, accurate to roughly ten centimetres, so a device can tell not just that another is near but how near. The FiRa Consortium maintains the interoperability standards behind it.
That precision makes UWB strong for secure ranging, where knowing the exact distance helps confirm that two devices really are beside each other rather than being relayed from farther away. It resists some of the tricks that fool coarser signals.
For proximity identification, UWB is the option to reach for when the setting demands a sharp answer about who is closest. In a crowd of candidates, finer ranging makes the nearest pairing easier to resolve with confidence.
The Parousya method
Ultra wideband gives the Parousya method its most precise sense of nearness. Where several candidates are packed together, UWB ranging helps the server settle on the single closest pairing.