ULTRA WIDEBAND
Ultra Wideband (UWB) is as old as radio itself, the very first spark-gap transmitters used at the dawn of radio (on the RMS Titanic for instance) were essentially ultra-wideband in nature.
In terms of practical application, UWB has a number of significant properties.
Firstly, it is possible to distinguish between pulses arriving at the receiver via the direct path between the receiver and the transmitter and pulses arriving via other non-direct paths caused by reflections and thereby measure the distance between the transmitter and receiver very accurately, thereby allowing the use of TDOA (Time Difference of Arrival), acknowledged as the best method for RTLS. At a bandwidth of 1300MHz it is possible to measure accurately down to +/-10cm. It is simply not possible to do this to the same level of accuracy with other narrowband radio schemes.
Secondly, because the transmitted signal occupies such a wide bandwidth, it is highly immune to multi-path fading – an effect that was well known to everyone who listened to MW and LW radio at night; the cyclical increasing and decreasing of volume due to the signals bouncing off the ionosphere and interfering with each other. Modern narrow band schemes suffer the same fate causing severe problems in “RF hostile” environments where there are lots of reflections.
Ultra Wideband has very attractive benefits:
- Ability to very precisely measure the time of flight of the radio signal from transmitter to receiver => very accurate distance measurements (range & precision) – orders of magnitude more precise than existing systems;
- Very high immunity to multipath fading;
- Avoids “Spectral Crowding” of ISM bands.
DecaWave’s ScenSor allows Direct Path to be identified even if it is severely attenuated relative to other indirect paths.
See also: "Experimental Impulse Radio IEEE802.15.4a UWB Based Wireless Sensor Localisation Technology: Characterisation, Reliability and Ranging"
(Tyndall Institute research paper) [Download]
