Real Time Location Systems ( RTLS )

Real time location systems (RTLS) use 3 or more fixed RFID reader stations to accurately pinpoint the location of the RFID tag in 2 or 3-dimensional space. In some tracking applications it is advantageous to know the exact location of an object, versus knowing the current area (or zone) of the item. There are many different ways to calculate the position of the RFID tag, using measurements such as received signal strength (RSS), time difference of arrival (TDOA) and angle of arrival.

Ultra-Wideband ( UWB )

Conventional RFID technology has limitations when it comes to RTLS accuracy. Due to the nature of the RFID signal, multipath signals can decrease position accuracy, as the readers can’t easily distinguish between the original transmitted signal and other signals that bounce off objects. Since RTLS algorithms use RSS and TDOA to calculate object position, both of these calculations can be slightly off due to multipath, thus decreasing the accuracy of the item location. Ultra-wideband (UWB) solves the problem of multipath, by using a pulsed RF signal. Multipath signals show up as a series of pulsed signals, but the reader only needs to use the first received pulse signal to calculate location, which in fact is the originally transmitted signal.

Ultrasonic

Recently, an alternative ultrasonic indoor positioning system has been developed. It combines the zonal accuracy of the first system with a vastly increased update rate. Therefore it won't overlook pieces of equipment when the number of items in a room grows, as the original system does. It may even be used for precise tracking of crowds of people as they move rapidly from room to room. The battery drain is also lower, potentially making the tags smaller.