Oct 1, 2015

Real-time Location Systems

Real Time Location Systems (RTLS) are systems designed to track the location of objects or people in real time. The precision timing capabilities of UWB radio transmission technology lends itself to RTLS. Given precision timing, it becomes possible to create a system of static reference Anchors and mobile trackable Tags.

Tags can be located when in range of the reference anchors through a variety of algorithms. One such algorithm is Multiple Two Way Ranging (MTWR) where the tags initiate TWR transactions with each of the anchors and position is computed through triangulation of the resulting distance measurements. MTWR requires multiple transmissions per anchor-tag pair resulting in limitations on the total number of devices and overall beacon rates.

Another popular algorithm used in RTLS systems is Multilateration. Systems using this algorithm require only a single tag transmission, or beacon, in or to produce a location. Multilateration uses the beacon reception Time-Difference of Arrival (TDOA) values to mathematically determine the location of the transmission. Given the TDOA of a tag beacon at two anchor locations it becomes possible to draw a hyperboloid representing all possible locations from which the beacon could have originated. Multilateration is the process of mathematically determining the intersection of multiple hyperboloids resulting in a single point location for the beacon. Multilateration is mathematically intense and requires a method of dealing with overdetermined systems where the final answer varies depending on which anchors are used for the calculation. The algorithm also suffers geometric issues when the tag beacon originates from 'outside the box', or areas not surrounded by reference anchors.

Ciholas RTLS (VM)

The Ciholas RTLS uses a proprietary algorithm known as Vectorization and Mapping (VM) to determine the location of mobile devices. Like Multilateration, VM requires only a single transmission, or beacon, from the tag device in order to produce a precise location. This allows the VM system to optimize battery life on the tag as well as support beacon rates well above those possible with TWR based systems. The VM algorithm collects all anchor receive timestamps for a single tag beacon and generates an output position that best matches the data. Un-like Multilateration the VM methodology enables the system to generate the best possible answer even in an overdetermined system.