Positioning

RTLS is a system that traces the position of mobile tags in real time using the distances or angles between fixed and mobile nodes. Mobile nodes are also called as tags or mobile terminals and they are small devices attached on the target persons or assets. Fixed nodes usually are sensors to measure the distances to tags. They are similar to satellites for GPS which is widely used for locating outdoors and are used as references for ranging distances.

Many kinds of method are used for ranging distances according to the required coverage and resolution, such as infra red, ultrasound, WiFi, UWB, ZigBee, etc. For example, ultrasound technology can locate things accurately up to tens of centimeters within tens of meters’ distance and cannot penetrate walls and thus it’s suited for indoor applications. On the other hand, RF technologies including UWB can support resolution up to several meters which is somewhat low compared with ultrasound but they can penetrate walls easily and cover much longer distances. The software which gathers this information on distances and calculates the positions is called location engine. The location engine calculates the position mainly based on trilateration similarly to GPS. The distance information suffers from many kinds of errors due to physical limits, multi-path interferences, and other noises caused by obstacles. The location engine takes these into account and tries some intelligent steps to make the results most stable and accurate.