The location accuracy of an RTLS system is a critical parameter as it determines greatly what kind of business benefits can be achieved with the system. An elementary accuracy of 10-15 meters can be achieved by almost any RTLS system, but how much value does it bring to the organization if the location is off by two rooms, or even a floor.
Some applications, such as wireless intrusion detection (WIDS), can live with less granularity, but several studies show that room level accuracy or better is required for most healthcare applications. Other industries have similar requirements on accuracy.
The simplest form of radio based location system estimates the location by the wireless access point the device is associated to.. This gives rough 10 to 50 m accuracy indoors, depending on the density of the network and the type of environment. This method, while being simple to implement, suffers greatly from its simplicity: If the tracked device is not very close to the access point, the accuracy will be weak. .
A bit more advanced location method is trilateration. With trilateration the signal strength is measured from multiple access points, minimum three, and the location estimate is calculated from these measurements. The accuracy is a bit better, but still weak (8 to 25 meters indoors, worse outdoors). The main issue is that trilateration assumes circular, “ideal” coverage patterns – but the Wi-Fi signals are heavily attenuated by walls and even the human body, making the coverage patterns all but circular. The method also suffers from multipath and noise.
By applying filtering to the above estimates the accuracy gets better and the random jumps of the location estimates become less frequent. Several commercial products and research projects have demonstrated that applying different filtering techniques, such as Kalman filtering (http://en.wikipedia.org/wiki/Kalman_filter), improve the accuracy. With filtering, the average accuracy can reach around 10 meters, but floor hopping still occurs frequently.
Ekahau’s location algorithms provide typically down to 3 meter average accuracy and 100% floor accuracy enterprise wide, over a VoIP grade Wi-Fi network. This location accuracy makes the Ekahau solution the leading Wi-Fi RTLS system on the market and with optional infrared technology this performance can be even further improved to bed level accuracy.
The next part of this article series looks into the innovations behind Ekahau’s location algorithm that enable industry’s best accuracy.