What accuracy can be achieved?

A question we get very often is how accurate is the RTLS evaluation system that comes with the DWUSB?

The answer is it depends.

In a typical gym with good anchor geometry and no occlusions (line of sight from tag to all anchors), with 10 anchors, the system is about +/- 10 cm laterally and about +/- 20 cm vertically for any single tag beacon, with about 97% reliability. This varies depending on location in the environment as the geometry will vary.

This is shown in our demo videos on the web site:


If you do some location averaging, the results get better as one might expect. This has roughly the same effect as having more anchors.

The demo system is, of course, just for demo and evaluation, so it doesn’t represent the best that can be achieved necessarily in a specific application. For example, if you have lots of anchors, tag beacons at a high rate, and you average the results for a long time, you might be able to get down to millimeters. This is similar to measuring plate tectonics (millimeters of movement per year) using GPS signals (only a few meters accurate for single measurements).

An absurd example would be putting an anchor every 10 cm on a gym ceiling. That would be about 70,000 anchors! The system would be very accurate, sub 1 millimeter! Note that the demo software is presently limited to 10 anchors maximum, so you can’t actually build such a thing from the kit right now (but do contact us if you would like a system like that, we can design one for you).

A slightly more reasonable system might be an anchor every meter, or 700 anchors to cover a gym. This would give sub 1 cm level accuracy.

To fully assess what accuracy a real application can achieve takes detailed examination of where the anchors are placed, how many tags there are, how often they beacon, how fast is the response time, and so forth. The fundamental trade off is accuracy versus response time and/or anchor count.

Also, it should be noted that there is a difference between accuracy and precision. In reality, the numbers above are precision, how repeatable the position data is, and not necessarily accuracy, how true the numbers are to the actual location. Consistent error will hurt accuracy but not precision. For example, errors in anchor survey, or antenna group delay variation, or many other things can introduce accuracy errors, but the system could still be very repeatable. Any precise but inaccurate system can be made to be accurate by warping the measured data to fit the desired result. It should be noted that the gym videos on our web site are NOT warped or fitted, that is straight direct results mapped onto the floor lines.

Mike C.