Ranging error in Indoor Environment with one TAG and one ANCHOR

Hey guys,
I have done an experiment about one to one range, and there is a strang result that the range error presents as negative value and the absolute value of the error decrease with the real distance increasing.As the picture shows below, in which x axis is the real distance and y axis is the range error.

What confused is that if the rate difference between the two clock cause the range error, then the error should be constant rather than increasing.
On the other hand, the reflecting signal just cause error with positive value.

So, I wanna if anyone can help with this experiment result.


A constant offset in range is normally the result of poor antenna delay calibration.
An range dependent error, especially at short ranges, is normally related to signal strength compensation issues.

Thanks for ur reply!
I am very interested in “signal strength compentation”, do u mean spikes will be above the detection threshold because of reflaction or multipath?

And if there are papers can explain this issue, especially why it takes a large effect in short ranges.


The issue is that the device is looking for the signal to cross a threshold. Since the ramp rate on the signal is not infinite this means that a weaker signal will cross the threshold later than a strong signal.
This effect can account for around 10-15 cm of range error.
Since signal strength follows the inverse square law this is far more noticeable at short ranges. The change in signal level of a 10 cm movement at 1m is far more than it would be for the same movement at 10 m.

The application note on ranging error sources gives more details on this.