Table 1.

IR-UWB positioning system metrics.

IR-UWB Positioning Metric	Definition
Signal Strength (SS)	The target measures the signal strength for received signals from reference nodes in order to use signal strength as an estimator of the distance from them [86]
Time of Arrival (ToA)	The location is the intersection of circles with radius equal to the distance between the target and reference nodes and calculated as the one-way propagation time between them [87,88,89].
Time Difference of Arrival (TDoA)	It is based on comparing the time difference between the target and at least three reference nodes [90,91].
Angle of Arrival (AoA):	The location can be found from the intersection of the angle line for each reference node [92,93,94].