# Implementing an Industry 4.0 UWB-Based Real-Time Locating System for Optimized Tracking
## 3 Materials and Methods  
### Tracking Methods  
For each solution based on the above-mentioned technologies, a specific methodology estimates the exact position of the assets. To locate a specific object, a tag is attached to it, and, in accordance with the selected technological category (wireless, vision, and PDR tracking), the implemented technology provides an estimation of the object's position. In the case of wireless signals, the methodologies used to track the object are analyzed below:  
1. Angle of arrival (AoA). The AOA method estimates the position location by means of angular direction observations measured with respect to a reference axis using directional antennas or antenna arrays. 2. Time difference of arrival (TDoA). The TDoA method locates a signal source from the different arrival times at the receivers. Once the signal is received at two reference points, the difference in the arrival time can be used to calculate the difference in distances between the target and the two reference points. This difference can be calculated using the equation \(\Delta\)x = c \(\times\) (\(\Delta\)t), where c is the speed of light and \(\Delta\)t is the difference in arrival times at each reference point. To obtain a true \(\Delta\)t measurement, the transmitter and receiver must be synchronized. An implementation based on this technique with unsynchronized devices has been proposed [68], and it was able to calculate the position of the object with an increasing computational cost. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multirow{2}{*}{**Authors**} & \multirow{2}{*}{**UWB**} & \multirow{2}{*}{**BLE**} & \multicolumn{4}{c}{**Tracking Technology**} & \multirow{2}{*}{**Review**} & \multicolumn{2}{c}{**Manuscript Content**} \\  & & & & & & **Tracking** & & **Tracking** & & **System Architecture** \\ \hline [PERSON], [PERSON], 2016 [51] & \(\surd\) & & & & & & \(\surd\) & \\ \hline [PERSON], et al., 2017 [28] & \(\surd\) & & & \(\surd\) & & & \(\surd\) & \(\surd\) \\ \hline [PERSON], et al., 2019 [65] & \(\surd\) & & & & & & & \(\surd\) \\ \hline [PERSON], et al., 2017 [63] & \(\surd\) & & & & & & \(\surd\) & \\ \hline [PERSON], 2018 [32] & & & & & & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline [PERSON], et al., 2018 [69] & \(\surd\) & & & & & & & \(\surd\) \\ \hline [PERSON], et al., 2017 [31] & & & & & & \(\surd\) & & \(\surd\) \\ \hline [PERSON], et al, 2017 [52] & \(\surd\) & & & & & & \(\surd\) & \\ \hline [PERSON], et al., 2019 [36] & \(\surd\) & & & & & \(\surd\) & & \(\surd\) \\ \hline [PERSON], et al., 2015 [40] & & & \(\surd\) & & & & \(\surd\) & \\ \hline [PERSON], et al., 2019 [29] & & & & \(\surd\) & & & \(\surd\) \\ \hline [PERSON] et al., 2017 [30] & & \(\surd\) & \(\surd\) & & & & & \\ \hline [PERSON], et al., 2018 [34] & \(\surd\) & & & & & & \(\surd\) \\ \hline [PERSON], et al., 2015 [37] & \(\surd\) & & \(\surd\) & & & \(\surd\) & \\ \hline [PERSON], et al., 2018 [41] & & & \(\surd\) & & & \(\surd\) & \\ \hline [PERSON], et al., 2011 [38] & & & \(\surd\) & & & & \(\surd\) \\ \hline [PERSON], et al., 2019 [39] & & & \(\surd\) & & & & \\ \hline [PERSON], et al., 2016 [70] & \(\surd\) & & & & \(\surd\) & & \\ \hline [PERSON], et al., 2020 [71] & & & & & \(\surd\) & & \\ \hline [PERSON], et al., 2017 [72] & & & & & \(\surd\) & & \\ \hline Oesterreich T.D, Osnabrück F.T., 2016 [4] & & & & \(\surd\) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: RTLS technology categorization scheme. * _Time of arrival (ToA) or time of flight (ToF). Both methods estimate the position location of a tag by measuring the time that the signal needs to travel from the trans