## 3 Results of the Experimental Validation
### Quality of the Data Transfer in a Real-Case Scenario  
After the IMU units have been placed at the desired points on the body and the position of the master unit with best performances has been ensured, the data transmission error rate can still depend on several factors. Some are inherent in the internal settings of the DWM modules, and may be intentionally selected (or adjusted) by the system's designer, such as the channel used, preamble length, data-transmission rate, pulse-repetition frequency, data rate, and packet duration. Based on these factors, the achievable communication range can be between a few m and 200 m, and the packet loss also varies. In addition, external environmental conditions that are not under the user's control affect the achievable range as well as the packet loss. These external factors cannot be intentionally controlled. The ideal stable conditions could be in a laboratory environment where all the IMU unit and the main unit are not moving. The second testing case involves running on a treadmill in the same room. In this case the human moves the limbs having the connected IMU unit. Such movements could shadow or block the RF paths between the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Master** \\ **Position** \\ **Number** \\ \end{tabular} } & \multicolumn{5}{c}{**Packet Loss [\%] (n = 90,000 Samples, Duration = 900 s)**} \\ \cline{2-7}  & **Pelvis** & \begin{tabular}{c} **Right** \\ **Thigh** \\ **IMU** \\ \end{tabular} & \begin{tabular}{c} **Left** \\ **Thigh** \\ **IMU** \\ \end{tabular} & \begin{tabular}{c} **Left** \\ **Shank** \\ **IMU** \\ \end{tabular} & \
\begin{tabular}{c} **Right** \\ **Shank** \\ **IMU** \\ \end{tabular} &
\begin{tabular}{c} **Comments** \\ **TMO** \\ \end{tabular} \\ \hline
**1** & 0.0217 & 0.4917 & 0.3367 & 4.8067 & 1.9867 & public hall walk \\ \hline
**2** & 0.2033 & 0.0100 & 0.0100 & 0.0467 & 0.0217 & public hall walk \\ \hline
**3** & 0.1083 & 0.0150 & 0.0117 & 0.0100 & 0.0133 & public hall walk \\ \hline
**4** & 0.1500 & 0.0067 & 0.0083 & 0.0117 & 0.0117 & public hall walk \\ \hline
**5** & 0.0583 & 0.0117 & 0.0150 & 0.0150 & 0.0117 & public hall walk \\ \hline
**6** & 0.0217 & 0.0050 & 0.0017 & 0.0133 & 0.0117 & public hall walk \\ \hline
**6** & 0.0183 & 0.0033 & 0.0117 & 0.0050 & 0.0050 & treadmill walk \\ \hline
**7** & 0.0250 & 0.0177 & 0.0150 & 0.0150 & 0.0100 & 1.5 m behind subject, no backpack \\ \hline
**8** & 0.0133 & 0.0267 & 0.0483 & 1.8083 & 0.0917 &
\begin{tabular}{c} treadmill, \\ **back, no backpack** \\ \end{tabular} \\ \hline
**Lab test** & 0.0050 & 0.0000 & 0.0017 & 0.0017 & 0.0050 &
\begin{tabular}{c} desktop control test, \\ distance = 1.5 m \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Left: (1–6) six points on the backpack where the master unit was placed, 7 and 8 are for the cases without the backpack. Right: table showing percentage packet loss for IMUs placed at the pelvis, right/left thigh, and right/left shank. IMU units and the master unit, which can also affect the communication range as well as the packet loss. The third example, the environment of a public hall, brings new challenges due to the presence of other people moving around and the walls and architectural columns in the room. The fourth test environment was the example of a public street. In this scenario, a larger open space is added on one side, and moving metal objects in the form of bicycles and cars with different speeds on the other. The last case involves a number of Wi-Fi, Bluetooth and other protocols occupying and interfering with the same radio spectrum. The packet-loss results for all four environmental conditions are shown in Table 2. The subject in this case was also equipped with a complete set of WSA consisting of five IMU units attached to the subject's right/left hip, right/left thigh, and pelvis, as shown above in Figure 6. Each of the four sessions lasted 15 min, and the sampling rate was 100 Hz for each IMU and each variable.