## 4 Discussion  
This section covers all five experimental topics presented in the Results section. The first topic is the timing of the WSA traffic, shown by measuring the WSA current profile. Practically very important is the second topic with the measurement of the optimal position of the master device on the backpack and the third topic with measurements of the quality of the data transmission in a real scenario. The fourth was to check the data transmission in the presence of other microwave signals. At the end, measurements of the raw data signals from the IMU sensors are presented. The oscilloscope traces in Figure 5 show the sum of the battery supply current from five remote IMU units. In the top plot, the first 3.5 s represent the \"power-saving mode\" labelled (1), where the current is zero, as expected. Just before 4 s and almost up to 5 s in this graph, the \"wake-up\" phase occurs (2). This phase transitions to the \"listening mode,\" labelled (3) in the bottom graph of Figure 5. The receivers in all the DWM modules consume a larger portion of the constant current, and the traffic between the master and each IMU unit increases the circuit activity and the current consumption. This phase of listening for remote commands ends with a current glitch at the beginning of each synchronization interval (4). The synchronization interval begins with the synchronization packet sent by the master and received by each IMU unit. When the activity of IMU unit stops, the currents drop down to the response slots assigned to each IMU unit. The bottom graph has 5 ms/div, while the IMU unit respond synchronously every 1 ms. These five IMU responses are evident as the sample frame window (5). After completion of, in this case, three sample frames, the new synchronization packets are sent from the master unit to synchronize all the IMU units on a common time scale. The 240-mAh LiPo battery in the IMU unit can support this kind of full activity, including data transmission, for more than 6 h. In power-saving mode with RX sniffing, the battery will last for several days. Of course, the battery is fully conserved when the hardware on/off switch is used in the case of saving. The presented current supply profiles accurately confirm the scheduled activities on the master and IMU side, synchronization and data exchange, and appropriate timing, including various interruptions, sleep phases, and the chip function. Figure 6 and Table 1 in the Results section explain how the less error prone position of the master device on the backpack was determined. The IMU remote devices communicate with the master device via radio waves, either in direct or reflected mode. Even without the human body, the propagation models for WBAN have dominant factors that can affect the UWB channel [36]. Moreover, the coupling between the wearable antenna and the human body is dominant and degrades the performance of the antenna due to the presence of the body [37]. Second, the propagation channel in WBAN is affected by the continuous movement of the human body, which is due to the time-varying scattering of electromagnetic waves. To avoid any interruption of communication and loss of data samples, it is important to position the master device appropriately with respect to the position of the IMU unit. The optimal number of IMU units implemented, the appropriate positioning points, and the IMU positioning combinations on the human body for activity detection were extensively studied before [38]. Using the master unit in the less error prone position is crucial for the proper operation of the whole WSA set. The results in Table 1 shows the measured values for packet loss. The observation of data loss is one of the possible indicators; another possible parameter is S/N (signal to noise ratio). The highest packet loss was observed at master position 1, near the pelvis at the bottom of the backpack. Similarly, position (8) without the backpack is closer to the human body.