## 3 Results of the Experimental Validation
### Assessment of WSA Current Profile  
The WSA system is composed of one master unit, plus one to seven remotely placed IMU devices. In our case two of these IMU units are slightly different in a way that the insole signals are also being sampled and forwarded as a data payload via the UWB to the master unit. The master unit, as well as each IMU unit receive a supply voltage from independent LiPo batteries. To obtain very long discharge times for the batteries, the chips on the IMU unit are only supplied with the voltage for the minimum possible times and shut off for long periods in between. Three of the chips are the most energy demanding: the DWM radio module, the 9D sensory chip and the microprocessor itself. As described above in the description of the firmware, as well as more in detail in a sequence, five operational modes are interchanged in operation: power-save mode, waking-up phase, listening for remote instructions, synchronization interval and 10 ms of sampling frame.  
These modes can be represented in a transparent way by measuring and verifying the current consumption of the IMU units versus time. In general, the Hall principle current probe allows for the non-contact measurement of supply currents. For the graphs shown in Figure 5, all five supply lines from five independent IMU batteries are bundled and passed through the Hall probe and then to each IMU unit. This gives a reading that is the sum of all five IMU supply currents. Independent supply currents can be estimated in this way when all the other currents are absent or constant at a given time. This measurement was made using the AM503A current-probe amplifier and the A6302 current probe from Textronix. The output of the probe amplifier is calibrated to 50 mA/div when the scale of the oscilloscope is set to 10 mV/div. To display the current of five devices simultaneously, the scale of the four-channel Keysight MSO-X 3014a oscilloscope was set to 50 mV/div (i.e., 250 mA/div). The top curve, starting on the left, first shows the current level, which is zero, even if it does not perfectly match one of the horizontal lines. Figure 5 shows two oscilloscope traces: the top one at a horizontal time division of 1 s/div, and the second one at a horizontal time division of 5 ms/div. Thus, the first trace shows a rough time scale, while the second one provides a precise insight into the timing.  
The oscilloscope traces in Figure 5 show the sum of the battery current for five remote-control devices from the energy-saving mode (1) and the wake-up phase (2), both in the upper trace, after which the radio receiver is switched on and the steady-state current consumption is the highest. From the \"wake-up\" phase, the devices enter the \"listening\" mode (3), where the devices wait for remote-control instructions via the UWB. The next phase (4) comprises a 30-ms synchronization cycle ending with the reception of a synchronization packet from the master device. After receiving the synchronization timestamp, all the remote devices turn off the radio receivers, resulting in a decrease in the power consumption. Between the 30-ms synchronization cycles, the remote devices transmit the sensor data, the power consumption is lower (operation mode 5). The IMU data transmission, which occurs every 10 ms, can be observed as five current spikes in operation mode 5.  
The lower current trace gives an insight into the timing, in such a way that there is enough extra time in the 10-ms data sample frame (5) for a sixth, seventh or even more devices. Moreover, it is obvious that the 10-ms interval could be even shorter, without incurring any data-transmission costs. In this way the transmission rate can easily be increased beyond the presented example of 100-Hz sampling.