# Analyzing the Performance of WBAN Links during Physical Activity Using Real Multi-Band Sensor Nodes
## 3 Results
### Walking Scenario  
The average RSSI for each of the transmit power levels of each frequency band and subject are presented in Figures 12 and 13 for the wrist and ankle location, respectively. Figure 11: RSSI variation with time in the cycling scenario for 0 dBm of transmit power: (**top**) 433 MHz, (**middle**) 868 MHz, (**bottom**) 2.4 GHz. Figure 10: RSSI variation with time in the cycling scenario for the 433 MHz band for three different transmit power levels. Figure 12: Average RSSI in the walking scenario for all subjects and frequencies: sender node located on the right wrist. Figure 13: Average RSSI in the walking scenario for all subjects and frequencies: sender node located on the right ankle. These curves show the expected increasing tendency for all subjects with respect to the transmit power level and the inversely proportional relation between the RSSI and frequency. There are significant differences in performance among the different subjects, although in no case do these variations surpass the effect of the frequency band; i.e., in all cases the three lines corresponding to each frequency for the three subjects are grouped together without crossing any of the other frequency curves. Comparing the wrist and ankle location, a higher variation among the subjects is observed for the latter. This is probably due to the fact that the distance between the subjects' ankle and hip is more dependent on the subjects' height than in the case of the wrist. This is also supported by the fact that Subject C--the tallest of the three--generally obtains a worse RSSI performance than that of the other two subjects, due to a longer distance between his node locations. As in the cycling scenario, the RSSI variation with time clearly reflects the periodicity of the walking motion. Each iteration of the gait cycle, or stride, produces a distinctive peak shape with a maximum and minimum value that is periodically repeated at a rate equal to the subject's walking cadence. Figure 14 shows the distinctive periodic shape of the RSSI metric for the three subjects on the 433 MHz band, with the sender node on the subjects' wrist, and with a transmit power of \(-2\) dBm. It is clear that the different walking patterns--especially the arm swing--of the three people produce a distinct periodic peak shape in the RSSI curve. For instance, it can be inferred that Subject A swings her arm farther back than the other two, given that the nodes spend more time in NLOS, as reflected in the wider portion of the bottom part of her periodic shape. Oppositely, subjects B and C present periodic shapes, the minima of which are quasi-instant in time. Figure 14: RSSI variation with time in the walking scenario for the three subjects on the 433 MHz band for \(-2\) dBm of transmit power and with the sender node located on the right wrist: (**top**) Subject A, (**middle**) Subject B, (**bottom**) Subject C.  
The walking speed and cadence of the three subjects is also reflected in the graphs, with Subject B having the highest cadence in steps/min as noted in Table 2. The width of the periodic peak shapes also explains the relationship between the walking speed and cadence; e.g., Subject C walks faster with a lower cadence due to his longer stride, resulting in a wider shape. Figure 15 shows the RSSI variation with time for the three subjects on the 868 band, and with a transmit power level of \(-2\) dBm, but with the sender node located on the right ankle. Comparing the RSSI periodic pattern for the wrist and ankle locations, the gait cycle can be better inferred from the former, which provides a clearer shape and an easier to extract periodicity. The same can be observed from other measurements in the dataset for other frequencies and transmit power values. Thus, strategies and algorithms that exploit the periodicity of the walking motion would benefit from being applied on wrist node positions, as has been suggested by other studies in the field [14]. The transmit power level of the sender node has an effect on the shape of the RSSI periodic peaks.