# Analyzing the Performance of WBAN Links during Physical Activity Using Real Multi-Band Sensor Nodes
## 3 Results  
### Standing Scenario  
The results obtained from the measurements of the standing scenario can be seen in the following figures. Figure 5 shows the average RSSI of the received packets at the hip node from sender nodes on both locations--right wrist (LH-RW) and right ankle (LH-RA)--for all the transmit power levels of all the frequency bands. It is important to remember from (1) and (2) that while all three frequency bands have a transmit power range that starts on the \(-30\) dBm level, the 433 and 868 MHz transceivers have a maximum transmit power of 11 dBm but the maximum transmit power of the 2.4 GHz band is only 1 dBm. When some transmit power levels are not represented for a particular configuration, e.g., the values below \(-14\) dBm for the 868 MHz ankle position, it means that no packets were received for that particular level. This is also reflected in the corresponding PRR value in the following graph. The graph shows that the RSSI value is roughly inversely proportional to the frequency band, as expected from path loss equations. Additionally, for both sub-1 GHz bands, the ankle location results in a lower RSSI than the wrist location. The reason for this is a longer distance between both nodes. However, the opposite occurs for the 2.4 GHz frequency, where the ankle location gives a better performance in terms of RSSI than the wrist location. This is probably due to the fact that the signal path between the subject's hip and wrist is mostly obstructed by body tissue, whereas the hip-ankle link has a much higher proportion of free space and both nodes are partially in LOS. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Subject A** & **Subject B** & **Subject C** \\ Physical characteristics & Female, 33, 166 cm & Female, 56, 160 cm & Male, 42, 189 cm \\ Average speed & 5.9 km/h & 5.8 km/h & 6.5 km/h \\ Walking cadence 1  & 59 \(\pm\) 2 steps/min & 61 \(\pm\) 2 steps/min & 58 \(\pm\) 2 steps/min \\ Distance LH-ground & 92 cm & 100 cm & 107 cm \\ Distance RW-ground & 83 cm & 87 cm & 97 cm \\ Distance RA-ground & 15 cm & 19 cm & 18 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics and parameters of the three subjects in the walking experiment. In turn, Figure 6 shows the PRR calculated for each of the transmit power levels of each frequency transceiver. It can be seen that for the 433 MHz band, the PRR is very close to 100% for almost all power levels. On the other hand, for the 868 MHz band, the curves are much more similar to the ones that could be expected theoretically, where PRR increases along with the increase in transmit power--and consequently RSSI--until it saturates near the 100% level, when the RSSI sufficiently surpasses the sensitivity level of the receiver. This is also in agreement with other empirical studies in the field [11,13]. In concordance with the measured RSSI from the previous figure, for the 868 MHz band, the ankle location results in a much worse performance than the wrist. For the first nine power values no packet arrives at the receiver with a sufficient RSSI value to surpass its sensitivity, so the PRR is 0%. Additionally, in agreement with the recorded RSSI values, the 2.4 GHz band has a better performance in terms of PRR for the ankle location than that of the wrist location. It is interesting to note that while the 2.4 GHz PRR curves have the expected increasing tendency until saturating near the 100% level, they have some depressions at some power values. Since the measurements were taken sequentially in order of increasing power level  
Figure 5: Average receiver signal strength indicator (RSSI) in the standing scenario. Figure 6: Packet reception rate (PRR) in the standing scenario. and the curve depressions involve contiguous power values, a temporal component for this phenomenon can be inferred.