# Analyzing the Performance of WBAN Links during Physical Activity Using Real Multi-Band Sensor Nodes
## 2 Materials and Methods
### Scenarios
#### 2.2.2 Dynamic Scenarios  
Two dynamic scenarios have been characterized in this work: cycling and walking. For the cycling experiment, a stationary bicycle has been used in order to provide a more controlled and safe experiment, where a constant speed can be maintained. This is a good representation of the real activity since the distances between nodes and body movements are equivalent. In this scenario, the subject has the receiver node on her left hip and the sender node on her right ankle as can be seen in Figure 3. As the subject pedals, the percentage of free space and body tissue on the signal path changes, as well as the straight distance between both nodes, which varies from a minimum of 72 to a maximum of 97 cm. Since it is the result of the pedal turn, this distance variation has a periodic pattern can be exploited by algorithms and strategies to adapt the transmit power or schedule the sending of packets [14,15]. Figure 2: Standing scenario, with the receiver node on the left hip and sender nodes on the right wrist (**a**) and right ankle (**b**). Sitting scenario, with the receiver node on the left hip and sender nodes on the right wrist (**c**) and right ankle (**d**). In this scenario, the wrist node position was not measured since the subject's hand remains motionless in the handlebar for the whole exercise. Thus, it maintains a constant distance with the hip node and does not take part in the body movements being tested. The subject pedals with a constant cadence of 62 \(\pm\) 2 rpm, roughly equivalent to 23 km/h, for the whole duration of the experiment. Analogously to the static scenarios, the sender node iterates through all the transmit power levels of the three frequency bands referred in (1) and (2). While the subject cycles, the sender node sends 1000 packets to the receiver for each level, at a rate of 50 packets/s, so each power level is measured for 20 s. Thus, the complete experiment for this scenario takes 1220 s, corresponding to 22 \(\times\) 20 = 440 s for each of the two sub-1 GHz frequencies and 17 \(\times\) 20 = 340 s for the 2.4 GHz band. The receiver node registers the RSSI level of each packet and calculates the PRR for each power level and frequency. For the walking scenario, all experiments were performed outdoors. Given that the walking speed and gait cycle are very dependent on the subject, three people were asked to participate in the experiments. They were asked to walk at their usual walking speed on a flat path while wearing the test nodes in the same configuration of the static scenarios: a receiver node on their left hip and sender nodes on their right wrist and right ankle. With the regular body movements of the gait cycle, nodes change from being in LOS to NLOS, as the signal path is obstructed by parts of the subject's body [5,15]. Figure 4 shows the three test subjects at different points in the experiment. Figure 4: Subjects of the walking scenario at various points in the experiment: (**a**) Subject A, (**b**) Subject B and (**c**) Subject C.  
Figure 3: Node positions in the cycling scenario: (**a**) point of minimum distance, (**b**) point of maximum distance. Since the subjects' physical characteristics--height, age, etc.--have a strong influence on their gait cycle and consequently on the distances between nodes, some length measurements were taken prior to starting the measurements. Specifically, the height at which each of the three nodes was placed with respect to the ground was noted for the three subjects. After finishing the experiments, the average walking speed and cadence were also calculated for each of the subjects. All these data can be seen in Table 2.  
The measurements in the walking scenario followed the same procedure as the previous ones. While the subject walks, the sender nodes (on each of the wrist and ankle locations) send 1000 packets to the receiver on the hip at a rate of 50 packets/s, for each of the possible transmit power levels of each of the frequency bands.