## 4 Robustness Testing
### Environmental Conditions Test  
The environmental conditions test was conducted in the summer of 2018. All experiments were performed on cloudy dates without direct sunshine or conducted at locations with cover; the recorded air temperatures ranged from 27 \({}^{\circ}\)C to 32 \({}^{\circ}\)C. The signals were tested under the following conditions: (a) high-temperature environment (i.e., air temperature of 32 \({}^{\circ}\)C and iBeacon surface temperature of 45 \({}^{\circ}\)C recorded by thermometer); (b) strong wind, with speeds of 5.7 m/s recorded by nearby weather station; (c) obstruction of trees (Figure 2b); (d) high vehicle traffic (Figure 2c); (e) pedestrian traffic (Figure 2d); (f) pedestrian traffic blocking the line of sight between the iBeacon and mobile devices; and (g) control environment. In experiments (a), (b), (e), (f) and (g), two iBeacons were installed on a camera tripod at 1.5 m height, and the iBeacons were stuck on tree trunks and fences with plastic  
Figure 3: Analysis of maximum coverage test on (a) signal packet loss rate, (b) received received signal strength indicator (RSSI) and (c) standard deviation of RSSI. tape at 1.5 m height for experiments (c) and (d), respectively. As with the signal coverage test, the two mobile devices were fixed on camera tripods during the data collection. To ensure the stability of iBeacon signals, the tests started after the iBeacons were deployed for at least two hours under each environmental condition. For experimental conditions (a)-(e), the signals were measured from distances 1 m to 20 m at 1 m intervals for 1 minute. For experimental condition (f), the signals were measured from distances 2 m to 20 m with same interval and duration as (a)-(e). The signal data collected were compared with the control data collected in a typical outdoor environment with fewer environmental factors, as shown in Figure 2e (i.e., air temperature at 28 \({}^{\circ}\)C and iBeacons installed under the shadow of a tree crown with an internal temperature of 34 \({}^{\circ}\)C, wind speed of 3.3 m/s recorded by nearby weather station and no pedestrian and vehicle in the experimental environment). Figure 4 and Table 1 show the results of the environmental conditions test using two iBeacons where Figure 4 presents the (a) packet loss rate, (b) received RSSI and (c) standard deviation of RSSI; and Table 1 compares the overall packet loss rate, average and standard deviation of RSSI of 0.5 m to 20 m measurements. Comparisons were made with the control set data, although fluctuations of the RSSI and signal stability existed under normal conditions. Figure 4a indicates that the packet loss rate differed significantly between the control and some testing environments, including high temperature, pedestrian traffic near the iBeacons and mobile devices, and pedestrian traffic blocking the line of sight between iBeacons and the devices. Table 1 also suggests the obstruction by pedestrians and high temperature resulted in a relatively higher packet loss rate, while the effects of other factors were limited. Figure 4: Analysis of environmental conditions test on (**a**) signal packet loss rate, (**b**) received RSSI and (**c**) standard deviation of RSSI. By comparing the RSSI between the environmental conditions in Figure 4b and Table 1, the high temperature, strong wind and blocking of pedestrians lowered the signal strength when compared with the control set. The standard deviation of the RSSI also indicates the adverse effects at the high temperature and the blocking of the signal by pedestrians. Table 1 highlights that the signal stability was more severely affected if pedestrians were blocking the line of sight between the mobile device and the iBeacon in comparison to when the line of sight was not blocked. Our findings showed that signal fluctuation was present in the control data, which were collected from ideal outdoor settings, regardless of environmental conditions.