# Secure Utilization of Beacons and UAVs in Emergency Response Systems for Building Fire Hazard
## 6 Discussion  
### Position Accuracy  
The distance measurement using the beacon is based on the received Bluetooth signal strength. However, if signal interference due to surrounding obstacles occurs, the measured distance data may be inaccurate. Therefore, the proximity value of a beacon calculated using the Friis model formula has generally low accuracy such as 68%, due to frequent signal interference [24; 36]. To improve the accuracy, [PERSON] et al. [37] used the average value after storing the distance calculation results for 30 s. However, the method of taking the average value shows higher accuracy only when the experiment is performed by constructing the optimal environment without signal interference. If a large distance error is transmitted due to Bluetooth signal interference, the large error value, i.e., the outlier, affects the average value. In order to reduce the effect of outliers and improve the position accuracy measured by the beacon, we propose to apply the median of the proximity value \(r\) for a certain period of time to measure the occupant's precise location. In order to evaluate the accuracy of our system's proximity data, we performed the experiment using raw values, the average of all values and median values in a variety of emergency scenarios. For our experiments, it is assumed that the building is fully outfitted \begin{table}
\begin{tabular}{c|c c c c c|c c c c c} \hline \hline  & \multicolumn{4}{c|}{**Text**} & \multicolumn{4}{c}{**Image**} \\ \hline Message Size (Byte) & 32 & 128 & 512 & 2048 & 10,240 & 473 & 824 & 2453 & 8530 & 10,703 \\ Encryption (ms) & 0.6 & 1.1 & 5 & 40 & 180 & 15 & 36.5 & 106 & 220.5 & 306 \\ Decryption (ms) & 0.6 & 0.9 & 5 & 40 & 180 & 15 & 36.5 & 106 & 220.5 & 306 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Computation time on UAVs. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c|}{**Text**} & \multicolumn{4}{c}{**Image**} \\ \hline Message Size (Byte) & 16 & 32 & 64 & 128 & 256 & 512 & 1024 & 2048 & 4096 & 10,240 \\ Encryption (ms) & 0.31 & 0.5 & 0.7 & 0.86 & 1.79 & 4.1 & 13.4 & 36 & 71 & 164 \\ Decryption (ms) & 0.31 & 0.49 & 0.69 & 0.86 & 1.77 & 4 & 13.3 & 36 & 70 & 164 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Computation time on a smart sensor. with smart sensors and that each building occupant carries a beacon-embedded smart ID card that is used to locate the occupant during an emergency. Figure 11 shows four experimental conditions. We attached smart sensors to the front of the door in each room, and the installation radius between sensors was 3-5 m. Each experiment participant carried a beacon and was instructed to walk in a radius of 3 m, 4 m then 5 m away from a smart sensor. Figure 11a-c indicates that a user with a beacon is moving or standing at a distance of 3 m, 4 m and 5 m from the smart sensor, respectively. Figure 11d shows the experimental environment in which the participants were allowed to either remain in one location or to freely change their location while remaining within the 3-5 m radius from the smart sensor. Figure 12 shows the results of our position accuracy calculations. To evaluate position accuracy, we used the following three methods: the raw method [24], the average method [37] and the median method. The raw method accepts the proximity value calculated as the distance of the beacon from a single smart sensor. The average method and the median method both refer to methods in which the average or median of multiple proximities is obtained by calculating the location of the beacon over a set period of time. In order to evaluate the accuracy of these methods, we tested different periods of time for collecting the proximity data. These set periods of proximity data collection were set to 1 s, 5 s, 10 s, 15 s, 20 s and 30 s.  
One challenge to calculating precise locations with beacons is that smart sensors are affected by where a user holds the beacon, i.e., on the upper or lower body.