# Study on Drone Handover Methods Suitable for Multipath Interference Due to Obstacles
## 4 Proposal Method According to the Issue
### Evaluation Method and Results of Proposed Method #2  
Proposed method #2 selects the best AP for handover based on the moving average of SINR. However, when the drone's flight speed is high, proposed method #2 is unnecessary in some cases because the drone is connected to the next AP before finding the AP with a locally high SINR. Therefore, to confirm the effect of the proposed method on the speed of flight of the STA, we compared the average throughput when using proposed methods #1 and #2 on the map shown in Figure 17. The flight speed of the STA was varied from 20 to 50 km/h in increments of 10 km/h. The STA continues to upload the UDP data while performing a handover via the green point in Figure 17. The simulation parameters are listed in Table 2. To monitor the behavior of handover to APs with locally higher SINR, the evaluation method was based on the average throughput extracted from the portion of Figure 20 where the drone passes in the vicinity of AP2. The results of the average throughput for flight speeds comparing proposed methods #1 and #2 are shown in Figure 21. Proposed method #2 had a higher average throughput than proposed method #1 at flight speeds of 30 and 40 km/h. In particular, at a flight speed of 40 km/h, the proposed method #2 has a higher average throughput than proposed method #1. In particular, at a flight speed of 40 km/h, the average throughput of proposed method #2 was approximately 48% higher than that of proposed method #1. On the other hand, at a slower flight speed of 20 km/h, both proposed methods #1 and #2 handover to AP2 and stay connected to AP2 for a long time; therefore, proposed method #2 is ineffective. In addition, when the flight speed is 50 km/h, both proposed methods #1 and #2 pass through AP2 at high speed, and no  
Figure 19: Flowchart of proposed method #2.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Point** & **AP1** & **AP2** & **AP3** \\ \hline A & 28 & 0 & 0 \\ \hline B & 15 & 3 & 14 \\ \hline
**C** & 3 & **30** & 28 \\ \hline
**C (Ave.)** & 9 & 16.5 & **21** \\ \hline D & 0 & 3 & 30 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Example of moving average [dB] of acquired SINR in flight movement.  
handover is performed; therefore, proposed method #2 is also not effective. These results confirm that proposed method #2 is effective at flight speeds between 30 and 40 km/h.  
For a detailed evaluation of proposed method #2, we compared its throughput with that of proposed method #1 using the map in Figure 17. Figure 22 shows the throughput characteristics at a flight speed of 40 km/h; the best result is shown in Figure 21. When using proposed method #1, the STA is initially connected to AP1, and, as it moves, the SINR of AP1 decreases. When it moves closer to AP2, it establishes a connection with AP2, which has a higher SINR. However, after connecting to AP2, the SINR threshold of AP2 is immediately lowered and the connection is immediately converted to AP3. When an AP with a locally high SINR exists, the handover is repeated multiple times each time, resulting in a decrease in throughput. On the other hand, proposed method #2, searches for the next AP when the SINR of AP1 becomes lower than the threshold value. When moving near AP2, even though SINR increases rapidly, SINR is estimated to be low when calculating the moving average because of the low SINR of AP2 in the past. Therefore, AP2 was removed from the candidate handover destinations, and AP3 was selected as the next connection destination. By reducing the number of handover attempts in this manner, the throughput degradation was also reduced, and it was confirmed that the throughput was maintained on average.  
Figure 21: Average throughput of proposed methods #1 and #2 with respect to flight speed.  
Figure 20: Maps for evaluation of proposed method #2.