# Study on Drone Handover Methods Suitable for Multipath Interference Due to Obstacles
## 4 Proposal Method According to the Issue
### Overview of Proposed Method #1  
As described in Section 2.2, the conventional handover method cannot perform a handover to a base station with good conditions unless a beacon failure occurs, even in an environment where SINR is low and communication conditions are poor, and the connection to a base station with a low transmission speed continues. Method #1 proposes a connection destination selection method that operates based not only on the availability of beacon reception but also on handover timing and the MCS index with SINR as a threshold  
\begin{table}
\begin{tabular}{c c} \hline \hline  & **Conv. Method** \\ \hline Comm. method & IEEE802.11g standard \\ \hline Frequency band & 2.4 GHz \\ \hline Transmission power & 0.2 mW \\ \hline Flight speed & 5 km/h \\ \hline STA and AP height & 5 m above ground \\ \hline Hand over method & Beacon reception failure counts \\ \hline \hline \end{tabular}
\end{table}
Table 1: Evaluation parameters.  
Figure 13: Evaluation results of conventional methods.  
for optimal connection destination switching. Using the SINR as the threshold value, even if a connection to a base station with a low SINR continues without beacon reception failure, as shown in Figure 13 in the conventional method, a handover decision can be made, and the AP can proactively connect to an AP with better conditions.  
Figure 14 shows the handover procedure for proposed method #1. As a specific procedure in the proposed method, the STA first sets the SINR threshold before the system is operated. At the beginning of the system operation, the STA sets the SINR threshold for a certain period after receiving a beacon. If the SINR threshold is exceeded, the STA recognizes that it is in the communication area under the AP and maintains the connection. When the SINR of the AP to which the drone is connected drops below the threshold value due to the drone's movement, the system decides to perform a handover and determines the MCS index of each AP based on the beacon searched for in advance. The AP to be connected next is then determined.  
The algorithm for AP selection is as follows:  
**if (MCS index \(\geq\) 1, AP exists)**:  
Handover to the AP with the best SINR among the applicable APs.
**else if (MCS index \(\geq\) 1, AP does not exist)**:  
Handover to the AP with the best SINR among the APs with the same MCS index as the current one.  
SINR threshold compares the SINR value calculated from the beacon to the value set for the AP-switching threshold. In this study, SINR was set to 6 dB to guarantee the minimum transmission rate. Using this method, a handover to a base station with better conditions is performed even when the received power of the beacon signal is low.  
The flowchart of proposed method #1 is shown in Figure 15. In proposed method #1, SINR is calculated when a beacon is received and the data table of SINR is updated. It then compares the SINR threshold value with the calculated SINR value, and it disconnects from the AP if the SINR value falls below the threshold.  
Figure 14: Handover sequence of proposed method #1.