# Study on Drone Handover Methods Suitable for Multipath Interference Due to Obstacles
## 2 Related Work  
### Introduction of Relay Technology by Drone  
In this study, we propose a handover method suitable for drones in flight. In wireless communication, a handover is a technique in which a moving radio station switches its destination and continues to communicate. The communication requires stabilizing the communication speed and achieving seamless switching. For example, a handover in IEEE802.11 standard [23] local area networks (LANs) is a method in which moving stations (STAs) switch connections from one access point (AP) to another and continue to communicate. Before performing a handover, STAs search for possible APs by scanning the surrounding APs for information such as the signal strength of the new AP. For example, STAs compare the APs to which they are currently connected and analyze whether the new AP can provide a stronger signal or whether communication speed can be improved. However, the functionality implemented in commercial devices generally searches for surrounding APs at the time of disconnection, and an optimal handover trigger selection method for seamless connections has not yet been established. When a suitable AP is found from the search results, an authorization process is performed between the STA and the new AP, and then an association is established. Communication with the previous AP is disconnected. In these handover procedures, the switchover should be seamless, and the STA should continue a certain amount of data communication with the new AP during the switchover. Finally, the new AP takes over the STA's communications and provides the same services as the previous AP. Two types of roaming methods are specified in the IEEE802.11r standard [24; 25; 26; 27] as roaming methods when handovers are performed. One is over-the-air fast transmission (FT) roaming, and the other is over-the-DS FT roaming. First, over-the-air FT roaming is explained using Figure 4. The STA requests roaming from AP1, to which it is connected (communicating with the access point). Subsequently, the STA sends an FT authentication request to AP2 and receives an FT authentication response from AP2. The controller connected to AP1 and AP2 sends the STA pre-certification information to AP2. Finally, when the STA moves to the BSS to which the new AP belongs, it sends an FT reconnection request to the STA and receives an FT reconnection response from AP2 to complete roaming. The operation of over-the-DS FT roaming is explained in Figure 5. First, the STA connects to AP1 and requests roaming to AP2. Subsequently, the STA sends an FT authentication request to AP1 and receives an FT authentication response from AP1. The controller connected to both AP1 and AP2 sends the STA pre-certification information to AP2. Finally, when the STA moves to the BSS to which the new AP belongs, it sends an FT reconnection request to the STA and receives an FT reconnection response from AP2 to complete roaming. These roaming methods solve the problem of the large overhead of the authentication procedure in handover: the over-the-DS FT performs authentication before switching the APs, and the over-the-DS FT can further reduce the number of authentication procedures in the wireless section by cooperating with the backbone network. The over-the-DS FT can further reduce the number of authentication steps in the wireless section by coordinating with the backbone network. In other words, this method can effectively reduce the authentication procedure time by deploying a controller. However, the methods for the STA to switch AP connections and select APs to connect to are not specified, and the effect of physical disconnection on seamless handover has not been considered. In this study, we discuss how to select the optimal AP to connect to by minimizing the time spent on the handover of the switching decision mechanism and the protocol procedures involved in actual switching.