# Study on Drone Handover Methods Suitable for Multipath Interference Due to Obstacles
## 5 Conclusions  
Relay transmission using drones as radio stations enables flexible network construction in air through handovers with ground stations. However, the presence of structures or obstacles in the flight path causes multipath interference, and the propagation environment fluctuates significantly during flight. In such a communication environment, it is difficult for a drone to select an optimal ground station for a handover. Additionally, unlike a terrestrial network, the propagation environment of a flying drone is affected by structures and other factors that cause multipath interference based on the flight speed and altitude, making the propagation environment conditions even more complex. To solve these problems, we proposed handover schemes between drones and the ground that consider multipath interference caused by obstacles. Proposed method #1 performs optimal handover considering interference by setting a SINR threshold when searching for surrounding APs, and we confirmed that the proposed method can achieve a maximum throughput of 20 Mbps or higher when the conventional method achieves a throughput of 5 Mbps or lower. Proposed method #2 avoids unnecessary handovers based on travel speed, and the average throughput is improved by a maximum of approximately 48%. The evaluation results demonstrate the effectiveness of the two proposed methods and the realization of a seamless handover. For the actual operation of the proposed method, in proposed method #1, the drone collects beacon signals of each traced radio pass while moving outdoors and performs handover according to the SINR threshold value. At the same time, using proposed method #2, the moving average is calculated by using statistics collected from SINR in environments where SINR tends to be frequently high locally, such as urban areas. Handover is performed to the AP with the highest SINR calculated from the moving average. The drone flight speed at which proposed method #2 is effective is 30-40 km/h, which is a medium speed. Conceptualization, T.H., T.M. and S.U. ; method, T.H., T.M., T.I. and J.H. ; validation, [PERSON] and T.H. ; investigation, K.H., T.K. and K.M. ; resources, K.H. ; data curation, K.H. ; writing--original draft preparation, K.H., T.H. and T.K. ; writing--review and editing, T.H., T.K. and K.M. ; visualization, K.H. ; supervision, T.M., T.I., [PERSON] and K.M. ; project administration, T.H. and S.U. ; funding acquisition, T.H., T.M., T.I. and J.H. All authors have read and agreed to the published version of the manuscript. This research was supported by SCOPE (JP215004001) of the Ministry of Internal Affairs and Communications. Data Availability Statement: Data are available from the authors upon request. The authors declare no conflicts of interest. Figure 22: Comparison results of proposed methods #1 and #2 at a flight speed of 40 km/h. * [PERSON] et al. (2010) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] A Pre-registered Handoff Scheme in IEEE 802.11r Wireless Local Area Networks. In Proceedings of the 2010 International Conference on Communications and Mobile Computing, Shenzhen, China, 12-14 April 2010; pp. 466-470. [CrossRef]
* IEEE _Std 802.11r-2008_ ; IEEE Standard for Information Technology--Local and Metropolitan Area Networks--Specific Requirements--Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 2: Fast Basic Service Set (BSS) Transition. Amendment to IEEE Std 802.11-2007 as amended by IEEE Std 802.11k-2008. IEEE: Piscataway, NJ, USA, 2008; pp.1-126. [[https://doi.org/10.1109/IEEESTD.2008.4573292](https://doi.org/10.1109/IEEESTD.2008.4573292)]([https://doi.org/10.1109/IEEESTD.2008.4573292](https://doi.org/10.1109/IEEESTD.2008.4573292)). * [PERSON] (2008) Clancy, T.C. Secure handover in enterprise WLANs: Capwap, hokey, and IEEE 802.11R. _IEEE Wirel. Commun._**2008**, _15_, 80-85. [CrossRef]
* [PERSON] et al.