**2. Related Work**

Since UAV networking is an intensive technology that requires a variegated research domain, various research is being actively conducted in several ways. In this paper, recent research focusing on the various topics on UAV formation, energy-efficiency design, and the transmission power control is introduced in detail.

• **UAV formation**: The construction of an appropriate formation with many UAVs is progressing in various aspects. In fact, UAV positioning algorithms have been studied in consideration of network throughput [13], obstacle collision avoidance [14], and mission conditions [15]. Sabino et al. [16] proposed the multi-UAV placement scheme through the genetic algorithm. It should be noted that UAV formation control algorithms can be joined with our proposed system, since our system aims to improve the network topology of UAVs, which have the potential to frequently change their shape in three-dimensional space. With our dynamic topology control scheme, the UAV network can sustain an energy-efficient network while changing each UAV's position according to their mission.


In summary, there has been research considering the energy consumption of the wireless UAV network. However, due to the lack of the cooperability and the compatibility with the other OSI layers, the UAV network is not fully beneficial when previous strategies are applied. In addition, some attempts at controlling the mobility of the UAV for networking energy efficiency might not be helpful when operating the UAVs in a practical scenario, since each UAV's position decision will suffer from the confliction between the power efficiency and the mission performance. Our design adopts the distributed and reactive method, where each UAV collects neighbors' locations and determines their available links and the transmission power for energy-efficient networking.
