# An Experimental Tethered UAV-Based Communication System with Continuous Power Supply
## 1 Introduction  
Unmanned aerial vehicles (UAVs), also known as drones, have emerged as an innovative technology in multiple branches of engineering, including aeronautics, robotics, mechanical engineering, and electrical engineering, because they can perform various tasks independently. UAVs are used in numerous applications, such as agriculture, where they are used for sowing monitoring, insecticide spraying, and seed planting [1, 2]. They are also used in delivery services by companies such as Walmart, DHL, Google, and Amazon [3, 4] and in the inspection of power lines. Likewise, UAVs are already crucial in deploying 5G and the future 6G networks, fulfilling the functions of base stations and mobile relay systems. On the other hand, studies are being conducted on possible options for establishingwireless links with UAVs. Some alternatives include satellites, radio waves, free space optics, and in-band radio communication. In wireless communications, UAVs can facilitate fast response operations on demand. Additionally, they require adaptability and reconfiguration in response to the UAV's mobility, which is controlled according to the operator's needs. There are several fields in which UAVs can be applied in communications, such as cellular communications, to assist the existing terrestrial communication infrastructure. In this sense, UAVs can behave as base stations (BSs). They are intermediate nodes that receive a signal with information from a source node and retransmit it to a destination node. Their primary function is to extend communication over long distances, equipment, or access points. Another field of application for UAVs is rapid deployment to provide coverage or improve existing coverage in areas affected by natural disasters or where traffic is heavy due to mass events. The retransmission of communication signals is another field of application, using a UAV to establish a communication link between two or more users in an area. Last but not least, UAV systems are also used for information transmission and data collection, applications that are common in the Internet of Things (IoT) [5; 6]. The major challenge of the UAVs comes from the limitation of onboard power. These devices require significant power to operate; for example, a small commercial UAV typically requires 20 to 200 watts per kilogram of weight to stay aloft [7]. Even most commercial UAVs with lithium batteries can operate for approximately 20 to 40 min [8]. The energy consumed by the UAV depends on some factors, detailed as follows. * Larger UAVs require higher thrust to stay in flight, which demands more powerful engines and, consequently, higher power consumption. In addition to the weight of the UAV, the weight of the payload must be considered, which increases the thrust required. Additionally, the payload usually consumes energy directly from the UAV battery when connected to the UAV. Thus, both the total weight and the payload consumption increase the energy consumption of the UAV [9]. * The way the UAV is constructed reduces or increases drag when it flies, so it is recommended to use lightweight and aerodynamic materials to minimize energy consumption. UAVs with aerodynamic and symmetrical designs experience less air resistance, which results in faster and more efficient flight. This highlights the importance of aerodynamic considerations in UAV design [9]. * Weather conditions affect the flight stability and battery life of UAVs. One such condition is wind; as the wind increases, it destabilizes the flight, increasing drag and causing the propellers to consume more battery power. Another is extreme temperatures. In hot climates, the propellers draw more power from the battery, which can lead to overheating. In cold climates, the chemical activity in the batteries decreases, resulting in faster energy loss (often up to 50 percent faster). For these reasons, providing services poses a significant challenge to the UAV's power supply.