An Experimental Tethered UAV-Based Communication System with Continuous Power Supply

Abstract

Ensuring reliable communication in remote or disaster-affected areas is a technical challenge due to unplanned deployment and mobilization, meaning placement difficulties and high operation costs of conventional telecommunications infrastructures. To address this problem, unmanned aerial vehicles (UAVs) have emerged as an excellent alternative to provide quick connectivity in remote or disaster-affected regions at a reasonable cost. However, the limited battery autonomy of UAVs restricts their flight service time. This paper proposes a communication system based on a tethered UAV (T-UAV) capable of continuous operation through a wired power network connected to a ground station. The communications system is based on low-cost devices, such as Raspberry Pi platforms, and offers wireless IP telephony services, providing high-quality and reliable communication. Experimental tests assessed power consumption, UAV stability, and data transmission performance. Our results prove that the T-UAV, based on a quadcopter drone, operates stably at 16 V and 20 A, ensuring consistent VoIP communications at a height of 10 m with low latency. These experimental findings underscore the potential of T-UAVs as cost-effective alternatives for extending or providing communication networks in remote regions, emergency scenarios, or underserved areas.

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 establishing wireless 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. Recent research proposes several solutions, including renewable energy, wireless charging, and battery swapping. The most widely used method is battery replacement, which involves the UAV making constant trips to place a charged battery [10]. However, this process must be carried out accurately to avoid service interruptions. Additionally, the need for multiple batteries and swapping stations can lead to increased operational and logistical costs. One promising alternative is tethered unmanned aerial vehicles (T-UAVs), which provide a constant power supply, reduce battery dependency, enable continuous and stable data transmission, and offer greater security against UAV downtime. This paper addresses the design and implementation of a power network that ensures the extended operation of the UAV, as well as the development of a communication system based on a T-UAV, offering a unified communication system. The importance of this study lies in ensuring an uninterrupted communication service, which involves solving the problem of flight duration.

In recent years, research has focused on reducing one of the primary limitations of UAV deployment, i.e., energy consumption. Traditional UAVs are based on a battery inside, usually allowing flight times between 20 and 40 min, depending on the size, payload, and environmental conditions [8]. Several studies have investigated strategies to address energy constraints. Bianchi et al. [11] proposed a hierarchical real-time control strategy for UAVs that aims to minimize energy consumption while maintaining low computational complexity. This approach is grounded in optimal control theory but translates theoretical trajectories into implementable, rule-based references. Their solution achieves near-optimal energy use levels while remaining feasible for on-board real-time implementation. This work highlights the value of mission planning, trajectory smoothing, and reference generation to improve UAV energy efficiency.

Similarly, Mehmood et al. [12] explore energy-efficient communication architectures, focusing on the integration of UAVs into next-generation networks. The study highlights the energy trade-offs associated with different communication modes and proposes solutions, including cooperative relaying and T-UAVs. These systems, powered from the ground, allow continuous operation and eliminate battery limitations, offering a viable solution for scenarios requiring prolonged coverage. Despite growing attention to energy management in UAVs, few works have explored integrated solutions that combine trajectory optimization and real-time communication support.

To improve the contextual understanding of UAV communication, we consider the work of Alexan et al. [13] that proposes a two-layer encryption protocol for the secure transmission of military reconnaissance images over UAV-assisted relay networks. Their solution addresses the need for robust and secure communication in hostile or unpredictable environments, integrating genetic algorithms and DNA coding with low-density parity-coded-based transmission schemes. In addition, differences in control and autonomy levels between UAV platforms, particularly in reconnaissance applications, introduce operational complexities. As noted by Nowakowski et al. [14], the integration of UAVs into unmanned ground vehicle systems improves terrain analysis and mission adaptability in unknown environments. Their work highlights the role of UAVs in supporting decision making for autonomous ground systems, emphasizing the challenges of coordination and real-time data exchange that must be considered in integrated mission planning. Finally, Laghari et al. [15] present a comprehensive review of the widely used protocols, Wi-Fi, Zigbee, and LoRaWAN, detailing their respective strengths and limitations in UAV scenarios. Their findings reveal necessary trade-offs in range, data rate, power consumption, and security, which must be considered when selecting communication technologies for UAV deployments.

Our research aims to contribute to this gap by designing a power network for a T-UAV to support uninterrupted aerial communication services. Using continuous power delivery, we ensure extended operational times and robust data transmission, which makes it applicable to critical emergency response and IoT scenarios.

2. Background

In this section, an overview of UAVs and their potential network services, as well as the energy issues associated with them—including batteries, recharging methods, the utilization of renewable sources, and the tethered UAV system—will be presented.

2.1. Unmanned Aerial Vehicles

A UAV system can be remotely controlled by experienced personnel or operate automatically and autonomously through programmed software. UAVs have been known for decades. Their first applications were in the late 19th century, during the Spanish-American War, where they were used for military reconnaissance to take aerial photographs. Over time, these UAVs have evolved significantly; for example, the Tadiran Mastiff UAV was developed in 1973 for the Yom Kippur War. This system was designed with an advanced system of data links and electronics that allowed it to transmit real-time, high-resolution video to operators on the ground. This made obtaining critical information about the target areas easier, significantly improving surveillance and reconnaissance capabilities during the conflict [16]. This and other events evidenced the advantages of UAVs, highlighting the ability to perform high-risk missions and their potential to attack enemy territory.

Thanks to advances in science and technology, UAVs can now integrate a wide range of modules, such as high-resolution cameras, communication systems, and multispectral and thermal sensors, among others, as shown in Figure 1. This capability makes them much more functional and versatile tools for civilian applications. Additionally, the wireless communication systems used by UAVs are easier to implement due to their compact size and the ability to be quickly configured. They have good mobility and are inexpensive, making them suitable for use in various situations. Their rapid deployment makes them ideal for responding to unexpected events.

Despite their wide applications, systems designed with UAVs present a significant challenge in terms of energy consumption. The energy consumption of a UAV comprises two main components: (i) propulsion power, which is required for the UAV to fly and stay airborne, and (ii) payload power, which powers the communication and processing devices during flight. An obvious solution would be to use higher-capacity batteries, but this would result in a heavier power system, which would reduce the payload capacity of the UAV [17]. Several methods of powering the UAV are currently being studied, including wireless power, which offers advantages in extended flight applications and achieves a transmission efficiency of approximately 20 percent. The wireless transfer methods being explored include electromagnetic induction and magnetic resonance, which are suitable for charging when the UAV is near a fixed platform. Other methods include microwave or laser power transfer, which allow power delivery over longer distances and sometimes while the UAV is in flight. However, these methods still require high transmission accuracy and face challenges related to efficiency and safety, especially in environments with obstacles or variable atmospheric conditions [18,19]. Therefore, this paper proposes a solution based on the design and implementation of a T-UAV.

Figure 1. UAV structure, based on [20].

Figure 1. UAV structure, based on [20].

2.2. The Role of UAVs in Wireless Communications

This section presents the network service categories that can be supported by the UAVs.

2.2.1. Emergency Services

In emergencies caused by natural disasters such as floods, earthquakes, hurricanes, or fires, UAVs can intervene to provide a communications system that operates autonomously or as a complementary infrastructure. This alternative is crucial when the communication infrastructure becomes inoperative or is destroyed due to the impact of the disaster [21]. An alternative to solve this situation is to deploy UAVs to replace BSs.

Another way to use UAVs in emergencies is to implement them as relay systems to connect groups of isolated or dispersed users. This approach allows UAVs to operate as UAV-BSs, facilitating communication between mobile devices without Internet access. Using a relay bridge, UAVs can extend network coverage in affected areas, allowing users to share critical information, even without terrestrial communication infrastructure [22].

2.2.2. IoT Device Data Collection

Implementing IoT systems requires wireless facilities to collect data and retransmit it [23]. However, a drawback arises in rural areas or areas without wireless network infrastructure, such as in the case of data collection in agricultural areas. UAVs can be used to address this situation. In the field of IoT, it is possible to integrate UAV technology and wireless energy transfer. The objective is for the UAV to transmit radio waves to IoT nodes. These nodes receive and store energy, then use it to transmit information back to the UAV. To achieve efficient data acquisition from the UAV, it is essential to ensure that the energy is supplied in a directional manner [24].

2.2.3. Backhaul Network

Also known as backhaul, in telecommunications, this term refers to the infrastructure that connects the core network with the subnetworks. In cellular networks, this network is used to connect the BSs and the core network. Typically, this connection is established using optical fiber and microwave links, among other methods. However, when this network has been damaged, temporary connections can be established using UAVs. For this, several techniques or methods are available; one alternative is to create multi-hop networks using multiple UAVs in a specific topology (e.g., a linear topology).

2.2.4. Load Balancing

During mass user concentration events, such as concerts, BSs may experience overloading, leading to denial of service or a decrease in service quality [25]. Although infrastructures usually have a larger-than-usual capacity for users, these situations can temporarily saturate them. Therefore, using UAVs can help alleviate network congestion by acting as temporary BSs and signal repeaters, providing additional connectivity and extending network coverage. This helps to distribute the data load and improves network capacity.

2.3. Energy Recharge Techniques

The recharging procedure must take into account both the nature and behavior of the batteries as well as the charging or replacement strategies.

2.3.1. Battery Power

Around 90% of UAVs are equipped with lithium polymer (LiPo) batteries, which provide an average of up to 90 min of autonomy. This battery technology is ideal for small UAVs weighing less than 2 kg or for short-duration operations [26].

Table 1. Comparison of different batteries [20].

Characteristics	Ni-Cd	Ni-Mh	LiPo	Li-S
Specific energy (Wh/kg)	40	80	180	350
Energy density (Wh/L)	100	300	300	350
Specific power (W/kg)	300	900	2800	600

details the various batteries that can be used and their characteristics; these include specific energy, energy density, and specific power [20]. However, to extend the life of the UAV, the simplest solution would be to increase the battery capacity (i.e., use larger batteries), which would mean increasing the weight of the UAV, which in turn would require more power from the UAV engine due to the additional weight. These considerations would result in higher power consumption without addressing the issue of battery life.

2.3.2. Battery Swapping

This method can be performed either by swapping or by hot-swapping, as shown in Figure 2. In the first case, when the UAV battery is depleted, the drone must be directed from its current location to the ground control station (GCS) to replace it with another UAV that has a fully charged battery. The limitation of this method is the number of spare UAVs required and the service interruption time due to flying to and from the ground station [20]. With hot-swapping, the UAV descends to the GCS to have charged batteries inserted immediately, allowing it to resume operations in less time. However, this approach requires human assistance for battery swapping [20].

2.3.3. Wireless Recharging

In this method, there is no need for the UAV to descend to the GCS to recharge its batteries, as various wireless power transfer techniques can be used, classified according to their transmission range. These techniques fall into two main categories: (i) near-field transmission and (ii) far-field transmission [20].

For distances of less than one meter, near-field methods such as capacitive power transfer (CPT), inductive power transfer (IPT), and magnetic resonance coupling (MRC) are used. CPT is based on the flow of an electric field between two parallel plates separated by a dielectric material, which produces low power losses in metallic environments and is suitable for low-power applications. IPT, on the other hand, works on the weakly coupled transformer principle, using coils for transmission and reception and power electronic converters at both ends. This technology operates at KHz frequencies. MRC, an improvement on IPT, introduces an intermediate coil between the transmit and receive coils, minimizing losses and allowing operation at MHz frequencies. In addition, MRC is ideal for applications where multiple loads need to be powered simultaneously, such as charging multiple UAVs [20].

Regarding far-field transmission, distributed laser charging facilitates the transfer of energy using a laser beam. This technique can deliver up to 2 W of power over a range of 5 m. However, it requires a clear line of sight between the transmitter and receiver, as any obstruction will significantly affect the energy transfer [20]. The process involves a generator emitting a laser beam with a specific frequency and wavelength, which is directed at a photovoltaic cell installed on the UAV. This cell converts the laser beam into electrical energy to recharge the batteries. It is essential that the UAV is at a suitable altitude and that a device capable of identifying the point of maximum laser power is used to optimize the energy transfer, as shown in Figure 3 [19].

2.3.4. Solar Energy

Renewable energy, such as solar power, is a sustainable alternative for powering UAVs for long-duration operations. Integrating solar panels with advanced batteries, such as lithium-ion or solid-state batteries, enables the storage of energy generated during daylight hours for use at night or in low-light conditions. Leading solar-powered UAVs, such as Helio and Zephyr, have demonstrated their effectiveness in this area. The Helio achieved a continuous flight of more than 18 h, while the Zephyr set a record by flying continuously for 64 consecutive days, reaching altitudes of up to 20,000 m [27]. However, these systems face seasonal challenges due to the variability in the length of day and night. During the summer solstice, a 7.44 kg battery is sufficient to ensure night flight. In contrast, during the winter solstice, when nights are longer, a 12.4 kg battery is required to maintain continuous operation [27].

2.4. Tethered UAV

This system offers longer flight times and support for heavier payloads. It can also deploy a very high-capacity communications channel if fiber-optic networking is used. The key component of this system is the tether, which provides power and data to the UAV from a GCS [28]. T-UAV technology overcomes two limitations of UAVs: reduced flight time and the lack of a reliable backhaul link. This is achieved by a dual link between the GCS and the T-UAV, providing power and data efficiently and securely. The configuration of the T-UAV system consists of three essential components: (i) the UAV, (ii) the GCS, and (iii) the tether or cable. The GCS is located in a strategic area, either on the ground or on a roof, and provides the connection to the central network, which is responsible for data processing and the power resource provided by a source. The tether is used to transmit power and data from the GCS to the UAV, as shown in Figure 4 [29].

Although a T-UAV can fly uninterrupted for days, its mobility is limited to a specific range because of the tether’s length. This length depends on the height of surrounding buildings and the angle of inclination of the tether, which must be kept below a specific value to avoid entanglement or accidents. In a real environment, these constraints or factors are reflected as shown in Figure 5. In addition, the line of sight of the T-UAV is conditioned by these two factors.

Currently, several companies have been working on the development of T-UAVs for commercial use. In their research and development, they have reached a particular flight time and tether length, the details of which are presented in

Table 2. Comparison of T-UAV systems designed by different companies [28].

Company Names	Tether Length	Flight Time
Equinox Systems	150 m	30 days
Arial Insights	120 m	Multiple operation
Elistair	80 m	More than 10 h

. In addition, in [28], it is determined that the tilt angle that the tether must have to be safe varies between 10 degrees for suburban areas and 31 degrees for urban areas, with a tether length of 150 m.

T-UAVs can carry a payload of 3.5 to 6.2 kg, which includes all the processing equipment [29]. In addition to providing power and network connectivity, the GCS could also control the length of the cable to adjust coverage or deal with incidents.

3. Methodology

Below are the detailed procedures and methodology used for implementing a communications network based on an IP telephony service established on a single-board computer. Additionally, the design and implementation of a power network that enables the UAV to fly without interruption are presented.

3.1. Requirements Analysis

The following section describes the hardware and software components required for implementing the prototype.

• Single-board computer: This device is essential for implementing an IP-based communication system, so it must support the installation and efficient execution of the required software. It must create a wireless network to ensure data transmission, have connectivity interfaces such as Wi-Fi to establish links with other devices, and have a compact and lightweight design, ideal for placement inside the UAV. It must also be energy-efficient to ensure greater autonomy during system operation.
• IP telephony software: Open-source software is required to provide a suitable interface for configuring the IP telephony-based communication system. This software must be compatible with the operating system of the selected device and have detailed documentation to facilitate installation and customization.
• UAV: A lightweight UAV of simple design must be connected to a ground power supply system via a cable, significantly increasing flight time. This UAV must be capable of carrying a payload of approximately 1.5 kg to support the single-board computer, its battery, and the associated power cable. It must also be equipped with an integrated control system and a GPS module to ensure stable and controlled navigation during operation. It must also include a remote control for ease of operation and real-time monitoring, allowing in-flight adjustments.
• Power supply system: A ground-based power supply is required to allow the UAV to operate for an extended time. The proposed UAV-enabled communications system assumes the availability of a power grid (AC voltage), which feeds the power supply located at the GCS. In a future approach, the entire system could be portable and entirely battery-powered, as detailed in our previous work [30]. The power supply considered in the prototype must provide a constant voltage and current suitable for operating the UAV. In addition, it is crucial to select an appropriate cable to carry power between the power supply and the UAV, which must not only be capable of carrying the required voltage and current but also have an appropriate gauge to ensure the stability of the power supply, considering an objective distance of approximately 10 m. The cable should be lightweight to minimize the additional load on the UAV, thus optimizing its flight capability.

3.2. Elements for the Prototype

Once the project elements have been identified, the equipment and software needed to meet the requirements must be determined.

3.2.1. Comparative Analysis and Selection of Single-Board Computers

Information was collected on three devices to determine which one best meets the aforementioned requirements. To do this, a comparison was made between the Raspberry Pi 4B, the Arduino Uno, and the ODROID-C4, the details of which are presented in

Table 3. Comparison of device features for the implementation of the IP telephony service [31,32,33].

Features	Raspberry Pi 4B	Arduino Uno	ODROID C4
Processor	Quad-core Cortex-A72 at 1.5 GHz	ATmega328P (8-bit)	Amlogic S905X3 (Quad-core Cortex-A55 at 2.0 GHz)
RAM	2/4/8 GB LPDDR4	256 MB–1 GB	4 GB DDR4
VoIP Compatibility	Compatible (e.g., Asterisk, FreePBX, FreeSWITCH)	Not compatible	Compatible with Asterisk
Wi-Fi Module	Dual-band (2.4/5 GHz)-integrated	External module required	Needs an external adapter
Ports and Interfaces	GPIO, USB 2.0/3.0, HDMI, Ethernet	GPIO and USB	GPIO, USB 3.0, HDMI, Ethernet
Voltage	5 V input	5 V input	5 V input
Power Consumption	3–5 W	0.5–1.5 W	5 W maximum
Size and Weight	85.6 × 56.5 mm, 46 g	68.6 × 53.4 mm, 25 g	85 mm × 56 mm × 1.0 mm, 59 g
Operating Systems	Raspberry Pi OS, Ubuntu, among others	Arduino IDE	Armbian, Android, Ubuntu, among others
Price (USD)	Around $150	Around $20	Around $120

. This table indicates that the Arduino Uno cannot implement the unified communication service because it lacks a Wi-Fi module and operates solely with the Arduino IDE as its operating system. Although the Raspberry Pi 4B and the ODROID-C4 are suitable devices for this purpose, there are significant differences. The ODROID-C4 lacks a built-in Wi-Fi module, requiring the addition of an external module, which would increase the project’s cost and complexity. Additionally, the ODROID-C4 is not available in the country where the prototype was designed and implemented (Ecuador), which would increase the price due to shipping expenses. On the other hand, the Raspberry Pi 4B platform offers the necessary features for implementing the IP telephony service, including a high-performance processor, built-in Wi-Fi connectivity, and availability of documentation and installation guides. Due to these advantages, the Raspberry Pi 4B was chosen as the most suitable platform to deploy our T-UAV prototype.

3.2.2. Comparative Analysis and Selection of IP Telephony Software

Table 4. Comparison of software features for implementing the IP telephony service.

Features	3CX	FreePBX	Asterisk
Open-source	Yes	Yes	Yes
Raspberry Pi Compatibility	Compatible	Compatible	Compatible
Documentation and Support	Moderate (free version)	Extensive and active	Extensive and active
Main Features	Call management, extensions, video calls (limited in free version)	Advanced call management, extensions, IVR	Flexible platform with full support for extensions, IVR, and advanced customization
Configuration Type	Requires downloading the Raspberry Pi OS image; installation is complex and achieved via GUI or commands	The software image is directly stored in memory and configured via commands	The Raspberry Pi OS image is downloaded, and the softphone is installed using manual commands
Scalability	Moderate (limited free version)	High	Very high

shows a summarized comparison of three types of software for the implementation of IP telephony: (i) 3CX (version 20.0), (ii) FreePBX (version 17), and (iii) Asterisk (release 22.4.1). After analyzing the characteristics of software solutions, we concluded that FreePBX is the best suited to the requirements of the prototype. This is because it is relatively easy to install, offers the necessary functions for the UAV-enabled communications system, and has a wide availability of information and resources online, including blogs and tutorials that facilitate its use and installation.

3.2.3. Implementation of IP Telephony System

This section describes the procedure for installing and configuring an IP telephony service on a Raspberry Pi 4B, explaining each step necessary to ensure proper configuration and operation. The steps to follow are detailed below.

• Installation of the RasPBX operating system: A microSD card with an SD adapter is required to perform the installation. The minimum requirement for the card is a capacity of at least 8 GB, which is necessary to guarantee the correct functioning of the service to be installed. The microSD card must then be inserted into a computer. Next, the RasPBX operating system image must be downloaded. The latest version available is raspbx-10-10-2020, compatible with Raspberry Pi 4, 3, and 2 [34]. To begin with the configuration, follow the steps below:

  (a)

  Download the RasPBX image at [34].

  (b)

  Use the Win32 Disk Imager tool to copy the image to the SD card.

  (c)

  Create an empty text file with the name ’ssh’ and save it on the SD card.

  Once the image has been written to the SD card, it is inserted into the Raspberry Pi and connected to the power supply. The Advanced IP Scanner tool is then used to identify the network generated by the Raspberry Pi (specifically, its IP address), which is available for download at [35]. With this information, the computer terminal is accessed, and a remote connection to the Raspberry Pi is established using the SSH protocol, which facilitates remote administration of the device. During the SSH connection process, a password is requested; the default password is raspberry.
• Operating system upgrade: To avoid unwanted updates in the PHP repository and prevent possible errors during the system update, the command Listing 1 must be run. With the commands shown in Listing 2, the system is updated correctly without generating problems.

  Listing 1. Command to edit the APT source file for PHP.

  Listing 2. Commands to update the system.

• Creation of the access point: The Raspberry Pi must establish its wireless network in the proposed prototype. The programs hostapd and dnsmasq are used to do this. Hostapd allows the Raspberry Pi to function as an access point. In contrast, dnsmasq provides the services of DNS and DHCP, taking care of assigning IP addresses to the devices that connect to the network [36]. The commands in Listing 3 must be executed to install both programs.

  Listing 3. Commands to install hostapd and dnsmasq.

  Once hostapd is installed, it must be configured to function as an access point and allow the Raspberry Pi to provide a wireless network. To perform this configuration, the hostapd configuration file must be accessed using the command in Listing 4.

  Listing 4. Hostapd configuration file.

  Inside the configuration file, it is necessary to define the specific parameters to establish the network access point. For example, a user can assign the network name (SSID) as “ServiceVoIp” and set the password as “veronicar”. To do this, the following lines should be added to the file as shown in Figure 6. Furthermore, the configuration file must be configured at startup to ensure that hostapd uses the /etc/hostapd/hostapd.conf. To do this, the default hostapd configuration file must be opened with the command in Listing 5, and inside the file, the following line must be added:
  DAEMON_CONF=“/etc/hostapd/hostapd.conf”

  Listing 5. Default hostapd configuration file.

• DHCP server configuration: The DHCP server is essential for automatically assigning IP addresses to devices connecting to the network. To configure it, the user must access the corresponding file using the command in Listing 6 and add the line indicated in Listing 7.

  Listing 6. Command to edit the DHCP server configuration.

  Listing 7. Static IP configuration for the wlan0 interface.

• Dnsmasq configuration: In the proposed prototype, dnsmasq is used to manage IP address allocation and provide name resolution services on the wireless network created by the Raspberry Pi. First, the command in Listing 8 is executed to back up the configuration. Then, the dnsmasq configuration file is edited with the command in Listing 9, and the address range is set using the command in Listing 10.

  Listing 8. Command to back up the original dnsmasq configuration file.

  Listing 9. Command to edit the dnsmasq configuration file.

  Listing 10. DHCP address range configuration for the wlan0 interface.

• Routing and NAT enablement: Several system parameters must be configured to enable routing and NAT on the Raspberry Pi. First, the configuration file sysctl.conf is moved and backed up with the command in Listing 11. Next, to enable IPv4 packet forwarding, the command in Listing 12 must be executed. Finally, iptables is configured to enable the NAT with the command in Listing 13, and the configuration must be saved.

  Listing 11. Command to move and backup the sysctl.conf configuration file.

  Listing 12. Enabling IPv4 packet forwarding in the system.

  Listing 13. Command to enable NAT and save the iptables configuration.

• Saving the iptables rules’ configuration: To ensure that firewall rules persist after reboot, the /etc/rc.local file is edited by adding the command to restore the iptables rules on startup. The command in Listing 14 is used to open the file. Then, the line shown in Listing 15 is inserted just before the exit 0 statement.

  Listing 14. Command to edit the /etc/rc.local file.

  Listing 15. Line to restore the iptables rules at startup.

• Restart services: The dnsmasq service is restarted to apply new configurations, as shown in Listing 16.

  Listing 16. Command to restart the dnsmasq service.

• Activation and initialization of the hostapd service: The following commands are executed to unmask, enable, and start hostapd, ensuring the wireless access point operates correctly, as shown in Listing 17.

  Listing 17. Commands to activate and start the hostapd service.

• Verifying current iptables rules: The currently active firewall rules are checked with the command in Listing 18.

  Listing 18. Command to list the current iptables rules with details.

• Adding rules to allow SIP and RTP traffic: Firewall rules to permit traffic on UDP ports 5060 (SIP) and 10,000–20,000 (RTP) are inserted, as shown in Listing 19.

  Listing 19. Commands to add iptables rules for SIP and RTP traffic.

• Saving the current iptables rules: The active iptables rules are maintained by saving them to the configuration file with the command in Listing 20.

  Listing 20. Command to save iptables rules’ configuration.

• IP telephony system configuration: An access point is established with the above configurations. The next step is to connect to this network from a computer and log in to the system through the browser using the Raspberry Pi’s IP address. In FreePBX, the initial configurations of the service are set, which include creating a user, assigning a password, setting up an email for notifications, and naming the service. In addition, the day and time for updates are configured, as shown in Figure 7.
  When logged in as an administrator, the home screen is displayed as shown in Figure 8. Then, the user must select the Applications option, click on Extensions, and choose the extension type, as shown in Figure 9.
  Figure 10 shows the process of configuring an extension, where the user must enter the extension number, the user name, and the corresponding password. Two users were created for this prototype: (i) Maria and (ii) Pedro. Maria was assigned extension 100, while Pedro was assigned extension 101. Once the configuration was complete, all extensions created could be verified, as shown in Figure 11.
• Download and configuration of Zoiper: Zoiper is available for Linux, Microsoft Windows, and macOS operating systems. On mobile devices, it can be downloaded for Android and iOS. Once the softphone was installed, tests were conducted by configuring two users with the same data registered in FreePBX. For example, for the user Maria, the extension 100, the corresponding password, and the IP address of the device providing the IP service (i.e., the IP of the Raspberry Pi (192.168.4.1)) were assigned. Similarly, for the user Pedro, extension 101 was configured along with its key. These configurations are shown in Figure 12a and Figure 12b, respectively. This step concludes with the installation and configuration of the IP service on the Raspberry Pi. To perform the tests, at least two devices are required, such as a computer or a cell phone, which will allow making calls and verifying the correct connection.

3.2.4. UAV

A UAV is required to establish the communication system in accordance with the prototype requirements. For this purpose, a quadcopter UAV of the Holybro brand, model S500 V2, is used, as shown in Figure 13. This UAV features a lightweight design, is easy to assemble, and does not require welding; its structure is composed of various materials. The arms are made of polyamide and nylon that are reinforced with carbon fiber in the center, and the landing gear is made of carbon fiber tubes. The characteristics of the landing gear are specified in

Table 5. Holybro S500 V2 UAV features general, based on [37].

Feature	Detail
Weight	1230 g
Dimensions	383 × 385 × 240 mm
Maximum payload weight	1.5 kg
Propellers	4
Recommended voltage for 1.3 kg payload	16 V
Recommended current for 1.3 kg payload	16.37 A
Flight time	18 min in hover flight with a 5000 mAh battery

.

The UAV integrates a Pixhawk 6C flight controller and a Holybro SiK V3. The controller provides highly accurate and stable flight control. This controller enables autonomous mission execution, ensuring robust navigation thanks to its advanced processing power and control algorithms. The Pixhawk 6C operates at a frequency of 480 MHz, providing fast processing.

Table 6. Pixhawk 6C controller [37].

Feature	Detail
Speed	480 MHz
Flash memory	2 MB
RAM	1 MB
Weight	34.6 g

details the specifications of the Pixhawk 6C flight controller. On the other hand, the telemetry radio establishes a connection between the autopilot and the ground station through an antenna that offers a range of 300 m, which can be extended as needed. This device utilizes open-source firmware specifically designed to operate with MAVLink packages and is compatible with various tools, including Mission Planner, ArduPilot, QGroundControl, and PX4 Autopilot. It operates in two frequency bands depending on the region: (i) 915 MHz in America and (ii) 433 MHz in Europe [37].

Table 7. SiK V3 telemetry radio [37].

Feature	Detail
Reception sensitivity	−117 dBm
Communication	Full-duplex bidirectional via UART TDM interface
Dimensions	28 × 53 × 10.7 mm
Maximum output power	100 mW
Power supply voltage	5 V DC (via USB or JST-GH)
Weight	13.6 g

shows the technical specifications of the telemetry radio.

3.2.5. Power System Analysis and Design

• Analysis of UAV energy consumption: Table 5 shows that for a payload of 1.3 kg, the power consumption is approximately 16 V and 16.37 A. However, these values may vary depending on the weight carried, weather conditions, and other elements that influence system performance. Therefore, evaluating how power consumption varies as a function of the weight being transported is essential for selecting the right components for efficient UAV operation. For this purpose, initial tests were performed using a 1500 mAh, 4S, and 120C spec battery, as shown in Figure 14.

Two different weights were selected for the tests on energy consumption: (i) a reduced weight of 1155 g, which includes the UAV and the battery necessary for its operation, to analyze the system behavior under minimum load conditions, and (ii) a weight of 2100 g, which includes the UAV, the battery and 945 g weights, to observe the UAV performance under more realistic conditions, i.e., with a higher weight that simulates the system operating scenario. This approach enabled the collection of voltage and current consumption data in various scenarios, the results of which are presented in

Table 8. Electrical consumption parameters of the UAV obtained using a battery.

Weight [g]	Voltage [V]	Current [A]
1155	15.4	8.9
2100	15	20

.

Figure 14. The 1500 mAh battery, 4S, and 120C.

Figure 14. The 1500 mAh battery, 4S, and 120C.

From the electrical parameters obtained using a battery as a power supply, it was estimated that this prototype’s reasonable power consumption is 16 V and 20 A. This value corresponds to the consumption under an approximate weight required for the uninterrupted UAV-enabled communication system. Knowing the current needed for the system, the theoretical operating time of the UAV using an 1500 mAh battery was calculated using Equation (1). This formula considers that the battery’s rated capacity is consumed uniformly, without interruptions and loss of efficiency. The result obtained, 0.075 h, is approximately equivalent to 4.5 min of autonomy under ideal conditions.

$$T={\displaystyle \frac{1500\mathrm{mAh}}{20\mathrm{A}}}$$

(1)

$$T=0.075\mathrm{h}$$

(2)

An additional test was performed with the UAV, which included the Raspberry Pi, its power supply battery, and 1500 mAh, 4S, 120C battery to supply power to the UAV, as shown in Figure 15. During the experiment, the QGroundControl software version 4.4.2, available for download at [38], was used to monitor the voltage and current parameters of the UAV. These parameters varied as a function of horizontal and vertical velocity and height. With a total weight of 1.47 kg, it was observed that at higher altitudes, the current increased and the voltage decreased. This behavior is because, as the UAV ascends, it needs to generate more lift to counteract the force of gravity, which leads to an increase in energy consumption. This increase in energy demand translates into higher current consumption, as the motors must work harder to maintain the UAV’s flight. The results obtained are presented in Figure 16 and Figure 17, and the extracted data are shown in

Table 9. Electrical consumption parameters of the UAV obtained using a battery, including the Raspberry Pi 4B.

Altitude [m]	Voltage [V]	Current [A]
1.3	14.91	11.66
2.4	14.74	12.43

.

With the PlotJuggler application, downloaded from its official repository on GitHub [39], and using the log file in .ulg format generated by the flight controller during the UAV operation, the graph representing the variation of voltage and current was obtained. This visualization enables the analysis of the system’s energy consumption, as shown in Figure 18. This figure shows that the current remains stable at a value of 12.54 A, although it exhibits fluctuations due to variations in the power demands of the UAV, particularly during accelerations or decelerations, or to maintain flight stability. On the other hand, the voltage remains almost constant at around 14.73 V, indicating that the power system, comprising the battery and the voltage regulator, can handle current fluctuations efficiently, ensuring a stable power supply even when the UAV’s load varies.

• Power supply selection and characteristics: Based on the tests performed to determine the UAV power supply requirements, a voltage of 16 V and a current of 20 A were established as operating parameters. To meet these conditions, a switch-mode power supply was selected, whose specifications are presented in

  Table 10. Technical specifications of the power supply.

  Feature	Details
  Input voltage	110 V or 220 V
  Voltage range	0–24 V
  Voltage accuracy	0.1 V
  Current	20 A

  and illustrated in Figure 19. Because this supply provides a higher voltage than necessary, we chose to use a step-down voltage regulator, as shown in Figure 20, to lower the voltage to 16 V. Additionally, this regulator can continuously handle up to 20 A, thus satisfying the system requirements.

Figure 19. Switching power supply of 24 V and 20 A.

Figure 19. Switching power supply of 24 V and 20 A.

Figure 20. Voltage reducer module 20 A 6V-40 VDC.

Figure 20. Voltage reducer module 20 A 6V-40 VDC.

• Calculations for cable size determination: To select the appropriate cable, the specific energy parameters of the design are considered and are detailed below.

  -

  Voltage required by the UAV: 16 V.

  -

  Current required: 20 A.

  -

  Distance between the power supply and the UAV: 10 m.

  -

  Conductor material: Copper.

When power is transmitted through a cable, there are losses due to the resistance of the conductor material. These losses generate a voltage drop proportional to the length of the cable, the current flowing through it, and the resistance of the conductor. For this reason, the voltage reaching the UAV will be lower than the initial voltage at the source if not adequately compensated. The National Electrical Code (NEC) [40] and IEC 60204-1 [41] state that a maximum voltage drop of 10 % is commonly accepted in power supply systems to ensure safe and efficient operation, even with long-distance cables or high currents. Therefore, for this prototype, a maximum voltage drop of 10 % is considered. This condition ensures that the UAV receives a minimum voltage of 16 V at the cable end. Consequently, the source output voltage must be higher than the voltage required by the UAV. Equation (3) determines the calculation of the source output voltage. Thus, the source output voltage must be 17.7 V to compensate for the losses in the cable. Therefore, for this prototype, a maximum voltage drop of 10 % is considered. This ensures that the UAV receives a minimum voltage of 16 V at the cable end. Consequently, the source output voltage must be higher than the voltage required by the UAV. The Equation determines the calculation of the source output voltage (3). Thus, the source output voltage must be 17.7 V to compensate for the losses in the cable.

$$\lambda \times 0.9=16\mathrm{V}$$

(3)

$$\lambda =17.7\mathrm{V}$$

(4)

The total resistance of the cable, considering a current of 20 A and the established voltage drop of 1.7 V (17.7 V–16 V), is calculated using Ohm’s Law, as shown in Equation (5).

$$R={\displaystyle \frac{V}{I}}$$

(5)

$$R={\displaystyle \frac{1.7\mathrm{V}}{20\mathrm{A}}}$$

(6)

$$R=0.09\mathrm{\Omega }$$

(7)

The next step is to determine the wire gauge required to ensure this maximum resistance using the formula in Equation (8).

$$R=\rho {\displaystyle \frac{L}{A}}$$

(8)

where

• R: Resistance, measured in ohms ($\mathrm{\Omega }$).
• $\rho$: Resistivity, measured in ohm-meters ($\mathrm{\Omega }·m$).
• L: Length, measured in meters (m).
• A: Cross-sectional area, measured in square meters ($m^2$).

By clearing the area and substituting the corresponding values, the result is

$$A=\rho {\displaystyle \frac{L}{R}}$$

(9)

$$A=1.68\times {10}^{-8}\mathrm{\Omega }·m{\displaystyle \frac{20\mathrm{m}}{0.09\mathrm{\Omega }}}$$

(10)

$$A=3.73\times {10}^{-6}{\mathrm{m}}^2$$

(11)

The calculated cross-sectional area corresponds to an AWG #12 gauge copper wire, a standard commonly used in applications requiring moderate current-carrying capacity. This wire gauge is ideal for low-power signal transmission, as it offers a balance between resistance and carrying capacity, making it suitable for powering devices such as the UAV in the present project. Additionally, an audio cable with this gauge was chosen due to its design, which facilitates the straightforward identification of the positive and negative conductors, thereby avoiding polarity errors and potential system failures. Figure 21 shows the chosen cable.

Figure 21. The 12-gauge copper wire used in the UAV power system.

Figure 21. The 12-gauge copper wire used in the UAV power system.

3.2.6. Prototype Structure

With the necessary elements for the implementation of the prototype, a simple scheme was elaborated that illustrates the layout and location of the different components, including both the IP telephony communication system and the power system, shown in Figure 22. The UAV elements, such as the GPS, controller, and radio telemetry, are at the drone’s top. In contrast, the Raspberry Pi, its battery, and the voltage regulator are at the bottom. The UAV is connected by a 10 m long cable linked to a power supply on the ground. This power supply features a plug for connecting the system to the mains, providing the necessary power to operate the system. The components have been strategically arranged to optimize space and ensure efficient system operation.

3.2.7. Costs of Prototype Elements

The prices of all the components used in the construction of the prototype are detailed in

Table 11. Prices of the components of the designed prototype.

Components	Prices [USD]
UAV, Controller, GPS, and Telemetry Radio	540
Raspberry Pi Battery	45
Raspberry Pi	134
Power Supply	32
Voltage Regulator	15
#12 Audio Cable	11
Total Cost	777

, with a total cost of USD 777. Its economic viability is evident when compared exclusively with commercial tether-powered solutions for UAVs. For example, a Lifeline-branded T-UAV system, which includes a 60 m cable, is priced at approximately USD 6500 [42]. The costs of our proposed solution represent only 11.74 % of the cost of an equivalent commercial system.

4. Results

With the communication network configured and the power supply network designed, we proceed to the complete assembly of the prototype to verify its operation.

4.1. Prototype Testing in a Closed Environment

This test uses the power supply and regulator as part of the power system. The assembled prototype is shown in Figure 23. Subsequently, the UAV with all the integrated components is weighed, as illustrated in Figure 24, obtaining a total weight of 1940.8 g. The detailed breakdown of the weight of each prototype component is presented in

Table 12. Detailed weights of the prototype components.

Components	Weight [g]
Voltage Regulator	91.1
Raspberry Pi Battery	212.6
Raspberry Pi	112.7
Cable	554.4
UAV	970
Total	1940.8

, allowing an analysis of the weight distribution.

As an initial test to analyze the power management behavior of the source and controller, the system was connected to a power outlet in one of the university buildings. During the tests, the UAV oscillated between heights of 0.3 m and 0.6 m, with an approximate duration of each flight of 2 to 3 min. Voltage and current logs were downloaded and analyzed using the PlotJuggler application to assess energy consumption more accurately. Figure 25 shows the plots of voltage and current as a function of time during test flights performed in a closed environment. In the interval between 30 and 65 s of one of the flights, at a height of 0.3 m, it is observed that the voltage remains constant at 15.64 V while the current increases progressively until it reaches its maximum value of 9.12 A. However, near the second 65, voltage peaks are recorded while the current decreases. This behavior is due to the lateral movements of the UAV, which cause a change in the energy demand according to the adjustments in the speed of the motors.

When analyzing the time intervals of each flight, it was observed that although the voltage trend was stable during each phase of operation, its value varied between different flights. For example, Figure 26 shows a voltage of 14.97 V and a current of 11.57 A corresponding to a flight at 0.6 m altitude. In contrast, Figure 27 shows that the power consumption increased to 16.56 V and 10.01 A, corresponding to a flight at 0.4 m height.

4.2. Prototype Testing in an Open Environment

4.2.1. IP Telephony Service Performance Analysis

The voice-over IP communication system implemented in the Raspberry Pi was validated by configuring two softphones connected to the local network “VoIP Service” created in the device. The softphones were configured with the data specified in

Table 13. Extensions configured in the softphones for the communication system test.

Username	Domain	Password	User Name/Extension
Maria	192.168.4.1	Maria123	100
Pedro	192.168.4.1	Pedro123	101

. Figure 28 illustrates how this data was entered in the Zoiper application. The results show the successful establishment of the calls, as shown in Figure 29. The logs stored on the device that used the MizuDroid softphone for Android recorded two calls made: (i) one with a duration of 3 min and 12 s, and (ii) another with a duration of 11 min and 1 s. Additionally, the quality of the voice transmission was optimal, characterized by clear and uninterrupted audio throughout the communication, which confirms the functionality of the implemented communication system.

To analyze the operation of the communications system, various parameters can be analyzed during the establishment and development of the VoIP call. These parameters included the behavior of the wireless interface wlan0, which is shown in Figure 30. This figure shows that the transmission and reception rates remain stable, with values of approximately 24 kbit/s (TX) and 20 kbit/s (RX), respectively. The total bandwidth consumed during the call is approximately 44 kbit/s, indicating low network resource demand, which is consistent with the use of voice compression codecs. This efficiency confirms the system’s viability in scenarios with bandwidth constraints or reduced network infrastructure.

For the proposed prototype, the Raspberry Pi 4B is used as the processing platform. This device features a quad-core processor, which enables concurrent handling of multiple tasks; therefore, a load average of 4.0 would indicate full utilization of all available CPU cores. Accordingly, Figure 31 presents the CPU load behavior during a VoIP call, showing the system load average over 1-, 5-, and 15-min intervals. These values represent the average number of processes either running or waiting for CPU access during the specified periods. Throughout the call, the load average remains below 0.3 in all intervals, which is considerably lower than the theoretical maximum of 4. This confirms that the processing demand imposed by the IP telephony service is minimal and does not represent a significant load placed on the system.

Figure 32 shows the use of memory during the execution of the system. This figure shows that 16% of the RAM was used directly, while 3% was allocated to buffers and 17% to cache. The remaining 65% remained free, indicating ample availability of memory resources. The analysis of memory utilization revealed that no swap memory consumption was recorded, indicating that the system did not require secondary storage. Figure 31 and Figure 32 reveal that the proposed communications system operated efficiently with the established CPU and memory configuration, exhibiting stable and adequate operating behavior.

4.2.2. Power System Analysis

This test was held at 9:00 a.m. outdoors at the Escuela Politécnica Nacional. The weather was cloudy with some wind. This site was selected because of its grass surface, which could cushion a possible fall of the UAV, and the proximity of a power outlet to which the power supply was connected via an extension cord. In the first attempt, the UAV was held at a height of 4 m for 7 min, as shown in Figure 33. The voltage and current plots corresponding to this flight are presented in Figure 34. In these plots, the orange curve represents voltage, and the green curve represents current. The behavior of the graphs indicates that the voltage remained relatively constant while the current experienced a continuous increase. During a brief interval of instability in the system, a current of 15.04 A and a voltage of 16.64 V were recorded.

In the second test, performed in an open environment, the UAV flew for 3 min at a height of 0.8 m, with a 3 m long cable coiled on the bottom of the UAV, as shown in Figure 35. The corresponding voltage and current plots are presented in Figure 36. In this test, both voltage and current remained more stable compared to the previous test, where the UAV was operating at a higher altitude. The average power consumption recorded was 16.54 V and 10.50 A. The cable or the voltage regulator was checked for heat generation in both the closed and open environments. However, no increase in temperature was observed.

4.3. Data Obtained on the Different Flights

From the data obtained during the flights, the necessary information was compiled to generate

Table 14. Data obtained from tests conducted at different heights, both in open and closed environments.

	Closed Environment			Open Environment
Parameter	Test 1	Test 2	Test 3	Test 4	Test 5
Voltage [V]	15.64	14.97	16.56	16.64	16.54
Current [A]	9.12	11.57	10.01	15.04	10.50
Time [min]	1	2–3	2–3	7.4	3.2
Height [m]	0.3	0.4	0.6	4	1

to compare the energetic behavior of the UAV in different conditions. This table shows that as altitude increases, both voltage and current increase, with current being the parameter that varies most significantly. For example, when the UAV is at an altitude of 0.3 m, the current is 9.12 A, while at 4 m, the current increases to 15.04 A. This behavior is due to increased load and the additional effort required to maintain UAV stability at higher altitudes.

5. Conclusions

This paper presents a conceptual proposal for a tethered UAV-based communication system with continuous power supply, along with a detailed implementation of a proof-of-concept UAV-enabled communication system utilizing a Raspberry Pi 4B platform and a ground station. The prototype’s implementation was based on a thorough theoretical analysis of various sources related to communication technologies for UAVs and the power supply options used in these devices. Based on this analysis, the electrical requirements for designing and implementing the power supply network were determined, which was based on a tethered system. The results validate the viability of the proposed solution.

Regarding costs, the budget required for this prototype was exactly USD 777, a considerably affordable investment compared to commercial T-UAV systems, such as those from Lifeline, which are priced at USD 6,500. The cost difference of our solution highlights the proposed prototype’s economic viability, offering the possibility of testing, which favors its implementation in research scenarios or with limited financial resources.

With the T-UAV system, the flight time becomes indefinite thanks to the continuous power supply from the ground. In the tests performed with the prototype developed in this project, it was determined that the UAV requires a voltage of 16 V and a current of 20 A, values that served as the basis for designing the power supply system. Using a 1500 mAh battery as the power source, a theoretical flight time of approximately 4.5 min was estimated. However, the cable-powered system demonstrated its effectiveness by extending the flight time to 7 min during testing, thus validating its ability to significantly increase the UAV’s autonomy compared to using only a battery.

The energy performance of the UAV, with a total weight of 1940.8 g, was analyzed, noting that as the altitude changed, the electrical requirements varied significantly. As the height increased, so did the energy demand, highlighting that the current was the variable with the most significant fluctuation. This behavior indicates that at higher altitudes, the UAV faces more significant difficulties in maintaining its stability, which translates into a proportional increase in its energy consumption (mainly an increase in electric current).

Future work will include integrating the Raspberry Pi power supply into the system’s overall power network. This integration would address one of the project’s main limitations, as currently, only the UAV is powered from the ground. Additionally, to enhance the system’s operational continuity, a backup battery is planned for the UAV to ensure its service in the event of power supply interruptions or potential damage to the power cable. An alternative development approach is to make the entire communications system prototype entirely battery-powered, which implies the use of accordingly sized battery units in the GCS, offering portability and autonomy to the UAV-enabled communications system prototype. Regarding the power cable length, future work will also be devoted to designing a cable-pulling system that can reach altitudes exceeding 10 m and be applied in realistic post-disaster or energy scenarios.

Furthermore, to enhance the environmental robustness of the system, future work will focus on testing and adapting the platform to operate effectively in windy and rainy conditions. A comprehensive evaluation will be conducted under varying wind speeds. Additionally, waterproofing measures will be incorporated into the UAV design to enable operation during light to moderate rainfall, ensuring the system’s resilience and reliability in more realistic deployment scenarios.