⁽¹⁾INESC TEC, Faculty of Engineering of the University of Porto

  ⁽²⁾INESC TEC, Faculty of Engineeering of the University of Porto

The use of drones in 5G and beyond-5G communications has been gaining prominence in recent years, enabling new application scenarios that require an on-demand temporary network infrastructure. The ability of drones to carry 5G base stations on-board allows the implementation of a dynamic and intelligent network infrastructure that adapts to the position and traffic demands of its users. This concept is the basis of multiple scientific contributions of INESC TEC associated with research projects and PhD theses.

The current paradigm of permanent communications anywhere and anytime poses scientific and technological challenges in the planning and efficient implementation of mobile communications networks. There has been a growing need for better coverage, higher throughputs, lower latencies and greater density of connected devices. These requirements have traditionally been addressed assuming the planning of a fixed infrastructure, with a capacity scaled to support the network’s peak use, which can translate into an inefficient use of the network’s resources for most of the time. With fixed base stations, it is necessary to plan their (fixed) positioning, the antenna apertures, the radio channel configurations and the transmission power to create radio coverage cells with well-defined positions and ranges, which minimize interference with neighboring cells. With each new generation of mobile communications, there has been an increase in the offered quality of service (QoS), which has enabled the emergence and massification of new types of connected mobile services. In the case of 5G networks, they were planned to support new types of applications with more demanding throughput and latency requirements, compared to those that are possible to achieve in 4G networks. New application types include virtual / augmented reality, telepresence through holograms, telemedicine, real-time remote control of robots for search and rescue operations, among others.

However, some scenarios pose special challenges due to the unpredictability of their users or external factors, for example, emergency scenarios and spontaneous concentrations of people at events. In emergency scenarios, such as fires, earthquakes and floods, multiple teams of first responders move while fighting the emergency, and they need to communicate among themselves and with a central command station. In some cases, the existing infrastructure may not be operational due to damage caused during the emergency, which translates into a lack of mobile network coverage in those sites. Other cases may require an accurate control of search and rescue robots with low latency links and sufficient throughput for high quality video streaming. In scenarios of spontaneous concentrations of people at events, such as festivities or outdoor events – e.g.: festivity of São João, demonstrations and peregrinations –, high volumes of traffic may be generated due to live streams to social networks, video calls and multimedia content consumption. The spontaneity of the event, along with the high utilization of the mobile network’s resources and the unpredictable behavior of the crowd, may lead to the congestion of the existing infrastructure. In these unpredictable scenarios, there is a need to create an on-demand temporary network infrastructure to complement the existing one. 5G networks are the first to be planned in advance to enable the use of drones to provide or enhance wireless coverage in a myriad of scenarios. The drones are equipped with 5G base stations that forward traffic from user terminals to other 5G base stations in line of sight or using other network technologies that allow access to the operator's mobile network.

The use of drones to carry 5G base stations allows the creation of a dynamic network infrastructure, since drones can quickly move in the 3D space. The dynamic positioning ability translates into an optimization of the QoS offered to users, since the flying base stations can be repositioned over time to ensure coverage and meeting the users' QoS requirements. This QoS optimization results from the optimization of the access network – the link between the drone and the users – and the backhaul network – the link between the drone and the infrastructure. In terms of the access network, flying base stations can be positioned closer to the users that generate more traffic, in order to increase the effective network capacity in scenarios of spontaneous concentrations of people, or teams of first responders in emergency scenarios that require permanent network coverage. In terms of the backhaul network, drones can be positioned as relay nodes between users and remote base stations, enabling the establishment of a wireless link between them that overcomes existing obstacles (such as trees, buildings or mountains).

Despite the advantages of using drones to create a flying and dynamic network infrastructure, their use presents some known challenges that can be overcome depending on the application scenario. One of these challenges relates to the autonomy of drones, especially the electric ones, which is limited by the capacity / weight ratio of the batteries used both for propulsion and for powering on-board equipment. In certain scenarios, this limitation can be overcome considering that drones can land on surfaces near the users, avoiding hovering in the same position. Moreover, drones can be tethered (to a land vehicle, for example) with a cable that powers the drone, allowing permanent flight with more limited mobility. Finally, current legislation limits the use of drones, namely by prohibiting flying over crowds. In the latter, directional antennas can be used to cover areas around the drone more effectively, thus avoiding flying over people.

In conclusion, the ability of drones to create an on-demand network infrastructure to provide or enhance 5G mobile network coverage, which dynamically and intelligently adapts to the needs and requirements of its users, has established itself as a novel concept with applications in multiple sectors of the modern society. The scientific, technological and legislative challenges associated with the use of this equipment create multiple research opportunities to develop novel solutions that are more efficient, safer and greener, with the ability to meet the requirements of current and future generations.