The last 25 years have seen a huge advance in Unmanned Aerial Vehicles (UAVs), popularly known as drones. SESAR, the European Union’s Digital Sky technology pillar, has given a figure for the future: 400 000 commercial and government drones will be flying over European airspace by 2035, but there could be more.
If we calculate, to make an estimate, that there will be one drone every 10 km², in Spain there will be 50,000 more or less. And they will fly, if legislation does not change, at less than 150 metres above the ground.
Unmanned aerial vehicles (UAVs) can be fixed-wing or multi-rotor. They started as teleoperated vehicles and have become increasingly sophisticated. Autopilots, which automatically execute the flight path determined by an operator, now exist.
The established trajectory is sent via a radio link to the UAV and the UAV executes it, periodically sending its position data to the station. Today, however, to ensure that everything runs smoothly and that control is not lost, the operator must keep the UAV in sight.
This way of control is currently the most widely used, but it presents a large number of complications, and it is essential to resolve them in view of the increase in the number of vehicles that will populate our airspace.
On the one hand, the automatic planning of trajectories is complicated in complex environments, such as cities, areas with difficult terrain, high obstacles, etc. On the other hand, the short range of the communications used means that control of the UAV can be lost beyond a certain distance. There is an additional problem, and that is the need for one operator per drone.
An additional weakness is that each UAV is planned, operated and controlled individually without taking into account other vehicles in the area.
Flying with more drones closer
When the number of UAVs increases, control becomes more complicated. Considering that the drone will fly in a complex environment, where there may be high buildings and the operator supervising the UAV cannot maintain visual contact with the vehicle, it is necessary to automatically plan flight trajectories, coordinate them with other drones nearby and monitor their correct execution to avoid potential conflicts between aerial vehicles that could lead to accidents.
This is the context of the European H2020 project, Labyrinth. It addresses the automatic planning and control of multiple UAVs flying at the same time, ensuring the safety of civil transport in ports, roads, airports and for emergency support.
The perfect choreography
In these limited environments, planning is carried out for each set of UAVs. We determine the flight trajectories, which include not only the spatial positions (longitude, latitude and height above ground) but also the time in which they must pass each designated point.
The planning of these trajectories must avoid obstacles on the ground. It should be borne in mind that current legislation limits the maximum height above ground at which the vehicle can fly, which is less than 150 metres.
In the case of non-urban or industrial environments or urban areas of single-family homes, this is not a big problem, but in the case of large cities it is a major difficulty, as many buildings exceed 20 storeys (65 or 70 metres high) and in many cases there are skyscrapers that reach heights of 150 metres or more.
3D maps of each flight zone
In complex environments, planners need to use three-dimensional maps of the area they are going to fly over. These are obtained from Lidar maps or similar ones, provided by the Geographical Institutes in each country.
These maps can be converted into 3D spatial occupancy maps, which indicate for a certain spatial cell (a cube of given height, width and depth) whether that space can be crossed or not. With this information it is possible to determine safe three-dimensional trajectories, in which UAVs avoid obstacles.
Communication with the UAV must be immediate
A second difficulty is the need to keep all UAVs identified and receive information on their status during flight. Its exact position, speed, orientation, and other parameters must be known at all times. This is necessary to determine whether it is executing the trajectory correctly without significant deviations from the planned trajectory both spatially and temporally.
This requires a fast, secure and powerful communications system.
Traditionally, dedicated radio frequency links are used, but this, which is reasonable for a single UAV, is not feasible for a large number of UAVs in flight at the same time. The trend is for communications to be made using 5G mobile phone networks. This sends flight routes, UAV status information and environmental data that the UAV collects with its sensors.
Preventing in-flight hacks
This brings us to the third problem, which is the need to maintain the entire UAV traffic control and management system with a level of security that prevents unwanted intrusions into the system, what means, cybersecurity of the system.
The systems are starting to be tested in limited and controlled environments: ports, airports, agricultural and industrial areas. Once it has been proven to work, its use will be extended to other areas, including the city.
Thus, it is foreseeable that we will gradually begin to see an increase in the number of UAVs operating in our skies. In any case, their incorporation into our daily lives is something that will undoubtedly happen.
The complete article in The Conversation Spain (it is written in Spanish)