The unmanned autonomous vehicle (UAV) industry is preparing for a new era in which drones can operate outside an operator’s view. This will open opportunities for emergency response, minerals exploration, and infrastructure inspection. A key challenge is the scaling of communication networks. Today all drones need to be in the wireless range of a nearby transmitter or rely on a slower and more expensive satellite link.
Now researchers at the Autonomous Robotics Research Center of the Technology Innovation Institute have found a way to dynamically extend the range of 5G networks for drones. The core idea is to develop dynamic routing protocols to relay communication signals between remote drones, intermediate drones, and a base station. As the drones move around, the new algorithms dynamically finetune the network connections between the drones and the base station. This will make it possible to deploy a network of drones to monitor areas that may not have direct 5G coverage, for tasks such as monitoring a fire in a remote location.
The automotive industry has been exploring a similar concept called vehicle-to-vehicle (V2V) communication to allow cars to communicate about speed, lanes, related changes, and pedestrians. This is called sidelink communication as it connects one vehicle to another rather than up to a base station or down to a phone. But the vehicles can only move in two dimensions on roads.
In contrast, drones can move in three dimensions in any direction, so the routes between them change much more quickly. As the distance between drones changes, the new algorithm automatically finds the best route between drones at the edge and the base station every few seconds. This new technique is called UAV-to-Everything (U2X) since it allows each drone to communicate with the others in the swarm and the broader Internet via the base station. In the long run, the new techniques promise to lower costs and expand the range for managing drone fleets.
TII Associate Researcher Debashisha Mishra, said: “This sidelink technology has already been standardized and investigated for the automotive industry to avoid collisions and pedestrians. Our work is the first to envision how we might use sidelinks for drones.”
Extending the range
Today, there are three primary ways to communicate between drones in the field and operators: Wi-Fi, satellite networks, and mobile networks. Wi-Fi networks are the most cost-effective since they can take advantage of the unlicensed spectrum. However, they have a limited range compared to other kinds of networks and are susceptible to interference from other wireless spectrum users. Satellite networks have much better coverage but are much more expensive, particularly bandwidth-intensive like remote video monitoring.
Mobile networks sit in the middle because they have a better range than Wi-Fi and cost considerably less than satellite networks. In addition, mobile operators manage the licensed wireless spectrum to minimize interference. However, mobile networks today only work within the range of an expensive base station. This is where the new technology comes into play. It uses drones to relay signals over longer ranges or around obstacles by communicating between the multiple drones and the base station.
Another issue is the type of network architecture. Researchers have been exploring mesh networks or peer-to-peer networks that allow each device to communicate with any other over a dynamically connected network. But mobile operators have been reluctant to enable consumers and even enterprise customers to use their licensed spectrum to form the links between devices. The main concern is that the devices might interfere with base stations without tight controls. The alternative is to use unlicensed spectrum, but these may suffer interference from other devices on the network.
This new U2X approach works with the main mobile network to ensure communication between the drones and the mobile base station. This allows the drones to use a licensed spectrum in coordination with mobile network operators to improve the quality of service for the drones without creating new issues for the other mobile users of the network.
Positioning and scheduling
Mishra said there are two main challenges with setting up this new approach – the positioning of the drones and scheduling the radio transmissions. On the positioning side, they must ensure the drone swarm maintains a chain of connections to the base station. If one drone needs to break the chain, then the other drones move to complete that chain or form a separate chain to the base station. A team of researchers at the University of Bologna previously published research on coordinating the location of drones.
So, the TII team decided to focus on the scheduling aspect. At any given time, there may be multiple drones all trying to communicate simultaneously. The scheduling algorithm helps the drones negotiate to either talk between each other’s pauses or use different frequencies.
The team started with the Consensus Based-Bundle Algorithm, (CBBA) which was previously developed to help several drones, robots, and software agents bid for the resources to execute a given task. In this case, the resource is the wireless spectrum. CBBA does a good job when the resulting allocation of resources is relatively static. But in the case of drones moving around, their changing location also affects the wireless spectrum. So the TII team created a new protocol called Dynamic CBBA (D-CBBA), which allows the drones to renegotiate the best routes as their location changes.
“We want them to maintain a non-overlapping way of transmitting so they don’t interfere with one other,” Mishra said. They also developed a simulation to test the protocol on different numbers of drones communicating across different ranges. Mishra said the technique seemed to work well for 10-20 drones operating within about 10-20 km of a base station. This is sufficient for the most common use cases. Communication overhead became a more substantial issue with a higher number of drones.
The simulations allowed the team to optimize the algorithms. Mishra said the next step is to build a research prototype with actual drones to conduct field tests on the concepts. They also want to carry out more research on the time-varying nature of drone communication links. As the drones move around, some new links are created while others are destroyed over the course of minutes or even seconds. Better models will help the drones adapt at a faster rate.
Some of these concepts are already used in drone communications via proprietary protocols, such as military applications. Mishra said developing the appropriate APIs and building low-cost hardware to use the new approach with commercial mobile networks may take some time. He expects this new approach to be widely used in 2030, which is also when the first 6G networks are expected to emerge. There is still more work to address all the issues in mapping the sidelink connections. Mishra said, “We hope this will be a starting point that could inspire other research in this area.”