Unmanned aerial vehicles (UAVs, or better known as drones) regularly make headline news. They are probably the most controversial technological invention of our time. With lighter, smaller and cheaper UAVs, almost anyone can afford one for their amusement. More popular than ever in domestic applications, such as photography, surveillance, environment monitoring or search-and-rescue, UAVs are now required to work in difficult conditions with uninterrupted communication with the ground control station. Existing commercial UAV communication solutions have limitations that stop them from being widely used. In light of this, Prof. Chih-Yung Wen, Associate Head and Professor, Department of Mechanical Engineering, and his research team developed Multiple UAVs Communication Relay System to overcome those limitations, effectively extending the range of UAV communication up to 13 times across obstacles such as mountains or tall buildings.
Problems with existing UAV communication solutions
There are two problems with existing commercial UAV communication solutions. First off, their communication range is limited to about 10 km at most. “For search-and-rescue tasks requiring a flight range beyond 10 km, the UAVs tend to lose communication with ground control due to the distance,” said Prof. Wen. The second problem has to do with terrains and obstacles that block the line of sight between the vehicle and ground control. “In missions involving densely built-up areas or mountainous locations, radio signals are often blocked by the tall mountains or buildings. Without real-time data feedback from the UAVs and control signals from ground control, such missions are likely to fail,” added Prof. Wen.
Multi-UAV system to relay signals
Prof. Wen and his research team overcame these issues by employing a multi-UAV system to relay the signals to and from ground control. Ground control only needs to maintain uninterrupted signal with one UAV, which acts as a mother vehicle and a communication hub between the son and ground control. The son drone can then double as a mother to relay the signals to and from the third UAV, and so on and so forth. The system is expandable to up to 13 UAVs, essentially extending the range of the communication from 10 km to 130 km. “This new relay system uses the intermediary UAVs as relay points to enable the thirteenth UAV to operate up to 130 km away from the ground control station. In fact, the range can even be further extended if fixed wing UAVs instead of quadcopters are used as intermediary relay hubs because of their longer range of communication to begin with,” said Prof. Wen.
Besides, Prof. Wen’s multi-UAV relay system also solved the problem of operating UAV beyond the line of sight. The intermediary UAVs can be assigned to different heights and locations to go around an obstacle. As long as a line of sight is maintained between the mother and son UAVs, the radio signals can still be passed along. “For example, to communicate with a son vehicle behind a high mountain, a mother vehicle is assigned to fly above the mountain to relay the signals to the son vehicle.”
Besides the architecture of the relay system, Prof. Wen also developed a control base software called Mini Ground Control System (MiniGCS) that runs on tablets. “Most commercial communication solutions have their mission planner software on laptop and can only monitor one UAV at one time. By running on tablets, MiniGCS makes the whole package more lightweight and flexible. It also monitors up to 13 UAVs at the same time.”
In March 2017, the Multiple UAVs Communication Relay System won a Gold Medal with the Congratulations of Jury in the 45th International Exhibition of Inventions of Geneva, Switzerland.
