Remote controlling field robots becomes difficult when the robots go beyond obstacles, such as thick walls, buildings, forests, or mountains, due to the loss of line-of-sight radio propagation. Telemetry signals also get lost for this reason.
Conventional approaches have employed ad-hoc and multi-hop communication techniques in order to cope with the above problem, where a relay route via other robots helps to avoid disconnection from the target robot. However, the technique was originally designed for wireless Internet, which is not well-suited for robot control, since the control stops every time the relay route changes whenever the control link is momentarily disconnected.
However, a team of researchers from Japan’s National Institute of Advanced Industrial Science and Technology (AIST) has developed a layer 2-based wireless relay communication technology for the command/control and telemetry signals of remotely-operated target robots which are out of line-of-sight via other robots.
The technology enables continuous operation of a robot out of the line-of-sight with simultaneous and redundant transmission of command/control and telemetry signals via multiple relay routes through other robots. The team reconstructed the communication scheme from conventional ones such as that of wireless LAN before creating a new one dedicated to robot control on a relay transmission basis.
The new scheme also employs a time-division multiple access (TDMA) control protocol to share the communication media among different robot terminals with small response latency and low packet collision probability, resulting in an efficient use of time and constant freshness of command/control and telemetry data.
Conventional communication schemes designed for Internet access run searches and calculations to select the best relay route to transmit data, assuming unspecified relay nodes with small mobility. The new scheme removes the above procedures and implements a simplified procedure in layer 2, where the target robot receives the command/control and telemetry data via all of the possible routes with different TDMA slots, assuming a small number of specified relay nodes with high mobility. The target robot then simply selects the signal with the best quality among those signals.
With this technique, the response latency through one relay robot has been improved to about 50 msec, compared to that of conventional schemes, the latency of which varies from 10s to 100s of milliseconds depending on the communication traffic conditions. The technology also enables continuity of relay connection even with the frequent and random change of the relay route due to the movement of the robot, allowing operators to avoid momentary disconnection of the control link and ensure the stability of the control of the target robot.
Researchers from AIST and Japan’s National Institute of Information and Communications Technology (NICT) successfully demonstrated the validity of this technology by controlling an unmanned ground vehicle (UGV) in operation beyond the line-of-sight. A multi-rotor drone hovering at an altitude of 20-30m served as an aerial relay robot to connect the UGV to its operator.
In the demo, the target robot to be controlled was a slow-moving UGV. In the next demo, the team will try to replace the UGV with a multi-rotor drone that moves much faster.
This technology would be useful not only for robots in operation inside or close to buildings in disaster situations or in security applications, but also for aerial robots flying at low altitudes for monitoring or transportation in mountain areas. It could also be the basis for the deployment of a cooperative and autonomous wireless network with multiple robots to make wireless robot control safer and more reliable.
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