Unmanned Systems Technology 006 | ECA Inspector Mk2 USV | Antenna systems | Northwest UAV NW-44 | Unmanned ground vehicles | Navigation systems | Lunar X challenge

35 Remote control Wireless links are vital for remote control of an unmanned craft. Here the time delay, or latency, of the system is often an issue, and this is a function of the data rate and therefore the quality of the link. As the quality of the link falls – as a result of longer distance, changing weather conditions or multi-path reflections – so the data rate falls and the latency in a remote control system can increase. Many systems avoid using real-time control for remote piloting, and instead use sets of instructions to control the craft. This approach can be used with a much lower data rate than remote piloting, and ensures that the craft can be controlled as long as the signal is picked up by the craft. The return path from the craft to a ground station feeds back data that is used for the remote control as well as feeding back payload data such as video and sensor data. The control data can be at a lower bit rate and aggregated in the ground station to overcome the latency issues and ensure that the remote pilot has up-to-date information from the craft. If the link fails then the craft can automatically take up a holding position, usually circling at high altitude, which can allow the antenna to pick up the signal from the ground as the polarity becomes aligned. Antenna systems are also essential for fully autonomous craft, to provide the link back for high-definition video and other sensor data in real time. For ground vehicles, this sensor link back to the cloud will be vital for routing driverless cars to ease congestion and pollution by avoiding traffic problems. Polarisation The polarisation of an antenna describes the orientation of its electrical field, and it can be circular or linear, with linear polarisation usually vertical or horizontal. Polarisation is the key issue for many links with a UAV or UGV, as the quality of the link depends on how well the polarisation of the sending and receiving antennae is aligned. With linearly polarised links (either vertical to vertical or horizontal to horizontal) as a UAV banks, the antennae become mismatched and the signal strength can drop by as much as 25 dB, or about 80%. This is critical if the craft is being controlled by a remote pilot, and also impacts on data such as high-definition video being sent back. For ground vehicles the challenges are slightly different. They may have a polarisation alignment issue if the vehicle is moving over rough terrain, but the challenge is more about multi- path signals received from surrounding objects, reducing the quality of the link. This challenge of reflected and multi- path signals becomes much more significant for applications such as autonomous mining vehicles that Antenna systems | Focus Unmanned Systems Technology | February/March 2016 Antenna systems are essential for autonomous craft, to provide the link back for HD video and other sensor data in real time Polarisation relationships. Radio waves reflect, diffract, refract and scatter on their way from the transmitting antenna to the receiving antenna, and these anomalies can alter the signals’ polarisation (Courtesy of MP Antennas)