Autonomous drones, as a rule, rely on visual signals to accurately determine the location of landing sites or other landmarks. However, what happens when the street is dark, rainy, or foggy, and there is no ground-based power source for lighting? This is where the Millisign system comes to the rescue.
The Millisign system, developed by scientists from the Japanese Corporation NTT and Tokyo University, utilizes enlarged versions of RFID marks (identification by radio frequencies) commonly found on many products. In a typical system, the RFID wireless label is powered temporarily by a radio signal emitted by the RFID reader. The label then transmits a modified signal back to the reader using an integrated antenna.
In the Millisign system, a small drone equipped with a millimeter-range radar replaces a manual reader. When the drone’s radar emits a radio signal received by one of the large labels on the landing site, the label sends a return signal back to the drone. This signal indicates the location of the tags/sites relative to the drone. As a result, the drone can determine the location without visual sight – the more intense the signal received, the closer the drone is to its destination.
Millisign marks can not only be used for landing sites but also serve as navigation beacons along the drone delivery route.
It is noteworthy that Millisign tags include angular reflectors, enabling them to send and receive signals in a wide three-dimensional cone. The current version of the label, sized at 292 x 600 mm, can be read by an aerial drone at a distance of 10-15 meters.
However, one may wonder why drones do not simply utilize GPS. Tatsuya Iizuka, an engineer involved in NTT studies, explains, “When considering the landing scenario using GPS, two GPS modules on the UAV and the landing port are required to obtain relative positions, as well as the communication channel between them, which entails high costs for installation and maintenance.”