Contents I. Introduction
Unmanned aerial vehicles (UAVs) are aircrafts that are controlled by remote radio or an autonomous program without a human onboard. The embryonic stage of UAV can be traced back to more than 100 years ago. In the 1910s, the first automatic gyroscopic stabilizer was invented, which enabled an aircraft to keep its balance autonomously when flying forward. Thereafter, UAV technology rapidly evolved and UAVs were originally applied for military purposes, such as target drones, reconnaissance planes, and fighter aircrafts [1]. In the past few decades, the industrial chains of chips, batteries, sensors, controllers, and communications are becoming more mature. UAV platforms are gradually developing towards miniaturization and low-power consumption, which greatly reduce the manufacturing cost. With the opening of low-altitude airspace, small-scale and medium-scale drones have been increasingly used in civilian fields, including geological prospecting, disaster rescue, forest fire prevention, power grid inspection, remote sensing, aerial photography, express delivery, and agricultural irrigation. The investment scale of the UAV industries around the world has increased thirtyfold during the past 20 years [1], [2]. In the foreseeable future, the application of UAVs will become more widespread and promote the development of different kinds of linkage industries.
