Trajectory tracking and formation flight of autonomous UAVs in GPS-denied environments using onboard sensing

In GPS-denied environments like in indoor applications, location systems based on Vicon cameras, infrared cameras or UWB techniques are generally employed to provide location information of multiple mobile robots. The location systems require expensive and external equipments, which limits the applicable range of micro unmanned aerial vehicles (UAVs) in GPS-denied environments. In the paper, efficient control schemes based on onboard commodity sensors are presented for autonomous UAVs in indoor applications, where the horizontal displacement of the platform is provided by an optical flow sensor. With the aid of lightweight onboard sensors, a complete 6-degree of freedom (DOF) state of the UAV can be estimated. Control strategies are presented for low-level stabilization as well as high-level tracking and formation control. Experiments illustrate that the UAVs with onboard sensing and computation can achieve autonomous trajectory tracking and distributed formation flight based on a leader-follower scheme.