Tracking Control of a Multirotor UAV in a Network Environment with Time-Varying Delay

This paper presents a practical method to estimate and control the position of an unmanned aerial vehicle (UAV) considering a network environment with time-varying delay between a server and the UAV. The network delay entails undesirable effects to the stability of the UAV control system due to mismatch of trajectory and incorrect state observation. To deal with these problems, we propose the algorithm which consists of (1) path planner, (2) uplink delay compensator, (3) UAV controller, and (4) downlink delay compensator. We apply model predictive control (MPC) based path planner to calculate the reference trajectory. Uplink delay compensator revises the reference trajectory to compensate for the network delay so that the mismatch problem is solved. The revised reference trajectory is fed to the UAV controller. It produces the predicted trajectory of the UAV and sends to the server. The downlink delay compensator estimates the UAV's state using predicted trajectory so that the incorrect estimation problem is solved. Experimental results show improved tracking performance by the proposed delay compensation.