Quadrotor State Estimation With IMU and Delayed Real-Time Kinematic GPS

This article presents an estimation scheme for the six degree-of-freedom position and attitude of an aerial vehicle by integrating an inertial measurement unit (IMU) and a low-cost real-time kinematic GPS unit, which delivers a precise relative position measurement corrupted by a time-delay. Assuming that the time-delay is known, the extended Kalman filter is generalized to fuse the time-lagged position measurement from GPS with the synchronous attitude and angular velocity measurements from IMU. More specifically, it is formulated as an optimal prediction where the past state is corrected by the position measurement before being propagated up to the current time with the history of the IMU measurements. This provides a compact formulation to merge multiple sensors with varying time-delays in an optimal fashion. The efficacy of the proposed approach is illustrated by a numerical example, experimental data collected over a Navy research vessel, and an outdoor autonomous flight of a quadrotor unmanned aerial vehicle.