Nonlinear observer for INS aided by time-delayed GNSS measurements: Implementation and UAV experiments

A nonlinear observer structure for estimating position, velocity and attitude in a GNSS/INS system with delayed GNSS-measurements is proposed. The structure consists of an inertial measurement data buffer, a nonlinear state observer and a fast simulator. The inertial and magnetometer measurements are synchronized and delayed to coincide in time with the GNSS-measurements. The state observer will hence estimate the delayed states, and a fast simulator is employed to recover the current states using inertial measurements. The nonlinear observer is semi-global exponentially stable. The magnitude and effect of the GNSS delay is investigated, and implementation aspect of the nonlinear observer and the fast simulator are discussed. The proposed observer structure is verified by comparison to an observer without time-synchronization through use of simulations and experimental data from a UAV flight test.