Cooperative localization of low-cost UAV using relative range measurements in multi-UAV flight

This paper investigates the fault-tolerant localization problem when the GPS receiver of one low-cost UAV in a fleet works improperly due to failure. A cooperative localization algorithm based on inter-UAV range measurements is proposed. Similar to the principle of GPS, the UAV's location in 2D horizontal plane can be determined using the relative ranges to the other three UAVs at known location in inertial coordinate system. Considering the fact that accuracy of UAV's location is worse than a positioning satellite, a Kalman filter is employed respectively on the three UAVs to estimate their locations with a constant velocity (CV) model during each computing cycle. Based on the estimations and the geometric relationship of the relative ranges, the location of UAV with GPS communication malfunction is calculated. Furthermore, in order to know well about the accuracy and statistic characteristics of calculation result, the horizontal dilution of positioning (HDOP) at length is analyzed through constructing the error equations. Taking the calculation results as observation data, another Kalman filter is applied to the UAV with malfunction, which can calculate the variance of observation noise adaptively on real-time. At last, by programming in Matlab/Simulink, a simulation example with four UAVs in a 2D scenario is shown to evaluate the effectiveness of the proposed algorithm.