Cooperative localization based on the azimuth angles among multiple UAVs

In view of the potentials and benefits of using unmanned aerial vehicles (UAVs) in civil and surveillance applications, such as forest fire monitoring and fighting, earthquake and natural disasters monitoring and sensing etc., the cooperative flight of multiple UAVs has been paid more and more attention. Among the applications of multiple UAVs in cooperative flight, fault-tolerant cooperative localization against global positioning system (GPS) signal loss due to GPS receiver malfunction is one of key techniques for various practical applications. The current research on fault-tolerant cooperative localization of UAVs is mainly based on the distance between UAVs. However, cooperative localization based on the azimuth angles between UAVs has not been generally researched so far. This paper aims to solve the problem of fault-tolerant cooperative localization of UAVs by introducing the azimuth angles between UAVs. Firstly, the basic localization model is established and the formulas of localization in two and three dimensional coordinate systems are derived. Then the optimal reference planes are chosen with the principle of minimum horizontal dilution of positioning (HDOP). Kalman filter is applied to decrease the influence of observation errors on localization. Kalman filter and extended Kalman filter are designed against linear and non-linear systems, respectively. Finally, the simulation results indicate that the cooperative localization based on the azimuth angles achieves high localization accuracy.