Analysis of GPS-Based Relative Navigation Schemes for Earth Observation Missions Relying on Cooperating Satellites

In this paper performance of Carrier-phase Differential GPS (CDGPS) for relative navigation in applications where the inter-satellite distance highly varies along the orbit is investigated. Specifically, to satisfy high accuracy requirements, a hybrid filtering approach is proposed in which a dynamic filter is combined in cascade with a kinematic one. For the dynamic filter both an Extended Kalman Filter (EKF) and an Unscented Kalman Filter (UKF) are evaluated and compared to output high-accuracy estimates of the floating values of the carrier-phase integer ambiguities. These, once extracted with the LAMBDA method, are processed in the kinematic filer to come to highly precise relative position and velocity estimates.