LEO Satellites/INS Integrated Positioning Framework Considering Orbit Errors Based on FKF

In the global navigation satellite system (GNSS) denial environment, positioning can be achieved by utilizing opportunistic signals from noncooperative low Earth orbit (LEO) satellites. Combining LEO satellites with inertial navigation systems (INSs) can improve the availability of positioning. However, due to limitations in the visibility and orbital configuration of LEO satellites, the fault recovery capability is poor. In addition, the current strategy to obtain orbit parameters of LEO satellites imposes significant tangential position errors. All of these factors collectively restrict the accuracy of positioning. Hence, this article first considers the characteristics of the orbit and proposes a generalized Doppler measurement model based on equivalent emission time error (EETE), effectively reducing the influence of orbit errors and decreasing the state dimension. Then, a LEO satellites/INS integrated positioning framework based on adaptive federated Kalman filter (AFKF) is proposed, which exhibits strong fault tolerance. Besides, a mathematical model between the EETE error and the equivalent observed Doppler (EOD) error is established, providing a theoretical basis for positioning error evaluation. Vehicular experiments using real Iridium and Orbcomm signals demonstrated that the proposed framework significantly improves the positioning accuracy. Hence, this study provides an effective and reliable LEO satellites/INS integrated positioning method.