EM Manifold Estimation of GNSS Synchronization Parameters Under Constant Modulus Interference

Global Navigation Satellite Systems (GNSS) rely on estimating the signal propagation delay and Doppler shift to a set of visible satellites, which in turn allows to determine the receiver position, velocity and timing. However, the presence of interfering signals degrades the estimation of such synchronization parameters, reason why robust solutions must be accounted for. Considering constant modulus (CM) interferences, which include chirp and continuous wave signals, a recent solution proposed an expectation-maximization (EM) algorithm to estimate both interference and signal parameters, which relies on the von Mises distribution to exploit the interference CM property. In this contribution, we exploit the geometric properties of the CM family using a Riemannian framework, where CM interferences are modeled as a Riemannian manifold. This modeling allows the E-step of the EM algorithm to be replaced by a Riemannian gradient descent over that manifold. Results show that the proposed method improves the estimation performance and reduces the complexity compared to the classical EM approach.