Phase Locked Loop for R-Mode Navigation System

Global Satellite Navigation Systems (GNSS) have become the primary Position Navigation and Time (PNT) source in the maritime navigation domain, however natural and artificial interference may disrupt the GNSS signals causing performance degradation or service outages. In order to minimize the maritime navigational risk, a terrestrial backup system called Ranging Mode (R-Mode) is under development. Based on the signal of opportunity (SoOP) concept, the phase measurements of the medium frequency differential GNSS (MF DGNSS) signals can be exploited for positioning purposes. Among the possible techniques for phase estimation, the maximum likelihood (ML) and the discrete Fourier transform (DTFT) are currently used. Although they are suitable in a static scenario, for a dynamic one these techniques may be not the best choice since their performance are related to the observation time. In this work the phase locked loop (PLL) is considered as an alternative approach for phase estimation. The PLL design process is described and two self-interference mitigation techniques are proposed in order to improve its performance. The performance metrics are firstly assessed in a controlled simulated environment for validation, in both static and dynamic cases, and then applied on real measurement data.