Phase estimation for navigation purposes in maritime environments

Abstract

Trading in the modern world strongly depends on merchant shipping. The ongoing globalization is accompanied with an increasing vessel sizes and traffic density in ecological and economical sensitive areas. To prevent collisions and groundings Global Navigation Satellite Systems (GNSS) are used today as the primary source for position, navigation and timing information. Because of GNSS vulnerability the maritime world is looking for a backup system. R(anging)-Mode, a new system which utilizes existing maritime signals of opportunity is one candidate to provide absolute positioning and timing. Currently a R-Mode reference implementation on maritime radio beacons, which operate in the 300 kHz band, is broadcasted. Here, the legacy signal-, Minimum Shift Keying (MSK) modulated information, is extended by two continuous wave (CW) signals. The paper shows how the phase is estimated using time synchronous measurements of a Software Defined Radio with external time synchronization. In the first part the measurement setup is described, with special attention given to time synchronization using a GNSS stabilized rubidium clock, which is a key factor for good estimation results. Furthermore, a maximum likelihood estimator of the phase and a Hilbert transform based estimator are introduced. In the end the outcome is presented when applying these methods on recorded signals from German radio beacons located in Helgoland and Zeven.