Medium frequency R-Mode range estimation with phase locked loop approach

Kurzfassung

Ranging-Mode (R-Mode) is a maritime terrestrial navigation system under development, which is supposed to support the mariner with alternative positioning and timing for coastal operations in case the performance of the primary positioning, navigation and timing (PNT) system GNSS is degraded. It uses already existing maritime radio infrastructure for the transmission of synchronized ranging signals. Under consideration are the transmitters of the Very high frequency Data Exchange System (VDES) and the marine radio beacons which are operating in the Medium Frequency (MF) band. Due to different approaches, to use the available bandwidth for the legacy services, both R-Mode implementation differ significantly. This contribution is focused on MF R-Mode. Here the ranging signal is implemented as two aiding carriers that are added in the radio channel of each R-Mode enabled radio beacon. By measuring the phase of the additional carriers, it is possible to estimate the pseudorange to the transmitter site and subsequently calculate the 2-dimensional position. The currently used implementation of MF R-Mode receivers obtain the phase of the two additional signal components based on a Maximum-Likelihood (ML) estimation technique. This approach considers the signal of a given snapshot for the estimation of the phase. Accordingly, the obtained phase is delayed which can cause a reduction of the receiver performance in dynamic scenarios. To reduce the delay of provided phase observation we investigated into the Phase Locked Loop (PLL) which is able to provide instantaneously the signal phase. An important tuning parameter for the PLL is the loop bandwidth which influences the filtering capability and the ranging accuracy. In this contribution we describe in detail our implemented PLL. We show the results of applying the PLL on simulated and real data gathered during a measurement campaign and compare it with the ML approach of phase estimation.