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This paper presents an overview of the development of a terrestrial positioning system called Ranging Mode (R-Mode) in the Southern Baltic Sea region which utilizes already existing maritime radio infrastructure. Here, an R-Mode testbed is planned to be set up until 2020 that meets maritime user needs for resilient PNT. First measurements of radio beacon signals on-board a vessel sailing in the Southern Baltic Sea show the good availability of beacon signals in this region. A comparison of received signals with a coverage prediction based on the nominal range of radio beacons shows the shortcoming of this approach and emphasizes the need for more elaborated coverage predictions which consider all effects of medium frequency wave propagation at day and night. In the measurements results the skywave has a major impact on the beacon signal stability in the night. The time stability of the signal amplitude seems to be a good indicator for disturbed reception conditions. [ABSTRACT FROM AUTHOR]

In order to enable port operations, which require an accuracy of about 10cm, the German Aerospace Center (DLR) operates the Maritime Ground Based Augmentation Service (MGBAS) in the Research Port of Rostock. The MGBAS reference station provides GPS dual frequency code + phase correction data, which are continuously transmitted via an ultra-high frequency (UHF) modem. Up to now the validation of the MGBAS was rather limited. Either a second shore based station was used as an artificial user, or measurement campaigns on a vessel with duration of a few hours have been conducted. In order to overcome this, we have installed three separate dual frequency antennas and receivers and a UHF modem on the Stena Line ferry vessel Mecklenburg-Vorpommern which is plying between Rostock and Trelleborg. This paper concentrates on the analysis of the highly accurate phase based positioning with a Real Time Kinematic (RTK) algorithm, using correction data received by the UHF modem onboard the vessel. We analyzed the availability and accuracy of RTK fix solutions for several days, whenever the ferry vessel was inside the service area of the MGBAS. [ABSTRACT FROM AUTHOR]

Time delays caused by ground wave propagation are the primary source of systematic error limiting the performance of the medium-frequency R-Mode radionavigation system. To achieve the desired ranging accuracy and compensate these delays, we have conceived a comprehensive correction scheme based on the prediction and application of the Atmospheric and Ground wave Delay Factor (AGDF). The AGDF was computed and mapped in 2D for a number of MF R-Mode transmitters in the Baltic Sea that were embedded into the receiver and evaluated during a large-scale measurement campaign. Our results show that the proposed AGDF approach is valid for the MF R-Mode system and provides accurate corrections of ground wave propagation delays within the performance requirements.

Currently Global Navigation Satellite Systems (GNSSs) are the primary source for the determination of absolute position, navigation, and time (PNT) for merchant vessel navigation. Nevertheless, the performance of GNSSs can strongly degrade due to space weather events, jamming, and spoofing. Especially the increasing availability and adoption of low cost jammers lead to the question of how a continuous provision of PNT data can be realized in the vicinity of these devices. In general, three possible solutions for that challenge can be seen: (i) a jamming-resistant GNSS receiver; (ii) the usage of a terrestrial backup system; or (iii) the integration of GNSS with other onboard navigation sensors such as a speed log, a gyrocompass, and inertial sensors (inertial measurement unit-IMU). The present paper focuses on the third option by augmenting a classical IMU/GNSS sensor fusion scheme with a Doppler velocity log. Although the benefits of integrated IMU/GNSS navigation system have been already demonstrated for marine applications, a performance evaluation of such a multi-sensor system under real jamming conditions on a vessel seems to be still missing. The paper evaluates both loosely and tightly coupled fusion strategies implemented using an unscented Kalman filter (UKF). The performance of the proposed scheme is evaluated using the civilian maritime jamming testbed in the Baltic Sea.