Gregory Johnson, Kenneth Dykstra, Sophie Ordell, Serco, Inc.; Peter Swaszek, University of Rhode Island

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Abstract:

Global Navigation Satellite Systems (GNSS), especially the U.S. Global Positioning System (GPS), have become the primary Position, Navigation, and Timing (PNT) source for maritime operations. The GNSS position is used both for vessel navigation and as the position and timing source for other systems such as the Automatic Identification System (AIS). Unfortunately, it is well known that GNSS is vulnerable to jamming and interference, intentional or not, which can lead to the loss of positioning information or, even worse, to incorrect positioning information. As the user requirement is for dependable PNT information at all times, alternative and/or resilient methods of PNT are desirable. R-Mode (or Ranging Mode), which uses existing maritime radio signals as ranging sources, is one such alternative. To initiate the development of R-Mode, in 2013 the German Federal Waterways and Shipping Administration contracted for a feasibility study of R-Mode using medium frequency (MF) Differential GNSS (MF-DGNSS) and very high frequency (VHF) AIS signals as well as those signals in combination and in combination with eLoran [1]. At the ION GNSS+ 2014 some of these authors presented the results from that feasibility study and showed the potential positioning performance using the signals individually, and in combination [2]. In most of the shipping lanes on the North Sea it appeared that 10 meter or better positioning performance could be achieved. Based upon the potentials from the feasibility study, prototypes of a transmitter and receiver for MF-DGNSS R-Mode were then developed and tested in the Netherlands and Germany, and more recently in Canada. At the ION-ITM 2017, we reported details of this prototype transmitter and receiver pair, included some statistical analyses of the pseudorange estimates recorded to date [3]. Those early R-Mode trials reported in [3] were limited to signal stability studies as there were insufficient transmitters for positioning. The European Union’s R-Mode Baltic project plans to install up to nine transmitters for positioning trials in the Baltic Sea area. To further R-Mode studies on the US side of the Atlantic, in March of 2020 we conducted a demonstration of R-Mode positioning as part of the US Department of Transportation (DOT) PNT demonstration at Joint Base Cape Cod (JBCC). In this effort, three temporary MF-DGNSS R-Mode transmitter sites were established surrounding the test area at JBCC and both static and dynamic R-Mode receivers were employed; this was the first on-air live demonstration of R-Mode positioning. This paper presents current details of the prototype transmitters and receivers, results of the positioning performance achieved at this March 2020 trial, and the performance of ambiguity resolution techniques investigated.