Requirements for Resilient PNT

Nick Ward, Martin Bransby

Peer Reviewed

Abstract:	It is generally accepted that GNSS (GPS in the short term) will be the primary position and timing sensor for maritime navigation. The increasing availability of more than one GNSS (GPS, GLONASS, Beidou, Galileo and others) will increase resilience and integrity. However, all these systems share the same failure modes, because they use the same frequency bands and have very low power signals. Therefore true resilience will only be achieved by the use of complementary, dissimilar systems, such as radar, or low frequency, high power terrestrial systems, or autonomous on-board alternatives, such as inertial sensors. The relevant IMO Resolution (A.1046(27)) on the World Wide Radio Navigation System (WWRNS) does not distinguish between single systems that might meet the requirements by themselves and combinations of systems that might meet them together. The approach proposed in this paper is that in addition to the parameters of availability, accuracy, integrity and continuity set out in A.1046, the limitations of each system should be assessed, such as vulnerability to interference, or restricted coverage. By this means complementary systems could be selected to ensure overall resiliency is provided. This approach of considering the WWRNS as a compendium of systems fits in with the planned development by IMO of a Multi-system Receiver Performance Standard, a generic standard that will cover different systems and combinations of systems – specifying what is required, not how it should be done. Some of the alternatives can be made available in the short to medium term, in parallel with the expansion of GNSS. Some have been demonstrated to work, but would need lengthy regulatory measures to become generally applicable. Others are likely to require considerable technical development before they can be accepted as practical and economic options for maritime use. For example, eLoran is a proven system, meeting the IMO requirements for harbour entrance and port approach. However, it is not widely deployed at present. Studies have shown that ranging mode (R-mode) on DGPS beacons could provide a backup to GNSS, in areas where coverage from such beacons is good. This system has still to undergo practical testing and the necessary regulatory measures have still to be put in place. Absolute positioning using solid-state radar and enhanced radar beacons has been shown to work technically, but the regulatory process needed to implement it would be lengthy. Options such as inertial sensors require further development before they have the necessary stability, at acceptable cost, to provide a maritime backup. Other autonomous alternatives such as quantum technologies are at a very early stage of development. The proposed method can assess systems and combinations of systems, allowing the selection of complementary combinations. The various combinations of options for achieving resilience would need to take into account the different stages of development.
Published in:	Proceedings of the 2015 International Technical Meeting of The Institute of Navigation January 26 - 28, 2015 Laguna Cliffs Marriott Dana Point, California
Pages:	234 - 238
Cite this article:	Ward, Nick, Bransby, Martin, "Requirements for Resilient PNT," Proceedings of the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, California, January 2015, pp. 234-238.
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