Developing Resilient PNT for all Mariners

A. Grant, N. Ward, P. Williams and C. Hargreaves

Abstract:	GNSS, in particular GPS, has become the de-facto world standard for high-accuracy, high-availability radionavigation services. Its success has led to GNSS becoming ubiquitous for Positioning, Navigation and Timing (PNT) across all sectors of industry, transport, emergency services and the military. Since 2008, the General Lighthouse Authorities of the UK and Ireland (GLA) have been investigating the effect of GPS denial on vessel systems and marine Aids-to-Navigation. Trials have shown how many modern bridge systems are interconnected and have a dependence on GPS, or GPS derived information. This work, along with that of others, has led to the growing acceptance of the need for resilient PNT wherever GPS data is used for safety or critical operations, including a ship’s bridge. However, while it is recognised that resilient PNT is required, it is sometimes unclear how it can be realised. Realising resilient PNT requires a multi-faceted approach considering user requirements, available technical systems and the standardisation needed to enable its use. This paper considers these three aspects in an attempt to map what needs to happen in order to enable resilient PNT use in the maritime sector. Understanding user requirements is a difficult aspect as there are a wide range of users at sea, conducting different operations and with different regulation levels, ranging from leisure craft through to large tankers and cargo vessels. The loss of PNT data will affect all users but may have different implications or levels of risk. This paper will consider the needs of different users at a high level. The paper will consider the different technologies required to achieve resilient PNT and how best to manage the interaction of different PNT sources. The GLAs have studied several potential backup systems to augment GPS to provide reliable positioning and navigation at sea. The most promising and cost-effective of these within the GLA service area is eLoran. eLoran has the capability to meet International Maritime Organisation (IMO) standards for positioning Accuracy, Availability, Continuity and Integrity, and therefore enable the mariner to maintain operations if GPS is lost. Identifying a suitable alterative, or back up, PNT solution is only part of the problem. Modern vessels are fitted with numerous GPS receivers and data from these receivers is often distributed around the vessel, sometimes without a clear understanding of which receiver feeds which bridge system. As such, a common solution capable of being used in all of these installations is needed. The GLAs have been working with others, as part of the ACCSEAS project, to develop a prototype resilient PNT receiver. The receiver architecture is scalable in order to incorporate different alternative systems, as it is recognised eLoran may not be available in all locations and other systems may be more appropriate in different locations or depending on the operation at hand. This paper will report on the work undertaken to design, develop, build and test the prototype receiver. Ideally all GPS receivers on a vessel will be replaced, over time, with a resilient PNT receiver. However, developing a prototype receiver is only one step on the path to achieving this. The paper will conclude with a review of the current position regarding standardisation activities needed to realise resilient PNT. Standardisation is required to allow equipment to be used on vessels covered by the IMO SOLAS convention; however those outside this convention can use any equipment, and therefore resilient PNT equipment dissemination would need to be market led. It is recognised that test specifications will need to be developed and approved before any new equipment can be declared fit for use and therefore widely adopted. This work helps continue the story of resilient PNT, taking it from identifying the problems when GPS is lost and considering how to deal with it, through to developing a prototype receiver and supporting the international standards required to make resilient PNT a reality for all mariners.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	932 - 938
Cite this article:	Grant, A., Ward, N., Williams, P., Hargreaves, C., "Developing Resilient PNT for all Mariners," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 932-938.
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