State of the Art in Low Frequency (LF) Technology for Alternative Positioning, Navigation, Timing, and Data (APNT&D) (2011)

Many government and civilian organizations around the world are studying the problem of what to do when Global Navigation Satellite System (GNSS) based services are unavailable to provide Positioning, Navigation, Timing, and Data (PNT&D) information to public and private sector users. There is a general concern about the over-reliance on GNSS which is susceptible to degradation, outages, and unavailability, whether intentional or unintentional, and which operates in many cases without an additional system to provide Position, Navigation and Time (PNT) information for validation and backup. Two examples are given below. In May 2010, the International Civil Aviation Organization (ICAO) Navigation Systems Panel (NSP) working group developed a flimsy documenting “work being accomplished by the U.S. Federal Aviation Administration (FAA) to assess alternatives for providing PNT services when GNSS is not available due to RFI” [1]. During an FAA APNT public meeting in August 2010, UrsaNav and Nautel recommended the FAA consider a Low-Frequency (LF) Alternative Positioning, Navigation, and Timing (APNT) solution to maintain safety and minimize economic impacts from GNSS interference outages [2]. During the 49th International Association of Marine Aids to Navigation and Lighthouse Authority (IALA) Council Meeting, a side question was directed to Industrial Members as to what industry is working on or thinking about regarding the ever increasing reliance on GNSS-based navigation systems. There is a growing concern in the marine community that mariners are losing the basic knowledge and skills needed to navigate by other means and becoming too reliant on satellite technologies. It was noted that coastal navigation maintains traditional aids to navigation, such as, buoys, beacons, and racons, but with the planned removal of some Loran stations and other longer range systems, there is a lack of redundant aids for deep sea navigation [3]. The council recommended that “IALA should encourage the development of a global redundant system, or combination of systems, independent and dissimilar to GNSS, to facilitate e-Navigation” [4]. These concerns are causing organizations and countries to look for alternative solutions, and some countries have announced their strategy publicly. The Republic of Korea, has announced during the 51st IALA Council Meeting in Rio de Janeiro, in 2011, that it will deploy eLoran. This might prove to be a significant accelerator for the deployment of eLoran in other areas around the globe. This paper updates our earlier paper [5] with the results of recent tests and new insights. We concluded earlier that our solutions provide low-cost alternatives that lessen the dependence on GNSS, and meet the stringent requirements for Harbor Entrance and Approach (HEA) and ICAO FAA Working Group on Alternative PNT. We now show an independent verification that our LF solutions also provide timing to users with a performance that exceeds the requirements for Primary Reference Clocks (PRCs), as set by the International Telecommunication Union (ITU), and a quantification of the performance improvement of our new transmitter technology compared to existing technologies. Because our solutions are built upon state-of-the-art technology, they offer improved performance with more flexibility and newer capabilities over existing installations. They can easily and economically be installed world-wide, either by re-using existing infrastructure, complementing it with new installations, or deploying a temporary service using transportable installations.