An Initial Assessment of VDES ASM Channel Performance

Abstract

The volume of marine vessels using the Automatic Identification System (AIS) has been increasing since its inception in 2000. This increase is resulting in overloading of the two channels that carry the AIS transmissions. In response to this overloading of AIS, international organizations like the International Telecommunication Union (ITU), the International Maritime Organization (IMO), and the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) are developing the next generation AIS – called Very High Frequency (VHF) Data Exchange System (VDES). VDES is a technological concept utilizing terrestrial and satellite radio communication links in the VHF maritime mobile band to facilitate globally interoperable digital data exchange between ships, between ships and shore, between shore and ships, between ships and satellites, and between satellites and ships. It will increase the number of channels available for the exchange of safety and navigation information. The U.S. Coast Guard (USCG) Research & Development Center (RDC) is researching VDES to assess the suitability for implementation. To support VDES research, RDC developed a technology road map and plans to perform two field tests. The first field test was conducted in the New London, CT area from June – Sep 2021 and focused on the transmission of Sensitive but Unclassified Tactical Information Exchange and Display System (STEDS) messages using VDES Application Specific Message (ASM) channels. STEDS is presently implemented by the USCG on AIS channels. This project intends to assess the potential of transitioning this traffic to the ASM channels in the future. This test included shore side transceivers installed at RDC in New London and on Fishers Island, NY. Mobile transceivers were installed on several vessels. Position reports were transmitted from the vessels and received by the shore stations; Target of Interest (TOI) messages were sent from shore to ship. Transmissions were sent on both AIS and ASM channels for comparison purposes. Data was collected at all locations during normal operations and also on some directed routes and later analyzed to assess the performance of the ASM channels as compared to the AIS channels (primarily effective range and message reception percentage). This paper provides a primer on VDES and technical description of the ASM component of VDES as currently defined in the International standards, describes the test configuration and plan, presents the data collected, and the preliminary results of our analysis. The second field test (not reported in this paper) is planned for 2022, with the goal to continue the assessment of the performance of VDES (including the larger bandwidth VDES-terrestrial channels) and to identify issues that need to be resolved for potential operational implementation. These issues include how to manage the bulletin boards and channel management between adjacent base stations with overlapping coverage, including those on International borders.