VDE-Terrestrial Channel Performance Assessment

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 performed two field tests. The first field test was conducted in the New London, CT area from June – September 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. The results of Field Test 1 indicated that there are no technical obstacles to transitioning USCG STEDS traffic from AIS to ASM channels. The performance of the ASM channels with Forward Error Correction (FEC) is equivalent to that of the AIS channels. The second field test was also conducted in the New London, CT area with data collection from August – December 2022. The focus of the second test was to assess the performance of the VHF Data Exchange (VDE) terrestrial higher bandwidth channels and determine if it could meet USCG communications needs, both for internal (USCG to USCG) and for external (USCG to maritime public) communications. The test included an evaluation of the state of the market and interoperability of equipment from multiple venders. The results of the testing show that while the VDE high bandwidth channel can be used for moving larger amounts of data (such as generic files or small pictures) the range is less than that of the AIS and ASM channels. Additional research needs to be done to determine if this reduction in range on the VDE channels is associated with implementing the standard in VDES equipment or is a function of the system design itself. This paper discusses the testing and results and addresses future work plans such as SAR pattern transmission and VDES ranging mode.