VDES R-Mode Test Bed in Long Island Sound

For the past few years, the U.S. Coast Guard (USCG) Research & Development Center (RDC) has been researching the Very High Frequency (VHF) Data Exchange System (VDES) to assess its suitability for implementation. 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. It is designed to alleviate overcrowding on the existing two Automatic Identification System (AIS) channels. To date, RDC has performed two field tests in the New London, CT area to assess ASM and VDES terrestrial channel performance. The results of the first Field Test 1 indicated that there are no technical obstacles to transitioning USCG Sensitive but Unclassified Tactical Information Exchange and Display System (STEDS) traffic from AIS to Application Specific Message (ASM) channels. The performance of the ASM channels with Forward Error Correction (FEC) is equivalent to that of the AIS channels. The results of the second test showed 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. VDES (using AIS, ASM and VDE channels) can also be used as a Signal of Opportunity that can be used for ranging. With sufficient signals they can be used for positioning. RDC is currently embarked on an assessment of the use of VDES Ranging Mode (R-Mode) as an Alternative Position Navigation and Timing (APNT) system. A test bed is being established in Long Island sound with multiple base stations to provide an area with triple coverage so that positioning can be tested. This paper discusses the test bed (base station sites and coverage area, mobile units, equipment) that has been established and presents some results from field testing through the summer of 2024.