The VHF data exchange system

Abstract

The VHF Data Exchange System (VDES) is potentially one of the key elements supporting the International Maritime Organisation (IMO) concept of e-Navigation. Work is currently being undertaken within the International Association of marine aids-to-navigation and Lighthouse Authorities (IALA) and the International Telecommunication Union (ITU) to develop an international standard for VDES and secure access to radio spectrum. In 2014, a channel sounding campaign was conducted by the General Lighthouse Authorities of the United Kingdom and Ireland (GLA) and the Institute for Telecommunications Research (ITR) at the University of South Australia, which examined radio propagation conditions for all channels intended for use in ship-to-shore and shore-to-ship VDES communications. A comprehensive series of sea trials were conducted over five days, near Harwich in the United Kingdom. Five operational scenarios were examined, spanning four of the six IMO Maritime Service Portfolio area categories. System components and deployment were consistent with real world maritime use. This paper provides an overview of the VDES concept and presents results of the statistical analysis of Channel Impulse Response (CIR) data captured during the channel sounding campaign. The paper shows that, in the five environment types examined during the campaign, the channel fading can be approximated by a Rician distribution, and a set of tappeddelay line channel models is derived which can serve as a basis for waveform-level computer simulations. The integration of realistic channel models in such simulations makes it possible to assess the communication performance in different scenarios and under a range of propagation, weather and sea state conditions, replacing the need for repeated and costly sea trials during the initial system design phase. The results obtained support on-going work of the IALA eNavigation Committee to develop a comprehensive VDES channel model, based on sounding studies carried out in other parts of the world.