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VHF Data Exchange System (VDES), Edition 2.0 (G1117)


Year: 2017
Language: english
Author: IALA
Format: PDF
Quality: eBook
Pages count: 29
Description: International Telecommunications Union (ITU) has recognised the efficiency and the necessity for digital
communications, has produced technical standards and has revised the VHF marine band (Radio Regulations
Appendix 18) to designate channels for data transmission. It is recognized that both analogue voice
communications and digital communications will share the band. The VDES, as envisioned by IALA and presented
to ITU, addresses the identified need to protect AIS along with essential digital communications contributions for
e‐Navigation and GMDSS Modernization.
The VHF marine band (Radio Regulations Appendix 18) was initially used for transmission of voice
communications on 25 kHz channels. The ITU introduced the first marine data transmission system, DSC (Digital
Selective Calling) to help ensure that calling and distress communications attempts were successful. VHF DSC
transmits data at 1.2 kbps, slow by modern data standards, but very robust. At the request of the IMO to
improve safety of navigation, ITU introduced another VHF data transmission system, AIS, which provides
navigation and identification data for ships, shore stations, aids to navigation and search and rescue devices at 9.6
kbps.
ITU introduced a standard3, with options for 25 kHz, 50 kHz and 100 kHz channels at data rates up to 307.2 kbps
in order to improve spectrum efficiency in 2012. Both voice and data communications coexist in the VHF marine
band. The developments in maritime radio technology, including the introduction of software defined radios
(SDR) coupled with enhanced capabilities for digital data exchange over existing VHF marine band spectrum
resulted in the development of the VHF Data Exchange System (VDES). VDES builds on the experience gained
through the development of AIS, and also provides the capability to transmit to a specific vessel (addressed); to all
units in the vicinity (broadcast); to a group of vessels (addressed); or to a fleet of vessels (addressed).

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