Sea Technology

JUL 2018

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Navigation

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26 ST | July 2018 www.sea-technology.com GMDSS communications, including distress, urgency and safety-related messages. Therefore, the VDES appli- cations need to be uniquely identified and operated in a manner that ensures there is no unnecessary repetition of messaging to avoid data collisions and channel con- gestion. In order to assist the end-users in identifying possible options for the implementation of the VDES, a number of potential scenarios have been developed by IALA, in line with e-navigation MSPs. These scenarios include: SAR communications, maritime safety information, ship reporting, vessel traffic services (VTS), charts and publi- cations, route exchange and logistics. The VDES could use both addressed and broadcast communications to support SAR response, as an alterna- tive to GMDSS communications. After the implementa- tion, the VDES satellite component (VDES‐SAT) may be an effective means to extend the VDES to areas outside the coastal VHF coverage. The VDES‐SAT may deliver in- formation in a broadcast, multicast or unicast mode to a wide area, addressing many ships using only minimal radio spectrum resources (max 150 kHz). As a communi- cations medium, the VDES may be used to relay distress alerts and locating signals (SART, EPIRB, MOB, etc.). Ad- ditionally, the VDES can be used in SAR planning, execu- tion and decision making. Information regarding the safety of navigation and protection of the environment can be transmitted through the VDES. In addition, safety-related information could use the broadcast aspect of the VDES, both terrestrial and satellite, such as meteorological and hydrographical information. This also includes the ability to send infor- mation to a predetermined area or an area of particular interest. Ship reporting may include mandatory and voluntary reports required for a number of purposes by vessels to various shore authorities. Information forwarded through the VDES may transfer the reports for integration into na- tional and/or regional systems. The information may also be sent to the ship agent, owner, service provider or VTS. This ship reporting could use the addressed aspect of the VDES. The VDES could be used to monitor vessels and au- tonomously provide information to these vessels based on the predetermined parameters as defined by the shore authority. Additionally, the VDES could be used for the provision of VTS information services (IS), navigational assistance services (NAS) and traffic organization ser- vices (TOS). The provision of the up-to-date and adequate informa- tion on charts and publications could use the addressed uplinks, and the SAT downlink (single or merged chan- nels 2024, 2084, 2025, 2085, 2026 and 2086) is used for satellite-to-ship VDE downlinks. VDES Technical Characteristics The ASM should be capable of receiving on two parallel channels and transmitting on two independent channels using different time division multiple access (TDMA) schemes depending on the application and mode of operation, using the same principle as in AIS. Two separate TDMA receiving processes should be used to simultaneously receive on two independent frequen- cy channels, and one TDMA transmitter may be used to enable TDMA transmissions on one of two independent frequency channels. The modulation scheme for digital transmission is π/4 quadrature phase-shift keying (QPSK) with the transmission bit rate of 19.2 kbit/s. The mod- ulation technique and transmission bit rate provide the transmission of 512 bits in one time slot, which is defined as in the AIS (26.67 ms). The data transmissions for the purpose of the VDE are made within the spectrum allocated for the VDE1-A and VDE1-B. The spectrum may be used as 25-, 50- or 100-kHz channels. As for the ASM, the VDE uses TDMA techniques in a synchronized manner for the channel accessing. Moreover, the VDE uses adaptive modulation and coding to maximize spectral efficiency and through- put, i.e., the data rate. The modulation schemes are π/4 QPSK, 8-PSK and 16-quadrature amplitude modulation (QAM), which could be used on 25-, 50- and 100-kHz channels. When using π/4 QPSK modulation technique, the transmission bit rate on the 25-kHz channel is 38.4 kbit/s. While using the 8-PSK and 16-QAM modulation, the transmission bit rate on the 25-kHz channel is 57.6 kbit/s and 76.8 kbit/s, respectively. When using the same modulations on 50- and 100-kHz channels, the transmis- sion bit rate is doubled and quadrupled, respectively. The channels for the satellite link were introduced in the ITU's recommendation, but they were not accepted and established at WRC-15. It was only resolved to con- sider modifications of the Radio Regulations, including new spectrum allocations to the maritime mobile-satel- lite service to enable a new VDES satellite component, while ensuring that this component will not degrade the current terrestrial VDES components, ASM and AIS op- erations and not impose any additional constraints on existing services in these and adjacent frequency bands. Possible VDES Applications The VDES operates within the existing AIS environ- ment, simultaneously supporting requirements for the "Information regarding the safety of navigation and protection of the environment can be transmitted through the VDES. In addition, safety-related information could use the broadcast aspect of the VDES, both terrestrial and satellite, such as meteorological and hydrographical information."

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