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Modern communications basics

Updated 11 Oct 2019

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The growing importance of VSAT in marine communications underlines the fact that despite its conservative image, shipping has always been at the forefront of adopting the best means of communication possible.

Obviously technological change is only adopted once it has reached a stage where it can meet the unique demands of the maritime industry and in particular prove its reliability and robustness under the harshest of conditions. Few ship operators or their crews are concerned with the high science and engineering of the satellites themselves, but they do need to understand the fundamentals of satellite communications and the radio spectrum.

In essence, a satellite is an intermediate device that enables transmission of data to a ship or receiving data from a ship regardless of the different positions on the surface of the globe of the two parties. The other party can be a shore office or another ship.

All satellites make use of a beam, which is a pattern of electromagnetic waves transmitted by the satellite. The transmission from a satellite has a defined pattern and the beam can be wide or narrow covering a large or small area on earth. Using a system of varying frequencies and alignment of antennas onboard the satellite, each satellite can have several beams within which all or most of the satellite’s power is concentrated.

The antennae on the ship are rarely stationary due to the constant movement of the vessel when under way and thus require the dish to be mobile in all dimensions. The dish itself is hidden from view by the radome cover but viewed up close they are sophisticated pieces of equipment with motors and gearing enabling the dish to maintain a lock on the satellite under all but the harshest conditions.

Most ships’ communication systems are required to share channels with others, which is perfectly fine for simple communication needs but highly inefficient when dealing with the large quantities of data that some operators generate. This can be overcome by making use of a very small aperture terminal (VSAT) service. Subscribers to VSAT services are provided with exclusive or semi-exclusive use of satellite channels for sending and receiving voice and data at broadband speeds.

Usually they are charged for this on a monthly fixed fee subscription basis (although there may be limits on the data allowed before extra charges apply) as opposed to the rate per Mbit charged when using basic services. This enables a network to be created that permits the transmission of large quantities of data.

Not all ship types or fleet managers need large data flows for commercial reasons but passenger, offshore and container operations frequently do. For passenger vessels this will involve allowing passengers to use computers, tablets and smart phones as well as providing entertainment services. In the offshore industry it enables survey and other data to be transmitted at will and for container ships there is a need for large amounts of data for stowage plans and customer services.

Early satellite history

As far as shipping is concerned, the satellite communications era began with the establishment in the 1970s of Inmarsat, a not-for profit international organisation, set up at the behest of the IMO to provide a satellite communications network for the maritime community. Initially the service was used purely for commercial purposes allowing voice and telex communication with ships at sea equipped with an Inmarsat A terminal.

Without the advent of GMDSS and the mandatory requirement for most ships to be fitted with at least an Inmarsat C terminal, it is doubtful if the marine satellite communications sector would have expanded at anything like the rate it has. By having an Inmarsat terminal on board, ships immediately gained e-mail as a new method of communication.

Early Inmarsat services were described by an alphabetical reference being Inmarsat A, B, C, D and E. When the letter F was reached, the service was renamed Fleet followed by a number (33, 55 or 77) indicating the size of the antenna in centimetres.

Inmarsat A was the original Inmarsat service and offered analogue FM voice and telex services and, optionally, high speed data services at 56 or 64kbit/s. The service was withdrawn at the end of 2007.

Inmarsat B provides voice services, telex services, medium speed fax/data services at .6 kbit/s and high speed data services at 56, 64 or 128kbit/s. Inmarsat C is effectively a ‘satellite telex’ terminal with store-and-forward, polling etc. it can handle data and messages up to 32kb in length, transmitted in data packets in ship-to-shore, shore-to-ship and ship-to-ship directions. The message length for Inmarsat Mini C terminals may be smaller. Certain models of Inmarsat C terminals with GPS are also approved for GMDSS use.

Inmarsat D/D+ is a paging service, not regularly used on ships.

Inmarsat E was a global maritime distress alerting service using small EPIRBs that automatically relayed distress messages to maritime Rescue Coordination Centres. This service has been withdrawn.

Inmarsat Fleet 77 offers voice and the choice of mobile ISDN up to 64 kbit/s or an always-on Mobile Packet Data Services (MPDS) for cost effective, virtually global communications. Fleet 77 also meets the distress and safety specifications of the GMDSS for voice communication.

Inmarsat Fleet Broadband was introduced in 2006 when the first of Inmarsat’s i-4 satellites went into service. It offers a shared-channel IP packet switched service of up to 492kbit/s and a streaming-IP service from 32 up to X-Stream data rate. X-Stream delivers the fastest, on demand streaming data rates from a minimum of 384kbit/s up to around 450kbit/s. Most terminals also offer circuit switched Mobile ISDN services at 64kbit/s and even low speed (4.8kbit/s) voice services.

The Fleet service has recently been extended with Inmarsat offering a hybrid service that combines Fleet Broadband with its VSAT services. The first step was XpressLink which worked with Inmarsat’s Ku-Band VSAT and was followed by Fleet Xpress a Ka-band/L-band service that became available once Global Xpress commenced global commercial service. While waiting for all satellites in the Ka-Band constellation to be launched, the company introduced FleetBroadband Xtra (FBX), a regional Global Xpress/FleetBroadband service. Fleet Xpress was launched in 2016 and has proven popular, with around 10,000 ship users.

Since the advent of GMDSS, Inmarsat has become a private company and, although committed to maintaining the safety services, it is no longer focused solely on the marine sector as it once was. Recently, the IMO has decided that the GMDSS communications should be opened up to other satellite operators. The first to apply was the US-based Iridium and although the application initially progressed very slowly it has now been completed.

In May 2018, the IMO’s Maritime Safety Committee (MSC) officially recognised Iridium as a provider of GMDSS services. The Iridium Next satellite constellation completed in 2019 comprises 75 newly-launched satellites and allows for coverage where none existed before, including Arctic and Antarctic waters in Sea Area A4.

Iridium has also announced the signing of a Public Services Agreement (PSA) with the International Mobile Satellite Organization (IMSO) detailing the conditions for IMSO to act as a regulator and maintain oversight of Iridium GMDSS services. The signing of this agreement is a key step towards IMSO issuing Iridium a Letter of Compliance, stating that the company is ready to begin providing its GMDSS service.

The last hurdle is for Iridium and its selling partners to make available type-approved equipment which must also be certified by IMSO. The first terminal planned for certification, the Lars Thrane LT-3100S, is also on schedule to be type-approved in 2019. Several additional Iridium GMDSS terminals are planned to be available in the future.

SOLAS class vessels will need to wait until 2020 for the Iridium terminal to meet its mandated GMDSS carriage requirement, which is when the needed amendments made to the SOLAS Convention take effect. Vessels can begin using the service as soon as it is available, and anyone will be able to begin use of the new terminal for general communications needs.

Because of its GMDSS role, Inmarsat had dominated the marine satellite sector but it was not without competitors in the commercial communications arena. Iridium was one of those commercial competitors and once it has type-approved GMDSS equipment it will be in competition with Inmarsat, particularly in sectors where data capacity is not a main deciding factor. Other commercial satellite operators include KVH, Intelsat, SES, Telesat and Thuraya with several smaller regional players also active in the market.

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