Communications

Understanding the basics behind modern communications


Malcolm Latarche
Malcolm Latarche
ShipInsight

10 July 2019

Understanding the basics behind modern communications

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.