Very small aperture terminal
A Very Small Aperture Terminal (VSAT), is a two-way satellite ground station or a stabilized maritime VSAT antenna with a dish antenna that is smaller than 3 meters. The majority of VSAT antennas range from 75 cm to 2.4 m. Data rates typically range from 56 Kbit/s up to 40 Mbit/s. VSATs access satellites in geosynchronous orbit to relay data from small remote earth stations (terminals) to other terminals in mesh configurations) or master earth station "hubs" (in star configurations). VSATs are most commonly used to transmit narrowband data (point of sale transactions such as credit card, polling or RFID data; or SCADA), or broadband data (for the provision of Satellite Internet access to remote locations, VoIP or video). VSATs are also used for transportable, on-the-move (utilizing phased array antennas) or mobile maritime communications.
Most VSAT networks are configured in one of these topologies:
A star topology, using a central uplink site, such as a network operations center (NOC), to transport data back and forth to each VSAT terminal via satellite,
A mesh topology, where each VSAT terminal relays data via satellite to another terminal by acting as a hub, minimizing the need for a centralized uplink site,
A combination of both star and mesh topologies. Some VSAT networks are configured by having several centralized uplink sites (and VSAT terminals stemming from it) connected in a multi-star topology with each star (and each terminal in each star) connected to each other in a mesh topology. Others configured in only a single star topology sometimes will have each terminal connected to each other as well, resulting in each terminal acting as a central hub. These configurations are utilized to minimize the overall cost of the network, and to alleviate the amount of data that has to be relayed through a central uplink site (or sites) of a star or multi-star network.
Advances in technology have dramatically improved the price/performance equation of FSS (Fixed Service Satellite) over the past five years. New VSAT systems are coming online using Ka band technology that promise higher bandwidth rates for lower costs.
FSS satellite systems currently in orbit have a huge capacity with a relatively low price structure. FSS satellite systems provide various applications for subscribers, including: telephony, fax, television, high speed data communication services, Internet access, Satellite News Gathering (SNG), Digital Audio Broadcasting (DAB) and others. These systems are applicable for providing various high-quality services because they create efficient communication systems, both for residential and business users.
Constituent parts of a VSAT configuration
Block upconverter (BUC)
Low-noise block converter (LNB)
Orthomode transducer (OMT)
Interfacility Link Cable (IFL)
Indoor unit (IDU)
All the outdoor parts on the dish are collectively called the ODU (Outdoor Unit), i.e. OMT to split signal between BUC and LNB. The IDU is effectively a Modem, usually with ethernet port and 2 x F-connectors for the coax to BUC(Transmit) and from LNB (Receive).
Maritime VSAT is the use of satellite communication through a VSAT terminal on a ship at sea. Since a ship at sea moves with the water the antenna needs to be stabilized with reference to the horizon and the heading of the ship, so that the antenna is constantly pointing at the satellite it uses to transmit and receive signals.
Initially maritime VSAT was using Single Channel Per Carrier - SCPC technology - which suited large volume users like oil drilling rigs and oil platforms and large fleets of ships from one shipowner sailing within one or few satellite footprints. This changed when the company iDirect launched its IP-based Time Division Multiple Access (TDMA) technlogy that dynamically allocated bandwidth to each ship for shared bandwidth, lowering the entry level cost for getting maritime VSAT installed, which turned out to be of key importance to small-to mid-sized fleets, and thus to the market acceptance of VSAT.
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