A very-small-aperture terminal (VSAT) is a two-way satellite ground station with a dish antenna that is smaller than 3.8 meters. The majority of VSAT antennas range from 75 cm to 1.2 m. Bit rates, in most cases, range from 4 kbit/s up to 16 Mbit/s. VSATs access satellites in geosynchronous orbit or geostationary orbit to relay data from small remote Earth stations (terminals) to other terminals (in mesh topology) or master Earth station "hubs" (in star topology).
VSATs are used to transmit narrowband data (e.g., point-of-sale transactions using credit cards, 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 (utilising phased array antennas) or mobile maritime communications.
History
The concept of the geostationary orbit was originated by Russian theorist Konstantin Tsiolkovsky, who wrote articles on space travel around the beginning of the 20th century. In the 1920s, Hermann Oberth and Herman Potocnik, also known as Herman Noordung, described an orbit at an altitude of whose period exactly matched the Earth's rotational period, making it appear to hover over a fixed point on the Earth's equator.
Arthur C. Clarke's October 1945 Wireless World article (called "Extra-Terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?") discussed the necessary orbital characteristics for a geostationary orbit and the frequencies and power needed for communication.
Live satellite communication was developed in the 1960s by NASA, which launched Syncom 1–3 satellites. Syncom 3 transmitted live coverage of the 1964 Olympics in Japan to viewers in the United States and Europe. On April 6, 1965, the first commercial satellite was launched into space, Intelsat I, nicknamed Early Bird.
The first commercial VSATs were C band (6 GHz) receive-only systems by Equatorial Communications using spread spectrum technology. More than 30,000 60 cm antenna systems were sold in the early 1980s. Equatorial later developed a C band (4/6 GHz) two-way system using 1 m x 0.5 m antennas and sold about 10,000 units in 1984–85.
In the early 1980s, LINKABIT (the predecessor to Qualcomm and ViaSat) developed the world's first Ku-band (12–14 GHz) VSAT for Schlumberger to provide network connectivity for oil field drilling and exploration units. LINKABIT which had become part of M/A-COM went on to develop VSATs for enterprise customers such as Walmart, Holiday Inn, Chrysler, and General Motors. These enterprise terminals made up the vast majority of sites for the next 20 years for two-way data or telephony applications. A large VSAT network, with more than 12,000 sites, was deployed by Spacenet and MCI for the U.S. Postal Service in the 1980s. , the largest VSAT Ku-band network containing over 100,000 VSATs was deployed by and is operated by Hughes Communications for lottery applications.
In 2005, WildBlue (now ViaSat) started deploying VSAT networks deploying Ka-band. ViaSat launched the highest capacity satellite ever, ViaSat-1, in 2011 to expand the WildBlue base under its Exede brand. In 2007, Hughes Communications started deploying VSAT sites for consumers under its HughesNet brand on the Spaceway 3 satellite and later in 2012 on its EchoStar XVII/Jupiter 1 satellite. By September 2014, Hughes became the first Satellite Internet Provider to surpass one million active terminals.
Configurations
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 via satellite, A mesh topology, where each VSAT 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 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.