VSAT (Very Small Aperture Terminals)
VSAT (Very Small Aperture Terminals)
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 meter. Data rates, in most cases, range from 4 kbit/s up to 10 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.
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 35,900 kilometres (22,300 mi) 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 called it Syncom 1-3. It 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 80s, 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 Ku band 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. Today, 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 Ka band VSAT sites for consumers under its HughesNet brand on the Spaceway 3 satellite and later in 2012 on its EchoStar XXVII/Jupiter 1 satellite. By September 2014, Hughes became the first Satellite Internet Provider to surpass one million active terminals.
Advances in technology have dramatically improved the price–performance ratio of fixed satellite service (FSS) over the past five years. New VSAT systems are coming online using Ka band technology that promise higher data rates for lower costs.
FSS systems currently in orbit have a huge capacity with a relatively low price structure. FSS 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 provide high-quality service because they create efficient communication systems for both residential and business users.
Parts of a VSAT configuration
Block upconverter (BUC)
Low-noise block downconverter (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). The Astra2Connect has an all-in-one OMT/BUC/LNA that looks like a Quad LNB in shape and size which mounts on a regular TV satellite mount. As a consequence it is only 500 mW compared with the normal 2W, thus is poorer in rain. Skylogic's Tooway system also uses an integrated OMT/BUC/LNB assembly called a transmit and receive integrated assembly (TRIA), which is 3W.