Atualizada em 03/04/2012
Um terminal VSAT (Very Small Aperture
Terminal) é uma estação terrestre BIdirecional, com uma parábola
menor que 3 metros de diâmetro. A maioria das antenas usadas no Brasil
para VSAT são do tipo Off-Set (Foco Fora de Centro, ou Assimétrico) tem
diâmetro de 75 cm to 1.5 m.
As bandas disponíveis costumam ficar entre 56 kbps (up) a 4 Mbps.
Satélites utilizados para VSAT são geoestacionários para permitir o uso
de antenas fixas, e pequenas.
Texto reproduzido da WikiPedia
A Very Small Aperture Terminal (VSAT), is a two-way
satellite ground station with a dish antenna that is smaller than 3
meters (most VSAT antennas range from 75 cm to 1.2 m). VSAT data rates
typically range from narrowband up to 4 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).
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 (with phased-array antennas) or mobile
maritime (such as Inmarsat or BGAN) communications.
History and Usage:
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) 2 way system using 1 m x
0.5 m antennas and sold about 10,000 units in 1984-85.
In 1985, Schlumberger Oilfield Research co-developed the world's
first Ku band (12-14 GHz) VSATs with Hughes Aerospace to provide
portable network connectivity for oil field drilling and exploration
units. Ku Band VSATs make up the vast majority of sites in use today
for data or telephony applications.
The largest VSAT network (more than 12,000 sites) was deployed by
Spacenet and MCI for the US Postal Service. Other large VSAT network
users include Walgreens Pharmacy, Dollar General, Wal-Mart, CVS,
Riteaid, Yum! Brands (Taco Bell, Pizza Hut, Long John Silver's and
other Quick Service Restaurant chains), GTECH and SGI for lottery
terminals. VSATs are used by car dealerships affiliated with
manufacturers such as Ford and General Motors for transmitting and
receiving sales figures and orders, as well as for receiving internal
communications, service bulletins, and interactive distance learning
courses from manufacturers. The FordStar network, used by Ford and its
local dealers, is an example of this.
VSAT technology is also used for two-way satellite Internet
providers such as HughesNet, StarBand and WildBlue in the United
States; and Bluestream, SatLynx and Technologie Satelitarne in Europe,
among others. These services are used across the world as a means of
delivering broadband Internet access to locations which cannot get
less expensive broadband connections such as ADSL or cable internet
access; usually remote or rural locations.
Nearly all VSAT systems are now based on IP, with a very broad
spectrum of applications. As of December 2004, the total number of
VSATs ordered stood at over 1 million, with nearly 650,000 in service.
Annual VSAT service revenues were $3.88 billion (source:
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.
Star topology services like HughesNet, Spacenet Connexstar/StarBand,
WildBlue and others can be used to provide broadband wide area
networks, as well as to provide broadband Internet access.
Applications of this include intranet networking for front and back
office applications, managed store and forward solutions such as
digital signage, and interactive distance learning.
VSAT Frequency Spectrum Allocation
This table acts as a guide only.
3 to 7
10 to 18
18 to 31
VSAT was originally intended for sporadic store-and-forward data
communications but has evolved into real-time internet services. VSAT
uses existing satellite broadcasting technology with higher powered
components and antennas manufactured with higher precision than
conventional satellite television systems. The satellite antenna at
the customer's location includes, in addition to the receiver, a
relatively high-powered transmitter that sends a signal back to the
originating satellite. A very small portion of a transponder is used
for each VSAT return path channel. Each VSAT terminal is assigned a
frequency for the return path which it shares with other VSAT
terminals using a shared transmission scheme such as time division
An innovative feature of VSAT is that the technology has evolved to
the point that something that previously could only be done with large,
high-powered transmitting satellite dishes can now be done with a much
smaller and vastly lower-powered antenna at the customer's premises.
In addition, several return-path channels can co-exist on a single
satellite transponder, and each of these return-path channels is
further subdivided using to serve multiple customers.
In the system used by WildBlue, 31 different spot beams are used to
serve the continental United States instead of the one beam used by
conventional satellites. Thus, the same Ka-band transponders and
frequencies are used for different regions throughout the United
States, effectively re-using the same bandwidth in different regions.
The return path is transmitted from the customer's receiver in the
L-band to a device called a low-noise block upconverter. There it is
converted into the much higher frequency satellite transmission
frequency, such as Ku-band and Ka-band, and amplified. Finally the
signal is emitted to the dish antenna which focuses the signal into a
beam that approximately covers the satellite with its beam. Because
the transmission cannot be precise in these smaller dishes there is
some effort to use frequencies for the uplink that are not used by
adjacent satellites otherwise interference can occur to those other
Another satellite communications innovation, also used by satellite
trucks for video transmission, is that only a small portion of a
single satellite transponder is used by each VSAT channel. Previously
a single transponder was required for a single customer but now
several customers can use one transponder for the return path. This is
in addition to time-based subdivision.