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Wednesday, December 05, 2007

What you should know about VSAT (1)

Market Intelligence:

VSAT stands for Very Small Aperture Terminal - its a catchy acronym and as such has been adopted by all and sundry for every type of satellite product from small components of a system to complete systems. Also, because the term really hinges around the small size of the antenna, it has been used to describe both one-way and interactive systems.

Specifically, some experts in the industry, isolate television broadcast receivers because counting these as well would simply distort the numbers in the marketplace, but data, audio and, to some extent, voice systems are included.

Generally, these systems operate in the Ku-band and C-band frequencies. As a rule of thumb C-band (which suffers less from rain attenuation, but requires larger antennas) is used in Asia, Africa and Latin America whilst Ku-band (which could use smaller antennas, but suffers from rain fade in a monsoon-like downpour) is used in Europe and North America.

Typically, interactive Ku-band antenna sizes range from 75 centimetres to 1.8 metres and C-band from 1.8 metres to 2.4 metres. One way systems could use antennas as small as 45 centimetres.

One-way or broadcast systems rely on a transmitting station, which transmits one or more carriers to the satellite, which re-broadcasts the signal over its coverage area.

All receive-only VSATs under the satellite footprint could then receive the signal or the user/operator is able to define groups of VSATs from one to all on the network. Broadcast systems are used for data and audio.

The most popular application for data is the transmission of financial feeds - Reuters, Telerate and KnightRidder are good examples of companies with large data broadcasting networks - however, there are many other uses, such as software downloads, file transfers, transmission of press agency news items (with pictures) and the broadcast of paging messages for terrestrial transmission to the pagers themselves.

Interactive VSAT systems come in two main network topologies - star and mesh. The former tends to be based either on a shared access scheme like Time Division Multiple Access (TDM/TDMA), which is designed to support transactional processing applications, or on a dedicated link (the satellite equivalent to a leased line). The latter usually uses links, which are set-up and torn-down on request to establish a direct link between two sites on a demand assigned basis.

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