22.1 VSATs for Business Systems

VSATs, very small aperture terminals, are small earth stations capable of receiving from and sometimes transmitting to satellites. They represent an important addition to the telecommunications world because they can provide a service directly to the user at virtually any geographic location covered by a suitable satellite beam. They do not require any support from a local terrestrial communications network and can even be run from portable or alternative power supplies.

The term VSAT appears to have been coined around 1979 and was first used in connection with the systems offered by Equatorial in the USA. These early systems operated at C-band and represented a radical departure from the normal usage of satellite communications links.

VSATs can be used individually or, more usually, in networks of related users and they are often used in conjunction with a hub station. A hub station is usually a larger earth station at the centre of a star network. The small size of VSATs brings with it special system and equipment design problems, both for the VSAT itself and for the hub to which it operates. These problems are discussed later in this Chapter. The deregulated telecommunications policy in the USA meant that VSATs could be used at an early stage. In Europe, regulation prevented their use for a number of years. However, there are now many VSAT systems in Europe and the UK lottery is a well known example of a network which uses approximately 2500...