Ka-band satellites represent the next major opportunity for the satellite communications industry. The term Ka-band satellite is now generally recognised as a shorthand term for a new generation of communications satellites that will use on-board processing and switching to provide full two way services to and from small earth stations comparable in size to today's satellite television dish. To do this efficiently they will use multiple pencil like spot beams. A number of proposals also include use of inter-satellite links. A variety of orbits are being considered. Apart from the conventional geostationary orbit, both low earth and middle earth orbit systems have been planned.

Such Ka-band satellite systems have also been described in other terms such as "multimedia satellites", "ATM satellites", "broadband switched" and "broadband interactive satellites". The first two terms are generally inaccurate in that Ka-band satellites can be used for other applications than multimedia or providing an ATM platform. Indeed, it remains questionable whether many of the proposals are suitable for ATM. The most commonly used shorthand terminology is "Ka-band satellite" to describe such systems. The term "ATM Satellite" is incorrect because on-board switching can involve either ATM switching or circuit switching or both.

Moreover, there are in existence a number of Ka-band satellites that do not use on-board processing or pencil beams or inter-satellite links and whose use has either been confined to experimental work or conventional telecommunications or broadcasting traffic. However, use of on-board processing and switching are not confined to Ka-band satellites. Already the satellite communications industry is beginning to think about using even higher frequencies to provide services similar to or beyond those planned for the new generation of Ka-band satellites. 

On-board processing and switching (effectively the provision of the equivalent of a sophisticated telephone switchboard on a satellite) are already employed in satellites providing mobile communications to hand held receivers. One of a new generation of mobile satellite systems employs Ka-band communications for links between fixed ground stations that interconnect the public switched telephone networks to the satellites. However, the links between the satellites and the hand held receivers are in L-band. A number of GSO MSS systems under development also use OBP and switching.

Understanding the relationship between inter-satellite links, pencil spot beams and on-board processing and switching is essential in understanding the commercial role these satellites are aiming to fulfil. In effect, the switching capability is capable of making them operate like a public telephone network but with the facility to offer digital services with a wide variety of bit rates. Users will be offered `bit rate on demand' and its variation, `variable bit rate on demand' - that is to say they will only pay for the time that they use a link. This contrasts with conventional satellites where users usually have to pay for permanent leases. That only makes it economic to use satellites where there is a massive amount of information to be moved, such as TV channels and trunk telephony links.

In contrast, the Ka-band concept offers the equivalent of a local drop telephone circuit where the user pays for temporary lease of time. The Ka-band environment also allows an alternative, charging per bit of information moved.

However, such services require a lot of bandwidth because each link will usually be operating on a point to point basis. The prime method of using the available spectrum efficiently is to use multiple "pencil" spot beams, each covering only a small area of the earth. This allows frequency re-use in much the same way as a cellular phone network re-uses spectrum. Use of multiple spot beams in itself demands the use of on-board processing and switching to direct each transmission path between the different spot beams used for uplinking and downlinking. Similarly, inter-satellite links with similar Ka-band satellites will demand switching capabilities.

In effect, the on-board processing and switching capability is a network management facility. The Ka-band satellite operators will each become like telephone companies but with their telephone exchanges in the sky.

In the long term it looks likely that there will be a "merger" of services offered by mobile satellite systems with those offered by "mainstream" Ka-band satellites.