The idea of communicating via satellite was first proposed in a magazine article in 1945 by the author and scientist, Arthur C. Clarke (pictured). Clarke suggested that if a 'radio station' were to be placed in an orbit approximately 23,000 miles above the Earth's equator, it would match the rotational speed of the earth and appear to be stationary in the sky. This orbit has since become known as the Clarke belt and is the altitude at which the majority of communications satellites (comsats) are placed to achieve geosynchronous orbit. Clarke suggested that if three satellites were positioned at equal intervals above the equator, worldwide coverage could be achieved.

On October 4, 1957, the USSR launced the world's first ever artificial satellite, Sputnik. Sputnik was little more than a radio transmitter, and it only remained in orbit for a few months. Never the less, it opened the way for a revolution in communications technology. Significantly, it also spurred the US government under President Dwight D. Eisenhower to investigate new communications methods. This gave birth to the US Advanced Research Projects Agency, ARPANET and, ultimately the Internet. In 1962 the first live television pictures were relayed from an American satellite called Telstar.

 

Today, many of the live pictures and sound we see on our news programmes are received from satellites around the globe. In 1965, Clarke's dream was realised when the first ever geosychronous communication satellite was positioned in orbit above the Atlantic Ocean by NASA. By 1969, three satellites had been linked to achieve global coverage.

Satellite technology has improved beyond all recognition since the first satellites were launched. Today's satellites have multiple transponders - transmission devices capable of relaying signals sent from earth stations (or uplinks) back down across vast areas of ground known as 'footprints'. The University of Plymouth uses satellites that have footprints covering the whole of Europe.

 

It is possible to transmit to anywhere in the world using other satellites to relay or 'doublehop' signals farther afield.

Between 1989 and 2006 the University regularly broadcasted live television programmes for students and businesses across the South West of England. Projects such as WIRE Mediaspace, RATIO, TETRASUR and SANTTSUR (now known as MRCS tv ) used live satellite TV to good effect. See the research pages for more information on the history and outcomes of these projects.  A range of studio features were available to broadcasters including teleprompting, graphic design and chroma-key effects. The studio employed Betacam SP as a standard.

Customers who used the University's uplink facility included: National Westminster Bank, British Gas plc, Central Television, the British Library, and a firm who auctioned cattle via satellite!!

There was once only one way to transmit television signals to a satellite - analogue transmission (known as wideband FM). This technique used up a great deal of transponder space on the satellite and was expensive. In 1996 the University of Plymouth invested in a new digital standard known as MPEG2 (Moving Picture Experts Group - version 2). MPEG enabled the university to send high quality digital pictures and sound up to a satellite for a fraction of the cost paid when analogue technology was used.

 

This is because MPEG digitally compresses signals down to a fraction of their bandwidth size. Wideband FM signals occupies a bandwidth of 27 MHz, and the University must then rent time of half of a 72 MHz transponder on a satellite. The MPEG2 signal requires only 4 MHz of bandwidth (about one eighth of a transponder space. Because of this operating feature transmission costs can be reduced considerably.

 

The MPEG2 codec used in the uplink digitised audio and video, and transmited only the areas of the picture that were changing (i.e. moving). The reduced bandwidth was a direct result of this processing redundancy.

Some transmissions from the university contained sensitive or confidential information, and it was important to protect this so that only those who it was directed at actually enjoyed access. The University was able to send encrypted transmissions from the uplink so that reception was permitted only at specified receive sites.

 

Additionally, a bit pipe inside the MPEG2 data stream was used to transmit data over the entire footprint of the satellite, using a data capture card developed at the University.

Each RATIO centre and study centre throughout the South West of England was equipped with a data capture cards located inside a pc near to the satellite receiver. These devices, created by the university's Engineering Department within the Faculty of Technology, enabled teachers and trainers to send high speed data via redundant audio channels within the satellite's transponder. Data was sent at around 128 kbps, enabling teachers to send approximately 4-5 types sheets of text each second, direct to the computers of students around the region. Furthermore, data was sent selectively, using unique PIN numbers for each data capture care in a 'conditional access' environment.

Integration of satellite and terrestrial (cable, line of sight) technologies was undertaken, particularly in projects such as EURONET. This enabled existing infrastructures to offer alternative transmission routes. In Hull, for example, an advanced TV cable network exists. The University of Hull and the University of Plymouth, as partners in EURONET, investigated ways in which satellite TV could be transmitted via cable to thousands of homes in Humberside.

Videoconferencing technology was used to enable remote students to call back into the studio whilst a live programme was 'on air' to ask questions of the studio guests and experts (See diagram above). This technique was successfully used in the latter years of satellite uplinking in many of the university's live TV transmissions. Increased bandwidth and greater transmission speeds made it possible for long before academics in many parts of the university's dispersed campus to enter their local videoconference suite, or use a desktop version to broadcast a live programme to anywhere in the world.

In late 1998 Iridium low orbit satellite networks became available. This means that direct digital telephony is now possible, through the use of mobile telephones. In 2006, another five networks were put in place, allowing higher bandwidth data communication to and from any part of the globe. It is predicted that within a few years we will enjoy high speed internet communications via satellite, making ground based telephone networks unnecessary for this purpose. (Take a look at the Negroponte Switch to read about one viewpoint on this development).

 

The University of Plymouth is currently researching the effectiveness of VSAT (Very Small Aperture Terminals or 2 way satellite dishes) for Internet access. The results so far indicate that Internet access via satellite is far quicker than via terrestrial/modem access. And in the long run it's cheaper too.

 

More information can be obtained from the Mobile Communications Research Centre at the University of Plymouth.