Triple treat

BT has developed technology it claims will triple the capacity of satellite communications links, allowing far more information to be transmitted for the same cost.

The technology uses a frequency modulation technique similar to that used by GSM phone networks. The system only needs to be fitted to ground stations, making it relatively simple to upgrade existing satellite networks

Internet service providers use satellite connections for long distance point-to-point (trunk) links to the internet. While optical fibre is increasingly used in developed countries, satellite connections are far more cost effective in developing and remote areas, and the technology could significantly increase the efficiency of these links, said Mark Fitch, responsible for satellite network development at BT Exact.

‘There is a growing market for the use of satellite in ISP backbone connections, particularly from the UK and US to the middle and far east. BT has been turning the work away because we couldn’t do it reliably enough.’

The system could also be used to improve satellite news broadcasts, increasingly used by rolling news channels to report from remote war-torn regions, where the quality is often poor due to limited bandwidth. By tripling the capacity available, the technology could significantly improve broadcast quality.

The technique could also improve the efficiency of communications links used by the military, and could ultimately be used to upgrade direct-to-home satellite connections, reducing the cost and increasing the take-up of satellite television.

The modulation technique is known as multi-level Gaussian frequency-shift keying. The method, which involves sending data along a carrier signal by slightly shifting frequencies, is not new, and was used to build the earliest modems. ‘Basically it’s the way you wobble the carrier around to carry the information,’ said Fitch.

But until now the technique has not been used for satellite communications, and in conventional GSM networks the method has only two frequency states in which to send information, severely limiting how much and how quickly data can be transmitted.

In contrast, the BT modulation technique uses 16 frequency states, allowing much more information to be transmitted, said Fitch. ‘We are also introducing partial signalling, so before you end up at one state you start on the journey to the next one, so you can cram even more information into a given time.

‘We have achieved roughly twice the efficiency of the state-of-the-art systems. So where they can get roughly 155Mb/s reliably over satellite, we should be able to run about 3-400Mb/s,’ he said.

BT has developed the basic technology, but hopes to form a partnership with a modem manufacturer to build a prototype for trials and eventually take the system into production.

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