IN all communication systems the repeater or relay station has a vital role. The relay function is essentially simple. In the past, people relayed or passed messages by word of mouth, patterns of flags, beacons, or Morse code. Today we have electronic amplifiers that boost weak signals and blindly pass them on, and digital systems that detect and reconstruct the message in minute detail before retransmission. In all cases it is possible for messages to be lost, destroyed or distorted, and it falls to designers to minimise such events.

Five hundred years ago the beacon telegraph in Britain had repeater stations more than 10 miles apart. Twenty years ago repeaters on copper cable systems were spaced at only two kilometres on routes spanning continents. Today, repeaters on optical fibre cables are spaced at 50 to 200km or more.

Satellites also form a network of invisible repeaters. A more recent manifestation is now very visible in the form of cellular mobile radio base stations that outnumber the huge terrestrial microwave radio towers dotted at 40km across the landscape.

When we consider the future of mobile communications, it is interesting to look at the military and emergency services. They often use vehicles as the radio repeater stations to allow their people in the field to operate without the need for heavy, body-mounted equipment. This also gives far better radio coverage in most environments.

Despite the fact there seem to be radio masts and towers everywhere, you can still drive in the country, town and city, walk in any street, building or room, and the signal strength on a mobile phone will vary widely. It is not unusual to find dead zones where the signal strength is so low no service is possible. But it is often possible to see another mobile unit within short range that has good signal quality. So the obvious next step would be to make every mobile phone a potential repeater station. If the owner has it in the holster or bag and it is not being used - why not use it to gain access?

Could such a system be realised and what advantage would it give, and would people be concerned? First, it is technically feasible. Second, there is a need and it is desirable. Third, it would allow for far lower transmitter powers and thereby reduce interference and biological risks. Overall, it could see us able to communicate with far greater reliability and certainty than today. Moreover, as people and machines become ever more dependent upon mobile communication it is likely to become the only means of organising and operating a global system.

We already have electronic cameras, camcorders, PDAs, and many other items with infrared links that allow them to communicate over networks. With the advent of hard drives for cars and people we will, of necessity, be doing all this on an increasing scale anyway.

On the downside, there will be an increase in the control and signalling complexity to continuously scan for a mobile unit with a good connection when yours cannot see a good signal, or offering help, when you have good service. And there is then the matter of battery power. How come my battery is flat when I have not been using my phone?

Peter Cochrane holds the Collier Chair for the Public Understanding of Science & Technology at the University of Bristol. His home page is:
http://cochrane.org.uk