Technology: Live wire for mobile users: A radio-based network makes it easier to transmit data on the move

ALTHOUGH technological developments have made computers more portable, the data they hold - as the Department of Trade and Industry has recognised - is not so readily handled on the hoof.

Computers on the move, whether used by business people or delivery drivers, still need physical coupling to other computers before their information can be read - and acted on. Although computers can be fitted with modems, enabling users to communicate with other machines over ordinary telephone lines, this is only a partial solution. Using a modem in an office environment is one thing, using one on the move quite another.

One problem is ready access to telephones. Public payphones require the user to fit an acoustic converter to the handset first - a fiddly operation involving still more gadgetry to carry around. Even dedicated mobile computer users generally plug their laptops into the phones of hotels or clients rather than payphones at railway stations or airports.

Modems fitted to cellular telephones are a theoretical but expensive option. They are also subject to data-transmission problems because of line noise, and the familiar mobile telephone problem of engaged 'cells' preventing access.

As a result, the DTI has licensed three new telecommunications operators to provide a radio-based digital data network. A condition of the licence being granted is that each operator's network should cover 80 per cent of the UK population within five years - a level already reached by one operator, RAM Mobile Data, just over a year after being licensed.

The company's shareholders are all foreign - principally two US telecommunications companies, RAM Broadcasting Corp and BellSouth; France Telecom; Swedish Telecom; and Bouygues, a French construction company.

RAM's UK coverage, explains John Nicholson, vice-president of operations, resembles that of the two cellphone operators, embracing the big conurbations, the road and rail networks that link them, as well as airports and main railway stations. 'Logically, that's where the user population density is greatest,' he said.

Because the network employs digital 'packet-switching' technology, rather than traditional cellular 'line-switching', many users can share the same link. This makes the network cheaper to use than a cellular one: users pay for the bursts of data that they receive and transmit, rather than for the amount of time they are 'on-line'.

By the end of the summer, Mr Nicholson said, the network would include gateways to all the big electronic mail systems, as well as to a business's own computer system via a gateway into BT. Business people on the move will be able to send each other electronic mail, as well as swap spreadsheets with colleagues at the office, with just a few keystrokes. Radio modems (as opposed to telephone ones) will sell for pounds 500 at first., but Mr Nicholson expects prices to drop as volumes pick up.

As with many technological developments, availability spawns new uses. Conrail, the US freight rail operator and America's third largest rail network, has started equipping its locomotives with computers linked by radio modems.

Jerry Conway, the systems manager, said the move was a response to customer demands for faster service and more accurate shipment information. Local 'pickup' trains tour customers' sidings each day, picking up wagons scheduled to be collected for consolidation into long-distance freight trains.

On-board computers mean the pick-up trains can be notified of wgaons minutes before they arrive. Previously, schedules were frozen when the trains left the depot on a day's collection trip, which could be as long as 16 hours. Initial plans were to equip 315 locomotives, but the company now intends to fit radio modems to a further 125.

Early users of mobile data technology in Britain include the Greater Manchester Fire Service, which has run trials where PCs equipped with modems are fitted to vehicles attending incidents with chemical hazards. Detailed information on the handling of 50,000 chemicals can be called up on-screen at the scene.

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