Cells - the way to increase capacity

Radio telephones worked, but if lots of people wanted to use them, there simply weren't enough channels to carry all the calls.

TACS

To allow increased subscriber numbers, lower power transmitters and efficient use of frequencies, a new mobile phone system called Total Access Control System (TACS) was introduced in the UK in the early 1980's.

TACS allows direct dialling in and out, and has the mobile phones connected to smaller, lower-powered base stations arranged in a cellular pattern, so that although adjacent cells don't use the same frequencies, cells further away can do so. This idea was a product of Bell Laboratories in the 1970's. Think of a patchwork quilt, where the same colour can't be used for two adjacent patches, and you have the idea of how it is designed.

This cellular system is used for most of the modern mobile phone systems, even some satellite-based ones.

Cut-throat competition?

TACS was a roaring success. Coverage grew, and although the two UK networks (Cellnet and Vodafone) were ostensibly in competition, the line rentals and call charges were more or less identical. The cost of the mobile phones was subsidised by the Service Providers, who sometimes expected users to sign three year contracts. Mobile phones were normally fitted into cars, and the mobile phone business was initially aimed at fitting phones into salesmen's company cars.

As time went by, more and more hand-held units were sold, but they were neither cheap to buy nor to use. Normally the line rental was £30 per month, with calls at 25p per minute, minimum one minute.

Call volumes expanded so that extra capacity was needed, particularly in metropolitan areas. The networks persuaded the government to release additional frequencies, and Extended TACS (ETACS) was born, using frequencies "borrowed" from military allocations.

Popular tariffs

In an attempt to increase the number of customers, but not to greatly increase call volumes (the capacity wasn't available), both networks introduced "Low User" tariffs, where the line rental was "only" £17.50 per month, but calls were 50 pence per minute (no inclusive calls for free, of course). This was a big success, and subscriber numbers grew, helped by the cheaper and more readily hand-held mobile phones coming onto the market.

Snags

There was nothing to stop someone listening in to an analogue mobile phone call, using a scanner that cost under £200. It was also possible to capture the handset's details off-air, and make a "clone" of it, thereby making calls charged to someone else's account. This became a serious problem for networks at one time, though GSM has provided the solution to both snags.

Other systems

As well as TACS and its successor, the GSM system which has become the de facto world standard, these other networks have joined the mobile phones party over recent years:

• Nordic Mobile Telephony (NMT) which uses 450 MHz started in 1981
• American Mobile Phone System (AMPS) started in 1983
• Nordic Mobile Telephony (NMT), a 900MHz system, dating from 1986
• North American Digital Cellular (NADC) launched in 1991
• Digital Cellular System (DCS) on 1800MHz from 1992 (now called GSM 1800)
• Personal Digital Cellular (PDC) or Japanese Digital Cellular (JDC) 1994
• Personal Communications Systems (PCS) 1900 (a US variant on GSM) launched in 1995 in Canada, and 1996 in the USA

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