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History on mobile phones

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					                                History on mobile phones

The birth of the mobile phone

At first there were devices called radiotelephones. These were invented in the late
20’s early 30’s. After the Second World War, a few radiotelephones were fitted into
the cars of the rich and important in several countries. These units worked by
connecting to one or more base stations, and were half-duplex (meaning that although
the transmit and receive frequencies were different, you could either talk or listen, not
both at once).

Because of the wide channel spacing and high powers used, combined with the
limited range of frequencies available, there was only capacity for a few thousand
radiotelephones across the country.

As with early fixed phones, calls had to be connected by an operator, and it was some
years before automatic exchanges were widely introduced, though the first automatic
mobile system went live in Sweden in 1956. There was no possibility of portable
units: these devices could run your car battery down quickly.

In 1964 the Bell System introduced the American Improved Mobile Telephone
Service (IMTS). It was a full-duplex system – you didn't have to press a button to
talk. Speech went to and fro just like a normal telephone. It offered direct dialling,
automatic channel selection and reduced bandwidth to 25-30 kHz.
This was a major step forward, but before wider use of mobile phones could be
possible, some way of re-using frequencies had to be developed: this had been
designed by Bell Laboratories in the USA in 1947, but was not fully implemented for
another 20 years or so.

The first real mobile phone network system was a system called Total Access Control
System (TACS) and 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. This cellular system is used for most of the modern
mobile phone systems, even some satellite-based ones.

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.
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). This was a big success, and subscriber numbers
grew, helped by the cheaper and more readily hand-held mobile phones coming onto
the market.

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.

In 1982 the Conference of European Posts and Telecommunications (CEPT) formed a
committee called the Groupe Spécial Mobile.
This committee was to develop a standard for mobile phones that would use radio
spectrum efficiently, provide international roaming, give satisfactory voice quality,
have low equipment costs, be compatible with other systems such as ISDN
(Integrated Services Digital Network) and be ready to support new services as they
were developed.

This committee worked together, designing a system which depended on technologies
not available at the time, and following 1986 field tests of different radio techniques
proposed for the air interface, in 1987 they produced a proposal for a TDMA system
which was incorporated in an initial Memorandum of Understanding (MoU), signed
by telecommunications operators from twelve countries.

In 1989 CEPT's GSM passed the specifications to the European Telecommunications
Standards Institute (ETSI). The following year (1990) phase 1 of the GSM
specification was published. In 1991 the first commercial GSM mobile telephone
system went into service.

In 1992 GSM coverage was restricted to large cities, and around airports. The
networks rolled out, more countries signed up to the system, and by 1995 rural areas
were seeing GSM coverage. In 1995 Phase 2 of the GSM (by now renamed to Global
System for Mobiles) was published, adding additional features and services.

				
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