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Building the networks

Cellnet promotional material

Mobile services arrive in the UK

The Advanced Mobile Phone Service (AMPS) technology perfected in 1983 in the USA was sold under licence to other parts of the world. In the UK, AMPS was developed into a somewhat more sophisticated system called TACS - Total Access Communication System. The advantages of TACS were that it allowed for higher numbers of subscribers, used lower power and achieved more effective re-use of frequencies.

Cellnet, a British Telecom (BT) and Securicor joint venture cellular radio service was launched on January 7 1985. It ultimately replaced the existing Radiophone service operated by British Telecom. Its competitor, Racal Vodafone, was launched the same year. Both these pioneered mobile phone services operated on TACS in the 900MHz frequency range.

Cellnet promotional material

ETACS is developed (1987)

Britain's first generation mobile phone system, TACS, was a great success.

Although the service providers Cellnet and Vodafone were in competition, their line rental and call charges were similar, which meant they shared the expanding market more or less equally between them.

Early mobiles were expensive to buy and to use, with the first Motorola hand held mobile retailing for almost £3,000 and line rental around £25 per month, with calls costing 25p per minute.

Even with the high costs, more and more mobiles were sold, expanding call volumes and network traffic so that extra capacity was needed, particularly in metropolitan areas. So Cellnet and Vodafone persuaded the government to release additional frequencies and in 1987 Extended TACS (ETACS) was born, using frequencies freed up from military allocations.

Network busy

Creating capacity

Lack of network capacity is particularly crucial to mobiles because it not only restricts whom you can call - but whether your phone will work at all.

The first cellular systems had the ability to use 1,000 channels and though this seems a lot the number available to any user at a time was a lot less. Firstly the channels were shared between Celllnet and Vodafone and secondly a number were allocated as control channels to make the system work. If each channel was occupied for the duration of a call across the whole coverage area then capacity would have been a real issue but both TACS and ETACS were cellular systems. Cellular systems mean the coverage area was divided up into small cells, each with a base station with its own channels. By switching a call from one channel as the called crossed into another base station's patch meant that the fist channel could be freed up. It did mean that adjacent cells couldn't use the same channels so there was a tradeoff between the number of base stations and channels. Base stations covering large areas were more channel hungry but a greater number of base stations covering a small area meant better use of channels. More base stations did add to the cost of the network.

The analogue TACS and ETACS systems were soon replaced by the GSM network which not only offered better quality calls but also allowed better use of channels by allowing more than one call to use the same channel at the same time through clever encoding and by dividing the channel into small slots of time.

Entirely new frequencies were made available and in the UK this meant that another two providers (One 2 One and Orange) joined the market. This meant new phone designs were needed to exploit the additional channels bands. Phones were sold as dual band meaning that they would work on both of the two bands, though the user was still limited to the band allocated to their provider.

The dual band phones gave way to triple and quad band phones. This was important because other countries had allocated different bands of frequencies for their systems. GSM was an international standard the and so with multiband phones the opportunity arose to roam with a mobile whilst abroad.

GSM has now largely been superseded by third and fourth generation networks (3G and 4G) but the ability to make a call using GSM (also known now known as 2G) has been retained. This means that changing over to 3G and 4G could be progressive rather than overnight. It also allowed calls to be made within countries yet to adopt 3G and 4G by visitors using more modern phones.

How the cell system works

Click and drag the phone around to see how adjacent cells arrange handoff so that it never loses the radio signal.
How the cell sytem works
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