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First Generation (TACS) [Return to main Technology page]

In the early 1980's, the UK government wanted to introduce competition in the Telecomms industry. They decided to award two licences to operate cellular networks in 1982. One of the licences was awarded to BT, which formed a company with Securicor. Telecom Securicor Cellular Radio Ltd was born, which traded under the name Cellnet. The other licence was offered by holding a competition from which Racal-Millicom was selected out of the five applicants. This company was a member of the Racal Telecom group and is now known as Vodafone. The two companies along with the government jointly decided the standard for the UK networks. They agreed to base the network standard on the north American standard Advanced Mobile Phone System (AMPS) and this lead to the UK standard Total Access Communications System (TACS). Cellnet and Vodafone launched their networks in January 1985 and this was three months ahead of their licence requirement. They both expanded their coverage to 90% population requirement in 1987, two years ahead of the licence requirement. This was mainly due to strong competition between the companies. In just over two years from launch each network was supporting 400,000 customers, and continued to grow at such a pace that each company nearly doubled in size each year.

When Cellnet and Vodafone were initially licensed by the DTI, they imposed a condition, which meant neither company was allowed to sell directly to the customer. All products and services were offered via Service Providers who became responsible for setting customer contracts, billing, tariffs etc. This was done either directly by the Service Provider or via Dealers.

The basic concept behind cellular radio are not complex, the area to be covered by the system is divided into a number of regular cells, and each cell has a radio base station positioned to give coverage to that cell. The mobile connects to the nearest cell with the strongest signal and is then passed to a neighbouring cell with a stronger signal when the original signal becomes weak. This allows freedom for the mobile to move from cell to cell provided there is coverage in between

Basic System Parameters:

Frequency Band:
890 - 905 Mhz mobile Tx .......TACS 600 Channels
935 - 950 Mhz base Tx

890 - 915 Mhz mobile Tx .......TACS 1000 Channels
935 - 960 Mhz base Tx

872 - 905 Mhz mobile Tx .......E-TACS 1320 Channels
917 - 950 Mhz base Tx

Channel Spacing:
25Khz (with 12.5khz offset)

Voice Modulation:
FM, 9.5 Khz peak deviation

Signalling:
8 Kbits/s with Manchester encoding

Signalling Modulation:
Direct FSK, 6.4 Khz deviation

Signalling Protection:
5/11 fold redundancy + BCH block code

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