How the mobile telephone works

Press, 12 September 1988, Page 21

How the mobile telephone works

The technology which allows you to have a telephone in your car, or to carry around with you, has cost millions of dollars to develop and install, and the intricacies of its operation are far too complex to explain in anything less than an encyclopeadia. However, a basic explanation which should be of assistance to prospective customers is as follows:

Telecom Corporation have set up a netowrk of radio base stations each of which can cover an area around itself, called a cell. Each of these cellstations has a number of high-quality U.H.F. radio channels allocated to it, and is separated by several kilometres from any cell-station with the corresponding channels, to avoid interference between cells.

When a subscriber wishes to make a call from a mobile phone, say in a car, he dials the number he wants, and presses the "send” button on the phone. The phone then seeks a vacant channel on the nearest cellstation, usually the one in which cell the car is travelling, and sets up a radio link to it. The phone transmits a short “packet” of data, which identifies the subscriber, the type of phone, and a number of other important items.

which the cell-station checks (instantaneously) against electronic records held by the Mobile Switching Centre (M.S.C.).

Provided the records match, that is that the phone has been correctly connected and authorised to be used, and that the bills are paid up to date, the M.S.C. then connects the radio link to the ordinary telephone network, and the call is put through, completely automatically, to its destination, which could be anywhere in the world. At the same time, the M.S.C. sends the details of the call to the billing computer in Wellington, which stores it until the subscriber’s bill is composed, once each month. The whole process of connecting a call from a mobile normally takes no longer than an ordinary telephone toll call, and the quality of speech is generally as good, if not better, than a standard phone call.

When an ordinary telephone subscriber wants to call a mobile, he simply dials the mobile’s unique telephone number. The call is routed via the M.S.C., which finds the mobile, and its position within the network, and connects the call via the nearest cell-station with a vacant channel.