How Cellular Technology Works
[excerpt]

Cellular telephone communication is predicted to be one of the hottest new areas in voice communication in this decade. Improvements and innovations make it possible now to "reach out and touch someone" beyond the limits of twisted-pair wires.

A revolution is brewing in mobile telephone communications. Once an appliance firmly attached to the home or office, telephones are literally on the move. With cellular telephone technology, it is possible to have a fully functional telephone in the car, the briefcase, and even a coat pocket. With fully independent mobile cellular telephones not much larger than the standard handset, Dick Tracy's two-way wrist radio seems much less far-fetched than it did a decade ago.

Ameritech Mobile Communications, Inc., Schaumburg, IL, a subsidiary of the Bell regional holding company American Information Technologies, Inc., Chicago, predicts a $2.7 billion market for cellular communications by 1990, with an estimated 1.5 million subscribers. Such a predicted market is a considerable jump from a single demonstration network in Chicago that went into full service in 1983. One of the driving forces behind this potential explosion in communications is improved radio telephony techniques.

As the name implies, cellular mobile telephones have "cells" as their basic units. The cells are divisions of service areas, each with a radius of approximately eight to 10 miles. Placement of cells and their size is determined by usage loads. Within each cell is a low-power radio transmitter and receiver that links all of the mobile telephones within its reach.

"Open channel D"
When a user dials a telephone number on a mobile telephone, the phone signals the nearest cells that a radio channel is needed. The transmitter / receiver connects the phone to an available private channel, and to the mobile telephone switching office. There is usually no detectable delay in acquiring a "line." If a mobile telephone is contacting a non-mobile station, the low-power transmitter / receiver connects to the regular telephone system and the call is completed. If the call is to another mobile phone within the same cell, the call is placed through the cell's transmitter / receiver. If the call is to a mobile unit within another cell, the call is transferred via land-lines to the transmitter / receiver nearest to the mobile unit being called . . .

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