Error-Free Cellular Modems Link Mobile Computers / by Southwestern Bell Mobile Systems

Article excerpt

Southwestern Bell Mobile Systems is going on the road with a pair of cellular modems which permit error-free data transmission in the field.

Tying a portable computer with "The Bridge" and "The Span" marketed by Southwestern Bell, data is transmitted over cellular mobile telephone networks.

The modems were developed by the Spectrum Cellular Corp. in Dallas.

Beginning in December, the products will be available in Oklahoma City for $695 each through authorized agents and Southwestern Bell Mobile Systems' local sales force. The Bridge and the Span will also be marketed in Austin, Dallas, Houston, Kansas City, San Antonio, Tulsa, St. Louis and Wichita.

The Bridge modem is powered by a 12-volt automobile cigarette lighter and communicates with the Span, which attaches to a personal computer or mainframe. It uses an RS-232 port and permits 300 bauddata (equivalent to 300 bits per second) to be transmitted with no errors.

Bridge units also may communicate directly, which enables data to be transmitted over a cellular network from one portable computer to another.

The problem with cellular technology is the "hand-off," the technique that makes a multi-celled cellular system operate efficiently, officials said.

In cellular telephone systems, a city is divided into small geographic areas called "cells," each served by its own low-power ratio transmitter. As the caller drives across the serice area, the call is automatically passed from one cell to another. …


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