Importance

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Abstract

Communication apparatus using baseband, digitally formatted optical signals provides an infrared optical communication link between a terminal unit and station unit. Pulse width modulation or continuously variable slope delta modulation digital procotols are used to encode and decode the transmitted and received digital optical signals. A microprocessor senses the presence of a connection command signal to complete the optical communication link. In one embodiment of the invention, a station unit associated with a coin operated type pay telephone instrument communicates with a remotely located terminal unit to permit a user to access and be connected to the public telephone network via the terminal unit. The station unit senses the digitally formatted optical signal and decodes it to derive the supervisory and audio frequency signals and in response to the supervisory signals causes the telephone line to be connected to and disconnected from the station unit. Electrical signals from the telephone line are digitally encoded and transmitted via the optical communication link as baseband digitally formatted optical signals to the terminal unit where they are sensed, converted to electrical digital pulses, decoded and transformed to an analog signal to excite a transducer to produce an audible signal corresponding to the audio signal on the telephone line.

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First Claim