Digital Signal Processor: Voice-Frequency Transmission Treatment for Special-Service Telephone Circuits

The first, and still most heavily used, transmission medium in the telecommunications network is copper wire. Twisted pair metallic cables of various gauges, lengths, and sizes make up the bulk of the loop plant and local exchange trunk plant. The application of electronic amplifiers or repeaters to provide gain to compensate for the attenuation of signals on metallic cables was the first large-scale use of electronics in the telecommunications network. Repeaters are still used extensively. By necessity, the systems of the past that provided voice-frequency (VF) transmission treatment on a per-channel basis were analog systems. The large-scale use of sophisticated digital signal processing for these transmission treatment functions was precluded by cost, power consumption, and size of implementation. However, in recent years the capabilities of digital hardware have improved sig1585 nificantly, primarily as a result of the rapid development of integrated circuit technology. The digital signal processor (DSP), 1 a VLSI device with a large number of logic circuits, is an example of the sophistication that is now possible with digital hardware. The inherent capabilities of the DSP have made it possible to consider the use of digital filters to replace some of the traditional analog network functions in VF transmission systems. This paper reports on the results of an experimental study in which the DSP is used for this purpose. Among the most desirable features of the DSP, and especially important for this study, is the ease with which it can be programmed under computer control to provide transmission treatment functions.