System engineering considerations in DSI applications

Digital speech interpolation (DSI) gain and compatibility with digital hierarchy, equipment costs, speech quality, and compatibility with voiceband data transmission and echo control in DSI applications are analyzed. A DSI terminal should be compatible with conventional PCM and the existing digital hierarchy, and a gain of 2:1 is achievable with a voice quality close to that provided by PCM on non tandem links. A high quality digitally-controlled speech detector is essential, and a price of $100 per channel end will be competitive with other capacity enhancing techniques. The terminal should handle a mix of 10% voiceband data and 90% voice, and an echo suppressor function should be integrated into the processor. The control functions should not be degraded at bit error rates of 10 to the -4th power or lower.