This paper describes a speech predictive encoding communications (SPEC) system that is designed to accommodate the traffic ofNPCM telephone trunks in the capacity ofN/2PCM telephone channels. The system exploits the statistics of multichannel voice communication in a manner significantly different from the technique employed in the well-known time-assignment speech interpolation (TASI) system. Specifically, the SPEC system operates at the transmitter by removing redundant speech samples during talk bursts as well as during silence intervals. The receiver remembers the most recent sample transmitted through each channel. As long as a new sample is not transmitted, the receiver simply repeats the sample value stored in its memory. Each sample from each incoming trunk is examined every 125 μs to determine which samples must be transmitted and which are redundant. Because the SPEC system operates at this high speed and predicts redundant or missing samples at the receiver, it does not produce the speech clipping effects typical of TASI-like systems. Any voice-quality degradation due to increased call load and/or speech activity is manifested as an increase in noise power. The subjective result is a graceful degradation that is virtually imperceptible to the listener.

In the present paper the problem of image data compression is considered, and the evaluation of system performance with quantitative figures of merit as well as qualitative results is attempted. Three adaptive prediction techniques proposed by Balakrishnan are described and applied to video data for the removal of so-called redundant samples. Typical prediction efficiencies of several predictors are cited and compared. Encoding of "compressed" data for transmission in a noiseless channel is next considered. The efficiencies of several practical encoding procedures are compared with the efficiency of the ideal noiseless code. The most important results describe the performance of an image data compression system in a noisy channel. Davisson has related the sample error rate of the data reconstructed at the receiver to the channel error rate for a special case. This result is used as a quantitative basis for evaluating the effects of channel errors on the performance of a specific compression system. In addition, sample television pictures which depict the qualitative effects of channel errors are exhibited. Finally, an experimental laboratory facility is briefly described, and its use in this and future work is outlined.