Communications Satellite Corporation

Communications Satellite Corporation (comsat)

Raymond Henry Lanier

Robert Paul Ridings, Jr

Bit rate compression in a digital communications system is provided by transmitting voice information from n telephone circuits over the capacity conventionally allocated for transmission of voice information from n/2 circuits without appreciable degradation in quality. Alternatively, a doubling of the number of voice circuits may be provided with transmission at the same bit rate required for conventional transmission of voice information. Each frame period, at the transmitter, all n circuits are serviced and, utilizing an adaptive predictive encoding scheme, a maximum of only 3/8 n unpredictable samples in the given frame are transmitted over the available channel capacity.A sample assignment word (SAW), which identifies the circuits corresponding to the unpredictable samples, is transmitted therewith. Upon reception of the transmitted frame comprising the SAW and the unpredictable samples, the receiver updates the stored samples which were transmitted during previous frames as unpredictable samples by substituting the received unpredictable samples for the stored samples in accordance with the channel routing information provided by the SAW, thereby enabling proper reconstruction of all samples in the given frame. Means are provided for effectively recirculating the servicing sequence of the n circuits to optimize the adaptive predictive encoding scheme.

Adaptable zero order predictor for speech predictive encoding

A digital voice switch for detecting voice PCM samples in the presence of noise samples is disclosed. The switch includes a digital variable threshold generating means which adapts the threshold level to changes in the noise level. Advantage is taken of the fact that, over a given interval of time T, speech will occur as random talk spurts separated by periods of silence, while noise (Gaussian distributed) will be continuous. This difference between speech and noise makes it possible to detect the noise level with respect to the voice switch threshold level.

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Hyattsville, MD, United States of America

Raymond Henry Lanier