Patent
1975-03-17
1976-10-26
Stewart, David L.
H04J 306
Patent
active
039886743
ABSTRACT:
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 digital transmission of voice information. Each frame period, at the transmitter, all n circuits are serviced and, utilizing a predictive encoding scheme, only 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 transmission capacity conventionally allocated for transmission of digital voice information from 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 alleviate "overload." Means are also provided to insure proper reception of the SAW by the receiver. A unique frame synchronization technique requiring no increase in transmitted bit rate by transmitting synchronization information in an unused time slot only during periods of underflow is employed.
REFERENCES:
patent: 3754102 (1973-08-01), Clark
patent: 3836722 (1974-09-01), Muller
patent: 3927268 (1975-12-01), Sciulli et al.
Communications Satellite Corporation (Comsat)
Stewart David L.
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