US 4,066,844 A · Adaptable zero order predictor for speech predictive encoding communications systems

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 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.

Claims10

Dependent claims

In a digital communications system wherein information from a designed maximum plurality of voice circuits at a transmitting station may be transmitted to a receiving station via a transmission path of given power level, bit rate and bandwidth, apparatus for enabling the transmission of information from a number greater than said designed maximum plurality of voice circuits over said transmission path comprising:

a. means at said transmitting station for periodically sampling the amplitude of voice signals on each circuit of said plurality of voice circuits;
b. means for comparing for each said circuits, a present amplitude sample with a prior amplitude sample which has been transmitted to said receiving station, said comparing means generating difference signals in response to said comparisons;
c. means for comparing said difference signals with a plurality of aperture threshold values and generating an activity map for each aperture threshold value;
d. means for selecting the smallest aperture value which results in an activity map corresponding to activity in not exceeding a fixed predetermined number of circuits;
and
e. means for generating a transmission frame comprising a digital representation of those present amplitude samples conforming to the activity map of the selected aperture value and a digital word representing said activity map.

3 more elements

In a digital communications system wherein information from a plurality of voice circuits at a transmitting station may be transmitted to a receiving station via a transmission path, wherein each of the voice circuits is sampled at the Nyquist sampling rate at least once during each of successive sampling frame periods, wherein each of the resultant samples are encoded into digital signals and wherein the transmitter requires a minimum bit rate to transmit all of said digital signals for a given voice transmission quality, apparatus to enable the digital transmission at said given voice quality of either said information from said plurality of voice circuits over a transmission path at less than said minimum bit rate, or information from more than said plurality of voice circuits at said minimum bit rate comprising:

a. a first storage means at the transmitting station for storing, for each voice circuit, said digitally encoded samples from a prior sampling frame;
b. means, connected to said first storage means, for digitally comparing the sample from each respective voice circuit for a present sampling frame with the sample stored in the first storage means for such respective voice circuit and for providing a difference signal for each comparison representing the particular voice circuit whose sample is being compared;
c. means for comparing each difference signal with a plurality of aperture threshold signals and generating a digital representation of circuit activity for each of said aperture threshold signals;
d. means for selecting the smallest aperture threshold signal wherein the corresponding digital representation of circuit activity represents activity in less than a fixed predetermined number of circuits;
e. means for assembling and transmitting a digitally encoded transmission frame of information comprising said digital signals representing those present samples which differ from the selected aperture threshold signal and the digital representation of circuit activity corresponding to the selected aperture threshold;
f. means at the receiver for receiving said digitally encoded transmission frame;
g. a second storage means for storing for each voice circuit previously transmitted, digitally encoded samples from a prior sampling frame;
and
h. means connected to said receiving means for substituting for the samples stored in the second storage means, respective transmitted present samples in accordance with said identifying signals.

6 more elements

Dependencies are inferred from the claim text.

Adaptable zero order predictor for speech predictive encoding communications systems

Life of this patent

Adaptable zero order predictor for speech predictive encoding communications systems

Life of this patent

Abstract

Claims10