Communications Satellite Corporation

Communications Satellite Corporation (comsat)

Samuel Joseph Campanella

Henri G Suyderhoud

Michael Onufry, Jr

Krishnamoorthy Virupaksha

Hans Dodel

A variable slope delta coding processor using adaptive prediction in which a digitized signal is transmitted with approximately half the channel bandwidth required by previous techniques without any substantial sacrifice of received signal quality. An estimate of a digital sample is subtracted from a digital sample of an input signal to produce an error signal. The sign bit of the error signal is transmitted as a single bit output signal. A predetermined number of immediately adjacent single bit output signals are utilized to calculate an adaptive step value using a compression technique. A set of reconstructed signal values is built up, one for each of the input signal, with each reconstructed signal value being calculated as the sum of the adaptive step size value and the estimate of the sample of the input signal. For each new sample of the input signal, an oldest reconstructed signal value is discarded and replaced by a newly calculated value. A set of predictor coefficients is built up utilizing a steepest descent algorithm. The predictor coefficients and the reconstructed signal values are convolved to obtain the estimate of the input signal sample, and the process is then repeated for the next sample of the input signal.

Variable slope delta coding processor using adaptive prediction

An echo suppressor for use in the send path of the four-wire part of a long distance telephone circuit employs frequency-selective center clipping. The bandwidth of the channel in which echo occurs is subdivided in contiguous bands or subchannels by appropriate filtering, and each resulting signal is center clipped by a center clipper. Threshold control voltages are predicted from knowledge of the average speech amplitude distribution characteristic as a function of frequency. This characteristic is subdivided into the same frequency bands as that used by the center clippers, and the ratios of energies in the bands are used to equalize the ratios of the control voltages that determine the center clipper thresholds. This technique is implemented through the use of a peak rectifier, the input of which is coupled to the receive path of the echo suppressor and the output of which is connected to each of the filtered subchannels by a resistive dividing network. The values of the resistances in each dividing network are determined so that the ratios of the various voltages appearing at these networks are proportional to the ratios of the average energies of the telephone speech in the respective frequency bands. These voltages are then applied to the center clippers to regulate each clipper threshold so that it is proportional to the applied voltages.

Echo suppressor using frequency-selective center clipping

A low cost digital echo suppressor having break-in logic for overriding send-line interrupt operation. The send and receive signals are multiplexed and digitized. The digitized received signals are summed over a period of time to determine interrupt operation. The difference over a period of time of the receive and send line signals controls break in logic for overriding the interrupt operation.

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Gaithersburg, MD, United States of America

Samuel Joseph Campanella