Simulation of an Adaptive Speech Communications System Applicable to Time-Varying,Narrowband Channels

Abstract

An adaptive speech and channel coding scheme is described, applicable to the communication of intelligible speech over very narrowband, noisy channels. A fixed- channel bit rate of 1200 bits per second (b/s) is assumed and the channel E_b/N_o can drop below 3 decibels. A family of speech coders, derived from a parent coder operating at 1200 b/s, is described which, when combined with a variable rate (punctured) convolutional code, yields an adaptive system capable of operating over a range of channel conditions. The locations of the channel E_b /N_o threshold points between the various schemes were derived through simulation.

Keywords

Digital signal processing speech processing codec channel coder low bit-rate speech transmission

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