Simulation of an adaptive speech communications system applicable to time-varying, narrowband channels

An adaptive speech and channel coding scheme is described, applicable to the communication of intelligible speech over er narrowband, noise 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.