Integrated design for digital transmission of speech signals over noisy channels

This paper presents an integrated adaptive communication system for speech transmission over time-varying noisy channels for wireless communications. All major subsystems, including variable-rate speech coding, variable-rate channel coding and variable-level modulation are adaptive and configured according to one of several available system operating states. The transition between the system states is controlled by the estimation of reconstructed signal quality. Dual-adaptive DPCM is employed as the speech encoder with both fast and slow adaptation. Transmit power adjustment is performed independently at both ends of the duplex system. Simulation results show that the quality of reconstructed speech signal is robust with respect to various rates on the fading of time-varying Rayleigh channels.