A CELP-based hybrid digital-analog (HDA) joint source-channel speech coder

A joint source-channel coding system for transmitting speech on a bandlimited additive white Gaussian noise (AWGN) channel is presented. The proposed method uses a hybrid of digital and analog modulation techniques. The digital part of the system consists of an FS-1016 CELP speech coder followed by a rate-3/5 parallel concatenated (turbo) error correcting code. The analog part, which transmits the quantization error due to the FS-1016 CELP coder consists of a linear encoder and decoder. The advantage of the proposed system is that it achieves excellent rate-distortion/capacity performance that is common in digital systems while maintaining a "graceful degradation" characteristic that is common in analog systems. Comparisons are made with three purely digital systems and two purely analog systems. A formal listening test shows that, at high channel SNR, the improved performance of the proposed hybrid system versus the purely digital systems is noticeable to the average listener.