Two-channel conjugate vector quantizer for noisy channel speech coding

A two-channel conjugate vector quantizer is proposed in an attempt to reduce quantization distortion for noisy channels. In this quantization, two different codebooks are used. The encoder selects the channel code pair that generates the smallest distortion between the input and the averaged output vectors. These two codebooks are alternately trained by an iterative algorithm which is based on the generalized Lloyd algorithm. Coding experiments show that the proposed scheme has almost the same SNR as a conventional vector quantizer for an error-free channel. On the other hand, it has a significantly higher SNR than the conventional one for a 1% error rate. This scheme also has merits in computational complexity and storage requirements. The scheme is confirmed to be effective for a medium bit-rate speech waveform coder