Combined variable low-bit-rate speech-channel coding over noisy channels

This paper presents a novel algorithm for combined variable low-bit-rate (VLBR) speech-channel coding over noisy channels. The algorithm is derived based on the channel optimized vector quantization (COVQ) soft-input decoding techniques. A variable low-bit-rate vector quantization based CELP (VLBR-VQCELP) speech-channel codec is designed as a candidate for applying this proposed algorithm directly. Simulation results based on the subjective listening tests show that this algorithm can improve the low-bit-rate speech quality significantly over AWGN and Rayleigh fading channels respectively, relative to the hard decision decoding. Instead of separately using the channel coding, we apply the joint speech-channel coding algorithm to improve the system performance without increasing the transmission bandwidth and the system complexity.