Feature enhancement for a bitstream-based front-end in wireless speech recognition

In this paper, we propose a feature enhancement algorithm for wireless speech recognition in adverse acoustic environments. A speech recognition system is realized at the receiver side of a wireless communications system and feature parameters are extracted directly from the bitstream of the speech coder employed in the system. The feature parameters are composed of spectral envelope and coder-specific information. The proposed feature enhancement algorithm incorporates feature parameters obtained from the decoded speech and an enhanced version into the bitstream-based feature parameters. Moreover, the coder-specific parameters are improved by reestimating the codebook gains and residual energy from the enhanced residual signal. HMM-based connected digit recognition experiments show that the proposed feature enhancement algorithm significantly improves recognition accuracy at low SNR without causing poorer performance at high SNR.